Oxygen Adsorption Effect of Amorphous InGaZnO Thin-Film Transistors

The effect of oxygen adsorption at the back channel of a-IGZO thin-film transistors (TFTs) is investigated. It is shown that for TFTs with the channel layer sputter-deposited at a high O-2/Ar flow rate ratio (R-O/Ar), the threshold voltages in vacuum and O-2 ambient do not show any difference; for devices fabricated at a low R-O/Ar, the threshold voltages in vacuum are lower than those in O-2. In addition, the devices in O-2 show a more significant threshold voltage shift than those in vacuum do under a positive gate bias stress. The surface-state model is used to explain this observation. It is inferred that the oxygen adsorptions are physical and chemical, respectively, in the high- and low-R-O/Ar cases, and the transition from physical to chemical adsorption occurs when a positive gate bias stress is applied.