Enhanced electrical performance and reliability of Ti-IGZO thin-film transistors with Hf_1-xAl_xO gate dielectrics

A thin-film transistor (TFT) with a Ti-IGZO channel layer and Hf_1-xAl_xO gate dielectric is proposed to improve the performance and reliability of the device. The experimental results show that in three types of TFTs based on HfO₂/IGZO, Hf_1-xAl_xO/IGZO and Hf_1-xAl_xO/Ti-IGZO gate dielectric/channel structures, the Hf_0.88Al_0.12O/Ti (2.0%)-IGZO TFT exhibits the best device performance with the subthreshold swing of 86 mV dec^-1, field-effect mobility of 28.63 cm²V^-1s^-1 and on/off current ratio of 3.26 × 10⁸. In particular, it shows a hysteresis voltage as low as 0.02 V and a threshold voltage shift after 1000 s positive/negative gate bias stress/white light illumination of 0.134 V/-0.089 V/-0.195 V, compared with 0.45 V and 0.612 V/-0.507 V/-0.657 V of the HfO₂/IGZO TFT. These improvements are due to the incorporation of Ti into the IGZO channel, which reduces defect density, while adding Al to HfO₂ improves surface roughness to inhibit surface scattering and charge capture during stress testing.