Self-oscillation up to 9 MHz based on voltage triggered switching in VO2/TiN point contact junctions

We demonstrate self-sustaining electrical oscillations with frequency of MHz range based on out-of-plane voltage-triggered switching in VO2 thin films grown on conductive layers. VO2 films deposited by a reactive sputtering method at a low temperature of 250 °C on conductive TiN layers showed thermally induced out-of-plane insulator-metal transition with two orders of change in resistance. By applying dc voltage to the layered device in a point contact configuration, self-sustaining electrical oscillations were triggered and the highest frequency of 9 MHz was achieved. Dependence of the frequency on the film thickness, as well as on the source voltage and on the series resistance, was examined in order to clarify the oscillation mechanism and the factors that affect the frequency. The oscillation frequency, which is dominated by recovering time from metallic to insulating state, decreased with increasing film thickness, indicating that the resistance of VO2 film determines the time constant for the recovery path. Self-sustaining oscillation phenomena achieved in point contact devices has great potential for applications in MHz band generators and micro-inverters.