CA2051390A1

CA2051390A1 - Transparent conductive coatings

Info

Publication number: CA2051390A1
Application number: CA 2051390
Authority: CA
Inventors: Wilfred C. Kittler
Original assignee: Individual
Current assignee: Andus Corp
Priority date: 1989-04-11
Filing date: 1990-03-19
Publication date: 1990-10-12
Also published as: JPH04504388A; WO1990011975A1; EP0467955A1; AU5437790A

Abstract

ABSTRACT OF THE DISCLOSURE

An article having a transparent, conductive, infra-red reflective coating with improved stability, comprising a substrate having a coating comprising a metallic layer of material such as silver, the coating having on at least one of its surfaces a dielectric metal oxide layer of a material such as tin oxide doped with a metal such as copper.
Optionally the metallic layer is sandwiched between two such dielectric metal oxide layers.

Description

W~ ~0/1197~ PCr/US90/~ 4 2~3~

~Ba~EaBE~ CONDUCTIVE COATINGS

Technical field of the inyentior.

This invention relates to transparent, conductive, infrared reflective coatings and methods therefor.

~ackaround of the inventiQn Thin coatings of noble metals such as silver, gold, and copper are often used as visible or solar light transparent, infrared light reflective, or electrically conductive coatings, or coatings combining a plurality of these characteristics. (As used hereinafter, "transparent" denotes substantial transparency to visible or solar light, and "conductive" denotes substantial electrical conductivity.) The visible or solar transmittance of such coatings can be increased dramatically by depositing dielectric anti-20 reflection layers on one or both sides thereof. TypicalmateriaIs suitable for antireflection layers include indium oxide, indium tin oxide, tin oxide, titanium oxide, zinc sulfide, and tantalum oxide. These antireflection layers may additionally perform the function of environmentally 25 protecting the metal coating, such as from corrosion or abrasion.
:
Dielectric-metal-dielectric ~DMD) multilayer coatings, ; in which a metal layer is sandwiched between two layers of 30 dielectric material, are well known in the art. Berning et al., ~. Qæ~ ~Q~_ ~m~, 4l, 230 (1957) discloses a DMD coating having a silver layer and dielectric multilayex antireflection coatings on either side for use as band pass filters. Holland et al., ~rit~ ~_ a~ hY~_, ~, 359 ~l958) 35 disclo~es a gold DMD coating which is transparent to visible light but infrared reflective. Additional publications WV90/11975 PCT/US90/~554 2~ 3~

layer DMD coating in which the metal layer is composed of two layers- a silver layer and a second metal layer of aluminum, titanium, tantalum, chromium, magnesium, or zirconium. The second metal layer protects the silver layer during the s subsequent deposition of a dielectric anti-reflection layer, and also improves mechanical strength and chemical resistance. The antireflection layer may be indium or tin oxide containing some lead oxide~ A small amount of nickel (less than 1%) may be added to the silver. Hart, in US
9,462,883 (1984), discloses various heat mirror constructions in which a thin metal layer is placed over a silver layer to protect the latter during the subsequent deposition of a dielectric layer on top. The metal laycr may be a transition metal, such as manganese, chromium, iron, platinum, copper, lS or gold, or a group IIIa-Va element, such as bismuth, indium, or lead.

Summa~y of ~he invention In this invention, it has been discovered that in a transparent, conductive, infra-red reflective coating comprising a metallic and dielectric layer, the environmental stability of the metal layer is enhanced if the dielectric layer is doped with a dopant metal.

Accordingly, this invention provides an article having a transparent, conductive, infra-red reflectiv~ coating with improved stability, comprising a substrate having on a surface thereof a transparent, conductive, infra-red reflective coating comprising a metallic layer sandwiched between two dielectric metal oxide layers, at least one of which is doped with a dopant metal selected from the group consisting of copper, gold, iron, nickel, 3S cobalt, molybdenum, tungsten, platinum, vanadium, tantalum, titanium, chromium, magnesium, zirconium, WO~/11975 - PCT/U590/01~4 2~7.~3~

Fig. 4 is an XPS depth profile of another coating according to this invention.

Fig. 5 compares the reflectance and transmission 5 characteristics of coatings of this invention and a prior art coating, before environmental st~bility testlng.

