Abstract:
The invention relates to a silver low-E coating for glass which is temperable and can be applied by means of sputter processes onto the glass. The individual layers of the coating are cost-effective standard materials. One embodiment of the invention for example is comprised of a glass substrate, an Si 3 N 4  layer disposed thereon of a thickness of approximately 15 nm, a TiO 2  layer of 15 nm thickness on the Si 3 N 4  layer, a 12.5 nm thick Ag layer on the TiO 2  layer, a NiCrO x  layer of approximately 5 nm thickness on the Ag layer and a terminating 45 nm thick Si 3 N 4  layer.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a non-provisional, and claims the benefit, of commonly assigned U.S. Provisional Application No. 60/893,764, filed Mar. 8, 2007, entitled “Temperable Glass Coating,” the entirety of which is herein incorporated by reference for all purposes. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a temperable glass coating according to the preamble of patent claim  1 . 
     Coatings on transparent glass or transparent synthetic material serve to reflect or absorb specific wavelengths or wavelength ranges of incident light. Known are coatings on optical lenses and on window panes, also referred to as architectural glass, as well as the coatings on motor vehicle window panes. 
     The most important function of a coating on architectural glass is the reflection of thermal radiation in order for a room not to become too warm during the summer and not too cool during the winter. In the process the visible light is to be minimally weakened, i.e. the coating should have high transmission in the visible range (approximately 400 nm to 700 nm under daylight vision and approximately 390 nm to 650 nm under night vision) and high reflection for thermal and infrared radiation (wavelength&gt;700 nm). 
     Layer systems fulfilling this function are referred to as low-E layer systems, “E” representing emissivity (=degree of emission or emission capability). This is intended to express that these layer systems only output low thermal radiation from a building room to the outside. 
     As a rule, heat regulation is attained thereby that onto glass electrically high-conducting layers are applied, frequently comprising a metal such as Cu, Ag, Au with a very low radiation emission coefficient. 
     Due to the light reflection of these low-E layers, which is often too high, these layers are sometimes antireflection-coated with the aid of additional transparent layers. By applying the transparent layers, the desired color tint of the glass pane can also be set. 
     A coated substrate is already known which comprises at least one metallic coating layer and further dielectric layers (EP 1 089 941 B1). This coated substrate is structured such that it can be tempered and bent. 
     A substrate provided with a multilayer system is furthermore known which is also temperable and bendable (U.S. Pat. No. 6,576,349 B2, U.S. Pat. No. 6,686,050 B2). The multilayer system utilized herein comprises two layers which reflect infrared radiation and which are each encompassed by two NiCrO x  layers. 
     Further, a heat-insulating layer system is known which, after the coating, is tempered and bent (DE 198 50 023 A1 or EP 0 999 192 B1). This layer system comprises a precious metal layer disposed on a TiO 2  layer, the two layers being encompassed by suboxidic NiCrO 2 . 
     Lastly, temperable coatings are also known which utilize substoichiometric Si x N y  or SiN x O y  (WO 2005/19127 A1, WO 2005/034192 A2). 
     The different layers are, as a rule, produced with the aid of sputter processes, in which by means of positive ions particles are knocked out of so-called targets, which particles are subsequently deposited on the substrate, which may be architectural glass. 
     The known layer systems entail at least one of the following cited disadvantages: 
     expensive or exotic starting materials for sputter targets 
     complex and complicated process control 
     complex layer structuring 
     inadequate optical properties 
     severe changes of the essential properties of the coated glass by a temper process. 
     The invention addresses the problem of providing a simple and cost-effective silver low-E coating, which only minimally changes its essential properties after tempering. 
     BRIEF SUMMARY OF THE INVENTION 
     A temperable substrate with a coating is disclosed according to one embodiment of the invention. The temperable substrate may include a glass substrate with a first layer comprising Si x N y O z  disposed thereon. A second layer comprising TiO 2  may be disposed on the first layer. A third layer comprising Ag may be disposed on the second layer. A fourth layer comprising NiCrO k  may be disposed on the third layer. A fifth layer comprising Si x N y O z  may be disposed on the fourth layer. The layers that include Si x N y O z , x/y≦0.75, y/z&gt;4, and 0&lt;k&lt;2. 
     A method of making the above mentioned temperable substrate is also disclosed. The method includes sputtering each of the layers on the substrate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The advantage attained with the invention comprises in particular that only standard target materials, such as boron-doped silicon (Si:B) or titanium-doped silicon aluminum (SiAl:Ti) as well as titanium oxide, silver or nickel-chromium are employed. 
     Since pure silicon is not conductive, silicon sputter targets must be doped, for example, with boron in order for them to be utilizable at all for DC or MF sputtering. The additives boron, aluminum or titanium, which are also contained in the layer, do not have a negative effect. Si 3 N 4  comprises only small quantities of oxygen (O m ) as layer material. 
     In the following the process parameters of a sputter process carried out in the production of the invented coating Si 3 N 4 —TiO 2 —Ag—NiCrO x —Si 3 N 4  on glass are compiled in the form of a table. The designations used indicate the following: 
     KT=Cathode 
     sccm=standard cubic centimeter per minute (also Nml per minute; Nml=standard millimeter) 
     AC=alternate current 
     DC=direct current 
     V=Volt (voltage) 
     A=Ampere (current) 
     W=Watt (power) 
     k=1000 
     F=10 −6    
     bar=0.1 MPa=10 5  Pa (Pa=Pascal=pressure) 
     planar=planar cathode 
     rot=rotating cathode 
     :=doped with 
     KT 1, KT 2 etc. are here the different cathodes of an inline process, past which a substrate—here glass—is successively moved. 
     m=number greater than or equal to zero. 
     
