Electrochromic WO3 Films with Controlled High-Rate Deposition By Hollow Cathode Gas Flow Sputtering

Abstract

An amorphous WO3 is one of the most important materials for electrochromic (EC) devices because of its blue coloration caused by electron injection. For the industrial applications including EC smart windows, there are strong demands for EC devices to be produced with a high deposition rate, with a higher stability and at lower costs. Gas flow sputtering (GFS) has the possibility for very high deposition rate because of using high density hollow cathode discharge and a large amount of sputtering gas (Ar) flow and the stability of the reactive sputtering process in the wide range of the reactive gas (O2) flow, so there is no “transition region” which should appear in the conventional reactive sputtering processes. In this study, reactive GFS was adopted to deposit amorphous WO3 films with the high EC properties with the high deposition rate. WO3 films were deposited on unheated ITO-coated glass substrate by GFS using two W metal targets which were mounted parallel with each other. Sputtering power was fixed at 1000 W. Ar and O2 flows were 5.0 slm and 10-125 sccm, respectively. Total gas pressures during the depositions were 70 Pa and 90 Pa. X-ray diffraction measurements showed that the all films were amorphous. The density of WO3 films were estimated from data measured by X-ray fluorescence and ICP spectroscopy. The films were electrochemically intercalated with protons and lithium ions. The deposition rates were almost constant with O2 flow during depositions. Figure shows the coloration efficiency of proton intercalated WO3 films as a function of O2 flow during depositions. The coloration efficiency had a tendency to decrease with increasing O2 flow during depositions. [1] N. Oka, Y. Shigesato, et al., Thin Solid Films 532, 1-6 (2013). Figure 1