CNTFET Gas Sensors Using SWCNT Mats: Method for Low-cost Fabrication, Solution to Improve Selectivity, Experimental Results using Interfering Agents

Abstract

The first paper showing the great potentiality of Carbon Nanotubes Field Effect transistors (CNTFETs) for gas sensing applications was published in 2000 [1]. It has been demonstrated that the performances of this kind of sensors are extremely interesting: a sensitivity of around 100ppt (e.g. for NO2 [2]) has been achieved in 2003 and several techniques to improve selectivity have been tested with very promising results [2]. The main issues that have not allowed, up to now, these devices to strike more largely the market of sensors, have been the lack of an industrial method to obtain low-cost devices, a demonstration of their selectivity in relevant environments and finally a deeper study on the effect of humidity and the possible solutions to reduce it. This contribution deals with CNTFETs based sensors fabricated using air-brush technique deposition on large surfaces. Compared to our last contribution [3], we have optimized the air-brush technique in order to obtain high performances transistors (Log(Ion)/Log(Ioff) ∼ 5/6) with highly reproducible characteristics : this is a key point for the industrial exploitation. We have developed a machine which allows us the dynamic deposition on heated substrates of the SWCNT solutions, improving dramatically the uniformity of the SWCNT mats. We have performed tests using different solvents that could be adapted as a function of the substrates (e.g. flexible substrates). Moreover these transistors have been achieved using different metal electrodes (patented approach [4]) in order to improve selectivity. Results of tests using NO2, NH3 with concentrations between ∼ 1ppm and 10ppm will be shown during the meeting.

Carbon nanotubes based transistors composed of single-walled carbon nanotubes mats as gas sensors: A review

“…The results shown in Fig. 7, confirm that each gas seems to interact in a specific way with each CNTFETs characterized by different metal electrodes [29]. Another very interesting approach has been developed by researchers at Nanomix Inc. and Pittsburgh University.…”

“…Current change as a function of exposure time for two series of CNTFETs achieved using different metals as electrodes. The current ratio between after (I) and before gas exposure (I 0 ) is evaluated for V ds = 1 Volt [29].…”

Gas sensing with carbon nanotubes

“…Therefore, we have focused our work on transistors using CNT mats as channels. [2][3][4] We deposit these multi-nanotube networks with a dynamic spray-gun deposition technique compatible with large surfaces (see Figure 1).…”