Angeliki Tataridou
email: angeliki.tataridou@grenoble-inp.fr

Gerard Ghibaudo

Christoforos Theodorou

Influence of series resistance on the experimental extraction of FinFET noise parameters

In this paper we demonstrate for the first time how the series resistance of an advanced CMOS device, such as the FinFET, can lead to an incorrect extraction of low-frequency noise parameters. In particular, the use of the carrier number fluctuations with correlated mobility fluctuations model is shown to be very sensitive to the transistor series resistance. We demonstrate how the classic fitting methods can lead to an underestimated value in the extraction of the mobility fluctuations factor Ω. Furthermore, we present an original method for suppressing this effect, by taking advantage of the series resistance immune Y-function.

I. INTRODUCTION

Low frequency noise (LFN) is attracting more and more interest in the last years, since it not only characterizes a device performance in terms of dynamic stability [START_REF] Ghibaudo | Impact of Scaling Down on Low Frequency Noise in Silicon MOS Transistors[END_REF], but can also give significant information about the defects inside the oxide [START_REF] Fleetwood | 1/f Noise and Defects in Microelectronic Materials and Devices[END_REF] or silicon [START_REF] Lukyanchikova | Non-trivial GR and 1/f noise generated in the p-Si layer of SOI and SOS MOSFETs near the inverted front or buried p-Si/SiO2 interface[END_REF] which is valuable especially in today's aggressively scaled devices like FinFETs [START_REF] Theodorou | Flicker noise in n-channel nanoscale tri-gate fin-shaped field-effect transistors[END_REF], [START_REF] Achour | In depth static and low-frequency noise characterization of n-channel FinFETs on SOI substrates at cryogenic temperature[END_REF]. The utilization of LFN for the assessment of the oxide/silicon interface quality requires the reliable extraction of noise parameters such as the trap density, N t , and the remote Coulomb scattering coefficient, α sc . This extraction is achieved using the well-established [START_REF] Ghibaudo | Improved Analysis of Low Frequency Noise in Field-Effect MOS Transistors[END_REF], [START_REF] Ioannidis | Improved analysis and modeling of lowfrequency noise in nanoscale MOSFETs[END_REF], [START_REF] Ioannidis | Drain-Current Flicker Noise Modeling in nMOSFETs From a 14-nm FDSOI Technology[END_REF] carrier number fluctuations with correlated mobility fluctuations (CNF/CMF) model [START_REF] Ghibaudo | Impact of Scaling Down on Low Frequency Noise in Silicon MOS Transistors[END_REF], which considers both the change of the flat-band voltage (V FB ) following the trapping/detrapping of free carriers and the mobility change due to the interface charge fluctuations [START_REF] Ghibaudo | Improved Analysis of Low Frequency Noise in Field-Effect MOS Transistors[END_REF].

S I d I d 2 = (1 + Ω I d g m ) 2 ( g m I d ) 2 S V FB (1)
S Vfb is the flat-band voltage fluctuations power spectral density, and Ω is the CMF coefficient given by [START_REF] Fleetwood | 1/f Noise and Defects in Microelectronic Materials and Devices[END_REF].

S V FB = q 2 λkTN t WLC ox 2 𝑓 γ , Ω = α sc μ eff C ox (2)
where, 𝜇 𝑒𝑓𝑓 is the effective mobility and 𝐶 𝑜𝑥 the oxide capacitance per unit area, λ is the tunneling constant in the dielectric (≈ 0.1 nm), kT is the thermal voltage, q is the elementary charge of electrons, f the frequency, γ the characteristic exponent close to 1, N t the volumetric trap density and W, L the channel width and length respectively.

This extraction is generally reliable in the case of long channel devices. However in short channel devices, the series resistance (R SD ) can degrade a FinFET's performance because it becomes important with respect to the reduced channel resistance. Therefore, the use of experimentally measured quantities such as the device extrinsic transconductance, g m , for the noise parameter extraction through (1) may jeopardize the precision of the extraction procedure. In this work we study, for the first time, the impact of R SD on the low-frequency noise (LFN) parameter extraction.

II. EXPERIMENTAL APPROACH AND DEVICE UNDER TEST

A very useful quantity in the LFN characterization and modeling is the input-referred gate voltage noise S Vg = S Id / g m 2 . It suppresses the impact of g m on the measured noise and expresses every fluctuation as a gate voltage variation, which allows for easier model implementations in circuit simulations. Concerning its application in the extraction of LFN parameters, a method very often used by our team in recent works [START_REF] Ioannidis | Improved analysis and modeling of lowfrequency noise in nanoscale MOSFETs[END_REF], [START_REF] Ioannidis | Drain-Current Flicker Noise Modeling in nMOSFETs From a 14-nm FDSOI Technology[END_REF] is to extract Ω from the slope of √S Vg vs I d /g m , thanks to the expression of (3):

√ S V g = √ S V FB (1 + Ω I d g m ) (3)
which is derived from (1) after normalizing with (g m /I d ) 2 .

Nevertheless, this method is obviously sensitive to the I d /g m factor, which in turn is influenced by the presence of R SD . For this reason, it is rather questionable whether the extraction of Ω by this established method is reliable. In order to monitor how the increase of R SD can impact the extraction of Ω, we repeated the same LFN measurements on the same FinFET device for various combinations of externally connected resistors, R ext , at both the drain (R ext /2) and source (R ext /2) terminals. The setup schematic is shown in Fig. 1.

The device under study is a n-channel FinFET fabricated at IMEC-Leuven, with number of fins N fin = 22 nm, fin height H fin = 26 nm, channel length L = 28 nm and fin width W fin = 4.5 nm. The LFN measurements were performed using the programmable bias point probe system NOISYS7 [START_REF] Chroboczek | Low frequency noise point probe measurements on a wafer level using a novel programmable current amplifier[END_REF], combined with a semi-auto 300 mm Cascade Micro Tech probe station. The simulations were performed using the FlexPDE [START_REF]Flex PDE[END_REF] solver and the Python Spyder [START_REF]Spyder IDE[END_REF] platform.

III. RESULTS AND DISCUSSION

Measurements of static I d (V g ) transfer characteristics were performed in linear region (V d =30 mV) for different R values. As shown in Fig. 2, there is a significant drain current degradation with R ext in strong inversion. The same behavior can also be observed from the √S Vg vs I d /g m plot shown in Fig. 5, where we note that the slope of the characteristics changes with R ext . This behavior with the series resistance was also confirmed by simulations, as shown in Fig. 6, where R ch =V d /I d is the channel resistance in ohmic region. This effect takes place because the presence of R ext degrades g m /I d , thus leading to an increase of the I d /g m ratio, and shifts the experimental data points to the right, resulting to the unreliable extraction of the CMF factor Ω. Combining this finding with the fact that the intercept remains the same for all R ext values and thus a constant value of S Vfb can be extracted, we conclude that the diverging characteristics will lead in an underestimation of the Ω factor. By extracting S Vfb from Fig. 4 and by taking a mean value of 5.24x10 -11 V 2 /Hz for S Vfb , we pursued to the linear fit of (3) in Fig. 5 in order to calculate the Ω coefficient for the different R ext . The dependence of this 'apparent' Ω on the presence of R ext can be seen in Fig. 7. As expected, the extracted Ω factor is reduced with R ext , revealing an underestimation due to the specific extraction process.

IV. NEW EXTRACTION METHODOLOGY

To eliminate the impact of R SD on the Ω extraction we can take advantage of the Y function, which is immune to the influence of series resistance [START_REF] Fleury | New Y-function-based methodology for accurate extraction of electrical parameters on nanoscaled MOSFETs[END_REF] and is given by (4):

Y = I d √g m ⁄ (4)
Fig. 8 depicts the Y-function plot for all the cases implying that the R ext has been successfully compassed from the drain current. Henry et al. [START_REF] Henry | New Y-function based MOSFET parameter extraction method from weak to strong inversion range[END_REF] published a new Y-function extraction method where I d /g m can be replaced as in [START_REF] Achour | In depth static and low-frequency noise characterization of n-channel FinFETs on SOI substrates at cryogenic temperature[END_REF]:

I d g m = n kT q + Y √β ( 5
)
where n is the transistor ideality factor and β = V d μ 0 C ox W/L its gain factor.

