Patent Publication Number: US-9416049-B2

Title: Low-e panels and methods for forming the same

Description:
The present invention relates to low-e panels. More particularly, this invention relates to low-e panels with novel materials and methods for forming such low-e panels. 
     BACKGROUND OF THE INVENTION 
     Low emissivity, or low-e, panels are often formed by depositing a reflective layer (e.g., silver), along with various other layers, onto a transparent (e.g., glass) substrate. The other layers typically include various dielectric and metal oxide layers, such as silicon nitride, tin oxide, and zinc oxide, to provide a barrier between the stack and both the substrate and the environment, as well as to act as optical fillers and improve the optical characteristics of the panel. 
     When used in, for example, windows, and depending on the particular environment (i.e., climate), it may be desirable for the low-e panels to allow visible light to pass through the window while blocking other types of solar radiation, such as infra-red. Such panels are often referred to as having a high light-to-solar gain (LSG) ratio. 
     Currently available low-e panels are able to achieve LSG ratios of 1.8, or even higher, by using coating with more than one reflective layer (i.e., “double silver” coatings, “triple silver” coatings, etc.) However, these coatings typically exhibit changes in, for example, optical performance (e.g., color) if they are exposed to a heat treatment, such as that often performed to temper the glass substrate. As a result, different coatings must be used depending on whether or not a heat treatment will subsequently be performed. 
     Stacks in which a heat treatment causes little or no change in performance, do exist for low-e panels suitable for some applications. However, these low-e panels typically only utilize a single reflective layer, and thus have relatively low LSG ratios (e.g., less than 1.5). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The drawings are not to scale and the relative dimensions of various elements in the drawings are depicted schematically and not necessarily to scale. 
       The techniques of the present invention can readily be understood by considering the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional side view of a low-e panel according to some embodiments. 
         FIG. 2  is a cross-sectional side view of a low-e panel according to some embodiments. 
         FIG. 3  is a graph depicting transmittance and reflectance for low-e panels according to some embodiments. 
         FIG. 4  is a table of data related to various performance characteristics for low-e panels according to some embodiments. 
         FIG. 5  is a simplified cross-sectional diagram illustrating a physical vapor deposition (PVD) tool according to some embodiments. 
         FIG. 6  is a flow chart illustrating a method for forming a low-e panel according to some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments is provided below along with accompanying figures. The detailed description is provided in connection with such embodiments, but is not limited to any particular example. The scope is limited only by the claims, and numerous alternatives, modifications, and equivalents are encompassed. Numerous specific details are set forth in the following description in order to provide a thorough understanding. These details are provided for the purpose of example and the described techniques may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the embodiments has not been described in detail to avoid unnecessarily obscuring the description. 
     The term “horizontal” as used herein will be understood to be defined as a plane parallel to the plane or surface of the substrate, regardless of the orientation of the substrate. The term “vertical” will refer to a direction perpendicular to the horizontal as previously defined. Terms such as “above”, “below”, “bottom”, “top”, “side” (e.g. sidewall), “higher”, “lower”, “upper”, “over”, and “under”, are defined with respect to the horizontal plane. The term “on” means there is direct contact between the elements. The term “above” will allow for intervening elements. 
     Some embodiments provide low-e optical coatings (and/or panels) capable of achieving high light-to-solar gain (LSG) ratios (e.g., greater than 1.9), which do not experience significant changes in performance (e.g., color, visible transmission, solar heat gain coefficient (SHGC), etc.) from undergoing a heat treatment, such as a tempering process. Such coatings may, for example, be used in windows/low-e panels in warm climates in which it is desirable to allow visible light to pass through, while preventing heat from entering the interior of the building. In some embodiments, the low-e stack includes a dielectric layer between the transparent substrate and the reflective layer (e.g., silver). The dielectric layer may include niobium, tin, aluminum, or a combination thereof. In some embodiments, the dielectric layer is made of niobium-tin-aluminum oxide. 
