Gate‐Induced Massive and Reversible Phase Transition of VO₂ Channels Using Solid‐State Proton Electrolytes

Abstract The use of gate bias to control electronic phases in VO₂, an archetypical correlated oxide, offers a powerful method to probe their underlying physics, as well as for the potential to develop novel electronic devices. Up to date, purely electrostatic gating in 3‐terminal devices with correlated channel shows the limited electrostatic gating efficiency due to insufficiently induced carrier density and short electrostatic screening length. Here massive and reversible conductance modulation is shown in a VO₂ channel by applying gate bias V_G at low voltage by a solid‐state proton (H⁺) conductor. By using porous silica to modulate H⁺ concentration in VO₂, gate‐induced reversible insulator‐to‐metal (I‐to‐M) phase transition at low voltage, and unprecedented two‐step insulator‐to‐metal‐to‐insulator (I‐to‐M‐to‐I) phase transition at high voltage are shown. V_G strongly and efficiently injects H⁺ into the VO₂ channel without creating oxygen deficiencies; this H⁺‐induced electronic phase transition occurs by giant modulation (≈7%) of out‐of‐plane lattice parameters as a result of H⁺‐induced chemical expansion. The results clarify the role of H⁺ on the electronic state of the correlated phases, and demonstrate the potentials for electronic devices that use ionic/electronic coupling.