DE1058805B - Process for producing translucent and electrically conductive gold coatings - Google Patents

Description

Procedure. for making translucent and electrically conductive ones Gold Coatings The invention relates to a method of making translucent ones and electrically conductive gold coatings on glass by cathodic sputtering in inert and oxygen-free atmosphere.

In the known methods, the gold coatings are applied immediately the glass or other suitable carrier (e.g. translucent plastic) upset. Such coatings have the disadvantage that they are sufficiently transparent have only a very low electrical conductivity and vice versa.

High conductivity and high transparency are incompatible, than all other things being equal, the former one strong and the latter one thin coating required. Inn general will be the highest conductivity of metals achieved, which are also translucent at a sufficiently low strength, but show practical tests, there, a metal film on glass or plastic that passes through Cathode sputtering or by evaporation, e.g. B. condensation of steam applied is, a much lower conductivity and lower optical transparency than it according to the specific conductivity and optical transparency constants would be expected.

So the electrical conductivity falls much faster than the thickness the shift. In practice, this often happens because of the graininess and the consequences thereof Surface roughness of the film, the percentage of which increases as the thickness increases going back. In addition, heating often increases the grain size at the expense the number of grains, so that the film becomes even less coherent and its conductivity is further degraded. If, for example, a very thin gold film, which immediately is applied to glass, heated to several 1d0 ° C, the grain becomes large enough that one can see separate grains in a high-power microscope, while then the conductivity is found to be very low.

In the meantime, in addition and in addition, one has hitherto had the opinion, that it is inevitable that with a thin metal film the conductivity is faster falls as the thickness because the interface itself has the peculiar property; bring in additional resistance (which of free and disorderly chemical Bonds - "surface states" - and a generally accepted theory has therefore been proposed. In such a case, the thinner the Film, the greater the surface area to volume ratio and therefore the greater greater the drop in conductivity below the value that would otherwise be expected would have been. The new and surprising thing about the invention is that with the new combined process a metal film of much greater uniformity and surface quality can be achieved than with the previously known methods.

It should also be stated that the atomization by Kntbo or through directly applied foils only very weakly on materials such as glass or plastic and therefore not very practical from this point of view either Have value.

Transparent items such as window panes have already been proposed where a transparent adhesive is attached to a glass or similar body Intermediate layer is pressed out directly by molecular forces and a uniform, Metal film that does not hinder the radiation path reliably on the intermediate layer is attached, the metal film having an electrical resistance of no more than 150 (preferably not more than 25) ohms per mm and the light transmission of the product is at least 50% (preferably at least 7011 / o). The intermediate layers were thereby of a metal oxide, a metal sulfide, a metallic halogen compound or a metal oxide of the sulfur group. In particular, the following were used: Oxides of lead, silver, aluminum, magnesium, nickel, zinc, thorium and rare Earth metals, ., admium, antimony, bismuth, mercury, copper, nold, Platinum, palladium, also sulfides, sulfates, selene, 3elenate, tellure, tellurate and Fluoride. As cheap metals for the metallic film were., Copper, iron, Silver, gold, and nickel are suggested, however other metals not named are not excluded. It was also proposed to use an adhesive, protective film to provide or in the case of hard metallic oxide over the metallic film of a metal film of gold, a protective film of magnesium fluoride over the gold film to be provided.

The invention is based on the discovery that for a metallic film made of gold) satisfactory results only with a limited series of substances for the intermediate layer between a carrier such as glass or plastic and the Goldzlm can be achieved and that a further improvement by a subsequent heat treatment can be achieved. It was also found that the metallic film applied by sputtering under suitable conditions should be.

It is characteristic of the substances used as an intermediate layer, that they are oxides of substances which under the conditions are relatively light can be reduced, which are given when the gold film by sputtering is sprayed on. This group consists of the oxides of cadmium, tellurium and antimony and bismuth (where bismuth is in the same group of periodic as antimony System).

