The Effects of Post Annealing Process on the Electrical Performance and Stability of Al-Zn-O Thin-Film Transistors

In this work, we studied the effects of post annealing process on the electrical performance and positive bias stability (PBS) of aluminum-zinc-oxide (AZO) thin film transistors (TFTs). Among all the devices, the TFT annealed in vacuum atmosphere exhibits excellent I-V characteristics, such as a saturation mobility ( $\mu _{{{\text {sat}}}}$ ) of 45.90 cm2/ $\text{V}\cdot \text{s}$ , a steep subthreshold swing of 263 mV/decade, a high $\text{I}_{{ \mathrm{\scriptscriptstyle ON}}}/\text{I}_{{ \mathrm{\scriptscriptstyle OFF}}}$ ratio of $7.56\times 10^{{{{8}}}}$ because of its excellent film quality. In addition, the positive bias stability of TFTs annealed in different atmosphere under positive bias (+5V, 2000s) were also conveyed. The threshold voltage shift ( $\Delta \text{V}_{{{\text {th}}}}$ ) was 0.3V (mixed gas, Ar:O2 = 3:3), 0.9V (vacuum), 1.0V (O2). These results can be explained by the $\text{O}_{{{\text {II}}}} /\text{O}_{{{\text {total}}}}$ of the AZO films. The AZO film annealed in mixed gas (Ar:O2 = 3:3) has the least oxygen vacancy density that leads to the least $\Delta \text{V}_{{\mathbf {th}}}$ under positive bias.