       
         
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Cathode 
               
             
          
           
               
                   
                 KT 1 
                 KT 2 
                 KT 3 
                 KT 4 
                 KT 5 
                 KT 6 
                 KT 7 
                 KT 8 
               
             
          
           
               
                   
                 Material 
               
             
          
           
               
                 Gas Inlet 
                 Si 3 N 4   
                 TiO 2   
                 TiO 2   
                 TiO 2   
                 Ag 
                 NiCrO x   
                 Si 3 N 4 :O m   
                 Si 3 N 4 :O m   
               
               
                   
               
               
                 Argon 
                 700 sccm 
                 500 sccm 
                 450 sccm 
                 450 sccm 
                 590 sccm 
                 480 sccm 
                 1000 sccm 
                 1000 sccm 
               
               
                 Oxygen 
                 20 sccm 
                 293 sccm 
                 274 sccm 
                 265 sccm 
                 10 sccm 
                 40 sccm 
                 50 sccm 
                 50 sccm 
               
               
                 Nitrogen 
                 585 sccm 
                 50 sccm 
                 50 sccm 
                 50 sccm 
                 0 sccm 
                 0 sccm 
                 1070 sccm 
                 1195 sccm 
               
               
                 Process 
                 AC rot 
                 AC rot 
                 AC rot 
                 AC rot 
                 DC planar 
                 DC planar 
                 AC rot 
                 AC rot 
               
               
                 Pressure 
                 4.91 μbar 
                 4.22 μbar 
                 4.36 μbar 
                 4.15 μbar 
                 4.34 μbar 
                 4.65 μbar 
                 8.83 μbar 
                 9.23 μbar 
               
               
                 Voltage 
                 340.0 V 
                 448.0 V 
                 446.0 V 
                 447.0 V 
                 408.0 V 
                 458.0 V 
                 265.0 V 
                 266.0 V 
               
               
                 Current 
                 102.0 A 
                 223.0 A 
                 224.0 A 
                 225.0 A 
                 7.0 A 
                 6.5 A 
                 223.0 A 
                 222.0 A 
               