It goes without saying that by applying the metal film, the oxide layer is not reduced either completely or essentially. Probably only one will find Reduction of the surface molecules takes place, but actually becomes more uniform Facilitates formation of the metal film. This reduction would be less likely occur under the milder conditions of vacuum evaporation. However, since the reduction the surface of the oxide layer is to be lightened, is according to the invention of sputtering the metal layer in an inert atmosphere, such as under argon, which is free of oxygen.

It was found that despite this, a low resistance was achieved by simply proceeding as described above, but a substantial improvement can be achieved by subsequently a heat treatment can take hold, which, however, is carried out at one temperature must be that does not damage either the metal film or the carrier. This heat treatment can be done in the atmosphere.

It is best to put another translucent layer over the metal film to arrange. This not only protects the metal film, but also prevents it from being exposed to heat insensitive and enables the heat treatment to be carried out at a higher temperature, when the outer layer is appropriately selected, e.g. B. from the same The material is like the intermediate layer. In the same way as the intermediate layer helps to create a closed metal film through the surface forces, which act between it and the lower surface of the metal film, so does the outer one Layer contributes to this through the presence between it and the outer surface of the metal film Surface forces to bring about an improvement. While without this extreme Layer a heat treatment at a temperature condition higher than 250 ° C damages the film, can heat treatment at about 350 ° using this outer layer C can be carried out without the film suffering, while at the same time the conductivity of the film is increased. By increasing the duration of the heat treatment lower temperatures can be used. However, below 250 ° C the treatment times required to achieve sufficient improvement the conductivity in the context of this invention may be unbearably long. It is understood that it is possible to heat treatment after the deposition of the Make a metal film on the carrier and another after the application of the outermost layer. Most translucent plastics are made at high temperatures damaged above 150 ° C and accordingly the best results will be according to of the invention only obtained when glass is used as the carrier.

If the material of the top layer should not be hard enough to to serve as an outer layer, then the outer layer can be made of a suitable material, z. B. antimony oxide or tin oxide exist, provided that these substances are not cause cracking of the metal film.

The invention has been made with particular reference to the electrical Properties of the metal film are described, d. H. so from the point of view of Achieving a low electrical resistance. However, it is also an object the invention to obtain particularly highly translucent products without the usual level of resistance to worsen. From this point of view, the Thickness of the intermediate layer and the outer layer is an important factor. It can be proven that when using oxides according to the invention, their refractive index is larger than that of the translucent support. The best results from From this point of view, both layers are obtained when quarter light wavelength layers are, d. H. so if their optical power multiplied equal to the actual power with the refractive index equal to a quarter wavelength of the desired light color or of the light to be transmitted through is, or better still, a little less than this quarter wavelength with consideration of the interaction of the metal film with the existing wave system, although this interaction is only of minor importance is when very thin metal films are used, as they are within the scope of the invention recommended. In other words, the metal film should be in the middle between the surfaces lie, the total thickness of the three layers - about half a Wavelength is. In many cases it is possible with thin interlayers and outer layers to work, and in this case the effect is translucent a little less and less affected by application and treatment of the metal film. Where z. B. a light transmission of 84% is achieved with two quarter wavelength layers, of which there is an oxide layer of the same thickness on each side of the gold layer, Then, with thicker metal layers, which only serve to achieve the desired Improve the conductivity of the metal film to preserve the passage of light 761 / o reduced. On the other hand, an unnecessarily high film thickness should be avoided as this increases the optical absorption when the two oxide films not of sufficiently translucent material are, and can there are even undesirable colors that have an optical interference effect are due.

In the case of the five metals mentioned, their oxides according to the invention be used to form the intermediate layer, the layer is said to be sputtered be carried out in an argon gas environment with traces of oxygen. The metal film should then be sprayed on in oxygen-free argon. The strength of the metal film depends on the desired conductivity, which is in the same order of magnitude move like the conductivity of the metal itself. Below the "order of magnitude" is to be understood as a value that z. B. one third of the specific conductivity of the metal is or, if possible, even better.

