Multi-mode humidity sensitivity of carbon nanotubes field-effect transistors

B. Lebental, H. Woo, E.D. Norman, F.Z. Bouanis, A. Gohier, C.S. Cojocaru
IFSTTAR, FR

Keywords: metrology, compact model, sensor

Summary:

Single-walled carbon nanotube-based field effect transistors with (CNTFET) have demonstrated a particularly strong sensitivity to humidity. It impairs the use of the transistors in logic circuits, while the devices are usually very unstable as humidity sensors. The humidity sensitivity is generally attributed to charge trapping and water adsorption, but a detailed understanding of the mechanisms is prevented by the diversity of reported behaviors as well as by the response variability observed even with batch-fabricated samples. We propose here a novel analysis of the different modes of humidity sensitivity in CNTFET based on a systematic, extensive multiparameter study of the electrical response of a series of CNTFET devices. We monitor systematically the characteristics of the transisor transfer curves with respect to humidity in a metrological approach. The significant variability is interpreted using a compact-model-based approach: we introduce a humidity-modulated voltage difference between effective gate voltage along nanotube and imposed gate voltage. We rigorously interpret the variation of all the parameters while confirming the existence of two regimes, one at low humidity involving water molecules adsorption around charge trap, the other at high humidity involving a charging effect in the full layer of adsorbed water molecules.