High-Performance Unannealed a-InGaZnO TFT With an Atomic-Layer-Deposited SiO 2 Insulator

Amorphous In–Ga–Zn–O (a-IGZO) thin-film transistor with an atomic-layer-deposited (ALD) SiO2 gate insulator was fabricated under a maximum processing temperature of 250 °C and compared with the counterpart with a plasma-enhanced chemical vapor deposited (PECVD) SiO2 gate insulator. It was demonstrated that the ALD SiO2 insulator could generate much better device performance than the PECVD one. This is attributed to a lower density of interfacial traps, weaker surface roughness scattering, and enhanced passivation of oxygen vacancies in the a-IGZO channel atop the ALD SiO2 film with more OH groups. Without the need of post-annealing, the ALD SiO2 device exhibited very good stability under a negative gate bias stress (−15 V), while maintaining superior performance such as quite high field effect mobility of 63.6 cm $^{2}~\text{V}^{-1}\text{s}^{-1}$ , a low threshold voltage of −0.10 V, a small subthreshold swing of 0.14 V/decade, and a large ON/OFF current ratio of $\sim 10^{8}$ .