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Nickel titanium aluminum barrier layers for silver based low-emissivity coatings

IP.com Disclosure Number: IPCOM000246236D
Publication Date: 2016-May-18
Document File: 2 page(s) / 64K

Publishing Venue

The IP.com Prior Art Database

Abstract

Thin films of silver are often used to lower the emissivity of surfaces of transparent materials, such as a pane of glass in a window, skylight, door, etc. The silver layer is not typically deposited in isolation, however. Other layers (normally made from metals, metal oxides, metal nitrides, or metal oxynitrides) are used to protect the silver and to improve the optics (transmission, reflection, and color) of the thin film. Each layer deposited may have multiple roles, such as providing chemical or mechanical durability, or anti-reflecting the silver. Normally, there is a thin metal, oxide, sub-oxide, nitride, or sub-nitride layer deposited directly on top of the silver. The purpose of this layer, called the barrier, is to protect the silver from damage during subsequent processing (such as from the plasma during deposition of other layers or during a heat treatment such as tempering). Many materials can and have been used as barriers. Common barriers include titanium metal, titanium sub-oxide, niobium, nickel chromium or nickel aluminum. A barrier could consist of a single homogenous layer, or there could be multiple or non-uniform layers used. A barrier may be as thin as half a nanometer, or as thick as about ten nanometers. Each barrier material has its own properties (such as adhesion to the silver, optical absorption, mechanical hardness, chemical durability, and film structure) that affect its performance. These properties also depend on the deposition parameters of the layers. The most challenging role for a barrier layer is protecting the silver layer in low emissivity coatings during the tempering process. Heating the materials often causes issues (such as oxidation, crystallization, and diffusion) that destroy or damage the low emissivity coating. The selection of materials that work as barrier layers for tempered coatings is smaller than those that work for coatings that do not undergo heat treatment. It has been found that a combination of nickel, titanium, and aluminum provides a particularly good balance of properties that works for both heat treated and non-heat treated films. For example, a homogenous mixture consisting of 50-70 weight percent nickel, 20-30 weight percent titanium, and 10-20 weight percent aluminum results in a high performing barrier layer. The nickel titanium aluminum material is useful as a barrier because it exhibits excellent adhesion to the silver, low haze after heat treatment, and provides thorough protection of the silver across a wide range of barrier deposition conditions (such as process pressure and sputtering target power density). Additional benefits include an appealing transmitted color and a useful (i.e. not too high or too low) level of optical absorption which allows both high solar transmission (passive solar style) and medium or low solar transmission coatings to be made with the same barrier material. An example of a coating making use of this barrier follows. A flat glass substrate is coated first with a dielectric layer comprising 10 nm of silicon dioxide, and then 10 nm of an oxide of a zinc tin alloy. Next, a 12 nm thick layer of silver is deposited on top of that oxide layer. A 1.6 nm barrier layer is deposited directly on top of the silver, from a sputtering target with a composition of 60 wt% Ni / 25 wt% Ti / 15 wt% Al. Finally, another 10 nm zin tin oxide layer is deposited to complete the coating. The percentages of the nickel, titanium, and aluminum can be changed for various reasons. Also, the specific materials, layer thicknesses, and layer arrangement of the coating are just examples. They too can be changed for various reasons. The nickel titanium aluminum layer may be deposited from one or multiple targets with essentially the same composition and containing all three of the elements, or from multiple targets with different compositions via co-sputtering. It is most usually deposited from a metal target (or targets) in an argon atmosphere. Both after deposition and after any subsequent heat treatment, the layer will still primarily be metallic, although it may oxidize to some degree (possibly in a nonhomogeneous manner). Ideally, the layer consists only of nickel, titanium, or aluminum, but up to 20% of the layer may consist of other materials without substantially affecting the performance. While the example above is a single silver low emissivity coating, the nickel aluminum titanium barrier materials can be used in any low-emissivity coating, such as a double-silver or triple-silver low-emissivity coating. In addition to being a barrier material, the nickel titanium aluminum material can also be used as an optical absorbing layer in a low-emissivity or solar control coating (or it may serve both roles simultaneously).

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Nickel titanium aluminum barrier layers for silver based low-emissivity coatings

     Thin films of silver are often used to lower the emissivity of surfaces of transparent materials, such as a pane of glass in a window, skylight, door, etc. The silver layer is not typically deposited in isolation, however. Other layers (normally made from metals, metal oxides, metal nitrides, or metal oxynitrides) are used to protect the silver and to improve the optics (transmission, reflection, and color) of the thin film. Each layer deposited may have multiple roles, such as providing chemical or mechanical durability, or anti-reflecting the silver. Normally, there is a thin metal, oxide, sub-oxide, nitride, or sub- nitride layer deposited directly on top of the silver. The purpose of this layer, called the barrier, is to protect the silver from damage during subsequent processing (such as from the plasma during deposition of other layers or during a heat treatment such as tempering).

     Many materials can and have been used as barriers. Common barriers include titanium metal, titanium sub-oxide, niobium, nickel chromium or nickel aluminum. A barrier could consist of a single homogenous layer, or there could be multiple or non-uniform layers used. A barrier may be as thin as half a nanometer, or as thick as about ten nanometers. Each barrier material has its own properties (such as adhesion to the silver, optical absorption, mechanical hardness, chemical durability, and film structure) that affect its performance. These properties also depend on the deposition parameters of the layers.

     The most challenging role for a barrier layer is protecting the silver layer in low emissivity coatings during the tempering process. Heating the materials often causes issues (such as oxidation, crystallization, and diffusion) that destroy or damage the low emissivity coating. The selection of materials that work as barrier layers for tempered coatings is smaller than those that work for coatings that do not undergo heat treatment.

     It has been found that a combination of nickel, titanium, and aluminum provides a particularly good balance of properties that works for both heat treated and non-heat treated films. For example, a homogenous mixture consisting of 50-70 weight percent nickel, 20-30 weight percent titanium, and 10- 20 weight percent aluminum results in a high performing barrier layer. The nickel titanium aluminum material is useful as a barrier because it exhibits...