Pierre Desproges

Université De Montpellier

Nicolas Champauzas

CNTFET-based Biosensor Technology for Kinase Activity Monitoring

La science consiste à faire ce qu'on fait en sachant et en disant que c'est tout ce qu'on peut faire, en énonçant les limites de la validité de ce qu'on fait."

Pierre Bourdieu, Questions de sociologie (1984) "La recherche a besoin d'argent dans deux domaines prioritaires : le cancer et les missiles antimissiles. Pour les missiles antimissiles, il y a les impôts. Pour le cancer, on fait la quête."

I would like to thank May Catherine Morris, from IBMM, for initiating this project, for introducing me to the complex subject of kinases despite my gaps and for the time invested in this manuscript and my thesis.

I would like to thank Arnaud Virazel, from LIRMM, for introducing me to the team and trusting me with his class.

I would like to thank Serge Bernard and Aïda Todri Sanial, from LIRMM, for leading me through the subtleties of conducting a research project.

I would like to thank Vincent Kerzerho, Michel Renovell and Fabien SOULIER, from LIRMM, for their support and constructive advises.

I would like to thank Mohamed Moez Belhaj, from LIRMM, for sharing his clean room expertise.

I would like to thank Frederic Pichot from Montpellier University clean room for guiding me through the discoveries of new devices and for sharing his clean room expertise.

I would like to thank Christophe Roblin from L2C, Montpellier University, for sharing his expertise on lithography and for the considerable time it saved me.

I would like to thank PELLERANO Morgan from IBMM, Montpellier University, for being welcoming and open to intersectional science discussions at the roots of this project.

Finally, I would like to thank the Doctorate school EDI2S and the jury who gave me my chance. -Construction d'une base de connaissances scientifiques nécessaire à la conception et à la réalisation d'un système couvrant plusieurs disciplines de la physique: physique des semi-conducteurs, physique quantique, chimie, électrochimie, biochimie.

-Recherche des architectures et méthodes de fabrication existantes, pertinentes vis-à-vis de la conception d'un biocapteur répondant aux objectifs.

-Conception de l'architecture et du procédé de fabrication répondant selon la théorie et la littérature aux objectifs.

-Mise en place du procédé de fabrication et réalisation d'échantillons visant à une preuve de concept à travers l'optimisation des paramètres de fabrication.

-Mise en place et réalisation de la caractérisation des échantillons à différentes étapes de la fabrication.

-Il résulte de ces travaux de recherche une méthode répétable et démontrée pour réaliser des transistors en nanotubes de carbones dont l'impédance varie d'approximativement cinq pourcents pour une variation de tension de grille chimique de cent millivolts. Cette valeur correspond à la variation estimée de potentiel électrostatique due à une complète activation de la fonctionnalisation sélective des nanotubes.

Contexte de recherche 10.1.1 Problématique

Les principales limites de la recherche en biologie et biochimie sont fixées par la capacité de génération de données normalisées. La complexité des maladies et de leurs causes poussent les chercheurs à utiliser des approches statistiques. Ces approches supposent l'acquisition de données générées par des chaines d'acquisition permettant la discrimination de l'information des artefacts de mesure. Cette discrimination suppose de limiter l'intervention humaine en favorisant l'automatisation des tâches et la conception de capteurs sélectifs envers le signal biologique mesuré. Outre la capacité de génération d'un gros volume de données et la normalisation de ces données, la génération d'information est souvent limitée par l'utilisation de chaines d'acquisition couteuses en matériel et en temps de manipulation par un personnel qualifié.

Finalement, l'acquisition de données pertinentes en biologie est limitée par la capacité des capteurs à mesurer des signaux biologiques spécifiques, dans le temps ainsi que dans des milieux biologiques complexes.

Objectif de la recherche

L'objectif de cette thèse est la conception d'une technologie de biocapteurs utilisant des nanotubes de carbones en tant que substrat à une réaction chimique générant des variations locales de champ électrique. Les nanotubes devront être placés en tant que canaux de transistors à effet de champ, de façon à servir de transducteurs et amplificateurs de l'information électrochimique. La conception vise, en accord avec les problématiques posées précédemment, une chaine d'acquisition ne requérant pas de matériel lourd ainsi que la minimisation de l'intervention humaine lors de la mesure. L'objectif est aussi de concevoir une technologie apte au suivi de l'information ciblée dans le temps et dans un fluide biologique complexe.

Conception de l'architecture 10.2.1 Le rôle central du nanotube de carbone

Un nanotube de carbone peut être vu comme une partie d'un plan de graphène enroulé sur lui-même de façon à former un cylindre. Il peut être métallique ou semiconducteur en fonction de son orientation dans le plan graphene, mais aussi de son diamètre et du nombre de ses parois. L'intégrité de la structure hexagonale ainsi que la déformation du tube peuvent être des critères jouant sur les particularités électroniques. Suivant ces critères, les nanotubes utilisés seront de petit diamètre, sans modification préalables de leur structure et les canaux qu'ils créeront ne devront pas dépasser les deux microns.

Architecture du transistor

Le premier choix concernant l'architecture du transistor, est le métal utilisé comme contact pour la source et le drain. L'objectif sera de réaliser un transistor de type p de façon à pouvoir travailler avec un transistor partiellement ouvert proche du potentiel neutre. Le choix de métal s'est porté sur l'or, pour les propriétés du contact électronique et pour sa disponibilité en salle blanche.

Le second choix concernant l'architecture du transistor concerne l'utilisation de dopage des nanotubes de façon à augmenter la capacité d'amplification de la structure. Au vu de la complexité et du besoin d'expertise associé à la réalisation de dopage robuste et pouvant être mis à échelle, j'ai choisi d'utiliser une architecture de transistor se basant sur la variation de conduction des barrières Schottky (SB) à la frontière métal/nanotube. Cette barrière répond aux changements d'état dus à l'effet de champ malgré une variation de conduction du tube moindre qu'avec un profil de dopage MOS-like. Un inconvénient de ces SBCNTFET Schottky Barrier Carbon Nano Tube Field-Effect Transistor est leur sensibilité à certains changements de particularité du métal de contact. En conséquence, les contacts entre nanotubes et métal sont enfouis sous une deuxième couche de métal, améliorant leur qualité. De plus, le métal sera isolé de l'échantillon par un polymère inerte.

Le choix de conception suivant correspond à l'arrangement des nanotubes. L'objectif de la conception est de créer un capteur robuste de par sa fabrication. Pour ce faire, je choisis de travailler avec des tubes alignés et placés de façon à maintenir un certain contrôle sur la distance entre les tubes. Ce choix correspond à un placement tube par tube sur une structure existante servant de guide (mécanique ou électromagnétique) ; en opposition avec un placement des tubes en groupes créant des tapis de CNT, ou avec un placement des électrodes en fonction de la position de tubes placés de ix facon plus ou moins aléatoires sur un substrat vide. De façon à atteindre ce niveau d'organisation, le choix de méthode de déposition se porte sur la diélectrophorèsec.f. Section 10.3.2. Ce type de déposition suppose la séparation des nanotubes dans une dispersion, à une faible concentration (∼ ng/mL).

Premier design

Conception du procédé de fabrication

Ce résumé consiste en la description des procédés de fabrication avant réalisation des essais. Ces procédés listent les étapes de fabrication avec leurs paramètres et variations utilisées pour l'optimisation de la réalisation.

Dispersion

Solvant : La dispersion commence par le choix de solvant. La diélectrophorèse gagne en praticité à être utilisée avec une dispersion aqueuse. Cependant, j'ai réalisé des essais avec des solvants organiques courants comme l'éthanol et l'acétone. Sonication du surfactant : L'étape suivante a pour but de garantir la solubilisation du surfactant. Pour ce faire, la solution est stimulée par des ondes mécaniques dispensées par une sonde métallique. Les énergies de stimulation ont été testées entre 10W et 200W pour des durées allant de 10s à 2min.

CNT : L'étape suivante consiste en l'introduction des nanotubes dans la solution. La dispersion perd en efficacité avec l'augmentation de la concentration. Pour la déposition de CNT par diélectrophorèse, une concentration approximative de quelques ng/mL. Les concentrations testées vont de 2 * 10 -5 à 2 * 10 -4 w/w à l'introduction.

Présonication des CNT : De façon à améliorer les résultats en stimulation directe (avec la sonde mécanique) et réduire les risques de casse de tubes qui lui sont dues, la solution est précédemment stimulée par des ondes mécaniques dans un bain dont le contenant génère les vibrations. Les durées testées vont de 10 à 30min avec pour objectif de réduire la taille des plus grosses cendres.

CNT sonication : La stimulation avec une sonde est le passage le plus critique de la dispersion. Les paramètres vont de 10W à 200W pour la puissance et 10s to 2min pour la durée.

xi Centrifugation : L'étape suivante sépare les tubes présents dans la dispersion en fonction de leur densité. En effet, les tubes les moins denses sont les mieux séparés. La centrifugeuse est réglée pour dispenser vingt mille fois l'accélération de la gravité pour des durées comprises entre 15min et 2h.

Recovery and dilution :

La dernière étape est la récupération des nanotubes séparés. Pour ce faire, la couche supérieure de la dispersion est récupérée. La concentration de CNT doit être encore réduite pour correspondre aux standard de la diélectrophorèse, des essais ont été réalisés entre 10% et 0.1%. La dispersion est en suite prête à être utilisée en diélectrophorèse.

Diélectrophorèse

La diélectrophorèse consiste à placer des particules polarisables précédemment suspendues dans une solution. Les paramètres sont l'amplitude du champ, sa fréquence et la durée de stimulation de la dispersion. Le champ est testé entre quelques centaines de millivolts par micromètres jusqu'à vingt volts par micromètres. La fréquence est testée entre quelques centaines de hertz et quelques gigahertz. La durée est quant à elle testée entre une fraction de seconde et environ une minute.

Lithographie :

La diélectrophorèse dépend de la force du champ et donc de l'amplitude de la stimulation divisée par la distance entre les électrodes, ce qui implique que les quantités présentées précédemment dépendent de la réussite de la lithographie. La résine utilisée est la AZ5214, une résine reversible à haute résolution.

Déshydratation : Avant toute manipulation, les échantillons sont déshydratés sur une plaque chauffante pour environ une minute à une température d'environ cent-vingt degrés.

Spin-coating : Le spin-coating consiste à déposer des goutes de résine sur un échantillon qui ensuite subit une forte rotation. Les parametres sont la vitesse de rotation, testée entre 3000tr/min et 6000tr/min, la durée est fixée à 30s basée sur la littérature, et la rampe d'accélération testée entre 500tr/min/s et 2000tr/min/s. Première cuisson, durcissement : L'étape suivante est le durcissement de la résine par chauffage. L'objectif est d'évaporer le solvant présent dans la résine la rendant plus dure. La durée est fixée à une minute (durée couramment utilisée dans ce type de procédé). La température est testée entre 110 • C et 125 • C.

Exposition : L'exposition de la résine sous masque permet d'imprimer la forme du masque dans la résine. La qualité du contact est ajustée en mode contact sousvide, permettant de limiter la distance entre le masque et la résine. La durée d'exposition est testée, entre 1s et 5s correspondant au panel d'énergies conseillées par la notice technique de la résine.

Dispersion

L'objectif de la dispersion est de séparer les tubes les uns des autres et de trier les tubes les mieux séparés pour pouvoir les placer par diélectrophorèse.

Les dispersions dans les solvants organiques, acétone et éthanol, se sont trouvées n'être stables que pour quelques secondes ou dizaines de secondes. Cette durée est insuffisante pour pouvoir séparer des tubes en fonction de leur qualité de dispersion.

Les résultats de dispersion en fonction de la concentration de SDBS sont présentés dans Figure 10.3. La séparation des nanotubes est estimée en fonction de la couleur de la dispersion. Plus la dispersion est foncée mieux les tubes sont séparés. L'échelle verticale de Figure 10.3 exprime la couleur de la dispersion sur une échelle de gris sur 128 possibilités.

Les résultats de dépositions directes sur substrats pour estimer la séparation des tubes sont présentés en Figure 10.4. On peut voir sur la gauche des amas de tubes et les locations des profils dont les valeurs sont indiquées sur la droite. On y voit la hauteur d'un tube plongeant du fagot. Son épaisseur est estimée à 0, 9nm, valeur en concordance avec les particularités des tubes utilisés.

Les résultats des essais de concentration avec le surfactant CMC sont illustrés dans Figure 10.5. De façon similaire aux essais avec le SDBS, la concentration optimale semble se trouver autour de 0, 5%. Figure 10.11 illustre un zoom fait sur un site ne contenant qu'un seul nanotube avec un dispositif de microscopie à force atomique -AFM. On constate que le tube relie les deux électrodes. Table 10.1 montre les variations de sensibilité à l'effet de champ en fonction de l'environnement des nanotubes et de la configuration de la grille.

Lithographie

Diélectrophorèse

caractérisation des réseaux de transistors

Figure 10.13 illustre les phases linéaires et de saturation dans la caractérisation du courant en fonction de la tension source-drain. La cible est de la famille des enzymes appelée kinase. Les kinases sont des enzymes qui catalysent le transfert sur une protéine dite substrat d'un groupe phosphate (PO 2- 4 ) chargé électriquement. La réaction entre kinase et substrat est sélective et déterminée par la reconnaissance spécifique de la protéine substrat par la kinase.

La cible fait, plus spécifiquement, partie de la famille des Cyclines dependent Kinases (CDK). Les CDK/Cyclines coordonnent le cycle cellulaire, et permettent le bon déroulement de la croissance, de la réplication de l'ADN et la division d'une cellule mère en deux cellules filles. En particulier la kinase CDK4/cyclinD, est hyperactivée dans un grand nombre de cancers humains (mélanome, lymphome, cancers du poumon, etc). Par ailleurs, il existe un biocapteur fluorescent photochimique démontré permettant la mesure sélective de l'activité de ces kinases dans des milieux biologiques complexes (lysats de cellules humaines, biopsies de peau et xenogreffes de tumeurs): [START_REF] Prével | Biosensors and Bioelectronics Fluorescent peptide biosensor for monitoring CDK4 / cyclin D kinase activity in melanoma cell extracts , mouse xenografts and skin biopsies[END_REF].

Etat de l'art

La technologie proposée n'a pas d'équivalent direct. Plusieurs technologies ayant un objectif similaire existent pourtant. Voici deux exemples de technologies basées sur deux versions de mesure photochimique. [START_REF] Prével | Biosensors and Bioelectronics Fluorescent peptide biosensor for monitoring CDK4 / cyclin D kinase activity in melanoma cell extracts , mouse xenografts and skin biopsies[END_REF] présente un capteur d'activité kinase basé sur la mesure de changements de l'emission de la fluorescence d'une sonde sensible à l'environnement, dont la fluorescence est exaltée lors de la phosphorylation par la kinase. [START_REF] Xin | Visualizing Dynamic Activities of Signaling Enzymes Using Genetically Encodable FRET-Based Biosensors: From Designs to Applications[END_REF] démontre un capteur d'activité kinase basé sur les changements de FRET entre deux protéines autofluorescentes qui subissent un rapprochement lors de la phosphorylation par la kinase. [START_REF] Liu | Probing of protein kinase activity by electrochemistry[END_REF] démontre un capteur émettant une luminescence chimique proportionnelle à l'activité de la kinase cible. De façon similaire, [START_REF] Li | Enhanced Photoelectrochemical Method for Sensitive Detection of Protein Kinase A Activity Using TiO2/g-C3N4, PAMAM Dendrimer, and Alkaline Phosphatase[END_REF] démontre un capteur générant un photocourant proportionnel au taux d'activation de protéines par une enzyme kinase. xix Les capteurs électrochimiques, type de technologie dans lequel se place le développement de la thèse, se divisent en deux parties. Certains biocapteurs utilisent un marqueur. [START_REF] Kerman | Peptide biosensors for the electrochemical measurement of protein kinase activity[END_REF] labélise les molécules d'ATP de façon à pouvoir reconnaitre la phosphorylation des protéines fixées sur l'électrode. L'ATP marqué sera hydrolysé lors de sa reconnaissance par la kinase et le phosphate marqué sera transferé sur le substrat. La technologie la plus proche du développement en cours est démontrée par [START_REF] Freeman | Following a protein kinase activity using a field-effect transistor device[END_REF]. Figure 10.14 illustre la structure et le mode opératoire de reconnaissance du capteur. L'architecture de ce capteur est basée sur la modification de l'état d'une grille solide en oxyde d'aluminium, contrôlant un transistor en silicium. La structure transistor à grille chimique est conceptuellement similaire à l'objectif fixé. Les différences se situent dans l'utilisation d'une grille intégralement chimique (pyrène-CNT) et l'utilisation de ces mêmes nanotubes en tant que canal de la structure transistor. [START_REF] Nguyen | Basic study on Peptide Aptamer-modified Single-Walled Carbon Nanotube Field-Effect Transistor ( SWCNT FET ) for biomolecule analysis[END_REF], illustré par Figure 10.15 démontre une architecture aux objectifs fixés dans cette thèse mais visant une mesure de concentration de strépavidine. [START_REF] Prével | Biosensors and Bioelectronics Fluorescent peptide biosensor for monitoring CDK4 / cyclin D kinase activity in melanoma cell extracts , mouse xenografts and skin biopsies[END_REF] démontre l'efficacité du capteur CDKACT4 à discriminer une hyperactivité du complexe enzymatique CDK4/cyclinD. La partie sélective de ce capteur se trouve dans la séquence peptidique issue de la protéine rétinoblastome (pRb). En effet, le complexe CDK4/cyclinD est connu pour phosphoryler (transferrer un groupe phosphate) certaines parties spécifiques de pRbsites spécifiques de Rb, [START_REF] Anil | Cyclin D activates the Rb tumor suppressor by mono-phosphorylation[END_REF]. L'objet de la présente étude est de réutiliser cette séquence sélective sur un dispositif électrochimique permettant une mesure du ratio de peptides dérivés de Rb, [START_REF] Prével | Biosensors and Bioelectronics Fluorescent peptide biosensor for monitoring CDK4 / cyclin D kinase activity in melanoma cell extracts , mouse xenografts and skin biopsies[END_REF], phosphorylées.

La première étape est de concevoir un moyen de fixer ces protéines de façon à former une grille chimique. Les nanotubes de carbones ont un avantage en tant que substrat de molécules qui réside dans sa structure formée d'une maille hexagonale. Cette structure permet aux nanotubes de créer des liaisons capacitives, notamment avec les domaines pyrène d'autres molécules. Ces liaisons ont deux avantages. Premièrement, leur couplage capacitif permet le confinement partiel des charges FIGURE 10.15: Schéma représentant la mesure de concentrtion en strépavidine par électrochimie, utilisant une structure CNTFET et une grille chimique à base pyrène de chaque côté de la liaison, ce qui augmente la réversibilité de la réaction chimique d'activation. Ce confinement de charges est aussi cohérent avec l'objectif de mesurer un effet de champ. En effet, l'effet de champ dans un transistor se définit par une différence de densité de charges entre la grille et le canal (ici respectivement la molécule fonctionnalisante et le nanotube). Le second avantage à l'utilisation de nanotubes en tant que substrat à la réaction chimique est leur sensibilité à leur environnement électronique. Cette sensibilité s'explique par la structure tubulaire des nanotubes, plaçant toutes les charges du nanotube à sa surface. La seconde explication est la forte mobilité des charges dans les mailles atomiques hexagonales. 1pyrenébutanoïque succinimidyle ester (Pbase) est la molécule qui a été choisie de façon à faire la liaison entre les polypeptides sélectifs et le nanotube. Cette molécule se compose d'un domaine pyrène suivit par une chaine carbonée permettant la création de liens amides avec des protéines. Figure 10.16 représente le résultat de la conception en intégrant la grille sélective.

Procédé de conversion transistor/biocapteur:

La conversion du transistor en biocapteur se passe en quatre temps. Premièrement, la surface des nanotubes doit être nettoyée au maximum du surfactant pour laisser place à la fonctionnalisation. Ensuite, une deuxième couche de métal est ajoutée enfermant les contacts des nanotubes. Puis, les surfaces apparentes de métal sont couvertes d'une couche de polymère isolant. Enfin, le transistor est prêt à être fonctionnalisé par la mise en présence successive de Pbase, puis du polypeptide.

Résumé des résultats et développement à court terme

Les travaux présentés montrent une méthode de fabrication permettant la réalisation de transistors à effet de champ, utilisant des nanotubes de carbone en tant que canal sensible. La sensibilité obtenue est suffisante pour la réalisation du biocapteur et peut être encore améliorée par le nettoyage du surfactant des nanotubes. La prochaine étape est de montrer une preuve de concept non sélective, en montrant l'effet de la variation de la concentration d'ions phosphate sur la conductivité des nanotubes.

Characterizations

Introduction: From technological needs to a proof of concept 0.1 Research context

Our comprehension of biology is limited by our observation capabilities. Nowadays, biological and pharmaceutical research domains are limited by their capabilities to acquire normalized and robust data in large amount. This limitation is often due to the sensing methods or data acquisition methods.

Sensing methods often require human intervention of a qualified technician. Also an issue in data acquisition for biology, or biosensing, is the use of heavy equipment, also often requiring the intervention of a specialist. These issues are a source of the increased cost of biological measurements. The cost problematic impairs the systematic generation of data that could be used in research. It also prevents the use of known diagnostic techniques in developing countries.

The robustness of the data is limited by the normalization of the acquisition chain containing the biosensing technique. This normalization is measured by the capability of researchers separated in time or space to compare their data independently of the acquisition chain. Two methods are used to increase this data compatibility. The first consists in the reduction of human interaction and following increase in the precision of the manipulations and parameters by automation. The second method consists in the physics comprehensive modeling of the measurement chain allowing discrimination of the raw data from artifacts at the lowest level.

This thesis aims to answer to these problematics by creating a sensing technology based on nanostructure for measurement of biological quantities. This technology will aim for a cheap manufacturing compatible with industrialization and series production at low unitary cost. The technology will also aim to minimize human intervention in the acquisition chain in order to produce normalized data. Finally, the technology will aim to reduce intervention on the studied sample in order to further reduce human intervention and allow monitoring of the target.

Objectives Summary

The technical objectives are described in further detail along the relevant parts of the manuscript. The state of the art is also discussed in the relevant sections, with technical references for each design and process steps. Then a more conventional state of the art is depicted in Chapter 4, related to the first application design.

The technology has to be versatile to be adapted to different method of selectively modifying the ion concentration. Versatility is also required for the sensor to be adapted to the electronic front-end. In order to fulfill this objective the technology needs to be modular in its sensitive surface and scalable in the generated signal. From a manufacturing point-of-view, the process has to be robust to limit the variability between sensors and allow data normalization. The scalability and Contents low unitary cost of the manufacturing process are strong requirements for a widely spread usage of the sensor. This thesis presents the first steps of the work aiming at reaching these objectives.

Thesis outline and contributions

In the following chapters, I present the different steps that bring this thesis to its result: design of the sensor technology and design of its process complying with the objectives, then manufacturing and characterization of Carbone NanotTube Field-Effect Transistors -CNTFET -for biosensing application. Finally, an example of application developed during this thesis is described.

Part one: technology design

I started my work by studying the problematic and solutions described previously in this section. The objective of the following months were to build for myself a scientific background the various disciplines of physics sciences involved in the design and realization of a biosensor based on nanotechnology. I then listed scientific literature relevant to the design and realization of the technology. Next, I used the accumulated knowledge to design the technology and argument my choices in structure, materials or manufacturing methods. I concluded this first theoretical step by designing of a first approach model of the sensor allowing a graphic and qualitative demonstration of the measurement principles and allowing a rough estimation of quantified results.

Chapter 1 provides a description of the theoretical principles and literature examples leading to the design choices. A first model of the sensor concludes the chapter. The topics addressed are the sensitive surface built from CNTs and the design of the amplifying field-effect structure. The several choices made concern among others, the characteristics of the CNTs to use, the organization of these CNTs, the architecture of the transistors and the materials used to build this structure.

Part two: manufacturing process design and realization

The second part of the work consists of the design and optimization of a manufacturing process for the realization of the previously designed technology. I started by choosing the means and methods to be used in the realization. Then, I worked on optimization of the many parameters directing the results for each step.

Chapter 2 is an overview of the design of the sensor manufacturing process. It includes, lithographic patterning of the sensor, CNT dispersion and CNT placement. Each section provides an experimental protocol for each of the manufacturing process steps and comparison to the state of the art technologies. Each parameter is described with its effects on the process. I also describe their range of optimization based on theory and my methods of optimization. The parameters studied for the three main steps of manufacturing include among others: Dispersion: the nature and concentration of the molecules involved, the duration and power of the different stimulations Lithography: the nature of the resin, its method and parameters of deposition, the duration and power of UV exposure, the development duration Dielectrophoresis: the distance between electrodes, the duration, frequency and power of the stimulation.

Part three: manufacturing of the biosensor and result characterization

The next part of my work was to design and optimize set-ups for characterization of the results along the several steps of fabrication. I complemented these with the identification of the parameters critical to each step of the realization for quantification of the quality of the result. Finally, I prepared the next steps of the cleaning of the sensitive surface. Chapter 3 presents the results of the manufacturing process steps realization. CNT dispersion, lithography process and CNT placement using dielectrophoresis are respectively described in the first, second and third sections of the chapter. In addition, the electrical characterization of the CNTFET is provided in this chapter. A description of the envisioned next steps for short-term developments is given as a conclusion.

Part four: Chemical gate and application design

The project was originally directed to a kinase activity measurement as a proof of concept. In this optic I designed a chemical gate corresponding to the objectives and to the specificities of the proposed architecture.

Chapter 4 presents the first application designed for the technology in development. First, the target choice is described, followed by a state of the art section demonstrating the originality of the biosensor. Then, design choices are explained with the current chemical gate design. The anticipated manufacturing protocol is finally outlined with a short summary of the measurements demonstrating and quantifying the functionality of the sensor.

Part five: Result summary, scientific contributions

The main scientific contributions are listed by chapters as follow:

• Chapter 1:

-Novel use of VLSI principles and precise CNT placement for biosensing applications.

-Design of a sensor technology aiming to a realization through a repeatable and scalable nanotechnologic manufacturing process in a class seven clean room.

• Chapter 2:

-Compilation and modification of CNT dispersion protocols from literature toward single CNT dispersion for dielectrophoresis deposition and biosensing application.

-Design of a lithography set-up specific to CNT placement through dielectrophoresis.

-Optimization of a dielectrophoresis method for CNT placement based on short duration stimulation at high field intensity.

• Chapter 3:

-Realization of a dense matrix of transistors based on single CNTs showing sensitivity to the electronic state of the chemical gate.

-Dimensioning of a sensing matrix compromising between process feasibility and signal treatment considerations.

• Chapter 4:

-Design of a passive biosensing technology aiming to a monitoring of the biological signal.

-Original modification of an existing biosensing chemical gate for a new type of measurement.

The thesis is concluded with an evaluation of the completion of the objectives and the short to middle term developments.

Chapter 1

Design of the CNTFET sensor technology

This chapter describes the prototype conceived during the thesis. The several studies needed in order to realize a comprehensive design are summarized. Along sections, multiple topics related to the design are outlined. The conclusion of each section describes the related part of the model I created as a first-approach theoretical illustration of the sensor. The conclusion of the chapter summarizes the prototype I designed. In the second section, the heart of the technology that are CNTs are described regarding their roles in the prototype. Finally, the architecture of the sensor technology and several points of interest for future developments are discussed.

The central role of the carbon nanotube and field effect transistor structures

In this section, are described general particularities of carbon structures, especially toward electronic environment probing. We will see the advantages of graphene-like structures and their drawbacks. This will allow me to justify my choice in the use of carbon nanotubes from an electronic point of view. Secondly, the electronic structure of CNTs is addressed with the objective of creating a capacitive coupling to biological molecules -Pyrene moieties. I will address here my considerations in the choice of CNT for the sensor technology. Thirdly, I will describe the electronic structures of CNT field effect transistors -CNTFET -and the variations. The objective is to justify my choice for an architecture optimised between simplicity of realisation and a strong amplification of electrostatic changes in the CNT's environment. I will start here with an introduction on general principle of the use of CNTs in biosensing.

Carbon nanotubes -CNT -have been discovered in 1991 in Japan [START_REF] Iijima | Helical microtubules of graphitic carbon[END_REF] and have been since then the subject of intensives studies. In the recent years progress in synthesizing allows realization of systems at the industrial scale. Improvements have been made in the creation of important quantity at reduced cost and a better yield - [START_REF] Gedik | Chemical Vapor Deposition Synthesis of Carbon Nanotube Using Pyrolysis Gas Products of Apricot Kernel Shell[END_REF] [START_REF] Kumar | Natural and waste hydrocarbon precursors for the synthesis of carbon based nanomaterials : Graphene and CNTs[END_REF].

CNTs are studied using quantum solid state physics for the structure and the stand alone state, on the other hand the relation of the structure to its environment is studied by material chemistry disciplines. Three characteristics of the CNTs are important to understand regarding their specificities for biosensing. The first is that CNTs are structurally mesoscopic systems, which can be described as an intermediary state between macroscopic and atomic-size systems. Therefore, they can be described with quantum mechanics or classical mechanics depending on the dimension of the area considered. This principle allows CNTs to be a good interface between molecules and bulk electronic. The second characteristic, is the unique structure of CNTs. Their structure is that of tubes with all their particles and electrons at the surface. Therefore they are good candidates for biosensing applications. The third consideration is that in usual semiconducting physics the scattering of electrons in the considered volume is the principal conditioner of the electron displacement and degree of liberty. In CNTs the mean free path -MFP: the mean distance without scattering -is of approximately the size of the structure. This leads to considering the transfer of electrons as ballistic -for a more realistic quantification: the MFP in CNTs can be from 100nm to 1µm and the ballistic rate is about 0.9 depending on the length of the tube. It is also worth noting that CNTs are a strongly correlated structure which necessitate a thorough investigation in order to explain its characteristics. In addition, the electrons-electrons interactions can't be ignored to allow precise results.

Carbon structures and electronic properties

Carbon nanotubes are the central piece of this research and have been thoroughly studied in preparation of the design work. Appendix A describes the characteristics of carbon structures leading to hexagonal lattices and their properties based on [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF]. This appendix details the particularities of CNTs such as their sensitivity toward their electronic environment. It also aims toward an understanding of the mimetic bonds created between CNT sidewall and Pyrene. It also justifies the choice of CNTs over graphene nanoribons -GNR. Finally, the specificities of CNT physics are introduced to justify the choice of the CNT structure the most adapted to my objectives.

In this section I summarise Appendix A and the deductions relevant to the design of the sensing structure.

Here is a summary of the properties of CNTs relevant to the design. First, the graphene lattice will bind to other hexagonal carbon structures: the similarity of the organisation of π-electrons allows Van Der Waals bonds and augment their strength. Secondly, The high mobility of the π-electrons in the graphene lattice explains the unique sensitivity of hexagonal carbon structures to their environment. Finally, Van Der Vaals bonds between hexagon carbon structures create mechanically weaker links -from the in-plane σ-bonds -but also create a capacitive coupling between carbon layers [3] [87].

Here are some design considerations justifying the use of CNTs over graphene in the design. The electron properties of graphene and CNTs are related to their hexagonal carbon structure and they will lose some of their properties by sharing electron's orbitals with other structures. The consequence is that CNTs will be a better candidate for biosensing since all of the surface of a graphene nanoribbon is deposited on a mechanical substrate. The tubular structure of CNTs will maintain most of their atoms at distance of the interfering substrate reducing wave function mixing. This consideration supposes a structure with deposited carbon channel opposite to a suspended carbon channel. The suspended CNT or graphene structure would be in theory the best choice but considering the added complication in process and the limited potential gain we will chose to work with deposited CNTs.

The first issue to consider in choosing a CNT structure is the single/multi-wall quality of the nanotube. The first objective is to transfer changes in the electronic state of the environment of the nanotube through capacitive coupling. The second objective, as will be described in the following section is to amplify these changes through field effect in a transistor structure. The use of multiwall CNTs reduces the coupling through the walls compared to a single wall CNT. This is due to the fact that the coupling in done through multiple layers of graphene-like structure coupled with each-other. Moreover, multiwall CNTs have been shown to reduce amplification in FET structures compared to a similar single wall CNTs [START_REF] Yamamoto | Highly Sensitive Biosensors Based on High-Performance Carbon Nanotube Field-Effect Transistors[END_REF]. For those two reasons, I chose to use single wall CNTs and the study focuses on this type of tubes only.

Appendix A describes the unique electronic structure of CNTs: nanowires can have 1D conduction lines but they are spread in the section of the wire. In CNTs these lines are all at the surface of the material increasing its sensitivity. This property makes CNTs the best candidate for field effect based biosensing applications.

Appendix A describes the fact that CNTs conduction is directly due to their carbon lattice and that this structure needs to be conserved as pristine as possible to maintain electronic properties of CNTs. In order to do so I will use pristine CNTs, opposite to carboxyl-functionalised CNTs [START_REF] Liu | Chemical functionalization of single-walled carbon nanotube field-effect transistors as switches and sensors[END_REF]. I will also need to take specific care to maintaining the integrity of the CNT sidewalls.

Appendix A also addresses that the gap of CNTs is inversely proportional to their diameter. This property arguments for a choice on my part of a CNT with a small diameter for an optimised amplification in the design.

The average mean free path in CNTs is of a few hundred nanometers in appropriate electronic conditions. This property arguments for me to use tubes with a length limited to a couple micrometers in order to maintain electronic properties.

Finally, Appendix A shows that electronic properties of CNTs change drastically with their chirality. Leading to the fact that I will need CNTs with a high purity in chirality, in order to reduce metallic CNTs and electronic comportment variability.

CNT channel in CNTFET structure

I previously addressed the atomic structure of carbon nanotubes allowing me to describe their electronic structure. Through this study, I showed the interactions of CNTs toward their environment especially toward the electronics particularities of the CNT surroundings. In this section I will describe CNTs used as channels in CNTFET transistors. I will describe the different types of CNTFETs and their specificities. The objective is to justify my choice in structure for the design and precise which CNT I will use. This study is based on [4].

Physics properties of CNTs as transistor channels

I outlined previously that depending on the chirality of a CNT it can be semi-conducting or metallic -Figure 1.1. In order to produce a transistor with a strong amplification, the channel needs a gap. I will address here the effects of the properties of the tube on the transistor.

Diameter effect

CNTs are here treated as graphene sheets with a periodic boundary condition. In doing so, it is assumed that π orbitals are still orthogonal to σ orbitals in the graphene plane and so π orbitals are treated independently as in the graphene case. This assumption, however, is not valid for SWNTs due to the curvature of the graphene lattice which leads to hybridization between π and σ orbitals, consequently the degree of hybridization becomes larger as the diameter of a SWNT gets smaller. One of the consequences is that a small bandgap opens up in 1.1.2.1.3 Electromagnetism and scattering effects [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF] discusses that even when considered ballistic -no scattering effect -CNTs have a quantum limit in conductance due to the 1D line structure. Each sub band of the CNT will have a minimum theoretical resistance of R q = 6.5kΩ. In the previous part we considered the states in the length axis to be continuous by considering the length of the tube as infinite.

That assumption has been verified to be true for CNTs with a length of more than 1µm. Bellow this value small gaps have been estimated at E = 0.8meV/(L(µm)).

Under the influence of an applied magnetic field, electrons acquire additional phase factors -Aharonov-Bohm effect -proportional to the magnetic flux enclosed by the electron paths. In CNTs that effect will shift the 1D sub bands along the circumferential axis with an energy of 1meV per 1 Tesla for a d = 2.5nm SWNT -Figure 1.5. The sensor I am currently designing, reactions of the nanotube to magnetics can occur but will be considered as a source of noise.

Close to the previous considerations, a modification of the mechanical structure of a CNT changes its lattice properties. Therefore, it also changes the position of the K-points relatively to the allowed 1D conduction subbands. This effect can create a gap in metallic CNTs or render semiconducting CNTs metallic. In order to limit this effect, I will design a structure aiming to reduce the sharpness of angles that could bend the CNT -c.f. Section 2.3.

Another property addressed in [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF] is the scattering. Phonons in CNTs have been found to be of low energy -acoustic phonons -or with high energy -optical phonons. Acoustic phonons can be created at energies close to the band gap energy, they can be created at room temperature by an electron scattering, their mean free path -mean distance without scattering -is of around 1µm. Which means that a CNT of ∼ 1µm length can be considered as ballistic -scattering free -at least regarding acoustic phonons. Optical phonons are located in energy space farther from the Fermi level which means that that type of scattering is only possible for an electron with an energy noticeably above the energy level where the scattering can take place. A strong V ds is needed for this phenomenon to occur because an electron coming from a high energy source and going to a low energy drain can gain enough difference of energy to scatter. These phonons have a mean free path of 10to20nm and are significantly experienced with V ds > 0.4V -depending on the length of the tube. This effect is one of the main reasons for the saturation effect of CNTs far below the theoretical quantum conductance and the longer the tube the more it will saturate -Figure 1.6. 1.1. The central role of the carbon nanotube and field effect transistor structures 11

φ SB p ∼ E g /2 + φ CNT -φ M φ SB n ∼ E g /2 + φ M -φ CNT (1.1)
The barrier height at a metal CNT interface is defined by (1) for holes and (2) for electrons. [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF] It is for this reason that V ds in CNTFET measurement rarely go over V ds = 0.4V. In my developments, I will avoid this effect and limit the channel potential to 0.4V during chemical measurement.

Structures of CNTFETs

Here, I will describe the structures of CNTFETs and their specificities. I will start with channels structures, dominated by their link to the drain, source and gate. I will follow with the doping of the channel and the FET architectures that can be performed. The objective is to chose a structure for the CNTFET that is compatible with a sensor technology application and the previously mentioned specific objectives. The last paragraph summarize my decisions.

