Effects of controlling the interface trap densities in InGaZnO thin-film transistors on their threshold voltage shifts

In this paper, the threshold voltage stability characteristics of indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFT) are discussed. The IGZO TFTs were found to induce a parallel threshold voltage (V_th) shift with changing field effect mobility (μ_FE) or a sub-threshold gate voltage swing (SS) due to various thermal annealing conditions. The IGZO TFT that was post-annealed in an O₂ ambient was found to be more stable for use in oxide-based TFT devices and to have better performance characteristics, such as the on/off current ratio (I_on/off ), SS, and V_th, than other TFTs did. The mechanism for improving the V_th stability in the post-annealed IGZO TFT is a decrease in the number of trap sites for the electrons and the weak oxygen bonding in the IGZO thin films. The device's performance could be significantly affected by adjusting the annealing conditions. This mechanism is closely related to that of modulation annealing, where the number of localized trapped carriers and defect centers at the interface or in the channel layer are reduced.