Coated substrate

Abstract

The present invention relates to a coated substrate, a method of manufacturing the coated substrate, coated substrates manufactured by said method, and electrodes, devices or glazings comprising said coated substrates. The coated substrate has high visible light transmission, high NIR transmission, and low sheet resistance.

Description

[0001] Coated Substrate

[0002] The present invention relates to a coated substrate, a method of manufacturing the coated substrate, coated substrates manufactured by said method, and electrodes, devices or glazings comprising said coated substrates.

[0003] Transparent conducting materials (TCMs) are utilised as energy saving, low-emissivity coatings for architectural windows, as high scattering layers that form the front electrical contact of a wide variety of photovoltaic (PV) thin film modules and as glass coatings in a number of electronic devices including liquid-crystal displays, OLEDs and touchscreens, among other applications. As such, there is a continuing demand for TCMs with reduced sheet resistance and increased transmission that may be utilised in glazings, displays, photovoltaics and other applications.

[0004] Transparent conductive oxides (TCOs) are a widely used type of TCM. TCOs have high optical transmission at visible and near infra-red (NIR) wavelengths and a good electrical conductivity that is close to that of metals. Typically, TCOs are wide band gap semiconductors that rely on doping to improve the carrier concentration. Common TCOs include doped zinc oxide, doped tin oxide, and indium tin oxide (ITO).

[0005] However, it would be useful to develop new transparent conductive materials (TCMs) that can improve on the properties of the hitherto known materials.

[0006] Therefore, it is an aim of the present invention to provide a conductive coating of reduced sheet resistance and increased transmission of electromagnetic radiation, that is also compatible with typical processing requirements.

[0007] In a first aspect, the present invention provides a coated substrate comprising a substrate with a surface and a coating directly or indirectly upon the surface, wherein the coating comprises a functional layer comprising strontium, zinc and oxygen, with niobium and / or titanium.

[0008] The inventors have discovered that such a coated substate may provide exemplary transparency and very low sheet resistance. Functional Laver

[0009] The functional layer comprises a plurality of separate and discrete layers, including at least a first and a second layer, which are deposited as separate layers. There may be further layers present as required.

[0010] In some embodiments of the invention, the functional layer comprises two layers. In another embodiment of the invention, the functional layer may comprise three layers. In another embodiment of the invention, the functional layer may comprise four or more layers.

[0011] The functional layer may be formed by deposition of each of the first layer and the second layer over a substrate, followed by a heat treatment such as annealing. Alternatively, deposition may be carried out at high temperature, such as from about 275°C; such a high temperature deposition may not require a post-deposition heating step. The annealing is preferably carried out at elevated temperatures e.g. above about 275°C) under high vacuum, such as at a base pressure of below about 1 x IO-3mbar, such as about 1 x IO-6mbar. However, in another embodiment, it may be carried out at atmospheric pressure or in a reducing or inert atmosphere.

[0012] Overall, the functional layer comprises strontium, zinc and oxygen, as well as niobium and / or titanium.

[0013] In some embodiments, the functional layer comprises strontium, niobium, zinc and oxygen.

[0014] In some embodiments, the functional layer comprises strontium, titanium, zinc and oxygen.

[0015] In some embodiments, the functional layer comprises strontium, niobium, titanium, zinc and oxygen.

[0016] In other implementations, the functional layer may consist only of the above materials. However, in alternative implementations, the functional layer further comprises another material selected from at least one of aluminium, gallium, magnesium, tin, or indium, in preferably from 1 to 10 atomic % based on metals, more preferably from 2 to 5 atomic % based on metals. In some implementations, the at least one of aluminium, gallium, magnesium, tin or indium is deposited substantially homogenously in one of the layers of the functional layer, but after annealing at least some of the at least one of aluminium, gallium, magnesium, tin or indium may be redistributed within the functional layer so that a proportion of it is concentrated at or near the interface between the first layer and the second layer.

[0017] When the functional layer also comprises aluminium, it may be in the form of a mixed metal oxide, such as part of a mixed metal oxide with zinc, in which situation it is in the form of aluminium-doped zinc oxide (also known herein as ZAO or ZnO:AI).

[0018] Preferably, the first layer of the functional layer comprises from 50 to 100 atomic % zinc based on metals; while the second layer comprises from 5 to 70 atomic % strontium based on metals, from 5 to 90 atomic % niobium based on metals; and from 5 to 90 atomic % titanium based on metals. More preferably, the second layer comprises from 10 to 50 atomic % strontium based on metals, from 25 to 75 atomic % niobium based on metals; and from 25 to 75 atomic % titanium based on metals.

[0019] The first layer is preferably positioned between the substrate and the second layer. Preferably, the first layer is in direct contact with the second layer.

[0020] In some embodiments, the first layer is in direct contact with the substrate. Alternatively, the first layer is not in direct contact with the substrate, and there are one or more other layers positioned between the first layer and the substrate.

[0021] In some implementations, the functional layer comprises, in order from the substrate: a first layer comprising an oxide of zinc; and a second layer comprising an oxide of strontium and niobium (also referred to herein as SNO).

[0022] Alternatively, the functional layer comprises, in order from the substrate: a first layer comprising an oxide of zinc; and a second layer comprising an oxide of strontium and titanium (also referred to herein as STO).

[0023] Alternatively, the functional layer comprises, in order from the substrate: a first layer comprising an oxide of zinc; and a second layer comprising an oxide of strontium and niobium; and a third layer comprising an oxide of strontium and titanium. When present, the third layer is preferably in direct contact with the second layer, and on the other side of the second layer from the first layer.

[0024] When present, the third layer comprising an oxide of strontium and titanium is preferably between about 1 and 50 nm in thickness, more preferably between about 1 and 35 nm, more preferably between about 1 and 30 nm. A range between about 2 and 20 nm provides excellent sheet resistance values.

[0025] As used herein, any reference to a layer (A) being 'under' or 'below' another layer (B) means that the layer (A) is positioned between the layer (B) and the substrate. Conversely, any reference to a layer (A) being 'over' or 'above' another layer (B) means that the layer (B) is positioned between the layer (A) and the substrate.

[0026] First Laver

[0027] The first layer is preferably positioned between the second layer and the substrate. It preferably comprises an oxide of zinc. In some implementations, the first layer consists of an oxide of zinc. Oxides of zinc include any material that contains both zinc and oxygen, for example, zinc oxide, ZnO; zinc oxide doped with another metal such as aluminium, gallium, or magnesium; and zinc stannate (ZnSnOx).

[0028] The first layer comprising an oxide of zinc preferably comprises greater than 50 atomic % zinc based on metals. Preferably the first layer comprises greater than 60 atomic % zinc based on metals; preferably the first coating comprises greater than 70 atomic % zinc based on metals; preferably the first layer comprises greater than 80 atomic % zinc based on metals.

[0029] In some implementations, the first layer comprises an amount of at least one of aluminium, gallium, magnesium, tin, or indium; preferably the first layer comprises at least one of aluminium, gallium, magnesium, tin, titanium, or indium, in an amount of from about 1 to about 15% atomic % based on metals, preferably no more than 5 atomic %. Such elements may improve the conductivity of the coating.

