Coated articles are known in the art for use in window applications such as insulating glass (IG) window units, vehicle windows, monolithic windows, and/or the like. In certain example instances, designers of coated articles often strive for a combination of high visible transmission, low emissivity (or low emittance), and/or low sheet resistance (Rs). High visible transmission may permit coated articles to be used in applications where these characteristics are desired such as in architectural or vehicle window applications, whereas low-emissivity (low-E), and low sheet resistance characteristics permit such coated articles to block significant amounts of IR radiation so as to reduce for example undesirable heating of vehicle or building interiors. Thus, typically, for coatings used on architectural glass to block significant amounts of IR radiation, high transmission in the visible spectrum is often desired. However, low transmittance and/or high reflectance in the IR and/or near IR part(s) of the spectrum is also desired to reduce for example undesirable heating of vehicle or building interiors.
Unfortunately, low-E coatings often do not block significant amounts of ultraviolet (UV) radiation. In other words, low-E coatings typically provide only moderate or negligible UV protection, since the materials used in the layer stacks are transparent for short wavelengths (e.g., below 400 nm). In particular, materials used in such layer stacks such as tin oxide and titanium oxide cannot provide adequate UV protection given the small thicknesses of such materials required for low-E coatings. Thus, even with such coatings are provided on windows such as IG windows or vehicle windows, significant amounts of UV radiation makes its way through the window and into the building or vehicle. UV radiation tends to damage furniture and other elements inside of buildings or vehicles.
Materials such as vanadium oxide and cerium oxide absorb significant amounts of UV radiation. However, while such materials are characterized by a very steep onset of absorption for UV radiation, the onset of radiation absorption occurs in significant part in the visible part of the spectrum thereby leading to a significant distortion of colors when look through such a coating (e.g., a yellow shift). Accordingly, viewing characteristics tend to be degraded when layers of such materials are used.
There also exists a need in the art for improved chemical stability (chemical durability) and heat stability (stability upon heat treatment such as thermal tempering).
In view of the above, it will be appreciated that there exists a need in the art for a coated article including a low-E coating which is capable of blocking at some UV radiation in an efficient manner. Certain example embodiments of this invention relate to a coated article which permits significant UV absorption properties to be achieved.
In certain example embodiments of this invention, it has surprisingly been found that the provision of a layer consisting essentially of, or comprising, zirconium oxide (e.g., ZrO2), zirconium oxynitride, or zirconium silicon oxynitride (e.g., ZrSiOxNy) unexpectedly improves blocking (reflecting and/or absorption) of UV radiation in a manner which does not significantly degrade other optical properties of a coated article such as visible transmission and/or color. Surprisingly, when a layer comprising zirconium oxide or zirconium silicon oxynitride is provided as the uppermost or overcoat layer of the coated article (e.g., over a silicon nitride based layer), this results in improved chemical and heat stability in certain example embodiments.
In certain example embodiments of this invention, a layer of zirconium oxide or zirconium silicon oxynitride may be tuned in a manner so as to achieve a desired amount of UV blocking and/or absorption, as well as improved durability. It has been found that zirconium oxide or zirconium silicon oxynitride has optical constants (n and k) which allow adjustment of the onset of absorption by varying oxygen content of the layer for example. Moreover, it has been found that zirconium oxide, zirconium oxynitride, or zirconium silicon oxynitride has a refractive index (n) in a range which is very adaptable to low-E coatings, so that such layer(s) may be used in low-E coatings without significantly changing the visible appearance of the coated article or certain performance data. Thus, in certain example embodiments of this invention, the absorption edge of the curve defined by a layer of zirconium oxide or zirconium silicon oxynitride can be adjusted by changing the oxygen content thereof, which may be done for example by adjusting the amount of oxygen introduced into the sputtering chamber(s) during reactive sputter-deposition of the layer. In particular, for example, as oxygen content of the layer increases, the absorption edge of the curve defined by the layer of zirconium oxide or zirconium silicon oxynitride moves toward lower wavelengths away from certain visible wavelengths. Thus, in certain example embodiments, a balancing or tuning can be performed so as to achieve a desired balance between visible transmission and UV absorption.
In certain example embodiments of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising, in this order from the glass substrate outwardly: a first dielectric layer; a first contact layer; an infrared (IR) reflecting layer comprising silver located on the substrate over at least and contacting the first contact layer; a second contact layer comprising Ni and/or Cr located over and contacting the IR reflecting layer; a second dielectric layer comprising silicon nitride located over the second contact layer; and an overcoat dielectric layer comprises one or more of zirconium oxide, zirconium oxynitride, and/or zirconium silicon oxynitride located over and contacting the second dielectric layer comprising silicon nitride.