Mechanism and Origin of Hysteresis in Oxide Thin-Film Transistor and Its Application on 3-D Nonvolatile Memory

Hysteresis in the current-voltage characteristics of a ZnO thin-film transistor (TFT) has been studied. Electric dipoles at the interface of the dielectric and the channel have been proposed as the agents responsible for the hysteresis. From experimental results and theoretical analysis, the water diffusing into the active layer is found as the main origin of the hysteresis. Based on this finding, devices free of hysteresis were obtained by using heat treatment and a passivation layer to control water diffusion in the fabrication process. Conversely, the hysteresis characteristics can be engineered so as to benefit the application of electronic memory. The function of the TFT device that serves as a memory element was also investigated and demonstrated in this paper. Owing to its low temperature process and simplified structure (compared with the FeRAM), 3-D stacked or even transparent nonvolatile memory would be its potential application.