       FIG. 1  illustrates a low-e panel  100  according to some embodiments. The low-e panel  100  includes a transparent substrate  102  and a low-e stack  104  formed above the transparent substrate  102 . The transparent substrate  102  in some embodiments is made of a low emissivity glass, such as borosilicate glass. However, in some embodiments, the transparent substrate  102  may be made of plastic or a transparent polymer, such as polyethylene terephthalate (PET), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and polyimide (PI). The transparent substrate  102  has a thickness of, for example, between about 1 and about 10 millimeters (mm). In a testing environment, the transparent substrate  102  may be round with a diameter of, for example, about 200 or about 300 mm. However, in a manufacturing environment, the transparent substrate  102  may be square or rectangular and significantly larger (e.g., about 0.5-about 6 meters (m) across). 
     The low-e stack  104  includes a base layer  106 , a dielectric layer  108 , a seed layer  110 , a reflective layer  112 , a barrier layer  114 , a first over-coating layer  116 , a second over-coating layer  118 , and a protective layer  120 . Exemplary details as to the functionality provided by each of the layers  106 - 120  are provided below. 
     The various layers in the low-e stack  104  may be formed sequentially (i.e., from bottom to top) above the transparent substrate  102  using, for example, a physical vapor deposition (PVD) and/or reactive sputtering processing tool. In some embodiments, the low-e stack  104  is formed above the entire substrate  102 . However, in some embodiments, the low-e stack  104  may only be formed above isolated portions of the transparent substrate  102 . Although the layers may be described as being formed “above” the previous layer (or the substrate), it should be understood that in some embodiments, each layer is formed directly on (and adjacent to) the previously provided/formed component (e.g., layer). In some embodiments, additional layers may be included between the layers, and other processing steps may also be performed between the formation of various layers. 
     The base layer  106  is formed above the transparent substrate  102 . The base layer  106  may be made of a metal oxide and have a thickness of, for example, between about 100 Å and about 180 Å, such as about 150 Å. In some embodiments, the base layer  106  is made of zinc-tin oxide. Other suitable materials are, for example, titanium oxide, zinc oxide, tin oxide, and other metal alloy oxides, such as aluminum-tin oxide. The base layer  106  may be used to tune the optical properties (e.g., color, transmittance, etc.) of the low-e panel  100  as a whole, as well as to enhance silver nucleation. 
     The dielectric layer  108  is formed above the base layer  106 . In some embodiments, the dielectric layer  108  includes niobium and tin and may have an amorphous phase. In some embodiments, the dielectric layer  108  also includes aluminum. In some embodiments, the dielectric layer  108  is made of niobium-tin-aluminum oxide. In some embodiments, the dielectric layer is formed using physical vapor deposition (e.g., sputtering). The dielectric layer  108  may be formed by, for example, simultaneously sputtering (i.e., co-sputtering) niobium oxide from a first target and tin-aluminum oxide from a second target (e.g., in a PVD tool, an example of which is described below). In some embodiments, the dielectric layer  108  may include, by weight, at least twice as much tin-aluminum oxide as niobium oxide (i.e., at least twice as much tin-aluminum oxide as niobium oxide may be deposited during the forming of the dielectric layer  108 ). For example, the weight ratio of the sputtered niobium oxide to the sputtered tin-aluminum oxide may be about 1:2.3. In some embodiments, the dielectric layer has a thickness of, for example, between about 100 Å and about 180 Å, such as about 150 Å. The dielectric layer  108  may be used to provide a separation between the base layer  106  and the seed layer  110 . 
     The seed layer  110  is formed above the dielectric layer  108 . The seed layer  110  is made of a metal oxide and may have a thickness of, for example, between about 80 Å and about 120 Å, such as about 100 Å. In some embodiments, the metal oxide used in the seed layer  110  is zinc oxide. The seed layer  110  may be used to enhance the deposition/growth of the reflective layer  112  in the low-e stack  104  (e.g., enhance the crystalline structure and/or texturing of the reflective layer  112 ) and increase the transmission of the stack  104  for anti-reflection purposes. In some embodiments, the seed layer  110  may be made of tin oxide or may not be included at all. 
     The reflective layer  112  is formed above the seed layer  110 . In some embodiments, the reflective layer  112  is made of silver and has a thickness of, for example, between about 80 Å and about 120 Å, such as about 100 Å. As is commonly understood, the reflective layer  112  is used to reflect infra-red electro-magnetic radiation, thus reducing the amount of heat that may be transferred through the low-e panel  100 . 