Electronics of CNT-

Metal contacts I will describe here the specificities of the contacts to the source and drain of the CNTFET regarding electronics problematics. We will address the material properties in the next part: Section 1.2.1. These junctions are performed at the tips of the nanotubes and are defining the behavior of the channel for non-doped CNTFETs. When connecting a CNT to a metal contact the work function of the tube will align on the work function of the metal. This effect creates barriers of forbidden states called a Schottky barrier -SB Figure 1.7 described in [4]. FIGURE 1.7: Fermi level pinning in Metal-CNT connection. [4] We can note from these two equations from [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF] -Eq 1.1 that if the two work functions are equal, the two barriers are equal to E g /2. If we connect a CNT to a high work function metal the hole SB is theoretically null and the same happens for the electron SB if the work function is low -Figure 1.8. This effect has been experienced by applying H 2 on Palladium contacts -H 2 is known to lower the palladium's work function -and observing the height of the resulting SB -Figure 1.9. An important note is that a metal work functions is highly dependent on the environment, and the reported vacuum values cannot be used to accurately predict the SB heights at the metal-nanotube interfaces. This effect can be used to create CNT based chemical sensors although they do not use the field effect. This structure can measure the variation of work function of a CNT or a metal at the junction by a known compound. [4] also discusses the shape of the electronic interface between metal and CNT. Compared to Metal/Si barriers in a bulk set-up, the metal/CNT SB are very thin due to a low depletion depth. The depletion depends on the capacitance effect due to the junction of materials with different energy states, the charges around that junction will move toward an equilibrium. In bulk materials that capacitance is a plane at the contact of two 3D materials whilst in metal/CNT junction the capacitance is the intersection of a plane with multiple 1D lines -dots -diminishing the effect.

Finally, an alternative to CNT metal contact has been demonstrated recently by [START_REF] Engel | Graphene-enabled and directed nanomaterial placement from solution for large-scale device integration[END_REF]. The idea is to use conductive graphene as an intermediary. The graphene is deposited on the substrate. Then part of it is covered by a metal forming an electrode tipped by graphene. Two graphene tipped electrodes create a dielectrophoresis setup for CNT deposition on graphene. The advantage is that the SB is created between conductive graphene and conductive metal reducing its effects. This is beneficial is case of MOS-like CNTFET architecture. In our case the complexity of this process and the lack of studies confirming electronic results are strong drawbacks.

For my design, these properties show how important from an electronic point of view the choice of the contacting metal for the source and drain of the transistor is important. Depending on the metal work function, the created transistor will be a balanced or p-type or n-type transistor. Since the objective is to reduce interactions with the sample that is being measured, I want to work at around a zero gate potential. In order to do so, it is convenient to adjust the characteristics of the channel toward direct reception of the biochemical potentials. I address in the model of the electrochemical part -c.f. Section 4.3.1 -that the equivalent relative potential of the chemical gate would be of between 0V and -0.1V. In this case I will favor a strongly p-type CNT. An argument can be made that a strongly n-type transistor would give similar results. Clean room experiments show that manufactured CNTFETs tend to drift toward p-type due to oxygen adsorption [START_REF] Roch | Ambient effects on the electrical conductivity of carbon nanotubes[END_REF]. Therefore, by using a p-type transistor I work with the experiments conclusions instead of taking the rick of working against. By using a strongly polarized SB, I theoretically place the chemical working point in the amplification range of the transistor without external intervention. For this considerations I chose to use gold as a metal for drain and source contact -Figure 1.10. I treat here a transistor point of view, the material contact quality is also important in the choice of gold as a contact metal -c.f. Section 1.2.1. The third consideration in the choice of metal is its biocompatibility and reaction to complex biological field. The final consideration in my choice of using gold is its availability in clean room chemical vapor deposition -CVD. More specifically, the local expertise guarantees the quality of the home made production.

Gate effect on

CNTFETs I will describe here the different principles directing gate effects that can be expected in a CNTFET structure. I will conclude by summarizing how the gate effect will work in my concept.

First [4] discusses the fact that the gate effect is strongly dependent on the dielectric geometry. CNT semi conducting characteristics are strongly dependent on their symmetry and the gate electrical potential needs to be considered uniform in order to maintain these properties. For high performance microelectronics, CNTs are drowned in hi-k dielectrics often with surfactants such as NO 2 or HFO 2 witch can be removed by annealing after the dielectric deposition [START_REF] Javey | High Performance n-Type Carbon Nanotube Field-Effect Transistors with Chemically Doped Contacts[END_REF]. In these configurations weak Van der Waals forces link the CNT and the dielectric which maintains the properties of the CNT. The unavoidable coupling of phonons and electronic orbitals tion range is shaded. [START_REF] Wilhite | Metal-nanocarbon contacts[END_REF] will reduce the mobility of the charges but only slightly thanks to the low coupling strength. In a plane configuration of the gate the surface potential on the dielectric will need to be important enough to be considered uniform along the diameter of the tube [4].

Another important effect described in [4] is the quantum capacitance of the tube, the variation of the state of the channel is defined as in Eq 1.2. With C g the gate capacitance and C q the internal capacitance of the nanotube.

∂ ĖF ∂V g = qC g C g + C q (1.2)
With E F = qV a , E F the Fermi level of the channel and V a the local electrostatic potential. If the geometric capacitance C g dominates V g is directly related to V a -Eq 1.3.

∂E F ∂V g = q (1.3)
If the quantum capacitance C q dominates the gate potential will need to be increased to have the same effect on the tube. The geometric capacitance can be approximated but it is hard to estimate or measure the quantum capacitance. In my concept, the gate is built from pyrene groups bond to the sidewall of CNTs. In this case estimating a value of capacitance is hazardous at best and supposes to know the pyrene coverage rate.

The effects of the previously outlined modifications on the CNTFET are summarised by [START_REF] Heller | Identifying the mechanism of biosensing with carbon nanotube transistors[END_REF] in Figure 1.11, related to their electrical characteristics. The effect that I want to observe is the density of charged species around the CNT. For example, PO 2- 4 ions can be adsorbed on a substrate close to the CNT creating an electrostatic potential. This is also called the gate effect Figure 1.11(a). I addressed previously that some chemicals can have interactions with metals, modifying their work function. Since the height of the Schottky barriers at the contact depends on work function of the metal contact such interaction modifies the overall conductance of the system In this section I outlined the different modifications that can undergo a CNTFET. In my design I will consider gate effect from PO 2- 4 ions as our signal to be transduced and any other effect described here as noise that I want to reduce. In order to address the variability of SB upon metal work function modification I will cover any metal surface that is in contact with the sample during measurement with an inert polymer. The use of a Pyrene gate reduces the capacitance and mobility effects. A future addition to the sensor in order to increase the selectivity would be to add a protective layer on the CNT sidewall after functionalisation. The objective would be to create a selective layer for the gate effect by covering the non-functionalised surface of the sidewall with a molecule creating little interferences with the CNT. This would allow to stop interfering molecules to approach the CNT's sidewall. This would reduce noise from undesired modifications of the surrounding's electronics [START_REF] Amanda | BIOSENSORS BASED ON CARBON NANOTUBE FIELD EFFECT TRANSISTORS (CNTFETs) FOR DETECTING PATHOGENIC MICROORGANISMS[END_REF]. On the other hand, this protective layer needs to be only nanometers thin and inert toward proteins in order to stay neutral toward the selectivity of the sensor.

CNT Chemical doping

In bulk technologies the doping of materials is realised by replacing atoms from the original material by donor atoms -five electrons in the valence orbital -or acceptors -three electrons in the valence orbital. In CNTs that process would require to replace a carbon atom in the CNT lattice changing deeply its properties. On the other hand, charges of CNTs are in its surface and therefore very sensitives to their surroundings. By placing very electronegative species close to the CNT, a gate effect equivalent to a negative V g can be observed. And equivalently by placing poorly electronegative species close to the CNT a gate effect can be observed corresponding to a positive potential V g . For example, in Figure 1.12 the "opening" and "closing" of a CNT channel has been recorded in a gas flow. In part A of this example, a p-type transistor is opened with an electronegative molecule -NO 2 . In part B the same transistor is closed by an electropositive molecule NH 3 . This effect is very similar to the gate effect presented previously except that for doping CNTs the objective is to create a constant, controlled and durable gate effect. The main issue in this process is that the molecules are only linked to CNTs through week electrostatic forces, which makes them unstable. Polymers have been found to be a good compromise because of their stability despite their reduced effect on the CNT. Stable and biocompatible functionalisation is an extensively researched subject [START_REF] Katz | Biomolecule-functionalized carbon nanotubes: Applications in nanobioelectronics[END_REF], [START_REF] Liu | Chemical functionalization of single-walled carbon nanotube field-effect transistors as switches and sensors[END_REF]. In summary chemical doping is a complex and volatile process that will be avoided in this project if possible. This is particularly relevant to the structure as we will see in the next part.

CNTFET structures: MOS-like, SBCNTFET and BTBTCNTFET

The main CNTFET architectures are described in [4]. First, a MOS-like CNTFET can be created from a CNTFET channel by building it with reduced Schottky barriers through a controlled doping of the CNT channel -Figure 1.13. This structure creates in the CNTFET a band structure equivalent to that of a classic MOSFET -Figure 1.14. Although it would theoretically show better amplification than a Schottky Barrier CNTFET -SBCNTFET -the variability of the doping process and its complexity regarding the possibilities in the materials at disposition forbid us to use such a structure.

Another structure, presented in [START_REF] Hai-Liang | Performance optimization of conventional MOS-like carbon nanotube FETs with realistic contacts based on stair-case doping strategy[END_REF], is also similar to the silicon technologies: the band to band transfer field effect transistors -BTBTFETs -are realised with a qualitatively similar profile than for MOS-like doping. The difference is that with a strong enough doping the charges will be able to tunnel through the gap at the limit of the doping areas creating a transistor -Figure 1.15. These transistors are used in special cases, for my development the drawbacks of a doping profile stay the same as previously without the advantage of the stronger amplification. The BTBT structure is not adapted to the current development.

By adjusting the doping rate -e.g. I outlined here the complexity of working on the energy profile of a CNTFET with doping.

Considering the sensor technology application and the means at my disposal it is realistic to keep my work around SB-CNTFET. The doping of CNTs is a precise, complicated and not well controlled matter requiring specific material and expertise. I will limit my work on the channel structure to the metal/CNT junction and the gate effect. Two gates will be built,first an electronic back gate for the characterisation. Secondly, a chemical gate, described in 4, to allow contact between the biological field containing the target and the CNT. This gate will be used for measurement.

1.1.2.2.5 SBCNTFET design [4] describes how the CNT/metal contact changes with the diameter of the CNT. For balanced electron/hole SB, the conduction variation depending on the polarisation of the transistor is described as follows. If V GS > V DS /2, the conduction band edge is pushed down by the gate voltage. Therefore, electrons can tunnel from the source contact into the channel region and produce electron current. For V GS < V DS /2, the valence band is lifted up by the gate voltage. Holes can tunnel from the drain contact into the valence band and produce a hole current -I use here n-FET conventions, in p-FETs the source and drain are switched. The minimal leakage current is achieved at V GS = V DS /2, at which the electron transfer is equal to the hole current. The minimum leakage current in that state, exponentially depends on the SWNT bandgap and increases faster than the open state current with the decrease of the gap. Therefor the I on /I o f f ratio diminishes with the increase in tube diameter. In our case we want to prioritize the optimisation of amplification in the FET structure. Therefore we will chose to work with a CNT of a low diameter ∼ 0.9nm with a gap of around 1eV.

An other important aspect of the CNTFET structure, described in [START_REF] Kordrostami | Fundamental Physical Aspects of Carbon Nanotube Transistors[END_REF], is the gate thickness and its screening effect on the electrostatic potentials of the source and gate contact. We can see in Figure 1.19, the variations of the profile of the electrostatic potential created by the gate depending on the oxide thickness. The experiments on CNTFETs from [START_REF] Kordrostami | Fundamental Physical Aspects of Carbon Nanotube Transistors[END_REF] lead to conclude that the SB thickness depends mostly on and is approximately equal to the gate insulation thickness. In my sensor technology concept, the back gate is 300nm thick and will only be used for characterization. The chemical gate is in theory of 0.33nm thick corresponding to the distance between a Pyrene moiety and the sidewall of the CNT. On the other hand the chemical gate will not fill the whole sidewall surface. The reasons are that the CNT is deposited on the back gate and because of the never ideal rate of functionalisation.

Another characteristic of CNTs described by [4] is that the ballistic limit depends on the length of the tube, the light exposure and the supply voltage. V ds ≤ 0.4V/µm insures a low rate of phonon scattering in ambient conditions. Despite the existing scattering rate, the loss in performance -I on -is not as important as could be expected. As explained previously the back-scattered electrons in 1D lines will encounter a higher barrier from the source side, creating an accumulation of charges in the channel but no negative current. The same thing is true for holes. The scattering effect also reduces the average carrier velocity which is compensated by an increase in carrier density to maintain the equilibrium current. This characteristics of CNTFET structures confirms my choice to work with high bandgap CNTs.

Section summary and CNTFET model

I depicted in this chapter the advantages of carbon structures for microelectronics. More especially I described the advantages of CNTs in biosensing and the characteristics that are researched for the application. Then, I described the different structures of CNTFETs with their advantages and drawbacks. Finally, I addressed several considerations concerning the chosen structure. Similarly to the previous section I will here outline the quantitative dimension of the design through the modeling point of view.

The objective of this model is to anticipate on the results and confirm expected phenomenons. In our case, I searched for a model based on architectural parameters and that would also be physics comprehensive. CNTs and CNTFETs have been and still are extensively studied as the replacement for Si technologies [START_REF] Hills | Modern microprocessor built from[END_REF]. Because of that, models have been created from the more precise particle physics point of view to the purely result-fitting analytic methods. The most representative and most functional model that I found is the VS-CNTFET model from Stanford. Figure 1.20 shows the structure and schematics of this model.

One of the limits to this model regarding the case at hand is that the structure modeled is that of a MOS-like CNTFET. Despite that the model is still a good approximation of the structure especially since the architectural parameters of the model allow us to reduce the error created from the difference in architecture. The use of this model will allow to validate characterisation of CNTFETs from the solid back gate. The second limit is that it is based on a solid gate parameter hence the complexity of representation of the chemical gate. We saw in the previous chapter that the difference of ions concentration would provide a gate potential of ideally between 0V and -0.1V. The issue is that potential is applied as an electrical field through the chemical gate -the couple pyrene and CNT. This chemical gate is very difficult to model in solid equivalent due to the non homogeneity of the chemical layer. On the other hand, it would be very interesting to use the future results of characterisation in order to highlight the relationships between this specific functionalisation and a solid gate effect. Demonstrating an analytic tie between chemical and solid gate would allow simple and effective modeling of the future sensor technologys built from the technology in design.

The results of the model are presented in Figure 1.21. Realistically, due to the several interferences discussed above, I expect a conductivity variation of 5% circled in red.

CNTFET architecture

In this section, I will discuss the contact between CNT and metal, its quality and how to improve it. Then I will address the architecture of a SBCNTFET for biosensing. I will start by addressing the organization of CNTs in the structure. Then I will describe the gate structures and the use of a reference electrode for measurement. Finally, I will describe considerations regarding the sensor in its entirety. I will conclude this chapter by describing the full prototype as designed.

CNT/metal contact

I outlined in the previous section the electronics properties of the CNT/metal contacts. In this section, I will discuss the mechanical parameters influencing the quality of the contact. This contact quality is partly determined by the compatibility of the metal lattice to the carbon lattice. The second characteristic is the part of the tube that is contacted -sidewall or tips -the third is the surface of contact. Depending on the structure of this contact, an alternative barrier to the previously discussed SB can arise. Since this second barrier is not modified by the gate effect, it tends to reduce the amplification of the transistor structure. The objective here is to understand this unwanted barrier arise and how to limit its effects.

As previously, the properties of CNTs are approximated using graphene modeling in similar conditions. In Figure 1.22 the properties of a graphene/metal interface are modeled using density functional theory -DFT. This model allows identification of the metals susceptible to create a strong link to CNTs. Another consideration to arise from those studies is that the quality of the contact depends strongly on the distance between the carbon structure and the metal lattice. These results have been confirmed in [START_REF] Wilhite | Metal-nanocarbon contacts[END_REF], by the arising of a secondary barrier from the expected SB. This specific barrier can be reduced by using current stimulation -Figure 1.23. Indeed the research team showed that by pushing current through the contact, the distance between the structures can be reduced durably -Figure 1.24. Another issue regarding the contacts of the CNTs to metals is their compatibility as materials as observed by [4]. We can see in Figure 1.25 that Rh and Pd interact strongly with nanotubes, resulting in a uniform surface coating while Al and Pb show weak interactions with poor dispersion on the nanotube surfaces, resulting in bundles on the surfaces. Pd and Rh enable more transparent contacts to SWNTs than other metal. The lower the diameter the more important these effects are. This may indeed be due to the weak interactions of Al and Pb with nanotubes that results in a vacuum layer formation -I.e. longer bonds -at the sidewall interface, preventing an efficient injection of the carriers. Au and Fe are in intermediary states showing not particularly good natural contacts but opening the expectation of notable improvements of the quality of the contact upon electrical stimulation. [113] describes that when a CNT is deposited or covered by metal, two types of contact are created. The first, depending on the structure of the tube -open tips or closed tips -creates an ohmic contact at the tips of the structure. These contacts are often strong due to the charges availability at the limits of the hexagonal carbon lattice. The second type of contact is created between the CNT sidewall and the metal lattice Figure 1.26. In this case, the contact between metal electrons and π-electrons from the carbon structure creates weaker bonds. The impact of this sidewall contact was studied and we can see in Figure 1.27 that it modifies the overall contact resistance for its first micron of added length. This contact has a planar structure and the surface is a more appropriate parameter to discuss its properties. In our case, the size of the contact electrodes and the length of the tubes creates an overlap and a contact of between 0.25and0.5µm of length on each side. This shows the importance of enclosing the nanotube in metal in order to increase the surface of the sidewall/metal contact.

Considering these remarks and the previous considerations concerning the synthesis of CNTs the choice have been made to buy CNTs as ash and deposit them during the process. This follows the objectives of cost efficiency and simplicity of the process. The following consideration supposes this type of process and are different from issues that one could have with CNTs synthesised directly in place. ." [START_REF] Wilhite | Metal-nanocarbon contacts[END_REF] The last contact issue presented here is related to realization and lithography. Indeed, I outlined with the help of [START_REF] Wilhite | Metal-nanocarbon contacts[END_REF] that to optimise a contact between CNT and metal one needs to optimize the surface of contact. The shape of that contact is determined by the shape of the metal on which the CNT is deposited. This profile depends on the lithography technique used to deposit the contact metal layer. In order to optimize the contact surface, we need to reduce the sharpness of angles so that the CNT can bend along the surface. This consideration pushes toward the use of lithography with lift off and over-carved resin to guarantee metal walls with a positive slope -c.f. Section 2.3.

The second characteristic that needs to be taken into account here is the thickness of the metal creating the contact. Indeed, in classical bulk electronics the thickness of the contacts is most often determined by its desired maximum current density. In our case, a second parameter enters the equation. The fact that CNTs are all length and deposited on the metal layer pushes us to consider the height of the contacting metal section. Indeed, we saw that CNT electronics properties were depending on their structure. By bending a CNT we take the risk to modify it deeply, turning a semiconducting CNT into a metallic one. Furthermore, a CNT can be placed is a suspended state if its contacts are high enough. This structure parameter has two main effects. First, in our case, it could mean an augmentation of the sensitivity of the sensor, mostly due to the increased surface of functionalisation. The second effect is the reduction of the control of the channel state from the back gate. This should not create issues in the measurement steps since the back gate is only used for characterization of the transistors. Indeed, the final version of the sensing technology does not requires the back-gate structure c.f. Chapter 4.4.1. This structure is used for characterisation, development and research purposes. On the other hand, the characterization could lose in precision. The effect of the height of the contact and the suspension of the CNT channel is a complicated and not well-known matter that would require its own experimental investigation.

An alternative resolving these mechanical issues is the use of graphene as an link between CNT and metal as demonstrated by [START_REF] Engel | Graphene-enabled and directed nanomaterial placement from solution for large-scale device integration[END_REF]. The CNT is deposited on a monoatomic layer which reduces the mechanical constraints on the CNT -Figure 1.28. The issue is that since I chose to work with a SB-CNTFET architecture, which uses the variation of SB as an amplification mechanism. The use of graphene as an intermediary reduces this effect and is incompatible with the chosen structure.

CNT structures for CNTFET manufacturing

There are several methods to realise a CNTFET resumed in [START_REF] Venkataraman | Carbon Nanotube Assembly and Integration for Applications[END_REF] and some examples in [START_REF] V K Sangwan | Controlled Growth , Patterning and Placement of Carbon Nanotube Thin Films[END_REF] and [START_REF] Valentin | High-density selective placement methods for carbon nanotubes[END_REF]. We chose to not synthesize CNTs and work with bought CNTs due to equipment limitations, cost and efficiency. The next step is to work on placement/alignment of the tubes. This procedure is realised with the nanotubes in liquid suspension, therefore we worked on a CNT dispersion -c.f. Section 2.1. The choice of manufacturing method mostly depends on the expected structure of the channel. Two parameters define a CNT structure for a channel. First, the organization of the tubes. Second, the density of the tubes deposited -CNT film to single spaced CNTs In a more practical fashion the structure of organization of the CNTs translate to using already created metal electrodes to guide them [START_REF] Zhang | Alternating current dielectrophoresis of carbon nanotubes[END_REF]. The second method, addressed first here, consists in placing the electrodes after CNT deposition. Some techniques allow orientation of CNTs in an aqueous field during deposition allowing an organization of the CNTs on the surface without already in place electrodes - [114], Figure 1.31. Most of processes depositing CNTs first will create unorganized CNT bundles [START_REF] Park | A review of fabrication and applications of carbon nanotube film-based flexible electronics[END_REF]. Several issues arise from such a hazardous structure. First, the non-uniformity of the resulting layer of tubes reduces reproducibility of the process. Second, the electrodes creating the transistor need to be manually placed depending on the location of the deposition. The final issue due to this type of process comes from the orientation of the nanotubes. Indeed, by placing them without some guide, CNTs can end-up crossing each other. This issue becomes problematic when a tube does not come in contact with both of the source and drain electrodes. This create sites for functionalisation that will react to chemistry without transducing the signal. This creates a new source of variability but also reduces the sensitivity of the sensor. By placing drain and source electrodes first, we allow a better organization of the nanotubes structure. These electrodes can be used to apply an electrical field in the suspended CNTs in order to direct them to their placement locations. This method called dielectrophoresis is described in Section 2.2.

The second characteristic of the structure described in [START_REF] Park | A review of fabrication and applications of carbon nanotube film-based flexible electronics[END_REF] is its density. Optimizing the amplification of the sensor will drive our decisions here. Building a sensor technology can require as much sensitive sites as possible in a surface area to optimize its sensitivity. This density of receptive sites depends directly on the density of nanotubes. Considering only this parameter one could say that CNT films being as dense as possible are better suited for biosensing applications. However, issues arise from this structure. First, a guided deposition of a film can create a poorly homogeneous film depending on the regularity of the electrodes leading to some variability in the process. Second, CNTs in a too dense configuration would impede access of the functionalisation to most of the sidewalls surface. Finally, CNTs in a film structure will screen each other from external electronic variations, including the chemical gate effect [START_REF] Gerald | of carbon nanotubes Channel length scaling behavior in transistors based on individual versus dense arrays of carbon nanotubes[END_REF]. One last consideration is the self-limitation of CNT in placement. In a close fashion to the screening effect, CNTs reduce the electrical field around themselves. This creates a self-limiting density upon deposition, meaning that the CNTs will be deposited a short distance from each other [START_REF] Vijayaraghavan | Ultra-large-scale directed assembly of singlewalled carbon nanotube devices[END_REF]. This supposes some prerequisite. First, a non-dispersed bundle of CNTs will act as a single particle and they will not separate themselves due to the self-limiting placement effect. Second this effect depends on the strength of pull of the CNT, strongly attracted Outlined insets show highresolution images of a channel (two channels in 100nm case)." [START_REF] Wu | Top-Down Patterning and Self-Assembly for Regular Arrays of Semiconducting Single-Walled Carbon Nanotubes[END_REF] Chapter 1. Design of the CNTFET sensor technology CNTs will be deposited more tightly together than lightly pulled CNTs.

In my design, I want to create a reliable and robust process with as little variability as possible while focusing on the amplification effect of the sensor. Following this objective I chose to deposit the drain and source metal first and use it in a dielectrophoresis set-up for alignment and placement. I chose to work with single CNT configuration to optimize the amplification from the field effect. This choice supposes to realize a high purity dispersion of singly separated CNTs. One the other hand, the reduced CNT density in the dispersion compared to a film deposition relaxes some of the constraints on the dispersion -c.f. Section 2.1.

Sensor technology gate structure and potential reference

I outlined previously that the objective is to measure a local potential variation. In order to do so, the sensor needs a reference to the biological field potential. Moreover, the potential is measured between the CNT and its surroundings. Considering the objective to have a sensor as passive as possible toward the biological target, the goal is to obtain an internal CNT potential as close to the biological field potential. I addressed previously that the conduction in SBCNTFETs is due to the SB. We also saw that a charge going through the source had enough energy to go through the drain barrier. We could also cite the quasi-ballistic properties of CNTs to explain that the far greater loss in potential along the CNT is found in the source SB section. This means that the CNT potential in itself is very close to the drain potential. In conclusion, in order to create a sensor based on CNTFETs as passive as possible toward the biological field containing the biomarker, the reference of the sensor needs to be applied to the drain of the transistor. This consideration is also important for future developments of the project, as the created sensor needs to be integrated in a drain-referenced set-up.

We discussed previously two types of gates, the chemical gate and the back gate. The chemical gate is used to measure the local variation in potential and the back gate is used before measurement in order to characterize the sensor. This characterization setup in only needed during the development of the sensor in order to confirm expected results in the characteristics of the transistor. In a final version, the sensor technology would need to be characterized through its chemical gate in order to include the whole of the measurement chain. This would allow us to build the sensor on an inert substrate such as quartz. The sensor is, in its development version, built on a SiO 2 insulating layer for the back-gate that attracts small positive ions such as H + .

The gate structure is an extensive subject that needs to be investigated in practical experiments for each case. These architectures allows in some cases to improve the transmitted signal through different means by intervening with the biological field. One of the first examples, given by [START_REF] Chu | Beyond the Debye length in high ionic strength solution : direct protein detection with field-effect transistors ( FETs ) in human serum[END_REF], uses an external gate in order to rearrange the biological field with the aid of an electrical field -Figure 1.32. This allows discriminating between the electrochemical target fixed on the receptor and other free ions increasing the observation distance -Debye's length. Another option would be to vary the working point on the characteristic of the transistor through back-bate stimulation. Allowing, similarly to the previous structure, selective modification of the CNT's environment and optimization of its observation of the targeted ions. Finally, the variation of the stimulation potential or of the back-gate in a sinusoidal signal at low frequency -100Hz -can reduce the fouling of the sensitive surface [START_REF] Yamamoto | Noise Reduction of Carbon Nanotube Field-Effect Transistor Biosensors by Alternating Current Measurement Noise Reduction of Carbon Nanotube Field-Effect Transistor Biosensors by Alternating Current Measurement[END_REF]. Although these solutions could improve the quality of the measurement, they do not respect the objective of passivity toward the biological sample. Alternative gate use will be considered as possible future improvements in case of a lack in sensitivity.

Sensor point of view

Following [START_REF] Kim | Sensors : The First Stage in the instrumentation and measurement[END_REF] a sensor is defined by its response to a stimulus. This response can be observed through changes in a potential or a current to be conditioned by an electronic front end. Then the signal is digitised and can be treated as data. In our case, the conductivity of the CNT channel will change upon modification of the electrochemical target's concentration. We chose to work at first with a constant stimulation potential between source and drain. In consequence, we will measure the output current and use it to deduce the change in conduction of our sensor.

In the previous considerations we focused on optimizing the ratio I on /I o f f . I o f f corresponds to a current with natural concentration of targeted ions around the CNT and I on the current at maximum stimulation. In order to better this ratio the objective was to reduce I o f f without reducing I on and increasing I on without increasing I o f f . Another consideration is the quantity of current delivered by the sensor. For example with our design as such we could create a sensor with only one transistor and with a I o f f of a few nA and I on of between fifty and a hundred nA. The ratio is close to optimal but it is difficult to measure a variation of a few nA. Another issue created by such a small structure would be the variability. We aimed during this design to produce a prototype with reduced variability in its manufacturing process. Despite that, there is always some divergence between created CNTFETs. In order to address these issues I will use a structure containing multiple CNTFETs in parallel. This reduces the effect of process variability and increases the current so it can be easily measured while not modifying the I on /I o f f ratio. With my CNTFET current estimated from a few to a hundred of nA we would need a million of transistors to create a sensor technology targeting a signal treatment in mA.

Another issue that needs to be regarded through the full sensor technology spectrum is the connection between functionalisation, CNTFET density and signal. This project aims to be a proof of concept for a platform of sensor technology development based on the developed technology. Although the previous considerations were common to the targets, this section addresses a study that will require to be performed for every individual targeted molecule depending on its concentration.From a modeling point of view, it is difficult to estimate the actual effect that has the phosphorylation of a protein on the CNTFET. Moreover, it is also complicated to predict the functionalisation-filling ratio of CNT sidewalls. In order to anticipate on future issues, I will illustrate the extreme cases of range misalignment.

First, on a single CNTFET, if an activation site fully opens the channel, meaning that a second site activation would be transparent, the sensor would saturate at very low concentration of activation. In that example, a single transistor would be either open or close and the ratio of opened channels would become the information. In that case, it would be in our interest to limit the functionalisation, in theory at one site per tube. On the other hand, a high activity biomarker would suppose a very large quantity of tubes in order to present a great enough quantity of sites to phosphorylation. Failing to do so would provoke a saturation of the sensor in the range that the sensor should be able to observe.

In the second case, most of the surface of the CNT needs to be covered by active functionalisation in order to attain a fully open state. In this case, the functionalisation rate would need to be high enough to attain that open state. In this case the sensitivity would be limited by the maximum functionalisation rate. In this configuration, a low activity target could push to reduce the quantity of CNT channel in order to reduce and optimize phosphorylation site quantity. In summary, the functionalisation of the sidewalls and the CNTFET density need to be optimized to fit the activation effect and density of the target. As explained previously these are complex to model and anticipate and the optimization will need to be experimental.

Summary of the design: schematics of the prototype

Here, I will summarise the results of the current chapter by presenting the designed sensor technology: Figure 1.33. This picture illustrates the structure of the sensor technology in a vertical cut with a gate structure corresponding to the application example developed in 4. We can recognise the usual elements constituting a sensor technology [START_REF] Grieshaber | Electrochemical Biosensors -Sensor Principles and Architectures[END_REF]. First, the target is depicted by the blue diamonds, here only the phosphate ions are represented. Then the selective layer is in orange. Then the CNTFET structure plays the role of amplifying element. Finally, the data is extracted from the current measurement, relative to the stimulating potential. This allows extraction of the conductivity of the sensor. By following this signal we can monitor the CDK4/cycD activity.

Figure 1.34 illustrates the architecture of the sensor from a top view. The substrate is represented in blue. The yellow surfaces are metal deposition. Distances in blue are pre-experimental estimates. The structure is made of two intertwined combs with each teeth -insert1 -posses hundreds of small teeth facing each other -insert2 -with a pitch of 2µm. Each couple of micro teeth facing each other creates a site for a transistor assembled by dielectrophoresis. The polymer insulation is not represented here.

Design of the manufacturing process for CNTFET biosensor

The previous chapter aimed to describe the prototype and justify the choices in the materials and architecture of the sensor. In this chapter, we will see the different parts of the realisation and their preparation. This work is based on literature and aims to the preparation of the experimental work. The results of the manipulations are presented in Chapter 3.

The first section addresses the dispersion of CNTs for biosensing and dielectrophoresis placement. The second part, outlines the dielectrophoresis principles and constraints. The third section, describes a lithographic process aiming for high resolution metal patterning. With these three steps one can create a reproducible CNTFET matrix that can be characterised. The conclusion of the chapter summarises the process flow.

Biosensor compatible dispersion

CNTs are bought as ashes and form bundles when put in most solvents. Therefore it is necessary to disperse them to place them singly in the architecture. In this section I will describe the theory and principles that allowed me to build the dispersion process. The development of the method is built around two axes. The dispersion should be optimised for dielectrophoresis -c.f. Section 2.1.1 -and compatible with biosensing applications -c.f. Section 2.1.2. The use of dielectrophoresis with an objective of placed and aligned single CNTs requires that CNTs be first separated to single CNTs in a stable state during the dispersion. We can observe this characteristic through the average particle size in the result of the dispersion process [START_REF] Jung | Evaluation of the individualization state in single-walled carbon nanotube solutions using absorption, Raman and photoluminescence spectroscopy[END_REF]. Biosensing applications require optimising the quality of the sensing surface, meaning the integrity of the CNT sidewall but also the dispersant and/or solvent ability to be removable. The result of the dispersion can be observed through atomic force microscopy -c.f. Section 3.1.

The dispersion chemistry is based on species interactions, specifically the hydrophobic and hydrophilic characteristics of species. We begin by discussing the relation between CNTs and other molecules. In the second part, the conservation or recovery of the quality of the sensing surface is discussed. First solvent and surfactant are chosen and tested as candidates. Then, sensing surface recovery tools are described. Finally, I will conclude this section by presenting the full process prototype with a range of parameters. These parameters are tested in Section 3.1 to their final value.

Individual tubes for high sensitivity

As stated previously the success of dielectrophoresis in placing single CNTs requires that they be separated during the dispersion process [START_REF] Le | Dispersion of carbon nanotubes in water and non-aqueous solvents[END_REF]. The amplification and sensitivity of the transistor are in part determined by the ratio of CNTs that are well placed and well separated -c.f. Chapter 1. A bundle of CNTs will be less sensitive than single CNTs self separated. The presence of CNTs, especially in a bundle, that are not connected with one or both of the electrodes will reduce sensitivity of the transistor. Consequently, the quality of the separation will determine the quality of the deposited channel for CNTFET building. The optimal result consists of only single CNTs that will then be placed one by one, pulled independently by the dielectrophoretic force -c.f. Section 2.2. This high quality separation allows us to take advantage of the self-separation characteristic of CNTs during dielectrophoresis. The second advantage of a good dispersion is that it reduces the risk of bundle with crossed CNTs to be placed.

CNT separation

CNTs dispersed in a solution create a colloid -dispersion of solid molecules in a liquid solution. If we introduce CNTs in water, they will agglomerate in bundles due to the fact that they interact strongly with each other and very poorly with water [START_REF] Nasir | Molecular dynamics simulations of carbon nanotube dispersions in water: Effects of nanotube length, diameter, chirality and surfactant structures[END_REF]. Indeed CNTs are unable to form hydrogen bonds with water but are very sensitive to capacitive coupling especially with each other. The first objective of the dispersion will be to reduce the coupling between CNTs in the bundle. This allows splitting them from each other - Important effects in chemistry involved in CNT dispersion are due to steric effects [START_REF] Guo | Multi-walled carbon nanotube dispersion by dispersants with different chemical structures[END_REF]. These are effects related to the morphology of species. For example, a reaction that could electrically occur can be made impossible by the geometrical structure of the species. In our case molecules will have to bend to the curvature of the nanotubes in order to create stable bonds. Because of that effect, the dispersion characteristics and optimal parameters depend strongly on the diameter of the nanotubes.

Electrochemical bonds depend on the electronic structure of the parties. For a CNT, its electronic structure is determined by its chirality. Furthermore, CNTs with close diameters can have different reactions to the same dispersion parameters/molecules [START_REF] Tan | Dispersion of Single-Walled Carbon Nanotubes of Narrow Diameter Distribution[END_REF]. In order to limit this effect, the chosen CNTs have a defined chirality of [START_REF]Dielectrophoresis of Single-Walled Carbon[END_REF][START_REF] Bautista-Toledo | Removal of the surfactant sodium dodecylbenzenesulphonate from water by simultaneous use of ozone and powdered activated carbon : Comparison with systems based on O 3 and O 3 / H 2 O 2[END_REF]. In the actual product, bought from Sigma-Aldrich, the CNTs are selected from a process SG76 -see CNT [START_REF]Dielectrophoresis of Single-Walled Carbon[END_REF][START_REF] Bautista-Toledo | Removal of the surfactant sodium dodecylbenzenesulphonate from water by simultaneous use of ozone and powdered activated carbon : Comparison with systems based on O 3 and O 3 / H 2 O 2[END_REF] product information -which contains a consequent ratio of ( 7

CNT atomic bonds Pristine CNTs can only interact through Van der

Waals bonds on their sidewall, they can't create hydrogen bonds and so are strongly hydrophobic [START_REF] Kharissova | Special Studies and Characterization of CNT Dispersions[END_REF]. The exception are CNTs with open tips. We will not consider that case in this study due to the negligible molecular interaction of the tips compared to the sidewall of micrometre long tubes. As an illustration, in our case the surface of a tip is inferior to 1 nm 2 while the average surface of the nanotube sidewall is around 5000 nm 2 . The distance between CNT and water has been reported to be around 0.1 to 0.5 nm of vacuum, which is also true for the space between CNTs in a bundle - The interactions governing the CNT aggregating process are of the type, induced dipole to induced dipole -between CNTs, see [START_REF] Filip | Influence of electron quantum confinement on the strength of carbon nanotube bundles[END_REF] for more specific information. CNTs can create bonds with other molecules depending on the similarity of the structure and the availability of π-electrons for π stacking interactions -Figure 2.5. Unfortunately, CNTs bind poorly with the most commonly used organic solvents but they will bind with lipid chains, single strand DNA, amphiphilic detergent and others [START_REF] Katz | Biomolecule-functionalized carbon nanotubes: Applications in nanobioelectronics[END_REF]. It is worth noting for the next steps of development that these molecules can be replaced by a molecule with a better affinity. For example pyrene would replace lipid chains on the sidewall of a CNT other time [START_REF] Tasis | Chemistry of carbon nanotubes[END_REF]. CNTs dispersed in a classic solvent like acetone will need a lot of mechanical energy to disperse due to the poor bond between them. I experimentally noted that they were less stable over time. I tested, in the clean room, acetone and ethanol as dispersant; they produce visual stability of respectively minutes and seconds -c.f. Section 3.1. In order to create a reproducible and robust manufacturing protocol the dispersion needs to be visually stable for hours.