The combination of ( 4) and ( 5) considering that nkT/q is negligible in the strong inversion region results to (6):

√ S V g = √ S V FB [1 + Ω ( Y √β )] (6)
Therefore, if we plot √𝑆 𝑉𝑔 vs Y instead of I d /g m , as shown in Fig. 9, we can obtain a linear dependence which is not affected by the change in R ext . This way a new, R SDindependent value of Ω can be extracted, combining all groups of points. We extracted a value of Ω = 6.5 V -1 , much higher than the one extracted when R ext = 0 Ω (1.75V -1 ), revealing that the CMF contribution can indeed be completely overshadowed by the presence of a high series resistance value. It might be argued that by plotting √𝑆 𝑉𝑔 versus (V g -V t ) would also give a straight line, but this is true when the mobility is degraded only due to the series resistance through the first order attenuation factor θ 1 ≈β*R SD /V d . However, in the possible presence of the second order mobility attenuation factor θ 2 , the linearity with V g -V t is lost [START_REF] Boutchacha | Improved modeling of lowfrequency noise in MOSFETs -Focus on surface roughness effect and saturation region[END_REF]. But if we use the Y-function expression [START_REF] Ioannidis | Improved analysis and modeling of lowfrequency noise in nanoscale MOSFETs[END_REF] [START_REF] Fleury | New Y-function-based methodology for accurate extraction of electrical parameters on nanoscaled MOSFETs[END_REF] that accounts for the influence of θ 2 , a great linearity is achieved, as illustrated in Fig. 10, allowing for the proper extraction of Ω.

Y′ = √ β 1 -θ 2 (𝑉 𝑔 -𝑉 𝑡 ) 2 (𝑉 𝑔 -𝑉 𝑡 ) (7)
Moreover, concerning the channel length influence on this effect, since the impact of series resistance becomes negligible in long channel devices, we expect that both I d /g m and Yfunction methods will give the same results. This was confirmed by simulations, where a 100 times longer channel was tested, for the same value of R SD = 1 kΩ. As can be seen in Fig. 11, the series resistance affects significantly the L = 0.1μm parameter extraction, whereas for L = 10μm there is no R SD influence on the extraction precision. Therefore, the Y-function method we propose is valid regardless the channel length.

V. CONCLUSION

The impact of R SD on the extraction of noise parameters and especially on the Ω coefficient has been studied for FinFETs of 4.5 nm wide channel. It was found that the degradation of g m /I d due to the presence of R SD results to the unreliable extraction of Ω and in high values of R SD the mobility fluctuation due to charged traps can be heavily underestimated. To respond to this challenge, a new extraction methodology is proposed which utilizes the Y-function to successfully eliminate the R SD influence.

Fig. 1 .

 1 Fig. 1. Experimental set-up for monitoring the R SD influence.

Fig. 2 .

 2 Fig. 2. Drain current versus gate voltage characteristics for various values of external resistance, R ext .

Fig. 3 .

 3 Fig. 3. Drain current noise power spectral density versus frequency for zero external resistance, R ext =0 Ω at various gate bias values in strong inversion.

Fig. 4 .Fig. 5 .

 45 Fig. 4. Normalized drain current noise vs drain current along with the CNF and CNF/CMF fitting models for the different external resistance values, R ext .

Fig. 6 .

 6 Fig. 6. Simulation results of square root of input-referred noise, √S Vg , versus the ratio of drain current and transconductance, I d /g m for various R SD /R CH ratios.

Fig. 7 .

 7 Fig. 7. Extracted CMF factor Ω versus the different R ext values.

Fig. 8 .

 8 Fig. 8. Y-function versus gate voltage for the different external resistance values.

Fig. 9 .

 9 Fig. 9. Square root of input-referred noise versus Y-function for the different external resistance values, R ext .

Fig. 10 .

 10 Fig. 10. Simulation results of square root of input-referred noise, √S Vg , versus different X variables.

Fig. 11 .

 11 Fig. 11. Simulation results of normalized with area square root of input-referred noise, WL√S Vg , versus different X variables.

ACKNOWLEDGMENT

The authors would like to acknowledge the Horizon 2020 ASCENT EU project (Access to European Nanoelectronics Network -Project no. 654384). They would also like to thank Thomas Chiarella and Jerome Mitard from IMEC-Leuven for their technical help and general support.


Ki-Sik Im
email: ksim@kumoh.ac.kr

Sung Jin An

Christoforos G Theodorou

Gérard Ghibaudo

Sorin Cristoloveanu

Jung-Hee Lee

J.-H Lee

Effect of Gate Structure on the Trapping Behavior of GaN Junctionless FinFETs

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Abstract-We investigated the performances of GaN junctionless nanochannel fin-shaped field-effect transistors (FinFETs) with two different types of gate structures; overlapped-and partially covered-gate. DC, low-frequency noise (LFN), and pulsed I-V characterization measurements were performed and analyzed together in order to identify the conduction mechanism and examine both the interface and buffer traps in the devices. The fabricated GaN junctionless device with overlapped gate structure exhibits improved DC and noise performance compared to the device with partially covered-gate, even though its gate length is much larger. The LFN behavior was found to be dominated by carrier number fluctuations (CNF). At off-state, the device with partially covered-gate exhibits generation-recombination (g-r) noise on top of 1/f noise. This superposition is correlated with the severe current collapse revealed by pulsed I-V measurements. In contrast, the device with overlapped gate shows clear 1/f behavior without g-r noise. Index Terms-GaN, Junctionless, Nanochannel, FinFET, Low-frequency noise, generation-recombination noise, Current collapse.

I. Introduction

ighly-doped Gallium nitride (GaN) nanochannel fin-shaped field-effect transistor (FinFET) without AlGaN/GaN heterojunction was initially proposed and demonstrated by our groups [START_REF] Im | Heterojunction-free GaN Nanochannel Finfets with High Performance[END_REF]- [START_REF] Im | High-Performance GaN-Based Nanochannel FinFETs With/Without AlGaN/GAN Heterostructure[END_REF]. The conduction mechanism of this transistor is governed by the bulk current flowing through the inside of the heavily-doped GaN nanochannel arrays, which is totally different from the two-dimensional electron gas (2-DEG) channel in AlGaN/GaN heterojunction FinFETs. The GaN junctionless device exhibited outstanding device performances (high I on /I off ratio, excellent subthreshold swing, and large breakdown voltage), added to its simple epitaxial growth and fabrication process [START_REF] Im | Heterojunction-free GaN Nanochannel Finfets with High Performance[END_REF]- [START_REF] Im | High-Performance GaN-Based Nanochannel FinFETs With/Without AlGaN/GAN Heterostructure[END_REF]. The fully gate-covered nanochannel structure has been adapted to GaN-based FinFET, omega FinFET, and gate-all-around (GAA) FET because this architecture provides superior device performances, such as improved on-current and reduced current collapse owing to decreased access resistance and less back-gating effect [START_REF] Im | High-Performance GaN-Based Nanochannel FinFETs With/Without AlGaN/GAN Heterostructure[END_REF]- [START_REF] Jo | AlGaN/GaN FinFET With Extremely Broad Transconductance by Side-Wall Wet Etch[END_REF].

Generally, GaN contains a large density of defects, impurities, and dislocations due to the lack of native substrate material. These defects can behave as charge trapping centers, which gradually degrade the device performance and give rise to severe reliability concerns. Low frequency noise (LFN) measurements have great merits in analyzing the interface and/or oxide traps [START_REF] Mcwhorter | 1/f Noise and Germanium Surface Properties in Semiconductor Surface Physics[END_REF] and can also help identifying the conduction mechanism in semiconductor devices. There have been many studies dedicated to LFN for AlGaN/GaN MISHEMTs, AlGaN/GaN FinFETs, AlGaN/GaN omega FETs, AlInGaN/GaN Fin-HEMTs, and GAA FETs with/without AlGaN/GaN heterojunction [START_REF] Vodapally | 1/f-noise in AlGaN/GaN nanowire omega-FinFETs[END_REF]- [START_REF] Im | Low-Frequency Noise Characteristics of GaN Nanowire Gate-All-Around Transistors With/Without 2DEG Channel[END_REF]. It is generally admitted that the origin of the noise mechanism in most of GaN-based 3-dimensional (3D) devices is mainly due to the carrier number fluctuations (CNF) [START_REF] Mcwhorter | 1/f Noise and Germanium Surface Properties in Semiconductor Surface Physics[END_REF]. However, no detailed noise investigation has been conducted regarding the conduction mechanism of GaN junctionless FinFET. In this work, we characterize novel GaN junctionless FinFETs with two different types of gate structures, overlapped-and partially covered-gate, by considering DC, LFN, and pulsed I-V measurements.