     The barrier layer  114  is formed over the reflective layer  112 . The barrier layer  114  may include, for example, nickel, titanium, niobium, or a combination thereof. For example, in some embodiments, the barrier layer is made of nickel-titanium-niobium oxide. The barrier layer  114  may have a thickness of, for example, between about 30 Å and about 100 Å, such as about 80 Å. The barrier layer  114  is used, for example, to protect the reflective layer  112  from the processing steps used to form the subsequent layers of the low-e stack  104  and to prevent any interaction of the material of the reflective layer  112  with the materials of the other layers of the low-e stack  104 , which may result in undesirable optical characteristics, such as poor color performance, of the low-e panel  100 . 
     Still referring to  FIG. 1 , the first over-coating layer  116  is formed above the barrier layer  114 . The first over-coating layer  116  may be made of a metal oxide and have a thickness of, for example, between about 100 Å and about 180 Å, such as about 150 Å. In some embodiments, the first over-coating layer  116  is made of the same material as the base layer  108  (e.g., zinc-tin oxide). 
     The second over-coating layer  118  is formed above the first over-coating layer  116 . The second over-coating layer  118  may be made of a metal oxide and have a thickness of, for example, between about 100 Å and about 180 Å, such as about 150 Å. In some embodiments, the first over-coating layer  116  is made of the same material as the seed layer  108  (e.g., zinc oxide). 
     The first and second over-coating layers  116  and  118  may be used to further tune the optical properties of the low-e panel  100  as a whole. Additionally, in some embodiments, the first and second over-coating layers  116  and  118  may enhance the LSG ratio of the low-e panel  100 . 
     Still referring to  FIG. 1 , the protective (or capping) layer  120  is formed above the second over-coating layer  118 . The protective layer  120  may be made of dielectric material, such as silicon nitride, and have a thickness of, for example, between about 200 Å and about 300 Å, such as about 250 Angstroms (A). The protective layer  120  may be used to provide additional protection for the lower layers of the stack  104  and further adjust the optical properties of the low-e panel  100 . The protective layer  120  may also be considered to be an over-coating layer (i.e., a third over-coating layer). 
     Additionally, although not shown in  FIG. 1 , it should be understood that an additional protective layer may be formed between the transparent substrate  102  and the base layer  106 . This additional (or lower) protective layer may be made of the same material (e.g., silicon nitride) as the (upper) protective layer  120  and have a thickness of, for example, between about 100 Å and 250 Å. This additional protective layer may protect the other layers in the stack  104  from any elements which may otherwise diffuse from the transparent substrate  102  and may be used to tune the optical properties (e.g., transmission) of the low-e stack  104  and/or the low-e panel  100  as a whole. 
     One skilled in the art will appreciate that the embodiment depicted in  FIG. 1  is a “single silver” low-e panel (i.e., having one reflective/silver layer). However, in some embodiments, the low-e panel  100  (or the low-e stack  104 ) is formed as a “double silver,” or even a “triple silver,” low-e panel (i.e., having two or three reflective/silver layers). In such embodiments, other layers in the low-e stack  104  may be replicated more than once along with the reflective layer. For example, in a double silver low-e panel, a set of additional layers, including an additional dielectric layer, seed layer, reflective layer, barrier layer, and first over-coating layer, similar to those described above, may be sequentially formed between the first over-coating layer  116  and the second over-coating layer  118 . 
     An example of a “double silver” low-e panel  200  is shown in  FIG. 2 . The low-e panel  200  includes a transparent substrate  202  and a low-e stack  204  formed above the transparent substrate  202 . The transparent substrate  202  may be similar to that described above. The low-e stack  204  includes a first (or lower) base layer  206 , a first dielectric layer  208 , a first seed layer  210 , a first reflective layer  212 , a first barrier layer  214 , a second (or upper) base layer  216 , a second dielectric layer  218 , a second seed layer  220 , a second reflective layer  222 , a second barrier layer  224 , a first over-coating layer  226 , a second over-coating layer  228 , and a protective layer  230 . Each of the layers of the double silver low-e panel  200  may have the same properties (e.g., material, thickness, etc.) as the similarly named layers of the low-e panel  100  shown in  FIG. 1  and described above. 
