Electrochromic Tungsten Oxide Film Deposition

Tungsten trioxide (WO3) has been studied for many years. It is one of the best materials for use in the fabrication of electrochromic (EC) devices, such as electrically tintable glass for use in buildings and automobiles. WO3has the desirable characteristics of transparency, chemical stability—as in the stoichiometry doesn't change with time after deposition—and relatively low cost. Typically, WOx, where 3>x>2.75, is desired for the EC application for the following reasons: (1) in the x>3 region, the oxygen is rich such that the WOxfilm may not be bleachable after lithium atom insertion; and (2) in the region x<2.75, the film is no longer transparent.

A deposition method for electrochromic WOxfilms involves cyclic deposition of very thin poisoned and metallic tungstenoxide layers to build up a film with a desired general stoichiometry with x in the range of 3>x>2.75. The method may include: charging a deposition chamber with oxygen gas to poison a tungsten metal target; initiating sputtering of the target while reducing the oxygen partial pressure being supplied to the chamber and pumping the chamber; sputtering target for time t1+t2to form first and second tungstenoxide layers, where the first layer is deposited during time t1from a poisoned target and the second layer is deposited during time t2from a metallic target, and where the stoichiometry of the film comprising the first and second layers is a function of t1and t2; and, repeating until a desired film thickness is achieved.

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