G Wenga

E Jacques

A-C Salaün
email: asalaun@univ-rennes1.fr

R Rogel

L Pichon

F Geneste

Step-gate polysilicon nanowires field effect transistor compatible with CMOS technology for label-free DNA biosensor

Keywords: Polycrystalline silicon nanowire FET (poly-Si NW FET), Bio-sensor, DNA hybridization, Spacer formation technique, CMOS compatibility

Currently, detection of DNA hybridization using fluorescence-based detection technique requires expensive optical systems and complex bioinformatics tools. Hence, the development of new low cost devices that enable direct and highly sensitive detection stimulates a lot of research efforts. Particularly, devices based on silicon nanowires are emerging as ultrasensitive electrical sensors for the direct detection of biological species thanks to their high surface to volume ratio. In this study, we propose innovative devices using step-gate polycrystalline silicon nanowire FET (poly-Si NW FETs), fabricated with simple and low cost fabrication process, and used as ultrasensitive electronic sensor for DNA hybridization. The poly-SiNWs are synthesized using the sidewall spacer formation technique. The detailed fabrication procedure for a step-gate NWFET sensor is described in this paper. Nocomplementary and complementary DNA sequences were clearly discriminated and detection limit to 1fM range is observed. This first result using this nano-device is promising for the development of low cost and ultrasensitive polysilicon nanowires based DNA sensors compatible with the CMOS technology.

Introduction

DNA detection technology has been developed rapidly due to its extensive application in clinical diagnosis, bioengineering, environmental monitoring, and food science areas. In particular, successful healthcare in the near future will largely rely on a precise diagnosis of a pathological state and knowledge of particular features of the patient relevant for the disease.

This "personalized medicine" is expected to yield both better therapeutic results and cost reduction, and is the subject of intense research efforts. In particular, biomarkers have received great interest as tools for early disease detection, diagnosis and treatments in cancer, cardiovascular diseases or even non-invasive prenatal diagnosis. Among these biomarkers, circulating nucleic acids (DNA, mRNA and miRNA) are gaining great attention in several pathologies, because their detection is minimally invasive (blood sample), acceptable to patients, and highly accurate. Much attention has been paid on the development of miniaturized and sensitive detection methods for detection of these nucleic acids. There are several obvious advantages related to the miniaturization of biological sensors: i) reduction of sample and reagent consumption, ii) increase of the sensitivity and specificity, iii) low cost systems requirements, iv) cost-effective disposable chips because of mass production, v) better process control, because of a faster response of the system [Furuberg et al., 2008].

Development of new technologies for biomarkers detection involves both biological and economic challenges. The cost reduction is a major key for the future widespread applications of the devices in biomedical diagnoses that require mass production devices. Low cost and portable devices for rapid analysis of biomarkers may then revolutionize disease diagnosis and healthcare. In this study, we propose simple and low-cost silicon nanowires based sensor for specific nucleic acids detection.

