Poly(vinyl alcohol) as a gas accumulation layer for an organic field-effect transistor ammonia sensor

Abstract

Ammonia (NH3) gas sensors based on organic field-effect transistor (OFET) using poly(vinyl alcohol) (PVA) as a gas accumulation layer were fabricated. The results showed the percentage responses of saturation current (Ion) was 50.3% under 0.5ppm NH3, which is over one order of magnitude higher than that of pure PMMA dielectric. Also, it showed that there was a remarkable shift in the field-effect mobility after exposed to NH3 gas. Moreover, the percentage responses of Ion would increase to 66.9% and 30.2% under 0.5ppm and 0.2ppm NH3 after applied a gate voltage pulse, respectively. The sensing properties of these OFET gas sensors can realize absorption and desorption with opposite gate bias, exhibiting non-volatile states of Ion and VT under the programming-erasing bias as used for memory elements. By analyzing the morphologies of dielectric and organic semiconductor, and the electrical characteristics of OFET sensors, the interaction between NH3 and PVA will be strengthened under the influence of the applied electrical field on the hydroxyl dipoles. The bias-induced re-orientation of the hydroxyl dipoles can modulate the influence of NH3 on the trapping (absorption) and detrapping (desorption) processes of charge carriers at the pentacene/PVA interface.