Fig. 6 compares the reflectance and transmission characteristics of coatings of this invention and a prior art o coating, after environmental stability testing.

e~ on of pr~f~r~ emhodi~nt~

An embodiment of the invention is shown in Fig. la, ~15 which depicts in cross-section an article 1 comprising a substrate 2 having deposited thereon a DMD co~ting 3 comprising dielectric layers 4a and 4b and metallic layer 5.
At least one of dielectric layers is doped with a dopant as described in more detail hereinbelow, improving corrosion 20 resistance of the metallic layer. Both dielectric layers can be doped, although where the substrate is a relatively impervious material such as glass, the inner dielectric layer 4b need not be doped. Con~ersely, where the substrate is a relatively pervious material such as a thin polymeric film, 25 it is preferred that both dielectric layers be doped.

Yet another embodiment of the invention is shown in Fig.
lb. Article 6 compriqes a substrate 7 having deposited thereon a coating 8 comprising a dielec~ric layer 9 and 30 metallic layer 10, the dielectric layer being doped as discussed above. Thus, this e~bodiment differs from the one shown in Fig. la in that there is no dielectric layer interposed between the substrate and the metalllc layer. This embodiment may advantageously be used where the substrate is 35 a relatively impervious material, so that there is a lesser WO ~/1197~ PCT~SgO/~1~54 7 2 ~

theory, it is believed that in such an embodiment a corrosion protection effect is derived from the partial oxidation of the dopant metal in the dielectric layer. ~

s For the purposes of this inven~ion, it is not necessary that the dielectric layer(s) be doped with the dopant metal across its entire thickness, although such an embodiment is not excluded. In a preferred embodiment of the invention, the dielectric layerts) are doped only along those regions thereof near the metallic layer. This represents an effective compromise between providing a sufficient degree of protection without adversely affec~ing the transmissive qualities of the dielectrlc layer, and hence of the entire coating.

Substantial variance in the amount of dopant metal used is permissible, as can readily be determined empirically by those skilled in the art. For a dopant metal such as copper, in a dielectric layer of tin oxide, doping levels of up to 28 20 atom % are possible, without seriously reducing the transmittance. With other dopants which form more transparent oxides than copper, such as aluminum, considerably higher doping levels, up to 50 atom %, are tolerated without serious reduction in transmittance, as shown in Ritchie et al., U.S.
25 Pat. 4,710,441 ~1987).

The coatings of this invention have significantly 30 improved environmental stability, but yet their functional properties (e.g., visible/solar transmittance and infrared reflectance) are not significantly impacted. These coatings are useful in visible/solar transmissive but infrared reflective conductive coatings, e.g, DMD or Fabry-Perot 35 coatings. In a Fabry-Perot coating, plural metallic layers are sandwiched between dielectric layers, for example ~/11975 PCT/US9n/01~
~J~ 0 copper was deposited to thickness of 130 angstroms, using and 82:18 atom % Sn:Cu target in an argon/oxygen atmosphere.
Next, a layer of silver 120 angstroms thick was dèposited, as described above, followed by another layer of copper-doped s tin oxide 130 angstroms thick, and finally followed by a 300 angstrom-thick tin oxide layer. An XPS depth profile of this coating, showlng the distribution of the copper in the tin oxide dielectric layers, is shown in Fig. 3.

o Thus, a DMD coating having two dielectric layers of tin oxide sandwiching a conducting layer of silver 120 angstroms thick is prepared. Each of the tin oxide layers has a total thickness of 430 angstroms, of which the 130 angstroms nearest the silver layer are doped, while the regions further .15 removed from the silver layer are not doped. Those skilled in the art will appreciate, herein, as a matter of convenience, the dielectric layers have been deposited stagewise, one doped and one undoped, but that such stage-wise deposition is not a requirement of this invention.

This example shows another DMD coating according to our invention, in the embodiment in which the dopant is 25 distributed througout the dielectric layers.

A dielectric layer 430 angstroms thick of tin oxide doped with copper was deposited on 4 mil PET by reactive magnetron sputtering in a sputter roll coater, using an 82:18 30 atom % Sn:Cu target in an argon/oxygen atmosphere. Next, an 120-angstrom silver layer was deposited, followed by another dielectric layer of copper-doped tin oxide the same as the first layer. An XPS depth profile of this coating is shown in Fig. 4.

