Crystalline vanadium dioxide (VO2) shows a sharp insulator-metal transition (IMT) at relatively low temperature of around 68℃. Even in the polycrystalline VO2 film, IMT with resistance change over several orders of magnitude is realized. Voltage addition on the VO2 film leads to current jump at certain voltage with negative resistance (NR). In such I-V characteristics with NR, voltage across VO2 shows automatic transition between high and low resistance positions, which is called “self-oscillation phenomenon”. In this study, we fabricated VO2 thin films on conductive TiN layers, in which IMT with resistance change more than two orders of magnitude for out-of-plane direction was realized. Utilizing the VO2/TiN layered structure, we observed I-V characteristics with NR and self-oscillation with frequency higher than 1 MHz. Dependence of oscillation frequency on some parameters, such as source voltage, load resistance, and VO2 films thickness was examined. Furthermore, coupled-oscillation phenomenon achieved by capacitively-coupled two VO2 oscillators was investigated. Characteristic coupling with synchronized oscillation frequency and phase was observed. Coupled-oscillator is expected to be used for integrate and fire neuron element in neuro-morphic computing.
![](https://www.jstage.jst.go.jp/pub/vss/62/6/62_20180357/figure/62_20180357.jpg)
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