MATERIAL COMPRISING A FUNCTIONAL LAYER MADE FROM SILVER, CRYSTALLISED ON A NICKEL OXIDE LAYER

Abstract

A process for obtaining a material including a transparent substrate coated with a stack of thin layers which are deposited by cathode sputtering, the stack of thin layers includes at least one silver-based functional metal layer and at least two antireflective coatings, each antireflective coating including at least one dielectric layer, so that each functional metal layer is positioned between two antireflective coatings, the process including: (a) depositing an antireflective coating including at least one thin layer based on crystalline nickel oxide, wherein the at least one thin layer based on crystalline nickel oxide is devoid of a nickel and chromium alloy, then (b) depositing at least one silver-based functional metal layer above and in contact with the thin layer based on crystalline nickel oxide.

Claims

1. A process for obtaining a material comprising a transparent substrate coated with a stack of thin layers which are deposited by cathode sputtering, the stack of thin layers comprising at least one silver-based functional metal layer and at least two antireflective coatings, each antireflective coating comprising at least one dielectric layer, so that each functional metal layer is positioned between two antireflective coatings, the process comprising: (a) depositing an antireflective coating comprising at least one thin layer based on crystalline nickel oxide, wherein the at least one thin layer based on crystalline nickel oxide is devoid of a nickel and chromium alloy, then (b) depositing at least one silver-based functional metal layer above and in contact with the thin layer based on crystalline nickel oxide.

2. The process for obtaining a material as claimed in claim 1, wherein all the layers of the stack are produced and a crystallization heat treatment is carried out in a chamber for deposition by cathode sputtering.

3. The process for obtaining a material as claimed in claim 1, further comprising stage (c) during which the substrate coated with the stack of thin layers is subjected to a heat treatment at a temperature greater than 400 C.

4. The process for obtaining a material as claimed in claim 3, wherein the temperature is greater than 500 C.

5. The process for obtaining a material as claimed in claim 1, wherein the cathode sputtering is assisted by a magnetic field.

6. The process for obtaining a material as claimed in claim 1, wherein the at least one silver-based functional metal layer comprises monocrystalline grains oriented so that the grains have the family of {200} planes parallel to a surface of the transparent substrate.

7. The process for obtaining a material as claimed in claim 1, wherein the at least one thin layer based on crystalline nickel oxide has a thickness of at least 0.5 nm.

8. The process for obtaining a material as claimed in claim 1, wherein the at least one thin layer based on crystalline nickel oxide has a thickness of less than 4 nm.

9. The process for obtaining a material as claimed in claim 1, wherein the transparent substrate is a glass substrate.

10. The process for obtaining a material as claimed in claim 1, wherein the transparent substrate coated with the stack is a bent or tempered glass, or both a bent and tempered glass.

11. The process for obtaining a material as claimed in claim 1, further comprising an upper protective layer as the last layer of the stack.

12. The process for obtaining a material as claimed in claim 11, wherein the upper protective layer is a TiO.sub.2 layer.

Description

EXAMPLES

[0127] Stacks of thin layers defined below are deposited on substrates made of clear soda-lime glass with a thickness of 2 mm.

[0128] For these examples, the conditions for deposition of the layers deposited by sputtering (magnetron cathode sputtering) are summarized in table 1 below.

[0129] The layers of titanium oxide deposited as dielectric layer of the antireflective coating or as blocking layer can be completely or partially oxidized. For this, a ceramic target of substoichiometric TiOx is used and deposition is carried out in an oxidizing atmosphere, in order to obtain a completely oxidized layer of TiO.sub.2, or in an inert atmosphere, in order to obtain a substoichiometric layer.

