Improvement of phase transition properties of magnetron sputtered W-doped VO2 films by post-annealing approach

In this work, we investigate the improvement of the thermochromic properties of W-doped vanadium dioxide (VO₂) films induced by annealing temperatures. Firstly, W-doped VO₂ films with different W contents were successfully prepared on quartz substrates by direct current (DC) reactive magnetron sputtering. The results show that the W element not only decrease the phase transition temperature of VO₂ film but also seriously decrease the infrared modulation performance of the film. Secondly, Undoped and W-doped VO₂ films with different annealing temperatures were prepared and characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM) tests. The effect of annealing temperature on the chemical states, crystal structure, and surface morphology of W-doped VO₂ films was analyzed. It is found that VO₂ film with the 1.4 at.% ratio of W contents has excellent metal–insulator phase transition performance compared to undoped VO₂ film at the annealing temperature of 400 °C, i.e., narrower hysteresis width (4.3 °C) and lower phase transition temperature (37.4 °C). More importantly, the infrared amplitude modulation of the film is closer to that of undoped VO₂ films. This is attributed to the enhanced (011) diffraction peak intensity and larger particle size and obvious grain boundary in the film. This work shows proper annealing temperatures can maintain the phase-change amplitude modulation performance of W-doped VO₂ films while lowering the phase transition temperature and have great potential for infrared modulation applications.