II. EPITAXY GROWTH AND DEVICE FABRICATION

The heavily-doped GaN layer was simply grown on a sapphire (0001) substrate by metal organic chemical vapor deposition (MOCVD). The epitaxial layers consist of 2 μm-thick highly-resistive undoped GaN buffer layer and 150 nm-thick Si-doped n-type GaN layer which were sequentially grown on sapphire substrate. Hall effect measurements at room temperature showed a carrier density of 1 × 10 18 cm -3 , an electron mobility of 280 cm 2 /V•s, and a sheet resistance (R sh ) of 1490 Ω/sq.

Effect of Gate Structure on the Performance of GaN Junctionless FinFETs

Ki-Sik Im, Sung Jin An, Christoforos G. Theodorou, Gérard Ghibaudo, Fellow, IEEE, Sorin Cristoloveanu, Fellow, IEEE, and Jung-Hee Lee, Senior Member, IEEE H For the device fabrication, mesa etching for device isolation was performed using inductively coupled plasma-reactive ion etching (ICP-RIE) using a Cl 2 gas. After depositing a 20 nm-thick HfO 2 and 100 nm-thick SiO 2 hard mask layer, a fin pattern with fin width (W fin ) of 100 nm along <11-20> direction was defined by electron-beam lithography (EBL) and etched by ICP-RIE. A tetramethyl ammonium hydroxide (TMAH) wet solution (5% solution at 90 ºC) was applied to decrease the slope and size of the fin and to reduce the plasma damage and surface roughness [START_REF] Im | Fabrication of AlGaN/GaN Ω-shaped nanowire fin-shaped FETs by a top-down approach[END_REF], [START_REF] Kim | Effects of TMAH Treatment on Device Performance of Normally Off Al2O3/GaN MOSFET[END_REF], which resulted in 36 parallel fin arrays with width (W fin ) of 50 nm, height (H fin ) of 200 nm, and length (L fin ) of 2 µm. Si/Ti/Al/Ni/Au stack for ohmic contacts was then deposited by electron-beam evaporator, followed by rapid thermal annealing (RTA). Finally, Ni gate metal was deposited to form the gate length (L g ) of 0.5 µm and 2 µm for the partially covered-and the overlapped-device, respectively. It is noticed that L g of the FinFET with overlapped-gate structure is not the length of the gate metal, but rather corresponds to the L fin of the device. The device structure is illustrated in Fig. 1.

III. CHARACTERIZATION RESULTS AND DISCUSSION

Fig. 2 shows the drain current, transfer, and output curves of the fabricated GaN junctionless nanochannel FinFETs. Both devices show similar characteristics, such as a threshold voltage, V th , around -0.5 V, I on /I off ratio of 10 5 , subthreshold swing of 110 mV/dec, broaden transconductance g m , and low saturation voltage of ~ 3 V. The reason for the negative V th is the uncompleted depletion in off-state of the heavily-doped GaN fin channel with width of 50 nm. The broad g m curves that extend to a gate voltage (V g ) of 1.5 V indicate the improvement of the device linearity due to (i) the current contribution of surface accumulation channel formed at higher V g in addition to the channel current through the fin body and (ii) the small dynamic access resistance of the FinFETs [START_REF] Jo | AlGaN/GaN FinFET With Extremely Broad Transconductance by Side-Wall Wet Etch[END_REF], [START_REF] Lee | Nanowire Channel InAlN/GaN HEMTs With High Linearity of gm and fT[END_REF]. From the hysteresis under the double sweep of the V g in Fig. 2(a), it is clearly observed that the partially covered-device suffers from the severe trapping effect with high hysteresis of 220 mV when compared to the value of 40 mV for the overlapped-device. The maximum drain current (I d,max ) and maximum transconductance (g m,max ) are however different. The device with partially covered-gate is shorter (L g = 0.5 μm) and exhibits higher I d,max and g m,max values than those of the device with the overlapped-gate and L g of 2 μm. Even though the L g for the device with partially covered-gate is 4-times shorter than the device with the overlapped-gate, the I d,max for the partially covered-device exhibits only 1.4-times higher value than that of the overlapped-device due to the larger access resistance (Fig. 2(b) and Fig. 2(c)).

LFN measurements were performed at room temperature, varying the gate bias from subthreshold to strong accumulation region in the linear region at V d = 0.1 V. A fully automatic LFN measurement system from Synergie Concept is used in the frequency ranges from 4 Hz to 10 4 Hz [START_REF] Lee | Nanowire Channel InAlN/GaN HEMTs With High Linearity of gm and fT[END_REF]. The drain current noise spectral densities (S Id ) in Fig. 3(a According to the CNF model, LFN originates from trapping-related fluctuations in free carrier concentration, which is mostly ascribed to the trapping/detrapping of free carriers between the interface traps and the surface channel. The CNF equation can be expressed as follows, showing S Id /I d 2 is proportional to (g m /I d ) 2 [START_REF] Mcwhorter | 1/f Noise and Germanium Surface Properties in Semiconductor Surface Physics[END_REF], [START_REF] Ghibaudo | Improved analysis of low frequency noise in field-effect MOS transistors[END_REF],

𝑆 𝐼𝑑 𝐼 𝑑 2 = ( 𝑔 𝑚 𝐼 𝑑 ) 2 𝑆 𝑉𝑓𝑏 𝑤𝑖𝑡ℎ 𝑆 𝑉𝑓𝑏 = 𝑞 2 𝑘𝑇𝜆𝑁 𝑡 𝑊𝐿𝐶 𝑜𝑥 2 𝑓 (1)
where C ox is the gate dielectric capacitance per unit area, q is the electron charge, kT is the thermal energy, λ is the oxide tunneling attenuation distance, N t is the volumetric oxide trap density, WL is the channel area, and f is frequency. On the other hand, the Hooge mobility fluctuations (HMF) model, which is more suitable for explaining the conduction mechanism in the volume of devices [START_REF] Hayat | The excess noise in buried-channel MOS transistors[END_REF]- [START_REF] Jeon | Low-frequency noise behavior of junctionless transistors compared to inversion-mode transistors[END_REF], suggests that S Id /I d 2 is proportional to 1/I d [START_REF] Ghibaudo | Improved analysis of low frequency noise in field-effect MOS transistors[END_REF]. However, S Id /I d 2 of the devices investigated in this work is well proportional to (g m /I d ) 2 , as shown in Fig. 3, which indicates that the noise of the GaN junctionless FinFETs is dominated by CNF rather than HMF, even though the channel in the fin body is separated from the Al 2 O 3 /GaN interface by the depletion region. This noise characteristic is consistent with the observed results in Si junctionless FinFETs [START_REF] Akarvardar | Low-Frequency noise in SOI Four-Gate Transistors[END_REF]- [START_REF] Jeon | Low-frequency noise behavior of junctionless transistors compared to inversion-mode transistors[END_REF]. In these works, it was shown that the diffusion through the depletion region or direct tunneling from the bulk neutral region to the interface results in the flat-band voltage fluctuations [START_REF] Jang | Low-frequency noise in junctionless multigate transistors[END_REF]- [START_REF] Jeon | Low-frequency noise behavior of junctionless transistors compared to inversion-mode transistors[END_REF].