Despite the fact that CNTs bond poorly with water, I propose to work in an aqueous media for two reasons. First the ability to evaluate multiple surfactant without drastically changing of dispersion and dielectrophoresis protocol. Another argument toward water-based dispersion is that CNT dielectrophoresis is well documented in aqueous mediums but less thoroughly in most others, [START_REF] Zhang | Alternating current dielectrophoresis of carbon nanotubes[END_REF].

This is due to the advantages of water toward dielectrophoresis. For example, the water permittivity (ε r = 78.5 @ 25 • C) is stronger compared to that of ethanol and most common organic solvents (ε r = 24.3 @ 25 • C). Thanks to this characteristic water will better convey the electric state applied from the electrodes to the nanotubes -c.f. Section 2.2. In addition, the fact that water has a high boiling point compared to organic solvent is a strong advantage for the dielectrophoresis set-up. I tested dielectrophoresis with acetone and ethanol, the solvent evaporates in seconds of electrical stimulation while water allows minutes of work.

Separation through chemical reaction

CNTs can be bought pristine or with modification of their sidewall. Modifications are introduced, by creating defects with an acid in the hexagonal lattice, then groups of atoms can be covalently attached to the CNT's sidewall. This alteration reduces the coupling between CNTs helping separation - [START_REF] Tasis | Introducing functional groups onto the surface of carbon nanotubes helps to solubilize these useful molecules and facilitates their study[END_REF]. One issue is that breaking of the carbon hexagonal lattice modifies the electronic properties of the CNTs reducing amplification of the electrochemical state [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF]. Another issue is that the groups created for CNT separation might covalently bond to the molecules used for dispersion. Such a covalent reaction would be irreversible and lock the functionalised groups with the surfactant [START_REF] Di Crescenzo | Non-covalent and reversible functionalization of carbon nanotubes[END_REF]. In that case, the surfactant would need to be part of a cycloaddition toward the final chemical biosensor. In my process, I choose to work with pristine CNTs and not to modify their side-wall structure covalently. This choice is motivated by the objective of a strong amplification of the field effect applied to the CNT -c.f. Section 1.1.

[53] addresses multiple dispersant/surfactants for CNT dispersion in water especially through their structure. A dispersant improves the separation of molecules and a surfactant increases the bond between particles and solvent. A molecule can play both roles and be called either. Our choice of molecule needs here to hold the two-fold role of splitting the bundles of CNTs and keep individual CNTs in a homogeneous dispersion. These dispersants often contain at least two domains, one hydrophobic and one hydrophilic creating an amphiphilic structure. In a water solution, this type of molecules will regroup in micelles, which are organised such as hydrophobic domains are on the inside and the molecules are presenting to the solution their hydrophilic parts -Figure 2.6. The most common of these molecules are soaps and detergents that can bind strongly to lipids and to water allowing washing process.

According to [START_REF] Kharissova | Special Studies and Characterization of CNT Dispersions[END_REF], in a CNT dispersion these molecules will surround the CNTs, binding them with their hydrophobic domain and presenting their hydrophilic domain to the solvent. Many non-synthetic molecules could disperse CNTs such as polycyclic aromatic hydrocarbon -PAH Figure 2.7 -containing hexagons of carbon in their structure that can bind and adsorb to the sidewall of a CNT. In amphiphilic structures the hydrophilic domain is more strongly polarised than the hydrophobic one and it influences its electronics properties. When a bond is created between hydrophobic domain and the CNT sidewall, their state is shared and the CNT is then partially coupled to the polarised dispersant. By doing so, the coupling to other CNTs is reduced and the distance between them increases - [START_REF] Fatemi | Study of dispersion of carbon nanotubes by Triton X-100 2015.pdf[END_REF] Figure 2.8. This decreases the strength of the bond between the CNT and the rest of the bundle. Once enough dispersant is adsorbed on a CNT, its distance with the bundle is high enough so that the dispersant molecules can thread their way between the bundle and the CNT in separation. When enough dispersant surrounds the CNT it cannot reconnect with other CNTs. Furthermore, according to [START_REF] Kharissova | Special Studies and Characterization of CNT Dispersions[END_REF], dispersant micelles enclosing the CNTs have the tendency to repulse each other -depending on the dispersant nature -creating a homogeneous dispersion.

[2] addresses the structure of the surfactant/CNT composite. More specifically, the research team outlines that the micelle structure created by a dispersant enclosing a CNT depends on the equilibrium of the forces regulating its affinity with its surroundings -Figure 2.9. A surfactant poorly hydrophilic, with an affinity between its hydrophilic domains and toward CNTs in the same order, will have the tendency to create groups and aggregates on the CNT surface. That effect will cause parts of the sidewall to stay surfactant-free. On the other hand, a very hydrophilic surfactant -more affinity toward water than to each other -with affinity with CNT in the same order will spread itself in a hazardous fashion. This configuration will leave space for water between dispersant molecules, limiting the surface coverage yield. Finally, if the affinity of the surfactant toward CNTs is significantly stronger than its affinity to water or each other, it will create a continuous micelle around the CNT. That last configuration is the ideal case but it needs thorough investigation of the manufacturing parameters to obtain while using a reversible adsorption.

Separation through mechanical stimulation: Sonication

As addressed in [START_REF] Kun | Sonication-assisted dispersion of carbon nanotubes in aqueous solutions of the anionic surfactant SDBS : The role of sonication energy[END_REF], the dispersion reactions described previously, most often need a very long time to occur and have poor yield without external energy supply. In order to catalyse the dispersion process and increase the yield, a series of mechanical stimulations can be used. The main mechanical stimulation is sonication. It is used in my process, for amphiphilic micelles destruction first and later to help splitting the CNT bundles.

The sonication technique consists in the application of a sonic wave to a liquid. It creates variations of pressure in the liquid proportional to the wave's amplitude and frequency. [START_REF] Huang | Dispersion of Carbon Nanotubes: Mixing, Sonication, Stabilization, and Composite Properties[END_REF] addresses the two main techniques for applying that strength are used. The first, tip stimulation, consists in the introduction of a vibrating tip of a probe in the dispersion -Figure 2.10. The stimulation tip is controlled externally to allow power, duration and cycle adjustment -activity over a second in percent. The second method consists in a vibrating bath with water to transfer the energy to the Becher containing the dispersion -Figure 2.11. The main advantage of the sonic bath is the homogeneity of the sonic wave and the low energy of the stimulation that does not destroy c-c bonds of the CNTs. On the other hand, a sonic probe can supply more energy and separate the bundles with a better yield. By introducing high power ultrasound into a liquid medium, the sound waves are transmitted in the fluid and create alternating high-pressure and low-pressure cycles. If enough energy is supplied, during the low-pressure cycle, high-intensity ultrasonic waves create small vacuum bubbles in the liquid. When the bubbles can no longer absorb energy, they collapse violently. During the implosion, very high temperatures ∼ 5, 000K and pressures ∼ 2, 000 atm are reached locally -Figure 2.12. The implosion of the cavitation bubble also results in liquid jets of up to 280 m/s velocity. These effects result in shear forces applied to the species in the solution. These forces can separate CNTs enough for the surfactant to surround individual CNTs according to [START_REF] Kun | Sonication-assisted dispersion of carbon nanotubes in aqueous solutions of the anionic surfactant SDBS : The role of sonication energy[END_REF].

For CNT dispersion, sonication can be used for two purposes. First, dispersant molecules are introduced in a solution of solvent. The sonication is used for breaking the micelles of dispersant, increasing their efficiency in dispersing CNTs [120]. After introducing CNTs in the solution, the colloid is stirred and sonicated again. This growth, and collapse of a bubble induced by ultrasonication [START_REF] Ashiri | Obtaining a novel crystalline/amorphous core/shell structure in barium titanate nanocrystals by an innovative one-step approach[END_REF] time sonication will be used to help the dispersant split the bundles -Figure 2.13. When shear forces create distance between CNTs the molecules of surfactant will be able to bond to the free surface of the CNT sidewalls. The sonication in this step is the main dispersion yield factor with the surfactant molecule. The main drawback of sonication is that the wave frequency and amplitude need to be carefully dimensioned. CNTs are solid particles and they can be irremediably modified by strong shear forces due to sonication [START_REF] Kharissova | Special Studies and Characterization of CNT Dispersions[END_REF]. The most current effect is the shortening of the CNTs increasing the variability of the next steps of the process.

An optimised sonication strength would need to be strong enough to increase the dispersion yield but not too strong that it would damage CNTs. In order to address this issue we use both sonication techniques. First the larger bundles are reduced in size with a sonic bath step, then the small bundle to single CNT separation is realised through sonic tip stimulation.

Dispersion purifying and quality evaluation

The second part of the dispersion process consists in the separation of the CNTs from residues. Indeed CNTs that can be bought contain residues from synthesis in the form of carbon ashes and graphene flakes -CNT(7,6) product information. Furthermore, no separation process gives perfect results, in our case some bundles will resist to separation. The energy needed to separate enough tubes that we would be able to consider the dispersion perfect would break CNTs and create residues in the form of pieces of CNTs.

After selective separation of the dispersion, the quality of the separation can be evaluated. As outlined by [START_REF] Jung | Evaluation of the individualization state in single-walled carbon nanotube solutions using absorption, Raman and photoluminescence spectroscopy[END_REF], the objective is to observe the average size of the particles. The techniques commonly used are based on light absorption or reflection. My design's objective is to have an optimal electronic amplification effect. Therefore, considering the characterisation devices at my disposal, the dispersion results will be formally validated by electric characterisation of the transistor. In order to evaluate the dispersion before CNT deposition, we will use a home-made light absorption technique -c.f. Section 3.1.

Centrifugation

A CNT dispersion never has a hundred percent yield and there always are impurities in the original CNT material. Therefore, centrifugation is used in order to separate single dispersed CNTs from residual bundles and carbon flakes. As shown in [START_REF] Di Crescenzo | Non-covalent and reversible functionalization of carbon nanotubes[END_REF], this technique separates particles in a liquid depending on their density and can be used to identify the state of CNTs -bundles, functionalisation. Centrifugation is realised by rotating a test tube at high speed. The created centrifugal strength adds itself to gravity accelerating and augmenting the natural decantation process. The bottom layer of the solution contains the denser particles and the higher layers contains the lighter particles of the colloid.

[79] outlines that we will find a supernatant layer -floating layer -containing single dispersed CNTs in the result of centrifugation. We will also find CNT bundles and ashes at the bottom of the container. In the bottom are found non-dispersed agglomerates of CNTs and dispersant. After centrifugation, I recover the supernatant CNTs and evaluate the dispersion quality. I also keep the dispersion sample for evaluation of the stability over time -c.f. Section 3.1.

Separation quality assessment

The purity of a CNT colloid is defined by its light absorption as addressed in [START_REF] Kharissova | Special Studies and Characterization of CNT Dispersions[END_REF]. The more CNTs are dispersed one by one the more they absorb light at constant concentration. The homogeneity of the colloid can be correlated with the homogeneity of the light absorption - The results of dispersion characterisation are exposed and discussed in Section 3.1.

Sensitive surface quality

As outlined in [START_REF] Di Crescenzo | Non-covalent and reversible functionalization of carbon nanotubes[END_REF] and [START_REF] Yue | Electrostatic gating in carbon nanotube aptasensors[END_REF], in order to manufacture a biosensor, it is important for the dispersion functionalisation to be fully reversible -does not leave residues or modifies the CNTs. In other words, the affinity of the dispersant toward CNTs needs to be strong enough to have a good dispersion but not too strong, that it cannot be removed. Strong arguments have been made toward aqueous based dispersions especially for use in a dielectrophoresis set-up. I will, in my exposition of the design of the process, consider candidates regardless of previous arguments. In the context of this study, it seems unreasonable to make an exhaustive list of surfactants and dispersants. Therefore, I will describe several families of molecules used for dispersing CNTs. First, the role and specificities of surfactants are discussed. Then the role and specificities of dispersant are addressed. Several surfactants are presented with their advantages and drawback; first aqueous compatible surfactant then surfactants used in organic solvent. For a more exhaustive list of dispersant and surfactant refer to [21]. In the second part of this section, we will see techniques for the removal of adsorbed molecules from the sidewall of the nanotubes.

Surfactant for CNT dispersion

Many molecules have been proven suitable dispersants - [START_REF] Oxana | Dispersion of carbon nanotubes in water and non-aqueous solvents[END_REF], they are most often split in two class depending if the used solvent is water or an organic solvent. These dispersants can be molecules that can dilute in water such as Sodium dodecyl sulfate -SDS -, Sodium dodecyl benzene sulfonate -SBDS -or sodium cholate - The molecular structure of these dispersant is always composed of lipid chains, carbon pentagons or hexagons. According to the hydrophobic bond's strength, the more the structure is similar to a CNT side wall the stronger the bond is. However, the harder it is to remove after placement. Three parameters will determine which molecule to use in my process. First its affinity toward CNTs, second its affinity toward its designed dispersant and last its affinity toward each-other. According to [START_REF] Kharissova | Special Studies and Characterization of CNT Dispersions[END_REF], these three parameters once optimised are the key to a well separated and stable dispersion. [START_REF] Kharissova | Special Studies and Characterization of CNT Dispersions[END_REF] outlines the roles of surfactant and dispersant. A surfactant is defined by its surface interaction with CNTs and its interaction with the solvent, which it is destined to disperse CNTs. A dispersant on the other hand is a solvent -main component of the solution -that can interact with CNTs and disperse them on its own. A dispersant can be assisted by a compatible surfactant. In order to interact with the CNT structure, a dispersant needs to be able to bond with Van der Waals strengths to the CNT sidewall lattice. [START_REF] Kharissova | Special Studies and Characterization of CNT Dispersions[END_REF] shows that the simplest stable CNTs dispersions have been achieved by using solvent molecules able to efficiently interact with CNTs, such as phenylethyl alcohol or N-methylpyrrolidone (NMP). NMP has been demonstrated to enter the bundles during sonication and remain strongly bound to the nanotube surface. It can be removed after deposition by heating to 340 • C and it leaves no residue. Its main drawback is due to its poor polarizability reducing dielectrophoresis efficiency. Good and relatively stable dispersions have been obtained also by sonicating CNTs with N,Ndimethylformamide (DMF) -Figure 2.16. The study of this molecule's interactions with CNTs confirm a high affinity toward hydrogen bond acceptance, a negligible affinity for the hydrogen bond donation and a strong ability to create π bonds. Its main drawback is its low boiling temperature forbidding manipulations such as dielectrophoresis. A dispersion stable for days was obtained by sonicating CNTs in N,N-diethylacetamide (DEA).The good dispersion was imputed with the stability of the dispersion to polar and π-stacking interactions. Although a lot of dispersant seems like good candidates for my design considering purely chemical arguments, the use of dielectrophoresis pushes me toward a water dispersion with the use of surfactant. Another argument is the biocompatibility of these molecules. Despite the fact that most are promoting a removal without residues the reality of a clean room process argues for a biocompatible molecule.

Dispersants

Surfactant in aqueous field

I will present here some examples of surfactant structures, for more details refer to [START_REF] Adam | Optimizing Surfactant Concentrations for Dispersion of Single-Walled Carbon Nanotubes in Aqueous Solution Supporting Information[END_REF], [START_REF] Oxana | Dispersion of carbon nanotubes in water and non-aqueous solvents[END_REF] or [START_REF] Kharissova | Special Studies and Characterization of CNT Dispersions[END_REF].

One of the most commonly used type of molecules corresponding to the first class are polycyclic Aromatic Hydrocarbon -PAH Figure 2.7. These molecules are composed of polycyclic carbon domain able to bond through Van der Waals interactions to CNTs and a polarised domain able to create hydrogen bonds. The structure of the polycyclic carbon domain rules the bonds with the CNT sidewall. For example, a pyrene group containing carbon hexagons and π electrons will bind easily the similar CNT sidewall structure. This functionalisation leaves virtually intact the inherent properties of SWCNTs, as observed by several photo-physical measurements. The second domain of the molecule is hydrophilic and will define the relation between the composite CNT/surfactant and the stability of the colloid over time.

Other commonly used surfactant molecules are detergents such as SDS or SDBS. Figure 2.15 shows the structure of such molecules, with an alkyl tail -C n H 2n+1 -and anionic head -SO 4 . The tail can bind to the CNT while the head allows hydrogen bonds to water. The main drawback of these molecules is their biocompatibility and the damage they create when released in sewage or nature - [START_REF] Pan | Effect of sodium dodecyl benzene sulfonate (SDBS) on the performance of anaerobic co-digestion with sewage sludge, food waste, and green waste[END_REF], [START_REF] Zhang | Concentration-dependent toxicity effect of SDBS on swimming behavior of freshwater fishes[END_REF].

Another family of surfactant described by [START_REF] Kharissova | Special Studies and Characterization of CNT Dispersions[END_REF] comes from bile acids such as sodium cholate. One of its advantages is its biocompatibility. Another is the fact that unlike molecules with long alkyl chains the surfactant does not wrap itself around the CNT. This makes it easier to efficiently remove once the CNT is deposited. This group of surfactants contains a steroid back-bone allowing it to interact by π stacking and Van der Waals bonds with CNT sidewalls and allows dispersion in aqueous fields.

Finally, the last family of molecules studied here are sugar-like molecules such as glucose Figure 2.18 or CMC Figure 2.19. The second is a good candidate due to FIGURE 2.17: Molecular structure of Zn-protoporphyrin [21] its polymer structure consisting of repetitive carbon hexagons able to link to CNTs sidewall. The oxygen and hydrogen species around the hexagons allow the bonding to water. Furthermore, CMC is a biocompatible molecule that can be removed through chemical treatment [START_REF] Takahashi | Dispersion and Purification of Single-Wall Carbon Nanotubes Using Carboxymethylcellulose[END_REF]. I propose SDBS and CMC as surfactants for the dispersion trials . The first for its proven efficiency according to [START_REF] Adam | Optimizing Surfactant Concentrations for Dispersion of Single-Walled Carbon Nanotubes in Aqueous Solution Supporting Information[END_REF], the second for its biocompatibility. These molecules are often very efficient toward CNT separation. However their removal from the sensing surface gives limited results. Considering the previous arguments toward aqueous dispersion and against organic solvent dispersions, this family of molecules have not been practically tested.

Surfactants in organic solvents

CNT sidewall cleaning

The CNT sidewall is at the center of the sensing mechanism and its cleaning has been previously studied by [START_REF] Rossi | Removal of sodium dodecyl sulfate surfactant from aqueous dispersions of single-wall carbon nanotubes[END_REF] or [START_REF] Bautista-Toledo | Removal of the surfactant sodium dodecylbenzenesulphonate from water by simultaneous use of ozone and powdered activated carbon : Comparison with systems based on O 3 and O 3 / H 2 O 2[END_REF] among others. The integrity of the sidewall of the CNTs determines the integrity of the electronic structure of the CNTs. If not pristine the sidewall of CNTs will receive electrochemical noise from the residues molecules and create a reduced amplification of the electrochemical signal through field effect. It will also reduce access to the CNTs from the functionalisation molecules. Cleaning of the surface of a CNT will need to be optimised considering the removal of residues and the non-modification of the sidewall structure. An advantage for the process I am designing is that since 1-pyrenebutanoic acid, succinimidyl ester -Pbase -has been chosen as a support for the biochemical functionalisation -prefunctionalisation. Some residues will be removed and replaced by the pyrene group of this molecule due to its stronger affinity to CNT sidewall.

During the trials for removal the temperature and duration of the removal will depend on the density and thickness of the chemical layer around the CNT. More surfactant will leave more residues and a thick layer will increase the relative quantity of residues due to recombination of the molecules during combustion. This curing can be realised in atmospheric pressure or in low pressure. This considerations also push toward a limitation of the quantity of surfactant used in the dispersion.

Chemical removal can be realised with acid or solvent removal. Acid assisted removal of the surfactant will depend -In the same way than the thermal treatment -on the specificity of the molecule compared to CNTs. For solvent assisted removal the parameters are the solubility of the surfactant in the solvent and duration of the step as previously depending on the thickness of the surfactant layer around the CNTs. In both chemical removal techniques, the sample and solutions can be lightly heated depending on the boiling point of the chemical used. This accelerate the reaction.

Both chemical reaction techniques are dependent on the thickness of the surfactant layer. It is in my interest to limit the quantity of molecules adsorbed on the CNT sidewall from the dispersion.

Summary of the pre-experimental Dispersion process

This section summarize the decisions taken during the design of the dispersion process. Here are listed the chemicals selected for trials from the the previous considerations. In addition, the parameters that I need to optimise during experiments are discussed, with their range of exploration. The resulting pre-experimental process is summarised in Figure 2.21. The results of the experiments following the preexperimental process are presented in Section 3.1.

Solvent For the solvent, I chose to work with water for dielectrophoresis. Organic solvent such as ethanol and acetone without surfactant will also be tested to confirm theory. Surfactant Three surfactants have been chosen for trials : SDBS, CMC, sodium cholate. The surfactant is introduced in the solvent -water -and the solution is manually stirred. Surfactant concentration has been shown to be the more efficient between 0.1% and 2% depending on the molecule and its critical micelle concentration.

Solvent-surfactant interface

Then I introduce an intermediary molecule between surfactant and solvent. This step has shown positive results depending on the surfactant, with a concentration variating between 0.1% and 10%. I use phosphate buffered saline to act as an ionic interface between surfactant and water.

Surfactant sonication

The next step is the preparation of the surfactant and the use of sonication to break its micelles. Here, sonic tip stimulation is applied until no observable particles are left in the solution. The parameters of sonication in this step are the sonic wave energy -10W to 200W -and the application duration -10s to 2min. The stimulation is maintained until no residue is observable. The high limit of stimulation is bound to the temperature of the liquid -c.f. Section 3.1.

CNT The next step consists in introducing CNTs in the solution. The higher the CNT concentration, the harder it is to disperse. In applications using CNT films or dense random deposition/arrays, a high density is necessary. For single CNT depositions ng/mL concentrations are used, they have their own specificity and are mostly used for assisted CNT alignment such as dielectrophoresis. Here we use a starting concentration of 2 * 10 -5 to 2 * 10 -4 w/w.

CNT pre-sonication Then comes steering and sonication of the obtained colloid. First, the dispersion is put in a sonic bath for 10 to 30min. This allows reduction of the size of the biggest groups of CNTs in order to prepare the dispersion and optimise the efficiency of the next sonication.

CNT sonication Then I use sonic tip stimulation. The parameters are the power of stimulation from 10W to 200W and the duration 10s to 2mn.

Centrifugation The next step is centrifugation with an acceleration of twenty thousand times gravity. Centrifugation is applied to the colloid for 15min to 2h in order to fully separate the different phases. A too long centrifugation have been shown to reduce the concentration of the dispersion without increasing its quality.

Recovery and dilution

The fifth and final step is the separation of the supernatant containing singly dispersed CNTs. In this step most techniques are mechanical -use of a pipette -and imply to either leave dispersed CNTs in the first colloid or to take, in the resulting solution, some poorly dispersed CNTs -small bundles close to the supernatant. The extract is then diluted at a 1% concentration to an approximate CNT concentration of hundreds of ng/mL. From that point the dispersion is ready to be used in a dielectrophoresis set-up.

CNT placement : Dielectrophoresis

The objective of this step in the process is to align and place CNTs at predefined sites. As outlined in Section 1.2 the amplification objective supposes to have single CNTs or very small bundles bridging the source and drain electrodes. The general principles and literature examples are outlined. These examples are used as base for creation of a robust and controlled placement protocol. This protocol focuses on optimizing the ratio of filled sites and limiting the parasitic paths creation. [START_REF] Iakoubovskii | Techniques of aligning carbon nanotubes[END_REF] presents several techniques for CNT alignment. The use of one technique rather than another is dependent on the result expected and the material at disposal. For example, direct synthesis of aligned CNTs is a technique giving very regular and controlled results but supposes the availability of heavy and expensive machinery for CNT synthesis. Other techniques such as stretching or membrane filtering allow alignment but not placement of the nanotubes. Similarly, the use of magnetic field or sonic wave permits alignment of CNTs in a colloid but not to place them on specific sites on a surface. I propose to work with dielectrophoresis -DEP -, which allows alignment and placement of CNTs on specific sites. This technique uses an alternative electric field and the difference in polarizability of the species in a liquid to manipulate them.

[36] also outlines the methods for alignment observation. Different set-up are used for CNT observation. Microscopes that can observe matter in a precise fashion -∼ nm -such as electron microscopy, atomic force microscopy allow observation of the shape of the nanotubes after placement. Light techniques, such as photoluminescence or Raman spectroscopy, allow observing the optical characteristics of CNTs and deduce their physical characteristics. I propose to observe the results of my alignment and placement process with AFM due to its precise results in the physical structure of the deposited CNTs and the availability in the clean room at the University of Montpellier. Another argument toward AFM is that it can be used in a liquid phase to observe the functionalisation of the full biosensor. A comparative image using the same technique is more precise and robust in identifying added molecules -selective layer.

Dielectrophoresis has two main uses. First, it allows alignment and placement of polarizable nanorods such as CNTs but also ZnO nanowires for example [START_REF] Tao | Fabrication, calibration, and recovery of chemical nanosensor array for ammonia detection[END_REF]. Another common use of dielectrophoresis is the separation of metallic CNTs from semi-conducting CNTs [START_REF] Mattsson | Dielectrophoresis-Induced Separation of Metallic and Semiconducting Single-Wall Carbon Nanotubes in a Continuous Flow Microfluidic System[END_REF]. Indeed, the dielectrophoretic force is dependent on the electronic characteristic properties of the particle. Furthermore, CNTs have different electronic structures depending on their chirality, size and metallic/semiconducting properties. In the current process, we use already separated CNTs with a high concentration of semiconducting CNTs. The data sheet of the bought nanotubes does not precise the concentration of semiconducting CNTs. However, the chirality distribution allows to estimate this concentration to be over 80%.

Following these considerations [START_REF]Dielectrophoresis of Single-Walled Carbon Nanotubes[END_REF] outlines that the results and optimization of CNT dielectrophoresis is extremely dependent on experimental conditions. In this section, I will start by addressing the theory of CNT dielectrophoresis. Then I will outline the experimental conditions and parameters ruling dielectrophoresis based on literature. Finally, I will describe the pre-experimental process protocol for dielectrophoresis with the parameters to optimize and the range of exploration for trials.

Theory and general considerations

In order to be concise I will use the theoretical framework of [START_REF] Chen | Quantitatively Control of Carbon nanotubes Using Real Time Electrical Detection Dielectrophoresis Assembly[END_REF]. For a more extensive description of the physics phenomenon see [START_REF]Dielectrophoresis of Single-Walled Carbon Nanotubes[END_REF]. The dielectrophoretic forces originate from Pohl's theory [START_REF] Herbert | Theories of Electronic Behavior in Macromolecular Solids[END_REF]. This theory describes the comportment of a polarisable solid in a polarisable fluid when affected by an alternative electrical field.

F DEP = 1 2 v p ( f CM ) * ∇|E| 2 (2.1)
Eq 2.1 express this force depending on v p the volume of the particle, ∇|E| 2 is the root-mean-square of the applied field and f CM is the Clausius-Mossotti factor expressing the relative polarizability of the particle/solvent couple. When f CM is positive, the dielectrophoretic force is positive, meaning that the particle will be attracted toward the source of the electrical field due to the higher variation of field close to its source. If f CM is negative the particle is pushed away from the source of the field and toward the regions of the liquid medium with lower field amplitude. In order to model this effect, [START_REF]Dielectrophoresis of Single-Walled Carbon Nanotubes[END_REF] and [START_REF] Vijayaraghavan | Ultra-large-scale directed assembly of singlewalled carbon nanotube devices[END_REF] used finite element models -FEM. For a detailed description of the framework refer to [START_REF]Dielectrophoresis of Single-Walled Carbon Nanotubes[END_REF]. The first step of the modelling process is to describe the structure to simulate in space. The second step is to define the materials occupying the different volumes of the modeled sample. The third step consists in the creation of a mesh to define a finite quantity of points in space for Side view of substrate, electrodes, particles and non-uniform electric field. [START_REF] Chen | Quantitatively Control of Carbon nanotubes Using Real Time Electrical Detection Dielectrophoresis Assembly[END_REF] calculation. The lines of the mesh connect these points which represent the state of the system. Finally, the boundary conditions and differential equations are defined. The solving algorithm applies the differential equations along the lines of the mesh in order to determine a coherent set of values representing the state of the system. In order to model dielectrophoresis, researchers start by modeling the variating potential: Figure 2.24. This potential will create a dielectrophoresis force orthogonal to the constant electrical field lines: Figure 2.25. This simulations allowed [START_REF] Vijayaraghavan | Ultra-large-scale directed assembly of singlewalled carbon nanotube devices[END_REF] to explain the self-limiting effect of dielectrophoresis on CNTs. Indeed, a CNT bridging between electrode will be polarized by the electrodes and create an electrical field around itself -5nm depending on experimental conditions. This field will create a repulsive dielectrophoretic force for other CNTs. In a similar set of simulations, [START_REF] Ying | Simulation on Electrical Field Distribution of Dielectrophoresis for Carbon Nanotube[END_REF] observes the effects of the electrode shape on the dielectrophoretic force. More specifically, they outline the effects of the electrode width -Figure 2.26 -and of the length of the arc of the electrode tip -Figure 2.27. Their conclusions are that the tip should be as narrow as possible in order to augment the dielectrophoretic force. In other words, the radius of the arc of the tip ." [START_REF] Vijayaraghavan | Ultra-large-scale directed assembly of singlewalled carbon nanotube devices[END_REF] should be as short as possible. Finally, the researchers advise a needle-shaped electrode in order to optimize dielectrophoresis results. In order to estimate the alignment rate of the CNTs, [START_REF] Blatt | Influence of Structural and Dielectric Anisotropy on the Dielectrophoresis of Single-Walled Carbon Nanotubes[END_REF] models the nematic order parameter S. This parameter allows estimation of the alignment of particles in a liquid crystal. The results of the simulation show that with a stimulation frequency of over 1GHz some particles will start to orient themselves orthogonal to the dielectrophoretic force.

The CNT movement is determined by [START_REF] Wenshan | Advanced Dielectrophoresis for high-performance single-walled Carbon Nanotube Electronics[END_REF] using Newton's second law Eq 2.2. It only considers the dielectrophoretic force -F DEP -and viscous force due to relative velocity. m represents the mass of the CNT, f is the translation friction factor and (uv) is the relative velocity. f is defined as in Eq 2.3, with ν the viscosity factor, l and r the length and radius of the CNT. Finally the speed of the particle is defined as Eq 2.4.

m dv dt = F DEP + f * (u -v) (2.2) f = 3πνl ln(l/r) (2.3) v = ( F DEP f + u)(1 -e -( f /m)t ) (2.4)

Dielectrophoresis process parameters

In this section, experimental parameters of the dielectrophoresis set-up are outlined. They are divided in three categories. First, architecture parameters refer to the structure of the stimulation electrodes and the substrate. Secondly, chemistry parameters relate to the component of the solution on which the DEP is applied. Finally, the electrical field properties are outlined. The objective here is to determine the effects of relevant parameters and estimate a range of exploration for the process.

Architecture of the DEP set-up

Two types of structures can aim for two general types of results. First, stimulating structures can be structured as wide electrodes that can be considered as two wide walls. They can also be designed as thin electrodes of ∼ µm.

[95] demonstrated the creation of an array of CNTs -Figure 2.28. This type of structure is often realized with wide electrodes but can present different types of results depending on other experimental conditions. In [START_REF] Biddut K Sarker | Semiconducting enriched carbon nanotube align arrays of tunable density and their electrical transport properties[END_REF] the authors created an array of CNTs individually connecting both electrodes. On the other hand with a similar structure [START_REF] Naieni | Investigation of the dynamics of carbon nanotube deposition in dielectrophoresis[END_REF] created networks of CNTs bridging the two electrodes -Figure 2.29. Considering the properties of CNTFET architectures discussed in Section 1.2, the array structure would provide more amplification of field effect. The reasons for this CNT structure difference is due, in part, to the distance between electrodes being close to the median length of the CNTs in [START_REF] Biddut K Sarker | Semiconducting enriched carbon nanotube align arrays of tunable density and their electrical transport properties[END_REF] while being multiple of the CNT median length in [START_REF] Naieni | Investigation of the dynamics of carbon nanotube deposition in dielectrophoresis[END_REF]. As discussed in Section 1.2, CNT networks have the drawback to often include crossing CNTs as shown by [START_REF]Dielectrophoresis of Single-Walled Carbon Nanotubes[END_REF] in Figure 2.30.

The second type of architecture presented here, generally aims toward single CNT structures of deposition. For example, [START_REF] Zhang | Alternating current dielectrophoresis of carbon nanotubes[END_REF] bridges two electrodes with a single CNT for a quasi-optimal electrical field amplification -Figure 2.31. Later, [START_REF] Vijayaraghavan | Ultra-large-scale directed assembly of singlewalled carbon nanotube devices[END_REF] demonstrates a DEP set-up for ultra-large-scale directed assembly of single-walled carbon nanotube devices -Figure 2.32. This type of structure gives very good results in the amplification of a single CNTFET but also in the density of CNTFET. Unfortunately, stimulating structure does not guarantee the results. [START_REF] Moraes | Electrical behavior of devices composed by dielectrophoretically deposited carbon nanotubes for gas sensing applications[END_REF] creates networks from a triangular stimulation electrode -Figure 2.33. This shape effect is also demonstrated in [START_REF] Zheng | Large-scale directed assembly of single-walled carbon nanotube devices by alternating current coupling dielectrophoresis[END_REF] with round electrodes being connected by a single site while electrodes with a flat extremity are bridged by multiple sites creating arrays of CNTs -Figure 2.34. [START_REF] Chen | Quantitatively Control of Carbon nanotubes Using Real Time Electrical Detection Dielectrophoresis Assembly[END_REF] demonstrates the effects of stimulation duration -the longer the stimulation the more tube per site -independently of the shape -Figure 2.35. Depending on the stimulation characteristics, the result can be of the type single CNT(s) or CNT network also called thin film.

Other architecture artifacts can be used in order to direct the DEP assembly of CNTs. First, [START_REF] Krupke | Simultaneous Deposition of Metallic Bundles of Single-walled Carbon Nanotubes Using Ac-dielectrophoresis[END_REF] uses a floating electrode set-up -Figure 2.36 -in order to limit the quantity of tube per site Figure 2.37. In this architecture the floating electrode is coupled to the stimulated back-gate -and transmit the electrical stimulation -until a CNT contacts both electrodes. When electronic contact is created between electrodes through the CNT the floating electrode loses its coupling to the back gate drastically reducing the induced DEP force. Another use of a floating electrode has been addressed by [START_REF] Chaturvedi | Controlled deposition of aligned carbon nanotubes by floating electrodes dielectrophoresis[END_REF]. Indeed, the authors demonstrates the creation of parasitic paths and unwanted deposition on a classic two electrode set-up - Another modification of the set-up architecture in order to gain in control of the DEP was demonstrated by [START_REF] Cao | Precise Alignment of Individual Carbon Nanotubes for Nanoelectronics[END_REF]. The authors uses a polymer in order to protect the surface of the sample except on the deposition site -step (d) of Figure 2.40. This modification reduces the creation of parasitic paths and unwanted deposition.

CNTFET assembly with dielectrophoresis is used since the late 1990 and are still developed recently. For example, [START_REF] Engel | Graphene-enabled and directed nanomaterial placement from solution for large-scale device integration[END_REF] presents an alternative to metal electrodes by aligning CNTs on graphene tipped electrodes with DC electrophoresis -Figure 2.41. [START_REF] Zheng | Large-scale directed assembly of single-walled carbon nanotube devices by alternating current coupling dielectrophoresis[END_REF] shows that DEP placement could be used on supple substrates.

Chemistry of DEP set-up

As illustrated by [2], a surfactant creates a double layer around a CNT -Figure 2.9. This double layer modifies the particularities of the CNT such as its conductivity toward the solvent or the size and internal electronic characteristics of the particle that should be considered for DEP modeling. This is one of the explanations for the difference in comportment between simulations and practical results and for the complexity of having control over experimental conditions. Indeed, [START_REF] Krupke | Surface conductance induced dielectrophoresis of semiconducting single-walled carbon nanotubes[END_REF] showed that the dielectrophoretic force was dependent on the conductivity of the CNT/surfactant composite toward its solvent. The stimulation of a metal electrode in an electric field can create a Helmholtz double-layer. [START_REF] Vijayaraghavan | Ultra-large-scale directed assembly of singlewalled carbon nanotube devices[END_REF] showed that it does not intervene for a stimulation of over 200kHz. Indeed, this effect appears for a frequency inferior to the ionic charge relaxation frequency: τ -1 = σ/ ≈ 200kHz with σ = 0.1S/m and ≈ 85 0 .