Silicon nanowires have recently been developed as transducers for ultrasensitive biosensors and chemical sensors [Lin et al., 2009;[START_REF] Gao | Silicon Nanowire Arrays for Label-Free Detection of DNA Anal[END_REF]Stern et al., 2007;Patolsky et al., 2006, Wu et al., 2009]. As their surface can be sensitive to charged species combined with their small size and high surface to volume ratio, silicon nanowires (SiNWs) are the subject of intense research activities for high sensitivity sensor fabrication. The highly sensitive detection based on silicon nanowires enable a change in current due to a field-effect, when the analytical molecules bind to specific recognition molecules at the surface of the nanowire [Elfström et al., 2007]. Because SiNWs synthesis can be compatible with the established silicon technology, enormous research efforts to design and develop new generation of high performance biological and chemical sensors by incorporating the SiNWs as the functional sensitive units are performed. SiNWs based sensor integration will allow reliability and lower manufacturing cost, in addition to the advantageous electronic features of embedded detection and signal processing in silicon technology. Many articles have recently reviewed different approaches for silicon nanowire synthesis. The growth of SiNWs can be achieved in a topdown approach, by using sophisticated expensive lithography techniques, or in a bottom-up approach [Patolsky et al., 2005] by self-assembly growth. The latter approach, however, suffers seriously from the difficulty in precisely positioning the device location. It is a major difficulty to the potential device integration and the reliability of the SiNWs-based sensors. In a top-down approach, SiNWs can be prepared using various advanced methods such as ebeam, AFM or deep UV lithography techniques. Excellent electrical properties of monocrystalline silicon nanowires for biosensing have been demonstrated in the literature on Silicon-On-Insulator wafers [Stern et al., 2007;Li et al., 2004;[START_REF] Cui | Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species[END_REF]. The main disadvantage of these methods using advanced lithographic tools with nanometer size resolution rests on the high cost generated. Recently, an interesting approach has been demonstrated to synthesize polycrystalline silicon nanowires (poly-SiNWs) using a classical fabrication method commonly used in microelectronic industry: the sidewall spacer formation technique [Hsiao et al., 2009;Lin et al., 2009;[START_REF] Demami | Fabrication of polycrystalline silicon nanowires using conventional UV lithography[END_REF][START_REF] Demami | Silicon nanowires based resistors as gas sensors[END_REF]. Assets of this technological process rest on low cost lithographic tools use, classical silicon technology compatibility and the possibility to get numerous parallel nanowires with precise location on the substrate. Throughout the fabrication, no expensive lithography tools are needed for definition of nano-scale patterns. The detailed fabrication procedures for a step-gate NWFET sensor is described in this paper and we will show that the proposed method, low-cost and simple, is potentially suitable for future practical manufacturing. Here, we demonstrate that the step-gate SiNW FETs can be used as highly sensitive biological sensor for DNA hybridization detection. 25-mer no-complementary and complementary DNA strands will be used as a proof of concept. This first result suggests that this nano-device is promising for the development of low cost and label-free polysilicon nanowires biosensor compatible with the CMOS technology.

Materials and methods

Materials

3-Aminopropyltriethoxysilane (APTES) and glutaraldehyde (25%) in aqueous solution were purchased from Sigma-Aldrich. All synthetic oligonucleotides were purchased from EUROFINS MWG including 5-amino-modified DNA probe (NH2-5'-TCA-ATC-TCG-GGA-ATC-TCA-ATG-TTA-G3'). Two 25-bases sequences are used as targets: complementary target (5'CTAACATTGAGATTCCCGAGATTGA3'), non complementary DNA target (5'TAAAGCCCAGTAAAGTCCCCCACC3'). Fluorescently DNA 5-amino-modified and 3'fluorescein modified DNA (NH2-5'-TCA-ATC-TCG-GGA-ATC-TCA-ATG-TTA-G3'-flu) are used as probes. Phosphate buffered solution (PBS) with pH 7.4 was purchased from Sigma-Aldrich.

Fabrication of poly SiNW FETs

Polysilicon nanowires field-effect transistors are fabricated using a 5 masks process. The process described below is CMOS compatible and the maximum temperature process doesn't exceed 600°C, which means that sensors can be fabricated on silicon substrate as well as on inexpensive glass substrates. N-type transistors with various parallel polysilicon nanowire channels are fabricated using the sidewall spacer method described below. This method is commonly used in submicron scale device silicon technology to insulate device active area. In our case, the spacer at nanometric scale made of polysilicon constitutes the nanowire. This is an alternative way to synthesize SiNWs in a 2D configuration, and it allows the fabrication of parallel SiNWs network over a large area in coplanar structure. The key nanowire fabrication steps are illustrated on figure 1. At first, substrate is covered with a SiO 2 dielectric film deposited by APCVD (Atmospheric Pressure Chemical Vapor Deposition) at 420°C. Then, a 100nm thick in-situ doped silicon layer is deposited by LPCVD (Low Pressure Chemical Vapor Deposition) in an amorphous state at 550°C and crystallized by thermal annealing under vacuum at 600°C during 12 hours. After patterning, a reactive ion etching (RIE) leads to the formation of the step-gate (Fig. 1a) covered by a 100nm thick APCVD oxide acting as gate insulator (Fig. 1b). After, two layers of polysilicon are successively deposited. The first one is an undoped layer and the second one is a heavily in-situ N-type doped polysilicon layer (Fig. 1c). A patterning and a plasma etching are achieved to create an aperture in the gate insulator (Fig. 1d). The two layers (undoped polysilicon and heavily doped polysilicon) are successively etched. Accurate control of the polysilicon layers etching rate leads to the formation of nanometric size sidewall spacers used as undoped nanowires (Fig. 1e). Source and drain regions are made of heavily in-situ N-type doped polysilicon. Then, the polysilicon nanowires are capped with a 70nm thick APCVD oxide. Finally, an aluminum layer is deposited by thermal evaporation (Fig. 1f) and patterned to define gate, source and drain contacts (Fig. 1g). Fig. 2 shows a SEM image of a polysilicon nanowire obtained by sidewall spacer formation technique.