When matching S Id /I d 2 and (g m /I d ) 2 , the flatband voltage fluctuations (S Vfb ) are obtained to be 1 × 10 -8 V 2 •Hz -1 and 4.5 × 10 -9 V 2 •Hz -1 for the partially covered-and the overlapped-devices, respectively. Considering the actual gate length for the overlapped-device is L fin = 2 µm, the corresponding trap density (N t ) calculated using Equation (1) with λ = 0.11 nm is 2.1 × 10 20 cm -3 •eV -1 and 2.2 × 10 20 cm -3 •eV -1 [START_REF] Sakong | 1/f Noise Characteristics of Surface-Treated Normally-Off Al2O3/GaN MOSFETs[END_REF], lower than the values reported from the GaN-based 3D devices [START_REF] Vodapally | 1/f-noise in AlGaN/GaN nanowire omega-FinFETs[END_REF]- [START_REF] Im | Low-Frequency Noise Characteristics of GaN Nanowire Gate-All-Around Transistors With/Without 2DEG Channel[END_REF]. This result suggests that the trap density of the GaN junctionless device is lower than the interface trap density in devices with surface channel.

Fig. 4 shows S Id × f as a function of frequency at off-state (V g = -1 V) for variable V d from 0.1 V to 5.0 V. No spectral deformation is observed for the overlapped-device, which reflects that there is no generation-recombination (g-r) noise component because the noise well follows a 1/f behavior, even though the active channel of the devices becomes fully depleted at off-state. However, for the partially covered-device, the product S Id × f clearly presents two noise components: one is 1/f and the other is g-r noise, described through the following equation [START_REF] Theodorou | Origin of the low-frequency noise in n-channel FinFETs[END_REF].

𝑆 𝐼 𝑓 = 𝐾 𝑓 + ∑ 𝐴 𝑖 𝑓 1+( 𝑓 𝑓 𝑜𝑖 ) 2 𝑁 𝑖=0 𝑤𝑖𝑡ℎ 𝜏 𝑖 = 1 2𝜋𝑓 𝑜𝑖 (2)
where the first term explains the 1/f noise component with coefficient of K f and the second term is the sum of g-r noise components including the plateau value of A i , the cutoff frequency f oi , and τ i is the trap time constant. S Id × f for the partially covered-device (Fig. 4(b)) dramatically decreases at approximately cutoff frequency (f oi ) of 30 ~ 40 Hz due to the existence of g-r noise component, which indicates that the device has larger trap time constant in GaN buffer layer than that of the overlapped-device. In the overlapped-device buffer trapping is effectively reduced.

To further examine the buffer trapping effect observed from noise experiments, pulsed I-V measurements for both devices were conducted using Keysight B1500 semiconductor device analyzer with pulse width of 1 ms, as shown in Fig. 4(c) and(d). The pulse conditions are three quasi-bias of (1)

V g,Q = V d,Q = 0 V, (2) V g,Q = -2 V, V d,Q = 0 V, and (3) V g,Q = -2 V, V d,Q = 10 V.
The drain voltage is swept from 0 to 10 V at V g = 2 V. The partially covered-device exhibits relatively large current collapse for all pulse conditions. The reason for this large current collapse is the wider effective trapping region, the ungated region between the gate and the drain electrode as shown in Fig. 1 [START_REF] Im | Performance improvement of normally off AlGaN/GaN FinFETs with fully gate-covered nanochannel[END_REF], which includes the planar region between the gate and the drain, as well as the uncovered neutral fin array region which is not fully depleted. On the other hand, the overlapped-device shows much smaller current collapse, probably due to the reduced electric field at the gate edge caused by the overlapped gate structure along with smaller trapping region. The results obtained from the pulsed I-V characteristics of the GaN junctionless devices well match with the g-r noise performances at off-state.

  ) show 1/f γ shape with γ close to 1 in the entire frequency bandwidth. Regardless of the gate structure, both devices exhibit almost identical drain current noise level S Id at I d = 0.02 mA.

Fig. 1 .

 1 Fig. 1. Schematic illustration of the proposed GaN junctionless FinFETs (a) overlapped-and (b) partially covered-gate structure. Inset of Fig. 1(a) shows cross-sectional TEM image of the perfectly rectangular GaN nanochannel fin.

Fig. 2 .

 2 Fig. 2. (a) Transfer curves (double sweep of gate voltage) of the fabricated GaN junctionless FinFETs with overlapped-(filled rectangular) and partially covered-gate (empty rectangular) structure at Vd = 0.1 V. Corresponding Id -Vd curves for devices with (b) overlapped-and (c) partially covered-gate structure.

Fig. 4 .Fig. 3 .

 43 Fig. 4. Product SId × frequency versus frequency in the fabricated GaN junctionless devices with (a) overlapped-and (b) partially covered-gate structure at Vg = -1 V with Vd varied from 0.1 V to 5 V. Pulsed Id -Vd curves for the devices with (c) overlapped-and (d) partially covered-gate structure at Vg = 2 V sweeping Vd = 0 ~ 10 V.

Manuscript received Oct. 2019. This work was supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (MEST) (No. NRF-2018R1A6A1A03025761, NRF-2019R1I1A1A01064011). This research was partially supported by Nano•Material Technology Development Program through the NRF funded by the Ministry of Science, ICT and Future Planning (2009-0082580).

K.-S.


Ricard Zapata-Barrero

Carmen Itzel Ruiz

Hassan Bousetta

Yvan Gastaut

Maria Lucinda Fonseca

Abdelrahman Alamarah

Tamimi Phg

Angeliki Dimitriadi

Tamirace Fakhoury

Maria Gabrielsen Jumbert

Andrew Geddes

Adriana Kemp

Ferruccio Pastore

Mohamed Saib

Musette Cread

Algeria Peter Bouzaréa

Scholten

Musa Shtewi

Thomas Lacroix
email: thomas.lacroix@cnrs.fr

Louise Hombert

Keywords: City networks, migration governance, France, Italy, Spain

Mediterranean Migration Studies" (Acronym: EUMedMi) and coordinated

Background Rationale and Content

• In July 2018, a Euro-Mediterranean Research Network on Migration (EuroMedMig) was launched during the 15 th IMISCOE Annual Conference in Barcelona, with an initial composition of 18 Members in the Steering Committee. Countries covered are: Algeria, Belgium, Egypt, Europe (EUI), Greece, Israel, Italy, Jordan, France, Lebanon, Morocco, Palestine, Portugal, Spain, Norway, Netherlands, Tunisia and Turkey. It has initially received institutional support from The Union for the Mediterranean and academically recognized as an IMISCOE Regional Network.

Filippo Furri is PhD Candidate in Anthropology, Université de Montreal: his research focuses on migration and european reception policies. In particular, he has been working for several yearson "local/urban hospitality" and on the notion of a "refuge city". Currently he is a researcher associated with the MECMI (UQAM-LESC 2018-2021) research program (death in a migratory context) and with the Ecos-Sud C17H01 program (2018-2021): « La construction nationale à l'épreuve de l'"étranger" ». He is member of the Euro-African Network Migreurop, which analyzes European migration policies, and since 2018 he works as consultant for the ICRC and orther organizations (as Majalat/EuromedRights).

Suggested citation:

Lacroix, T., Hombert, L., and Furri, F. ( 2020) "Migration and municipal militancy in the Mediterranean."

EuroMedMig Working Paper Series, no. 4 (September):

Introduction

City networks involved in migration issues have mushroomed over the world. Some gather a few cities from a local or a national area, others spread their connections at continental or even global scales; some nurture a political agenda challenging migration policies, others provide guidance in immigrant integration; some are spontaneous initiatives of like-minded mayors, others are sponsored by national and international organisations such as the United Nations, the Council of Europe or the High Commission for Refugees (HCR) (Lacroix, forthcoming). The European Union has been a fertile ground for the development of such networks (Oomen 2019;Caponio 2018). Over the last two decades, the European Union and their member states have increasingly relied on cities and their groupings to support the implementation of a new generation of integration policies. A wealth of projects, institutions and forums have been funded by the EU and other international organisations to support city-level initiatives. But, with the security turn endorsed by state authorities in migration management, and more recently, the upcoming of populist leaders to official responsibilities, a new range of networks have appeared. More militant, more politicised, they express a critical voice with regard to current policies and advocate for alternative approaches to migration management.

The so-called "migration crisis" in 2015 and 2016 exacerbated the mobilisations of cities.