These chemical considerations are dependent on the composition of the dispersion, for example [START_REF] Chaturvedi | Controlled deposition of aligned carbon nanotubes by floating electrodes dielectrophoresis[END_REF] uses a dispersion in a non-aqueous solvent with a non-polar surfactant changing the effect of the electrical field on the CNTs.

Finally, the main chemical parameter for DEP, is the concentration. Indeed, [START_REF] Cao | Precise Alignment of Individual Carbon Nanotubes for Nanoelectronics[END_REF] shows that a self-limited deposition is only possible if CNTs approach the sites one by one. This requirement is made easier to attain with a dispersion concentration in the range of ng/mL. Furthermore, the authors showed that a lower concentration allowed a better control of the deposition and a reduced rate of bundle configuration over single CNTs.

Electrical field properties

Here, I will outline the properties of the electric field obtained by stimulation of the DEP electrodes. The DEP strength is proportional to the square of the electrical field c.f. Eq 2.1. The speed of the particle toward the placement cite is proportional to the DEP force -c.f. Eq 2.4 [START_REF] Chen | Quantitatively Control of Carbon nanotubes Using Real Time Electrical Detection Dielectrophoresis Assembly[END_REF]. I will start by addressing the effects of frequency on the deposition. Then, I will outline the variations of results due to the field strength and stimulation amplitude. Finally, I will describe the effects of duration on the obtained results.

Frequency

The range of frequencies that can be used is wide, as demonstrated by [START_REF] Krupke | Surface conductance induced dielectrophoresis of semiconducting single-walled carbon nanotubes[END_REF] and [START_REF] Zhang | Alternating current dielectrophoresis of carbon nanotubes[END_REF]. They showed DEP results from 300kHz for the first and results up to 100MHz for the second. Both types of structures are represented, [START_REF] Krupke | Surface conductance induced dielectrophoresis of semiconducting single-walled carbon nanotubes[END_REF] obtained CNT networks at 3MHz and 300kHz. [START_REF] Chaturvedi | Controlled deposition of aligned carbon nanotubes by floating electrodes dielectrophoresis[END_REF] demonstrated CNT networks from 1 to 5MHz. [START_REF] Naieni | Investigation of the dynamics of carbon nanotube deposition in dielectrophoresis[END_REF] later experienced CNT networks at 500kHz. On the other hand, [START_REF] Vijayaraghavan | Ultra-large-scale directed assembly of singlewalled carbon nanotube devices[END_REF], [START_REF] Zheng | Large-scale directed assembly of single-walled carbon nanotube devices by alternating current coupling dielectrophoresis[END_REF] and [START_REF] Zhang | Alternating current dielectrophoresis of carbon nanotubes[END_REF] demonstrated single-CNT CNTFETs deposited at respectively 300kHz, 500kHz and 5MHz.

Despite this versatility of results, literature examples can give some direction. First, high frequencies show some issues as expected from theory -c.f. Section 2.2.1. For example, frequencies over 1MHz have been shown by [START_REF]Dielectrophoresis of Single-Walled Carbon Nanotubes[END_REF] to pull specifically on metallic CNTs. The same literature example also describes orthogonal CNTs for frequencies over 1GHz, as illustrated in Figure 2.30.

[13] experiments frequency variation with two types of CNTs and two different set-up -Figure 2.42 and Figure 2.43. These experiments confirm that the frequency is proportional to the electric field strength, which is proportional to the DEP strength, which is in turn proportional to the placement rate. A conclusion from the authors is that DEP depends on the type and chirality of the CNT, also confirming theory results.

Electric field strength I addressed above how the frequency modifies

the strength of the field and its limits. Here I describe the effects of the strength of the field due to the stimulation amplitude. Functional DEP has been demonstrated for ) varied by tuning the sinusoidal frequency at 10V for 45s. [START_REF] Cao | Precise Alignment of Individual Carbon Nanotubes for Nanoelectronics[END_REF] values from 1V/µm by [START_REF] Naieni | Investigation of the dynamics of carbon nanotube deposition in dielectrophoresis[END_REF] up to 20V/µm by [START_REF]Dielectrophoresis of Single-Walled Carbon Nanotubes[END_REF]. They both stimulate their samples for tens of seconds to minutes and realize respectively low and high density films of CNTs. These examples confirm the theory that the field strength is proportional to the DEP force and the placement density.

For CNTFET realization with DEP and single CNT structure, the most used value of field strength is of 2.5V/µm: [START_REF]Dielectrophoresis of Single-Walled Carbon Nanotubes[END_REF] [START_REF] Vijayaraghavan | Ultra-large-scale directed assembly of singlewalled carbon nanotube devices[END_REF] [95] and [START_REF] Zheng | Large-scale directed assembly of single-walled carbon nanotube devices by alternating current coupling dielectrophoresis[END_REF]. None of the research teams present a theoretical reason for this value, only experimental results. More specifically, [START_REF] Vijayaraghavan | Ultra-large-scale directed assembly of singlewalled carbon nanotube devices[END_REF] experienced that the self-limiting placement effects of CNTs diminished before disappearing for a field of over 2.5V/µm. Finally, [START_REF]Dielectrophoresis of Single-Walled Carbon Nanotubes[END_REF] argues that the best results are obtained with a strong electric field by augmenting the proportion of filed sites and reducing the rate of miss aligned CNTs especially with frequencies close or over 1MHz -c.f. Section 2.2.1.

Stimulation duration

I outlined above the use for a high electric field strength and its limits. We saw the effects on the speed of the CNT in the chemical field. However, the objective being to place the CNTs, the directly important data is not the speed, but the displacement created by the speed. Indeed, a stronger field will attract CNTs from farther away and with a higher speed. On the other hand, CNTs will always need time to reach the placement sites. The consequence is that with the same field strength, time will allow CNTs from farther away to be placed. The stimulation can last up to minutes - [START_REF] Naieni | Investigation of the dynamics of carbon nanotube deposition in dielectrophoresis[END_REF] -augmenting the density of CNTs in the network/film or the proportion of filled deposition sites. However, in single CNT configuration, the longer the stimulation, the higher the risk of parasitic particles interference, particles such as ashes or miss-aligned CNTs - [START_REF]Dielectrophoresis of Single-Walled Carbon Nanotubes[END_REF]. [START_REF] Cao | Precise Alignment of Individual Carbon Nanotubes for Nanoelectronics[END_REF] showed in their experiments -Figure 2.44 -that a stronger field with a lower duration gave results with more single CNTs, less bundles and less misaligned CNTs. Finally, a strong advantage of working on the duration parameter is that it can be automated [START_REF] Chen | Quantitatively Control of Carbon nanotubes Using Real Time Electrical Detection Dielectrophoresis Assembly[END_REF]. The system measures the current going through the electrodes and with a system of threshold detects when a CNT is deposited. The main issue with such a system in a high density set-up is that every site needs to be separately automated for single CNT deposition control on each site.

Summary of the pre-experimental Dielectrophoresis process

The DEP parameters related to the architecture are addressed in Section 2.3. Indeed, the DEP process addressed here describes the placement manipulation but the electrode architecture is built beforehand with lithography. Some remarks can still be made in this chapter. The substrate is made of SiO 2 for back-gate insulation. This structure is electronegative, attracts positive ions, and could have an effect on the DEP depending on the ionic charge of the surfactant. I propose to aim for a single-CNT structure of channel with the objective of a strong field effect amplification. In order to improve the realization of this structure we work with deposition sites shaped as two needles facing each other. The objective will be to have as thin as possible needle tips in order to focus the electric field in a thin line between teeth. This increases the quality and precision of the placement. Finally, the distance between electrodes is a parameter for field strength variation. Multiple samples with distances from 0.5µm to 1.5µm will be tested with different stimulation amplitudes and frequencies.

Before describing the set-up in itself, some precision need to be made concerning the dispersion process. First, we will use DEP in water because of its wide references in literature despite the fact that recent but sparse results showed better yields with a toluene-based solution - [START_REF] Wenshan | Advanced Dielectrophoresis for high-performance single-walled Carbon Nanotube Electronics[END_REF]. Several dispersant will need to be tested in order to experience on their effects on placement, alignment and the electronic characteristics of the resulting CNTFET. Finally, the experiments given in this chapter confirm the fact that I should work with low concentration dispersions. Tests will be realized with concentrations of approximately ng/mL to hundreds of ng/mL.

The DEP is based on a four probe electrical characterization set-up -Figure 2.45. This tool allows plugging of micro probes with 3D precise placement to commonly used electrical connections. The electrical circuit for stimulation is illustrated in Figure 2.46. It consists of two independent AC voltage supply lines adjusted to be at 180 • from each other in order to maximize the potential difference. The supply voltage is a sinus with an amplitude of 0.5V pp -for a 1V pp between electrodes -to 10V pp for a distance between electrodes of 1µm. I will modify these amplitudes depending on the distance between electrodes with respect for the field amplitude referenced from literature. The frequency of the stimulation will vary from 300kHz to 1MHz as advised by literature. The oscilloscope is used in the set-up for precise alignment of the two phases and precise control of the DC voltage to zero for both lines. Finally, the duration of the stimulation will be tested form ∼ 1sec to 1min. This range should allow me to observe the rate of deposition in the first seconds and the accumulation over longer periods.

The manipulation unfolds as follows. First, I place the sample on an insulating mechanical support for fixation. Then, I place it at the center of the probe station. I place the probes at their starting positions, i.e. at a few microns from the first pads to stimulate. At that point, I switch on the stimulation supply. Then I cast a 3µL of dispersion on the deposition sites. Finally, I apply the stimulation for the expected duration through the probes. After deposition, the sample is thoroughly but gently rinsed with water. Finally, the sample is dried with N 2 .

Lithography

The subject of this section is the lithographic process. More precisely, the decisions leading to the resulting pre-experimental process are discussed. The pre-experimental process is presented in conclusion of the section. Unlike for the previous subjects of the chapter -c.f. Section 2.1 and Section 2.2 -I had some expertise in lithography before starting my thesis. The pre-experimental research presented here is based on technical reports, application notes and data sheets. As an introduction to lithography, the choice of UV-lithography versus electron-beam lithography is discussed. Then, the theory of the photoreactivity of photoresists based on diazonaphthoquinone sulphonate -DNQ -is addressed. This introduction finishes by the presentation of the plan of the section.

The principles of e-beam and UV lithography are equivalent except that they use respectively electrons and photons as an image transfer vector. For both techniques two modes of image transfer exist. First a small beam -∼ 50nm for e-beam and hundreds of µm for UV -is moved over the substrate activating sequentially small areas. This technique as the main advantage that it can use a trace from a computer design and report it on a substrate with good precision. The main drawback is that the sequential mode takes a long time to cover high surfaces. This mode is mostly used for mall surfaces, relative to the size of the beam, on a small quantity of samples. On the other hand, the parallel mode has the advantage of a short time of operation since all the surface of the sample is treated at the same time. The inconvenient is that it needs a mechanical mask to stop the electrons or photons at relevant places to report the image.

The clean room at Montpellier University only possess a sequential mode e-beam lithography while the two modes are present for UV lithography. Furthermore, I had an easier access to experts on UV lithography than e-beam lithography. Another consideration is that considering the precision needed, the mask would have to be realized with e-beam lithography. Therefore, I decided to have the mask made by an outside source with more expertise and technical abilities. I built a pattern with Cadence and converted it in GDSII for realization at the IEMN clean room through the French RENATECH network. I will discuss further in this section the design of the pattern but not the realization of the mask.

The central piece of any electronic lithography is the resin. In UV-lithography we use UV-sensitive chemical elements in order to create a reaction that will change the solubility of the resin. The composition and properties of such photoresists are described in [START_REF] Microchemicals | [END_REF]. The light effects are described in [START_REF] Microchemicals | Exposure of Photoresists[END_REF]. Finally, the effects of exposure on solubility are exposed in [START_REF][END_REF]. I will here synthesize the conformational changes of the resin leading to the variation in solubility. First, the base of photoresist is polymer chains such as Novolak -Figure 2.47. This molecule is a polymerized phenolic resin made of formaldehyde and phenol used in positive resins. The chain length of the resin molecules will determine some of the properties of the resin such as viscosity and stability. These properties are relevant to the resolution that can be attained with the resin and to the metal deposition method that will be used -c.f. Section 2.3.2. Similarly, negative resin can be based on phenolic polymers but with a melamine cross linker -Figure 2.48. The considerations on the chain length are similar to those on Novolak chains.

The photo sensitive element in these resin is diazo-naphthoquinone sulphonate -DNQ Figure 2.49. This element, depending on its place around the polymer - When the DNQ molecule is bonded to the hydrophobic side of the polymer, the polymer is not soluble by alkyl chains. When this side of the chains is freed from the bond to DNQ, the polymer can create bonds to alkyl chains and becomes soluble in alkyl solvents. Another reaction worth to note here is that the carboxyl mediated bond between DNQ and the chain polymer can be definitively removed by heating. At that point, the DNQ becomes passive and the polymer chain comes back to a non-soluble state in alkyl chains. The reaction in negative solvent can be of two types. First, a similar reaction that of positive resin can be realized with DNQ. Due to the nature of the polymer chain, the effect will be opposite. Indeed, in negative resins, the polymer is initially soluble in its solvent and becomes insoluble upon light excitation of DNQ by UVlight. Another type of negative resin is composed of a photoreactive polymer that will cross-link with itself and become insoluble in its developer.

I addressed here the relevant reaction of photosensitive resist to light and heat for UV-lithography. In this section, I will be contextualizing the work on the resin by addressing the mask pattern, substrate properties, mask lithography methods and the reactions of photosensitive resins to their environment. In a second part, I will outline the methods for the main steps of the lithographic process. I will also justify FIGURE 2.50: "The schematic process of development of DNQ-based photoresists at the molecular level: In the unexposed state, the photoinitiator is located on the hydrophobic side of the phenolic resin chains, the indene carboxylic acid formed during exposure expands to the hydrophilic side. There, it separates a proton from the resin, which is thereby negatively charged and now soluble in aqueous alkaline developers. Carbon atoms are shown here in black, hydrogen atoms light grey, oxygen atoms blue, nitrogen atoms red, and Sulphur atoms yellow. " [START_REF][END_REF] the choice of resin and lithography techniques. The last part of the section addresses the parameters of the practical steps of the process. I will conclude this section with the pre-experimental process, outlining the parameters and range of exploration.

Context for UV-lithography

Mask pattern

I start this part by describing the pattern of the mask that was outsourced. This design is the result of considerations addressed in Section 1 and Section 2.2. The mask is realized with electron-beam lithography and will be used in UV-lithography. Therefore, I can design a mask with a precision of pattern copy of about 100nm and theoretical minimum features of approximately 300nm. The first condition is due to the size of the electron beam. The second is due to the theoretical minimum size of pattern that can be transferred through UV lithography according to [START_REF] Lloyd R Harriott | Limits of Lithography[END_REF]. The mask is made of quartz with a layer of chromium that is selectively etched to form the pattern. It is square shaped with a side length of three inches. It is created as a clear field mask. The pattern is designed as shown in Figure 2.51 to 2.55. First, I reduced the work space in order to comply with the aligner. The space for the mask in the MJB4 mask aligner that I use in this process is of five inches. The projected pattern needs to be close to the center of the dispositive, so I move the mask in order to do so. With a three inches mask in a five inches space the displacement is limited. Therefore, I limit the workspace of the mask to four parts delimited by a forbidden area -hatched in green in The quantity of sites and their specificities are listed in Table 2.2. The goal is to search for variations in efficiency and results of the dielectrophoresis depending on the quantity of teeth in each line -n • 3 to 10 -the quantity of lines composing the network -n • 11 to 17. n • 1, n • 2 and n • 18 to 20 have longer teeth to observe the variation of DEP when the field posses an increased variation of strength comparing the onsite strength and between-sites strength. The lines n • 21 to 25 are designed with access lines of 5µm wide in order to observe variation in interference between lines. The variation between patterns 13 and 14 are the width of the teeth and the pitch between them. Pattern 13 is denser with a pitch of 2µm against 3µm for pattern 14. n • H (mm) L (mm) P (µm) w (nm) l (nm) S1 (nm) S2 (nm) Pattern 13 also has thinner teeth of 1µm wide against 1.2µm for pattern 14. Pattern 14 can be seen as the safe version, taking some distance from the theoretical limits. Pattern 13 represents the ideal lithographic process case with a denser network and thinner sites leading to better placed CNTs. The difference between patterns 13 and 14 is due to the variability in the quality of the resulting UV-lithography. Indeed, Figure 2.58 shows the variations of exposition intensity when the gap in the mask gets close to the wave length of the light. The light beam diffracts creating wave-like variations in the resin exposure. The objective in our process is to obtain an energy profile close to the second image from the left -c.f. Section 2.3.2. In order to do so, I keep the characteristic distances where this profile is researched between two and three times the approximate wavelength of 300nm.

1 5 5 2 1 1 0 0 2 5 2.5 2 1 1 0 0 3 2.5 5

Substrate choice and preparation

Chapter 1 defines the substrate for the prototype as built from a conductive layer with an insulating layer on top. I use mono crystal silicon wafers with a thickness of 25µm. The substrate has been p-doped to degeneration by the manufacturer turning it into a conducting substrate [START_REF] Microchemicals | SIO 2 , SI 3 N[END_REF]. The thickness is standard for lithography work with a mask aligner. The surface of the substrate is made of a disc cut by a flat spot The intensity distribution of the light in the air gap between the photo mask and the resist surface (from black to red to yellow and white) corresponds to the single slit diffraction pattern when a resist film is exposed through differently sized openings of a photo mask. The light intensity distribution on the surface of the resist (from black to blue and increasingly purple to white, also represented as green plot) in case of a narrow slit (far left) relative to the exposure wavelength and gap represents a point or line source, and for a wide slit (far right) to an increasingly parallel figure through the opening of the photo mask on the resist surface." [START_REF] Microchemicals | Exposure of Photoresists[END_REF] informing on the direction of the crystal. The diameter of the substrate is of two inches or four inches depending on the availability in the clean room. The substrate is covered with a 300nm-thick layer of silicon dioxide as a the gate dielectric. The deposition is realized with Plasma Enhanced Chemical Vapour Deposition -PECVD. Better results can be obtained with thermal oxidation, especially considering the dielectric strength of the obtained layer. Despite that I used PECVD because of its availability in the clean room, its simplicity of manipulation and the regularity of the results. For more information on the subject, [START_REF] Microchemicals | SIO 2 , SI 3 N[END_REF] goes into more details in the difference between methods.

After deposition, the substrate is diced in rectangles of approximately 1.5 cm so it can cover the pattern surface and reduce the effects of the side of the sample on the resin layer -c.f. Section 2.3.2. This procedure consists in using a scalpel or a very thin blade to scribe the side of the substrate perpendicular to the flat side giving the orientation of the crystal. Then, with a little pressure on the blade, the substrate bears along the crystal direction. Two issues arise from this manipulation. First, the breaking creates particles of silicon that need to be carefully removed to avoid interference with the lithography process. The second is that the dioxide silicon layer tends to break irregularly and create hedge like structures on the side of the samples. The simplest method is to use the scalpel to scrub them mechanically. The residues are then cleaned with the silicon residues.

Another characteristic of the substrate that is worth noting is its reflectivity. Indeed, since I work with a photo transfer a reflection of the light on the sample can create interferences [START_REF] Microchemicals | Exposure of Photoresists[END_REF]. These interferences can add to the diffraction effect completely disturbing the image. The most common methods for exposure of photoresist layers are the direct projection onto the whole substrate with a mask aligner (left, usually the photomask and resist are in close contact), the stepwise exposure of rectangular partial surfaces by a reduction optics (stepper, center) or the direct writing of the structures with a laser (right).

Exposure methods

Three versions of light exposure exist in UV-lithography -

The mask aligner at my disposal in the clean room is a MJB4 from SUSSMi-croTech. I will detail the use of the device in the next paragraphs of the section, for more information refer to [START_REF] Sussmicrotech | Manual mask aligner[END_REF].

Photosensitive resin and environment

The main influence of the environment on photosensitive resin is light - [START_REF] Microchemicals | [END_REF]. Indeed, uncontrolled light exposure of the resin will activate it and reduce its efficiency in the actual process. Since resins are sensitive to UV light but also to close to UV light -Figure 2.60 -the lithography part of the clean room is lit with yellow light. Other than frequency, the intensity of the light will have effect on the critical exposure duration -Figure 2.61. Resins are sold in adapted black containers built to reduce the impact of ambient light on the resin. Despite that it is advised to keep the main container of resin in a dark storage. Another environmental effect on the resin is the temperature.The resolution of the resin decreases over time. The speed of the resolution decrease increases with the temperature. An ambient temperature of 25 • C conserves the resin until its expiration date. In order to obtain the higher resolution, the manufacturer advises to store the resin in a fridge between 5 and 10 • C.

The main drawback of such a storage is that one needs to let the resin contained heat back up to ambient temperature in order to avoid condensation of ambient water in the container. Condensed water will create irregularities in the resin and degrade its characteristics. Ambient humidity needs to be controlled during the process. A too strong humidity -∼ rH > 60% -will reduce the adhesion of the resin on the substrate. A too low humidity -∼ rH < 30% -will reduce the rehydration rate of the resin -c.f. Section 2.3.3. The last environmental parameter having an effect on the resin is the ventilation. Indeed, during process steps where some product needs to be evacuated from the resin as a gas, the ventilation will modify the results. This property of the process pushes me to work in a highly and regularly ventilated environment. Fortunately, most clean room use laminar flux ventilation, especially in chemistry workbench. The expiration date of the product is the limit duration at which the resin will still give nominal results for the advised storage conditions -25 • C in darkness. The state of the resin is actually constantly evolving and should be regularly tested in order to be able to compensate for property deviation.

Technique choice

.

In this section, my choice of photoresist is addressed. My choice in deposition technique, in mask contact method and metal deposition method is also justified.

resin type and metal deposition

Three types of photoresists are developed. Figure 2.62 presents the type of results that can be expected upon exposure to light on selected parts of the substrate. For a positive resin, built from DNQ and Novolak, exposure to light will modify the structure of the composite and allows it to be dissolved by alkaline developers. This creates a positive image of the mask: where there is chromium on the mask there is resin on the substrate. For negative resins, exposure to light will create a cross linking of the phenol polymer. While the non-exposed regions can be dissolved by the developer, the cross linked regions stay solid during development. This technique creates a negative image of the mask. The last type of resin is a reversible resin that can create a positive or negative image of the mask depending on the post exposure manipulations. These resins are built from Novolak and DNQ and can be used like positive photoresists. For a reversed image, the substrate is baked in order to release DNQ from Novolak polymer chains. The previously exposed regions lost their sensitivity to light while the rest of the resin is still photosensitive. The substrate is then exposed on its entire surface in a flood exposure. The development will reveal the exact opposite volume from the positive version. I explained in chapter Chapter 1 that in order to limit bending of CNTs I needed to create a slope on the deposition sites. Two types of metal patterning can be used as presented in Figure 2.63. First, metal deposition, where the substrate is covered with a layer of metal that will bond to the substrate where the resin has been removed. Second, the removal of metal from a layer directly on the substrate, where the resin has been dissolved. The second method is mostly used for mask manufacturing by selectively etching chromium of a quartz or soda-lime substrate. In my process deposition of metal on selective parts of the substrate is more compatible. Etching on silicon dioxide can create issues and most etching methods require specific expertise. Metal deposition, on the other hand are automated processes for which I had access to experts.

Metal depositions create a negative image of the resin mold in metal once the resin is removed. Therefore, in order to create positive slopes on the metal structure, I need to create negatives slopes with the resin. The most often used technique to create specific slopes and metal profile is Chemical Vapor Deposition -CVD. It has the advantage to create homogeneous metal layers that can follow resin profiles very precisely. Another advantage of creating negative resin slopes is presented in Figure 2.64. The lift off technique gives better results with negative slopes. They increase the separation between the part of the metal that composes the result and the part that should be removed with the resin.

Positive resins are mostly used when straight and vertical resin walls are needed. In our case, negative resin and reversible resins are more appropriate. Figure 2.65 presents the method of under-exposure allowing creation of an undercut in reversal resins -the technique with negative resins is similar. The difference between negative resin and reversible resins is the crosslinking of the polymer chains. Reversible resins keep a low polymer chain length due to low crosslink rate. Therefore, they are more sensitive to rounding due to heat during baking and metal deposition. On the other hand, negative resins are difficult to remove from silicon dioxide substrate especially once cross-linked.

resin specifics and deposition

In addition to the polymer chain and the photoactive component, photoresists also contain other molecules. I will focus here on the effects of these molecules on the resolution of the resin. The resolution defines the size of the smaller object that can be realized with the resin. First, hardening agents are used for reducing the rounding process. As discussed earlier, positive and reversal resin have a low rate of cross linking and will soften upon exposure to heat -> 130 • C. These agents reduce this rounding effect by decreasing the softening of the resin.

The resolution of a resin is defined by the difference between solvability of the resin that needs to be removed compared to the solidity of the insoluble part of the resin. Figure 2.66 illustrates the ratio of the remaining film thickness to the original film thickness d'/d 0 after the development as a function of the exposure dose. This ratio can be increased by contrast agents sharpening the resin walls as shown in Figure 2.67.

In order to explain the role of the third type of molecule acting on the resolution of the resin, I first need to address the thickness of the resin. In a high resolution lithography, light will tend to diffract and create artifacts on the resin -c.f. Section 2.3.2.3. A thinner resin layer will reduce diffraction effects. The thickness of the resin is dependent on the solvent ratio and the coating technique. For example, the deep coating technique which consists in dipping the substrate in the resin. This method is mostly used for large surface substrates and most often thick resin layers. The second technique consists in the spraying of the resin. The advantages is that it allows covering of irregular surfaces that could be impossible to treat with spin coating. Drawbacks are the non-uniformity of the layer over the substrate and the difficulty to create thin < 1µm and homogeneous layers of photoresist. The third commonly used coating technique is the spin coating. Its advantages are its rapidity of execution, the smoothness of the layer and the control of the layer thickness depending on the rotating speed. Finally, the fourth type of molecules increasing the resolution are solvents. A solvent is used to control the viscosity of the composite. The less viscous a resin is the thinner its layer will be once deposited on the substrate. In spin-coating techniques the solvent concentration of the resin is directly related to the thickness of the final photoresist layer as shown is Figure 2.69. A resist can be diluted in its solvent after purchase in order to reduce the thickness. It is important to note that a higher solvent concentration reduces the durability of the resin.

Exposure methods

The dimensions of the design are limited by the technology resolution and the UV wavelength. Close to these dimensions, < 10 times the wavelength, diffraction effects start to appear -Figure 2.70. In order to limit these effects I aim to minimise the distance between the mask and the substrate during light exposure. The mask aligner on which I work possess three types of contacts: Soft, Hard and Vacuum contact. They each have a smaller gap than the previous as exposed in Table 2.3. During my trials, I tested the two negative and reversal resin from Microchemicals with the highest resolution: AZ2020 (negative) and AZ5214 (reversal). After several tests I decided to work with AZ5214, despite the more complex process, due to the actually attained resolution fitting my requirements unlike AZ2020. Another drawback of AZ2020 and crosslinking resins is that they tend to create a solid layer on silicon dioxide that is problematic to remove. From this point-on, I will describe the parameters of lithography for the AZ5214 resin. I will use a technique of subexposition as described above in order to create undercuts in the resin. I will also use a high-speed spin coating to reduce the thickness of the photoresist layer. Finally, I will use vacuum contact parameters on the MJB4 in order to reduce the gap between substrate and mask.

Technical parameters

In the previous section, the method that I will use for high-resolution lithography. In this paragraph, the parameters of the steps of the lithography process are outlined. The effects of these parameters are addressed. Finally, the pre-experimental process is presented as a conclusion, describing the range of exploration of the parameters during the lithography trials.

The first step before lithography is to clean the substrates and the mask. Indeed, a precise lithography requires a perfectly clean and flat surface. The substrate cleaning is realized with acetone and isopropanol. Two glass containers are used for each solvent. The first one is for cleaning; it will contain residues. The second one is for rinsing; it should contain a very limited amount of polluting particles. Acetone is used first to dissolve the resin -activated or not -and remove dusts or silicon residues. Then, after acetone rinsing, isopropanol is used to remove acetone residues. The advantage of isopropanol is that it evaporates without leaving traces on the substrates. In both solvent, a furrow swabbing of the substrate is strongly advised. It will help dissolve polluting particles and desorb them from the substrate.

The third usual step in cleaning, is water rinsing and nitrogen drying. In my case, since I work on a silicon dioxide layer, the water rinsing is ill advised, as the water will adsorb on the substrate and reduce resin adhesion. On the other hand, this reaction takes place, although at a slower pace, with ambient humidity. In order to counteract this reaction, it is advised to dehydrate the substrate before spin coating. Dehydration consists in baking the substrate on a hot plate at > 120 • C for ∼ 1min. The inconvenient of this method is that a hot substrate will accelerate the evaporation of the solvent in the resin. This creates the risk of increasing the thickness of the coated layer of resin. A compromise is attained by letting the substrate cool for a few seconds but not enough that water could reabsorb on its surface.

Once the substrate are clean and dry, the next step is resin coating. As addressed earlier I will use a spin coating technique. I outlined above the effects of the resin composition on the thickness of the sample. I will now describe the effects of the two parameters of spin coating: speed and duration. The main parameter of the spin coater is the max speed at which it can turn. Figure 2.72 shows the evolution of the thickness of the resin layer depending on the rotating speed. A higher speed will increase the centrifuge force and therefore decrease the thickness of the photoresist layer. The upper limit of the speed is defined by the material at disposal for manipulation.

The second parameter is the duration of the movement. There is no real upper limit to the duration of the spin except time loss. On the other hand, Figure 2.73 presents resin thickness depending on time for two types of resin. A thick and viscous resin will attain its final layer after a few tens of seconds of rotation. For a more liquid resin or a thinner layer this duration can be of a few seconds.

After spinning, some solvent is still present in the resin. In order to reduce this content and harden the resin, the next step consists in a baking step. This step should be at a temperature less than 130 • C for photoactive molecules conservation. It also should be kept short in order to reduce the risk of over-cooking the resin. Overheating of the resin makes it brittle and its color turns to brown. An overheated resin, even without going over the limit temperature of 130 • C, losses some of its particularities and reduces the quality of the result. Before exposure, DNQ based resins need to uptake a small amount of water. This water is necessary to the reaction upon exposure and can create defects in the result post development as shown in Figure 2.75. This rehydration uses ambient humidity and consists in waiting between baking and exposure in a humidity-controlled area. The exposure step parameters can be separated into two categories: energy parameters and geometric parameters. The first addresses the quantity of energy needed for the resin to react. The second type of parameters modifies the space density of the light stimulating the resin. There is two energy parameters. First the power of the light emitter. In my case, the MJB4 is equipped with a 350W mercury source. The second parameter, on which I can act, is the duration of exposure. The full exposure energy for a 1µm is of approximately 30mJ/cm 2 . This value will have to be explored during trials due to its strong dependence on experimental parameters. For example the thickness of the resin modifies the required amount of energy as shown in Figure 2.76. Furthermore, I outlined earlier the need for negative slope resin patterns. This requirement will push me to optimize the exposure duration toward the desired metal shape.

The second effect due to exposure parameters is the quality of the contact and the distance mask-substrate. Another parameter related to quality exposure is the orientation of the substrate regarding the light direction. In order to have a symmetrical and maximized exposure, the sample needs to be orthogonal to the light direction. MJB4 mask aligner allows to adjust this angle variation through the Wedge Edge Compensation -WEC Figure 2.77. This manipulation compensates the variation of thickness of the substrate and should be repeated for every sample. Another feature of the MJB4 that is helpful for high resolution is that the optics are built specifically to reduce diffraction effects, as shown in Figure 2.78. The next step is specific to reversal resin and called reverse bake. The objective here is to break the bonds between DNQ and the hydrophilic side of the polymer. Unfortunately, the heat will also deactivate, although slower, the still photosensitive DNQ molecules, as shown in Figure 2.79. The reverse bake should be realized at a temperature and duration that will allow reaction of the linked DNQ without significantly reducing the quantity of sensitive DNQ. A good reaction rate in the activated resin part will guaranty its insolubility in the developer. A limited loss of active DNQ guaranties the solubility of the resin in the active still active areas. Non-optimal parameters for reverse baking lead to loss in contrast of the resin. The flood exposure is used to expose the part of the reversible resin that was not exposed the first time and is still active. After this step, these areas of the resin will become soluble in the solvent. A maximum limit of flood exposure can be reached due to heating of the sample upon light excitation. On the other hand, the flood energy is advised to be three times the full exposure energy. Finally, the development consists in the dipping and stirring of the sample in developer. The duration depend on the thickness of the resin layer and of the contrast that has been attained. This process step is strongly dependent on the upstream parameters. In order to give a rough idea of the duration, a good development rate should be over 1µm/s. The developpement also allows a last correction on the shape of the resin and could help in the desing of the negative slope profile -Figure 2.80.

Summary of the pre-experimental lithography process

The lithography steps are listed here following the process sequence. The relevant parameters and their range of optimization are addressed with respect to the previous reflections of the section. The results of experimental manipulations concerning the lithography process are illustrated in Section 3.2. As addressed above, the chosen resin is AZ5214. I will address here a process specific to this resin and the objectives described previously in this thesis -c.f. Section 1.2 and Section 2.2.

Cleaning

The first and last step of the lithography process is cleaning. Indeed, it is essential for the quality of the results that all material and tools be cleaned before and after a lithography process. The only exception are the successfully carved substrates going to further processing.

Tools are cleaned, as is usual in clean room, with acetone, followed by isopropanol and water rinsing.

The new or unsuccessful substrates are cleaned thoroughly cleaned. Any micro particle left on the substrate can reduce to zero the chances of success of the process. The first step consists in spraying the substrate, while held by tweezers, with acetone. Then I use a swab repeatedly from top to bottom only. I regularly change the tweezers placement in order to be able to clean the full surface. Then, I copiously rinse the substrate with isopropanol a few times while changing the tweezers position in between. The only quantifiable parameter here is repetition. No water rinsing is needed, but a plasma treatment can help remove reluctant resin traces.

The plasma treatment also dehydrates the substrate. The recipe for resin cleaning in the CTM plasma reactor consists in a 100% O 2 plasma for 5min at 80% of the reactor power.

The mask is first cleaned with acetone with the same method as the substrate. Then, before isopropanol rinsing, the mask is put if a sonic bath, dipped in acetone, to help remove residual resin. The parameters here are duration and heat. Since, the power of the sonic bath depends on the material available. The heat is limited due to the use of acetone that evaporates at low temperature. No additional heat is needed especially since the sonication creates heat on its own. The temperature management is used to control that the bath does not go over 40 • C. In order to reduce evaporation, the container is closed with a paraffin cover. The tested durations go from 10min to 1h. An oxygen plasma treatment can be used in order to remove nanometric resin residues complicated to remove otherwise.

Dehydration After cleaning and before spin coating, the substrate is dehydrated. The process takes between 30s and 1min on a hot plate with a temperature between 110 • C and 150 • C. It is important to modify the cooling duration depending on the baking temperature so that the substrates contacts the resin under 120 • Cboiling temperature of the resin solvent -and over 80 • C -approximate temperature of rehydration having a consequential rate.

spin-coating

The spin coating step has as main parameter the programmed rotation speed. The set-up allows the adjustment of an acceleration to a maximum speed and a duration. I discussed earlier the effects of the rotating speed. This parameter will need to be optimized toward the thinner resin layer possible while maintaining the regularity of the coating. The acceleration allows further thinning of the resin with its increase. On the other hand, it allows a control on the homogeneity of the layer if reduced. In order to obtain the expected results, I will test rotating speeds from 4000rpm to 6000rpm -maximum allowed by the set-up -with ramps of 500rpm/s to 2000rpm/s. As discussed earlier the duration has little effects on the layer if it is long enough. The final thickness is attained at the most after tens of seconds. I will use a commonly used duration of 30s to guaranty the result.

In order to further improve the regularity of the layer, the resin can be left to rest for a few seconds between spin-coating and baking. The inconvenient of this technique is that if side beads are present they will be dispersed on the substrate and thicken the central layer.

First bake -hardening

The first bake process is used in order to harden the resin. This state is attained by evaporating the solvent left in the composite. The duration is fixed to a commonly used 1min and the temperature will be tested between 110 • C and 125 • C. The objective here is to harden the resin as much as possible without over-cooking it. The loss in properties is visible on the results but also when the resin turns brown and brittle.

Rehydration

The rehydration process in thin resin processes -∼ 1µm -consists in the control of the ambient humidity. The relative humidity of the lithography room should not be under 30%. The time necessary to pass from baking to exposure is enough for the rehydration to happen.

Exposure I discussed earlier the contact parameter of the exposure step. This contact can be adjusted by two duration corresponding to the two steps necessary to create the contact. In the first step, a vacuum is pulled from the space between the substrate and the mask. The second step consists in pushing N 2 behind the substrate while pulling a vacuum from the between the mask and substrate. These durations are usually of 10s each but can be modified. I will test these values from 5s to 20s in order to try to improve the results or reduce the processing time without quality loss.

The exposure duration depends on the measured power of the light source at the last control and the total exposure energy. For AZ5214 the exposure energy is of ∼ 30mJ/cm 2 per micron of thickness, with a measured light power of 6.35mW/cm 2 . Considering the variations of thickness and the objective of under-exposure, I will test exposure durations between 1s and 5s.

Reverse bake As expressed above, the reverse bake parameters aim to optimize the deactivation and hardening of the already reacted resin part, while maintaining the properties of the non-reacted resin part. This step is crucial and depends strongly on the layer of resin and the expected resin profile. I will test temperatures from 110 • C to 125 • C with durations between 50s to 1min30s.

Flood exposure It is worth to note that before flood exposure the resin needs a little time to rehydrate. This step is probably the less critical of all. There is no mask, so no contact. The exposure should be of > 200mJ/cm 2 . The only limit is the heat created by the light exposure. I will test flood exposure duration from 30s to 1min in order to reduce process duration.