[0130] For some examples, the thicknesses of the layers are varied by modifying the deposition power

TABLE-US-00001 TABLE 1 Deposition Targets employed pressure Gas Index* Si.sub.3N.sub.4 Si:Al (92:8% by 1.5 * 10.sup.3 mbar Ar 47% - N.sub.2 53% 2.00 wgt) ZnO Zn:Al (98:2% 1.5 * 10.sup.3 mbar Ar 91% - O.sub.2 9% 2.04 by wgt) NiCr Ni:Cr (80:20 2 * 10.sup.3 mbar Ar at 100% at. %) Ag Ag 8 * 10.sup.3 mbar Ar at 100% TiO.sub.2 TiOx 1.5 * 10.sup.3 mbar Ar 88% - O.sub.2 12% 2.32 SnZnO Sn:Zn (60:40% 1.5 * 10.sup.3 mbar Ar 39% - O.sub.2 61% 2.09 by wgt) NiO Ni 2.5 * 10.sup.3 mbar Ar 97% - O.sub.2 3% at.: atomic; wgt: weight; *at 550 nm

[0131] The materials and the physical thicknesses in nanometers (unless otherwise indicated) of each layer or coating which constitutes the stacks are listed in the tables below as a function of their positions with respect to the substrate carrying the stack.

TABLE-US-00002 Glazing Comparative According to the invention C1a C1b A1a A1b A2a A2b A3a A3b Antireflective Si.sub.3N.sub.4 10 10 10 10 10 10 10 10 coating ZnO 5 5 5 5 5 5 5 5 Blocking layer OB NiCr 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Functional layer Ag 10 10 10 10 10 10 10 10 Antireflective NiO 10 10 1 1 5 5 coating ZnO 10 10 10 10 5 5 Si.sub.3N.sub.4 30 30 30 30 30 30 30 30 Substrate (mm) glass 2 2 2 2 2 2 2 2 Crystallization no yes no yes no yes no yes heat treatment Glazing According to the Comparative invention C2a C2b C3a C3b C5 A4a A4b A6 Upper protective TiO.sub.2 2 2 2 2 2 2 2 2 layer Antireflective Si.sub.3N.sub.4 30 30 30 30 30 30 30 30 coating ZnO 5 5 5 5 5 5 5 5 Blocking layer OB NiCr 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Functional layer Ag 10 10 10 10 10 10 10 10 Antireflective NiO 10 10 1 1 1 coating ZnO 10 10 10 10 10 10 Si.sub.3N.sub.4 30 30 30 30 30 30 30 30 Substrate (mm) glass 2 2 2 2 4 2 2 4 Crystallization no no no no no no no no heat treatment Heat treatment no yes no yes no no yes no Complete stack

[0132] A crystallization heat treatment can be carried out before deposition of the silver-based functional layer by laser treatment. For the examples described above, the heat treatment of the complete stack is also carried out by laser treatment.

TABLE-US-00003 Glazings According to Comparative the invention 1 2 3 4 5 6 7 8 9 10 Protective layer TiO.sub.2 2 2 2 2 2 2 2 2 2 2 Antireflective Si.sub.3N.sub.4 30 30 30 30 30 30 30 30 30 30 coating ZnO 5 5 5 5 5 5 5 5 5 5 Blocking layer NiCr 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Functional layer Ag 10 10 10 10 10 10 10 10 10 10 Blocking layer NiCr 0.5 1 3 Growth layer TiO.sub.x 0.5 1 3 NiO 0.5 1 3 Antireflective ZnO 5 5 5 5 5 5 5 5 5 5 coating SnZnO.sub.x 30 30 30 30 30 30 30 30 30 30 Substrate (mm) glass 2 2 2 2 2 2 2 2 2 2 Heat treatment yes yes yes yes yes yes yes yes yes yes Complete stack

[0133] For the examples described above, the heat treatment of the complete stack is carried out in a Naber furnace simulating a tempering with an annealing at 620 C. or 680 C. for 10 minutes.

