Effects of Sputter Parameters on Electrochromic Properties of Tungsten Oxide Thin Films Grown by RF Sputtering

Abstract

Abstract The electrochromic properties of tungsten oxide films grown by RF sputtering were investigated. Among the sputterparameters, first the Ar:O 2 ratios were controlled with division into only an O 2 environment, 1:1 and 4:1. The structure of eachfilm prepared by these conditions was studied by X-ray diffraction, X-ray photoelectron spectroscopy and Rutherfordbackscattering spectroscopy. The sputter-deposited tungsten oxide films had an amorphous structure regardless of the Ar:O 2 ratios. The chemical compositions, however, were different from each other. The stoichiometric structure and low-density filmwas obtained at higher O 2 contents. Electrochemical tests were performed by cyclic voltammetry and chronoamperometry at0.05 M H 2 SO 4 solutions. The current density and charge ratio was estimated during the continuous potential and pulse potentialcycling at − 0.5 V and 1.8 V, respectively. The film grown in a higher oxygen environment had a higher current density anda reversible charge reaction during intercalation and deintercalation. The in-situ transmittance tests were performed by He-Nelaser (633 nm). At higher oxygen contents, a big transmittance difference was observed but the response speed was too slow.This was likely caused by higher film resistivity. Furthermore, the effect of sputtering pressure was also investigated. Thestructure and surface morphology of each film was observed by X-ray diffraction and scanning electron microscopy. A roughsurface was observed at higher sputtering pressure, and this affected the higher transmittance difference and coloration efficiency.Key wordstungsten oxide, RF sputtering, electrochromism.