Investigation of Electrical Performance and Operational Stability of Sputtered InSnZnO (ITZO) Thin Film Transistors

Abstract

We investigated the electrical properties and operational stability of amorphous indium-tin-zinc-oxide (a-ITZO) thin-films transistors (TFTs). We fabricated the a-ITZO TFTs using deposition by radio frequency sputtering at room temperature followed by a rapid thermal annealing (RTA) process at different temperatures and oxygen pressure (PO2). This is a more practical annealing route compared to a conventional furnace. Based on film densification and oxygen vacancy optimization, the a-ITZO TFTs exhibited 9.8 cm2/Vs, 0.82 V/decade and 1.39 V, for saturation mobility, sub-threshold swing and threshold voltage, respectively. Operation stability tests and hysteresis behavior of a-ITZO TFTs suggest that oxygen vacancy concentration of a-ITZO thin films gradually decreases under higher PO2, consequently affecting the threshold voltage and the shift seen after a gate bias stress test. This observation suggests that gate bias stress and hysteresis stability of an a-ITZO device is due to the effect of oxygen-controlled pressure in the RTA process. This a-ITZO TFTs electrical characterization qualitatively coincides with X-ray photoelectron spectroscopic analyses of oxygen vacancy concentration in a-ITZO thin films. Thus, our systematic a-ITZO thin film optimization using the oxygen-ambient RTA process is a practical basis for high-performance amorphous oxide semiconductor TFTs’ post-annealing methods.