Origin of variation in switching voltages in threshold-switching phenomena of VO2 thin films

We investigated the origin of the variation in switching voltages in threshold-switching of VO2 thin films. When a triangular-waveform voltage signal was applied, the current changed abruptly at two switching voltages, i.e., VON (insulator-to-metal) and VOFF (metal-to-insulator). VON and VOFF were measured by changing the period of the voltage signal, the temperature of the environment, and the load resistance. We observed that either VON or VOFF varied significantly and had different dependences with respect to the external parameters. Based on the mechanism of the metal–insulator transition induced by Joule heating, numerical simulations were performed, which quantitatively reproduced all of the experimental results. From the simulation analysis, the variation in the switching voltages for threshold-switching was determined to be thermal in origin.