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 ({>}{\rm 10}^{9}) , steep subthreshold swing (71-187 mV/decade), and high mobility (21-45 {\rm cm}^{2}/{\rm V}{\cdot}~{\rm s} ). Very small variation in device characteristics among the devices with the same channel dimensions is also confirmed.