I. Evaluation of the Sheet Resistance

[0134] The sheet resistance (Rs), corresponding to the resistance of a sample with a width equal to the length (for example, 1 meter) and with any thickness, is measured on a Napson device. The first test series compares the effect of the nature of the growth layer and of its method of crystallization. The sheet resistance results obtained for coated substrates which have or have not been subjected to a crystallization heat treatment are taken up in the table below.

TABLE-US-00004 Glazing C1a C1b A1a A1b A2a A2b A3a A3b Rs (0.05 ohm) 5.53 5.55 5.80 5.66 5.28 5.15 5.55 5.27

[0135] A crystallization heat treatment carried out before deposition of the silver layer on the material of the prior art not comprising a growth layer based on nickel oxide does not have a positive effect on the sheet resistance.

[0136] Example A1a illustrates a material comprising a layer of noncrystalline or not very crystalline nickel oxide before deposition of the silver layer. This is because this layer is not deposited on a layer capable of inducing crystallization by epitaxy and no crystallization treatment is carried out. The sheet resistance of this material is thus high. By comparison, example A1b according to the invention differs in that a crystallization heat treatment was carried out before deposition of the silver layer. The sheet resistance of this material is lower than that of example A1a. The layer of crystalline nickel oxide can make it possible to lower the sheet resistance values.

[0137] Examples A2a and A3a illustrate materials according to the invention comprising a layer of nickel oxide crystallized before deposition of the silver layer. This is because the layer of nickel oxide is deposited on a layer of zinc oxide capable of inducing crystallization by epitaxy. The two materials thus prepared without crystallization heat treatment have a low sheet resistance, in particular at least as good as that of the material C1a comprising solely a layer based on zinc oxide. It is interesting to note that, without additional crystallization heat treatment, the best results are obtained for the material A2a comprising the sequence layer based on zinc oxide and layer based on nickel oxide of low thickness.

[0138] Finally, examples A2b and A3b illustrate materials according to the invention comprising a layer of nickel oxide crystallized before deposition of the silver layer. The crystallization is obtained both by epitaxy, as the layer of nickel oxide is deposited on a layer of zinc oxide capable of inducing crystallization, and by additional crystallization heat treatment using a laser. The two materials thus prepared have a low sheet resistance, in particular lower than that of the materials A2a and A3a not comprising the additional crystallization heat treatment. This reflects the synergistic effect of the crystallization both by epitaxy and by heat treatment on a low sheet resistance value being obtained. Finally, the best results are obtained for the material A2b comprising the sequence of a layer based on zinc oxide and of a layer based on nickel oxide of low thickness.

[0139] The second test series demonstrates the importance of the crystallization of the layer based on nickel oxide before deposition of the silver layer. The sheet resistance results obtained for coated substrates: [0140] which have not been subjected to a crystallization heat treatment, [0141] which have or have not been subjected to a heat treatment carried out on the complete stack,
are taken up in the table below.

[0142] For this, the laser heat treatment is carried out on the complete stack.

TABLE-US-00005 Glazing C2a C2b C3a C3b A4a A4b Rs (0.05 ohm) 4.89 3.97 6.02 4.80 5.21 4.22

[0143] A heat treatment carried out on the complete stack results in all cases in a decrease in the sheet resistance values. However, it is observed that the lowest sheet resistance values are obtained for the material of the prior art not comprising a growth layer based on nickel oxide but only a layer of zinc oxide. The silver-based functional layer absolutely has to be deposited on a growth layer based on crystalline nickel oxide in order to obtain a positive effect related to the presence of this layer. A heat treatment after deposition of the silver layer does not make it possible to obtain an improvement in terms of sheet resistance with respect to a stack of the prior art comprising only a layer of zinc oxide.

II. Evaluation of the Mechanical Strength: Peel Test

[0144] The mechanical strength was evaluated by a peel test which gives information on the cohesion of the layers constituting the stack. This peel test consists in causing a PVB sheet to adhere, under the application of heat and pressure, to the substrate coated with the stack. The PVB layer placed in contact with the stack is then separated at one end and is folded back and pulled from the coated substrate under an angle of application of force of 180 degrees. The force necessary to tear off the PVB sheet is a measurement of the adhesion of the PVB sheet to the stack and of the cohesion of the layers.