Cities facing the emergency of the immediate needs of exiles arriving in their constituency filled the void left by the paralysis of national governments. In this context the Mediterranean area, epicentre of the tensions between national actors, police agencies, migrants, NGOs and local authorities, has been the crucible of intercity mobilisations. The rich associational landscape, the drowning of migrant boats and the criminalisation of pro-immigrant support, the surge of populist parties and counter movement of solidarity have formed the background against which city militancy in migration-related issues thrived.

This new generation of city network has received lesser scholarly scrutiny. Focusing on the Mediterranean, this paper examines the networking dynamics at play among politicised city movements. This paper is the outcome of an ongoing research programme named "Localacc" funded by the Institut Convergence Migrations. The research design combines different methodologies: a database analysis of networks around the world, participant observation of city networks in Europe, case-study analysis on municipalities involved in city partnerships, interviews with local, national and international stakeholders. This paper more specifically benefits from case studies undertaken in Spain, Italy and France, participant observation in the Sea to City campaign and interviews with actors of the Global Compact for orderly and safe migrations. It shows that these networks are primarily embedded in their national contexts. And yet, one observes an effort to bridge current mobilisations and upscale their activism at a cross-Mediterranean level. The analysis highlights the influential role of certain mayors and civil society movements spanning borders.

Their respective role will be illustrated by the presentation of an ongoing initiative led by a group of NGOs, Open Arms and Seebrücke, with the support of two cities, Palermo and Barcelona, the Palermo Charter Platform Process (PCPP). Before presenting these different initiatives, we will give a brief overview of extant dynamics of migration-related city networking in Europe and beyond.

City networking and migration: from policy support to political activism

In Europe, the spread of city networks is embedded into the building of the European Union. [START_REF] Russeil | Quelles expertises urbaines pour une 'Europe des villes' ? Le réseau « Eurocities » et ses experts[END_REF]. Since the early 2000s, a flurry of new networks and institutions have been created (Arrival cities, Open cities, Integrating Cities, Solidarity cities, CLIP, Intercultural Cities, etc.), while migration and integration issues became high on the agenda of older organisations. These networks also share similar purposes, such as supporting project-building endeavours and the dissemination of best practices. They have largely contributed to promoting the concept of diversity in the integration agenda of European cities.

More recently, the security turn taken by the European management of migrant populations spurred the emergence of a new generation of city networks. The history of this form of urban militancy can be traced back in the eighties in the United States [START_REF] Lippert | Sanctuary practices in international perspectives : Migration, citizenship and social movements[END_REF][START_REF] Ridgley | Cities of refuge: Immigration enforcement, police, and the insurgent genealogies of citizenship in U.S. sanctuary cities[END_REF]. In the early eighties, in the Reagan organisations refused to acknowledge the status of refugee to immigrants fleeing conflicts in Central America (Nicaragua, Costa Rica, El Salvador). In reaction, church organisations called for "civil disobedience", advocating for the reception and support of exiles in defiance of the national policy. San Francisco, in 1985, became the first "sanctuary city" by refusing to support immigration enforcement in its constituency. The movement spread over the US in the following years, before becoming dormant with the end of the refugee wave in the early nineties. It gained momentum once again in the early 2000s with the surge of undocumented population. The Clinton laws following the Oklahoma bombings and the Patriot act following the World Trade Centre bombing triggered an increase of undocumented people by putting an end to the residence permit of people who had committed an infraction [START_REF] Boe | Vies familiales en sursis. Des extensions de l'illégalité migratoire aux États-Unis[END_REF]. In this context, the sanctuary city movement reactivated to prevent the identification and deportation of people with no legal permit of residence. It now includes nearly 200 members in the US and eleven in Canada.

The City of Sanctuary network in the United Kingdom is, in that regard, a forerunner in Europe. Although their names are similar, the UK movement is not an offshoot of its US The European movement differs from the North American one in their primary target: asylum seekers, on the one hand, undocumented people on the other. But, together, they form a body of militant organisations that differ greatly from the co-opted networks created with the support of European and international institutions. While co-opted networks benefit from public funding since their foundation, militant ones are grassroots endeavours. While the former tends to be grounded in partnerships with international and European institutions, the latter tend to collaborate with civil society organisations. While the former have been part and parcel of a reform of migration policies, the latter were triggered by the consequences of migration policies.

While the former are trans-european, the latter have, more often than not, a national scope. While the former focus on integration and diversity at large, the latter focus on more contentious issues:

the welcoming policies of recently arrived or in transit migrants (in Europe); the provision of services to undocumented people (mostly in the US). Their claims encroach on domains usually reserved to national authorities: the attribution of visas and immigrants' rights in a variety of domains (welfare, education, housing, etc.). This distinction between the two categories of networks may be, at times, difficult: as will be seen in the Spanish case, city networks with public funding may also target the welcoming of asylum seekers and organisations such as Eurocities are vocal advocates for a more open approach to immigration. And conversely, one may find examples of grassroots networks seeking to pragmatically fill a void in the national policy agenda without politicised aims. Militant and co-opted networks are two poles of a gradient of militancy from the most to the less confrontational ones. And yet, understanding the respective dynamics of both kinds of networks is key to comprehend how policy agendas are shaped, circulate and transform in the realm of migration governance.

The "firewall" policy is a case in point. First implemented in the US, this policy aims at avoiding any provision of support and information to immigration enforcement authorities that might lead to deportation. This includes the absence of request of any proof of residency or the absence of automatic transfer of any relevant information [START_REF] Crépeau | The case for 'firewall'protections for irregular migrants : Safeguarding fundamental rights[END_REF]. A few cities such as New York have been as far as providing a municipal ID card enabling undocumented The following section presents the emergence and evolution of militant city networks in three countries: Spain, France and Italy. It examines the conditions of their initiation and upscaling, the role of civil society organisations, the issues driving their involvement and their positioning with regard to state authorities.

Urban militancy: France, Spain, Italy

In the second part of this paper, the reader will find a descriptive account of municipal militancy in three Mediterranean states. Its aim is to elicit a reflection on the emergence of this

France: the ANVITA

There is a long history of involvement of French cities on migration issues. The "politique de la ville" launched in the eighties, granted to cities a larger role in the management of poverty in working-class neighbourhoods, with a specific salience on immigrant integration (Epstein et to the management of migrants with statutory international protection, while asylum seekers would be taken in charge by centres for extraordinary hospitality. The 877 SPRAR projects in place, facing this measure and its corollaries (the suppression of humanitarian protection, replaced by a much more limited extraordinary protection, etc.), were seriously affected.

In June 2018, against the background of the preparation of the reform planned by Salvini and of a strain put on the European reception system, in particular with regard to search and rescue operations at sea, Recosol and other civil society actors convened an international meeting in Bardonecchia. The aim was to raise awareness about the dire situation of migrants and ask

European countries and the EU to streamline reception and asylum procedures. The forum prefigured the mobilisation triggered by the enforcement of the so-called Salvini decree. The latter, among other things, removed the possibility for asylum seekers to register in their city of residence, thereby banning access to a local civil status and services attached (access to education, health services, etc.). This entailed the casualisation of a very high number of people.

Many municipalities expressed their disagreement on the ground that, it destabilises the cohabitation between migrants and local populations and impedes integration processes, with potentially very negative repercussions, in economic, social and security terms, on the community at large. Among the municipalities which have openly positioned themselves against Matteo Salvini most are part of Recosol. The map below, compiled by Cristina del Biaggio,

shows the extent of the movement over the Italian territory. The map shows the variety of stance taken against the decree amongst local authorities: some expressed their disagreement while others maintained the registration of asylum seekers in direct contradiction with the decree.

Interestingly, the opposition to Matteo Salvini included from right-hand municipalities, which perceived these measures as disruptive and restricting their capacity of control they exert over the migrant population, noticeably thanks to and through the web of accommodation they maintain to circumscribe and locate people. In parallel to the mobilisation, legal procedures were launched to assess the constitutional validity of certain aspects of the decree, notably the measure which removes entitlement for registration and local civil status.

Map of the local resistance to the Salvini decree

Cristina Del Biaggio, 2019

b) The role of mayors One of the particularly vocal mayors opposed to Matteo Salvini was the one of Palermo.

