Electrochromic tungsten oxide film deposition

A method of depositing a stoichiometrically controlled tungsten oxide thin film comprising:

• charging a deposition chamber with oxygen gas for time t0 to poison the surface of a tungsten metal target with oxygen;
• sputtering of said tungsten metal target and reducing the oxygen partial pressure being supplied to said deposition chamber while vacuum pumping said deposition chamber, wherein the oxygen partial pressure is gradually decreased in said deposition chamber as said tungsten metal target is sputtered;
• depositing tungsten oxide sputtered from said tungsten metal target for a time t=t1+t2 to form first and second tungsten oxide layers on a substrate, wherein said first tungsten oxide layer is deposited during said time t1 from said tungsten metal target with the poisoned surface and said second tungsten oxide layer is deposited during said time t2 from said tungsten metal target with a metallic surface, and wherein the stoichiometry of the film comprising the first and second tungsten oxide layers is a function of t1 and t2;
• and
• repeating said charging, sputtering and depositing until a desired film thickness is achieved;
• wherein there is no sputtering and no depositing during said charging.