Effects of bias voltage on microstructure and properties of vanadium dioxide films deposited by DC magnetron sputtering

Abstract

Vanadium dioxide (VO₂) is a conventional semiconductor material with a phase transition, and its properties strongly depend on the preparation process. In this study, VO₂ thin films were fabricated on c-type sapphire substrates by direct current (DC) magnetron sputtering, and the deposition was conducted under different bias voltages to investigate their impacts on the microstructure, morphology, electrical properties, and optical properties of the films. Raman spectra of the films exhibited molecular bond vibrations with specific spectral peaks of VO₂ and vanadium pentoxide (V₂O₅). In situ variable temperature Raman spectroscopy revealed the characteristics of the films during the phase transition of VO₂. Scanning electron microscopy (SEM) images showed that as the bias voltage increased, the surface structure of the film gradually became dense, and the surface morphology was smoother. The thin film deposited at a bias voltage of −100 V exhibited excellent optical and electrical properties, with an optical modulation amplitude of 78.25% at 4.5 μm. The energy distribution study demonstrated that the energy provided by the bias endowed ions with more kinetic energy, thereby improving the film formation quality. Moreover, V₂O₅ was directly generated under a high bias voltage. Consequently, our results confirmed the formation of VO₂ with related structural, optical, and electrical properties under various bias conditions in the magnetron sputtering process, providing a strategy for fabricating stable and high-quality VO₂ thin films.