Leoluca Orlando decided to personally register asylum seekers with the civil status, refusing to implement the decree with a view to mark that his city was and wanted to appear as "open", hospitable and welcoming. The positioning of Orlando was not trivial: mayor of the city since 2012, and already mayor between 1985 and 1990, and between 1993 and 2000, he maintains very close relationships with a constellation of national institutions and civil society actors. He has been at the forefront on reception and integration issues for several years. The municipality participates in a variety of networks and programmes which advocate for migration, open borders, and cohesive societies: EUROCITIES, ECCAR (European Coalition of Cities against Racism), the UNICEF programme UPSHIFT, Solidarity Cities, amongst others. The mayor is famous for the writing of the "Palermo Charter", which aims at promoting international mobility as an unconditional human right through the suppression of residence permits 4 . The municipality is also known for the multiple initiatives taken in favour of the reception of immigrants in its port. This positioning, his political contacts with actors in Spain and Germany and his embedding on the international scene make him one of the mayors most involved in defending the rights of migrants, in supporting NGOs at sea.

Leoluca Orlando is not the only Italian mayor with an international stature being influential in the European and international debate on alternatives approaches to welcoming and integrating migrants. One can mention the forerunning experience of Venice's mayor Massimo Cacciari, involved in several international solidarity networks in the 1990s; the outstanding experiences of the village of Riace and its mayor Domenico Lucano (2004Lucano ( -2014)), as well as the city of Lampedusa headed by Giusi Nicolini (2012)(2013)(2014)(2015)(2016)(2017). The latter took part in 2015 with Ada Colau (Barcelona), Anne Hidalgo (Paris) and the mayor of the island of Lesbos, Spyros Galinos, in the creation of a network of refuge cities, with a connection between border islands and welcoming metropolises. This project itself failed, but it prefigured a new initiative developed around the Barcelona-Palermo connection (see below).

Spanish Cities' mobilisations

Like in France and Italy, Spanish cities have a track record of presence and involvement in European city networks. This particularly so for Barcelona, the city which, according to our track record of migration-related city networks around the world, is the municipality which displays the largest number of memberships (Lacroix forthcoming). It hosts the headquarters of United Cities and Local Governments (UCLG), the United Nations organisation representing local governments. It is also a founding member of Eurocities and is an active member of a range of EU funded networks involved in migration issues. The other major player is Madrid with an equally large range of experience in city-led initiatives. The particularly high level of involvement on the international scene is to be understood in the specific political context of the competition between Catalunya and the central government: Catalonian municipalities have found in such area a way of developing their own international agenda distinct from the governmental one (Zapata-Barrero 2006;Ostergaard Nielsen 2006).

The so-called "migrant crisis" staged the tensions between the Catalan and Spanish A second network of Spanish host municipalities was created in spring 2016: the "Red de Municipios de Acogida de Refugiados". More precisely, this network is in fact a sub-network specialised on issues of migrant populations' reception, within the mayors' association of the Federación Española de Municipios y Provincias (FEMP). Less critical and militant than the Ciudades Refugio network, this network was nonetheless born out of the observation that the EU and national governments were unable to properly welcome people seeking refuge in Europe.

The FEMP president, Abel Caballero, thus declared that the municipalities could no longer tolerate "Europe's indecency in the lack of refugees' reception" and that they were then ready to implement this welcoming that "the EU and its governments were not doing" (Federación Española de Municipios y Provincias, 2016). This network has many objectives, such as the development of a "protocol for the reception of refugees" common to the member cities, The padrón municipal is the register in which all the inhabitants of a municipality have been registered since 1858. Registering in the padrón -the empadronamiento -allows access to the health system, schooling and even regularisation. 7 The Generalitat de Catalunya is the political institution representing the autonomous community of Catalonia. departments as well as the Catalan Federation of Municipalities (Federació Catalana de Municipis) or the Catalan Association of Municipalities (Associació Catalana de Municipis). In both cases, these are local and inter-municipal organisations that are trying to provide a dignified reception for migrants, a reception they do not believe the Spanish government is providing. The Palermo process is still a work in progress. It received funding from the Rosa Luxembourg Foundation. Its first outcome is the launch of the "From Sea to City" campaign on June the 20 th . The campaign is articulated around five objectives : 1) a combined effort to lobby the European Commission on the migration policy; 2) the creation of a framework of action linking Search-and-Rescue operations and city welcoming; 3) advocating for direct sources of EU funding for both cities and civil society organisations; 4) the creation of legal corridors for the mobility of asylum seekers within Europe; 5) securing the access of fundamental rights in housing, health and other welfare domains. This series of aims and demands mirror the mixed positioning of cities and NGOs in this debate. The demand for specific channels of EU funding for the benefit of cities is a central claim of a number of "co-opted" European city networks, including Eurocities. It reflects the will to gain room for manoeuvre with regard to state tutorship and to be acknowledged as legitimate players in the European policy architecture. By contrast, the provision of services and the securing of rights for asylum seekers is at the core of urban militancy since the early days of the sanctuary city movement. The three other points result from the specific alchemy between militant municipalism and Search-and-Rescue activism. As shown in this paper, collaborations between local authorities and civil society organisations are commonplace. But those are usually organisations versed into reception issues within the urban space, not immigrant rescue operations outside its limits. This explains why the "Sea to City" campaign includes three demands that have to do with migration policy rather than integration or welcoming stricto sensu. The creation of legal corridors within the EU to facilitate the circulation of asylum seekers between the port cities and cities of the European hinterland (especially in Germany) is, in this regard, a groundbreaking novelty. Legal corridors are for immigrant circulation what firewalls are for immigrant settlement: a legal framework enabling cities and other actors to operate without the interference of immigration enforcement institutions. For the moment, the campaign is limited to European actors. It remains to be seen if the discussion will be broadened to incorporate partners from the southern side of the Mediterranean, and beyond if legal corridors could link cities hosting refugees in the Middle East with European host cities. This would be an actual breakthrough reshaping in a radical way the design of the European migration policy.

The birth of a

Conclusion: upscaling city activism

The presentation of these four case studies provides an overview of the factors driving the emergence and upscaling of grassroots city networks involved in migration issues. The contrast between militant and EU-supported networks supported is striking. While the former has primarily been driven by the international agenda on integration, the latter have been spurred by national political contentions. In Italy, the RECOSOL movement created an environment favouring pro-immigrant sentiments among mayors. When Matteo Salvini came to power and enforced a strongly anti-immigrant policy, it immediately triggered a mobilisation of municipalities. In France, the Calais "Jungle" and its subsequent dismantling propelled the mobilisation of cities. Finally, in Spain, the reception of refugees from the Middle East and Africa However, these drivers (political contentions and the personal involvement of local leaders) have concurred to the formation of national-level city activism. This contrasts with co-opted networks that have formed at a pan-European level. The last case study provided in this paper, the PCPP, offers a rare example of international networking effort with a militant agenda. This case-study points to the role of civil society actors behind the scene. The PCPP was initiated by a demand of Search-and-Rescue NGOs such as Open arms, Seebrücke and SOS Méditerranée in want of a stronger collaboration with Mediterranean local authorities. If the PCPP is conclusive, it will lead to the constitution of a cross-Mediterranean city network of safe harbours (with an extensive definition of the Mediterranean area since it includes Germany!). This role of civil society actors is not specific to the Mediterranean. Their role has been key in the expansion of the sanctuary movements in the UK and the US. In Belgium, the movement of Communes hospitalières is an outcome of a campaign launched in 2012 by a coalition of Belgian NGOs, the CNCD 11.11.11. However, the PCPP is, to our knowledge, the first initiative supported by both CSOs and local authorities at the international level. Moreover, the presence of Search-and Rescue organisations rather than integration has oriented the focus of the PCPP towards migration management.