[0030] In some implementations, the oxide of zinc is aluminium doped zinc oxide ZnO:AI. Such an oxide of zinc is readily prepared and shows excellent results. Preferably the aluminium doped zinc oxide ZnO:AI comprises from 1 to 15 atomic % aluminium based on metals and from 85 to 99 atomic % zinc based on metals, more preferably the aluminium doped zinc oxide ZnO:AI comprises from

[0031] 1 to 5 atomic % aluminium based on metals and from 95 to 99 atomic % zinc based on metals.

[0032] As used herein, the term "essentially free of" is taken to mean that the indicated substance is not present except for unavoidable impurities.

[0033] In some implementations, the first layer comprising an oxide of zinc has a thickness of greater than or equal to 26 nm; preferably greater than or equal to 30 nm; preferably greater than or equal to 35 nm; preferably greater than or equal to 37.5 nm; more preferably greater than or equal to 50 nm; yet more preferably greater than or equal to 75 nm. The inventors have discovered that the excellent electrical properties of the coating may be enhanced by increasing the thickness of the first coating layer. However, an increased thickness of first layer will increase absorption and lower light transmission of the coating. Therefore, preferably the first layer comprising an oxide of zinc has a thickness of less than 300 nm, preferably less than 275, or 250 nm or less, or 225 nm or less.

[0034] Second Laver

[0035] In one embodiment, the second layer comprises an oxide of strontium and niobium. In another embodiment, the second layer is an oxide of strontium and niobium and / or consists of an oxide of strontium and niobium.

[0036] In another embodiment, the second layer comprises an oxide of strontium and titanium; or it consists of an oxide of strontium and titanium.

[0037] Preferably, the second layer comprises an oxide of strontium and niobium.

[0038] As used herein, an oxide of strontium and niobium may have the formula SrxNbyOzand an oxide of strontium and titanium may have the formula SrxTiyOz. The ratio of z to x and y is such that it satisfies the relationship z:x+y being from 1: 1 to 3: 1.

[0039] In some implementations, the oxide of strontium and niobium SrxNbyOzhas an atomic proportion of niobium based on total strontium and niobium, y / (y+x), of greater than 0.40, preferably greater than 0.50, more preferably greater than 0.55, yet more preferably greater than 0.60, even more preferably greater than 0.65. The inventors have found that a high proportion of niobium improves the electronic properties of the coating. However, if the proportion of niobium is too high the structure of the layer may be adversely affected. Therefore, preferably the atomic proportion of niobium based on total strontium and niobium, y / (y+x), is less than 0.9, preferably less than 0.8.

[0040] In some implementations, the oxide of strontium and titanium SrxTiyOzhas an atomic proportion of titanium based on total strontium and titanium, y / (y+x), of greater than 0.40 and preferably less than about 0.65, more preferably between about 0.45 and 0.55.

[0041] In some implementations, the second layer has a thickness of from 1 to 500 nm; preferably the second layer has a thickness of from 5 to 450 nm; preferably 8 to 400 nm; more preferably 15 to 390, or 25 to 390, or 30 to 380 nm.

[0042] Additional Coating Lavers

[0043] The present invention does not exclude additional coating layers within the coating that the skilled person may include to provide additional functionality. Additional coating layers that may be employed by the skilled person include one or more selected from:

[0044] - a third layer comprising an oxide of strontium and titanium over the second layer, where the second layer comprises an oxide of strontium and niobium;

[0045] - one or more fourth layers between the first layer and the substrate. These may be used as and characterised as 'blocking layers' for the prevention of ion migration and may be particularly beneficial when the substrate is soda-lime silica glass; and / or

[0046] - one or more fifth layers over the functional layer, located on the side of the functional layer which is furthest from the substrate. These may be used as and characterised as 'capping' layers, which function as protection due to exposure to the atmosphere; and / or

[0047] - one or more layers between the first layer and the second layer;

[0048] - one or more absorption layers, such as WNX, provided for absorbing visible light; and / or

[0049] - one or more infra-red reflection layers, such as Ag; and / or

[0050] - one or more low-emissivity layers, such as fluorine doped tin oxide.

[0051] Non-limiting examples of blocking and capping layers may include one or more selected from an (oxy)nitride of silicon, an (oxy)nitride of aluminium, an oxide of silicon, an oxide of aluminium, an oxide of zinc, an oxide of tin, an oxide of zinc and tin, an oxide of zinc and aluminium, an oxide of zirconium, an oxide of titanium, an oxide of zirconium and titanium, an oxide of nickel, an oxide of chromium, an oxide of nickel and chromium, an oxide of strontium and niobium, or an oxide of strontium and titanium. Exemplary but non-limiting materials include silicon nitride (SiNx), aluminium nitride (AINX), ZnSnOx, ZrOx, TiOx,ZrTiOx, ZnO, ZnO:AI, TiOx, ZrOx, NiOx, CrOx, NiCrOx, an oxide of strontium and niobium (SrxNbyOz), or an oxide of strontium and titanium (SrxTiyOz). Preferably, used are one or more materials selected from silicon nitride (SiNx) and zinc stannate (ZnSnOx). These materials can each be used as a blocking layer and / or as a capping layer. In some embodiments, the same material or materials are used as both the blocking and capping layers.

[0052] In one embodiment, the one or more layers between the first layer and the substrate may comprise individual layers of silicon nitride and ZnSnOx, and in that order from the substrate. Alternatively, they may comprise an oxide of strontium and niobium.

[0053] In another embodiment, the capping layers comprise individual layers of silicon nitride and ZnSnOx, located on the side of the functional layer which is furthest from the substrate, and in that order from the substrate.

[0054] If there is a third layer comprising an oxide of strontium and titanium, then this layer is preferably between about 1 to about 50 nm; more preferably about 2 to about 40 nm; more preferably about 3 to about 30 nm.

[0055] Where there are one or more layers between the first layer and the second layer, preferably the first layer comprises zinc oxide and the one or more layers between the first layer and the second layer comprise a metal selected from aluminium, gallium, magnesium, tin, or indium; preferably aluminium.

[0056] According to another embodiment of the invention, the functional layer may comprise repeating sets of the first and second layers. By this is meant that a second layer is deposited on and in direct contact with a first layer, and another first layer of the same material as the initial first layer is deposited on and in direct contact with the second layer; and another second layer of the same material as the initial second layer is deposited on and in direct contact with the second first layer, and so on. There may be 2, 3, 4 or more repeating sets of the first and second layers. The repeated sets of each of the first and second layers may be the same thickness as the first set of the first and second layers. Alternatively, the repeated sets of each of the first and second layers may have a different thickness to the first set of the first and second layers.

[0057] However, preferably there is only one first layer and one second layer; or it is alternatively preferred that there may be also one or two sets of repeated sets of the first and second layers.

[0058] Substrate

[0059] The coated substrate comprises a substrate. Preferably, the substrate is selected from glass, resin, plastic, fused silica, quartz, sapphire, silicon, ceramic, metal, or semiconductor layers. Preferably, the substrate is glass. Where the substrate is glass, preferably it is soda-lime silica glass, as soda-lime silica glass is readily available and has excellent transparency and durability. For example, the soda-lime silica glass may be a low-iron soda-lime silica glass, as this has yet further improved visible transparency.

