Optimizing the Performance of the Atomic-Layer-Deposited Zinc–Tin-Oxide Thin Film Transistor by Ozone Treatment and Thermal Annealing

This study investigated alterations in the physical and electrical characteristics of amorphous ZnSnO (a-ZTO) thin films deposited by atomic layer deposition and a-ZTO thin film transistors (TFTs) subjected to various post-deposition annealing (PDA) processes. The ozone treatment at 19 Torr pressure and 320 °C temperature, followed by additional thermal annealing at 600 °C for 1 h in a furnace under an air atmosphere, remarkably improved device performance, showing a ∼390% increase in mobility compared to the as-deposited TFT. PDA processes affected the structural relaxation-driven carrier doping effect, oxygen defects, and hydrogen concentrations, influencing the reliability of the TFTs. Increasing PDA temperature generally increased the a-ZTO film density and decreased Urbach energy-related tail states, significantly increasing carrier mobility. In the negative gate bias stress tests, an abnormal hump was observed in the transfer characteristics, which was attributed to Sn-related ions trapped in the SiO2 gate insulator. In contrast, positive gate bias stress tests did not exhibit the hump but only a consistent shift of the transfer curve. The ozone and thermally treated sample showed significantly decreased threshold voltage shifts during the positive gate bias stress test. Finally, contact resistance between the Ti source and drain metals with the a-ZTO channel decreased by ∼30% under optimized PDA compared to the as-deposited TFT. This reduction stemmed from the smooth interface between the contact metal and channel due to the densification and decreased tail states in the a-ZTO thin film.