     It should be noted that depending on the materials used, some of the layers of the low-e stack (e.g., low-e stack  104  and low-e stack  204 ) may have some materials in common. For example, in the embodiments described above, the base layer and the first over-coating layer may be made of the same material (e.g., zinc-tin oxide). Similarly, the seed layer and the second over-coating layer may be made of the same material (e.g., zinc oxide). 
     It should also be understood that the low-e panel (e.g., low-e panel  100  and low-panel  200 ) may be a portion of (or installed in) a larger, more complex device or system, such as a low-e window. Such a window may include multiple glass substrates (or panes), other coatings (or layers), such a thermochromic coating formed on a different pane than the low-e stack, and various barrier or spacer layers formed between adjacent panes. 
     Low-e panels formed in accordance with embodiments described herein showed very little change in visible transmission (or transmittance) and reflection (or reflectance) due to the heat treatment (e.g., 72.1% as-coated and 74.9% after heat treatment).  FIG. 3  graphically illustrates the transmittance and reflectance, both before and after heat treatment, for low-e panels in accordance with some embodiments. In particular, line group  302  depicts transmittance, with the solid line in line group  302  depicting the transmittance before heat treatment (i.e., as-coated) and the dashed line in line group  302  depicting the transmittance after heat treatment. As shown, the transmittance for visible light (i.e., 380-780 nm) is relative high, peaking at about 80%, both before and after heat treatment (i.e., the heat treatment changed transmittance very little). 
     Still referring to  FIG. 3 , line group  304  depicts reflectance for electro-magnetic radiation passing through the low-e panels from the side of the substrate with the low-e stack (i.e., the coating side). The solid line in line group  304  depicts this reflectance before heat treatment, and the dashed line depicts this reflectance after heat treatment. As shown, the reflectance for the coating side increases dramatically (to over 90%) for electro-magnetic radiation with wavelengths longer than that of visible light (i.e., greater than 780 nm) and is affected very little by the heat treatment. Line group  306  depicts reflectance for electro-magnetic radiation passing through the low-e panels from the side of the substrate opposite the low-e stack (i.e., the substrate (or glass) side). The solid line in line group  306  depicts this reflectance before heat treatment, and the dashed line depicts this reflectance after heat treatment. As shown, the reflectance for the substrate side, though not quite as high as the coating side, increases dramatically for electro-magnetic radiation with wavelengths longer than that of visible light and is affected very little by the heat treatment. 
     Other characteristics of the low-e panels described herein (e.g., including the niobium-tin-aluminum oxide layer dielectric layer(s) described above) are shown in the table depicted in  FIG. 4 . “AC” indicates data for the as-coated low-e panels, and “HT” indicates data for the low-e panels after a high temperature treatment (e.g. tempering). Data are presented for both monolithic low-e panels (e.g., Monolithic Optics) and dual-pane low-e panels (e.g., IGU Optics). Due to the distribution of cones in the eye, the color observance may depend on the observer&#39;s field of view. Standard (colorimetric) observer is used, which was taken to be the chromatic response of the average human viewing through a 2 degree angle, due to the belief that the color-sensitive cones reside within a 2 degree arc of the field of view. Thus, the measurements are shown for the 2 degree Standard Observer. 
     The various characteristics listed in  FIG. 4  will be understood and appreciated by one skilled in the art. For example, intensity of reflected visible wavelength light, (e.g., “reflectance”) is defined for glass side “g” or for film side “f”. Intensity from glass side reflectance, (e.g., R g Y), shows light intensity measured from the side of the glass substrate opposite the side of the coated layers. Intensity from film side reflectance, (e.g., R f Y), shows light intensity measured from the side of the glass substrate on which the coated layers are formed. Transmittance, (e.g., TY), shows light intensity measured for the transmitted light. 