` W~ ~/11975 P~T/US90/D1~54 11 2 ~

The reflectance and transmission of these coatings are compared in Fig. 5 ~before testing) and Fig. 6 (after testing). -s These results show that the coatings of this invention have superior environmental stability, compared to the conventional coating. The outdoor exposure effectively destroyed the conventional coating, whi.le the coatings of this invention still retained useful properties.

It is cautioned that, where less severe tests were carried out, for example in an office ambient environment, or exposure to fumes in a chemical storage cabinet, or exposure in environmental chambers (e.g. 600 C/95% relative humidity 1S or lO00 C dry heat), the testing conditions may not besufficient to differentiate between coatings of this invention and the conventional coating.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

What is claimed is:

1. An article having a transparent, conductive, infra-red reflective coating with improved stability, comprising a substrate having on a surface thereof a transparent, conductive, infra-red reflective coating comprising a metallic layer sandwiched between two dielectric metal oxide layers, at least one of which is doped with a dopant metal selected from the group consisting of copper, gold, iron, nickel, cobalt, molybdenum, tungsten, platinum, vanadium, tantalum, titanium, chromium, magnesium, zirconium, nickel, aluminum, bismuth, lead, and alloys thereof.

2. An article according to claim 1, wherein both dielectric metal oxide layers are doped with a dopant metal.

3. An article according to claim 1, wherein the at least one oxide layer which is doped with a dopant metal is doped with said dopant metal across at least the 30% of the thickness thereof nearest the metallic layer.

4. An article according to claim 1, 2, or 3, wherein said dielectric metal oxide layers are made of a material selected from the group consisting of tin oxide, indium oxide, indium tin oxide, titanium oxide, zinc oxide, and tantalum oxide.

5. An article according to claim 4, wherein said dielectric metal oxide layers are made of a material selected from the group consisting of tin oxide, indium oxide, and indium tin oxide.

6. An article according to claim 1, 2, or 3, wherein said dopant metal is selected from the group consisting of copper and gold.

7. An article according to claim 1, 2, or 3, wherein said metallic layer is made of a metal selected from the group consisting of copper, gold, and silver.

8. An article according to claim 1, 2, or 3, wherein said dopant metal is present in said dielectric metal oxide layers in the regions thereof near said metallic layer.

9. An article according to claim 1, 2, or 3, wherein said coating is deposited by puttering.

10. An article according to claim 1, 2, or 3, wherein the heat of formation of the oxide of said dopant metal is greater than the heat of formation of the metal oxide of the metal of said metallic layer but lesser than the heat of formation of the metal oxide of said dielectric metal oxide layer.

11. An article according to claim 1, 2, or 3, wherein said coating has deposited thereover at least one metallic and at least one dielectric layer, to form a Fabry-Perot coating.

12. A method of making an article having a transparent, conductive, infra-red reflective coating with improved stability, comprising the steps of providing a substrate;
depositing on a surface of said substrate a first dielectric metal oxide layer;
depositing on said first dielectric metal oxide layer a metallic layer; and depositing on said metallic layer a second dielectric metal oxide layer, thereby forming a transparent, conductive, infra-red reflective coating comprising metallic layer sandwiched between two dielectric metal oxide layers;
at least one of said first and second dielectric metal oxide layers being deposited containing a dopant metal selected from the group consisting of copper, gold, iron, nickel, cobalt, molybdenum, tungsten, platinum, vanadium, tantalum, titanium, chromium, magnesium, zirconium, nickel, aluminum, bismuth, lead, and alloys thereof.

13. A method according to claim 12, wherein both first and second dielectric metal oxide layers are deposited containing a dopant metal.

14. A method according to claim 12, wherein the dopant metal is deposited across at least the 30% of the thickness of the metal oxide layer which has been doped.

15; A method according to claim 12, 13, or 14, wherein said dielectric metal oxide layers are made of a material selected from the group consisting of tin oxide, indium oxide, indium tin oxide, titanium oxide, zinc oxide, and tantalum oxide.

16. A method according to claim 15, wherein said dielectric metal oxide layers are made of a material selected from the group consisting of tin oxide, indium oxide, and indium tin oxide.

17. A method according to claim 12, 13, or 14, wherein said dopant metal is selected from the group consisting of copper and gold.

18. A method according to claim 12, 13, or 14, wherein said metallic layer is made of a metal selected from the group consisting of copper, gold, and silver.