[0060] In some implementations, the coated substrate may have a sheet resistance Rs of less than 100 Q / n (Ohms per square), preferably the coated substrate has a sheet resistance Rs of less than 60 Q / n, preferably the coated substrate has a sheet resistance 'Rs' of less than 50 Q / n, more preferably the coated substrate has a sheet resistance Rs of less than 30 Q / n. The inventors have found that such sheet resistances are achievable by the present invention.

[0061] In some implementations, the coated substrate has a visible light transparency, TViS, of greater than 70%, preferably greater than 75%, more preferably greater than 80%, yet more preferably greater than 85%. The TViSis measured over the spectral range from 380 nm to 780 nm.

[0062] In some implementations, the coated substrate has a near-infrared radiation transparency, TNIR of greater than 50%, preferably greater than 70%, more preferably greater than 80%, yet more preferably greater than 85%. The TNIR is measured over the spectral range from 780 nm to 2500 nm.

[0063] According to a particular embodiment of the first aspect, there is preferably provided a coated substrate comprising a substrate with a surface and a coating directly or indirectly upon the surface, wherein the coating comprises: a first layer of thickness greater than or equal to 26 nm comprising aluminium doped zinc oxide ZnO:AI comprising from 1 to 10 atomic % aluminium based on metals and from 90 to 99 atomic % zinc based on metals; a second layer with a thickness greater than 25 nm comprising an oxide of strontium and niobium SrxNbyOz having an atomic proportion of niobium based on total strontium and niobium, y / (y+x), of greater than 0.50; and wherein: the coated substrate has a sheet resistance Rs of less than 100 Q / D and a visible transparency Tvis of greater than 80%.

[0064] Typically, in order to achieve these levels of sheet resistance, a step of annealing must be carried out, or the deposition needs to be carried out at elevated temperature.

[0065] According to another embodiment, the SrxNbyOzin this embodiment could be replaced with SrxTiyOz.

[0066] Alternatively, there may be a third layer comprising an oxide of strontium and titanium SrxTiyOzprovided in direct contact with the second layer, the layer having an atomic proportion of titanium based on total strontium and titanium, y / (y+x), of between about 0.40 and 0.65.

[0067] According to a second aspect, the present invention provides a method of manufacturing a coated substrate, comprising the steps of: i) providing a substrate; ii) forming a coating on a surface of the substrate, the coating comprising a first layer comprising an oxide of zinc and a second layer comprising an oxide of strontium and niobium SrxNbyOzin direct contact with the first layer; and iii) heating the coating at a first temperature for a first length of time.

[0068] The heating in step (iii) may be carried out for any length of time desired, such as a period of at least 1 hour, or for a period of less than 30 minutes. The heating may also be carried out at any desired pressure. However, when the coating contains blocking and / or capping layers, the heating may be carried out at atmospheric pressure, or in a low-pressure vacuum, such as 1 x IO-2mbar or less. Alternatively, when the coating does not contain blocking and / or capping layers, the heating is preferably carried out under vacuum, such as at no more pressure than about 1 x 10'3, or no more than about 1 x IO-5mbar.

[0069] According to another embodiment, in step (ii) above, the SrxNbyOzcould be replaced with SrxTiyOz.

[0070] Alternatively, in the second aspect, there may be a further step between steps (ii) and (iii), in which a third layer comprising an oxide of strontium and titanium SrxTiyOzis formed in direct contact with the second layer.

[0071] There may also be further steps for the deposition of other layers, such as the blocking and / or capping layers, one or more absorption layers, one or more infra-red reflection layers, and / or one or more low-emissivity layers.

[0072] The inventors have discovered that such a method provides a coated substrate of particularly excellent conductivity and visible and near infra-red light transmittance.

[0073] Optional features of the first aspect of the invention may be applied in their entirety to the second aspect alone or in combination.

[0074] Preferably, the first layer is between the second layer and the substrate. Preferably, the second layer is provided directly over the first layer during step (ii).

[0075] Preferably the first layer is formed by a technique such as, but not limited to, physical vapour deposition, chemical vapour deposition or atomic layer deposition; preferably the first layer is formed by physical vapour deposition. Preferably the second layer is formed by physical vapour deposition, chemical vapour deposition or atomic layer deposition; preferably the second layer is formed by physical vapour deposition. In some implementations the first layer is formed by chemical vapour deposition, and then the second layer is deposited upon the first layer by physical vapour deposition. Chemical vapour deposition is advantageous for some embodiments of the invention, as it may be combined with the float glass process to provide high quality coatings on glass, particularly soda-lime silica float glass, in an "online" continuous manner. Physical vapour deposition is advantageous for some embodiments of the invention, as it may provide high quality coatings. The deposition may be carried out at elevated temperatures, such as for example above about 300°C, or above about 500°C.

[0076] Alternatively, deposition of the layers may be carried out at high temperature, such as from about 275°C. Such a deposition may not require a post-deposition heating step.

[0077] In some implementations of the second aspect of the invention, the first layer comprising an oxide of zinc is formed by physical vapour deposition from a target comprising zinc and oxygen in an atmosphere comprising less than 10% oxygen by volume.

[0078] In alternative implementations of the second aspect of the invention, the first layer comprising an oxide of zinc is formed by physical vapour deposition from a target comprising zinc in an atmosphere comprising more than 10 volume % oxygen, wherein the target comprises less than 5 atomic % oxygen and between 1 and 15 atomic % aluminium based on metals.

[0079] The method comprises a step of heating the coating. The heating step may be accomplished by oven, furnace, induction, laser annealing or flash annealing, or other conventional means.

[0080] Where a laser beam is used to heat the second coating layer, preferably this is focused upon the second layer and includes a system for rapid displacement of the laser in a direction perpendicular to the effective travel of the substrate.

[0081] Preferably the first temperature in step (iii) is in excess of 300°C, preferably the first temperature is in excess of 400°C, more preferably the first temperature is in excess of 500°C.

[0082] Preferably during the heating step (iii) the functional layer is heated to a first temperature for a first time of at least 1 minute, preferably the first time is at least 2 minutes, more preferably the first time is at least 3 minutes, more preferably the first time is at least 5 minutes. However, where the heating method is by a rapid processing method such as flash annealing, the heating step may be less than a minute.

[0083] In alternative implementations of the second aspect of the invention, the step of heating the coating is carried out under an oxygen free atmosphere, preferably a reducing oxygen free atmosphere. The inventors have found that if step (iii) is carried out under a reducing atmosphere comprising hydrogen and at least one of nitrogen or argon, then the conductivity of the coating is worse compared to vacuum annealing.

[0084] According to a third aspect, the present invention provides a coated substrate manufactured according to the method of the second aspect of the present invention.

[0085] Preferably, the coated substrate comprises a coating having a sheet resistance change ARs, wherein ARs = RSAD - RSHT and where RSAD is the sheet resistance of the coating before step (iii) of heating the coating; and RSHT is the sheet resistance of the coating after step (iii) of heating the coating, wherein ARs is greater than 50 Q / n, preferably greater than 100 Q / n, even more preferably greater than 150 Q / n, yet more preferably greater than 200 Q / n.

[0086] All optional features of the first and or second aspects may be applied to the third aspect of the invention in any combination, and vice versa.

