Field-induced water electrolysis switches an oxide semiconductor from an insulator to a metal

Water is composed of two strong electrochemically active agents, H+ and OH− ions, but has not been used as an active electronic material in oxide semiconductors. In this study, we demonstrate that water-infiltrated nanoporous glass electrically switches an oxide semiconductor from insulator to metal. We fabricated a field-effect transistor structure on an oxide semiconductor, SrTiO3, using water-infiltrated nanoporous glass—amorphous 12CaO·7Al2O3—as the gate insulator. Positive gate voltage, electron accumulation, water electrolysis and electrochemical reduction occur successively on the SrTiO3 surface at room temperature. This leads to the formation of a thin (~3 nm) metal layer with an extremely high electron concentration (1015–1016 cm−2), which exhibits exotic thermoelectric behaviour. The electron activity of water as it infiltrates nanoporous glass may find many useful applications in electronics or in energy storage. Water is composed of the electrochemically active species, H+ and OH−, but has not been used as an active electronic material. In this study, a field-effect transistor is developed that uses water-infiltrated nanoporous glass as the gate insulator; this new application of water may be useful in electronics and energy storage.