An analysis on applicability of Ti-doped ZnO films as the channel layer of TFTs

In this paper, Ti-doped ZnO TFTs on SiO₂/Si substrates by simultaneous RF sputter of Zn and DC magnetron sputter of Ti are successfully fabricated. With undoped ZnO TFTs, as-grown Ti-doped ZnO are compared with post-annealed Ti-doped ZnO TFTs in the furnace at O₂ atmosphere of 300 °C. As the annealing time increases, the electrical characteristics such as sub-threshold slop (SS) and on/off current ratio of Ti-doped ZnO TFT become better. In order to find out the reason of performance improvement, the optical analysis is carried out. The data of XRD and AFM indicate that grain size and RMS (root mean square) roughness increase in accordance with annealing time, and the potential barrier and work function of Ti-doped ZnO is smaller than that of undoped ZnO, which indicates that the performance improvement by post-annealing in O₂ atmosphere is due to a crystalline reformation in Ti-doped ZnO films.