Tuning the Metal-Insulator Transition Properties of VO 2 Thin Films with the Synergetic Combination of Oxygen Vacancies, Strain Engineering, and Tungsten Doping.

Vanadium oxide (VO 2 ) is considered a Peierls-Mott insulator with a metal-insulator transition (MIT) at T c = 68° C. The tuning of MIT parameters is a crucial point to use VO 2 within thermoelectric, electrochromic, or thermochromic applications. In this study, the effect of oxygen deficiencies, strain engineering, and metal tungsten doping are combined to tune the MIT with a low phase transition of 20 °C in the air without capsulation. Narrow hysteresis phase transition devices based on multilayer VO 2 , WO 3 , Mo 0.2 W 0.8 O 3, and/or MoO 3 oxide thin films deposited through a high vacuum sputtering are investigated. The deposited films are structurally, chemically, electrically, and optically characterized. Different conductivity behaviour was observed, with the highest value towards VO 1.75 /WO 2.94 and the lowest VO 1.75 on FTO glass. VO 1.75 /WO 2.94 showed a narrow hysteresis curve with a single-phase transition. Thanks to the role of oxygen vacancies, the MIT temperature decreased to 35 °C, while the lowest value (T c = 20 °C) was reached with Mo 0.2 W 0.8 O 3 /VO 2 /MoO 3 structure. In this former sample, Mo 0.2 W 0.8 O 3 was used for the first time as an anti-reflective and anti-oxidative layer. The results showed that the MoO 3 bottom layer is more suitable than WO 3 to enhance the electrical properties of VO 2 thin films. This work is applied to fast phase transition devices.