Surface modification for probes immobilization

Probes immobilization is performed by functionalization of the SiNW capping layer (SiO 2 ).

Figure 3 describes the procedure used to immobilize the DNA strands onto the nanowires surface. At first, such functionalization of the SiNW devices is carried out using APTES to convert surface silanol groups (SiOH) to amines. The silicon atom in the molecule of APTES will perform a chemical bond with the oxygen of the hydroxyl group. Samples are heated to 100°C for one hour to ensure complete drying of the surface to be treated as the APTES reacts rapidly in contact with water, then samples are immersed in an APTES vapor for five minutes and then re-heat to 100°C for one hour. After this first step, amino groups (NH 2 ) are the terminal units from the surface. Next, Glutaraldehyde is used as a grafting agent for DNA immobilization. Glutaraldehyde binding is achieved through its aldehyde group (COH) that will ensure a chemical bond with the amino group of APTES. For this step, samples are placed in a desiccator under vacuum containing glutaraldehyde in liquid state that evaporates and settles on the samples during 12h at room temperature. For probes immobilization, 3'amino group of DNA strands are linked to the aldehyde groups of the linker. A 10µl drop solution of synthetic 400ng/µl DNA probes is deposited onto the NWs for 1h. The major challenge in surface modification is the control of DNA probes immobilization over functional groups. To check the efficient probes immobilization, fluorescently DNA probes modified with fluorescein are immobilized and fluorescence images are observed.

Target DNA hybridization

After probes immobilization, a drop with DNA targets is deposited on the nanowires surface to hybridize to the DNA probes. Complementary and no-complementary targets are used, with various concentrations after dilution with PBS solution. After 1h, samples are washed with PBS to remove excess targets and NWFET static electrical characteristics are performed.

Results and discussion

Electrical measurements of the step-gate poly-Si NWFETs

Static electrical characteristics are collected at room temperature using a HP4155B semiconductor parameter analyzer. Figure 4 presents output I D -V DS and transfer I D -V GS characteristics for the 70nm curvature radius SiNW based n-channel FET. Fig. 4a highlights the field effect modulation of drain current with positive gate voltage, linear and saturation regions are observed. Transfer characteristic (fig. 4b) shows current drain switched between 'on' and 'off' state by varying potential of the gate electrode and the switching ratio between 'on' and 'off' state is ~ 1.7x10 4 . Threshold voltage, V T , and optimum field effect mobility, µ FE , are determined according to the classical electrical conduction model used for the MOSFET (Metal Oxide Semiconductor Field Effect Transistor). µ FE is deduced from the maximum slope of the I D -V GS curve plotted in the saturation mode, and V T is determined by the intercept of the I D -V GS curve in linear mode with the gate axis voltage. The field effect mobility (~ 60 cm 2 /V.s) and the high threshold voltage (V T 7.5 V) values are related to the poor crystalline quality of the channel. Indeed, note that the step-gate NWFET channel is located on the sidewall of the patterned gate (fig. 5) which is the lateral seed layer containing a higher defect density than the upper polycrystalline SiNW surface. Electrical properties of polycrystalline silicon are strongly controlled by defects caused by dangling bonds and strained bonds within the grain boundaries [Fortunato, 1997]. These grain boundaries and intergranular defects as well as gate insulator/SiNWs interface defects mainly located in the channel region degrade the carrier transport. However, the influence of the gate voltage on drain current shows that the device can be sensitive to charged molecules. In particular, negative charges carried by the phosphate groups of DNA bound onto NW surface will play the role of chemical gates that exert an electric field.

