Effects of gate dielectric and process treatments on the electrical characteristics of IGZO TFTs with film profile engineering

In this paper, high-performance InGaZnO (IGZO) thin-film transistors were fabricated with film-profile-engineering scheme. The impacts of gate dielectric, O₂/Ar ratio during the sputtering of the IGZO, and annealing ambient on the device performance were investigated. It is found that the turn-ON voltage of the device is closely related to the gate dielectric material. For the devices with Al₂O₃ as the gate dielectric, decent performance in terms of high ON/OFF current ratio (> $10^{\mathrm {\mathbf {8}}}$), extremely steep subthreshold swing (62 mV/decade), and good mobility (19.8 cm²/V $\cdot $ s) is obtained. The influences of O₂/Ar flow ratio are distinct for the devices with Al₂O₃ gate oxide. Significant improvement in the stability of the devices to the environment is achieved with the anneal done in a low-pressure N₂ ambient.