High Mobility dc Sputtered Amorphous In-Sn-Zn-O Thin-Film Transistors
Chumin Zhao, Mitsuru Nakata, and Jerzy Kanicki
We investigated the electrical properties of dc sputtered amorphous In–Sn–Zn–O (a-ITZO) thin-film transistors (TFTs) fabricated under various process conditions. Fabricated a-ITZO TFTs achieved high field-effect mobilityof around 30 cm2/Vs, threshold voltage of 1.0 V, subthreshold swing of 0.38 V/dec. An analytical field-effect mobility model is proposed for a-ITZO TFTs with key parameters extracted using the least square error linear fitting and second order derivative methods. The impacts of a-ITZO channel thickness and oxygen gas flow ratio on device performance were evaluated. We found that effective trap states of a-ITZO reduce with increasing channel thickness, which leads to improved device performance. The variations in device performance at different oxygen gas flow ratio could be explained by the acceptor-like excess oxygen states. Finally, the a-ITZO TFT bias-temperature stress induced electrical instability was studied. In comparison to amorphous In–Ga–Zn–O (a-IGZO) TFTs, improved electrical stability was observed for a-ITZO TFTs using exactly the same BTS conditions. The enhanced device mobility and electrical stability of a-ITZO TFTs are very desirable properties for next generation high resolution flat-panel displays or detectors.