19. A method according to claim 12, 13, or 14, wherein said dopant metal is deposited in said dielectric metal oxide layers in the regions thereof near said metallic layer.

20. A method according to claim 12, 13, or 14, wherein said coating is deposited by sputtering.

21. A method according to claim 12, 13, or 14, wherein the heat of formation of the oxide of said dopant metal is greater than the heat of formation of the metal oxide of the metal of said metallic layer but lesser than the heat of formation of the metal oxide of said dielectric metal oxide layer.

22. A method according to claim 12, 13, or 14, wherein at least one further metallic layer and at least one further dielectric layer are deposited on said coating, to form a Fabry-Perot coating.

23. An article having a transparent, conductive, infra-red reflective coating with improved stability, comprising a substrate having on a surface thereof a transparent, conductive, infra-red reflective coating comprising a metallic layer and a dielectric metal oxide layer doped with a dopant metal selected from the group consisting of copper, gold, iron, nickel, cobalt, molybdenum, tungsten, platinum, vanadium, tantalum, titanium, chromium, magnesium, zirconium, nickel, aluminum, bismuth, lead, and alloys thereof.

24. An article according to claim 23, wherein the metallic layer is in contact with the substrate.

25. An article according to claim 23, wherein the metal oxide layer is doped with the dopant metal across at least the 30% of the thickness thereof nearest the metallic layer.

26. An article according to claim 23, 24, or 25, wherein said dielectric metal oxide layer is made of a material selected from the group consisting of tin oxide, indium oxide, indium tin oxide, titanium oxide, zinc oxide, and tantalum oxide.

27. An article according to claim 26, wherein said dielectric metal oxide layer is made of a material selected from the group consisting of tin oxide, indium oxide, and indium tin oxide.

28. An article according to claim 23, 24, or 25, wherein said dopant metal is selected from the group consisting of copper and gold.

29. An article according to claim 23, 24, or 25, wherein said metallic layer is made of a metal selected from the group consisting of copper, gold, and silver.

30. An article according to claim 23, 24, or 25, wherein said dopant metal is present in said dielectric metal oxide layer in the region thereof near said metallic layer.

31. An article according to claim 23, 24, or 25, wherein said coating is deposited by sputtering.

32. An article according to claim 23, 24, or 25, wherein the heat of formation of the oxide of said dopant metal is greater than the heat of formation of the metal oxide of the metal of said metallic layer but lesser than the heat of formation of the metal oxide of said dielectric metal oxide layer.

33. A method of making an article having a transparent, conductive, infra-red reflective coating with improved stability, comprising the steps of providing a substrate;
depositing on a surface of said substrate a metallic layer; and depositing on said metallic layer a dielectric metal oxide layer containing a dopant metal selected from the group consisting of copper, gold, iron, nickel, cobalt, molybdenum, tungsten, platinum, vanadium, tantalum, titanium, chromium, magnesium, zirconium, nickel, aluminum, bismuth, lead, and alloys thereof, thereby forming a transparent, conductive, infra-red reflective coating comprising metallic layer and a dielectric metal oxide layer.

34. A method according to claim 33, wherein the dopant metal is present across at least the 30% of the thickness of the metal oxide layer nearest the metallic layer.

35. A method according to claim 33 or 34, wherein said dielectric metal oxide layers is made of a material selected from the group consisting of tin oxide, indium oxide, indium tin oxide, titanium oxide, zinc oxide, and tantalum oxide.

36. A method according to claim 35, wherein said dielectric metal oxide layer is made of a material selected from the group consisting of tin oxide, indium oxide, and indium tin oxide.

37. A method according to claim 33 or 34, wherein said dopant metal is selected from the group consisting of copper and gold.

38. A method according to claim 33 or 34, wherein said metallic layer is made of a metal selected from the group consisting of copper, gold, and silver.

39. A method according to claim 33 or 34, wherein said dopant metal is deposited in said dielectric metal oxide layer in the region thereof near said metallic layer.

40. A method according to claim 33 or 34, wherein said coating is deposited by sputtering.

41. A method according to claim 33 or 34, wherein the heat of formation of the oxide of said dopant metal is greater than the heat of formation of the metal oxide of the metal of said metallic layer but lesser than the heat of formation of the metal oxide of said dielectric metal oxide layer.