Effect of post-annealing temperatures on thin-film transistors with ZnO/Al₂O₃ superlattice channels

Oxide-based thin-film transistors (TFTs) were fabricated using ZnO/Al₂O₃ superlattice channels deposited by atomic layer deposition. Here, a post-annealing treatment was performed at various temperatures (200-550°C) and the properties of the oxide TFTs were evaluated. An annealing temperature up to 250°C showed enhanced TFT performance, while further increases in the annealing temperature resulted in an abruptly invisible switching property due to the high conductivity of the channel layers. With respect to annealing temperature, increased electrical conductivity in the superlattice films was attributed to the increase of conducting crystalline layers due to the inter-diffusion behavior between the ZnO and Al₂O₃ layers. The formation of the conducting layer was related to substitution by Al^{3 +} ions into Zn^{2 +} sites in the inter-diffusion region. The ZnO/Al₂O₃ superlattice TFT with the best field effect mobility, 30.2 cm²/Vs, was observed for an annealing temperature of 250°C.