CNTFETs fabricated using an Original Dynamic Air-Brush technique for SWCNTs deposition : application to gas sensing P. Bondavalli, G.Feugnet and L.Gorintin Thales Research and Technology, 128 Rt Dpt, Palaiseau 91767, France, paolo.bondavalli@thalesgroup.com , gilles.feugnet@thalesgroup.com , louis.gorintin@thalesgroup.com ABSTRACT This contribution deals with Carbon Nanotubes Field Effect transistors (CNTFETs) based gas sensors fabricated using a completely new dynamic air-brush technique for SWCNTs deposition. The extreme novelty is that our technique is compatible with large surfaces, flexible substrates and allows to fabricate high performances transistors exploiting the percolation effect of the SWCNTs networks achieved with extremely reproducible characteristics. This technique is extremely interesting considering that it is suitable for industrial transfer. More precisely, we have developed a machine which allows us the dynamic deposition on heated substrates of SWCNT solutions, improving dramatically the uniformity of the SWCNTs mats. The CNTFETs have been developed for gas sensing applications. Indeed we have fabricated arrays of CNTFETs achieved using different metal electrodes to exploit the change of metal/SWCNTs junction characteristics as a function of the gas detected in order to identify a sort of lectronic fingerprinting. This phenomenon is related to the change of the metal work function and so of the Schottky barrier and seems to be extremely selective. Although the deposition technique has been developed to fabricate CNTFETs, this technique is extremely versatile and can be used for other kinds of applications such as fabrication of bolometers (e.g. nanotubes), replacements of ITO layers (e.g. nanotubes, graphene), in OLED (e.g. graphene), for light and cheap ultracapacitors on flexible substrates (e.g. using carbon nanotubes or nanohorns). This technique could really allow these nanomaterials to strike the market on these applications. During the presentation examples, for all these applications, will be shown. 1 INTRODUCTION The first paper demonstrating the efficiency of Carbon Nanotubes Field Effect transistors (CNTFETs) for gas sensing applications was published in 2000 by Kong et al. [1]. Since then, many teams have obtained very interesting results concerning the sensitivity of this new kind of sensors. We can mention, for example, the results obtained by Qi et al. in 2003 [2] which were able to detect 1ppt of NO 2 (using functionalized CNTFETs) and, the same year, Snow and co-workers that were able to detect 1ppm of Di- Methyl-Methyl-Phosphonate using carbon nanotubes networks based transistors [3-4]. These results seem to prove that the main issue for this kind of sensors is not the sensitivity. Indeed the real concern consists in finding a suitable technique to achieve an highly selective sensor that could be used in every-day life applications or in operational context. 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. 2]. 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 polymer continues to be empirical. Another approach is the bio-functionnalisation, using DNA sequences of the Single-Walled-CNTs (i.e. SWCNTs) to improve the sensitivity for specific gases, performed by researchers at Pittsburg University [5]. Finally we can mention the approach developed jointly by researchers at Nanomix Inc. and Pittsburgh University [6- 7]. They deposed nanoparticles of different metals on networks of SWCNTs connecting, by percolation, two Pd electrodes (i.g. “metal decoration”). Therefore they fabricated an array of CNTFETs each one characterized by a different metal “decoration”. They exposed this array to several gases (NO, H 2 , CO, CH 4 , H 2 S, NO 2 , NH 3 ) and they observed a specific change of the transfer characteristics of each transistor as a function of the nature of the nanoparticles and of the gas. These results made researchers think that large array of “metal-decorated” CNTFETs could be used in order to recognize univocally the gases identifying their electronic fingerprinting. All the approaches that we have presented appear to be very interesting from a scientific point of view but the technological steps for the fabrication of the sensors (e.g. polymer/bio-fonctionnalisation or metal decoration) are quite complex and the their industrial exploitation has not been achieved yet. Our approach for solving the selectivity problem, is to achieve a sensor comprising an array of SWCNT-based transistors where each transistor will be fabricated using different metals as source/drain electrodes. Considering that no cheap and rapid method, up to now, exists for separating semiconductor from metallic specimens, we decided to use SWCNT mats as transistor channel. The principal advantages are two. Firstly the use NSTI-Nanotech 2012, www.nsti.org, ISBN 978-1-4665-6274-5 Vol. 1, 2012 228