[0087] According to a fourth aspect, the present invention provides an electronic device comprising a coated substrate according to the first aspect of the invention, or a coated substrate according to the third aspect of the invention.

[0088] In some embodiments, the device according to the fourth aspect of the invention may form part of an integrated circuit component, which may comprise processing units, circuit dies, controllers and / or other micro-electronic features. In particular, the device may be a glass cored integrated circuit component comprising through-glass-vias (TGVs). Alternatively, the device according to the fourth aspect of the invention may form part of a sensor, transistor, or a capacitor.

[0089] According to a fifth aspect, the present invention provides an electrode comprising a coated substrate according to the first aspect of the invention, or a coated substrate according to the third aspect of the invention. In some embodiments, the electrode according to a fifth aspect of the invention is suitable for photovoltaic cells, variable transparency glazings, displays such as OLED, LED, TFT displays, or other devices which require a transparent conductive layer.

[0090] According to a sixth aspect, the present invention may act as part of an electrode which can be used in, for example, a photovoltaic cell or a variable transmission glazing comprising an electrode according to the fourth aspect. Preferably the photovoltaic cell comprises at least one of a crystalline silicon junction, a polycrystalline silicon junction, an amorphous silicon junction, a cadmium telluride layer, a copper indium gallium selenide layer, a copper indium selenide layer, a perovskite layer, a dye-sensitized layer, an organic layer, or two or more of these layers. Preferably the variable transmission glazing comprises at least one of an electrochromic, liquid crystal, suspended particle, or adjustable microblind device.

[0091] According to a seventh aspect, the present invention provides a glazing comprising a coated substrate according to the first aspect of the invention, or a coated substrate according to the third aspect of the invention. In some implementations, the glazing is an architectural glazing, such as an insulated glazing unit. In some implementations, the glazing is a vehicular glazing. Vehicular glazings suitable for the present coated substrate include sidelights, rooflights, windscreens, side windows, quarterlights and the like. In addition, such vehicular glazings include other external glass areas of the vehicle, such as spandrels and finishers, and other internal glass areas of the vehicle, such as displays, consoles, fascia pieces and the like. In some implementations, the glazing may be used in a solar module.

[0092] The skilled person will appreciate that optional or preferable features of aspects of the present invention may be applied to other aspects according to their needs and requirements. As such, all optional features of the first and second aspects may be applied to the third, fourth, fifth, sixth and seventh aspects in any combination, and vice versa.

[0093] Throughout this specification, the term "comprising" or "comprises" means including the component(s) specified but not to the exclusion of the presence of other components. The term "consisting essentially of" or "consists essentially of" means including the components specified but excluding other components except for materials present as impurities, unavoidable materials present as a result of processes used to provide the components, and components added for a purpose other than achieving the technical effect of the invention, such as colourants, and the like. The term "consisting of" or "consists of" means including the components specified but excluding other components.

[0094] Whenever appropriate, depending upon the context, the use of the term "comprising" includes the recitation of alternatives wherein "comprising" is replaced with "consisting essentially of", "consisting of", or "is". Similarly, the use of the term "comprises" includes the recitation of alternatives wherein "comprises" is replaced with "consists essentially of", "consists of". The present invention will now be described by way of example only, and with reference to, the accompanying drawings, in which:

[0095] Figure 1 illustrates schematically a coated glass substrate containing the first and second layers according to the present invention;

[0096] Figures 2a and 2b illustrate alternative coated substrates containing repeating sets of the first and second layers according to the invention;

[0097] Figure 3 illustrates a graph of the influence of increasing first layer thickness upon sheet resistance;

[0098] Figure 4 illustrates a graph of the influence of increasing first layer thickness upon visible and NIR transmission;

[0099] Figure 5 illustrates a graph of the influence of increasing second layer thickness upon sheet resistance;

[0100] Figure 6 illustrates a graph of the influence of increasing second layer thickness upon visible and NIR transmission;

[0101] Figure 7 illustrates a graph of the influence of increasing second layer thickness upon sheet resistance when the coating contains cap and blocking layers;

[0102] Figure 8 illustrates a graph of the influence of increasing second layer thickness upon visible and NIR transmission when the coating contains cap and blocking layers;

[0103] Figure 9 illustrates a graph of the influence of increasing first layer thickness upon sheet resistance when the coating contains cap and blocking layers; and

[0104] Figure 10 illustrates a graph of the influence of increasing first layer thickness upon visible and NIR transmission when the coating contains cap and blocking layers.

[0105] Figure 1 illustrates schematically a coated glass substrate 100 comprising: a substrate 110, here of soda lime silica glass, with an upper surface 111. The first surface 111 comprises a coating 120, and the coating comprises a first layer 121 in direct contact with the substrate 110 and a second layer 122 in direct contact with the first layer 121.

[0106] In a preferred embodiment of the invention, the first layer 121 comprises an oxide of zinc, such as ZAO, in direct contact with the substrate 110, while the second layer 122 comprises an oxide of strontium and niobium. According to one embodiment, there is only one each of the first layer and second layer. However, in other embodiments, there are repeating sets and two or more of each of the first layer and second layer. Figures 2a and 2b each show these embodiments.

[0107] In Figure 2a, the glass substrate 110 is a 4 mm float glass sheet, which has an upper surface 111, on which is deposited a coating 120, and the coating comprises a first layer 121 of 75 nm ZAO in direct contact with the substrate 110, and a second layer 122 of 18.5 nm of an oxide of strontium and niobium in direct contact with the first layer 121. In this Figure, there are two sets each of the first layer and second layer, with each of the first layers being ZAO and being of equal thickness in this example and each of the second layers being an oxide of strontium and niobium and also being of equal thickness in this example. However, it will be appreciated that these thicknesses do not have to be equal, and may be varied as required.

[0108] In Figure 2b, the glass substrate 110 is again a 4 mm float glass sheet. In this Figure, there are four sets each of the first layer 121 and second layer 122, with each of the first layers being 37.5 nm ZAO and each of the second layers being 9 nm an oxide of strontium and niobium.

[0109] Figure 3 shows a graph of the influence of increasing first layer thickness upon sheet resistance. In this graph, it can be seen that there is a marked decrease in the sheet resistance with increasing thickness of the ZAO, with the lowest value coming at about 150 nm.

[0110] Figure 4 shows a graph of the influence of increasing first layer thickness upon transmission of visible light and near infra-red radiation. In this graph, it can be seen that there is a slight decrease in TNIR values up to a thickness of 150 nm before it increases slightly again, and a slight increase in the TViSvalues up to a thickness of 100 nm before it decreases slightly again. However, the values remain largely consistent. The data for Figures 3 and 4 is shown in Table 2 below.

[0111] Figure 5 shows a graph of the influence of increasing second layer thickness upon sheet resistance. Again, a very sharp initial reduction is seen as the second layer is introduced, which continues gradually as the thickness of the second layer increases.

[0112] Figure 6 shows a graph of the influence of increasing second layer thickness upon transmission. In this graph, it can be seen that there is a continual decrease in TNIR values, and a slight increase in the TViSvalues up to a thickness of about 20 nm before it decreases slightly up to a thickness of about 100 nm before increasing slightly again. However, the values remain largely consistent for the Tvis values at larger thicknesses. The data for Figures 5 and 6 is shown in Table 4 below.