Probes immobilization

Electrical response after DNA hybridization

Hybridization phenomenon is detected on electrical characteristics of the SiNWFET. The transfer characteristic of the transistor after probes immobilization is used as reference (see circles in figure 7). Then, we load a drop of a solution containing a complementary DNA targets (concentration 10fM) on the transistor. After incubation and rinsing, we observe (see squares in Figure 7) a shift of the characteristic in the direction of the lower positive voltages (negative shift) due to the detection of negative charges carried by the phosphate groups of the hybridized complementary DNA. Indeed, negative surface charges act as chemical gate that exert an electric field, inducing a cumulative effect with a positive bias voltage in n-channel formation. Since the surface charge acts as an additional gate, current in the n-channel of the NW-FET at fixed positive step-gate bias increases if negative concentration increases on the surface. As a result, lower threshold voltage of the I D -V GS curve of the NWFET is observed.

In addition, non-complementary DNA targets have been tested to check specific hybridization. We observed that the electric characteristics remained unchanged, indicating that no additional charges were present on the surface and also that there is no-specific binding of DNA targets on glutaraldehyde.

These preliminary results indicate that specific DNA molecules may be detected using the SiNW technology described in this paper. The detection range and the lowest detectable concentration have been estimated. The relationship between current variation (ΔI D = I D targets -I D probes for V GS =8V) and target concentration is plotted on figure 8, and reveals a logarithmic dependence. Concentration as weak as 1fM is detected and this first result using innovative step-gate polysilicon nanowires field effect transistor is promising for the development of low cost and ultrasensitive polysilicon nanowires based DNA sensing applications compatible with the CMOS technology.

Conclusions

The detailed fabrication procedure for a step-gate polysilicon NWFET sensor is described. We demonstrate that this device can be used as biological sensor for detection of DNA hybridization. This sensor has experimentally demonstrated its high sensitivity using synthetic sequences as probes and targets. No-complementary and complementary sequences were clearly discriminated and detection limits to 1fM is achieved. Thus, the poly-Si NW FET can be an interesting alternative to conventional DNA-hybridization detection because, in a few minutes, they can analyze biomolecular interactions in realtime and in a label-free way. The first results are promising for the development of low cost, label-free and sensitive polysilicon nanowires based DNA sensing applications compatible with the CMOS technology. Fabricate a large amount of devices, control the electrical properties and reduce the cost to a reasonable range will be an important issue for using Si NW FET in biomedical applications. Next studies will focus on the sensitivity limitations, in particular on the detection of DNA mutations which is of crucial interest in molecular biology. Particularly, it is a relevant tool for the diagnosis of several diseases, like some types of cancer related to inherited mutations.

Figure captions

Fluorescently

  DNA probes modified with fluorescein are immobilized on unmodified surface and on functionalized surface. Fluorescence images are observed to check the efficiency of probes immobilization. DNA strands cannot be linked on the nanowire without functionalization and thus the fluorescence was not observed on fig 6-a. The intensity of fluorescence on sample with functionalization suggests effective DNA strands immobilization (fig.6-b).

Figure 1 .

 1 Figure 1. Key fabrication steps of poly-Si NW FET. (a) Step-gate formation on a Si substrate

Figure 3 .

 3 Figure 3. Schematic of poly-Si nanowire surface functionalization of. (1) The APCVD oxide

Figure 4 :

 4 Figure 4: Electrical characterization of poly-Si NWFET: a) output characteristics I D -V DS and

Figure 5 :

 5 Figure 5: Schematic illustration of structural defects in the core of the polycrystalline silicon

Figure 6 :

 6 Figure 6: (a). Functionalized surface without DNA. (b) Fluorescence observed after DNA

Figure 7 :

 7 Figure 7: I D -V GS curves obtained from a functionalized step-gate poly-SiNW transistor (2

Figure 8 :

 8 Figure 8: Poly-Si NWFET (L=3µm) drain current shift versus target DNA concentration. The

Fig

  Fig. 2.

  Fig.3

Fig. 5

 5 Fig. 5

Fig

  Fig. 6.

  Fig. 7

Acknowledgments

This work was supported by the Agence Nationale de la Recherche (France) with the Project Sena (ANR-09JCJC-0072-01).


