Tungsten Oxide Film

Several methods are used to form tungsten oxide films. The methods include sputtering, chemical vapor deposition, and plasma enhanced chemical vapor deposition, in which sub-atmospheric pressure must be maintained. In these methods, large, complex and expensive equipment is needed, and the methods involve significant energy consumption and relatively high operating costs. The films produced by current methods are tungsten oxide films of WO3, without suboxides, and which are colorless or faint yellow, single color films.

It has been suggested that tungsten containing films be formed by a metallo-organic deposition (MOD) method, wherein an organic metal compound is applied to a substrate which is heated to form the desired metal oxide film. Most MOD processes for deposition of transition metal oxides use carboxylate salts. However, tungsten carboxylates have not been easily synthesized.

It is an object of this invention to provide an MOD method for producing a tungsten oxide film by pyrolyzing at least a portion of an alkyl amine tungstate compound; in which the alkyl amine tungstate compound is a soluble alkyl ammonium salt of tungstic acid; in which time and temperature of heating are varied so as to provide a desired color gradient in the tungsten oxide film and suboxides of the tungsten oxide (WO3); and which utilizes a precursor which produces a high tungsten oxide yield thereby forming a relatively dense tungsten oxide film.

It is a further object to provide tungsten oxide films which include suboxides of tungsten oxide (WO3); which have an average ratio of oxygen atoms to tungsten atoms equal to or less than 3:1; which are denser than films produced from currently known MOD precursor compounds; which have a color gradient, that is, a single continuous film marked by regions of different colors; and wherein the regions of color are electrochromic.

In this method, tungsten oxide films are formed without vacuum equipment. Uniform faint yellow to white (colorless) films having essentially no organic matter or impurities are produced, or films having regions of color across the substrate are produced ranging from nearly colorless or faint yellow to deep brown, which offer the potential for inexpensively and controllably darkening windows.

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