A Comparative Study on the Effects of Annealing on the Characteristics of Zinc Oxide Thin-Film Transistors With Gate-Stacks of Different Gas-Permeability

The effects of different thermal processing on the characteristics of zinc oxide (ZnO) thin-film transistors (TFTs) with either gas-permeable or sealed gate-stack were studied and compared. The characteristics of a TFT heat-treated in a nonoxidizing ambience or under a sealed configuration degraded with increasing annealing temperature, though the former offered a comparatively wider process margin. On the other hand, the oxidization of the channel region of a TFT allowed by a gas-permeable gate-stack resulted in significant improvement in the transistor characteristics, e.g., eliminating the hysteresis and increasing the field-effect mobility to a relatively high value of 55 cm²/Vs. The difference in behavior is attributed to the annealing-dependent generation and annihilation of defects in ZnO under different coverage configurations, and suggests a general guideline on the thermal processing of ZnO TFTs.