No abstract

Low-frequency (∼2 Hz) current self-oscillations were first obtained in a millimeter-sized two-terminal planar device with a vanadium dioxide (VO2) film. The film temperature distribution dynamics was investigated within one oscillation period. It was established that the formation and disappearance of a conductive channel occur in a film in less than 60 ms with oscillation period 560 ms. The experimentally observed temperature in the channel region reached 413 K, being understated due to a low infrared microscope performance (integration time 10 ms). The VO2 film temperature distribution dynamics was simulated by solving a 2D problem of the electric current flow and heat transfer in the film. The calculation showed that the thermally initiated resistance switching in the film occurs in less than 4 ms at a channel temperature reaching ∼1000 K. The experimental results and simulation are consistent with the current self-oscillation mechanism based on the current pinching and dielectric relaxation in the VO2 film at the metal-insulator phase transition.

The temperature dependence of electrical capacitance of planar microstructures with vanadium dioxide (VO2) film near the insulator-metal phase transition has been investigated at the frequency of 1 MHz. Electrical capacitance measurements of the microstructures were performed by the technique based on the using of a two-terminal resistor-capacitor module simulating the VO2 layer behavior at the insulator-metal phase transition. At temperatures 325–342 K, the anomalous increase in microstructures capacitance was observed. Calculation of electric field in the microstructure showed that VO2 relative permittivity (ε) reaches ∼108 at the percolation threshold. The high value of ε can be explained by the fractal nature of the interface between metal and insulator clusters formed near the insulator-metal phase transition.