[0113] Figures 7-10 all show graphs of the influence of increasing thicknesses of the first and second layers upon sheet resistance and transmission when the coating also contains cap and blocking layers either side of the first and second layers.

[0114] In these examples, the cap and blocking layers are silicon nitride and zinc stannate. There are layers of both silicon nitride and zinc stannate between the first layer and the substrate, as well as on the other side of the second layer form the substrate. All the layers of the silicon nitride and zinc stannate are 15 nm in these data.

[0115] In Figure 7, again one can see the sharp initial reduction in the sheet resistance with introduction of the second layer and with increasing thickness of the second layer until it levels off at about 70 nm, before dropping again after about 200 nm.

[0116] In Figure 8, the relationship between the transmission of visible light and near infra-red radiation with increasing thickness of the second layer is shown.

[0117] Both variables are relatively constant up to about 150 nm, when the near infra-red transmission starts to fall slightly. The visible transmission only falls slightly after a thickness of about 250 nm. The data for Figures 7 and 8 is shown in Table 11 below.

[0118] The relationships of the same variables are compared in Figures 9 and 10 with an increasing thickness of the first layer.

[0119] In Figure 9, one can see the reduction in the sheet resistance with increasing thickness of the ZAO layer until a thickness of about 130 nm, before it begins to increase slightly again.

[0120] In Figure 10, the relationship between the transmission of visible light and near infra-red radiation with increasing thickness of the first layer is shown. It can be seen in both cases that the visible and near infra-red transmissions are largely constant with increasing thickness of the ZAO layer. The data for Figures 9 and 10 is shown in Table 13 below. The invention is further illustrated, but not limited, by the following examples.

[0121] For all examples the coatings were deposited on 4 mm thick standard soda-lime silica float glass panes with a light transmittance in the region of 90% using AC and / or DC magnetron (or pulsed DC) sputtering devices, medium-frequency sputtering being applied where appropriate.

[0122] While the coatings according to the invention used first layers comprising an oxide of zinc comprising ZAO, alternative oxides of zinc are not excluded, and may be used as an alternative if desired. Similarly, while the coatings according to the invention used second layers comprising an oxide of strontium and niobium comprising SNO, alternative oxides of strontium and niobium are not excluded; nor are oxides of strontium and titanium.

[0123] Unless otherwise stated coating layers were prepared using DC sputtering at room temperature under the following coating conditions shown in Table 1:

[0124] Table 1

[0125] A first series of examples were prepared by sputtering a layer of aluminium doped zinc oxide ZAO on 4 mm soda-lime silica float glass from a ceramic target, followed by sputtering a 37 nm layer of an oxide of strontium and niobium, SNO, directly upon the ZAO layer. All samples according to the invention after deposition and prior to annealing had a sheet resistance that was not measurable using the apparatus, and therefore have a sheet resistance of greater than 1 x 104Q / n. The coated substrates were annealed at 535 °C under high vacuum with a base pressure of 1 x IO-6mbar for 5 hours, and then visible and NIR transmission, sheet resistance and emissivity were all measured. The atomic proportion of niobium based on total strontium and niobium of the SNO layer was measured by XPS to be between 0.65 and 0.70 for all examples measured.

[0126] Examples are provided in the Tables below. Table 2 shows the variation of TViS, TNIR, sheet resistance and emissivity with a variation in the thickness of the ZAO layer. The layer of SNO is kept at a constant thickness of 37 nm.

[0127] Examples El-1, El-2 and El-3 are comparative examples which are not part of the present invention. A sheet resistance of "NC" indicates that no electrical conductivity could be measured, and the example is considered to be non-conducting.

[0128] Table 2: Glass / ZAO / SNO stack with 37 nm SNO and different ZAO thicknesses

[0129] It can be seen that a coating of 75 nm zinc oxide alone has a sheet resistance in excess of 1000 Q / n as in El-2; and a coating of 150 nm zinc oxide alone has a sheet resistance has a lower but still very high sheet resistance of 840.8 Q / n as in El-3; while a coating of 37 nm SNO alone is non-conducting as in El-1 with a sheet resistance in excess of 1 x 104Q / n.

[0130] However, by depositing the 37 nm SNO layer over the ZAO layer, the excellent performance of El-8 of 73.2 Q / n is obtained, i.e. the sheet resistance is reduced by over an order of magnitude compared to the comparative examples El-2 and El-1.

[0131] Similarly, comparing Example El-11 with comparative example El-3, the inclusion of a layer of 37 nm SNO together with the layer of ZAO reduces the Rs from 840.8 Q / n down to 42.7 Q / n, a reduction of about 95%.

[0132] Overall, the Rs value decreases as the thickness of the ZAO layer increases, up to a thickness of about 150 nm, after which the Rs starts to increase again. However, it remains at a reasonably low level even up to and beyond a thickness of 300 nm for the ZAO layer - which exhibits an Rs value still only of 93.5 Q / n. This is depicted in Figure 3.

[0133] The impact of the increasing first layer thickness upon transmission of visible light and near infrared radiation is depicted in Figure 4, showing a slight decrease in TNIR values up to a thickness of 150 nm before it increases slightly again, and a slight increase in the TViSvalues up to a thickness of 100 nm before it decreases slightly again. However, the values remain largely consistent with increasing first layer thickness.

[0134] The addition of a SNO layer on the ZAO layer above a threshold value of 25 nm zinc oxide thickness allows for the production of transparent conducting coatings, and zinc oxide thickness of 37 nm or more allows the production of transparent conductive coatings with sheet resistance below 350 Q / n, zinc oxide thickness of 50 nm or more allows the production of transparent conductive coatings with sheet resistance below 150 Q / n, and zinc oxide thickness of 150 nm or more allows the production of transparent conductive coatings with sheet resistance below about 50 Q / n. Furthermore, the application of the SNO layer to ZAO improves the transparency of the coating. As such, coatings according to the present invention can provide very low sheet resistance, with high transmission in both the visible and near infra-red spectra.

[0135] The examples according to the invention were compared to alternative transparent coated substrates, as in Table 3.

[0136] Table 3

[0137] Example Cl is a comparative example comprising a soda-lime glass substrate and is formed on a layer of titanium oxide (75 nm) directly on the substrate, then sputtering a layer of an oxide of strontium and niobium (37 nm) directly on the titanium oxide layer.

[0138] Example C2 is also a comparative example comprising a soda-lime glass substrate and is formed on a layer of SiO220 nm) and a layer of SnO2(20 nm) directly on the layer of SiO2, and then sputtering a layer of an oxide of strontium and niobium (37 nm) directly on the tin oxide layer.

[0139] It can be seen that the sheet resistance of each of Example Cl and C2 after heat treatment (5 hr, 1 x IO-6mbar) is not measurable, and therefore greater than 1 x 104Q / n. Such products are not commercially acceptable.

[0140] In comparison, the Example El-8 in Table 2 is the same as Example Cl, but uses 75 nm of ZAO as the first layer rather than 75 nm of TiO2. However, in contrast to Example Cl, Example El-8 does provide a satisfactory sheet resistance value of 73.2 Q / n.

