Effects of source/drain electrode thickness on water-induced instability of laminated organic single-crystal field-effect transistors

Abstract

Water is known to be the main cause of operational instability in organic electronic devices under ambient conditions. The water-induced hysteresis of lithography-friendly bottom-gate-bottom-contact-type organic field-effect transistors (FETs) with a laminated single-crystal channel was investigated using varying electrode thicknesses. As the amount of water in the air gap enveloped by the semiconductor layer and insulating substrate, adjacent to the electrode, increases, the mechanism dominating the hysteresis phenomenon shifted in the following order: (1) current increase owing to the decreasing charge-injection barrier because of a drain-induced change in the electrode work function, (2) current decrease because of the gate bias stress, and (3) current increase because of the gate enhancement effect owing to the dipole orientation of the water molecules penetrating the semiconductor-insulator interface. Changes in the electrode thickness had the same effect on the hysteretic behavior as the relative humidity of the experimental environment. Thus, this study provides a comprehensive understanding of the water-induced operational instability of laminated organic single-crystal FETs and should aid the realization of stable-operation organic devices, as well as foreign-molecule sensors, by controlling the electrode thickness.