To mention a specific example, it can be made with an intermediate layer of bismuth oxide of a strength of 400 A, a film of gold of a thickness of 140A and an outer layer of bismuth oxide with a strength of 400A Optical light transmission of 82% with an electrical resistance of 7 to 8 Ohms between two opposite boundary lines of each square section of film can be achieved. This triple layer is a heat treatment of 350 ° over Exposed for 3 minutes and a slight improvement in optical transmission reached to 84 ° / a and the said resistance to 3.5 ohms between two opposite The boundaries of the square sections of the film are reduced.

The examples given in the table below illustrate in detail the results that can be achieved by the invention, including the effects of changes in the thickness of the gold and oxide layers. The thicknesses are all given in Angstrom units and where two thicknesses are given for the oxide layers, the greater thickness is that of the quarter-wave layers. In all cases, glass was chosen as the carrier, and all layers were applied by cathode sputtering, while the two oxide layers were applied in argon gas and the gold layer in oxygen-free argon gas. The heat treatment was carried out at 350 ° C in a few minutes in air with the exception of the use of tellurium oxide, at which a temperature of 300 ° C was selected. Fabric and starch strength A Ohmic Optical the intermediate layer of the gold film fabric and strength volume resistance permeability AA of the outer layer Ohm ° / o Bismuth oxide W, ismutoxide 400 85 400 5.6 82 400 110 400 4 80 400 140 400 3.5 84 400 280 400 1.4 71 100 75 100 6.5 78 Antimony Oxide Antimony Oxide 500 80 500 20 78 500 110 500 11 79 500 140 500 7 76 150 80 150 22 71 Lead oxide lead oxide 400 80 400 10 77 400 110 800 6.2 74 100 80 100 8 70 Cadmium Oxide Cadmium Oxide 500 80 500 13 73 500 100 500 10.5 75 100 80 100 12.5 74 Tellurium oxide tellurium oxide 600 80 600 25 80 600 100 600 8.5 78

Claims (7)

CLAIMS 1. Process for making translucent and Electrically conductive gold coatings on glass by cathode sputtering in inert and an oxygen-free atmosphere, characterized by the use of an intermediate layer from oxides of Cd, Pb, Te, Sb or Bi. 2. The method according to claim 1, characterized in that that then a heat treatment is applied at a maximum of 350 ° C by which, however, does not harm the wearer. may suffer. 3. The method according to claim 1, characterized in that then a thin over the gold film as protection translucent layer of the same oxide that is applied underneath the Gold layer was applied to the translucent support. 4. Procedure according to Claim 1 and 3, characterized in that both oxide layers have a somewhat smaller one Have strength than a quarter light wavelength. 5. The method according to claim 1 and one or more of the following, characterized in that after application. the second oxide layer of the carrier to a temperature of at most 350.degree. C. during a period of time which is sufficient for the electrical conductivity to improve the gold film without damaging the carrier. 6th Method according to Claim 1 and one or more of the following, characterized by a gold film between 70 and 300 Angstrom units thick, the lies between two layers of bismuth oxide, the -electrical conductivity of the gold film is not less than a third of the specific conductivity of gold and the optical transmittance is not less than 70%. 7. Procedure according to claim 6, characterized by a gold film approximately in thickness 140 Angstrom units between two layers of bismuth oxide of a thickness of approximately 400 angstroms, the sheet resistance of the gold film no greater than 3.5 ohms and the optical transmittance of the fabric is not significant is less than 84% using a heat treatment for about 3 minutes at most 350 ° C. B. Method according to claim 1 and one or more of the following, characterized by a gold film approximately 280 angstrom units thick, which is sandwiched between two bismuth layers of approximately 400 Angstrom units is, wherein the sheet resistance of the gold film is not significantly greater than 1.4 Ohms and the optical transmittance of the product is not less than 710 / a, using a heat treatment not exceeding 350 ° C for 3 minutes. Into consideration Printed publications: German Patent No. 694 018.