Low-emissivity coatings are known in the art. Low-E coatings typically comprise at least one functional layer such as an infrared (IR) reflecting layer. The IR reflecting layer(s), or functional layer(s), may be of or based on silver or gold in typical instances. Low-E coatings are typically used in window applications such as in IG (insulating glass) window units, monolithic window, architectural windows, and/or in vehicle windows.
The thin IR reflecting layers (e.g., based on silver) are often used to reflect IR radiation. These silver-based layers are susceptible to damage, and generally require protective layers on both sides to protect them. The layer directly under and contacting the silver based IR reflecting layer in some instances is of zinc oxide, and may be referred to as a seed layer. This zinc oxide-based layer may be doped with aluminum.
However the ZnO-based layer may be relatively soft, which results in a lack of overall chemical and mechanical durability of the layer and the coating. Also, an un-doped ZnO-based layer, or a doped ZnO:Al-based layer may be stressed in a low E-stack. This can result in the formation of weak spots, and contributes to overall poor durability, including corrosion of the coating. The IR reflecting layer can become damaged, chemically and/or mechanically, due to such stress in the ZnO:Al layer. The stress of the coating can become particularly problematic during or due to thermal tempering, when the glass substrate with the coating thereon is heated to a high temperature (e.g., at least 580 degrees C.) and then rapidly cooled down.
There is therefore a need in the art for a coated article having a layer, to be located proximate or near (e.g., under) an IR reflecting layer and/or a silver based layer, that enables a coated article to realize improved durability and/or optical characteristics.
In certain example embodiments of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising at least the following layers moving away from the glass substrate: a dielectric layer comprising zinc oxide doped with boron and at least one of gallium and/or aluminum; an infrared (IR) reflecting layer comprising silver and/or gold located on the substrate over and directly contacting the layer comprising zinc oxide doped with boron, a dielectric layer on the substrate over at least the IR reflecting layer; and wherein the layer comprising zinc oxide doped with boron includes from about 0.01 to 8% boron. The layer comprising zinc and boron may be called a “seed” layer because it is directly under and contacting an IR reflecting layer and/or a layer comprising silver.
In other example embodiments of this invention, there is provided a coated article including a coating supported by a substrate, the coating comprising at least the following layers, moving away from the substrate: a substantially transparent seed layer comprising a first material and a second material, wherein the dielectric seed layer has a hardness of at least about 9 GPa; a layer comprising silver located on the substrate over and directly contacting the seed layer, at least one dielectric layer over at least the layer comprising silver; wherein the first material is a metal, and the second material is used to dope an oxide of the first material in the seed layer. The coated article may or may not be heat treated (e.g., thermally tempered). The second material may be boron in certain example embodiments, although other material such as gallium and/or aluminum may instead be used.
In another example embodiment of this invention, there is provided a method for making a coated article, the method comprising the steps of sputter depositing from a substantially metallic target a dielectric layer comprising zinc oxide and boron on a glass substrate over at least one dielectric layer, wherein the substantially metallic target comprises at least about 85% zinc and about 0.01 to 8% boron; and sputter-depositing an IR reflecting layer comprising silver and/or gold on the glass substrate over and directly contacting the layer comprising zinc oxide doped with boron.
In yet another example embodiment of this invention, there is provided a sputtering target for sputter depositing a dielectric layer comprising boron-doped zinc oxide, wherein the target is substantially metallic, and comprises at least about 85% zinc and from about 0.02 to 5% boron.
In still other example embodiments of this invention, there is provided a method for making a coated article, the method comprising the steps of sputter-depositing a dielectric layer comprising zinc oxide doped with boron on a glass substrate over at least one dielectric layer, wherein the layer comprising zinc oxide doped with boron is deposited in a sputtering atmosphere comprising at least about 50% oxygen; and sputter-depositing an IR reflecting layer comprising silver and/or gold on the glass substrate over and directly contacting the layer comprising zinc oxide doped with boron.