Preliminary Measurements of Selective Sensing of DMMP and NH3 Using CNTFET Array Based Gas Sensors Fabricated Using Meta
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Preliminary Measurements of Selective Sensing of DMMP and NH3 Using CNTFET Array Based Gas Sensors Fabricated Using Metal Diversified Electrodes for Electronic Fingerprinting Paolo Bondavalli1, Pierre Legagneux1, and Didier Pribat2 1 Nanocarb, Thales Research and Technology, 128 Rt Dpt, Palaiseau, 91767, France 2 LPICM lab, Ecole Polytechnique, Site de Polytechnique, Palaiseau, 91128, France ABSTRACT This paper deals with preliminary measurements for prove-of-concept of a Carbon Nanotubes Field Effect Transistors (CNTFETs) based sensor array which could improve dramatically gas selectivity. CNTFET based sensors exploit the extremely sensitive change of the Schottky barrier heights between Single Wall Carbon NanoTubes (SWCNTs) and drain/source metal electrodes: the gas adsorption creates an interfacial dipole that modifies the metal work function and so the bending and the height of the Schottky barrier at the contacts [1,2]. Using CNTFET array fabricated using SWCNT mat as channel, we have achieved a sort of electronic fingerprinting of different gases. Actually, we want to demonstrate that the change of the metal electrode work function strictly depends on the metal/gas interaction: CNTFET transfer characteristics will change specifically as a function of this interaction. In this study we have fabricated different CNTFETs using three metal contacts (Au, Pd, Mo) and exposed them to two gases, DMMP and NH3, which have the same “electron-withdrawing” behavior. The CNTFETs array has been exposed to 1ppm of DMMP and 10ppm NH3 and we have identified two electronic fingerprinting. The totality of our measures have been performed at ambient conditions. INTRODUCTION The first paper showing the great potentiality of Carbon Nanotubes Field Effect transistors (CNTFETs) for gas sensing applications was published in 2000 [3]. Since then, many teams have focused their interest on this new kind of sensors. These devices exploit the extremely sensitive change of the Schottky junctions built up between carbon nanotubes (CNT) and drain/source metal electrodes: the gas adsorption induces an interfacial dipole that changes the metal work function and so the bending and the height of the Schottky barrier at the contacts [1, 2]. It has been demonstrated that this kind of sensors can reach a sensitivity of 1ppb for DiMethyl-Methyl-Phosphonate (DMMP, a sarin simulant) [4]. The real issue is to improve the selectivity, thus reducing the risk of false alarm and various methods have been proposed so far. Among these methods, the deposition of polymers on the CNTFETs (functionalization) is extensively studied and very promising results have been already obtained [see e.g. ref. 5]. However, the use of polymers could present several drawbacks such as increasing the sensor response time and decreasing its lifetime as methods currently used to desorb gas molecules (thermal anneal and UV exposition) should degrade these polymers. Another issue is the lack of knowledge on the real physical effect of polymers: up to now the choice of po
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