The tungsten oxide film may be deposited on the substrate by any suitable method including such conventional deposition techniques as, e.g., sputtering, chemical vapor deposition (CVD) and the spray method. As would be apparent to those skilled in the art in view of the present disclosure, the tungsten source employed in such methods will vary with the technique used. The process of depositing a film of tungsten oxide according to sputtering generally involves the application of a radio frequency voltage to a solid tungsten metal target exposed to an oxygen-containing atmosphere at reduced pressure. Chapman is hereby expressly incorporated by reference for its teachings of sputtering techniques. Another useful film deposition technique which may be employed to deposit a tungsten oxide film according to the present invention, is the well-known CVD process. It generally involves the flowing of gaseous reactants, one of which is a tungsten compound such as tungsten carbonyl, over a heated substrate. Thin Film Processes edited by J. L. Vossen and Werner Kern is herein expressly incorporated by reference for its teaching of such a process. Still other useful processes for depositing the tungstenoxide film on the surface of the substrate will be apparent to those skilled in the art in view of the present disclosure. The temperature of the substrate during the deposition process may vary and is not critical to the invention. For example, the tungstenoxide film may be deposited at room temperature or at an elevated temperature, the latter being the case when such films are deposited on a hot glass ribbon being produced by the well-known float glass process. The latter may involve temperatures in the range of 80° C. to about 700° C.

Generally, the tungsten oxide film is deposited on the substrate in a thickness of preferably between about 200 and 6000. The desired thickness of the film is determined by various factors, including reactant concentrations temperature and substrate velocity.

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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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Tungsten oxide films are of critical importance forelectrochromic device technology ,such as for smart windows capable of varying the throughput of visible light and solar energy.

Tungsten oxide films (WO(3)) are deposited by thermal evaporation techniques using the starting materials of tungsten (W) and tungsten oxide (WO(3)). By varying deposition parameters, three main types of WO(3) film exhibiting different optical properties form. These are blue, gray, and colorless films. The samples are characterized optically and morphologically. Blue-colored samples exhibit a broad selective absorption peak around 1000nm. Absorption of gray-colored samples spreads out in the visible region in an exponential form. The refractive indices of samples are between 1.9 and 2.1. The energy gap of blue and colorless samples is 3.32 eV, but that of the gray-colored samples is 3.18 eV and smaller. X-ray diffraction studies reveal that evaporated WO(3) films are amorphous. Fourier transform infrared spectra of samples were studied to evaluate bond properties. Colorless near-stoichiometric tungsten oxide films exhibit three absorption peaks in the 1000-600-cm(-1) window. These peak locations, in terms of cm(-1) window. These peak locations, in terms of cm(-1), are 669,737, and 813. In the colored samples, these three absorption peaks split into two peaks ~20 cm(-1) apart.

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After a Cu substrate is contacted with tungstenoxide powders, thermal reduction treatment is carried out under hydrogen atmosphere. Namely, the present method includes the steps of putting a substrate of Cu, Ni, Fe, Co, Cr, W, or the like in an upper, middle, or lower portion of a tungsten oxide (WO3or WO2.9) layer and carrying out thermal treatment thereon under a hydrogen atmosphere.

Such a coating method is widely applicable to another species of the metal substrate such as Ni, Fe, Co, Cr, W, and the like as well as Cu. Therefore, the tungsten oxide thin film method according to the present method is applicable to any kind of metal substrates.

A tungsten thin film according to the present method can be coated 500 nm˜25 μm thick by carrying out thermal treatment for 10 minutes to six hours at a temperature range between 650˜1050° C.

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