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

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Ionic liquid gating is a key technique for tuning the electronic properties of materials, particularly inducing metal-insulator transitions.
• The precise mechanism of carrier doping in metal oxide films via ionic liquid gating remains an active area of research.
• Tungsten oxide (WO3) is a promising metal oxide for electronic applications, but its conductivity modulation needs further investigation.

Purpose of the Study:

• To investigate the mechanism of metal-insulator transitions in WO3 films induced by ionic liquid gating.
• To explore the role of oxygen vacancies in modulating the conductivity of WO3 films.
• To correlate experimental observations with theoretical calculations.

Main Methods:

• Fabrication of flat and smooth WO3 films on SrTiO3 substrates using pulsed laser deposition.
• Measurement of field-effect transistor characteristics under varying gate voltages and atmospheric conditions (argon and oxygen).
• Density functional theory (DFT) calculations to study the electronic structure of oxygen-deficient WO3.

Main Results:

• A clear dependence of film behavior on oxygen pressure was observed, indicating environmental influence.
• Metallic behavior in WO3 films was achieved and attributed to oxygen vacancy formation at the oxide-ionic liquid interface.
• DFT calculations confirmed metallic behavior even at low oxygen vacancy concentrations, highlighting the contribution of W and O orbitals to conductivity.

Conclusions:

• Ionic liquid gating effectively induces metallic behavior in WO3 films by creating oxygen vacancies.
• Oxygen vacancies play a critical role in the conductivity modulation of WO3, leading to the observed metal-insulator transition.
• The study provides a comprehensive understanding of the ionic liquid gating mechanism in WO3, supported by theoretical validation.