Effect of oxygen on the electrochromism of RF reactive magnetron sputter deposited tungsten oxide

High coloration efficient WO3, deposited by reactive sputtering, is influen ced by the oxygen concentrations in a sputtering system. In this study, a s urvey on the effect of oxygen concentration in the rf sputtering atmosphere and the subsequent deposited film was studied to reveal the microstructura l changes in relation to the electrochromic properties. The electrochromic properties determined include cyclic voltammetric behavior, coloring and bl eaching response time, x(LixWO3), optical density changes and coloration ef ficiency. Experimental results show that the maximum current, as well as th e x(LixWO3) value, occurred in the O-2/Ar flow ratio at 0.3-0.4. This may b e compromised by the low valence tungsten ions that play a role in expellin g cations in the films deposited at a low O-2/Ar flow ratio and hypothetica lly due to the limitation of electron conduction for high oxidation films d eposited at high O-2/Ar flow ratios. The response time, decreased with the increasing O-2/Ar flow ratio, can be considered separately by the ion diffu sion difficulty already established elsewhere. As a whole, the optimized O- 2/Ar flow ratio would be in the range of 0.3-0.4 for transmittance control applications. (C) 2000 Elsevier Science S.A. All rights reserved.