In this regard, the PCPP highlights the specific nature of the Mediterranean political space: a liminal space at the crossroads of different Nations States in which gravitates a range of public, private and civil society actors. It is a favourable environment for the emergence of such a mobilisation: a space of political tensions in which evolve civil society organisations and political personalities with an international stature. The confrontational nature of this political context may explain why the co-opted municipal networks have failed to embody a "safe harbour" voice, thereby leaving a space for the emergence of alternative and more militant groupings.

  counterpart. It was launched in 2005 in the wake of the reform of the asylum policy undertaken by the Cameron government. The reform led to the scattering of refugees and asylum seekers over the British territory, thereby leading to the formation of refugee communities in places which had never hosted such a population before. This scattering triggered a mobilisation first of civil society organisations and then of municipalities willing to undertake welcoming policies towards refugees. The network now boasts 110 cities in the UK and Ireland (Darling, Barnett, & Eldridge 2010). This type of network spawned from 2015 onward, with the surge of asylum seekers coming from Africa and the Middle East: the Association Nationale des Villes et Territoires Accueillants in France, the Communes hospitalières in Belgium, the Fearless cities or Solidarity cities in Europe and beyond, etc.

  people to have access to the range of local welfare services[START_REF] De Graauw | Municipal ID cards for undocumented immigrants : Local bureaucratic membership in a federal system[END_REF]. In Europe, the notion of firewall was spread in policy circles by organisations such as the European Council of Refugees and Exile or NGOs such as C-MISE or the Platform for International Cooperation on Undocumented Migrants. But it never really took hold in European cities. By contrast, thanks to an active lobbying of cities such as New York or Bristol, this notion largely informed the Global Compact for Safe, Orderly and Legal Migration (GCM) signed in Marrakech in 2018. The document mentions "local authorities" fourteen times, making clear that the latter are key partners for its implementation. Even if the term firewall does not appear in the document, it did in preliminary versions and was part of the discussion process that predated its signature. The goal 15, for which the imprint of local authorities has been the most decisive(Thouez, forthcoming), introduces the principle of a "non-discriminatory access" (meaning whatever the legal status) to health services and education. As stated by the objective 15(e): "Incorporate the health needs of migrants into national and local health-care policies and plans, such as by strengthening capacities for service provision, facilitating affordable and non-discriminatory access (…) and 15 (f): "Provide inclusive and equitable quality education to migrant children and youth, as well as facilitate access to lifelong learning opportunities, including by strengthening the capacities of education systems and by facilitating non-discriminatory access to early childhood development". This appearance of the notion of firewall in the GCM is a rare of example of grassroots militant mobilisation whose outcome has been upscaled at the global level. Most remain confined at the national level. In addition, these mobilisations have been restricted to the support of migrants' rights already settled in the arrival cities. International City of Refuge Network is an interesting exception. This network of cities was launched after an initiative of the International Parliament of Writers (IPW) in 1993, with the aim to host artists whose life is at threat in their country of origin. The initiative was spurred by Jacques Derrida, Vaclav Havel and other writers in the wake of the Salman Rushdie affair. It is, to our knowledge, the only network facilitating the migration of individuals and not their settlement only.

  phenomenon and the key factors that underpin their development. As mentioned in the introduction, this study is part and parcel of a wider research programme on welcoming policies undertaken by cities and city networks in Europe and North America. The case studies are still under way at the times these words are being written. They mostly draw on Internet search and interviews with stakeholders (leaders of associations and representatives of cities and city networks). The section on the Palermo Process is informed by participant observation in the Seato-city campaign. Authors have attended the online preparatory meetings and launch of the campaign. It was complemented by interviews with NGOs representatives (Open Arms and Seebrücke) and city networks (ANVITA, ReCoSol).

  Kirszbaum 2019). Large French cities such as Lyon, Nantes, Strasbourg or Lille have been relatively involved in European city networks such as Eurocities(Flamant 2014). But a more militant stance is observed since 2015. A case in point is the creation of the Association Nationale des Villes et Territoires Accueillants (ANVITA) in France. A turning point was the decision to open a humanitarian camp in the city of Grande-Synthes. In March 2016, taking an opposite stance to Calais, the mayor of Grande-Synthes chose to open a reception camp for transit immigrants in accordance with the UNHCR standard. A second camp was opened in Paris few months later. The aim was not only to respond to pressing needs regarding the dire situation of immigrants, but also to propose a counter humanitarian model to the security-oriented management that prevailed in Calais. The camps crystallised the media attention: it was the first time that mayors were asserting such a stand against the grain of current immigration policies. A second step was taken after the dismantling of the Calais "Jungle" in October 2016. The disbanding of the camp was followed by the resettlement of the immigrant population in other parts of France, including in smaller cities and villages that had not been concerned by the inflows of refugees until then. This triggered a demand for more resources, skills and guidance. The reception of immigrants was done on a voluntary basis. It brought to the light that a sizeable proportion of local authorities (and their population) was actually willing to receive immigrants.Finally, in December 2017, a petition was published in the newspaper Le Monde, signed by mayors of large cities in France (including Bordeaux, Lille and Strasbourg 1 ). The petition asked for more financial support to enable local authorities to cater for the needs of vulnerable immigrants in wintertime. But the text also asked to relax the police pressure on immigrants. The petition was signed by mayors belonging to both right and left parties. It revealed that the opposition to the state policy did not follow the right/left cleavage. This mobilisation prefigured the creation of the ANVITA in September 2018. At its core stands the group of municipal leaders from the Green Party led by Damien Carême, the mayor of Grande-Synthe. Beyond this municipality, the founding members include Grenoble (green), the 1 st arrondissement of Lyon (PS), Ivry s/Seine (communist), Montreuil (communist), Briançon (socialist), Nantes (socialist), Strasbourg (socialist), Saint-Denis (communist). The aim of the network is to promote a policy and practices articulated around the principle of unconditional welcoming (accueil inconditionnel). Since its creation, the context of emergency urged the involvement of new cities less for ideological reasons than for pragmatic reasons: the immediate needs for support and advice accelerated the networking process. The situation widened the recruitment of cities beyond the core of actors that had shown interest in migration and integration issues for ideological reasons. It now includes 31 members. One also observes a greater engagement with civil society organisations. In October 2019, the ANVITA organised jointly with the Organisation pour une Citoyenneté Universelle (OCU), a conference gathering a range of local authorities and organisations from around the world, including representatives on the New York and Ouagadougou mayors' office. So far, the activities of the ANVITA have been focusing on the sharing of experiences and good practice. It published in 2019 guidelines for welcoming policies, "Comment accueillir (how to welcome)". More recently, the ANVITA released an oped in favour of the regularisation of undocumented people during the Covid-19 lockdown 2 . Members of the ANVITA (2020) Source: https://villes-territoires-accueillants.fr/ Thomas Lacroix, 2020 Legend: Founding members Adherent local authorities 2 https://blogs.mediapart.fr/les-invites-de-mediapart/blog/070520/pour-une-re-gularisation-inconditionnelleet-pe-renne-des-personnes-sans-papiers2.2 Italy: the anti-Salvini decree movementThe question of the reception of refugees and vulnerable immigrants is relatively recent in Italy. Local authorities have been stakeholders of the reception of policy of asylum seekers within the SPRAR programme in the early 2000s(Accorinti & Wislocki, 2016;[START_REF] Bini | The reception of asylum seekers in urban areas : The case of the city of Milan. Belgeo[END_REF][START_REF] Gois | The third way. Humanitarian corridors in peacetime as a (local) civil society response to a EU's common failure[END_REF]. Launched in 2002, the SPRAR programme gathers most of cities supporting reception projects in Italy. This early municipal engagement has informed two types of mobilisations: the RE.CO.SOL network and the Anti-Salvini Campaign. Below, we focus on the role of mayors in these dynamics.a) RECOSOL and the Anti-Salvini decree campaignAt the same time (2003) a network of "solidary communes" (RE.CO.SOL) was created 3 . It counted, at the time of its foundation, around a hundred members and now boasts around 300.Recosol was initially created to support international solidarity projects: the network promotes collaborations in Italy and abroad with other stakeholders engaged in "domains such as peace, solidarity, environment, responsible consumption, civil rights, immigration". The network's activities include the exchange of "good practices", and a model of decentralised cooperation between small and medium-sized municipalities, around developing projects and practices compatible with the limited budget capacities. The network has set up projects in Algeria, Mali, Niger, Palestine, Peru, Moldova and Romania.Gradually, Recosol became more and more active on local reception policies, in collaboration with ASGi (association of legal studies), the Ministry of Internal Affairs and the SPRAR programme: many municipalities in Recosol are part of SPRAR or participate in other reception project (managed by associations or NGOs). However, with the successive migration "crises"(2008; 2011; 2015) in the Mediterranean, the conditions of arrival gradually deteriorated and the various governments, instead of strengthening the capacities of SPRAR, preferred to reinforce containment and control systems. They increasingly transferred the responsibility of first reception to emergency humanitarian organisations, coordinated in 2011 by the "Protezione Civile" and from 2015 onward directly by the Prefectures. This transfer contributed to the proliferation of temporary reception structures (CAS, extraordinary reception centre) entrusted to private institutions (service cooperatives, hotels) less controlled, often failing to meet basic requirements. In 2016, the hotspot approach added a new layer to the "emergency" approach to 3 https://comunisolidali.org/ migration management. This trend was already explicit since 2011, but it reached another level in 2018 with the arrival of Matteo Salvini (Lega, extreme right populist) at the Ministry of Internal Affairs (the main interlocutor of SPRAR municipalities). The Salvini decree, which came into force in October 2018, limited the remit of the SPRAR system (renamed SIPROIMI)