Development

The development is executed in a AZ726 puddle. It consists in the dipping of the substrate and stirring. In order to maintain an isometric etching the movements should be kept regular and as symmetric as possible. The main parameter is the duration of the chemical development. The more the layer of resin is thin the shorter the development will be. This step will decide of the final resin profile. The expected carving speed are of about a couple microns per minute. The development duration is expected to be between 20s and 1min.

Rinsing and observation

The substrate is then thoroughly rinsed. This ensure that the development reaction is stopped. The sample is then dried with N 2 . The first observations are made in the lithography part of the clean room -under yellow light -with a specifically filtered microscope.

From CNTFET to biosensor

In the previous sections of this chapter, I described the three process steps for the realization of a CNTFET. First, CNT dispersion and the first layer of metal patterning are executed in parallel. The result of both allows to perform dielectrophoresis placement of the CNT on the metal pattern. Now at this point, a CNTFET assembly is present on the sample and can be characterized.

In order to fulfill my objective of completing a biosensor and showing a proof of concept, the transistor network has to be modified. In this section, the process steps for CNTFET to biosensor conversion are outlined. The cleaning of the sensitive surface is described first. Next, the deposition of the second layer of metal on top of the first is addressed. Then, the deposition of a passivation layer is described. The final preparation consist in the realization of a container for the target biological sample adapted to the sensor and in electric connections normalised for external communication. This process should allow me to create a sensor in a set-up adapted for research and experiments. The modifications necessary for the final applicationready versions and the industrialization of the process are discussed in Chapter 4.4.1.

CNT and sensitive surface cleaning

This step consists in removing unwanted chemicals from the surface of the sensor that will be in contact with the biological target. This area consists in the apparent SiO 2 between electrodes and the surface of the CNTs. The parts of the CNTs that will be buried in metal are not my main focus here but the desorption of residues would increase the contact quality. This cleaning process will need to be used at least twice. First, after dielectrophoresis, the surfactant should be removed as much as possible in order to reduce the overall residue quantity. The second cleaning step should take place after the second layer and passivation layer are deposited. The objective here would be to remove resin residues. One thing to keep in mind here is that during functionalisation, Pyrene groups from Pbase should replace most of the molecules with less affinity on the CNT sidewalls. The several to-be-tested surfactant and the resin used in lithography have less affinity toward CNTs than Pyrene. Therefore the objective is twofold, first clean as thoroughly as possible the SiO 2 substrate. Second, reduce the quantity of residues on the CNT sidewalls to ease the replacement by Pyrene and increase the functionalisation yield. The main issue in this cleaning step is that it needs to be optimised between removing a maximum of the residues without degrading the sensor, i.e. CNTs and the resin passivation layer.

Two common methods can be used for residue removal. [START_REF] Rossi | Removal of sodium dodecyl sulfate surfactant from aqueous dispersions of single-wall carbon nanotubes[END_REF] presents a chemical method for removal of sodium dodecyl sulfate from CNTs. In the first removal step, the choice of remover will be oriented by the surfactant and the protection of CNT sidewalls. [START_REF] Tasis | Chemistry of carbon nanotubes[END_REF] describes the molecules and processes used in CNT sidewall modifications. In the second step, the passivation resin also needs to be unharmed by the chemical remover forbidding the use of organic solvents. [START_REF] Microchemicals | [END_REF] describes the resistance of resins to different chemicals. In our case the cleaning process should be realized with an aqueous acid such as hydrochloric acid that does not systematically dissolve the resin and does not modify the CNT sidewall lattice.

The thermal method consists in heating the substrate at a temperature high enough to remove chemical moieties but not too high that it would degrade the sensor. During the first cleaning there is not resin left on the sensor so it can be heated as high as 400 • C without suffer any changes. This temperature is enough to break most hydrogen bonds between a chemical and the SiO 2 layer. [START_REF] Gyu | Effects of surfactants and alignment on the physical properties of single-walled carbon nanotube buckypaper[END_REF] demonstrated annealing removal of surfactant and the fact that such a technique leaves residues on the CNT sidewalls and should be completed with chemical cleaning. For the second cleaning step of my process, a layer of resin is present, coating the metal electrodes. In this configuration the maximum annealing temperature should not be over 130 • C, otherwise incurring the risk to create cracks in the resin and make it brittle -c.f. Section 2.3.

CNT enclosure and passivation layer

As addressed in Chapter 1 the enclosure of the metal/CNT contacts is expected to increase amplification from the CNTFET structure. It also guaranties the mechanical stability of the CNTs provided that both their tips are buried in metal. The second layer consists in the deposition of resin on top and around the metal electrodes in order to reduce interactions with the biological sample. Both of these process steps are realized with lithography in a similar fashion as in Section 2.3. I will outline in the following the specificities of these two process steps regarding the first layer.

CNT enclosure

In order to realize the enclosure layer, I need to reproduce precisely the previous lithography step. The expected result is illustrated by Figure 2.81. The variation in process will have as objective to compensate for the difference in experimental conditions. Indeed, the first layer was deposited on a flat surface. On the other hand the second layer will be deposited on the first.

This difference creates variations of the process. First, the spin-coating of the resin needs to be adapted to the surface. The quantity of resin will need to be slightly increased to compensate for the roughness of the surface. The expected structure of the spin coated layer is presented in Figure 2.82. In order to improve the evenness of the surface, the sample is left to rest for tens of seconds between spinning and hardening.

The exposure process is similar except for a risk of underexposure in the thickness of the resin at the CNT site. This could create pathways for metal between The baking process should be similar to the original due to the little effect of the resin thickness on this step if it is of approximately 1µm. Because the developed layer thickness is similar to the thickness of the first layer, the development duration should vary only to accompany exposure variation.

One of the most problematic variation between the first and second layer is alignment of the patterns. The use of a precise mask aligner is necessary for this step. I use the same MJB4 aligner than in the previous section. The alignment is realized with a microscope and alignment patterns -Figure 2.84. The mask aligner allows to move the substrate along the horizontal plane with a micrometric precision. At this step -before vacuum contact and exposure -the mask is ready for exposure and the substrate is placed a few millimeters from its contact height. The substrate can be then aligned with the mask in the x and y axes but also in a rotation around z. The objective is to align the layers as precisely as possible. The complexity of this step increases with the size of the pattern to align. FIGURE 2.84: Patterns for mask alignment [84] Another issue that could impede with this step is the strength of the bond between CNTs and metal. Indeed, precise lithography requires a high speed spin coating. The success of this steps supposes that the CNTs can sustain the centrifuge force of the spin without moving. In case of a loss in CNTs at that step, I would advise to use current stimulation in the transistor in open configuration before spin coating. [START_REF] Wilhite | Metal-nanocarbon contacts[END_REF] demonstrated the increase in bond strength between CNTs and metal through this stimulation technique.

Passivation layer

As discussed in Chapter 1, metals can interact with biological samples. In order to reduce these interactions, considered as parasitic in this set-up, I coat the metal electrodes with a polymer inert toward biological fields. The effect of this insulating layer is to stop chemical reactions on the metal surface but also stop electrical conduction. This effect creates a capacitance between metal electrodes and biological field. In order to reduce this capacitance effects the resin needs to be thick enough depending on the frequencies used for measurement. Indeed, I outlined in Chapter 1 that on a second approach an alternative current source stimulation could improve the measurement results. The use of an AC potential supposes a minimum thickness of passivation depending on the frequency used. On the other hand, this polymer layer reduces the access of the target enzyme to the protein probe, potentially reducing the activation rate of the polypeptide and the sensitivity of the biosensor.

During the previous lithography steps, I used the reversal resin in a negative setup. In this step, I want the resin to be developed at the CNT deposition site and to resist development on the metal electrodes. Compared to the previous lithography processes, in step, the resin should be dissolved where it was not and stay solid where it was dissolved. Therefore, as a first approach, I will use the same resin as previously -AZ5214 -but in a positive configuration creating the passivation layer. The spin coating step in similar to the previous ones with the constraints of the second layer increased due to the increased inhomogeneity of the substrate. The passivation layer will be of approximately 1µm, allowing me to maintain parameters for hardening baking. For exposure, as previously, a thorough alignment of the mask on the sample is required. Resin walls slope needs to be optimized according to Figure 2.85. This allows freeing of the CNTs from the resin while maintaining coating on the metal layer. This result is attained with a thorough investigation of the exposure and development duration parameters. It is worth to note that here the developed regions are the deepest and the non-developer-soluble are the thinner regions. This implies a strong contrast in the exposed resin. In this section, I outlined the transformations required to use the previously built CNTFET as a biosensor. After these process steps a biological sample deposited on the sensor would be in contact with the CNTs and the passivation layer only. The CNTs are sensitive to their electrostatic environment as discussed in Chapter 1 creating a field effect sensitive biosensor.

Liquid container and electrical connections

The final steps of the biosensor manufacturing consists in creating a fluidic system for the biological sample to be measured and realizing lasting electrical connections.

In a first approach the liquid containment system will consist on only a reservoir for the biological sample. This container can be built from a centrifuge container, cut in a cylinder by removing the tip and the closing system. The plastic cylinder can be glued on the sensor substrate. The shaping of the liquid system can also be realized through a molding method used in [START_REF] Moutaux | An integrated microfluidic/microelectrode array for the study of activity-dependent intracellular dynamics in neuronal networks[END_REF]. The authors are working at the laboratory IES that is part of Montpellier University. This technique gives robust and repeatable results at the resolution used in my design. Although it would be an over-complicated process for a first approach, this technique would allow the realization of a microfluidic system necessary for rapid sequential use of the sensor in a point of care application.

Electrical connections to the sensor are of two types. First, the connections with a solid part of the sensor i.e. drain, source and back-gate. Source and drain connections have been addressed in the design of the mask by placing wide access pads -∼ 100µm * 100µm. The back-gate is used only in characterization set-ups and can be bonded to a metal wire. These connections can be realized through welding in the clean room. The second type of connections is found in the chemical gate. This electrode contacts the electronic circuit and the liquid sample. In our case, as developed in Chapter 1, the chemical electrode is used as an electrical reference for the system. [START_REF] Minot | Carbon nanotube biosensors: The critical role of the reference electrode[END_REF] studied the effects of this electrode and the effects of its nature. A metallic electrode made of non-reactive material such as Pt will create a chemical double layer at its surface and a local potential. On the other hand, a chemical electrode, typically Ag/AgCl, will change the composition of the solution by releasing ions but will transmit the sample potential with less artifacts. I propose to work with a Ag/AgCl electrode for the precision toward the electrochemical potential. Both types of electrodes will need to be investigated particularly for long use duration such as data monitoring.

Full process overview

The full process flow is illustrated in The chemical characterisation can be realised directly after dielectrophoresis. It consists in signal conductivity measurements of the channel while different concentrations of PBS are deposited on the sensitive surface. This measurement allows to prove the sensitivity of the set-up to different concentrations of phosphates without selectivity. This type of measurement can be repeated along the process flow in order to follow the evolution of the chemical sensitivity of the sensor.

Chapter 3

Characterizations

This chapter presents the several experiments realised in order to create the sensing technology. The first section describes the dispersion optimisation. The second section addresses the lithography process. The third part demonstrates CNTFET realisation through DEP. The fourth section describes the different characterisations extracted from the CNTFETs. Finally, the limits of the realisation are addressed with the next steps toward proof of concept of the sensing technology.

Dispersion realization

This section outlines the different realizations constituting the optimization of the pre-experimental process -c.f. Section 2.1. I realised approximately a hundred dispersions during these three years. Around eighty aimed at the optimisation of the dispersion process. Then ten where SDBS dispersions for the first deposition trials. Finally, the last ten where dispersions with CMC as a surfactant for the second version of the deposition.

Solvent

As discussed in Section 2.2 water as a solvent has the strong advantage of a lower evaporation rate than organic solvents. Despite that,trials with acetone and ethanol where realised without surfactant. The dispersions consisted in 50mL of solvent into which were added 0.5mg of CNTs as ash. The result was then dispersed with a sonic tip for several duration with different power of stimulation. The results were stable for a couple of minutes at best with acetone. The results of ethanol dispersion are illustrated by Figure 3.1 after two cycles of stimulation at sixty watts and less than a minute of rest.

The poor results in dispersion quality and stability pushed me to work with an aqueous solvent and a surfactant.

Surfactant

Three surfactants have been chosen for trials : SDBS, CMC, sodium cholate. Since every parameter of the dispersion needs to be optimized for each surfactant, The trials realized for SDBS dispersion optimization are first discussed. The variations of process due to change in surfactant are discussed in a second time. The trials started with the objective to demonstrate the separation of CNTs to single CNTs or small bundles ∼ 10nm. The next objective is to identify the optimum parameters to increase CNT separation. The optimal concentration of SDBS has been identified as 0.5% independently of the other parameters. The method for identification consists in a visual successive approximation evaluation. I use a black and white color sheet

Surfactant sonication

The next step is the preparation of the surfactant and the use of sonication to break its micelles. Here, sonic tip stimulation is applied until no observable particles are left in the solution. The parameters of sonication in this step are the sonic wave energy -10w to 200w -and the application duration -10s to 2min. The stimulation is maintained until no residues are observable. A higher power reduces the duration of the process although not significantly but it creates more heat. The sample can become difficult to manipulate by hand. On the other hand, a lower power increases the stimulation duration more and more significantly with each removed watt. Trials where realized and no notable difference in dispersion was observed after a stimulation of 60W for 100sec. This value was chosen as a compromise. It is worth to note that this results varies significantly with the efficiency of the steering of the surfactant when first introduced. Cutting the surfactant particles in the liquid to reduce their size helps hasten the process.

CNT addition

The next step consists in the introduction of CNTs in the solution. The higher the CNT concentration, the harder it is to disperse. The solution is based on 50mL solvents and the weight of CNTs added to the solution was between 0.5mg to 2mg. No significant changes were observed over 1mg implying a lower rate of dispersion. On the other hand, it is complex to measure a weight at a 100µg precision. For these reasons, I choose to work with 1mg of CNTs in the following trials.

It is worth to note that CNTs tend to fall at the bottom of the liquid but need help to go through the surface of the solution.

CNT pre-sonication

The next step consists in steering and sonication of the obtained colloid. First, the dispersion is put in a sonic bath for 10 to 30min. This allows reduction of the size of the biggest groups of CNTs in order to prepare the dispersion and optimize the efficiency of the tip sonication. The set-up is illustrated by

CNT sonication

The next and main step is sonic tip stimulation. The parameters are the power of stimulation from 10W to 200W and the duration 10s to 2mn. The set-up is illustrated in Following the trials the sonic tip stimulation was found to be optimal by using two steps of sonication of 120w for 30sec with a 1min waiting step in between for cooling. Approaching this stimulation power and stimulation, the variation in result becomes

Centrifugation

The next step is centrifugation, with an acceleration of two hundred thousand times earth's gravity. The centrifuge force is applied to the colloid for 15min to 2h in order to fully separate the different phases. Similarly to previous results, the centrifugation efficiency was evaluated independently from other parameters using visual colorimetry. The results changes where significant for the first 30min of centrifugation. Figure 3.12 and Figure 3.13 illustrate the variation in the sample before and after a 30min centrifugation. The particles floating in Figure 3.12 form a compact block at the bottom of the sample in Figure 3.13. Figure 3.14 illustrate the results after 90min, no changes are observable and as discussed in Section 2.1, an over centrifugation can remove single CNTs from the colloid.

Recovery and dilution

The final step before DEP deposition is the separation of the supernatant containing singly dispersed CNTs and the following dilution of the obtained colloid. The results of this step are observable by DEP placement which is the goal of the process. For this reason the results of this dilution are treated in Section 3.3.

AFM observation of single CNTs

The colloid was diluted and drop-casted on a silicon substrate at 70 • C for AFM observations. The main issue in observing CNTs is that they tend to reform bundles when deposited on a surface and dried. The second issue encountered during my manipulations is that the AFM needle tends to pick-up surfactant molecules creating artifacts in the result. Finally, without placement, it is a laborious work to find nanometric structures in square centimeters. The image resulting from AFM were treated with gwyddion, an open source software for microscope imagery treatment. Figure 3.15 illustrates the AFM set-up. Figure 3.16 illustrates the side of a CNT bundle from which some CNTs pock out. Figure 3.17 illustrate the identification method through multiple profile extraction.

Surfactant variation

The second surfactant to be trialed is CMC. The results from SDBS dispersion deposition where positives but I was unable to remove SDBS in a satisfactory amountc.f. Section 3.3. Another issue developed in Section 3.4 came from the combined effect of the slide in characteristic due to the surfactant molecule and the back-gate electric field strength. The CMC dispersion is similar to the one with SDBS except that I use PBS as an interface between water and CMC.

Dispersion results

During these dispersion trials, I succeeded in creating a singly-dispersed CNT colloid ready for DEP placement. The actual results of dispersion depend on the characterization of the final transistor and its electrical field amplification -c.f. Section 3.4.

Lithography processing

Here are listed the work and conclusions relevant to the design of the sensing technology concerning the lithography steps. The effects of the parameters experienced through trials are also outlined. Finally, the variations of lithography results for dielectrophoresis are illustrated. Lithographic trials consists in depositing and carving the photosensitive resin. This process can be repeated on the same sample. Indeed, the resin can be fully removed with acetone in order to repeat rapid trials. The full process -from cleaning to development -takes approximately two hours. Then, the substrates are sent to metallisation in groups of twelve. Over the thesis duration, I lifted-off metal from approximately sixty samples. Forty of theses were successful and had CNTs deposited on.

Mask and pattern

The first result from lithography comes from the work of IEMN engineers. The mask is made of a 300nm layer of chromium deposited on a quartz support and selectively etched through electron beam lithography. The numeric pattern was presented in Section 2.3. Here are some illustrations of the result. First, Figure 3.21 shows the mask with the sixteen patterns that can be independently lithographed on a resin coated substrate. The fourteen full patterns aim to create a sensing network. Their The two patterns designed for trials differ by the shape of their teeth and pitch creating the deposition sites.

Spin speed

The first part of the lithographic process relevant to the thesis is the spin coater speed and acceleration ramp. The mean measured thicknesses are of 1.8µm at 3000rpm, 1.4µm at 4000rpm, 1.1µm at 5000rpm and 0.9µm at 6000rpm. Considering the risk of diffraction, the speed of 6000rpm is chosen for the process. Figure 3.27 illustrates results at a speed of 4000rpm. Figure 3.28 illustrates results at a speed of 5000rpm. It is worth noting that these results are created by the distance between the mask and the substrate. The thickness of the resin is one factor, modified mostly by the spin speed. However, it is not the only reason for the distance between substrate and mask during exposure.

Spin acceleration ramp and side beads

The second factor notable in spin coating is the acceleration to the maximum speed. The stronger the acceleration, the thicker the beads are. On the other hand, the homogeneously flat surface at the center of the substrate increases with the ramp. At first, I tried for a compromise between both with as a constraint to have enough

Substrate clamping and edge effects

The substrates I use are made from monocrystalline silicon. They can be spitted along the structure of the silicon crystal. The issue arise from the SiO 2 layer that I deposit on top as a gate insulator. This layer, although 300nm thick, does not break along the silicon crystal axes. This creates little positive and negative dents in each of the substrate parts. These teeth create a hay like structure dramatically worsening the side beads at the edge. The solution is to scratch the edges of the sample with the scalpel used to clamp. This creates more particles that need to be cleaned but reduces the resin beads.

First bake temp

The temperatures of 125 • C with a duration of 1min [START_REF] Roblin | Oral communications[END_REF]. I started with these values and explored around. I did not experience any increase in the contrast of the pattern while staying close to these values and in the range of exploration defined in Section 2.3. Therefore, I chose to keep this process step as is.

Exposure contact

The contact distance is the first critical parameter of the lithographic process. I illustrated in Figure 3.27 and Figure 3.28 the effects of a contact with a distance of over 1µm. In order to reduce this distance, the aligner is adjusted on vacuum contact mode. Figure 3.31 illustrates the placement of the mask in order to choose the pattern to lithograph. As shown in Figure 3.32, the substrate needs to be centered on its support in order to maximize result quality.

Exposition duration

The dose of light received by the resin is the second critical parameter. I tested exposure durations of 5s to 1.5s.

Reverse bake

The reverse bake, similarly to the hard bake is based on a recipe from [START_REF] Roblin | Oral communications[END_REF]. This step's optimization consists in the optimization of the contrast of the resin. Experimentally, a strong contrast gives some margin in the chemical development step. On the other hand, an unsuccessful reverse bake lets the resin soluble or insoluble on the full surface depending on a respectively not fully reversed resin or an over-reversed resin. Similarly to the hard bake step, the baking patterns were explored without notable increase of result from the original recipe.

Flood duration

The flood duration is probably the less critical step of the lithography. The objective is to expose the resin enough without losing time. I started with a duration of 1min and went down to 30sec. The results start to visibly change -optical microscopearound 40sec. But I expect non visible particles arising between 40 and 50sec. I keep in my protocol a duration of 1min since I am not as constrained by time as in an industrial process.

Development

The chemical development duration is the third and last critical parameter of the lithographic process. This time span acts inversely to the exposure duration. The developer carves the resin. The undercut is then be deeper when developed longer. The results are here better observed after lift-off on the resin shaped metal layer. The development duration is found to be around 25sec. A more precise of the development duration is given in Section 3.2.12.

Environment effects

Two environment parameters have been found to impede the process quality. The first, a common issue in clean room, are the dusts and aerosols. Figure 3.36 illustrates a substrate that has not been cleaned enough. Even with a perfect clean of the materials some particles, like exhales aerosols can still find their way onto the substrate.

Considering the size ∼ µm of these particles it is easy to understand how they could create issue in the pattern reproduction. The second environmental property that can impede the lithography protocol success in humidity. Although variations of process have not been noticed for a too dry air, a strong humidity can interfere with resin reactions. Figure 3.37 illustrate a worst case scenario obtained on a 70% humidity day. Humidity regulation was not working properly on top of a rainy day.

Lift off The lift off step is commonly realized in a similar fashion to cleaning. Meaning that one can use a swab and slide it top to bottom repeatedly until unwanted particles are removed. In my design, the motifs are so small and regular that with this method the unwanted metal tends to stick on the final pattern. Electrostatic forces between the two electrodes also tend to increase this effect. The strength with which the unwanted metal piece bridges and sticks between electrodes is increased.

Results

The results of the lithography are positive in the sense that the pattern of the mask can be copied on a substrate as a metal layer with a precision of 100nm. This is important because 100nm is the approximate minimum margin needed between stacked layers. Furthermore, the superposition of these layers needs such a precision in order to build the structure as intended -c.f. Section 2.3. The development duration is used as a parameter to create this variation. These results depend on the strong contrast of the resin and its retention through the lithographic process. For the addition of the second and third layer this less than one second margin is hardly compatible with manufacturing. The commonly used solution to this issue is the dilution of the developer. This increases the development duration but it would also increase the process variation between layers closer to manufacturing compatible parameters. Another issue worth mentioning is the regularity along the pattern. Although the 100nm precision can be maintained on a square of one millimeter side length. Such a precision is rarely attained on the five millimeter side length of the full pattern. An industrialisation of this process would address this issue. We can also note on these photographs the angle of the metal layer due to the undercut as a slightly darker yellow line along the metal profile. Figure 3.46 shows a typical result of lithography observed through AFM. The metal layer is 250nm thick and the red dashed lines show the width of the walls. This width varies from 350nm to approximately 250nm leading to a minimum slope angle of 45 • compatible with my low angle sharpness approach for CNT deposition.

Dielectrophoresis

I present in this section how I used the two previous results along with dielectrophoresis to place and align CNTs as CNTFET channels. The first issue with this step of the process is that it rests on the results of CNT dispersion and sub-micron lithography. Therefore, the robustness and repeatability of the DEP relies these results. Over the three years of thesis, I deposited CNTs on forty samples. Of the forty depositions, twenty presented field effect sensitivity. A possible answer to that non-incidence is the sum of the thickness of the SiO 2 layer and the irregularities in its structure reducing its permittivity. Another explanation that could add to the insulator effect, is the electrical field screening created by the layer of surfactant that coats the surface of the dielectric after deposition. The source and drain of the future transistor and here used as stimulation electrodes and plugged on each output of the alternative current generator. The oscilloscope measures the phase difference between the two potential and allows me to adjust it to phase opposition. The oscilloscope also measures the peak to peak potential of the difference of the two signals. This measurement is realized with a

DEP parameters

The first DEP parameter, discussed in Section 2.2 is the frequency. This parameter can increase the pull of CNTs toward the structure but also create issues such as misalignment. In my experiments, I observed that the rate of CNT deposition was increasing with the frequency. The variation is most observable between 1kHz and 100kHz. With a lower frequency, little to no CNTs were placed and no variation of conductivity was observed due to field effect. For frequencies of over 100kHz the variation becomes less and less observable and the other parameters become prominent in the deposited structure. In order to follow literature guide lines, I used a frequency of 500kHz. This value can be further improved by a thorough and time costly investigation of the results. The second parameter is the field strength. This parameter acts specifically on CNTs in the colloid, since they are the most polarisable structure composing it. There is two ways to modify the field strength: the distance between the tips and the stimulation potential. The final sensor as a fixed distance for the channel. But this variation allowed me to use lithography trials, independently of the site length, to observe effects of the variation of the field.

From my experiments the results are similar if a field strength is the same even with different distances and stimulation amplitudes with a distance varying from 0.7nm to 1.1nm. Out of that range, the size of the particles strongly comes into account. For smaller sites, ashes tend to appear in higher quantity. For longer sites, a In the previously defined margin of 0.7nm to 1.1nm, three types of CNT structure arise from the DEP stimulation depending on the strength of the field. These trials were realized with a 5s stimulation duration. First Figure 3.50 shows a typical result for a field strength of 0.5V/µm. We can barely see a path between the first and third pairs of teeth from the left. AFM confirmed that every site contained a few CNTs. This type of structure shows repeatable field effect sensitivity as described in Section 3.4. We can also see in this picture typical line shaped structures on the opposite side of the electrodes from the deposition sites. The second structure illustrated with Figure 3.51 shows a configuration representative of a 5V/µm stimulation. This structure is composed of groups of CNTs bridging the electrodes. They most often present field effect sensitivity but the I on /I o f f ratio is reduced due to an increase in I o f f . An explanation is that the surfactant creates parasitic paths insensitive to field effect adding a continuous component to the signal. The second explanation is suggested by theory is that CNTs tend to screen each other. Finally, the surfactant not aggregated around CNTs in the colloid is also attracted by dielectrophoresis. This effect can create a variation in the ratio CNT/surfactant increasing the screening effect from the surfactant. Finally, Figure 3.52 illustrates a result obtained with a field of 20V/µm. This type of result varies in its structure and is to be avoided in AFM set-up. Indeed the amount of surfactant in the sites creates artifacts in the observation polluting the AFM tip and providing with unusable data. Furthermore, this type of structure only presents rarely and in a reduced fashion, compared to the two other structure, a sensitivity to field effect. These observations confirm the theory and design decision to reduce as much as possible the quantity of tubes in each site. Another parameter leading to the placement of CNTs is the duration of the stimulation. The placement is due to the displacement resulting from the application of the dielectric force. This means that a similar result should arise from a lower strength applied for a longer period of time. Except that the dielectrophoretic force varies with the polarizability of the particles -c.f. Eq 2.1. Due to this particularity, CNTs accelerate faster than other particles in the colloid. As a result, a strong and short stimulation is be more selective toward CNTs and reduce the ratio of residues such as carbon ashes. a field of 1Vµm for one minute. We can see the accumulation of carbon particles in dark and the surfactant in blue. On the other hand, Figure 3.54 shows a typical result for a stimulation with 20Vµm for one second. In this network a wide majority of the sites are filled with a configuration visually corresponding to positive results. These results were confirmed by electrical measurements. This result was further improved by reducing the field strength to 10Vµm while maintaining the duration to less than a second. This results could be further improved by using an automated on/off stimulation switch with a threshold detector as demonstrated by [START_REF] Chen | Quantitatively Control of Carbon nanotubes Using Real Time Electrical Detection Dielectrophoresis Assembly[END_REF]. Another interesting result of these manipulations is the observation of the variation of the placement along the stimulation lines. Figure 3.55 shows the result of a stimulation with a field of 0.5V/µm for 10s with a dispersion concentration tenfold less than for other trials. This result shows a higher density of placed tubes at the extremities of the stimulation lines. This type of deposition, due to its reduced dielectrophoretic strength is more dependent on the presence of particles in its proximity. Then due to the reduced concentration the extremities visibly attracts more CNTs due to the reduced density of attracting sites in the surroundings. This effect have been confirmed by the low site quantity lines which in this configuration attract more tube per site than networks. Another explanation compatible with my experiments although not experimentally demonstrated is that the potential loss in the access lines reduces the potential, even if so slightly, enough to modify the CNT structure between the extremities and the center of the patterns. The wider lines created to observe such a variation show a similar behaviour. This would direct the future research toward this issue to focus on the thickness of the metal -here 250nm. A second direction could be the capacitive effects of the insulators -i.e. SiO 2 and CNT dispersion. The last DEP parameter discussed here is the structure of the lithography and its effects on the CNT deposition. Indeed, the shape of the teeth plays a strong role in the shape of the electrical field between electrodes. Figure 3.56 shows a typical deposition structure due to the diffraction effect in the lithography process resulting in the division of the tips of the teeth in two. We can see that the split teeth create double paths. Another failed lithographic trial gave me short, almost flat teeth.

AFM observations of deposited CNTs

Although my final result is the amplification effect observed through characterization. It is important, for DEP optimization, to observe the relationships, first between deposition parameters and deposited CNT structure, secondly between deposited CNT structure and transistor characterization. In order to do so, I observed the structures of the deposited CNTs with AFM. Figure 3.64 shows issues arising from a failed lithography. First between the deposition sites we can observe bundles of tubes. These parasitic paths appear for too short teeth, with an approximate limit of 500nm. The duration of the deposition also tends to create such structures. The second observation of these images if the low alignment rate of the CNTs due to the split teeth. This can explain the reduced sensitivity of this structure despite the apparent separation of the nanotubes.

DEP results and improvements

These depositions confirm results from literature and the theory of DEP. Moreover, the coherence in the reaction of the tubes to different stimulations and trials give good confidence in the robustness and repeatability of the designed manufacturing process.

A few remarks can be made on these results regarding the structure and the surfactant residues. First, the surface of the SiO 2 is covered in bubble like structures. These are groups of surfactant molecules bond to the dielectric during deposition. This small layer modifies and screens the filed effect emitted by the back-gate. The second remark is that this surfactant tends to drown the nanotubes reducing their sensitivity to electrical fields.

Another issue put forward by these trials is that the maximum surface that can guarantee a homogeneous deposition needs to be investigated. Indeed, the lithography limits in surface and the increased density notes at the extremities of the networks in deposition suggest that the mask should be redesigned. This new design should include independent deposition site networks of a maximum size to be optimised. My trials allowed me to realise homogeneous depositions on squares of hundreds of microns side length to a couple millimeters in rare cases.

CNTFET characterisation

This section starts with my trials and results with the first surfactant: SDBS. Then, the trials and results using CMC, the second surfactant, are illustrated. The results common to both surfactant experiments are then addressed. This section is concluded with a synthesis of the characterization results regarding my objectives and the short term developments. During the thesis, I produced twenty samples presenting field effect sensitivity, based on patterns 13 and 14 of the mask.

Before illustrating the characterizations, the electrical set-up is presented. After AFM observation, the created transistors were characterized through electric measurements. The set-up used in these measurements is shown in Figure 3.65. Parallel probes are used to measure floating potentials. The resistors around the transistor are used to amplify the current signal and measure it as a voltage. Depending on the characterization, V ds or V gs is kept constant while the other supplies a potential, shaped as a symmetric double ramp, to the transistor. The frequency of the variating potential has a frequency of 60mHz so that the characteristics can be considered as static. The four green arrows represent the four probe of the station and their use in the circuit. Two are supplying V ds . One is supplying V gs . The last measures the supplied gate potential. All measurements are realized with an oscilloscope and extracted for computer treatment.

CNTFET from SDBS dispersion

The first objective of electrical characterization is to demonstrate the presence of a transistor through observation of expected results. The CNTFET structure should show a non-linear comportment at low increasing V ds and a saturation effect following a further increase in V ds . The second electrical particularity of the transistor structure is that it shows a sensitivity to the variation of V gs under the shape of a variation of conductance. This conductance variation is observed through the variation of current in the transistor with a constant V ds . The variation of current due to variation of V gs should also show a saturation areas with V gs exceeding a value Two types of faulty results appeared along the trials. First, some lines show a short circuit comportment. This behavior is most often present when the deposition results in high density packs of CNT/surfactant composite -c.f. Figure 3.52. This case is differentiated from a metal short circuit by preemptive measurement of the continuity of the lines before deposition. The second faulty configuration appears when no tube bridges source and drain leaving the line as an open circuit. These two cases are well identified as characteristics and are dissociated from the results presented in the following.

A typical I ds versus V ds measurement from a positive result is shown in Figure 3.66. During the trials with SDBS, I could only show the diode-like behavior of the structure along variation of V ds . An issue limiting my trials with a variating V ds is the destruction of the structure -or at least of its electronics particularitieswith a repeated V ds stimulation of more than two volts. This issue is further discussed in Section 3.4.3. This result leaves unfortunately the doubt on the presence of a transistor or a diode. The second measurements concern the gate potential sensitivity demonstrating the field effect sensitivity. Figure 3.67 shows the response of a single site deposition pattern to the polarization of the substrate. Figure 3.68 shows the response of a seven site deposition pattern to the polarization of the substrate. Although the clear sensitivity to field effect is a good result. Some remarks need to be made on these characteristics. First the p type comportment of the structure was expected. On the other hand, the closing of the valence band in a p-type CNTFET should appear at a higher backgate potential. This is an issue for the sensor structure since the objective is to operate close to zero volts. This could be due to the electrochemical characteristics of the surfactant. Two effect can be discussed with different consequences. The surfactant coats the nanotubes, but also the back-gate. These layers create a first screening effect that reduces the control of the back-gate on the channel. The second is the addition of a chemical gate potential due to the nature of the molecules. This can be coherent with the surfactant used if the alkyl tails of the surfactant are the major influence on the CNT state.

The second remark, is that the current should not decrease with an increase of the back gate potential once the conduction switches from the valence band to the conduction band. In Figure 3.68, the conduction from the valence band appears to attain an "off-state" around minus three volts. The current should then increase even if so slightly with the opening of the conduction band.

Finally, in Figure 3.68 we can see an acceleration of the increase in current, around V gs = -7V, that should not appear. At this point the increase in current should decelerate, showing a saturation of the structure.

The first issue is treated in the next section with the trials using the second surfactant. The second and third issues were identified as leakage through the back-gate. .70 shows the same set-up with a substrate that has been deposited with a 1%w/w SDBS solution. V ds is null, with source and drain connected to the ground. We can see here the diode like behavior of the substrate and back-gate. When the substrate potential is positive we can see an injection of current in the channel. I d increases with the substrate potential. I s decreases with the increase of the substrate potential. This is coherent with an increase in the channel potential. When the substrate stimulation reaches a negative threshold, the current in the source increases and the current in the drain decreases. This is coherent with the decrease of the channel potential.

This behavior is due to the leakage of charges from the substrate to the channel through the gate insulator. This has been confirmed by surveilling the gate current during stimulation of non-deposited substrates. This effect was not obvious at first, due to the fact that it appears with the characterization and increases with further stimulation. The sample of First, the temperature of CVD was tested at two hundred and two hundred and eighty degrees. The higher temperature deposition appears to show more resistance to leakage. The second parameter is the lithography. The more a sample undergoes lithography processes the more leakage appears. Two hypothesis can be formulated from this observation. First, the repeated heating and cooling of the structure can create mechanical fatigue in the oxide. The second is a chemical interaction modifying the structure that could come from the developer. In my development, the leakage issue was circumvented by identifying the gate potential threshold to approximately height volts in air and four volts in liquids. I rarely go over these potentials, in order to reduce the risk of breakage of the insulating layer. The second correction to the set-up is the surveillance of the gate current and of the difference between drain and source current to guarantee no leakage can interfere with characterization.

CNTFET from CMC dispersion

The aim of the second version of the deposition varies by the surfactant used for dispersion of the CNTs. The set-up is the same. The objective here is three fold.

First, the manipulation aims to show the saturation of the characterization along the variation of the source-drain potential. This would demonstrate the presence of a transistor and not only a single diode. The second objective is to show that the close-to-ground-potential work-point is viable. And that the previous negative result was due to the surfactant. Finally, the characterization should demonstrate the transistor properties without external artifacts, i.e. leakage current.

Figure 3.72 shows the source current, green, the drain current, blue and the substrate potential, yellow, for a CMC/CNT deposition. The drain-source potential is point four volts. This specific site shows very little field effect -common variation of drain and source current when the gate potential is positive. On the other hand, it shows a leakage current when the gate potential reaches one volt. The low threshold potential is due to the repeated characterization cycles realized to illustrate the evolution of the insulating layer. The first note on that measurement, is that the threshold effect of the back-gate leakage is for a positive potential. The second remark is that this potential reduces with an increasing amount of stimulation cycles. This confirms the gating effect of the surfactant on the back-gate and the use of reduced back-gate stimulation in order to preserve the electric rigidity of the insulator.

Figure 3.73 shows the difference in results between leakage and field effect. When the gate leaks in the channel, the drain and source current are not equal due to the transferred charges. On the other hand, when the transistor opens or closes without leaks, the two current are equal -noise excepted. Another observation can be made comparing Figure 3.72 and Figure 3.73. The current does not always spread in the source and drain symmetrically. Moreover, the symmetry can vary with the sample. This implies that the deposition is not perfectly symmetrical in its electrical properties. Figure 3.74 illustrate a result without leakage.

