Effects of High-Temperature Annealing on Operation Characteristics of a-In-Ga-Zn-O TFTs

We report operation characteristics of amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) annealed in dry O ₂ at temperatures up to 700 ^° C. The largest TFT mobilities were obtained by annealing at 200 ^° C-300 ^° C and the smallest subthreshold voltage swing ( S) was obtained at 200 ^° C, while those annealed at higher T exhibited poorer mobilities and S values. The TFTs annealed at ≥ 600 ^° C were crystallized and exhibited further poorer characteristics probably due to grain boundary issues; while, the deterioration by the 400 ^° C-500 ^° C annealing is attributed to depletion of hydrogen and consequent de-passivation effects. Device simulations and photoresponse spectroscopy extracted systematic variation of trap densities in the a-IGZO layer.