Effects of deposition parameters on RF-sputtered WO3 thin films

In the absence of additional oxygen, thin films of tungsten oxide (WO3) were prepared on ITO conductive glass substrates by radio-frequency (RF) magnetron sputtering. The effects of sputtering power, working air pressure, substrate bias voltage and substrate temperature on the surface morphology, microstructure, optical properties and electrochromic (EC) performance of the films were systematically investigated. The research shows that the sputtering power of 80-100 W can ensure a moderate deposition rate of ∼10−2 nm/s and help to obtain nondense films. Similarly, the working air pressure of 1.0 Pa also leads to the deposition of loose films, which benifits for the improving of optical transmittance and EC performance of WO3 thin films. The applied substrate bias has little effect on the optical properties, but it will degrade the coloring and/or bleaching efficiency of WO3 thin films and greatly reduce their optical modulation. When the substrate temperature rises to 600 °C, the film begins to crystallize and exhibits a rods-patterned porous structure, which leads to a small increase in the optical modulation.