Figure 3.75 shows the variation of current depending on the back-gate potential. The sample has been rinsed with de-ionized water after deposition and left to dry for half an hour. After evaporation a thin layer of water was still present. The stimulation is realized through the back-gate. This sample shows a sensitivity to field effect that can be regularly found in the CMC based deposition results.

The first observation is that the characteristic has been displaced to the right, compared to SDBS based results. The second is that we can discern neither high negative potential saturation nor limit to the closing of the transistor with a positive potential. Finally, the sample presents a hysteresis also commonly found in SDBS based results. Figure 3.76 shows the decrease in hysteresis when the same sample is further dried with evaporation for an hour. We can also note in that illustration that the current, at same field effect, has slightly diminished. Figure 3.78 shows results on the same transistor network with a ten micro-liter drop of water caster on the sensitive surface. The stimulation is transmitted through the back-gate. In this illustration we can see the hysteresis common to this type of results. The second observation is the saturation effect observable at positive gate potential of more than one volt. Although it is a good result, it is not enough to show all the expected characteristics. The sensitivity in this configuration is comparable, although slightly lower, to that of the humid conditions -c.f. Figure 3.75. Finally, Figure 3.79 shows the same site with ten microliter of water on the sensitive surface. The stimulation is supplied through a probe dipped in that water drop creating a first approach chemical gate. We can see in this illustration that both saturation regions are attained. We can also observe an increased sensitivity as expected from theory.

Table 3.1 summarizes the sensitivities for the configurations presented in variation. Here the sensitivity from the chemical gate is of 6.6% over the same variation. Figure 3.80 illustrate characteristics from the same pattern on different substrates with CMC/CNT deposited with the same parameters. The most important observation here is that the conduction first opens in a non-linear shape and saturates when attaining a threshold. This measurement confirms the presence of a network of CNT-FETs between source and drain. These measurements are difficult to observe due to the destruction of the transistors upon stimulation with a source-drain potential of over approximately two volts.

general conclusions on CNTFET characterization

In the previous sections, I discussed remarks that required few confirmations to be conclusive. For example, the nature of the structure can be shown with the previous illustrations. The tendencies in the results are now discussed. These would need more experiments to be confirmed and quantified to be more than just tendencies. First, the open transistor current appears to be mostly mitigated by the pattern when realized with the same parameters leading to a similar CMC/CNT structure. Indeed, a pattern with only one site -c.f. Figure 3 The second remarks concerns the closed transistor current. Figure 3.80 shows the characteristics of two lines lithographed from the same pattern. We can see that although the on current is similar, the off current is significantly different. This effect is explained by the presence of residues such as CNT ashes and non-coating surfactant molecules. This increase in off current with increase of residues has been confirmed with a couple of samples but needs further investigation to be confirmed. The variation of results between surfactant natures implies a few observation. First, the final working point is further modified by the removal of the surfactant. The expectation is that the result will be characterised somewhere between the two observed characteristics. This is due to the reaction of the channel to SDBS as if it was an electropositive molecule. This deduction also comes from the fact that CMC is an electronegative molecule. The second remark concerning the surfactant is that its removal should increase the sensitivity to field effect from the back-gate, but also from a chemical gate.

Manufacturing results and short terms developments

This section summarizes the results of the manufacturing experiments regarding the objectives of the thesis. The second part addresses the short-term development of the research work.

Results summary

This section summarizes the results of the clean room experiments. The focus is placed on the results regarding the objectives defined in Chapter 1 and Chapter 2.

The dispersion main objective is to realize a dispersion containing single CNTs separated enough that they could be placed in single channel structures with dielectrophoresis. This objective is fulfilled as shown by the single CNT structures illustrated. On the other hand, the further optimization of the dispersion separation could reduce the ratio of small bundles to single CNTs in the placement results. The second limit of the dispersion is the cleaning of the surfactant. Indeed, SDBS and CMC have proven resistant to simple cleaning treatments such as dilution in water or acetone.

The main objective of the lithography is to realize a deposition of material with a high enough precision. This precision needs to allow adding of a second and third layer of material that would form an enclosed and insulated contact -c.f. Section 2.3. This precision is estimated at a hundred nanometers and was attained during trials. On the other hand, only experiments can prove the feasibility of the process. For example, alignment between the layers can become an issue. So can become the consistency of the results along the surface of the pattern. This subject is developed further in Objectives completion and future developments.

The dielectrophoresis aims to the alignment and placement of the dispersed CNTs. The objective of this placement is to create field effect sensitive transistors. The presence of placed CNTs was shown with the different structure arising from DEP. The main objective was fulfilled but the results can be improved by further optimizing the parameters. Automating the deposition duration cold also prove to create strong improvements in robustness of the results.

The characterization objective is to demonstrate the presence of CNTFETs and characterize them. The aim of these transistors was to show a field effect sensitivity, especially close to the ground potential. The objective is realized in itself.

Short-term developments

These developments concern the couple of months after the redaction of this manuscript. Two developments are planned for this period.

First, a manipulation showing a proof of concept without selectivity is anticipated. The objective is to characterize the sensitivity of the sensing structure toward phosphate ions. The manipulation consists in exposing the sensor to multiple concentrations of phosphate buffered saline. This solution contains phosphate ions but also others such a sodium, chlorine, potassium and magnesium. This experiment is limited as a proof of concept due to the lack of discrimination between the effects of each ions. On the other hand, it is a method of characterization that would illustrate the chemical sensitivity better than an external electrode. It would also allow the following of this chemical sensitivity following the next steps of production.

The second short term development is the cleaning of the sensitive surface. The removal and freeing of the sensitive surface -CNT sidewall -is critical to the sensitivity of the sensor. Although Pyrene moieties from Pbase should replace the surfactant molecules due to their better affinity toward CNTs -c.f. Chapter 4, a good preparation of the surface increases the functionalisation ratio and subsequently the sensitivity.

Chapter 4

Practical application of the technology 4.1 Choice of target

The biomarker choice is primordial to adjust the parameters of the proposed technology into a relevant design sensor. The conditions for the choice of a biomarker that would fully take advantage of the previously defined development goals are listed next. First, the biomarker should suppose a modification of the electrostatic environment. This would allow using a field effect amplification structure to transmit the biological signal. It would be an advantage if the chosen biomarker did not have an existing electrochemical sensor. This would allow the design of a new sensor instead of extending the capabilities of an existing one. Another condition is that the monitoring of the biomarker should prove an improvement in the observation of the biological signal. Similarly, the use of multiple sensors for parallel measurement of biomarkers from the same family would allow the full extent of the aimed technology developments. Finally, the chosen biomarker should have at least one existing biosensor, demonstrating chemical selectivity and the regression from received signal to biological information. This would allow the development to focus on the amplification structure and the objectives defined above.

The chosen biomarker family is enzyme group called kinases. These enzymes are defined by their scheme of action. Indeed, kinases enzymes use an adenosine triphosphate -ATP -molecule and deposit the third phosphate on a selected protein. Figure 4.1 illustrates this reaction. "ATP is an organic compound that provides energy to drive many processes in living cells, e.g. muscle contraction, nerve impulse propagation, and chemical synthesis. Found in all known forms of life, ATP is often referred to as the molecular unit of currency of intracellular energy transfer" [START_REF] Burnett | The enzymatic phosphorylation of proteins[END_REF], [START_REF] Hunter | Protein kinases and phosphatases: the yin and yang of protein phosphorylation and signaling[END_REF]. Kinase substrate specificity is defined by its physicochemical and structural features. Mg2+ ions are important for coordination of ATP binding and formation of a transition state in the phosphoryl transfer reaction.

From an electronics point of view, the electronegative characteristic of phosphate molecules make them a target of choice. The second interesting particularity of phosphate groups transferred from ATP is that they contain two electrons more than their neutral charge. This PO 2- 4 ion is particularly interesting for electrochemical recognition, because its presence should be observable through observation of the electrical field.

Overall phosphorylation levels of a given protein substrate are the consequence of the balance in activity of a kinase counteracted by that of a phosphatase. The variation of this signal is mediated by a variation of activity of a kinase enzyme and its counterpart, called phosphatase, dephosphorylating the same protein sequence. The proposed technology aims to a sensor passive toward its target and able to monitor a biological signal. This is particularly of interest for kinase activity measurements because it would allow the observation of the evolution of activity of a specific kinase and phosphatase through time.

The sensor also aims to its integration in a multisensor matrix. A multisensing platform combined with bio-signal monitoring would improve the robustness of the data.

In order to produce a proof of concept, the development is oriented to a specific protein kinase, a member of the cyclin-dependent kinase family -CDK. Kinase activity and selectivity is regulated upon binding with a protein of the cyclin family , [START_REF] Do Morgan | Principles of CDK regulation[END_REF], [START_REF] Morris | Kinetic Mechanism of Activation of the Cdk2/Cyclin A Complex: KEY ROLE OF THE C-LOBE OF THE Cdk*[END_REF]. This CDK/cyclin complex will perform phosphorylations on a specific sequence. CDKs were initially identified for their function in cell cycle progression and later found to be involved in a wide variety of biological functions, [START_REF] Lim | Cdks, cyclins and CKIs: roles beyond cell cycle regulation[END_REF], [START_REF] Peyressatre | Targeting Cyclin-Dependent Kinases in Human Cancers: From Small Molecules to Peptide Inhibitors[END_REF]. Protein phosphorylation signals are involved in diseases such as cancer and can cause the disease or its progression.

The chosen biomarker for the proof of concept is the CDK4/cyclinD complex. This choice is due to the existing photochemical sensor developed in Montpellier. Indeed, the CDKACT4 technology - [START_REF] Prével | Biosensors and Bioelectronics Fluorescent peptide biosensor for monitoring CDK4 / cyclin D kinase activity in melanoma cell extracts , mouse xenografts and skin biopsies[END_REF] -presented in Section 4.3.1, proved its selectivity and efficiency in reporting the activity of CDK4 kinase in vitro, in cell extracts and in human biopsies and tumour xenografts.

State of the art

The state of the art presented here consists in the presentation of several methods for kinase activity measurement. Then, I compare the state of the art with an example of architecture close to the aimed structure, but targeting a different molecule.

General methods of molecular observation can be used to observe kinase enzymes. These methods are most often based on radioactivity or mass spectrometry. I will focus this section on biosensors specific to the kinase biomarker, opposite to general observation methods that can be used for kinase activity observation.

The first technology presented is based on a photochemical sensing method based on fluorescence to visualize chemical properties. This type of sensors has fluorescent properties that are altered when the kinase phosphorylates the substrate moiety of the sensor (ie the bioreceptor). Two variations of this technology exist. First, the fluorescence resonance energy transfer -FRET. Uses the variation of wave length of the fluorescence to observe the phosphotransfer - [START_REF] Xin | Visualizing Dynamic Activities of Signaling Enzymes Using Genetically Encodable FRET-Based Biosensors: From Designs to Applications[END_REF]. substrates in ECL-PKA biosensor [START_REF] Li | Enhanced Photoelectrochemical Method for Sensitive Detection of Protein Kinase A Activity Using TiO2/g-C3N4, PAMAM Dendrimer, and Alkaline Phosphatase[END_REF]demonstrates the results of a photoelectrochemical method for protein kinase A detection. Figure 4.5 shows the measurement operations. First, the reaction of phosphorylation takes place in solution. Then the phosphorylated substrates are separated my magnetics means. Finally, the sensor in itself is used as a signal amplifier generating a photocurrent proportional to the amount of immobilized peptides. Here are first presented examples of two types of electrode shaped biosensors, referenced by the properties of their chemical layer.

First, sensors can use the reactions of residues naturally present during the reaction. This type of sensor does not use labels. [START_REF] Liu | Probing of protein kinase activity by electrochemistry[END_REF] shows a measurement of kinase activity by detection of residues known to react to an electrical stimulation. Figure 4.6 presents the mechanism of this sensor. The tyrosine residues that have been phosphorylated do not react with the electrode unlike their non-phosphorylated counterparts. This difference allows quantification of the targeted kinase enzyme. The second type of sensors based on electrochemical measurement labels the ATP molecule with a known red-ox active reagent -often ferrocene. For example, [START_REF] Kerman | Peptide biosensors for the electrochemical measurement of protein kinase activity[END_REF] presents a sensor based on the recognition of phosphorylated substrates on the electrode surface. The existing technology closest to the current objectives and aiming toward kinase activity measurement is presented by [START_REF] Freeman | Following a protein kinase activity using a field-effect transistor device[END_REF]. This biosensor, illustrated by Figure 4.8, uses a transistor structure with the source/drain conductivity variating with the electronic state of the gate. This architecture uses a selective chemical gate creating an electrical potential around the gate insulator -here AlO 3 . The channel architecture is based on a bulk silicon transistor structure.

Finally, [START_REF] Nguyen | Basic study on Peptide Aptamer-modified Single-Walled Carbon Nanotube Field-Effect Transistor ( SWCNT FET ) for biomolecule analysis[END_REF] presents a biosensor based on a field effect transistor structure. Moreover, this structure uses CNTs as channels for the transistor architecture -c.f. Figure 4.9 -and a chemical gate based on a capacitive coupling between Pyrene moieties and CNT sidewalls -c.f. Figure 4.10. The design difference between the objective of the thesis and this example is the peptide substrate. In [START_REF] Nguyen | Basic study on Peptide Aptamer-modified Single-Walled Carbon Nanotube Field-Effect Transistor ( SWCNT FET ) for biomolecule analysis[END_REF], the sensor uses a biotin containing substrate to selectively bond to streptavidin.

As a summary, the method of kinase activity measurement fitting the more closely to the objectives of the project is the use of a transistor structure without label. Indeed, methods of kinase activity measurement require treatment of the biological field containing the biomarker. Others require human manipulation or are not suited for monitoring of the biomarker. Finally, the hypothesis behind the design proposed in this thesis is that a CNT-FET architecture controlled through a chemical gate -c.f. [105] -would increase the sensitivity of a sensor similar to [START_REF] Freeman | Following a protein kinase activity using a field-effect transistor device[END_REF]. The proof of concept given by the selective gate characterisation is needed to confirm this hypothesis.

As a conclusion, there is a need for developing a new sensor for CDK4/cyclinD activity monitoring.

In addition, the biosensor should be able to measure a biological signal in complex biological fields. This would allow monitoring of the biomarker in natural conditions and reduce human intervention due to sample preparation.

the transduction process of biological signal, the design of the chemical gate, and the steps to turn the created transistor into a selective biosensor selectivity in biochemistry, transduction of electrochemical information and The chemical domain of the new sensor is discussed and compared with its inspiring chemical biosensor predecessor regarding detection and selectivity.

Chemical gate design

This section is divided into two parts. Along the first section the biochemical sensor that inspired my design is described. In the second part, the chemical part of the biosensor I conceived is addressed and my design choices are explained. The conclusion of the section describes the model I built.

Existing photochemical measurement

This sensor called -CDKACT4 -was developed by a biochemistry research team led by May C. Morris at the Institut des Biomolécules Max Mousseron (IBMM) -University of Montpellier . The different steps of the design can be found in [START_REF] Nhu | Fluorescent Protein Biosensor for Probing CDK / Cyclin Activity in vitro and in Living Cells[END_REF][START_REF] Prével | Biosensors and Bioelectronics Fluorescent peptide biosensor for monitoring CDK4 / cyclin D kinase activity in melanoma cell extracts , mouse xenografts and skin biopsies[END_REF]. This sensor has been proven functional in melanoma cell extracts, skin biopsies and melanoma xenografts [START_REF] Prével | Biosensors and Bioelectronics Fluorescent peptide biosensor for monitoring CDK4 / cyclin D kinase activity in melanoma cell extracts , mouse xenografts and skin biopsies[END_REF]. This proof of concept shows that the chemical biosensor can report on activation from a specific enzyme in complex cell lysates. This sensor can detect the rate of activation of CDK4/cycD and discriminate an over-expression in a cell lysate, which is associated with cancerous cells. The next sections describe the CDKACT4 technology based on its designer's publications.

Peptide domain for selective phosphorylation

The selective domain of the CDKACT4 sensor consists of a peptide sequence selected from the retinoblastoma protein -pRb. The specific sequence corresponds to a part of pRb recognized by the CDK4/cycD, around the site number 790. In a functional cell cycle, CDK4/cycD phosphorylates pRb on this specific sequence : GGYKFCSSPLRIPG . This effect is reproduced in the sensor.

Phosphoamino acid binding domain -complementary to the substrate

The second domain of the CDKACT4 sensor is engineered from a WW domain, which is a polypeptide known to bind/interact with the presence to a phosphorylated serine or threonine. In the CDK activity measurement technology, the WW domain can be called a phosphor amino acid binding domain -PAABD. Both domains are linked by a short proline/glycine-rich sequence with mechanical degrees of liberty. When the substrate sequence derived from pRb is phosphorylated, the sensor undergoes an intramolecular conformational change. The PAABD domain

Measurement method and trials

In the CDKACT4 technology, presented by [START_REF] Prével | Biosensors and Bioelectronics Fluorescent peptide biosensor for monitoring CDK4 / cyclin D kinase activity in melanoma cell extracts , mouse xenografts and skin biopsies[END_REF], the rate of phosphorylation is measured through the fluorescence of the dye conjugated to the pRb sequence. The fluorescence response is proportional to the rate of activation by CDK4/cycD. Measurements are performed using a microplate reader (POLARstar; BMG Labtech, Ortenberg, Germany). In order to demonstrate the sensitivity and selectivity of the sensor several measurement were performed including the observation of the efficiency of CDK4/cycD inhibitors. This biosensor is an activity biosensor, which reports on changes in catalytic activity of the enzyme rather than on changes in its concentration. Figure 4.12 presents the response of the sensor to cell extracts expressing active CDK4/cycD compared to the response to the same cell extracts with the addition of a CDK4/cycD inhibitor. The enzyme concentration did not change between trials but its activity did. Figure 4.13 presents a characterisation of the CDKACT technology. For a relevant estimation of the sensitivity of the sensor, the resulting data should be compared to this characteristic. Here the activity is modified through the concentration of inhibitor. This method can be reproduced on a different technology allowing direct comparison of sensitivity and its components such as data discrimination or signal versus noise ratio.

Design of the new electrochemical measurement

In this section, I will describe how I designed the selective chemical layer of the new biosensor from the CDKACT4. The objective of the design is to at least maintain sensitivity and selectivity from the previously exposed sensor while reducing at its lowest, manual manipulations and heavy equipment use. This would increase the robustness while reducing the production cost of the final product. In this part, the new sensor technology is addressed in its use of the findings from the CDKACT4 sensor, especially for selectivity. Then, we will see how the bio information of the selective phosphorylation rate is used as a basis for electrochemical measurement in my new design.

Selectivity

I choose to build the selectivity in the new biosensor from the unmodified pRb short sequence. Indeed, I aim to maintain the demonstrated selectivity of the sequence. The measurement from the new sensor will be through an electronic signal so the fluorescent dye and its place for linkage to the sequence become irrelevant. Since the fluorescence is not used in our new transduction method, the PAABD domain also becomes ineffective.

The main advantage of this structure in my new design is its simplicity. Indeed, recurrent issues in electrochemical biosensing are due to the size of the enzyme used as a chemical recognition element. This reduces functionality of the receptive molecule due to reduced mobility and reduces the rate of activation from the biomarker due to loss in accessibility from the enzyme [START_REF] Hoang | Immobilized Enzymes in Biosensor Applications[END_REF]. In the current design, only a short protein sequence, also called peptide aptamer, is used. The enzyme complex accomplishes the work of gathering the catalytic -ATP -and of identification of its target. Furthermore, phosphotransfer convalently bonds the phosphate group at a known location -c.f. Section 4.3.1. Finally, with a short prefunctionalisation link, the electronic target can be only nanometers away from the transductive surface.

Transduction

This section starts with general considerations toward electronic state and charge transfer. Then, solutions demonstrated in literature are addressed. Finally, I will describe the result of my design process.

The transduction method depends on the physical quantity that is being transferred. Observation of the electronic state should take place through a capacitive structure using the field effect. Measurement of charge transfer requires a conductive structure. In our case, we want to observe the electrostatic field produced by phosphate groups on the selective protein sequences instead. This is for two reasons:

First, charge transfer allows observation of events but not of the overall density state. In this case of Faraday current observation, the final electronic signal represents a flow of events. For an observation of the field effect, the final signal will represent the electrochemical state. Furthermore, a variation of this signal represents the variations of the state i.e. the events, although they are most often harder to detect.

The second advantage of field effect transduction is that the enzymatic activity that we want to observe is composed of activation and deactivation of the probing protein sequence through adding and subtracting phosphate groups. If a charge transfer occurs between the aptamer and the transduction structure, the equilibrium between activation and deactivation will be biased. This consideration is the first of several aiming at the passivity of the biosensor toward the biological field containing its targeted biomarker.

The field effect and charge transfer are concurrent. Indeed, the electrostatic field responsible for the field effect is due to the difference of density of charges either side of an insulating mater. On the other hand, charge transfer supposes that the difference of charges balances itself through transfer. Figure 4.14 illustrates the two types of charge observation. In order to link our recognition element -the aptamer sequence -to the transduction element we need a molecule that will favor field effect over charge transfer. This molecule needs to strongly bond to the sequence, while retaining some measure of mobility. On the other side, the molecule needs to create a capacitive connection to the field effect amplifying structure. The 'tail' of the prefunctionalisation molecule, connected to the protein sequence needs to be able to create an amid bond to the protein. This allows a strong bond and transfer of electronic properties. A too long tail would reduce the field effect and a too short tail would reduce the mobility of the aptamer sequence and its accessibility for the target.

The 'head' of the molecule needs to be connected to the amplifying structure through bonds creating a capacitive effect. Several methods exist to realize that type of transfer. The most common would be to covalently bond the prefunctionalisation molecule -or link molecule -to a conductive layer, most often metal/gold. That layer plays the role of gate electrode and is placed on an insulating layer -the gate insulator [START_REF] Oh | Biosensors and Bioelectronics A carbon nanotube metal semiconductor fi eld effect transistor-based biosensor for detection of amyloidbeta in human serum[END_REF]. Two issues arise from such a configuration. First, the charge transfer from the link molecule to the metal electrode has no guarantee to be reversible. Reversibility of the reaction is necessary for monitoring measurement. Second, the high density of charges in a metal is so strong that it reduces the effect of the low amount of charges transferred from chemical reactions. In order to address these problems, nanostructures are used. For example gold nanoparticle specifically address this issues while maintaining the already known advantages of the gold assembly [START_REF] Li | Gold nanoparticlebased biosensors[END_REF]. Nanowires are also a solution that have been explored [START_REF] Namdari | Recent Advances in Silicon Nanowire Biosensors : Synthesis Methods , Properties , and Applications[END_REF]. In the present case we chose to work with CNTs. The advantage of CNTs for the matter at hand is that they can bond through their sidewall to other carbon molecules [START_REF] Sireesha | Functionalized carbon nanotubes in bio-world : Applications , limitations and future directions[END_REF]. The wrapping of the selective protein around the CNTs in an option but with obvious issues of mobility of the probe [START_REF] Saifuddin | Carbon nanotubes: A review on structure and their interaction with proteins[END_REF]. Bonding the protein to a molecule formed of an alkyl chain could have been an option but the coupling between CH 2 chains and CNTs is relatively poor [START_REF] Zhou | Supported lipid bilayer/carbon nanotube hybrids[END_REF]. Indeed, CNTs bond particularly well to other hexagonal structures of carbon. Moreover, they create capacitive bonds to these structures through their common π-electrons and Van Der Waals interactions [START_REF] Poumirol | Etude des propriétés électroniques du graphène et des matériaux à base de graphène sous champs magnétiques intenses To cite this version[END_REF].

I chose to work with the molecule 1-Pyrenebutyric acid N-hydroxysuccinimide ester, also called Pbase -Figure 4.15. This molecule has been previously used as a prefunctionalisation in biosensing applications [START_REF] Nguyen | Basic study on Peptide Aptamer-modified Single-Walled Carbon Nanotube Field-Effect Transistor ( SWCNT FET ) for biomolecule analysis[END_REF], [START_REF] Yue | Electrostatic gating in carbon nanotube aptasensors[END_REF]. Furthermore, it expresses the particularities I need in my prefunctionalisation. Indeed, it can create an amid bond with a protein -Figure 4.16, the 'tail' made of CH 2 structures is mobile enough but not too long as discussed previously. Finally, it ends in a pyrene group, shown to create a capacitive link to CNT sidewalls [3].

Amplification

In a previous chapter, -Section 1.1 -focused on CNTs from the electronic point of view. In this section, I will outline general considerations on the amplification structure from a chemical/electrochemical point of view, focusing on the interactions between pyrene and CNT. I addressed previously, that one of the main issue with electrochemical biosensors was the charge density of the gate. There is two sides of this effect. I pointed out previously that a high density gate electrode would be poorly sensitive to the amount of charges being displaced by biochemical reactions. Similarly, a low-chargedensity gate electrode would create a small reaction in a high charge density channel. The proposed solution suppresses this issue by using pyrene on CNTs as a gate. Indeed, pyrene have an electronic charge equivalent to that of most small molecules, defined wave functions opposite to electronic bands. CNTs have 1D electronic structure giving them a charge density between small molecules and bulk structures, called mesostructures.

Another advantage of CNTs from an electrochemical point of view is that when binding to the sidewall of a CNT, a pyrene group shares the orbitals of its π-electrons with those of the CNT. By doing this, the high mobility of the CNT's π-electrons is also shared increasing the sensitivity of the π-electrons from the pyrene group to their electrostatic environment. In our case, the electron's state in the pyrene group will become more sensitive to the presence of the phosphate group on the aptamer sequence because of their bond to the high mobility electrons from the CNT. This effect has been shown to extend the sensitive space around the CNT to beyond Debye's length [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF].

On the other hand, that sensitivity is not selective and can become an issue by amplifying unwanted electronic modifications of the environment into noise. A solution that would require extensive study and experiments would be to protect the non-functionalised surface of the sidewalls of the CNTs with an inert molecule [START_REF] Amanda | BIOSENSORS BASED ON CARBON NANOTUBE FIELD EFFECT TRANSISTORS (CNTFETs) FOR DETECTING PATHOGENIC MICROORGANISMS[END_REF], [START_REF] Khosravi Farhad | Ultrasensitive Label-Free Sensing of IL-6 Based on PASE Functionalized Carbon Nanotube Micro-Arrays[END_REF].

Model of the electrochemical potential in the new sensor

I addressed in this section how I will use part of a protein as a recognition element. Furthermore, I described the selective structure of the biosensor in design. Then, I described how I intend to link this polypeptide to a CNT sidewall through an intermediary molecule. Finally, I described how this aptamer allows measurement of a variation of selectively deposited ions in the proximity of the CNT inducing transduction of the biological information. These explanations were limited to qualitative considerations purpose. Indeed, it is a complex issue to quantify the density of functionalisation of a CNT sidewall or the effect of a phosphate ion adsorbed on the polypeptide, among others. In order to have a rough idea of what to expect I created a simple analytic model of this section of the prototype. I will here describe this model and its limits.

This model is based on the Nernst potential around an impermeable membrane.

E = RT zF * ln C out C in (4.1)
With, R the Reynolds constant, T the temperature, z the quantity of charges involved in the reaction, C out and C in the concentrations outside and inside the membrane. In the current design, the CNT potential is equal to the potential of the sample under measurement at a natural ion concentration -see details in Section 1.2.1 -of 0.5 to 2mmol/L [START_REF] Bevington | Factors Controlling the Intracellular Concentration of Orthophosphate (Pi) in Mammalian Cells[END_REF] and corresponds to C in -we will take a value of 1mmol/L. In order to estimate the high concentration present around the CNT I built a schematics of an optimal functionalisation rate -all the surface of the CNT is covered with pyrene moieties.

With this method I estimated the maximum phosphate ion density to be of ∼ 100mmol/L. This corresponds to a Nernst potential of -0.1V -Figure 4.19. This first approach is limited mainly because it does not account for screening ions present in the proximity of the CNT schematised as the membrane.

Chemical gate process design

The last part of this chapter addresses the steps for modifying this CNTFET into a CNTFET-based biosensor. These steps were not performed during the thesis due to lack of time. The following part summarise the theoretical preparation based on literature.

Functionalization

The last step of the process consists in the adsorption of Pbase as an interface molecule c.f. Chapter 1, and of addition of the polypeptide adding selectivity to the sensor. Previously, I defined the parameters of the process with a range of exploration for experimental optimization. In this process step, I will define central values extracted from literature as starting points for optimization. Functionalisation steps commonly used in biosensing are described by [START_REF] Maehashi | Label-free protein biosensor based on aptamer-modified carbon nanotube field-effect transistors[END_REF], [START_REF] Nguyen | Basic study on Peptide Aptamer-modified Single-Walled Carbon Nanotube Field-Effect Transistor ( SWCNT FET ) for biomolecule analysis[END_REF], [START_REF] Yue | Electrostatic gating in carbon nanotube aptasensors[END_REF] and more recently by [START_REF] Seo | Rapid Detection of COVID-19 Causative Virus (SARS-CoV-2) in Human Nasopharyngeal Swab Specimens Using Field-Effect Transistor-Based Biosensor[END_REF] on graphene.

This functionalization is realized in three steps. First, Pbase is adsorbed on the CNT sidewalls. Then the selective protein is bonded to the Pbase molecule through amine bond. Finally, the substrate is rinsed in order to reduce residues.

It is worth noting that the succinimide ester in Pbase can react with water. This reaction turns Pbase into pyrene butanoic acid. This acid cannot create bonds with proteins reducing the final functionalization rate. For this reason, Pbase is dissolved in dimethylformamide (DMF). DMSO and methanol can also be used to create that dissolution.

According to [START_REF] Nguyen | Basic study on Peptide Aptamer-modified Single-Walled Carbon Nanotube Field-Effect Transistor ( SWCNT FET ) for biomolecule analysis[END_REF] an hour is enough for a high rate functionalization of CNTs by Pbase. A concentration of 5mM was used in [START_REF] Nguyen | Basic study on Peptide Aptamer-modified Single-Walled Carbon Nanotube Field-Effect Transistor ( SWCNT FET ) for biomolecule analysis[END_REF] for a CNT concentration similar to the concentration expected in my realization. This concentration and the exposure duration will need to be optimized regarding the final sensor CNT density. After Pbase adsorption, the sample is then rinsed with N 2 gas. Then 0.5mM of peptide is dropped and kept for eighteen hours at room temperature on the sensitive area. Finally, the sample is rinsed with deionized water and N 2 gas. Similarly the parameters need to be investigated regarding the specific case.

The last step consists in the protection of the sensitive surface toward non specific reactions. [START_REF] Maehashi | Label-free protein biosensor based on aptamer-modified carbon nanotube field-effect transistors[END_REF], [START_REF] Nguyen | Basic study on Peptide Aptamer-modified Single-Walled Carbon Nanotube Field-Effect Transistor ( SWCNT FET ) for biomolecule analysis[END_REF] and [START_REF] Thermofisher | Amine-Reactive Probes | 2 Labeling Proteins[END_REF] advise the use of PBS then ethanolamine to deactivate and block excess reactive molecules. Using another method, compatible with previous rinsing, [START_REF] Robert | Noncovalent functionalization of carbon nanotubes for highly specific electronic biosensors[END_REF] creates a passivation layer for the non-functionalised CNT surface using Tween20. This and other surfactants can be used thanks to the strong bond between pyrene and CNTs that will not be removed by less compatible structures. Non-ionic detergents for protein solubilisation are commonly used for CNT sidewall passivation. The main drawback of these molecules is that they can bond to proteins and in our case reduce the activity of the selective polypeptide.

The issue with this process is that Pbase solvents are organic solvents, also dissolving the resin used for passivation of the metal layer. A solution would be to use an alternative functionalisation process developed in [START_REF] Thermofisher | Amine-Reactive Probes | 2 Labeling Proteins[END_REF], followed by adsorption of the composite on the CNT sidewalls.

The first part of this process consists in bonding Pbase and the polypeptide. First, proteins are dissolved at ∼ 1mg for 1mL of buffer, a 0.1 to 0.2M solution of sodium bicarbonate. The use of a basic solution -pH8.3 -maintains the structure of the Pbase molecule during the reaction. Next, Pbase is dissolved at 5mg in 0.5mL of DMF. Then, while stirring the protein solution, part of the Pbase solution is slowly added -50 -100µL. This volume corresponds to 0.5 -1mg of Pbase. The reaction is stirred for one hour at room temperature. The resulting solution contains one-fourth to one-third of activated Pbase. The final solution can be balanced in PBS, BSA or another buffer of choice. The final step is to adsorb the composite on the CNT sidewalls. Since the Pbase molecules have already created amine bonds to the polypeptides, they can be dissolved without the use of organic solvents. Another advantage of such a process is that it can be parallelised with other tasks until the last deposition reducing the overall process duration.

Finally, [START_REF] Cao | Electrochemical and theoretical study of π-π Stacking interactions between graphitic surfaces and pyrene derivatives[END_REF] demonstrates the electrochemically assisted adsorption of graphene composites on graphitic surfaces. The proof of concept can be realised after the full process is complete. The sensitivity and selectivity of the full sensor can be proved. First, tests are realised in a controlled solution containing ATP, magnesium, and active CDK4cDc. Thereafter, the sensor can be tested in a complex bio-field such as cell lysates of known characteristics regarding the cell cycle i.e. cancerous and non-cancerous cells. This test would allow to prove that the sensor can discriminate a controlled CDK4cDc activity from an over-expression.

Objectives completion and future developments

The first objective of the thesis is to design an architecture that could be modulated depending on the specific target. The literature and theory on which is based the design suggest that this type of architecture is scalable. The experiments showed tendencies toward this affirmation. However further investigations are required to demonstrate and quantify how the structure fits the objective. This investigation should start by repeating the previous CNTFET manufacturing process and quantify more precisely the filling of the sites. This would allow to dimension an optimal pixel size regarding the quantity, shape and distribution of the transistors. This dimensioning needs to be coherent with the sensitivity to the target, with the generation of a front-end compatible current and with the integration in a sensing matrix for mapping or multisensing.

The second axis of development focuses on the chemical recognition. The parts of this axis are the passivity of the sensor toward the biological field and the measurement of the signal in a complex field. The final objective of this axis is to demonstrate monitoring of the targeted signal. The short-term objectives focus mainly on the demonstration of the sensitivity. With this first proof of concept the first manipulations on functionalisation and selective sensitivity could begin and lead to confirm the monitoring capabilities of the technology. The demonstration and quantification of the selective sensitivity is essential for the completion of the prototype.

The third axis of development focused on the preparation of the process to industrialisation. The objective is to create sensors with a low variability and a low unitary cost. The demonstrated variability in the created CNTFET networks can be further reduced as discussed previously. The investigation of the limits in the precision will aim to demonstrate a pixel containing the three layers of deposition -two metal, one insulation -and demonstrating the quality of the contact CNT/metal along its surface -c.f. Section 2.4.

The last development axis is to create a technology that could be easily modified in order to change the target. The addition of the functionalisation at the last steps of the process insures, in theory, the completion of this objective. The demonstration will need two steps. First the demonstration of the previously described prototype c.f. Chapter 4. Then, its further functionalisation with different selective substrates. orbital. CNTs and graphene planes are considered as mesoscopic systems -between classic and quantum physics -for which it is usual to use a tight binding approach -or molecular orbitals approach. We saw previously that the graphene carbon atoms where linked by two types of bonds, strong σ-bonds for which the electrons are tightly restricted -10eV gapand the π-bonds for which the electrons are nearly free. These can travel, without more energy than provided by ambient temperature, from the valence band to the conduction band and take part in the overall current. They are the particles we will study in this document.

List of Figures

The results of this study have been confirmed by angle-resolved photoelectron spectroscopy -ARPS -and observing the motion of the electrons in graphene. First the carbon atom motif is redefined in order to have a carbon atom in the centre of three third of carbon atom linked to the first -Figure A.9. From there we can express the wave function of the orbitals created by the π-bond in that structure. We apply the Hamiltonian operator to the previous equation to find the energy dispersion. Multiple manipulations are necessary to shape the equation and render it usable for space representation of the dispersion. FIGURE A.9: Carbon atoms distribution with one full carbon atom in the centre and three third of the surrounding atom [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF] We can see in -Figure A.10 that the conduction and valence bands meet at the carbon atoms location, also called k-points, making graphene a zero-bandgap conductor. It can conduct electricity thanks to the thermal energy being enough to send a valence electron in the conduction band independently of the Fermi level. It is important to note the Γ point, which is the centre of the hexagon, the k point, which is the carbon atom location, and the M point equidistant from two carbon atoms. This demonstration shows how electrons can move around in the graphene plane. This property of the graphene 2D crystal also explains the low scattering rate and ballistic transport properties of carbon structures made of hexagons.

We will now see the properties of electrons inside this structure, especially close to carbon atoms.

A.1.4 Electrons close to the K-point

In order to improve our comprehension of the electrical properties of graphene and CNTs we need to take a closer look to the k-point in graphene where the two bands making graphene a zero band-gap semiconductor [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF] meet. We consider the overlap probability to be very small in that point -this hypothesis is realistic because the k-point is far from other carbon atoms. This hypothesis is equivalent to the first lattice hypothesis. The speed of electrons if defined by the variation of dispersion which applied to our system gives a speed corresponding to a value of 106m.s -1 confirmed by the speed experienced in observations -ARSP. The dispersion equation becomes linear around K-point. The variation of the dispersion being constant we can deduce constant speed corresponding to the comportment of a mass-less particle.

To explain the mobility and conductivity in graphene we need to consider the quantity of free states depending on the size of the matrix and the maximum electron speed. These two characteristics also explain the strong conductivity. It is important to note that this consideration supposes to hypothesise on the ballistic characteristic of the conduction in graphene and further CNTs.

