We investigated the transfer characteristics and the gate-bias stability of amorphous indium-gallium-zinc oxide thin-film transistors when the channel layer was exposed to hydrogen, oxygen, air, or vacuum at room temperature during measurements. The threshold voltage and the drain current were changed by the ambient atmospheres. The threshold voltage shift (ΔVth) under gate-bias stress was faster in hydrogen than in oxygen and vacuum. It is suggested that hydrogen exposure degrades the gate-bias stress stability due to surface accumulation layer creation. The characteristic trapping times, τ, in H2, O2, air, and vacuum were 5×103, 1.5×104, 2×104, and 6.3×104 s, respectively.

The transfer characteristics of amorphous indium zinc oxide thin-film transistors were investigated. The active layer in the bottom gate structure of the transistor was fabricated using room-temperature rf-magnetron sputtering. The device operated as an n-type enhancement mode exhibited a clear pinch-off behavior and an on/off ratio of ∼106. The field-effect mobility of 9.6cm2∕Vs and subthreshold slope of 0.3V∕decade were obtained. The positive threshold voltage shift was observed under the positive gate bias stress. The field-effect mobility and subthreshold slope remained nearly unchanged within the time of the gate bias stress. The time dependence of the threshold voltage shift was well matched with the stretched-exponential time dependence model.