     The color characteristics are measured and reported herein using the CIE LAB a*, b* coordinates and scale (i.e. the CIE a*b* diagram, Ill. CIE-C, 2 degree observer). In the CIE LAB color system, the “L*” value indicates the lightness of the color, the “a*” value indicates the position between magenta and green (more negative values indicate stronger green and more positive values indicate stronger magenta), and the “b*” value indicates the position between yellow and blue (more negative values indicate stronger blue and more positive values indicate stronger yellow). 
     Emissivity (E) is a characteristic of both absorption and reflectance of light at given wavelengths. It can usually represented as a complement of the reflectance by the film side, (e.g., E=1−R f ). For architectural purposes, emissivity values can be important in the far range of the infrared spectrum, (e.g., about 2,500-40,000 nm). Thus, the emissivity value reported here includes normal emissivity (EN), as measured in the far range of the infrared spectrum. Haze is a percentage of light that deviates from the incident beam greater than 2.5 degrees on the average. 
     Data are also shown for the difference between heat treated and as-coated low-e panels. The value ΔE* (and Δa*, Δb*, ΔY) are important in determining whether or not upon heat treatment (HT) there is matchability, or substantial matchability, of the coated panels. For purposes of example, the term Δa*, for example, is indicative of how much color value a* changes due to heat treatment. Also, ΔE* is indicative of the change in reflectance and/or transmittance (including color appearance) in a coated panel after a heat treatment. AE* corresponds to the CIELAB Scale L*, a*, b*, and measures color properties before heat treatment (L 0 *, a 0 *, b 0 *) and color properties after heat treatment (L 1 *, a 1 *, b 1 *):
 
Δ E *=√{square root over ((Δ L *) 2 +(Δα*) 2 +(Δ b *) 2 )}
 
where ΔL*=L 1 *−L 0 *, Δα*=a 1 *−a 0 *, and Δb*=b 1 *−b 0 *.
 
     The color change of glass side reflection can be calculated as Rg ΔE*. The color change of light transmission can be calculated as T ΔE*, T|Δa*| and T|Δb*|. The luminance change of light transmission can be calculated as T ΔY. 
     Low-e panels (and/or low-e windows) utilizing the low-e stacks described above, particularly in a double (or triple) silver configuration, may demonstrate a high LSG ratio (e.g., greater than 1.9). Additionally, these low-e panels may show very little or no change in performance after undergoing a heat treatment. For example, in some embodiments, the low-e panels exhibited very low emissivity (i.e., normal emissivity (EN) both before (i.e., as-coated) and after heat treatment (e.g., 0.018 as-coated and 0.012 after heat treatment). The solar heat gain coefficient (SHGC) of the low-e panels was also affected very little by the heat treatment (e.g., 36.4 as-coated and 38.9 after heat treatment). Further, the low-e panels described herein exhibit a low R g  ΔE* value (i.e. the color change on the glass side) when comparing the as-coated and the heat treated data (i.e., “HT-AC”). As shown, the low-e panels described herein exhibit R g  ΔE* values of 2.42. 
     As an additional benefit, any additional manufacturing costs may be minimized because many of the layers in the low-e stacks described herein utilize materials used in the other layers (e.g., niobium, zinc, tin, etc). As a result, the total number of targets that are required to form the low-e stacks may be minimized, which reduces manufacturing costs. 
       FIG. 5  provides a simplified illustration of a physical vapor deposition (PVD) tool (and/or system)  500  which may be used to formed the low-e panels and/or the low-e stacks described above, in accordance with some embodiments. The PVD tool  500  shown in  FIG. 5  includes a housing  502  that defines, or encloses, a processing chamber  504 , a substrate support  506 , a first target assembly  508 , and a second target assembly  510 . 
     The housing  502  includes a gas inlet  512  and a gas outlet  514  near a lower region thereof on opposing sides of the substrate support  506 . The substrate support  506  is positioned near the lower region of the housing  502  and in configured to support a substrate  516 . The substrate  516  may be a round glass (e.g., borosilicate glass) substrate having a diameter of, for example, about 200 mm or about 300 mm. In other embodiments (such as in a manufacturing environment), the substrate  516  may have other shapes, such as square or rectangular, and may be significantly larger (e.g., about 0.5-about 6 m across). The substrate support  506  includes a support electrode  518  and is held at ground potential during processing, as indicated. 
