Bias-stability improvement using Al₂O₃ interfacial dielectrics in a-InSnZnO thin-film transistors

We report amorphous-indium-tin-zinc-oxide (a-ITZO) thin-film transistors (TFTs) obtained using an aluminum-oxide (Al₂O₃) interfacial dielectric using atomic layer deposition between a silicon-nitride (SiN_X) gate dielectric and an a-ITZO active channel layer. The effect of the Al₂O₃ interfacial layer on the suppression of charge trapping in a-ITZO TFTs is presented. In transparent oxide TFTs, reducing the shift in threshold voltage by stress-including negative-bias stress (NBS) is one of the key issues in improving the stability performance of TFTs. The NBS stability of an a-ITZO TFT using an Al₂O₃/SiN_X double-layered dielectric is superior to that using an SiN_X single-gate dielectric, because of the smooth surface with a root-mean-square roughness of 0.147 nm and a low defect density of less than 3×10 ¹¹ eV^-1 cm^-2, which increases hydrophobicity. The a-ITZO TFTs using the Al₂O₃ interfacial dielectric show little change in the threshold voltage (∼0 V), and a long trapping time of ∼5000 s when a gate voltage of -25 V and drain voltage of 1 V are applied for 10 000 s. We show that the gate dielectric has a profound effect on the electrical stability, and suggest a way of improving the stability of a-ITZO TFTs.