A.2 CNT structure

A.2.1 Dispersion equation in carbon nanotubes

A CNT is a rolled up graphene sheet, giving it a unique systematically mesoscopic structure. The diameters of CNTs is limited by the stability of its structure. The length can be of a few micrometres to several millimeters but the diameter of a CNT is limited. Indeed, a CNT too wide would collapse on itself. These considerations allow to say that the wave vector will be continuous in the axial direction -considering a long enough CNT > 100nm -and quantified in the circumferential direction. The conducting/semiconducting characteristic of the tube depends on the states available around k-point by these 1D lines. If a line goes through the K-point, the valence and conduction band meet and the tube will be metallic -zero bandgap semiconductor -and if not, the tube is semiconducting. The first thing to note is that unlike in graphene CNTs have a high density of state near the Fermi level. If the tube is semiconducting, that makes it a very good candidate for optic applications according to Fermi's golden rule.

The first thing to do in order to study CNTs is to define a new Brillouin zone different from graphene. That zone has to be a representative unit of the structure as was the hexagon in graphene. That zone will be made of a circumferential vector -Figure A.11 -defined as C h and a transverse vector long of one hexagon -the symmetry is the same as graphene in that direction. This vector is then decomposed in the a 1 , a 2 base. The couple (n, m) defines structure of the nanotube and is called its chirality with C h = n a 1 + m a 2 . If C h is short enough the states along this axis are quantisised. We study here tubes with a diameter of under 3nm corresponding to a perimeter of under 10nm. We can say that in our case the allowed states in the circumferential direction will always be quantisised. In a similar way we will use nanotubes of micrometers long, creating continuous electronic states along the length axis.

This considerations allows to define CNT's electron's allowed states as 1D conduction bands. Depending on the distribution of these lines one or more can go through a k-point creating a metallic CNT due to the contact between valence and conduction bands in that point of space.

The reciprocal lattice is defined by the two vectors in k-space K 1 -circumferential -and K 2 -transverse. The states are continuous in K 2 and quantified in K 1 direction according to the previous considerations. We can express the wave vector and the continuity condition in the circumferential direction. C h and K 1 are parallel, so we can write the representation of the wave vectors as lines in the K 2 direction -Figure A.12. In order to create a semiconducting graphene channel one needs to deposit or synthesize a layer of graphene on a substrate, then cut it in order to reproduce the natural boundary conditions of CNTs. This creates a similar 1D conducting lines CNTs -shaded [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF] structure. The condition for the semiconducting properties to arise in graphene nanoribbon -GNR -is similar to the condition for a semiconducting CNT : are the 1D conduction lines going through the k-point. The cutting step needs to be extremely precise ∼ nm to obtain a decent yield in semiconducting GNR. This process is extremely complex and costly. On the other hand, CNTs can be bought with a high semi-conducting ratio -∼ 98%. For this, I choose to work with CNTs.

It is worth to note for the design the effects of the curve of the graphene plane into a CNT. First, the lattice will change, especially in the circumferential direction, limiting the use of results built from the graphene lattice. The two sides of the graphene plane are becoming unbalanced modifying the presence rate and energy of π-bonds. These quantities are fundamental to the dispersion equation introducing an error depending on the curvature of the tube. As previously the effect is more important following the circumferential axis. Finally, regarding the semiconducting nature of CNTs, in very small CNTs, the angle of the lattice creates a very small gap. On the contrary, a very big tube will not have a gap even if it respects the condition exposed previously.

A.2.3 CNT gaps and optic considerations

The density of states near the Fermi level in semiconducting CNTs is very important, especially in the lower parts near the gaps. This phenomenon is called Van Hove singularity and explains the specific characteristics of CNTs regarding photoluminescence. For example, in the (10 -0) CNT, the lower gap corresponds to the energy of a 1100nm wavelength photons -near infrared. From the dispersion equation, we can draw the density of states as a function of energy -Figure A.16 -and we can observe the peaks corresponding to the Van Hove singularities, which are symmetric in the direct gap. Thanks to these properties, CNTs can be characterised using optic techniques, in diameter, in chirality (n, m) and defects rate -Figure A.17 -. This allows highly discriminatory selection of CNTs after synthesis in order to create high purity products.

It is worth to note, that we neglect the interactions between electrons in graphene without making significant approximation. However, that deviation becomes significant with the curvature of CNTs. The main effect is the fact that strongly correlated excitons -correlated electron-hole pairs -have a better chance to go through a gap. The exciton effect is significant for gaps of under 0.4eV, and it is responsible for part of the sensitivity of CNTs to their environment. Excitons explain especially the sensitivity to the permittivity of the environment [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF]. This is because the fem depending on the excitons affects particles far out of the CNT's Debye Length [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF]. Excitons also explain the difference between the theoretical energy of the gaps and the experienced photo luminescent energy. It also makes in evidence the importance of the surroundings of the CNT during characterisation.

A.2.4 Phonons in CNTs

A phonon is a quasi-particle representing the vibration of a crystal. We will describe the phonons in the graphene plane and interest ourselves in the Raman actives phonons especially in CNTs. That way we can have a better understanding of the most used tool for CNT characterisation. There are two types of phonons, the acoustics phonons when all the lattice atoms are moving in phase in the same direction. That type of phonon implies that there is no deformation of the lattice and doing so that there is no magnetic momentum between the atoms. The second type is the optic phonons, which is out of phase between atoms and creates magnetic momentum in the crystal lattice. The first type is low energy and directly linked to heat. For example the fact that there is many quantum states in the z-axis of the graphene FIGURE A.20: experimentally observed RBM frequency ω RBM of isolated SWCNTs protruding vertically from a silicon substrate plotted as a function of tube diameter d t . [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF]

-

  Compréhension de la problématique et construction des objectifs y répondants.

Figure 10 .

 10 Figure 10.1 présente le résultat de la conception dans une coupe verticale. Les losanges bleus représentent les éléments cibles . La partie orange représente la grille sélective. Les accès métalliques en or sont représentés en jaune. Le polymère protecteur est illustré en bleu. Les couches en gris et vert représentent respectivement l'isolant de grille et le substrat utilisé comme grille arrière.

FIGURE 10 . 1 :

 101 FIGURE 10.1: Illustration de la conception en coupe verticale

FIGURE 10 . 2 :

 102 FIGURE 10.2: Illustration de la conception en vue de dessus

Figure 10 .

 10 Figure 10.6 montre le pattern utilisé pendant les essais pour démontrer la faisabilité et les limites du placement par diélectrophorèse, ici sur le masque.

FIGURE 10 . 3 :

 103 FIGURE 10.3: Résultats de dispersion, en bleu, après 15min de centrifugation, en orange après 30min de centrifugation

FIGURE 10 . 5 :

 105 FIGURE 10.5: Résultats de dispersion, en bleu, après 15min de centrifugation, en orange après 30min de centrifugation

FIGURE 10 . 7 :

 107 FIGURE 10.7: Dépot de résine sur un échantillon

Figure 10 .

 10 Figure 10.8 montre un résultat de lithographie, après développement de la résine.On peut voir le substrat (en bleu) aux endroits où la résine a été gravée.

FIGURE 10 . 8 :

 108 FIGURE 10.8: résine dévelopée après 3.5sec d'exposition

Figure 10 .

 10 Figure 10.9 illustre le résultat après déposition de métal et élimination du surplus de résine et métal par lift-off.

Figure 10 .

 10 Figure 10.10 montre un résultat après déposition de nanotubes.Figure10.11 illustre un zoom fait sur un site ne contenant qu'un seul nanotube avec un dispositif de microscopie à force atomique -AFM. On constate que le tube relie les deux électrodes.

Figure 10 .

 10 Figure 10.12 montre une caractérisation illustrant la sensibilité du transistor à l'effet de champ.

FIGURE 10 . 9 :

 109 FIGURE 10.9: Résultat après lift-off pour un dévelopement de 25sec

10. 5 10 . 5 . 1

 51051 Conception d'une grille chimique pour mesure d'activité kinase Choix de la cibleLe choix de la cible résulte d'une expertise reconnue dans l'observation des enzymes kinases venant de l'équipe de May C.Morris à l'IBMM, d'un choix de leur part d'explorer une diversification des méthodes de mesures et d'un interet de la part des chercheurs du LIRMM, Aïda Todri Sanial et Serge Bernard, de s'inverstir dans la recherche d'une solution.

FIGURE 10 . 13 :

 1013 FIGURE 10.13: Charactérisation de deux CNTFET, Id = f (V ds ), créés à partir du même modèle

FIGURE 10 . 14 :

 1014 FIGURE 10.14: Schéma représentant la mesure d'une activité kinase par électrochimie

FIGURE 10 . 16 :

 1016 FIGURE 10.16: Illustration de la conception en coupe verticale

FIGURE 1 . 1 :

 11 FIGURE 1.1: (a) A first Brillouin zone of graphene with conic energy dispersions at six K points. The energy dispersion near one of the K points are schematically shown along with the cross-sections by allowed states and resulting 1D energy dispersions for (b) a metallic SWNT and (c) a semiconducting SWNT. [4]

FIGURE 1 . 2 : 1 . 1 . 2 . 1 . 2

 1211212 FIGURE 1.2: Diameter induced gap[4]

FIGURE 1 . 3 :FIGURE 1 . 4 :

 1314 FIGURE 1.3: A schematic of a typical setup for electrical transport measurements of SWNTs. Typically, I DS as a function of V DS or V GSis measured for transport experiments[4]

FIGURE 1 . 5 :

 15 FIGURE 1.5: Relative positions of the allowed states around K points and the resulting 1D subbands of a semiconducting SWNT (a) without and (b) with an external magnetic field. Note that the 1D subbands are not degenerate anymore under a magnetic field. [4]

FIGURE 1 . 6 :

 16 FIGURE 1.6: Saturation effect in CNTs depending on V ds and tube length.[4]

FIGURE 1 . 8 :FIGURE 1 . 9 :

 1819 FIGURE 1.8: Variation of the channel polarity depending on the metal contact material. (a) Al-contacted (S/D) nanotubes exhibit n-FET characteristics while (d) Pd contacts result in p-FETs. Nanotubes are chemically intrinsic. [4]

FIGURE 1 .

 1 FIGURE 1.10: (a) Metal-CNT contact resistance versus metal work function. (b) Contact resistance versus work function behaviors for metals with work functions between 4.2 and 5.7eV. CNT work func-tion range is shaded.[START_REF] Wilhite | Metal-nanocarbon contacts[END_REF]

Figure 1 .

 1 11(b). I also outlined the fact that the capacitance of the gate can modify the comportment of the transistor Figure1.11(c). Finally, the shared orbitals between a CNT and its surroundings modifies the orbitals of the CNT's electrons reducing their mobility Figure1.11(a).

FIGURE 1 . 11 :

 111 FIGURE 1.11: Effect observed in a CNT transistor channel without charge transfer, (a) Gating effect due to electrostatic field applied on the CNT, (b) Schottky barrier variation due to the modification of the metal's work function, (c) Capacitance effect where the adsorption of molecules reduces the sensitivity of the channel to the gate effect, (d) mobility variation due to the mixing of the CNT orbitals with the adsorbed molecule's orbitals.[33]

FIGURE 1 . 12 :

 112 FIGURE 1.12: Electrical response of a semiconducting SWNT to gas molecules. (A) Conductance (under V g = 4V, in an initial insulating state) versus time in a 200ppm NO 2 flow. (B) Conductance (V g = 0, in an initial conducting state) versus time recorded with the same S-SWNT sample as in (A) in a flow of Ar containing 1%NH 3 .[46]

Figure 1 .

 1 16 and Figure 1.17 -the structure of the channel can be improved to be very close to the structure of a Si-MOSFET. The conduction of the channel is then modified by the height of the Valence/Conduction band itself controlled by the gate potential -Figure 1.18.

FIGURE 1 . 13 :FIGURE 1 . 14 :

 113114 FIGURE 1.13: Nanotube device structures. (a) SB-MOSFET with metal contacts and (b) MOS-like CNTFET structure with heavily doped S/Dcontacts.[4]

FIGURE 1 . 16 :

 116 FIGURE 1.16: Two-dimension sketch of SDC-CNFET structure[START_REF] Hai-Liang | Performance optimization of conventional MOS-like carbon nanotube FETs with realistic contacts based on stair-case doping strategy[END_REF]

FIGURE 1 .

 1 FIGURE 1.19: effect of the variation of oxide thickness on the band structure[START_REF] Kordrostami | Fundamental Physical Aspects of Carbon Nanotube Transistors[END_REF]

FIGURE 1 . 20 :FIGURE 1 . 21 :

 120121 FIGURE 1.20: Structural and electrical schematics of the VS-Stanford model [54]

FIGURE 1 .

 1 FIGURE 1.22: DFT-optimized positions for a graphene surface on (a) Ti and (b) Pd. (c) Interaction energy versus electrode separation between a graphene sheet and various metals. [113]

FIGURE 1 .

 1 FIGURE 1.23: "(a) An energy-band model for Au -CNT contact with a tunneling gap of spacing z and voltage V between them, qφ is work function, ζ is Fermi energy measured from the bottom of the Au valence band, and E F is Fermi level position. ∆ζ = ζ FAuζ FCNF is the difference between Au and CNT Fermi energies. The energy-band diagram is shown for (b) V = 0, (c) V = 0, and (d) V > 0. (e) Measured I-V before and after multiple current stressing cycles, with current-stressing conditions shown. Solid circles are modeling results at 300 • K, fitted to measured I-V data, resulting in z = 7.3, 5.9, and 5.0 Å. The inset shows improvement in I-V linearity upon current stressing, with solid line indicating initial behavior." [113]

FIGURE 1 .

 1 FIGURE 1.24: "Resistance of two-terminal CNT test devices versus stress current (a) without W and (b) with IBID-W deposited onCNT/Au electrode contacts."[START_REF] Wilhite | Metal-nanocarbon contacts[END_REF]

FIGURE 1 . 25 :

 125 FIGURE 1.25: Images of nanotubes coated with a thin film (< 5nm)of various metals.[4]

FIGURE 1 . 26 :

 126 FIGURE 1.26: Schematic representation of two different metal-CNT contact configurations, (a) end contact and (b) side contact. SEM micrographs of CNT bundles suspended between two electrodes with (c) end contacts, and (d) a hybrid wrap-around configuration (side and end contacts). [113]

Figure 1 . 29 ,

 129 Figure 1.30.

FIGURE 1 . 28 :FIGURE 1 . 29 :

 128129 FIGURE 1.28: Geometrical and electrostatic conditions in graphenebased placement of nanomaterials. a Cross-section of a standard metal electrode used for electric-field-assisted assembly of nanomaterials and a graphene layer, having a thickness of 1.5nm, which is used for the same purpose.[START_REF] Engel | Graphene-enabled and directed nanomaterial placement from solution for large-scale device integration[END_REF]

FIGURE 1 .

 1 FIGURE 1.31: "a) A schematic diagram showing the use of depletion forces to form thin rafts within PMMA channels. b) UV-vis spectrum (lower curve) of the CNT solution used to form the rafts. For comparison, the normalized UV-vis spectrum of an unsorted solution is shown in the top curve. c,d) AFM images showing CNT structures formed by the depletion forces as shaped by PMMA channels with pitches of 100nm (c) and 200nm (d).Outlined insets show highresolution images of a channel (two channels in 100nm case)."[START_REF] Wu | Top-Down Patterning and Self-Assembly for Regular Arrays of Semiconducting Single-Walled Carbon Nanotubes[END_REF]

FIGURE 1 . 32 :

 132 FIGURE 1.32: Working mechanisms of EDL FET sensor technologys. (a) Schematic representation of the experiment to determine the dependence of voltage drop and hence drain current on a large range of distances between gate opening and active channel. Gate electrode is vertically positioned on top of the active channel separated by the PDMS spacer of varying heights. (b) Calculated current gain vs. active channel to gate opening area distance graph. (c) The sensor is designed to operate in the denoted linear region and the applied gate voltage creates a potential gradient across the solution. (d) Depiction of saturation region where the potential gradient is only near the electrode surface. (e) Detection of CRP in linear region and saturation region of gap distances. (f) Conventional FET sensor technology schematic model. Charge of the target protein modulates the conductivity of FET. (g) Sensing mechanism in our sensor Distribution of charge density prior to the introduction of target proteins. (h) Protein binding induced gate voltage drop causes local charge density redistribution in the gate electrode area leading to subsequent changes in the charge density on the active channel. [19]

FIGURE 1 . 33 :FIGURE 1 . 34 :

 133134 FIGURE 1.33: Illustration of the designed sensor technology, vertical cut

Figure 2 . 1 .

 21 Then Cover them individually with surfactant in order to keep them part in a stable homogeneous dispersion.

FIGURE 2 . 1 :

 21 FIGURE 2.1: purified SWCNT before dispersion (left), after dispersion (right) [91]

  ,6) CNTs -Figure 2.2. CNTs the good ratio after selective enrichment is confirmed through light absorption experiment -Figure 2.3.

FIGURE 2 . 2 :FIGURE 2 . 3 :

 2223 FIGURE 2.2: Chirality produced by the process CNT(7,6) product information

Figure 2

 2

FIGURE 2 . 4 :

 24 FIGURE 2.4: Simulation of the separation of two CNTs in four steps from top-left to bottom-right. It shows a systematic empty space between CNT and water [107]

FIGURE 2 . 5 :

 25 FIGURE 2.5: Two types of known structures adsorbing on CNTs : Hexagonal carbon cycles along the CNT axis and alkyl chains wrapping around the CNT. [16]

FIGURE 2 . 6 :FIGURE 2 . 7 :

 2627 FIGURE 2.6: Amphiphilic molecule with hydrophobic domain highlighted in green(left), micelle created by the polymer in water (right)[START_REF] Gupta | Polyether based amphiphiles for delivery of active components[END_REF]

FIGURE 2 . 8 :FIGURE 2 . 9 :

 2829 FIGURE 2.8: Molecular dynamics self-consistent simulation of two CNT in water (top) and two CNT with two dispersant molecules in water (bottom), the distance between CNT increases with the close presence of the surfactant. [92]

FIGURE 2 . 10 :

 210 FIGURE 2.10: Sonication system with sonic probe Manufacturer website

FIGURE 2 .

 2 FIGURE 2.11: Ultrasonic bath Manufacturer website

FIGURE 2 . 12 :

 212 FIGURE 2.12: The schematic illustration showing the formation,growth, and collapse of a bubble induced by ultrasonication[START_REF] Ashiri | Obtaining a novel crystalline/amorphous core/shell structure in barium titanate nanocrystals by an innovative one-step approach[END_REF]

FIGURE 2 . 13 :

 213 FIGURE 2.13: Sonication of a CNT/surfactant colloid[START_REF] Oxana | Dispersion of carbon nanotubes in water and non-aqueous solvents[END_REF]

  Figure 2.14.

FIGURE 2 .

 2 FIGURE 2.14: resulting colloid after centrifugation : (a) without dispersion, (b) to (f) with better to better dispersion. Hansen-solubility, CNT dispersion manufacturer

  Figure 2.15. They can also be polymers used in organic or aqueous solvents such as Carboxymethylcellulose -CMC.

FIGURE 2 .

 2 FIGURE 2.15: SDS, SDBS, sodium cholate molecular structures[21]

FIGURE 2 .

 2 FIGURE 2.16: Example of dispersant structure: DMF [21]

FIGURE 2 . 18 :

 218 FIGURE 2.18: Structure of glucose wiki

FIGURE 2 . 19 :

 219 FIGURE 2.19: Structure of CMC wiki

  Most of surfactants in organic solvent are synthetic chain polymer -Figure2.20. These molecules are designed toward a specific solvent and to be compatible with CNT sidewall bonding. CNT compatibility is realised through carbon cycles -hexagonal carbon lattice -or alkyl chains -CH 2 chains also called lipid chain. Most are designed to contain two or three domains, with at least one hydrophilic and one hydrophobic composing an amphiphilic structure. A polymer -PFO-BPy -has been demonstrated to selectively wrap highly semiconducting SWCNT species and disperse them in toluene. The obtained dispersions were used to align and deposit semiconducting SWCNTs with exceptional electronic type purity.

FIGURE 2 .

 2 FIGURE 2.20: Example of a chain polymer able to disperse CNTs in toluene [21]

FIGURE 2 . 21 :

 221 FIGURE 2.21: Dispersion flow, steps are noted in the colored boxes, parameters and their range of exploration are noted in the colorless boxes

Figure 2 .

 2 [START_REF] Grieshaber | Electrochemical Biosensors -Sensor Principles and Architectures[END_REF] illustrate the alignment phenomenon called electro-orientation and responsible for the alignment of CNTs with the electrical field.

  Figure 2.23 illustrate the positive dielectrophoretic force on a CNT in a field stimulated by two electrodes.

FIGURE 2 .

 2 FIGURE 2.22: Electro-orientation of a non-sphere particle in a rotating electrical field[START_REF] Kharboutly | Modélisaton, réalisation et commande d'un système de micro-manipulation sans contact par diélectrophorèse[END_REF]

FIGURE 2 .

 2 FIGURE 2.23: DEP force on CNT in a non-uniform electrical field.Side view of substrate, electrodes, particles and non-uniform electric field.[START_REF] Chen | Quantitatively Control of Carbon nanotubes Using Real Time Electrical Detection Dielectrophoresis Assembly[END_REF]

FIGURE 2 .

 2 FIGURE 2.24: "Simulation of the potential distribution near the electrodes, for two orthogonal cross sections.(a & b) Φ at the substrate surface (xy plane at z = 0); (c & d) Φ perpendicular to the substrate (xz plane at y = 0). The potential drops uniformly between the electrodes in the absence of any deposited nanotubes (a & c) while the potential drop is concentrated around the metal-nanotube contacts, once a nanotube (magenta line) has been deposited (b & d)."[START_REF] Vijayaraghavan | Ultra-large-scale directed assembly of singlewalled carbon nanotube devices[END_REF]

FIGURE 2 .

 2 FIGURE 2.25: "Simulation of dielectrophoretic force fields near the electrodes. (a & b) ∇E 2 at the surface of the substrate (xy plane at z = 0); (c & d) ∇E 2 perpendicular to the substrate (xz plane at y = 0). The arrows indicate the direction of the force acting on a dispersed nanotube, while the background color is the magnitude of ∇E 2 . The dielectrophoretic force is attractive in all regions in the absence of deposited nanotubes (a & c), but it becomes repulsive between the electrodes, once a nanotube (magenta line) has been deposited (b & d)."[START_REF] Vijayaraghavan | Ultra-large-scale directed assembly of singlewalled carbon nanotube devices[END_REF]

FIGURE 2 . 26 :

 226 FIGURE 2.26: Electrode width effects on the field distribution with (top-left) 1µm (top-right) 2µm (bottom-left) 5µm (bottom-right) 10µm.[119]

FIGURE 2 .

 2 FIGURE 2.28: SEM image showing frequency dependence of s-SWNT assembly for a fixed solution concentration of 100ng/ml at (a) 50KHz (b) 300KHz, (c) 1MHz, (f) 2.5MHz and (g) 5MHz. Scale bars: 2µm. (d, e) Magnified image of (b) and (c). Scale bars: 1µm. The corresponding linear densities of the SWNTs in the array in Fig (a)-(d) are 3s -SW NT/µm, 12s -SW NT/µm, 25s -SW NT/µm, 7s -SW NT/µm and 6s -SW NT/µm. [95]

FIGURE 2 .FIGURE 2 . 33 :FIGURE 2 . 34 :

 2233234 FIGURE 2.30: SEM image showing a thin film of SWNTs deposited by DEP onto an array of interdigitated electrodes. [1]

Figure 2 .

 2 38. Then they create and demonstrate a new architecture aiming to limit these effects Figure 2.39.

FIGURE 2 . 36 :

 236 FIGURE 2.36: Schematic drawing of the wiring scheme (not to scale). The electrodes (yellow) are 20nm thick, 80 -150nm wide and have a gap of 400nm on a p-type Si substrate (blue) with 600nm thermally oxidized SiO 2 (green). Ag has been used as the top-layer electrode material.[START_REF] Krupke | Simultaneous Deposition of Metallic Bundles of Single-walled Carbon Nanotubes Using Ac-dielectrophoresis[END_REF]

FIGURE 2 .

 2 FIGURE 2.38: "Dielectrophoresis in progress. Pre-patterned contacts over Si/Si 3 N 4 substrate having gap of 10µm (a) before DEP showing probes positioned over pads to apply electric field (b) during DEP showing probes along with drop of CNT dispersion and (c) after DEP showing CNT deposited around both electrodes. Black arrows indicate parasitic paths between device electrodes and white arrows indicate unwanted deposition along electrode edges." [15]

FIGURE 2 .

 2 FIGURE 2.39: "CNT aligned by floating electrode dielectrophoresis (a) Electrode structure, field was applied across top elbow and bottom 'T' electrode, middle 'T' electrode was floating. Deposition of horizontally aligned CNT can be seen all around bottom 'T' electrode whereas no such deposition occurs around middle 'T' electrode. (b)& (c) CNT are deposited to bridge gaps between electrodes."[START_REF] Chaturvedi | Controlled deposition of aligned carbon nanotubes by floating electrodes dielectrophoresis[END_REF]

FIGURE 2 .FIGURE 2 . 41 :

 2241 FIGURE 2.40: Bottom-up integration scheme used to fabricate selfaligned: back-gated, lateral-gated and double lateral gated CNTFETs.[13]

FIGURE 2 . 42 :FIGURE 2 . 43 :

 242243 FIGURE 2.42: Alignment of CNTs (SWeNT Inc.) varied by tuning the sinusoidal frequency at 5V for 30s. [13]

FIGURE 2 . 44 :

 244 FIGURE 2.44: Alignment of CNTs into the 50nm wide, 1.5µm long trenches, according to different applied DEP voltage and duration at 5MHz. Inset: schematic of the trench. [13]

FIGURE 2 .

 2 FIGURE 2.45: 4 probe characterisation set-up

Figure 2 .

 2 50 -, will change the chain solubility toward the alkaline solvent used in development. In its original state, he DNQ molecule possess nitrogen -Figure 2.49

FIGURE 2 . 47 :FIGURE 2 . 48 :

 247248 FIGURE 2.47: The structural formula of phenolic resin which forms the matrix of most AZ and TI photoresists.[START_REF] Microchemicals | [END_REF]

FIGURE 2 . 49 :

 249 FIGURE 2.49: The photoinitiator, a diazo-naphthoquinone (DNQ) sulphonate (left) is converted into an indene carboxylic acid (right) under N 2 release (center) and H 2 O absorption by exposure to suitable wavelengths. [65]

Figure 2 . 51 .

 251 The objective of the design was to realize a 5mm by 5mm sensitive area limiting the quantity of patterns by workspace to four. The sixteen patterns are numbered with their placement in Figure2.51. Figure2.52 illustrates the variations between the patterns 1 to 4. The objective here is to test the maximum surface realizable with the process. Patterns 5 to 12, 15 and 16 have the same general shape that pattern 3 with four parts composing a sensor, each part can be separately stimulated or characterized. The microstructure of the pattern is described in Figure 2.51 to Figure 2.55, with the following image being a zoom on the red rectangle of the previous image. As described in the conclusion of Chapter 1, the patterns are constituted of two intertwined combs with each an access pad for electronic connection -Figure 2.53. Each of the combs teeth is lined with micrometric teeth facing each other -Figure 2.54. These facing teeth are the deposition sites for dielectrophoresis and have different shape and spacing according to the previously discussed experiments. The dimensions that vary are illustrated in Figure 2.55, the values of these dimensions are listed in Table 2.1. It is worth noting that due to the resolution of electron-beam lithography the results are expected to look more like the red line in Figure 2.56. Patterns 13 and 14 aim to test the dielectrophoresis set-up. They consists of several independent patterns, called lines, containing two access pads each Figure 2.57.

FIGURE 2 . 51 :

 251 FIGURE 2.51: Design of the mask in cadence. the forbidden zone is in hatched green, the light blue areas represent the metal layer.

FIGURE 2 . 52 :

 252 FIGURE 2.52: Zoom on the red rectangle of 2.51. L and H represent the length and width of each patterned sensor.

FIGURE 2 . 53 :

 253 FIGURE 2.53: Zoom on the red rectangle of 2.52. illustrates the intertwined combs; with the access pad of one comb at the bottom.

FIGURE 2 . 54 :

 254 FIGURE 2.54: Zoom on the red rectangle of 2.53. The vertical elements are alternatively from the top comb or the bottom comb. The facing teeth are each a site for CNT deposition.

FIGURE 2 . 55 :

 255 FIGURE 2.55: Zoom on the red rectangle of 2.54. Detailed shape and dimension of each teeth pair. w and l represen the size of the main rectangle. S1 and S2 represent the dimensions of the pentagon shaping the tip of the teeth.

FIGURE 2 . 57 :

 257 FIGURE 2.57: Design of the test bands, pattern 13

Figure 2 .

 2 [START_REF] Liu | Chemical functionalization of single-walled carbon nanotube field-effect transistors as switches and sensors[END_REF]. I exposed in the introduction the drawbacks of the laser exposure, with an emphasis on time -Figure2.59 (right). The second method -Figure2.59 (center) -consists in the use of two systems of lens. It is mainly used for multi-step exposure with different masks but lacks resolution. In the last version, the one I will use, the mask is in contact with the resin layer aiming for an optimal resolution.

FIGURE 2 . 59 :

 259 FIGURE 2.59:The most common methods for exposure of photoresist layers are the direct projection onto the whole substrate with a mask aligner (left, usually the photomask and resist are in close contact), the stepwise exposure of rectangular partial surfaces by a reduction optics (stepper, center) or the direct writing of the structures with a laser (right).[START_REF] Microchemicals | Exposure of Photoresists[END_REF]

FIGURE 2 . 60 :

 260 FIGURE 2.60: The emission spectra of different light sources as well as the absorption spectrum of a broadband photoresist in the shortwave visible and near ultraviolet spectral range. [64]

FIGURE 2 . 61 :

 261 FIGURE 2.61: An estimate of the exposure doses of typical positive photoresist films absorbed under different lighting conditions for different times. The color scheme ranges from green (uncritical for conventional resists and processes) to yellow and orange to red (exposed). [64]

FIGURE 2 . 62 :

 262 FIGURE 2.62: The schematic process sequence of the exposure (above) up to the developed resist features (below) in the processing of positive resists (left column), negative resists (centre) and image reversal resists (right); the latter in two possible modes. [70]

FIGURE 2 . 63 :

 263 FIGURE 2.63: The basic process sequence of the structuring of a (e.g. metal) layer via etching processes (left) and lift-off (right). [68]

FIGURE 2 . 64 :

 264 FIGURE 2.64: Resist profiles of an image reversal resist and directed evaporation of metal.The undercut allows separation of the metal onthe substrate from the metal on the resin.[START_REF]Image reversal resists and their processing[END_REF]

FIGURE 2 . 65 :

 265 FIGURE 2.65:The lower the dose of the first exposure in the image reversal resist processing, the more pronounced (tendency) the undercut attained after development.[START_REF]Image reversal resists and their processing[END_REF]

Figure 2 .

 2 68 illustrates a spin coating set-up. For these reasons I propose to work with a spin-coating method.

FIGURE 2 .

 2 FIGURE 2.66: "The contrast of photoresists defined as the increase of the dependency of the remaining resist film thickness after the development to the original resist film thickness d'/d0 from the logarithmically scaled exposure dose."[START_REF] Microchemicals | Exposure of Photoresists[END_REF]

FIGURE 2 . 67 :

 267 FIGURE 2.67: The diagram of the importance of a low (blue curve), high (green curve) and in an ideal case, the infinite (red curve) contrast in the photoresists with regard to dependence between exposure dose and achievable development rate.[START_REF] Microchemicals | Exposure of Photoresists[END_REF]

FIGURE 2 .

 2 FIGURE 2.68: A resist dispensed on a rotating substrate thins out through the spin force until the drying of the resist through the evaporation of the solvent stops a further spin off. [69]

FIGURE 2 .

 2 FIGURE 2.69: The resist film thickness attained by spin-coating used in relation to the solvent concentration. [64]

Figure 2 .

 2 71 illustrate the method of contact realized by the mask aligner MJB4. Considering my needs in resolution, I choose to work with a vacuum contact.

FIGURE 2 .

 2 FIGURE 2.70: "The intensity distribution of the light in the air gap between the photo mask and the resist surface (from black to red to yellow and white) corresponds to the single slit diffraction pattern when the distance between the photo mask and the resist surface is varied from zero (contact exposure, left) to a value of several exposure wavelengths (right) at a constant slit width of the photomask. From left to right, an increasingly distinctive diffraction pattern with corresponding inhomogeneous intensity distribution arises from a nearly rectangular figure of the light intensity."[START_REF] Microchemicals | Exposure of Photoresists[END_REF]

FIGURE 2 . 71 :

 271 FIGURE 2.71: Schematics of soft contact, hard contact, vacum contact [98]

FIGURE 2 .

 2 FIGURE 2.72: "The attained film thickness of an arbitrary resist (in arbitrary units, normalized to 1 at 4000rpm) as a function of the spin speed." [69]

Figure 2 .

 2 [START_REF] Morris | Kinetic Mechanism of Activation of the Cdk2/Cyclin A Complex: KEY ROLE OF THE C-LOBE OF THE Cdk*[END_REF] illustrate examples of rate of rehydration. We can see that for thin resin layers -∼ 1µm -a few seconds are enough to rehydrate the substrate.

FIGURE 2 . 74 :

 274 FIGURE 2.74: The rehydration time to attain an equilibrium water concentration in the resist is diffusion-limited and increases quadratically with the film thickness.[START_REF] Microchemicals | Chemical and Physical Processes in the Resist Film: Rehydration[END_REF]

FIGURE 2 .

 2 FIGURE 2.75: "A numerical simulation of the chronological sequence of the development of positive resist films which are differently rehydrated. Left: Inclined resist sidewalls from a constantly low development rate due to air which is too dry or missing rehydration. Centre: Steep resist sidewalls from a constantly high development rate due to sufficiently long rehydration with sufficient humidity. Right:A tub-shaped profile from an initially high development rate, which continues to diminish due to a too short rehydration with sufficient humidity."[START_REF] Microchemicals | Chemical and Physical Processes in the Resist Film: Rehydration[END_REF]

FIGURE 2 .

 2 FIGURE 2.76: "While optically thin photoresist films (upper row) are almost homogeneously exposed, resist films with a thickness of several penetration depths of the exposure wavelength (lower row) bleach with increasing light dose (from left to right) in the direction of the substrate. A dependency between the exposure dose and the development rate or the duration of the development, which is different for thin and thick resists, results in the later development."[START_REF] Microchemicals | Exposure of Photoresists[END_REF]

FIGURE 2 .

 2 FIGURE 2.77: "WEC-System in the Alignment Stage. Soft contact for precise leveling. Inline vertical pneumatic clamping avoids any shifts. l1 Mask Holder l2 Mask l3 Wafer l4 Chuck l5 Chuck stage l6 Spindle l7 Precise ball-bearing guide l8 Pneumatic brake l9 Leveling pistons." [98]

FIGURE 2 . 78 :

 278 FIGURE 2.78: Schematics of classic optics versus SUSS optics[START_REF] Sussmicrotech | Manual mask aligner[END_REF]

FIGURE 2 . 79 :

 279 FIGURE 2.79: With the image reversal bake step, a baking temperature and time-dependent part of the photoinitiator is destroyed.[START_REF]Image reversal resists and their processing[END_REF]

FIGURE 2 . 80 :

 280 FIGURE 2.80: This series of cross-section images in different stages of development shows how the undercut develops mainly after the development. [67]

FIGURE 2 . 81 :

 281 FIGURE 2.81: Expected structure of the metal/CNT/metal layers

  electrodes and would complicate passivation without benefits, Figure2.83. In order to reduce this effect, the sample could be less underexposed than for the first layer. As illustrated in Figure2.83, this would create more vertical resin and metal walls. It would also reduce the enclosure effect. But, it would allow me to guaranty the critical non connection between electrodes and integrity of the passivation coating.

FIGURE 2 . 83 :

 283 FIGURE 2.83: Cases of exposure for the second metallisation layer and focus on the effects on the CNT enclosure.

FIGURE 2 . 85 :

 285 FIGURE 2.85: Illustration of the effects of exposure on the quality of the coating, zoom on the critical contact area.

  Figure 2.86.

FIGURE 2 . 86 :

 286 FIGURE 2.86: Process flow with the names of the steps (ellipses) and the observations of the results, types and objectives (rectangles)

FIGURE 3 . 1 :

 31 FIGURE 3.1: Result of a CNT dispersion in ethanol after less than a minute from sonic tip stimulation

FIGURE 3 . 2 :FIGURE 3 . 3 :

 3233 FIGURE 3.2: Color sheet used in visual evaluation consisting of successive approximations

Figure 3 .

 3 5. A typical pre-sonication configuration is illustrated in Figure 3.6. A typical result from sonic bath dispersion is illustrated in Figure 3.7. The structure of the colloid changes upon stimulation and for around 20min. Over that duration, no significant increase in the post bath result nor in the final result where observed.

Figure 3 . 8 .

 38 Trials where realized for several power values and durations. Results are illustrated with their parameters in Figure 3.9, Figure 3.10 and Figure 3.11.

FIGURE 3 . 5 :

 35 FIGURE 3.5: Set-up for bath sonication

FIGURE 3 . 7 :

 37 FIGURE 3.7: Typical structure of the colloid after bath sonication

FIGURE 3 . 8 :

 38 FIGURE 3.8: Tip sonication set-up

FIGURE 3 . 10 :FIGURE 3 . 11 :

 310311 FIGURE 3.10: Dispersion after 60w for 30sec followed by 60w for 15sec and 120w for 15sec FIGURE 3.11: Dispersion after 60w for 30sec repeated 10 times

Figure 3 .