               
                 Power 
                 35.0 kW 
                 100.0 kW 
                 100.0 kW 
                 100.0 kW 
                 2.7 kW 
                 2.9 kW 
                 59.0 kW 
                 59.0 kW 
               
               
                   
               
             
          
         
       
     
     The TiO 2  layer has here a double function as an anti-reflecting dielectric and as a seed layer or blocker for the succeeding silver layer. Application of the TiO 2  layer as three layers (KT 2, KT 3, KT 4) takes place for the reason that at given substrate rate one cathode alone would not yield the adequate layer thickness. For the same reason the Si 3 N 4 :O m  layer is applied in two steps. Before tempering, none of the layers had a gradient. Special doping in the target material of the sputter process was omitted. 
     The dielectric layers—Si 3 N 4  and TiO 2 —are preferably sputtered from rotating magnetrons. For the TiO 2  layer ceramic TiO x  target can be utilized, which can be sputtered using MF techniques (approximately 10 kHz to 80 kHz) or AC techniques or also DC techniques. 
     The Ag layer and the NiCrO x  layers are typically sputtered from metallic targets by means of DC techniques. For all processes planar and/or rotating targets are conceivable. For TiO 2  and Si 3 N 4  coatings rotating targets have preferably been used for some time. For Ag and NiCrO x  layers planar targets are conventionally used, however rotating targets are also feasible. 
     As is evident based on Table 1, only small quantities of oxygen are required in the Si 3 N 4  processes. A high pressure is required in the concluding Si 3 N 4 . Si 3 N 4 :O can generally also be written as Si x N y O z , wherein x/y≦0.75 and y/z≧4 applies. The maximum oxygen flow for the NiCrO x  process occurs on the metal branch of the hysteresis, for which narrow apertures and a gas inlet below this aperture in the sputter chamber are preconditions. 
     The right columns of Table 1 show ratios N 2 :O 2 ≧20:1. However, the layers can also be generated for example at a gas flow ratio of N 2 :O 2 =4:1. The layer composition does not reflect this gas flow ratio of N 2 :O 2 . Rather different parameters exert their influence if relatively more oxygen than nitrogen is found in the layers. 
     By metal branch of the hysteresis the following is understood: if the characteristic at constant power and increasing oxygen flow is plotted against the generator data (current, voltage), the voltage increases up to a certain point, the breakover point. If the oxygen quantity is further increased, the voltage decreases markedly. The process has tipped over from metal mode into oxide mode. If the oxygen is again decreased, a point is reached at which the process tips back again into metal mode. However, the two breakover points are not identical, rather the curve describes a hysteresis (cf. FIG. 1 of EP 0 795 890 A2). 
     The small quantities of nitrogen in the TiO 2  processes are not unusual per se and typical when using metallic targets for the process stabilization. When employing ceramic targets, the nitrogen can be omitted. It is probable that due to the higher pressure and the oxygen in the uppermost layer of Si 3 N 4 :O two parameters are available, which permit the setting of the barrier effect and/or of the internal mechanical layer stress conformed to the coating and the coating installation. 
     This applies analogously also to the Si 3 N 4  base layer (KT 1), however, here the increased sputter pressure does not yield any advantages. 
     With the continuous variation of oxygen flow and working pressure in the two Si 3 N 4  processes (KT 1 or KT 7 and KT 8) variable parameters are available (thus virtual control levers) to conform the layer system to the particular tempering process. A “tuning range” is consequently available in order to attain for the particular coating installation, glass quality and further processing (specifically the tempering) an optimum conformation on the part of the coating. 
     The layer combination cited in the Table 1 before and after the tempering has the properties listed in the following Table 2. Herein the symbols and abbreviations of the CIE LAB color system indicate the following: 
     a*=color value on the red-green axis (dimensionless) 
     b*=color value on the yellow-blue axis (dimensionless) 
     Ty=transmission averaged in the visible range in percent 
     RGy=reflection averaged in the visible range from the glass side of the sample in percent 
     RFy=reflection averaged in the visible range from the layer side of the sample in percent 
     Haze=opacity or “milkinessD” (stray-light loss), stray-light component in % 
     R/sq=surface resistivity in Ohm (cf. Hans Joachim Glaser: Duennfilmtechnologie auf Flachglas, pp. 134-137). 
     The thickness of the first Si 3 N 4  layer is preferably 5 to 25 nm. The second layer of TiO 2  has preferably also a thickness of 5 to 25 nm. The third layer, comprised of Ag, is preferably 8 to 18 nm thick. The succeeding layer of NiCrO k  is 3 to 8 nm thick. The last layer of Si x N y O z  is preferably 25 to 65 nm thick. 
     