Olivier Moles

Annalisa Caimi
email: annalisa.caimi@gmail.com

DISASTER RISK REDUCTION THROUGH LOCAL KNOWLEDGE AND CAPACITIES ENHANCEMENT Local resources and multilevel cooperation: towards long-term prevention strategies

Keywords: Local building culture, disaster risk reduction, community-based approach, knowledge and technology transfer

In disaster prone areas, local communities have always faced natural hazards and, over time, have managed to develop different strategies to prevent and/or reduce their impact. Local builders have often integrated natural risks into their daily practices, developing in many cases singular techniques, building details or devices aiming at reducing the vulnerability of the built environment. Such indigenous knowledge can contribute to the development of disaster-resistant engineering through the analysis of vernacular building practices and the potentials offered by locally available resources (materials, knowledge and know-how). The aim of this article is to illustrate a number of practices based on an action-research process, integrating elements of local building cultures, and proposing a methodology for the enhancement of local capacities and know-how through technology transfer and knowledge sharing

INTRODUCTION

Around 75% of the world's population lives in areas that were affected by earthquakes, hurricanes or floods between 1980and 2000(UNDP 2004). Since then, social, political and environmental factors have led to an increased number of people having to deal with the impact of major natural phenomena (UN / ISDR 2009). Major disasters mobilize humanitarian aid to support the recovery of affected populations. Since the 1990s, risk reduction principles have been integrated as part of the support policies to assist affected populations, including the implementation of preventive measures designed to alleviate the existing separation between emergency and development measures (1). Since then, the post-disaster reconstruction phase has become a valuable opportunity to implement measures aiming at reducing the vulnerability of people and their built environment, in the long-term [START_REF] Abhas | Safer Homes, Stronger Communities. A Handbook for Reconstructing after Natural Disaster, Global Facility for Disaster Reduction and recovery[END_REF].

But it is only in the past ten years that some of the actors involved in reconstruction practices have started to implement approaches oriented towards the active involvement of beneficiary communities in the decision-making process and the management of reconstruction, with technical financial support provided by aid agencies [START_REF] Arshad | Urban Housing Reconstruction and Land Management[END_REF] (2). However, if the involvement of beneficiaries can encourage the reactivation and strengthening of social dynamics, very often the technologies offered by aid agencies do not guarantee the autonomy and capacity of the populations to deal with the management and prevention of risks associated with housing in the long run (Davindson et al 2007).

In areas prone to natural hazards, many of the buildings that make up the built environment are constructed almost exclusively through the experience and direct observation of builders (masons, artisans or local populations) without the support from an engineer or an architect. In relation to the frequency and intensity of natural hazards, some societies have managed to develop constructive and morphological features to provide solutions so as to reduce their impact, revealing a level of mastery in terms of architectural design and risk management [START_REF] Ferrigni | Ancient Buildings and earthquakes, The Local Seismic Culture approach: principles, methods, potentialities[END_REF].

Although the reproduction of such constructions is in itself proof of the relevance and reliability of these techniques, socio-cultural and environmental factors have lead to a loss of interest on the part of people to continue implementing traditional constructions. Also, difficulties in the application of validation methods to prove the relevance of such traditional knowledge by the scientific community make it difficult for experts and technicians to teach and implement these techniques in the field, hindering the development of norms and technical documentation.

CASE STUDY: A MULTILEVEL APPROACH

Over the course of 30 years, the French association CRAterre has developed an approach dynamically linking analysis, research, experimentation and the implementation of projects, between field practice and academic research. The cases below illustrate two specific principles defining CRAterre's processes:

Bringing technical support to strengthen the knowledge and skills in the field of construction, based on local practices and know-how. The analysis of architectures, resources and potentials existing on the site is the starting point for the development, in consultation with local communities, of improvements and / or new building solutions, through training and educational approaches.

Linking various stakeholders around a common issue (local communities, universities, aid agencies and donors) to establish a synergy of skills and knowledge. The exchange between various institutional entities (universities, organizations) and scopes of action (local, regional, international) represent an important factor, allowing for the implemented strategies to adapt to local capacities, availabilities and potentials.

