A low-temperature method, supercritical CO 2 ͑SCCO 2 ͒ fluid technology, is employed to improve the device properties of ZnO TFT at 150°C. In this work, the undoped ZnO films were deposited by sputter at room temperature and treated by SCCO 2 fluid which is mixed with 5 ml pure H 2 O. After SCCO 2 treatment, the on/off current ratios and threshold voltage of the device were improved significantly. From x-ray photoelectron spectroscopy analyses, the enhancements were attributed to the stronger Zn-O bonds, the hydrogen-related donors, and the reduction in dangling bonds at the grain boundary by OH passivation.

The effects of post-annealing on performance of ZnO-based thin-film transistors (TFTs) fabricated at room temperature were investigated. It was observed that high-temperature annealing resulted in a large decrease in resistivity of the ZnO channel layer and caused a large off-state current for ZnO TFTs, while low-temperature annealing had little effect on the off-state current. The evolution of electrical performance of ZnO TFTs annealed at a lower temperature showed that the threshold voltage decreased greatly and the sub-threshold slope improved evidently without great change of the resistivity of the ZnO channel as the annealing time prolonged. The possible mechanism is that the traps have been removed without activating the donor defects in the ZnO channel layer.