Low-emissivity coatings are well known in the art. Typically, they include one or two layers of infrared-reflection film and two or more layers of transparent dielectric film. The infrared-reflection film, which generally is a conductive metal like silver, gold, or copper, reduces the transmission of heat through the coating. The dielectric films are used to anti-reflect the infrared-reflection films in selected spectral regions (visible region of sun light) and to control other properties and characteristics of the coating, such as color and durability. Commonly used dielectric materials include oxides of zinc, tin, indium, bismuth, and titanium, among others.
Most commercially available low-emissivity coatings have one or two silver layers each sandwiched between two coats of transparent dielectric film. Increasing the number of silver films in a low-emissivity coating can increase its infrared reflection. In commercial coating processes the Ag films are supported by growth support layers (below) and protective layers above. Especially the protective layers above can add some additional (to the silver films) absorption to the layer-stack. For multiple silver films in a layer stack this can add up to total absorption levels not acceptable for some applications. This will also reduce the visible transmission of the coating, and/or negatively impact the color of the coating, and/or decrease the durability of the coating. In some processes, growth support layers are provided beneath silver films and protective layers are provided above silver films. An increase in the number of growth support layers and protective layers in a low-emissivity coating can increase the overall absorption of the coating. This can be undesirable in some cases. Perhaps for these reasons, low-emissivity coatings with three silver layers have not found much place in the market.
It would be desirable to provide a low-emissivity coating that includes three infrared-reflection film regions and has desirable coating properties and characteristics. It would also be desirable to provide deposition methods and equipment that can produce high quality coatings of this nature.