Anomalous Threshold Voltage Shift and Surface Passivation of Transparent Indium–Zinc–Oxide Electric-Double-Layer TFTs

Threshold voltage (V_th) instability and surface passivation effect of transparent indium-zinc-oxide electric-double-layer thin-film transistors (TFTs) are investigated. Unpassivated devices show a large negative threshold voltage shift of 0.68 V in the beginning of light-illuminated negative gate bias stress. Under longer time stress, anomalous positive V_th shifts are observed for both unpassivated and passivated TFTs, which is due to the mobile ions drifting in the SiO₂-based solid-electrolyte gate dielectric. After surface passivation, the devices show neglectable negative V_th shifts of less than 0.1 V due to the protection of channel against the photodesorption of adsorbed oxygen ions.