Metal-insulator transition mechanism in VO2 under electric bias

It is in controversy if metal-insulator phase transition (MIT) of VO$_{2}$ can be triggered by electric field/current. In this work, a series of two terminal devices with different gap length, width, and multiple-channel configurations were fabricated on epitaxially grown VO$_{2}$ thin films, to study its MIT mechanism under the electric bias. Micro-Raman spectroscopy was used to differentiate the rutile metallic phase from the monoclinic insulator phase. Voltage-current measurements indicated that a temperature-dependent critical current density (J$_{c}$) is required to induce MIT. Under the electric bias, the phase transition was observed to be a percolation process until a clear current path (or filament) is formed between the electrodes. Afterwards the pure metallic phase was identified along the current path, while outside of it become pure insulator phase. As current varies, current path width is proportionally changed to keep a constant current density. These observations indicate that a J$_{c}$ is necessary to maintain the metallic phase current path. Contributions of the current effect and Joule heat effect to the phase transition were discussed.