Reliability approach in spacecraft structures

This paper presents an application of the probabilistic approach with reliability assessment on a spacecraft structure. The adopted strategy uses meta-modeling with first and second order polynomial functions. This method aims at minimizing computational time while giving relevant results. The first part focuses on computational tools employed in the strategy development. The second part presents a spacecraft application. The purpose is to highlight benefits of the probabilistic approach compared with the current deterministic one. From examples of reliability assessment we show some advantages which could be found in industrial applications

Microdispositifs pour applications capteurs

L'essentiel de ce travail de recherche consiste à mettre au point un procédé de fabrication d'une nouvelle structure à effet de champ apte à augmenter la sensibilité de détection d'espèces chimiques ou biologiques. Le travail prévoit la réalisation d'une structure de type nanofilaire pour le canal du transistor. L'intérêt de cette configuration est d'obtenir une surface d'échange importante entre la couche active et l'environnement ambiant. L'objectif final est d'étudier les potentialités d'utilisation de ces structures dans la réalisation de microcapteurs à très haute sensibilité

Electrical properties of polysilicon nanowires for devices applications

4 pagesInternational audiencePolysilicon nanowires are synthesized using the well known and low cost technique commonly used in microelectronic industry: the sidewall spacer formation technique. Polysilicon layer is de-posited by Low Pressure Chemical Vapour Deposition technique on SiO2 wall patterned by conventional UV lithography tech-nique. Polysilicon film is then plasma etched. Accurate control of the etching rate leads to the formation of nanometric size side-wall spacers with a curvature radius as low as 100nm used as polysilicon nanowires. These polysilicon nanowires are first in-tegrated into the fabrication of electrical devices as resistors and electrical properties are studied in function of in situ phosphorus doping levels. I(T) measurements show that polysilicon nanowires dark conductivity is thermally activated according to the Seto's theory. In addition, field effect transistors made with such polysilicon nanowires used as channel region highlight promising field effect behaviour

Polycrystalline silicon nanowires synthesis compatible with CMOS technology for integrated gas sensing applications

International audiencePolysilicon nanowires are synthesized following a classical top-down approach using conventional UV lithography technique fully compatible with the existing silicon CMOS technology. N- and P-type in-situ doping of these nanowires is controlled over a large range of doping levels and electrical properties of these nanowires are analyzed. Results show that resistivity dependence with the doping level is both related to the nanowires size dependent structural quality and doping specie. Charged gas species (ammonia) sensitivity of these nanowires has also been studied. In addition, feasibility of N- and P-channel polysilicon nanowires transistors is demonstrated

Application des surfaces de réponse pour l’analyse fiabiliste d’une structure spatiale

Cette communication présente une application des surfaces de réponse pour l’analyse de la fiabilité d’une structure satellite. Les méta-modèles sont construits par régression itérative où seul les termes significatifs sont sélectionnés parmi une liste de régresseurs potentiels préalablement déterminée par une analyse de sensibilité. Les méta-modèles sont ensuite vérifiés par une méthode de bootstrap où les variations observées sur les prédictions sont prises en compte dans le calcul des probabilités de défaillance afin de valider le résultat

Silicon nanowires synthesis for chemical sensor applications

WOSInternational audienceSilicon nanowires (SiNWs) are synthesized following two methods: i) the VLS (Vapor-Liquid-Solid) growth technique (bottom up approach), and ii) the sidewall spacer fabrication (top down approach) commonly used in microelectronic industry. The VLS growth technique uses gold nanoparticles to activate the vapor deposition of the precursor gas and initiate a 100 nm diameter SiNWs network growth. In the case of the sidewall spacer method, a polysilicon layer is deposited by LPCVD (Low Pressure Chemical Vapor Deposition) technique on SiO2 wall patterned by conventional UV lithography technique. Polysilicon film is then plasma etched. Accurate control of the etching rate leads to the formation of spacers with a 100 nm curvature radius that can be used as polysilicon NWs. Each kind of nanowires is integrated into resistors fabrication. Electrical measurements show the potential usefulness of these SiNWs as chemical sensors

Polysilicon Nanowires for chemical sensing applications

International audiencePolycrystalline silicon nanowires are synthesized using a classical fabrication method commonly used in microelectronic industry: the sidewall spacer formation technique. Assets of this technological process rest on low cost lithographic tools use, classical silicon planar technology compatibility and the possibility to get by direct patterning numerous parallel nanowires with precise location on the substrate. Grounded and suspended polycrystalline silicon nanowires with a curvature radius as low as 150nm are integrated into resistors and used as gas (ammonia) sensors. Results show potential use of these nanowires for charged chemical species detection with an increase of the sensitivity with the increase of SiNWs exchange surface with the environment

Fabrication and electrical characterization of silicon nanowires based resistors

International audienceSilicon nanowires (SiNWs) are synthesized via the Vapor-Liquid-Solid (VLS) mechanism using gold (Au) as metal catalyst and silane (SiH4) as precursor gas. Au nanoparticles are employed as liquid droplets catalysis during the SiNWs growth performed in a hot wall LPCVD reactor at 480°C and 40 Pa. SiNWs local synthesis at micron scale is demonstrated using classical optical photolithography process. SiNWs grow with high density anchored at the dedicated catalyst islands. This resulting network is used to interconnect two heavily doped polysilicon interdigitated electrodes leading to the formation of electrical resistors in a coplanar structure. Current-voltage (I-V) characteristics highlight a symmetric shape. The temperature dependence of the electrical resistance is activated, with activation energy of 0.47 eV at temperatures greater than 300K

Variable range hopping conduction in N- and P-type in-situ doped polycrystalline silicon nanowires

International audienceTemperature dependence of electrical properties in N- and P-type in-situ doped polycrystalline silicon nanowires synthesized by the sidewall spacer formation technique has been studied. Experimental analysis has been carried out for a temperature range from 200K to 530K on in-situ doped polycrystalline silicon nanowires with doping level varying from 2×1016 to 9×1018 cm-3. Results show that for N- and P-type doped samples the temperature dependence of the conductivity follows the 3D variable range hopping model due to hopping between localized electronic states near the Fermi level. The corresponding densities of states are determined following exponentials (tail states) distributions associated to the statistical shift of the Fermi level

Growth-in-place deployment of in-plane silicon nanowires

International audienceUp-scaling silicon nanowire (SiNW)-based functionalities requires a reliable strategy to precisely position and integrate individual nanowires. We here propose an all-in-situ approach to fabricate self-positioned/aligned SiNW, via an in-plane solid-liquid-solid growth mode. Prototype field effect transistors, fabricated out of in-plane SiNWs using a simple bottom-gate configuration, demonstrate a hole mobility of 228 cm2/V s and on/off ratio >103. Further insight into the intrinsic doping and structural properties of these structures was obtained by laser-assisted 3 dimensional atom probe tomography and high resolution transmission electron microscopy characterizations. The results could provide a solid basis to deploy the SiNW functionalities in a cost-effective way