[0141] Therefore, preferably the layer of an oxide of strontium and niobium is deposited upon a layer of an oxide of zinc, which is itself preferably doped with aluminium. A further benefit of the coatings according to the invention is that they provide a transparent conductive oxide of significantly reduced roughness (such as up to about 5 times less) compared to those based on fluorine doped tin oxide, which may reduce short circuits in some electronic applications.

[0142] A second series of examples was provided in the same way as the first series, but in this series the thickness of the SNO layer was varied. This is shown in Table 4.

[0143] Table 4: Glass / ZAO / SNO stack with 150 nm ZAO and different SNO thicknesses

[0144] From Comparative Example 2-1 to Example 2-2 of the invention it can be seen that the conductivity of the coating dramatically improves from 835.5 to 103.7 Q / n even with the addition of only a very thin (9 nm) layer of an oxide of strontium and niobium, and it continues to improve as the SNO layer thickness increases. A SNO layer deposition thickness of greater than 20 nm may achieve sheet resistances less than 60 or 50 Q / n, and SNO layer deposition thickness of greater than 100 nm may achieve sheet resistances less than 40 Q / n. It appears that once the low sheet resistance has been obtained by the addition of a SNO layer, conductivity gains are more linear with increasing deposition thickness, as illustrated by Figure 5. As such, preferably the SNO layer thickness is greater than 1 nm, preferably greater than 5 nm, even more preferably greater than 10 nm, even more preferably greater than 20 nm, even more preferably greater than 50 nm, even more preferably greater than 100 nm. However, in some embodiments a thicker SNO layer may be undesirable, due to a decreased NIR transmission. Therefore, in some embodiments the SNO layer thickness is preferably less than 400 nm, more preferably less than 300 nm, even more preferably equal to or less than 150 nm.

[0145] The impact of the increasing first layer thickness upon transmission of visible light and near infrared radiation is depicted in Figure 6, showing a continual decrease in TNIR values, and a slight increase in the TViSvalues up to a thickness of about 20 nm before it decreases slightly up to a thickness of about 100 nm before increasing slightly again. However, the values remain largely consistent for the TViSvalues with increasing second layer thickness.

[0146] A third example was provided. Here, a sample was prepared by sputtering a 37 nm layer of an oxide of strontium and niobium, SNO on 4 mm soda-lime silica float glass, followed by sputtering a layer of ZAO from a ceramic target, directly upon the SNO layer. Thus, in this example, the second layer is closer to the substrate than the first layer. Again, the coated substrate was annealed at 535°C under high vacuum base pressure of 1 x IO-6mbar for 5 hours and then visible and NIR transmission, sheet resistance and emissivity were all measured.

[0147] Table 5: Effect of the order of the layers

[0148] The deposition of ZAO on SNO results in a sheet resistance which is equivalent to the sheet resistance of the ZAO when deposited alone. If this is compared with Example El-8 above, which has the same layer thicknesses but the layers in the reverse order, the impact of having the correct layer order can be seen. Example E3-1 has an Rs as high as 1469 Q / n, while Example El- 8 has an Rs value of just 73.2 Q / n. As such, the beneficial properties of the coating system are not seen when the layer comprising strontium and niobium is underneath the layer comprising zinc and oxygen.

[0149] A fourth series of examples was provided. In this series, samples were prepared by sputtering a layer of ZnO on 4 mm soda-lime silica float glass from a Zn metal target, rather than from a ceramic target. This was then followed by sputtering a 37 nm layer of an oxide of strontium and niobium, SNO, directly upon the ZnO layer. The coated substrates were annealed at 535°C under high vacuum base pressure of 1 x IO-6mbar for 5 hours and then visible transmission, sheet resistance and emissivity were all measured.

[0150] Table 6: Effect of the target material

[0151] Samples E4-1 to E4-6 were all of extremely high resistance such that they do not provide the beneficial properties desired. Therefore, it is preferred that the first layer is sputtered from a ceramic target and / or a target comprising zinc and aluminium. Preferably the first layer is deposited from a ceramic target comprising zinc and oxygen, more preferably the first layer is deposited from a ceramic target comprising zinc, aluminium and oxygen, yet more preferably the first layer is deposited from a ceramic target comprising zinc, aluminium and oxygen, wherein the atomic % of aluminium based on metals is less than 10%.

[0152] Alternatively, the first layer may be deposited from a metallic target comprising both zinc and aluminium, preferably a metallic target comprising greater than 90 atomic % zinc, from 1 to 10 atomic % aluminium and less than 5 atomic % oxygen, more preferably less than 1 atomic % oxygen. This provides samples which are usable. However, visible light transmission is only very slightly changed by the modification from a ceramic target to a metallic target. Table 6A

[0153] Table 6A shows that if one deposits a first layer of ZAO using a ceramic target, a sheet resistance value of 95.01 Q / □ is achieved. If the first layer of ZAO is deposited using a metal target, a higher sheet resistance value of 461.8 Q / n is achieved. While this value is higher, the coating becomes conducting. In contrast, if the first layer is zinc oxide and it is deposited using a metal target which does not contain aluminium (as in Example E4-6 in Table 6), the sheet resistance is extremely high such that it does not provide the beneficial properties desired.

[0154] A fifth series of examples was provided. In this series, samples were prepared by sputtering a layer of ZAO on 4 mm soda-lime silica float glass from a ceramic target, followed by sputtering a 37 nm layer of an oxide of strontium and niobium, SNO, directly upon the ZAO layer. The coated substrates were annealed at 535°C under a lesser vacuum base pressure of 1 x 101mbar for 5 hours and then visible transmission, emissivity and sheet resistance were all measured.

[0155] Table 7: Effect of the pressure during the annealing at 1 x 101mbar for 5 hours

[0156] The change in vacuum pressure of annealing has a significant impact on the conductivity of the samples, where samples annealed at less than high vacuum are essentially non-conducting. When samples were annealed at base pressure 1 x IO-3they became conducting, but with a measured sheet resistance between 200 and 300 Q / n. Therefore, preferably a method for providing the coated substrate comprises a step of annealing at a base pressure of 1 x IO-2or less, more preferably at a base pressure of less than 1 x IO-3, yet more preferably at a base pressure of 1 x IO-4or less, even more preferably at a base pressure of 1 x IO-6or less.

[0157] A sixth series of examples was provided. In this series, samples were prepared by sputtering a layer of ZAO on 4 mm soda-lime silica float glass from a ceramic target, followed by sputtering a layer of an oxide of strontium and niobium, SNO, directly upon the ZAO layer. The coated substrates were annealed for 5 hours under vacuum base pressure of 1 x IO-6mbar, comparing the effect of annealing temperature upon sheet resistance.

[0158] Table 8: Effect of the annealing temperature (under high vacuum for 5h)

[0159] It can be seen in each of these examples that the annealing temperature has a significant impact upon the conductivity and the sheet resistance value.

