Electrical Properties Of Metal Oxide Thin Films And Application In TFTs

The 20th century is the age of flat panel display, most of which is active matrix liquid crystal display (AMLCD). By introducing thin film transistors (TFT) as the switching unit in AMLCD pixel, the performance of display device can be greatly improved. The traditional amorphous silicon TFT has low field effect mobility, and it is very photosensitive, while polysilicon TFT’s production process is complicated and costly, consequently, the scope of their wider application is limited. However, if we use semiconductor oxide as the active layer, not only can we get a higher mobility, bu also the manufacturing process is easier, which shows a great prospect.In this paper, we study the fully transparent oxide TFTs to solve the disadvantage of amorphous silicon TFTs. We first investigated the electrical properties of In2O3, InZnO, ZnSnO and Ta2O5 films, respectively, to select the most suitable material and the best growth parameters. The carrier concentration of In2O3 and InZnO films is between 1019～1020cm-3, and the resistivity is between 10-3～10-2Ω·cm under different grown conditions.While for ZnSnO films, they are between 1015～1019cm-3 and 10-1～102-cm. For the consideration of the TFT device’s performance, we choose In2O3 film as the source and drain eletrode, ZnSnO films as the active layer and high k material Ta2O5 as the insulating layer. The gate eletrode is ITO.The best gas parameter to deposite Ta2O5 films is a working pressure of 2.0Pa and an 02/Ar radio of 2/20 atmosphere. The TFT device was post annealed in air for lh after removing Ta2O5 films.We fabricatd the fully transparent ZnSnO-TFTs by using SiO2 and Ta2O5 films as the insulating layer.The TFT devices exhibit good saturation characters and the gate voltage control ability. The ZnSnO-TFT using SiO2 as the insulating layer has a mobility of 3.0 cm2/(V·s), an on/off current radio of 8×103, a threshold voltage of 1.8V and a subthreshold swing of 6.5V/decade. The Ta2O5 based ZnSnO-TFT with a ZnSnO film’s thickness of 60nm has good electrical properties, of which the field effect mobility is 21.2cm2/(V-s), the on/off current radio up to 105, the threshold voltage 0.8V and the subthreshold swing 0.8V/decade. The performance of ZnSnO-TFT using Ta2O5 as the insulating layer is much better than that of SiO2 based ZnSnO-TFT.