  governments. As Mariano Rajoy's government (Partido Popular) had not been proactive in European discussions on the migrants' reception, the Barcelona City Council decided to take the lead in autumn 2015 by proposing a local reception policy and called on other cities to join them in this dynamic, by creating a network of "Ciudades Refugio". Two years later, the network counted around 25 cities, including Madrid, Valencia, Pamplona, Zaragoza, Cordoba and Malaga. As in the French case of ANVITA, this city network corresponds to a model of interurban militancy, bringing forward strong political demands and criticism to national governments' and European institutions' actions. In autumn 2017, in a speech at the Spanish Parliament (Congreso de los Diputados), the Ciudades Refugio network denounced the "immobility" of Mariano Rajoy's government in the reception of asylum seekers and refugees on Spanish territory. At that time, Spain had in fact received only 13.7% of the quota of migrants that it had committed to welcome as part of the relocation process negotiated two years earlier between European leaders (Amnesty International, 2017). A second criticism targeted the allocation of European funds assigned to Spain for immigration management on its territory, and particularly for the management of the country's southern border, which constitutes an external border of Europe. For the period 2014-2020, Spain has received 691.7 million euros under the Asylum Migration and Integration Fund (AMIF) and the Internal Security Fund. This is in addition to €29.6 million emergency aid released by the European Commission in 2018 to help Spain deploy additional staff along Spain's southern borders, organise repatriations and transfers from Ceuta and Melilla enclaves, and develop reception infrastructure(European Commission (2018). In 2017, through the voice of one of its spokespersons, Jaume Asens 5 , Deputy Mayor of Barcelona, the Ciudades Refugio network already deplored the security orientation and the lack of transparency in the use of these funds by the Spanish government, leaving the cities finance part of the reception at the local level with their own funds: Madrid City Council allocated around €4.5 million to refugee aid programmes between 2016 and 2017, while Barcelona City Council had assigned €1.5 million to emergency accommodation during the same period. Not complying to the management of migrants' reception carried out by the Spanish government, the network's cities therefore call either for a change in practice, towards a more humanist and supportive reception, or for a transfer of competences and resources -including European funding -to the local level, so that they can have the capacity to take in charge migrants and refugees' reception as they conceive fit.

  improving access to social services and empadronamiento6 for refugees, raising awareness among the local population of the plight of migrants, or simply the sharing of information and experience between municipalities and local governments. One of its specificities is to maintain an intense collaboration with organisations specialised in migration and social issues, such as the Comisión Española de Ayuda al Refugiado (CEAR), ACCEM, the Spanish Red Cross, the UNHCR and Amnesty International. The network, and more generally the FEMP, wishes in particular to position itself as an intermediary between the Spanish government, on the one hand, and local governments and municipalities on the other, as it was the case when the Aquarius arrived in the port of Valencia in 2018: the organisation has thus gathered the proposals of volunteer cities (more than 300) to receive the 629 survivors on the boat.Finally, it is worth noting the existence of interurban networks and initiatives at a subnational level, such as the Red Valenciana de Ciudades de Acogida or the Catalan coastal towns selfdeclared as « safe harbours » (puertos seguros). The first one is a municipalities' network in the Valencia region, most of the members already belonging to the national network Red de Municipios de Acogida de Refugiados. As stated by the Federación Valenciana de Municipios y Provincias (FVMP), which stands behind this local network, the aim of the latter is to « promote the objectives of the FEMP's Red de Ciudades Acogedoras network in order to disseminate them among the mayors of the Valencia Community" (Federación Valenciana de Municipios y Provincias, 2018). As for the second, the so-called Catalan "safe harbours", it is less a network than a local interurban initiative, promoted by the Generalitat de Catalunya7. In spring 2018, when lifeboats regularly struggled to find open harbours to receive migrants rescued at sea, the Generalitat took the decision to declare all ports in Catalan coastal cities as "safe harbours" where ships could come ashore without hindrance. In April 2018, the Interdepartmental Commission on Safe Ports (Comissió Interdepartamental de Ports segurs) was created to work on the development of a reception programme in these municipalities, bringing together Generalitat 6

  Mediterranean-wide movement: the Palermo Charter Platform Process In May 2017, Italy and the European Union started to devolve to Libyan coastguard the management of Search-and-Rescue operations in the Mediterranean 8 . This gradual transfer was confirmed in June 2018, when Libya delineated a large Search-and-Rescue area in international waters over which the UN International Maritime Organization acknowledged its capacity to intervene. In parallel, the arrival to power of the Five Star government and Matteo Salvini as the Ministry of Interior spurred the criminalisation of NGO activities in the Mediterranean. The SOS Méditerranée/MSF ship "Aquarius" was forced to divert to Valencia after it was refused to dock in Italy and Malta. The disembarking in Valencia of the 600 immigrants onboard was allowed by the mobilisation of local authorities. As seen above, after having received the green light from the central government, the "Red Valenciana de ciudades de acogida" and the city of Valencia mobilised to welcome the boat 9 . In a context of mounting pressure against their activities, European NGOs involved in Searchand-Rescue operations turned to local authorities to secure docking possibilities. Contacts had been made in May 2018 with Italian cities such as Palermo, Riace and Naples. The discussions gradually widened to include Berlin, Valencia, Zaragoza, Syracuse, Milan, Barcelona or Bologna. In February 2019 was held a meeting in Roma gathering city representatives from Spain, Germany and Italy and NGOs during which was launched the Palermo Charter Platform Process. From the NGO side, the process includes European Alternatives, Emergency, Humboldt-Viadrina Governance Platform, INURA, LasciateCIEntrare, Mediterranea Saving Humans, Open Arms Italy Office, SeeBrücke Germany, Tesserae, Welcome to Europe/Italy, and Watch The Med Alarm Phone. Beyond the cities mentioned above, the platform includes a number of cities from Spain, Italy and Germany. On the French, side the ANVITA and the NGO Migreurop are also active members of the consortium. The group recruits beyond the range of militant organisations with the presence of Eurocities and members of the European Parliament were present during preparatory meetings.

  in 2015 and the Aquarius crisis in 2018 set the stage for the formation of migration-related city networks. Another common trait is the pivotal role of key mayors: Damien Carême in Grande-Synthe, Leoluca Orlando in Palermo and Ada Colau in Barcelona played a key role in mobilising their counterparts.

« Face aux flux migratoires, nous, les maires, sommes au pied du mur » Le Monde,

2017/12/16

http://leolucaorlando.it/palermo-la-citta-dellaccoglienza/

La Vanguardia (2017), "'Ciudades refugio" piden que se les traspasen las competencias en materia de acogida ante el "inmovilismo" de Rajoy", 26th September 2017, consulted on line on April 21st 2020. Available at: https://www.lavanguardia.com/local/madrid/20170926/431581829147/ciudades-refugio-piden-que-se-lestraspasen-las-competencias-en-materia-de-acogida-ante-el-inmovilismo-de-rajoy.html

https://www.hrw.org/news/2017/06/19/eu-shifting-rescue-libya-risks-lives

https://www.fvmp.es/red-valenciana-de-ciudades-de-acogida/

Erasmus+ Jean Monnet Network Program (Project Reference: 611260-EPP-1-2019-1-ES-EPPJMO-NETWORK) entitled "Mapping European by GRITIM-UPF.