[0160] For the Example E6-2 of the present invention, the sheet resistance value is a respectable 77.8 Q / n when annealing at 385°C. However, an increase in the annealing temperature results in a significant reduction in the sheet resistance value: annealing at 435°C yields a sheet resistance value of 54.6 Q / n, and annealing at 485°C yields an even lower sheet resistance value of 42.6 Q / n; while increasing the annealing temperature further to 535°C yields a higher sheet resistance value of 133.8 Q / n. There is therefore an optimum temperature range for the annealing process which will result in lower sheet resistance values. It is between about 350 and 520°C, more preferably between about 400 and 500°C for this coating structure, but it will be appreciated that other coating structures may exhibit optimum sheet resistance values after annealing at different temperatures. A seventh series of examples was provided. This demonstrates that low Rs values can be obtained when also including a third layer of an oxide of strontium and titanium. The annealing was carried out at a temperature of 535°C.

[0161] Table 9: Properties with an STO third layer present

[0162] The Rs value in Example 7-1 with no STO layer is 59.0 Q / n. When the STO third layer is added, the Rs value decreases up to an addition of 7 nm STO, at which point it begins to increase again. However, a coating with a third layer of STO of 14 nm still has a lower Rs than a coating without it. Even with a third layer of STO of 28 nm, the Rs value is still an acceptable 73.6 Q / n.

[0163] In contrast, the comparative Example E2-1 (C) from Table 4, which has 150 nm of ZAO as a coating but no SNO or STO, exhibits a very high sheet resistance of 835.5 Q / n, which leads to an unacceptable product.

[0164] An eighth series of examples was provided to demonstrate that STO can be used in place of SNO as the second layer. Table 10: Properties with an STO as the second layer - annealing under high vacuum for 5h

[0165] Here it can be seen that an Rs value as low as 80.1 Q / n can be achieved with 3 nm STO after annealing at 435°C, and 98.9 Q / n can be achieved with 3 nm STO after annealing at 385°C. However, for this particular layer configuration, annealing at a temperature of 535°C is not especially conducive to achieving lower sheet resistance values.

[0166] A ninth series of examples was provided. This demonstrates the use of cap and blocking layers. In these examples, layers of 15 nm silicon nitride and 15 nm zinc stannate are used, in that order starting from the substrate, both above and below the ZAO / SNO layers. The coating therefore has the structure:

[0167] Glass I SiN (15 nm) / ZnSnOx (15 nm) / ZAO / SNO / SiN (15 nm) / ZnSnOx (15 nm)

[0168] Heat treatment was carried out in a muffle furnace in an air atmosphere, at 650°C for 5 minutes. The data below in Table 11 illustrates how variation of the thickness of the SNO layer impacts the Tvis and T^and Rs values. Table 11: Use of cap and blocking layers - variation of SNO thickness - annealing via heat treatment in a muffle furnace (650°C, 5 minutes) It can be seen that the Rs value decreases with an increase in the SNO layer thickness, while there is also an overall decrease in the TViSand TNIR values.

[0169] Table 12 below shows the properties after vacuum annealing for 5 hours at 535°C with differing thicknesses of SNO on top of a constant thickness of 75 nm of ZAO.

[0170] Table 12: Properties after vacuum annealing (535°C, for 5 hours)

[0171] As expected, the Rs value decreases with an increase in the SNO layer thickness.

[0172] While the Rs values are a little higher for the heat treatment carried out in a muffle furnace at 650°C and only for 5 minutes (165 v 132.6), the TViSand TNIR values are similar. However, importantly, the presence of the capping layer opens up other processing options as it enables the annealing to be carried out either in an air atmosphere or in a vacuum.

[0173] A tenth series of examples was provided. This demonstrates how variation of the thickness of the ZAO layer impacts the Rs, TViSand TNIR values when there are cap and blocking layers. The same layers of 15 nm silicon nitride and 15 nm zinc stannate are used as above, in that order starting from the substrate, both above and below the ZAO / SNO layers. Again, heat treatment was carried out in a muffle furnace in an air atmosphere, at 650°C for rapid thermal processing, and only for 5 minutes.

[0174] Table 13: Properties after annealing via heat treatment in a muffle furnace (650°C, 5 minutes)

[0175] Again, Rs decreases consistently with the increased thickness of the layer of ZAO, and achieves a very acceptable Rs of 80 Q / n.

[0176] The measurements herein were carried out using the following methodologies:

[0177] Sheet Resistance - Sheet resistance measurements were made using a Van der Pauw Ecopia HMS3000 Hall Measurement System. This system produces a potential difference across an electrical conductor when a magnetic field is applied in a direction perpendicular to that of the flow of the current. The Van der Pauw method involves applying a current and measuring voltage using four small contacts made on the corners of 10 mm x 10 mm square samples. The maximum measurable sheet resistance with this equipment is 1 x 104Q / n. XPS analysis - X-ray photoelectron spectroscopy (XPS) depth profiling was carried out on Thermo K-Alpha XPS using an argon ion etch beam operating at 1 keV, producing a beam current of 1.71 pA, and rastered over a 2.0 x 4.0 mm area. A 15 second etch time per level was used with 100 levels of total etching. The X-ray spot size used was 400 pm. The binding energy windows used in the acquisition of the profile were: AI2p, Si2p, Sr3d, Nb3d, Sr3p, Ca2p, Sn3d, Ols, Zn2p, Nals, Mgls, Ti2p. A survey spectrum (which collects the entire 0-1350 eV binding energy range) was also collected to enable the detection of any additional elements present within the coating. As XPS is a quantitative technique, the concentration of each element within a coating layer may be determined and used to calculate a stoichiometry. For each coating, an average stoichiometry was calculated, based on the average concentration of each element in the layer. The first few etch levels were removed to reduce the influence of surface contamination.

[0178] Visible and Near-infrared Light Transmission - Transmission measurements were performed using a Cary5000 UV-Vis-NIR spectrometer. The Cary 5000 uses a tungsten halogen lamp as a source for the incident light in the visible and infrared regions from 350-3300 nm. In addition to a Scintillating detector from 175-800 nm, the instrument utilizes a PbS detector to extend its detection range into the NIR from 800-3300 nm. A combination of a monochromator and slits are used to select a specific wavelength from the light source, which is then directed towards the sample for interaction. Prior to measuring the samples, a baseline correction is performed to compensate for any background effects. The TViSis measured over the spectral range from 380 nm to 780 nm. The TNIR is measured over the spectral range from 780 nm to 2500 nm.

[0179] Emissivity - Emissivity measurements were performed using a Perkin Elmer Frontier Optica Fourier Transform Infrared (FTIR) spectrometer with IR specular reflection set accessory. The FTIR spectrometer measures IR reflectance from the sample surface. The total normal reflectance was determined by taking a mathematical average of the reflectance curve at 24 specific wavelengths in the 5-25 pm range. Using the total normal reflectance value, the normal emissivity was then calculated in accordance with EN 12898:2019. Emissivity is defined as the ratio of the energy emitted by a given surface at a given temperature to that of a perfect emitter (black body with normal and corrected emissivity = 1,0) at the same temperature.

[0180] Refractive Index - A sputtered layer of SNO 114 nm in thickness on 4mm soda-lime silica glass was analysed using a Hunterlab Ultrascan Pro Spectrophotometer and then modelled in CODE 5.28 available from WTheiss to provide a measured refractive index of 2.06 as deposited, and 2.14 following annealing at 535°C and a pressure of 1 x IO-6for 5 hours.

