Electrically controlled metal-insulator transition process in VO2 thin films

We report the evolution process of VO2 thin films from the insulating phase to the metallic phase under current injection for the two-electrode-based thin-film devices. Based on electrical characterization and Raman microscopic detection, it was found that there exist two critical current densities, based on which the insulator-to-metal transition process can be divided into three stages. In stage I with low current injection, the VO2 film in the insulating (semiconducting) phase acts as a resistor until the first critical current density, above which the insulator-metal transition is a percolation process with metallic rutile and insulating monoclinic phases coexisting (stage II); while beyond a second critical current density, a filamentary current path with pure metallic phase is formed with the remaining part outside of the current path receding back to the pure insulating phase (stage III). We confirm that a critical current density is required for the onset of electrically induced insulator-to-metal transition in VO2 thin films.