In this paper, high-performance InGaZnO (IGZO) thin-film transistors were fabricated with film-profile-engineering scheme. The impacts of gate dielectric, O 2 /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 Al 2 O 3 as the gate dielectric, decent performance in terms of high ON/ OFF current ratio (>10 8 ), extremely steep subthreshold swing (62 mV/decade), and good mobility (19.8 cm 2 /V·s) is obtained. The influences of O 2 /Ar flow ratio are distinct for the devices with Al 2 O 3 gate oxide. Significant improvement in the stability of the devices to the environment is achieved with the anneal done in a low-pressure N 2 ambient. Index Terms-Film profile engineering (FPE), InGaZnO (IGZO), metal oxide, thin-film transistors (TFTs).