Implementation of Film Profile Engineering in the Fabrication of ZnO Thin-Film Transistors

A novel approach, which can delicately form a desirable film profile for deposited gate oxide, channel, and source/drain contacts of oxide-based thin-film transistors (TFTs) is proposed. To demonstrate the film-profile engineering concept used in this approach, a simple one-mask process was developed for fabricating ZnO TFTs with submicrometer channel length. The fabrication takes advantage of a suspended bridge hanging across the device to tailor the desirable profile of deposited films with proper tools. The fabricated devices show high ON/OFF current ratio (>10⁹), steep subthreshold swing (71-187 mV/decade), and high mobility (21-45 cm²/V·s). Very small variation in device characteristics among the devices with the same channel dimensions is also confirmed.