Electrochemichromism of rf reactively sputtered tungsten-oxide films

Abstract

Electrochemichromic proerties of tungsten-oxide films prepared by rf reactive sputtering from a metallic tungsten target have been investigated. The films, approximately 5200-6800-Å thick, were deposited on the substrate at 200 °C under a constant total operating pressure of 5×10−3 or 4×10−2 Torr using a mixture of Ar and 4-50% O2. Electrochromic properties of the reactively sputtered tungsten-oxide films depend considerably on the total operating pressure and oxygen concentration of the sputtering atmosphere. The transparent tungsten-oxide films, with a resistivity of approximately 106−1010 Ω cm and prepared under a total operating pressure of 4×10−2 Torr in an atmosphere containing more than 5% O2, have good electrochromic properties similar to those of the vacuum evaporated films form WO3 powder. But, the transparent oxide films, formed under a total operating pressure of 5×10−3 Torr in an atmosphere containing more than 16% O2, show a poor electrochromic property, although these films have a resistivity of approximately 107−1011 Ω cm. Upon electrochromic coloration, the optical spectra of tungsten-oxide films with a good electrochromic property show increased absorption in the visible and near infrared region, with the absorption band centered at ∼0.95 μm.