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Before 
                   
                 After 
                   
                   
                   
               
               
                   
                 Tempering 
                   
                 Tempering 
                   
                 Difference 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Ty 
                 82.25 
                 Ty 
                 82.58 
                 Ty 
                 1.33 
               
               
                   
                 a* 
                 −1.06 
                 a* 
                 −1.63 
                 a* 
                 −0.57 
               
               
                   
                 b* 
                 1.93 
                 b* 
                 1.26 
                 b* 
                 −0.67 
               
               
                   
                 RGy 
                 9.95 
                 RGy 
                 9.63 
                 RGy 
                 −0.32 
               
               
                   
                 a* 
                 −1.99 
                 a* 
                 −0.35 
                 a* 
                 1.64 
               
               
                   
                 b* 
                 −5.70 
                 b* 
                 −4.78 
                 b* 
                 0.92 
               
               
                   
                 RFy 
                 6.43 
                 RFy 
                 6.95 
                 RFy 
                 0.52 
               
               
                   
                 a* 
                 −0.54 
                 a* 
                 −0.82 
                 a* 
                 1.36 
               
               
                   
                 b* 
                 −5.36 
                 b* 
                 −3.87 
                 b* 
                 1.49 
               
               
                   
                 Haze 
                 0.16 
                 Haze 
                 0.33 
                 Haze 
                 0.17 
               
               
                   
                 R/sq 
                 4.80 
                 R/sq 
                 3.30 
                 R/sq 
                 −1.50 
               
               
                   
                   
               
             
          
         
       
     
     Table 2 shows that there are only minimal differences in the essential properties of the coating before and after tempering. The tempering was carried out at a temperature of approximately 620 to 700° C. The substrate was therein heated for 2 to 20 minutes and subsequently cooled very rapidly by means of compressed air. 
     Adhesive strength was tested by means of the so-called Erichsen Wash Test according to ISO 11998. The results were faultless for all samples. The storage life was also tested, and specifically according to the so-called Storage Test for Resistance to Moisture according to DIN EN ISO 6270 (DIN-50017). Here also only positive values were determined. 
     In addition, the transmission Ty is above 80%, the layer resistance is less than 5.0 Ohm/sq and for the colors in the reflection from the glass side applies −4&lt;a*&lt;0 as well as −7&lt;b*&lt;−2. The haze is less than 0.5%. The mechanical stability is robust, which could be determined by means of an Erichsen Brush Test with 200 strokes. 
     In some embodiments, the first layer has a thickness of 15 nm. In some embodiments, the second layer has a thickness of 15 nm. In some embodiments, the third layer has a thickness of 12.5 nm. In some embodiments, the fourth layer has a thickness of 5 nm. In some embodiments, the fifth layer has a thickness of 40 to 50 nm. 
     In some embodiments, a temperable substrate can include a layer for setting the transmission that is disposed between the second layer and the third layer. In some embodiments, this layer for setting the transmission can be transmission-increasing, can include ZnO, and can have a thickness of 4 to 20 nm. In some embodiments, this layer for setting the transmission can be transmission-increasing, can include ZnO:Al, and can have a thickness of 5 to 10 nm. In some embodiments, this layer for setting the transmission can be transmission-decreasing, can include NiCrO, and can have a thickness of 2 to 5 nm.