TABLE-US-00006 Glazing C5 A6 Tearing-off force (N) 3.2 12.5

[0145] These tests were carried out on the materials which have not been subjected to the high-temperature heat treatment. They clearly demonstrate the better adhesion of the combined stack related to the presence of the layer of nickel oxide crystallized before deposition of the silver layer. This excellent adhesion of the silver to the nickel oxide contributes to a better durability in the heat treatment being obtained for the stack comprising a layer based on crystalline nickel oxide below and in contact with a silver layer.

III. Optical Properties

[0146] The optical characteristics were measured for simple glazings comprising a 2 mm glass on which the stack is deposited.

[0147] These tests show the influence of the nature and of the thickness of the blocking underlayers on the optical properties before and after heat treatment.

[0148] The following characteristics were measured and combined in the table below: [0149] the emissivity values as percentage () calculated according to the standard EN 12898 before and after heat treatment, [0150] the values of absorption (Abs) before heat treatment and [0151] the haze evaluated by measuring after heat treatment.

[0152] The haze was evaluated by measuring the mean visible diffuse reflection with a Perkin-Elmer L900 spectrometer. The measurement consists in arriving at the mean of the diffused part of the reflection over the visible region, the specular reflection being excluded from the measurement and the base line taken on a nonhaze reference sample being subtracted. It is expressed as percentage with respect to a total reflection measured on a reference mirror.

TABLE-US-00007 Before heat treatment After heat treatment Glazing % Abs % % Haze % 1 4.49 6.6 11.44 1.22 2 6.05 11.9 4.81 0.34 3 5.83 14.8 4.75 0.13 4 5.40 26.4 4.87 0.29 5 5.62 8.1 4.11 0.23 6 5.64 8.0 5.20 0.37 7 5.55 8.0 4.54 0.30 8 4.93 7.9 4.37 1.45 9 4.86 7.8 4.68 0.34 10 4.78 8.0 4.36 0.58

[0153] Glazings 1 to 10 comprise a dielectric layer based on tin zinc oxide (SnZnO) in the antireflective coating located below the silver-based functional metal layer. The applicant has discovered that the presence of a layer of this nature and in this position of the stack promotes the formation of defects of dome type after heat treatment. The choice of the blocking layer located below the functional layer accentuates or decreases this tendency.

[0154] The addition of a blocking underlayer brings about an increase in the absorption in the visible region before tempering. However, the increase is weaker in the case of the use of an oxide-based blocking underlayer. Blocking layers based on nickel and chromium greatly increase the absorption in the visible region.

[0155] The addition of a layer according to the invention based on crystalline nickel oxide and of low thickness does not produce a significant variation in the emissivity values before and after heat treatment, contrary to the addition of an underlayer based on nickel and chromium.

[0156] After heat treatment, the glazings according to the invention exhibit a lower emissivity than that obtained with a blocking underlayer based on nickel and chromium. To obtain a low emissivity reports a reduction in the energy losses by radiation and thus an improvement in the thermal performance of the double glazing.

[0157] Specifically, the glazings comprising a blocking underlayer based on an alloy of nickel and chromium exhibit correct haze values but do not exhibit the advantageous properties of the invention in terms of emissivity and absorption.

[0158] The use of a blocking layer based on crystalline nickel oxide exhibiting a thickness of the order of 1 nm makes possible a significant decrease in the haze in comparison with a material devoid of blocking underlayer. It also makes possible a decrease in the haze at least equivalent to that obtained with a 0.5 nm blocking underlayer based on nickel and chromium conventionally used. However, in particular, the growth layer according to the invention makes it possible to obtain the lowest absorptions and the lowest values of emissivities, even before heat treatment, in comparison with the other blocking underlayers.