Effect of SiO2 and SiO2/SiNx Passivation on the Stability of Amorphous Indium-Gallium Zinc-Oxide Thin-Film Transistors Under High Humidity

We studied the environmental stability of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) with single-layer (SiO₂) and bilayer (SiO₂/SiN_x) passivation under high-humidity (80%) storage. During the 30 days of investigation, all single-layer passivated TFTs showed negative turn-ON voltage shifts (AVON), the size of which increased with storing time. The negative A VON is attributed to donor generation inside the active a-IGZO caused by the diffusion of ambient hydrogen/water molecules passing through the SiO₂ passivation layer. The X-ray photoelectron spectroscopy depth profile for the SiO₂ passivated structures confirms that the concentration of oxygen vacancies, which is initially larger at the a-IGZO/SiO₂ interface, compared with the bulk a-IGZO, decreases after 30 days of storage under high humidity. This can be explained as the passivation of oxygen vacancies by diffused hydrogen. On the other hand, all bilayer passivated TFTs showed good air stability at room temperature and high humidity (80%).