     The first and second target assemblies (or process heads)  508  and  510  are suspended from an upper region of the housing  502  within the processing chamber  504 . The first target assembly  508  includes a first target  520  and a first target electrode  522 , and the second target assembly  510  includes a second target  524  and a second target electrode  526 . As shown, the first target  520  and the second target  524  are oriented or directed towards the substrate  516 . As is commonly understood, the first target  520  and the second target  524  include one or more materials that are to be used to deposit a layer of material  528  on the upper surface of the substrate  516 . 
     The materials used in the targets  520  and  524  may, for example, include tin, zinc, tin, magnesium, aluminum, lanthanum, yttrium, titanium, antimony, strontium, bismuth, silicon, silver, nickel, chromium, niobium, or any combination thereof (i.e., a single target may be made of an alloy of several metals). Additionally, the materials used in the targets may include oxygen, nitrogen, or a combination of oxygen and nitrogen in order to form oxides, nitrides, and oxynitrides. Additionally, although only two targets  520  and  524  are shown, additional targets may be used. 
     The PVD tool  500  also includes a first power supply  530  coupled to the first target electrode  522  and a second power supply  532  coupled to the second target electrode  524 . As is commonly understood, the power supplies  530  and  532  pulse direct current (DC) power to the respective electrodes, causing material to be, at least in some embodiments, simultaneously sputtered (i.e., co-sputtered) from the first and second targets  520  and  524 . 
     During sputtering, inert gases, such as argon or krypton, may be introduced into the processing chamber  504  through the gas inlet  512 , while a vacuum is applied to the gas outlet  514 . However, in embodiments in which reactive sputtering is used, reactive gases may also be introduced, such as oxygen and/or nitrogen, which interact with particles ejected from the targets (i.e., to form oxides, nitrides, and/or oxynitrides). 
     Although not shown in  FIG. 5 , the PVD tool  500  may also include a control system having, for example, a processor and a memory, which is in operable communication with the other components shown in  FIG. 5  and configured to control the operation thereof in order to perform the methods described herein. 
     Further, although the PVD tool  500  shown in  FIG. 5  includes a stationary substrate support  506 , it should be understood that in a manufacturing environment, the substrate  516  may be in motion (e.g., an inline configuration) during the various layers described herein. 
       FIG. 6  is a flow chart illustrating a method  600  for forming a low-e panel according to some embodiments. The method  600  begins at block  602  by providing a transparent substrate, such as the examples described above (e.g., glass). 
     At block  604 , a dielectric layer is formed above the transparent substrate. The dielectric layer includes niobium, tin, aluminum, or a combination thereof. In some embodiments, the dielectric layer is made of niobium-tin-aluminum oxide. Block  604  may also include the formation of other layers above the transparent substrate, such as the lower protective layer and base layer described above, as well as the formation of various layers above the dielectric layer, such as the seed layer described above. 
     At block  606 , a reflective layer is formed above the dielectric layer (and any other layers formed at block  604 ). In some embodiments, the reflective layer is made of silver. Block  606  may also include the formation of other layers above the reflective layer, such as the barrier layer, the over-coating layers, and the upper protective layer described above. At block  608 , the method  600  ends. 
     Thus, in some embodiments, a method for forming a low-e panel is provided. A transparent substrate is provided. A reflective layer is formed above the transparent substrate. A dielectric layer is formed between the transparent substrate and the reflective layer using physical vapor deposition. The dielectric layer includes niobium, tin, and aluminum. 
     In some embodiments, a method for forming a low-e panel is provided. A transparent substrate is provided. A reflective layer is formed above the transparent substrate. The reflective layer includes silver. A metal oxide layer is formed between the transparent substrate and the reflective layer. A dielectric layer is formed between the transparent substrate and the metal oxide layer using physical vapor deposition. The dielectric layer includes niobium-tin-aluminum oxide. 
     In some embodiments, a low-e panel is provided. The low-e panel includes a transparent substrate, a reflective layer, and a dielectric layer. The reflective layer is above the transparent substrate. The dielectric layer is between the transparent substrate and the reflective layer. The dielectric layer includes niobium-tin-aluminum oxide. 
     Although the foregoing examples have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed examples are illustrative and not restrictive.