Polysilicon Nanowires for chemical sensing applications
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Polysilicon Nanowires for chemical sensing applications E. Jacques, L. Ni, A. C. Salaün, R. Rogel, L. Pichon Institut d’Electronique et de Télécommunications de Rennes, UMR 6074, Campus de Beaulieu, bâtiment 11 B, 263 avenue du Général Leclerc, 35042 Rennes cedex, France
ABSTRACT Polycrystalline 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. INTRODUCTION Semiconducting nanowires are currently attracting much attention as promising components for future nanoelectronic devices such as nanowire field effect transistors [1], photonic and optoelectronic devices [2], and as chemical or biological sensors [3-5]. As their surface can be sensitive to charged species combined with their high surface to volume ratio, silicon nanowires (SiNWs) are the subject of intense research activities for high sensitivity chemical sensor fabrication. The first application of SiNWs in biological and chemical molecule sensor was reported by Lieber’s group in 2001 [3]. In addition, because SiNWs synthesis is compatible to the established Si 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. Indeed, SiNWs based sensor integration will allow a lower manufacturing cost, in addition to the advantageous electronic features of embedded detection and signal processing in silicon technology. The intrinsic reliability of the well-known semiconductor CMOS (Complementary Metal Oxide Semiconductor) process also guarantees a reproducible and reliable diagnosis. SiNWs can be prepared by one of two approaches, “top-down“ and “bottom up”. In a bottom up strategy the individual base elements (atoms, molecules…) of the system are linked together to form larger subsystems. Synthesis methods most developed are layer-by-layer self assembly [6], Vapor Liquid Solid (VLS) and Solid Liquid Solid (SLS) growth techniques [7,8], and use of matrix template [9]. The main drawbacks of these synthesis methods for a 3 D integration are the difficulty in control of size and positioning of the nanowires. In this case, nanowires need to be selectively collected and manipulated to be assembled in a planar layout. The “top down” approach starts from bulk materials and scales down the patterned areas. In this way, several advanced nanopatterni
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