Haiti: valorization of local resources and skills

On January 12th, 2010 an earthquake of magnitude 7.0 struck Haiti. The farmers' organization Vive l'Espoir pour le Développement Kapwouj (VEDEK), working around Cap Rouge, sought support from Secours Catholique / Caritas France (SC/CF), for the repair of 100 houses on the basis of a financial aid adapted to the needs and capacities of each beneficiary. Aid was thus based on the damage caused to the houses and to the owners' abilities to contribute to their reconstruction, which allowed as many families as possible to benefit from the project.

Through this proposal, VEDEK aims to implement a longer-term vision regarding the identification of necessary technical improvements to reduce the vulnerability of buildings at risk in earthquake and hurricane prone areas, so that it may be integrated as part of current construction practices. SC/CF requested the assistance of CRAterre to support local partners in the process of evaluating needs, monitoring and determining constructive principles based on solutions adapted to local risks, potentials and capacities. A first on-site evaluation showed the relevance of vernacular building systems in relation to hazards affecting the area. The building systems implemented do take into account the impact of recurrent cyclones. Also, during the earthquake, they allowed the main structure of the buildings to resist, reducing the damage on the structures and greatly reducing the risks faced by the people inside the buildings.

To enable the reproducibility of the proposed improvements, two criteria are decisive: the access to materials and the availability of skills to implement constructive principles locally.

The use of materials available on the site, and commonly used for construction, has been privileged. The repair of houses was thus based on the recycling of debris and elements present as part of the existing structures, for rehabilitation purposes but also for the implementation of future constructions.

The development of local expertise in the field of construction in risk-prone areas was provided through training sessions aimed at local craftsmen from all over the region of Cap Rouge, making their new skills available to the whole population. Damaged houses were used as support for the explanation of the techniques that the artisans then put into practice on their own. Meanwhile, a sensitization campaign aimed at building professionals and the general public was conducted through radio broadcasts, site visits and meetings with project stakeholders. In this project, external interventions, both technical and financial, were calibrated to allow the local population to continue to integrate the new architectural proposals and gain access to the skills acquired by the artisans during training. Repairing housing structures while explaining their shortcomings to owners, enhancing and improving the existing building methods, suggesting technical solutions adapted to local capacities and resources, training and informing beneficiaries and stakeholders within the local construction sector are factors that can contribute to build capacities in local communities and foster the process of reducing vulnerability, in sustainable and accessible ways.

Bangladesh: synergy of knowledges

On November 15th, 2007, Bangladesh was hit by cyclone Sidr, a large cyclone which caused great devastation. Secours Catholique/Caritas France (SC/CF) and its partner Caritas Bangladesh (CB) became quickly involved in a project to rebuild homes. The first models available were the result of studies conducted by engineers and technicians, based on solutions and technical features which, although scientifically validated, did not include formal and constructive elements already present in the local architecture. The lack of integration of local building practices on the part of academic experts has sometimes led people to discredit and mistrust the solutions they themselves had developed against risk.

With technical support from CRAterre, a collaboration was then established between stakeholders working directly on the site and the Bangladesh University of Engineering and Technology (BUET), with the intention of improving the proposed solutions by deepening the study of local building cultures, associating them with some of the latest scientific results conducted on housing structures. In May 2009, a second cyclone, Aila, hit the areas previously affected, encouraging all partners to work together to develop a national emergency preparedness plan. A second project was launched, aimed at both strengthening the capacities of communities to cope with potential crises though their active involvement in all the stages of the project and the improvement of housing, and enhancing the actions implemented by CB in terms of speed and adequacy of response.

Bangladesh is affected by many natural hazards (cyclones, floods, earthquakes), but it also offers great diversity in terms of building materials (bamboo, earth, wood), and the ways of life of its people. Standard solutions, both methodological and technical, would not lead to appropriate results adaptable to different contexts and populations. Through the contribution of local disaster management committees, CB proceeds to the definition and analysis of different homogenous territories, according to local risks, building practices, resources and social customs. For each of these defined areas, prevention strategies will be implemented and reconstruction programs will be reviewed by BUET and CB, with the design of low cost housing adapted local conditions. The gathering of between different levels of research and action (local communities, universities, grassroots organizations, donors) and the synergy between the various stakeholders can benefit from the knowledge and skills specific to each group, and help create databases of sustainable strategies ,technically and scientifically validated, truly adapted to local contexts and building practices.

