Oxygen Vacancy in WO3 Film-based FET with Ionic Liquid Gating

Abstract

Ionic liquid gating is a versatile method for inducing a metal-insulator transition in field-effect transistor device structures. The mechanism of carrier doping in metal oxide films is under debate. Ionic liquid gating of a WO₃ film-based field effect transistor is discussed in this report. Flat and relatively smooth WO₃ films were deposited on SrTiO₃ substrates by pulsed laser deposition. Swept and constant gate voltage characteristics are measured in both argon and oxygen atmospheres. The results show a clear dependence on the oxygen pressure of the experimental chamber. Metallic behavior in the films is attributed to oxygen vacancy formation in the WO₃ layer induced by the high electric field at the oxide-ionic liquid interface. The density of states of a monoclinic supercell of oxygen deficient WO₃ was studied by density functional theory (DFT). Calculated W and O partial densities of states verify metallic behavior even at dilute oxygen vacancy concentrations and show the role of W and O orbitals in the conductivity.