 3 [START_REF] Robert | Noncovalent functionalization of carbon nanotubes for highly specific electronic biosensors[END_REF] shows multiple results from different

FIGURE 3 FIGURE 3 .

 33 FIGURE 3.12:Colloid sample before centrifugation

FIGURE 3 .

 3 FIGURE 3.15: AFM set-up

FIGURE 3 . 17 :FIGURE 3 . 20 :

 317320 FIGURE 3.17: Zoom on the previous illustration and profiles used to identify single CNTs to their thickness, here ∼ 1nm

FIGURE 3 . 21 :

 321 FIGURE 3.21: Mask for lithographic patterning

Figure 3 .

 3 23 from pattern 13 and Figure 3.24 from pattern 14 illustrate this difference.

Figure 3 .

 3 25 from pattern 13 and Figure 3.26 from pattern 14 quantify this difference with measurements.

FIGURE 3 . 22 :

 322 FIGURE 3.22: Zoom on the teeth composing the network

Figure 3 .

 3 [START_REF] Guo | Multi-walled carbon nanotube dispersion by dispersants with different chemical structures[END_REF] illustrates a resin layer lacking the uniform central surface.

Figure 3 .

 3 [START_REF] Gupta | Polyether based amphiphiles for delivery of active components[END_REF] shows a wide enough work-space at the center of the surface. Later, while performing a substrate profile, I stumbled upon a parameter more critical to side beads moreover to pattern/mask distance.

FIGURE 3 . 23 :

 323 FIGURE 3.23: Mask pattern 13 Line 4 FIGURE 3.24: Mask pattern 14 Line 4

Figure 3 . 33 ,

 333 Figure 3.34 and Figure 3.35 illustrate the results for 4s, 3.5s and 2.5s respectively on line n • 4. The variation creates a deeper undercut with a lower exposure. The undercut is observable in the optical microscope photographs through the darker part of the tips of the teeth. Considering the objective of soft angles, I chose to work with an exposure of 2.5s corresponding to a light dose of 20mJ.

FIGURE 3 . 25 :FIGURE 3 . 27 :FIGURE 3 . 29 :

 325327329 FIGURE 3.25: Mask pattern 13 Line 4 with measurements

FIGURE 3 . 30 :

 330 FIGURE 3.30: Resin spin coated with a sufficient thin and flat central area

FIGURE 3 . 31 :

 331 FIGURE 3.31: Pattern choice through mask placement

FIGURE 3 .

 3 FIGURE 3.36: A quarter of pattern with particles deposited on the resin

FIGURE 3 . 37 :

 337 FIGURE 3.37: Diffraction effects and loss in resin structure due to extreme humidity

Figure 3 .

 3 38 illustrates this issue. In order to reduce this drawback, I use a different method of lift-off consisting in the bath sonication of the substrate while maintaining it facing 45 • facing down. The unwanted metal parts are then detached by local pressure and can fall at the bottom of the becher reducing the risks of re-gluing to the substrate.Figure 3.39 illustrates the difference between samples before (right) and after (left) the lift-off step.

FIGURE 3 . 38 :

 338 FIGURE 3.38: Pattern post lift-off with a metal piece re-glued between the two electrodes.

FIGURE 3 . 39 :

 339 FIGURE 3.39: One lifted sample on the left compared with non-lifted samples on the right

Figure 3 .

 3 40 and Figure 3.41 show the results for a 24sec development.

Figure 3 .

 3 42 and Figure 3.43 show the results for a 25sec development. Figure 3.44 and Figure 3.45 show the results for a 26sec development.

FIGURE 3 . 40 :FIGURE 3 . 41 :FIGURE 3 . 42 :Figure 3 .

 3403413423 FIGURE 3.40: Result of a pattern 14 line 4 with a 24sec development FIGURE 3.41: Zoom on the previous result with measurements

FIGURE 3 . 44 :FIGURE 3 . 45 :

 344345 FIGURE 3.44: Result of a pattern 14 line 4 with a 26sec development FIGURE 3.45: Zoom on the previous result with measurements

Figure 3 .

 3 [START_REF] Krupke | Surface conductance induced dielectrophoresis of semiconducting single-walled carbon nanotubes[END_REF] shows a sample under stimulation. The two bottom probe transmit the stimulation. The two top probe measure the gate potential created by the stimulation. No variation of potential was observed in the back gate.

FIGURE 3 .

 3 FIGURE 3.46: AFM image of one side of deposition sites

FIGURE 3 . 48 :

 348 FIGURE 3.48: Probe set-up

FIGURE 3 . 50 :

 350 FIGURE 3.50: Low density deposition

Figure 3 .

 3 [START_REF] Le | Dispersion of carbon nanotubes in water and non-aqueous solvents[END_REF] presents a result arising from a stimulation with

FIGURE 3 . 51 :

 351 FIGURE 3.51: Medium density deposition

FIGURE 3 . 53 :

 353 FIGURE 3.53: Low stimulation amplitude and long duration typical result

Figure 3 .

 3 [START_REF] Lim | Cdks, cyclins and CKIs: roles beyond cell cycle regulation[END_REF] shows the results of the stimulation of such a structure. The results are close to the split teeth configuration but with small sheet like depositions joining the two parts of the same site. These structures, show in my experiments, a reduced

FIGURE 3 .FIGURE 3 . 55 :

 3355 FIGURE 3.54: high stimulation amplitude and short duration typical result

FIGURE 3 . 56 :

 356 FIGURE 3.56: Deposition in split teeth lithographed structure

Figure 3 .

 3 [START_REF] Liu | Chemical functionalization of single-walled carbon nanotube field-effect transistors as switches and sensors[END_REF] shows the raw data of the AFM observation. Some profile lines are shown top left and their recorded height is shown on the bottom right. This method insures the presence of CNTs and discriminates from a shaped assembly of other particles. I use in this section the pictures extracted from data treatment. Figure 3.60 shows the treated version of Figure 3.59.Two CNT structure arising from DEP deposition present an electrical field sensitivity. First, as illustrated in Figure3.60, a single CNT can be deposited on a site. This type of deposition shows the more sensitivity to field effect. The second structure, shown in Figure3.61, consists in an accumulation of single CNTs close from each-other or small bundles.

Figure 3 .

 3 [START_REF][END_REF] shows two similar structures that I treat as the same type due to their similar sensitivity. Indeed, this type of structure shows a partially decreased sensitivity to field effect compared to the single CNT structure. This variation is complicated to discriminate due to the presence of the two types of structures on most of the deposited samples.

Figure 3 .

 3 [START_REF] Microchemicals | Chemical and Physical Processes in the Resist Film: Rehydration[END_REF] shows an example of the two types of structures on two neighboring sites. A further optimization of the DEP stimulation and duration would allow to increase the control on the deposition and increase the sensitivity of the resulting transistor network.

FIGURE 3 . 57 :

 357 FIGURE 3.57: Deposition in flat teeth lithographed structure

FIGURE 3 . 59 :

 359 FIGURE 3.59: Raw data from AFM showing a single CNT bridging a deposition site

FIGURE 3 . 61 :

 361 FIGURE 3.61: Multiple CNTs bridging the same deposition site

FIGURE 3 . 63 :

 363 FIGURE 3.63: Single and multiple CNTs bridging neighboring deposition sites.

FIGURE 3 . 64 :

 364 FIGURE 3.64: Effects of the lithography of the deposition observed with AFM

FIGURE 3 .

 3 FIGURE 3.65: Characterisation schematics

FIGURE 3 . 66 :

 366 FIGURE 3.66: Typical result of Id = f (V ds ) with SDBS deposition

FIGURE 3 . 67 :

 367 FIGURE 3.67: Result for a pattern containing a single deposition site.

FIGURE 3 .

 3 FIGURE 3.68: Result for a pattern containing seven deposition sites.

Figure 3 .

 3 69 shows the response of a p-mos FET from CMOS technology. Line 1, in yellow, shows the substrate potential. The second line, green, shows I s . The third line shows I d . The currents are measured around a 10kΩ resistor giving a conversion factor of 100mV/µA. We can see that the transistor is closed with V g superior to -0.7V. Then it opens, reducing its impedance. The open resistivity of the transistor is very low compared to the resistors used as current convertors. Therefore the V ds potential of point four volts is split half way between resistors. Note that the two currents are equal except for the noise generated by the set-up.

FIGURE 3 .

 3 FIGURE 3.69: Oscilloscope screen copy for a p-mos CMOS transistor in the characterisation set-up

Figure 3 .

 3 Figure3.70 shows the same set-up with a substrate that has been deposited with a 1%w/w SDBS solution. V ds is null, with source and drain connected to the ground. We can see here the diode like behavior of the substrate and back-gate. When the substrate potential is positive we can see an injection of current in the channel. I d increases with the substrate potential. I s decreases with the increase of the substrate potential. This is coherent with an increase in the channel potential. When the substrate stimulation reaches a negative threshold, the current in the source increases and the current in the drain decreases. This is coherent with the decrease of the channel potential.This behavior is due to the leakage of charges from the substrate to the channel through the gate insulator. This has been confirmed by surveilling the gate current during stimulation of non-deposited substrates. This effect was not obvious at first, due to the fact that it appears with the characterization and increases with further stimulation. The sample of Figure 3.70 was stimulated for approximately ten minutes, about 100cycles, before showing such a net characteristic. The leakage increases further with subsequent stimulation as showed in Figure 3.71. This shows

FIGURE 3 . 70 :

 370 FIGURE 3.70: Illustration of the leakage current through the back-gate insulator

FIGURE 3 . 71 :

 371 FIGURE 3.71: Illustration of the leakage current through the back-gate insulator after approximately an hour of stimulation

FIGURE 3 . 72 :

 372 FIGURE 3.72: Illustration of the leakage current through the back-gate insulator with a CMC/CNT deposition

FIGURE 3 . 73 :FIGURE 3 . 74 :

 373374 FIGURE 3.73: Illustration of the leakage current through the backgate insulator with a CMC/CNT deposition on a line presenting field effect sensitivity

FIGURE 3 . 76 :Figure 3 .

 3763 FIGURE 3.76: Characterisation through back-gate with a humid sensitive area

FIGURE 3 . 77 :

 377 FIGURE 3.77: Characterisation through back-gate with a dried sensitive area

FIGURE 3 . 78 :

 378 FIGURE 3.78: Characterisation through back-gate with a 10µL drop of water casted on the sensitive area

  Figure 3.75 to Figure 3.79. These values are similar in most CMC/CNT deposited sites. The sensitivity of the transistor is strongly dependent on the structure of the gate. The stimulation of the sensor through chemical gate shows a first glance to the sensitivity toward electrochemical changes. The model -c.f. Section 1.3 -anticipated a variation of the sensor conductivity of 5% to 10% over 0.1V of electrochemical state

FIGURE 3 . 79 :

 379 FIGURE 3.79: Characterisation through chemical gate with a 10µL drop of water casted on sensitive area

FIGURE 3 . 80 :

 380 FIGURE 3.80: Characterisation of two CNTFET, Id = f (V ds ), from the same pattern on different samples

  .67 -generally presents an open current of approximately a hundred nanoamperes.

Figure 3 .

 3 68 shows the results for a patterns with seven sites and an open transistor current of a few hundred nanoamperes.

Figure 3 .

 3 75 to Figure 3.79 show results for a pattern containing approximately two thousand three hundred sites giving an open current of about three microamperes. Finally, Figure 3.80 shows an on current of about two microamperes for a pattern containing approximately one thousand five hundred sites. As introduced, this is a tendency and I do not have yet the data necessary to identify the variability parameters and to quantify the relationship.

FIGURE 4 . 1 :

 41 FIGURE 4.1: Schematics representing the phosphorylation of a protein by a kinase enzyme [106]

Figure 4 .

 4 2 presents the general mechanism of the FRET technology. The addition of a phosphate group on the substrate peptide promotes an intramolecular conformational change that brings two autofluorescent proteins together and promotes fluorescence resonance energy transfer following phosphorylation of the substrate. The second type of mechanism of the fluorescence-based biosensor involves a change in fluorescence intensity of an environmentally-sensitive fluorophore, following an intramolecular change upon phosphorylation of the substrate moiety -[88].

Figure 4 .

 4 3 presents an example using the mechanism of this technology. The phosphotransfer by an enzyme kinase creates a conformal change to the structure, similarly to the FRET sensor, except that the changes modify here the intensity of the fluorescence.

FIGURE 4 . 2 :

 42 FIGURE 4.2: FRET mechanism of action

FIGURE 4 . 3 :

 43 FIGURE 4.3: CDKACT mechanism of action [58] relates a biosensor technology based on electrogenerated chemiluminescence -ECL.Figure 4.4 presents the mechanism of this sensor. A gold electrode, functionalized with a peptide specific to the protein kinase A, is put in presence of gold nanoparticles. Depending on the ratio of phosphorylated substrates, the sensor will generate different intensity of luminescence.

  Figure 4.4 presents the mechanism of this sensor. A gold electrode, functionalized with a peptide specific to the protein kinase A, is put in presence of gold nanoparticles. Depending on the ratio of phosphorylated substrates, the sensor will generate different intensity of luminescence.

FIGURE 4 . 4 :

 44 FIGURE 4.4: Schematics of ECL increase with phosphorylated protein substrates in ECL-PKA biosensor

FIGURE 4 . 5 :

 45 FIGURE 4.5: Reaction in solution, magnetic separation and sensor functionalisation for kinase activity measurement with a photoelectrochemical method

FIGURE 4 . 6 :

 46 FIGURE 4.6: Schemcatics of non labeled electrochemcical recognition of kinase activity

  Figure 4.7 illustrates the steps for functionalization and activation of the sensor. The ATP giving the phosphate group has been labeled with ferrocene, a known red-ox active reagent. The ferrocene concentration modifies in turn the conductivity of the electrode.

FIGURE 4 . 7 :

 47 FIGURE 4.7: Functionalisation of a labeled electrochemical sensor. Activation of the sensor by selective deposition of a ferrocene labeled ATP moiety

FIGURE 4 . 8 :FIGURE 4 . 9 :

 4849 FIGURE 4.8: Schematics of the electrochemical measurement of kinase activity (top), functionalisation by a selective peptide (bottom), activation by phosphorylation of the peptide (bottom-right)

  will fold onto the pRb sequence promoting enhancement of fluorescence emission of the fluorescent probe -Figure 4.11.

FIGURE 4 . 11 :

 411 FIGURE 4.11: Illustration of the conformal changes of CDKACT4upon phosphorylation[START_REF] Prével | Biosensors and Bioelectronics Fluorescent peptide biosensor for monitoring CDK4 / cyclin D kinase activity in melanoma cell extracts , mouse xenografts and skin biopsies[END_REF]

FIGURE 4 . 12 :

 412 FIGURE 4.12: Fluorescence of 25nM CDKACT Rb-Cy3 was monitored over time upon incubation with 10mg A375 (CDK4/cycD over expressed) cell extracts alone (open circles) and with 20µM CDK4/cycD inhibitor (black circles) [88]

FIGURE 4 . 13 :

 413 FIGURE 4.13: Fluorescence of 25nM CDKACT Rb-Cy3 was monitored upon incubation with 10mg A375 cell extracts with different concentrations of CDK4 inhibitor [88]

FIGURE 4 . 14 :

 414 FIGURE 4.14: Illustration of the charge transfer versus field effect. (a) represents a structure with a conductive functionalisation.(b) represents a structure with a capacitive functionalisation. (c) schematises the charge transfer from the phosphate group to the amplifying structure. (d) illustrates the field effect with the charge from the phosphate group being confined to the functionalisation (dashed red rectangle)

FIGURE 4 . 15 :

 415 FIGURE 4.15: Structure of Pbase Sigma-Aldrich

FIGURE 4 .

 4 FIGURE 4.16: "N-hydroxysuccinimide esters (NHS esters) reaction scheme for chemical conjugation to a primary amine. R represents a labeling reagent or one end of a crosslinker having the NHS ester reactive group; P represents a protein or other molecule that contains the target functional group (i.e., primary amine)." Thermofisher

Figure 4 .

 4 [START_REF] Chen | Quantitatively Control of Carbon nanotubes Using Real Time Electrical Detection Dielectrophoresis Assembly[END_REF] Presents the result of the chemical gate design on the developed sensing technology.

FIGURE 4 . 17 :

 417 FIGURE 4.17: Illustration of the designed sensor technology with the designed selective layer, vertical cut

FIGURE 4 . 18 :

 418 FIGURE 4.18: Schematics of the optimal functionalisation rate

FIGURE 4 . 19 :

 419 FIGURE 4.19: Schematics of the Nernst equation estimate

Figure 4 .

 4 [START_REF] Di Crescenzo | Non-covalent and reversible functionalization of carbon nanotubes[END_REF] illustrates such a set-up. The authors' research opens possibilities in the use of electrophoresis or dielectrophoresis in increasing the CNT functionalisation yield.

FIGURE 4 . 20 :

 420 FIGURE 4.20: The CNT sidewall surface coverage by the functionalisation can be observed with AFM in liquid phase.

10. 1

 1 Illustration de la conception en coupe verticale . . . . . . . . . . . . . . ix 10.2 Illustration de la conception en vue de dessus . . . . . . . . . . . . . . . x 10.3 Résultats de dispersion, en bleu, après 15min de centrifugation, en orange après 30min de centrifugation . . . . . . . . . . . . . . . . . . . xiii 10.4 Profiles AFM permetant l'estimation de la qualité dispersion des nanotubes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii 10.5 Résultats de dispersion, en bleu, après 15min de centrifugation, en orange après 30min de centrifugation . . . . . . . . . . . . . . . . . . . xiv 10.6 Forme d'essai pour la diélectrophorèse, contenant sept sites de déposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiv 10.7 Dépot de résine sur un échantillon . . . . . . . . . . . . . . . . . . . . . xv 10.8 résine dévelopée après 3.5sec d'exposition . . . . . . . . . . . . . . . . . xv 10.9 Résultat après lift-off pour un dévelopement de 25sec . . . . . . . . . . xvi 10.10Nanotubes déposés entre les deux électrodes . . . . . . . . . . . . . . . xvi 10.11Nanotube seul reliant les deux électrodes . . . . . . . . . . . . . . . . . xvi 10.12Charactérisation de la sensibilité d'un transistor . . . . . . . . . . . . . xvii 10.13Charactérisation de deux CNTFET, Id = f (V ds ), créés à partir du même modèle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii 10.14Schéma représentant la mesure d'une activité kinase par électrochimie xix 10.15Schéma représentant la mesure de concentrtion en strépavidine par électrochimie, utilisant une structure CNTFET et une grille chimique à base pyrène . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xx 10.16Illustration de la conception en coupe verticale . . . . . . . . . . . . . . xxi 1.1 (a) A first Brillouin zone of graphene with conic energy dispersions at six K points. The energy dispersion near one of the K points are schematically shown along with the cross-sections by allowed states and resulting 1D energy dispersions for (b) a metallic SWNT and (c) a semiconducting SWNT. [4] . . . . . . . . . . . . . . . . . . . . . . . . 8 1.2 Diameter induced gap [4] . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.3 A schematic of a typical setup for electrical transport measurements of SWNTs. Typically, I DS as a function of V DS or V GS is measured for transport experiments [4] . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.4 Current I DS as a function of the gate voltage V GS for a (a) semiconducting, (b) metallic, and (c) semiconducting with a small bandgap SWNT V DS = 10mV for all data [4] . . . . . . . . . . . . . . . . . . . . . 9 1.5 Relative positions of the allowed states around K points and the resulting 1D subbands of a semiconducting SWNT (a) without and (b) with an external magnetic field. Note that the 1D subbands are not degenerate anymore under a magnetic field. [4] . . . . . . . . . . . . . 10 1.6 Saturation effect in CNTs depending on V ds and tube length. [4] . . . . 10 1.7 Fermi level pinning in Metal-CNT connection. [4] . . . . . . . . . . . . 11 1.8 Variation of the channel polarity depending on the metal contact material. (a) Al-contacted (S/D) nanotubes exhibit n-FET characteristics while (d) Pd contacts result in p-FETs. Nanotubes are chemically intrinsic. [4] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.9 Hydrogen response of a Pd-contacted SWNT-FET. Hydrogen reduces the work function of Pd metal contacts, therefore, increasing the SB height to the valence band while reducing the SB height to the conduction band. [4] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.10 (a) Metal-CNT contact resistance versus metal work function. (b) Contact resistance versus work function behaviors for metals with work functions between 4.2 and 5.7eV. CNT work function range is shaded. [113] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.11 Effect observed in a CNT transistor channel without charge transfer, (a) Gating effect due to electrostatic field applied on the CNT, (b) Schottky barrier variation due to the modification of the metal's work function, (c) Capacitance effect where the adsorption of molecules reduces the sensitivity of the channel to the gate effect, (d) mobility variation due to the mixing of the CNT orbitals with the adsorbed molecule's orbitals.[33] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.12 Electrical response of a semiconducting SWNT to gas molecules. (A) Conductance (under V g = 4V, in an initial insulating state) versus time in a 200ppm NO 2 flow. (B) Conductance (V g = 0, in an initial conducting state) versus time recorded with the same S-SWNT sample as in (A) in a flow of Ar containing 1%NH 3 .[46] . . . . . . . . . . . 1.13 Nanotube device structures. (a) SB-MOSFET with metal contacts and (b) MOS-like CNTFET structure with heavily doped S/D contacts.[4] . 1.14 Operation of a CNTFET compared to Si-MOSFET using band diagrams nanohub . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.15 "Scaled plot for the number of charges per unit energy (dn/dE) along the carbon nanotube axis in normal C-CNFETs with V g = -0.1V, V d = 0.4V. The "E c " and "E v " denoted white lines indicate the band diagram of the first sub-band. The horizontal colour lines represent the holes piling-up in the gated channel region. And the perpendicular bar shows the value of dn/dE." [31] . . . . . . . . . . . . . . . . . . . 1.16 Two-dimension sketch of SDC-CNFET structure [31] . . . . . . . . . . . 1.17 "The scaled plot for the number of charges per unit energy (dn/dE) along the carbon nanotube axis in SDC-CNFETs, where V g = -0.1V, V d = 0.4V. The "E c "-and "E v "-denoted white lines indicate the band diagram of the first sub-band." [31] . . . . . . . . . . . . . . . . . . . . . 1.18 I-V characteristics of nanotube nand p-MOS-like CNTFETs with doped contacts. [4] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.19 effect of the variation of oxide thickness on the band structure [47] . . 1.20 Structural and electrical schematics of the VS-Stanford model [54] . . . 1.21 Current characteristic for ideal functionalisation depending on PO 4 concentration. Circled in red, a more realistic range corresponding to more realistic functionalisation . . . . . . . . . . . . . . . . . . . . . . . 1.22 DFT-optimized positions for a graphene surface on (a) Ti and (b) Pd. (c) Interaction energy versus electrode separation between a graphene sheet and various metals. [113] . . . . . . . . . . . . . . . . . . . . . . . 1.23 "(a) An energy-band model for Au -CNT contact with a tunneling gap of spacing z and voltage V between them, qφ is work function, ζ is Fermi energy measured from the bottom of the Au valence band, and E F is Fermi level position. ∆ζ = ζ FAuζ FCNF is the difference between Au and CNT Fermi energies. The energy-band diagram is shown for (b) V = 0, (c) V = 0, and (d) V > 0. (e) Measured I-V before and after multiple current stressing cycles, with current-stressing conditions shown. Solid circles are modeling results at 300 • K, fitted to measured I-V data, resulting in z = 7.3, 5.9, and 5.0 Å. The inset shows improvement in I-V linearity upon current stressing, with solid line indicating initial behavior." [113] . . . . . . . . . . . . . . . . 1.24 "Resistance of two-terminal CNT test devices versus stress current (a) without W and (b) with IBID-W deposited on CNT/Au electrode contacts." [113] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.25 Images of nanotubes coated with a thin film (< 5nm) of various metals. [4] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.26 Schematic representation of two different metal-CNT contact configurations, (a) end contact and (b) side contact. SEM micrographs of CNT bundles suspended between two electrodes with (c) end contacts, and (d) a hybrid wrap-around configuration (side and end contacts). [113] 1.27 "SEM images and data obtained from a typical MWCNT sample. (a) Image of MWCNT with two Ag thin film contacts before any FIB cuts were made. The Ag contacts covering both ends of the MWCNT are evident. (b) Same MWCNT after nine FIB cuts were completed. (c) Resistance versus contact length obtained after each cut. Resistance includes both the contact resistance and the MWCNT resistance of the 4µm section of the MWCNT covered by Ag. Solid line is the best fit to the data which yield CNT resistivity ρCNT = 4.70kΩµm and contact resistivity per unit length ρC = 1.6kΩµm." [113] . . . . . . . . . . . . . 1.28 Geometrical and electrostatic conditions in graphene-based placement of nanomaterials. a Cross-section of a standard metal electrode used for electric-field-assisted assembly of nanomaterials and a graphene layer, having a thickness of 1.5nm, which is used for the same purpose. [23] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.29 Morphology of nanotubes deposited on Al and Au electrodes under similar experimental conditions. In the case of Al electrodes (a), the nanotubes form a dense and continuous network. On the other hand, only few nanotubes are deposited onto the Au electrodes (b). [50] . . . 1.30 SEM and AFM image of one individual SWNT deposited by dielectrophoresis [7] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.31 "a) A schematic diagram showing the use of depletion forces to form thin rafts within PMMA channels. b) UV-vis spectrum (lower curve) of the CNT solution used to form the rafts. For comparison, the normalized UV-vis spectrum of an unsorted solution is shown in the top curve. c,d) AFM images showing CNT structures formed by the depletion forces as shaped by PMMA channels with pitches of 100nm (c) and 200nm (d). Outlined insets show high-resolution images of a channel (two channels in 100nm case)." [114] . . . . . . . . . . . . . . . 1.32 Working mechanisms of EDL FET sensor technologys. . . . . . . . . . . 1.33 Illustration of the designed sensor technology, vertical cut . . . . . . . 1.34 Illustration of the designed sensor technology, horizontal view . . . . .

FIGURE A. 2 :

 2 FIGURE A.2: sp3,sp2,sp hybridisation[START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF]

FIGURE A. 5 :

 5 FIGURE A.5: Two carbon atoms configuration in graphene plain chem.libretexts.org

FIGURE A. 10

 10 FIGURE A.10: (a) Graphene reciprocal lattice with first Brillouin zone shaded, reciprocal lattice vectors and high symmetry points marked (b) Plot of the energy dispersion relation for the π-electrons in graphene along high symmetry directions (c) Full energy dispersion relation where valence and conduction band meet in k-pointmaking graphene a zero band-gap semiconductor[START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF]

FIGURE A. 11 :

 11 FIGURE A.11: schematic of the vectors C h -circumferential -T -trans-verse with a 1 , a 2 and the chirality angle θ[START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF]

FIGURE A. 12 :A. 2 . 2

 1222 FIGURE A.12: schematic of the wave vectors in (5,5) and (10,10) CNT[START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF]

FIGURE A. 13 :

 13 FIGURE A.13: Representation of the semiconducting and metallicCNTs -shaded[START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF]

FIGURE A. 14 :

 14 FIGURE A.14: Energy dispersion relation for armchair (5,5) (a) and (10,10) (b) SWC-NTs [39] FIGURE A.15: Energy dispersion relation for zigzag (6,0) (a) and (10,0) (b) SWCNTs.The (6,0) dispersion relation includes a line of allowed wave vectors passing through the k-point, ensuring that the tube is metallic. The (10,0) SWCNT on the other hand has a small direct bandgap.[START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF]

FIGURE A. 16 :

 16 FIGURE A.16: Electronic density of states for the semiconducting (10, 0) zigzag SWCNT as a function of energy. Each spike (van Hove singularity) originates from a maximum or minimum in a different branch of the dispersion relation. Each label E ii corresponds to the energy of an optically allowed transition. [39]

TABLE 10 .

 10

1: Sensibilité des transistors en fonction de la configuration de grille

  3.1 Dispersion realization . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lithography processing . . . . . . . . . . . . . . . . . . . . . . . . . . . .2.10 Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.11 Environment effects . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.12 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Dielectrophoresis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 DEP set-up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 DEP parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.3 AFM observations of deposited CNTs . . . . . . . . . . . . . . . 3.3.4 DEP results and improvements . . . . . . . . . . . . . . . . . . . 3.4 CNTFET characterisation . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4.1 CNTFET from SDBS dispersion . . . . . . . . . . . . . . . . . . .

3.1.1 Solvent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2 Surfactant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.3 Surfactant sonication . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.4 CNT addition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.5 CNT pre-sonication . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.6 CNT sonication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.7 Centrifugation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.8 Recovery and dilution . . . . . . . . . . . . . . . . . . . . . . . . 3.1.9 AFM observation of single CNTs . . . . . . . . . . . . . . . . . . 3.1.10 Surfactant variation . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.11 Dispersion results . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 3.2.1 Mask and pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Spin speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Spin acceleration ramp and side beads . . . . . . . . . . . . . . . 3.2.4 Substrate clamping and edge effects . . . . . . . . . . . . . . . . 3.2.5 First bake temp . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.6 Exposure contact . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.7 Exposition duration . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.8 Reverse bake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.9 Flood duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33.4.2 CNTFET from CMC dispersion . . . . . . . . . . . . . . . . . . . 3.4.3 general conclusions on CNTFET characterization . . . . . . . . 3.5 Manufacturing results and short terms developments . . . . . . . . . . 3.5.1 Results summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5.2 Short-term developments . . . . . . . . . . . . . . . . . . . . . .

TABLE 2 .

 2

				2	1	1	0	0
	4	2.5	2.5	2	1	1	0	0
	5	2.5	2.5	2	1	0.9	0	0
	6	2.5	2.5	2	1	1.1	0	0
	7	2.5	2.5	3	1.2	1	100
	8	2.5	2.5	3	1.2	0.9	200
	9	2.5	2.5	3	1.2	1.1	0	0
	10	2.5	2.5	2	1	0.9	200
	11	2.5	2.5	2	1	0.9	200
	12	2.5	2.5	2	1	1	100
	13	X	X	2	1	1	100
	14	X	X	3	1	1	100
	15	2.5	2.5	2	1	0.8	300
	16	2.5	2.5	3	1	0.7	400

1: properties of the patterns on the mask from IEMN, P represents the pitch between sites

FIGURE 2.56: Designed shape, in light blue surface. Expected limits of the metal layer after electron-lithography

  n • Line length (µm) quantity of Lines Length of teeth (µm) Width of lines (µm)

	1	2350	3	2.1
	2	2350	2	2.1
	3	3	2	1.1
	4	20	2	1.1
	5	200	2	1.1
	6	500	2	1.1
	7	1000	2	1.1
	8	2000	2	1.1
	9	3000	2	1.1
	10	4000	2	1.1
	11	5000	10	1.1
	12	5000	8	1.1
	13	5000	6	1.1
	14	5000	5	1.1
	15	5000	4	1.1
	16	5000	3	1.1
	17	5000	2	1.1
	18	2350	4	2.1
	19	2350	6	2.1
	20	2350	10	2.1
	21	2350	2	1.1
	22	2350	3	1.1
	23	2350	4	1.1
	24	2350	6	1.1
	25	2350	10	1.1

TABLE 2 .

 2

2: Structures of the teeth in the mask from IEMN patterns 13 and 14 FIGURE 2.58: "

Acknowledgements

The sp2 hybridisation constitutes the graphene plane -also benzene structuresand reorganise three hybridised orbitals in a plane with 120 • between each and leaving an un-hybridised orbital along the z axis -

A.1.2 Structure of graphene

The graphene structure is made of hexagons -graphene Brillouin zone -repeated along a plane (x, y). In graphite there is multiple planes bonded by Van der Waals force -along the z-axis -and the dimension of the graphene hexagon depends on the graphite inter layer structure. We will use in this document data related to the most In this structure two types of electronic bonds appear. Electrons in the graphene plane bond to their counterparts from the adjacent carbon atoms. They create strong sigma bonds with a distance between carbon atoms of 1.42 Å. The other type of link is created between the graphene planes forming the graphite matrix. We saw previously that electrons orthogonal to the graphene plane were close to free particles. In a two layer graphite structure two graphene flat clouds of electrons will link together creating Van der Waals bonds. In the Bernal graphite structure half of the carbon atoms are facing each-other and half are facing the center of one of the other layer's hexagon. The distance between graphene planes is of around 3.35 Å. The bond created with the π-electrons is mechanically less strong than with σelectrons. The transfer of charges is easier in the plane than between planes due to these properties. It has been shown that whilst the charge transfer in the plane has ohmic particularities, the relation between planes show capacitive properties [3].

The smaller pattern that can represent the structure of graphene is the C-C structure with mirror symmetry between the two carbon atoms. As a mathematical tool, we use the lattice of graphene, which is a description of the repeated hexagonal motif. I choose not to expose the math equations demonstrating the theory of the graphene dispersion equation but to focus on the principles and results relevant to the project at hand.

The following aims to the comprehension of what makes a CNT semi-conducting and a good tool for amplification. Furthermore, their specific electronic structure is central in explaining the properties that we will use in design and that make CNTs the best choice for field effect based biosensing.

A.1.3 Electronic dispersion relation

The objective is to describe the graphene band structure. Two options can be explored, the nearly free electron theory -using the analogy between a high quantity of electrons and gas of particles -or the tight binding theory -based on molecular FIGURE A.18: Sketch of low-lying excitonic energy levels near the extreme bandgap in a semiconducting SWCNT [START_REF] Vijayaraghavan | An Introduction to Graphene and Carbon Nanotubes[END_REF] plane is the reason for the negative dilatation coefficient of the material. The optics phonons are higher in energy and responsive to magnetic stimulation. The acoustic z-axis phonon in graphene turns to an expansion and retraction of the diameter of the tube -Figure A.19. That movement creates a variation in the lattice of the CNT making it a more energetic phonon. Whilst the Γ point in the graphene lattice is a zero energy point, it obtains non-zero energy in the curvature to CNT and the phonon becomes sensitive to electromagnetic energy. One can show by studying the variation in the susceptibility of the structure that the phonon pulsation is inversely proportional to the radius. That specific phonon type can be observed in CNTs thanks to Raman spectroscopy as the radial breathing mode -Figure A.20. Other analysis tools based on Raman spectroscopy are used to identify CNTs, especially the integrity of their structure. I will no go into detail of these techniques because they are out of the scope of the thesis.

Abstract : L'objectif de la thèse est la conception d'une nouvelle technologie de biocapteurs basée sur l'utilisation de nanotubes de carbones. Cette conception vise à utiliser ces nanostructures en tant qu'éléments transducteurs grâce à la conception d'une grille chimique et amplificateurs grâce à leur intégration dans une architecture de transistor à effet de champ. La grille chimique de la structure transistor sera conçue pour être sélective et en concordance avec la transduction de l'effet de champ. Dans ce but, la cible choisie est la famille des enzymes kinases. Le travail de thèse focalise sur la conception et réalisation d'une preuve de concept pour la technologie complète en visant une enzyme kinase spécifique.

Le travail de recherche se découpe en trois temps. Tout d'abord, le travail consiste en la définition de l'architecture du capteur. Ensuite, partant de cette définition, il est nécessaire de concevoir un procédé de fabrication dédié. Enfin, le capteur peut être réalisé, si possible jusqu'à la démonstration d'une preuve de concept.

La nouvelle technologie se base sur un biocapteur existant dont la sélectivité a été démontrée. La conception du capteur vise à alléger la mesure en temps humain et éviter l'utilisation d'équipements lourds. Nous sommes imposés comme contrainte que le capteur soit passif par rapport à l'échantillon biologique. En effet, le capteur doit être utilisé pour une mesure prolongée dans le temps pour permettre le suivi continu d'échantillons et ne doit donc pas perturber ces échantillons.

En ce qui concerne le procédé de fabrication, il a pour objectif d'être robuste et reproductible pour pouvoir produire des capteurs intégrables dans des chaines de mesure générant d'importants volumes de données normalisées. Le second objectif du procédé de fabrication est la réalisation de capteurs pouvant être réalisés en grandes séries et à bas coût unitaire.

Le manuscrit de thèse présente les recherches et déductions menant à la définition de l'architecture du capteur, du procédé de fabrication et des premiers résultats de réalisation. Après trois années de recherche, les travaux de réalisation présentent une structure à base de transistors, utilisant des nanotubes de carbone en tant que canal sensible à l'effet de champ et prédisposé à l'ajout de sélectivité par fonctionnalisation.

Abstract:

The thesis objective is the conception of a new technology of biosensors based on carbon nanotubes. This conception aims to the integration of these nanostructures as transducers in a chemical gate and as a base for a field effect transistor architecture. The chemical gate and transistor architecture will be designed with the goal of field effect transduction. The target chosen for this technology is the kinase enzyme family. More specifically, the thesis aims to the design and realization of a proof of concept for a specific target: the complex CDK4/cyclinD. The research is threefold. First, the work consists in the design of the new architecture based on literature. Then the second objective is to design a clean room process for manufacturing of the architecture. Finally, the goal of the thesis is to realize manufacturing of the sensor to the proof of concept. This new technology is based on an existing chemical sensor that demonstrated selectivity and sensitivity. The current design aims to reduce human interaction and the use of heavy equipment during measurements. The second design constraint is the passivity of the sensor toward the biological field containing its target. This would allow monitoring of the target and integration in a multisensor architecture.

The clean room process aims to be robust and reproducible for future integration of the sensor in an acquisition chain able to generate large quantities of normalized data. The second goal of the process design is to allow the production of large series of sensors at low unitary cost. This thesis manuscript presents the research work leading to the design of the new architecture followed by the design of the manufacturing process. Then the realization results are presented with the trials leading to the characterization of CNTFETs readily modified for selective biosensing.