Awareness on the part of technicians and academic experts of the relevance of some of the solutions present in vernacular architecture adds value to the knowledge developed by local populations, but also pave the way for research to make technical improvements including the understanding and validation of scientific principles developed empirically, locally.

LINKING KNOWLEDGE, EXCHANGING KNOW-HOW

First, by taking local potentials into account (materials, skills, knowledge, technical and financial means) allows local populations to build, maintain, repair and extend any building in a sustainable way, while reinforcing the skills of local builders.

Second, by creating opportunities for cooperation between different institutional structures (universities, laboratories, NGOs and government structures, other entities...), which may encourage the scientific study of techniques and local knowledge, promote their integration as part of vocational and academic programmes, allow their use in the definition of building norms and technical support available to different targeted groups (local populations, artisans, technicians, policy makers).

The development of an approach based on the creation of links between research, experimentation and practice in the field has the potential to promote a consistent process of enrichment of the different dynamics that can lead to reducing the vulnerability of communities the long term, contributing in their evolution towards self-determination.

Fig. 1 -

 1 Fig.1 -Haiti, Cap Rouge: local architecture (credits: Annalisa Caimi, 2011).

Fig. 2 -

 2 Fig.2 -Haiti, Cap Rouge: training of local masons for housing repair (credits: CRAterre, 2010).

Fig. 3 -

 3 Fig.3 -Haiti, Cap Rouge: creating public awareness (credits: CRAterre, 2010).

Fig. 4 -

 4 Fig.4 -Bangladesh: local architecture presenting features (pitched roof, natural wind breakers, high plinth) allowing for a better resistance to cyclones and floods (credits: CRAterre, 2009

Fig. 5 -

 5 Fig.5 -Bangladesh: assessment of local constructions (credits: CRAterre, 2009).

Fig. 6 -

 6 Fig.6 -Bangladesh: shelter provided by CB after cyclone Sidr, integrating features from the local building culture (credits: CRAterre, 2009).

  UN/ISDR (2009). Indigenous Knowledge for Disaster Risk Reduction: Policy Note. Bangkok: European Union. UN/ISDR (2008). Indigenous Knowledge for Disaster Risk Reduction: Good Practices and Lessons Learned from Experiences in the Asia-Pacific Region. We must, above all, shift from a culture of reaction to a culture of prevention." (K. Annan). International Decade for Natural Disasters Reduction 1990-1999 (United Nations) ; Hyogo Framework for Action 2005-2015; Disaster Preparedness Programme -DIPECHO (European Commission Humanitarian Aid).(2) Owner Driver Reconstruction Approach, some examples : Post-earthquake reconstruction in Gujarat, India (2001) ; Post-tsunami reconstruction in India and Sri Lanka (2004) ; Post-earthquake reconstruction in Northern Pakistan (2005) ; Post-earthquake reconstruction in Haiti (2010).Oliver Moles, associate research professor, CRATerre-ENSAG laboratory (France). Since 1990, Oliver Moles has initiated monitored and evaluated programmes for the promotion and upgrading of local building cultures constructive in over 30 countries, under the aegis of various organizations (UNESCO, UNIDO, FAO, UNDP, UN Habitat, MISEREOR, CARITAS, IFRC…).Annalisa Caimi, architect EPFL (Switzerland). Between 2005-2007, she developed a research on bamboo construction in India. In 2010, she obtained a post-master's degree on Earth Architecture at CRAterre-ENSAG (France). She is currently doing a PhD, at the National School of Architecture in Grenoble on indigenous building technologies related to natural hazards.

	Bangkok: European
	Union.
	UN/ISDR (2009). Risk and poverty in a changing climate. Invest today for a safer
	tomorrow. Global Assessment Report on Disaster Risk Reduction. Geneva: United
	Nations.
	UNDP (2004). Reducing Disaster Risk: a Challenge for Development. A Global Report.
	New York: Bureau for Crisis Prevention and recovery, United Nations Development
	Programme.
	Notes :
	(1) " Curriculum :