[0181] Surprisingly, the inventors have discovered that the conductivity of an oxide of zinc transparent conductive oxide may be increased significantly by the application of a layer of an oxide of strontium and niobium, and such a coating has particularly low sheet resistance and at the same time particularly high NIR transmission.

[0182] It will be appreciated that the examples above are intended to be purely illustrative of the present invention. However, the person skilled in the art would recognise that variations of the invention can be carried out without departing from the scope of the invention.

Claims

Claims1. A coated substrate comprising a substrate with a surface and a coating directly or indirectly upon the surface, wherein the coating comprises a functional layer comprising strontium, zinc and oxygen, with niobium and / or titanium.

2. A coated substrate according to claim 1, wherein the functional layer comprises a first layer and a second layer deposited as separate layers.

3. A coated substrate according to any preceding claim, wherein the functional layer comprises: a first layer comprising an oxide of zinc; and a second layer comprising an oxide of strontium and niobium.

4. A coated substrate according to claim 3, wherein the oxide of zinc is selected from one or more of zinc oxide; zinc stannate zinc oxide doped with another metal such as aluminium, gallium, or magnesium; preferably aluminium.

5. A coated substrate according to any preceding claim, wherein the first layer located is between the second layer and the substrate; and / or wherein the first layer is in direct contact with the substrate; and / or wherein the second layer is in direct contact with the first layer.

6. A coated substrate according to any preceding claim, further comprising a third layer over the second layer on the opposite side of the second layer from the substrate.

7. A coated substrate according to claim 6, wherein the third layer comprises a layer based on one or more materials selected from an (oxy)nitride of silicon, an oxide of zinc, an oxide of tin, an oxide of zinc and tin, an oxide of strontium and niobium or an oxide of strontium and titanium; preferably one or more materials selected from silicon nitride (SiNx), zinc stannate (ZnSnOx) and an oxide of strontium and niobium (SrxNbyOz); and when the third layer comprises an oxide of strontium and titanium, then this layer is preferably between about 1 to about 50 nm; more preferably about 2 to about 40 nm; more preferably about 3 to about 30 nm.

8. A coated substrate according to any preceding claim, wherein the coating comprises a fourth layer between the first layer and the substrate.

9. A coated substrate according to claim 8, wherein the fourth layer comprises a layer based on one or more materials selected from an (oxy)nitride of silicon, an (oxy)nitride of aluminium, an oxide of silicon, an oxide of aluminium, an oxide of zinc, an oxide of tin, an oxide of zinc and tin, an oxide of zinc and aluminium, an oxide of zirconium, an oxide of titanium, an oxide of zirconium and titanium, an oxide of nickel, an oxide of chromium, an oxide of nickel and chromium, an oxide of strontium and niobium, or an oxide of strontium and titanium; preferably one or more materials selected from silicon nitride (SiNx), zinc stannate (ZnSnOx) and an oxide of strontium and niobium (SrxNbyOz).

10. A coated substrate according to any of claims 6-9, wherein the coating comprises layers comprising silicon nitride and zinc stannate both below and over the functional layer.

11. A coated substrate according to any preceding claim, wherein the functional layer comprises, in order from the substrate: a first layer comprising an oxide of zinc; and a second layer comprising an oxide of strontium and niobium; and a third layer comprising an oxide of strontium and titanium.

12. A coated substrate according to any preceding claim, wherein the first layer comprises zinc oxide and the coating further comprises a third layer between the first layer and the second layer, where the third layer comprises a metal selected from aluminium, gallium, magnesium, tin, or indium.

13. A coated substrate according to any preceding claim, wherein the first layer has a thickness of greater than or equal to 26 nm; preferably greater than or equal to 30 nm; preferably greater than or equal to 35 nm; preferably greater than or equal to 37.5 nm; more preferably greater than or equal to 50 nm; yet more preferably greater than or equal to 75 nm; even more preferably greater than or equal to 150 nm.

14. A coated substrate according to any preceding claim, wherein the first layer has a thickness of less than 300 nm, preferably less than 250 nm; and / orwherein the second layer has a thickness of from 1 to 500 nm, preferably the second layer has a thickness of from 5 to 450 nm; preferably 10 to 400 nm; more preferably 125 to 390 nm.

15. A coated substrate according to any preceding claim, wherein the oxide of strontium and niobium SrxNbyOzof the second layer has an atomic proportion of niobium based on total strontium and niobium, y / (y+x), of greater than 0.40, preferably greater than 0.50, more preferably greater than 0.55, yet more preferably greater than 0.60, even more preferably greater than 0.65.

16. A coated substrate according to any preceding claim, wherein the coating further comprises one or more absorption layers for absorbing visible light; and / or one or more infra-red reflection layers; and / or one or more low-emissivity layers.

17. A coated substrate according to any preceding claim, wherein the functional layer comprises one or more repeating sets of the first and second layers.

18. A coated substrate according to any preceding claim, wherein the coating has a sheet resistance Rs of less than 60 Q / n, preferably the coated substrate has a sheet resistance Rs of less than 50 Q / n, preferably the coated substrate has a sheet resistance Rs of less than 40 Q / n, more preferably the coated substrate has a sheet resistance Rs of less than 30 Q / n.

19. A method of manufacturing a coated substrate, comprising the steps of: i) providing a substrate; ii) forming a coating on a surface of the substrate, the coating comprising a first layer comprising an oxide of zinc and a second layer comprising either an oxide of strontium and niobium SrxNbyOzor an oxide of strontium and titanium SrxTiyOz; and iii) heating the coating at a first temperature for a first length of time.

20. A method according to claim 19, wherein the heating in step (iii) is carried out for more than about 30 minutes.

21. A method according to claim 20, wherein the heating is carried out in a vacuum with a pressure of no more than about 1 x IO-3mbar, preferably no more than about 1 x IO-5mbar, more preferably no more than about 1 x IO-6mbar.

22. A method according to claim 10, wherein the heating in step (iii) is carried out for less than about 30 minutes, more preferably less than about 15 minutes; more preferably less than about 10 minutes.

23. A method according to any of claims 19-22, wherein the heating is carried out at atmospheric pressure; and / or at a temperature in excess of 300°C, preferably in excess of 400°C, more preferably in excess of 500°C.

24. A method according to any of claims 19-23, wherein the first layer is deposited using a ceramic target.

25. A coated substrate manufactured according to the method of any of claims 19-24.

26. A coated substrate according to claim 25, wherein the coating has a sheet resistance change ARS, wherein ARS = RSAD - RSHT and where RSAD is the sheet resistance of the coating before step (iii) of heating the coating; and RSHT is the sheet resistance of the coating after step (iii) of heating the coating, wherein ARS is greater than 50 Q / n, preferably greater than 100 Q / n, even more preferably greater than 150 Q / n, yet more preferably greater than 200 Q / n.

27. An electronic device or an electrode comprising a coated substrate according to any of claims 1 to 18, or comprising a coated substrate according to claim 25 or claim 26.

28. A photovoltaic cell or variable transmission glazing comprising an electrode according to claim 27.

29. A glazing comprising a coated substrate according to any of claims 1 to 18, or a coated substrate according to claim 25 or claim 26, or an electronic device or electrode according to claim 27, or a photovoltaic cell according to claim 28; preferably wherein the glazing is an architectural glazing, a vehicular glazing, or a solar module.

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