Use of a nitride barrier for avoiding silver migration into glass

p0001The present invention relates to the field of the metallization of glass substrates in particular for the manufacture of flat display screens. This metallization is used to form arrays of electrodes. These electrodes are opaque, they are generally made of silver.

p0002So far, the metallization of glass substrates for dense electrode arrays, of not less than 500 micrometers was carried out under vacuum by sputtering or vaporization. The deposited layer is relatively thick, of a few micrometers and length of deposition vacuum chamber is relatively long. The cost of such metallized substrates is high and the cost increases rapidly with the surface of the substrates.

p0003New methods of metallization, cheaper have been explored; these include photogravure photosensitive silver paste layers or not. This method is not compatible with a use on the front face of a display panel because it produces a yellow coloration in the glass substrate.

p0004Indeed, an area under the electrode, and extending from both sides of the electrode about 30 to 50 microns is colored in yellow due to the diffusion of silver into the glass.

p0005The light received by an observer from a part of the light produced by the electrical discharges inside the panel which is transmitted through the glass substrate and on the other hand, light reflected from the electrodes. It is in the areas of diffusion out that most of the light perceived by the observer.

p0006This coloring in the manner of a yellow filter, greatly degrades the colorimetry of the color display panel. It is not desirable that the perceived light is filtered in yellow.

p0007The present invention aims to remove this yellow avoiding the diffusion of silver into the glass without degrading the adhesion and chemical stability of the silvering.

p0008For this the invention relates to the use of a nitride barrier to prevent the distribution of money in a glass substrate.

p0009The nitride may be for example a titanium nitride, boron nitride, silicon nitride. Titanium nitride gives very satisfactory results in terms transparency.

p0010The nitride based barrier can be deposited by sputtering, vacuum evaporation or PECVD (for the English name of Plasma Enhanced Chemical Vapor Deposition), for example.

p0011Thick upper barrier about 50 nanometers is effective in stopping the spread of money.

p0012The present invention will be better understood using the following description illustrated in the single figure which shows in cross section the glass substrate, the barrier and the deposit based on silver.

p0013The known method of deposition by silver electrodes of photoengraving generating a yellow coloring comprises the following steps.

p0014Is deposited on a glass substrate by screen printing and drying a paste containing light-sensitive silver or not. When the silver-based paste is not photosensitive it is covered with a layer of a photosensitive resin.

p0015then exposing the deposit based on silver, optionally covered with resin to ultraviolet light through a mask and then is developed all. This is followed by curing the silver substrate at a temperature between about 540 ° C and 600 ° C. This heating operation causes the diffusion of silver in the substrate glass and the occurrence of a very troublesome yellow coloring if the glass substrate is the front face of a display panel. This color appears even for low concentrations of silver.

p0016A yellow colored glass substrate with silver transmits 54% of the emitted red light, 59% for hundred of the emitted green light and 12% of the emitted blue light.

p0017The present invention is to use a barrier 2 based on nitride interposed between the glass substrate 1 and deposition 3 silver-based to prevent the yellow coloring of the glass caused by the distribution of money in the glass. The single figure shows in section the arrangement of layers on the glass substrate 1.

p0018This barrier 2 The nitride is effective even after firing the deposit 3 based on silver to temperatures above 580 ° C.

p0019The barrier 2 The nitride may be deposited on the glass substrate 1, for example by sputtering or vacuum evaporation. A deposit by a chemical process, driven by a plasma, and known under the term of PECVD (Plasma Enhanced for Chemical Vapor Deposition) is also possible. PECVD allows obtaining a uniform deposit.

p0020Titanium nitride gives very good results. Indeed, in the presence of silver, titanium nitride which is gray in color becomes much clearer, which allows to obtain in the application as a front face of a display panel, well-transparent areas.

p0021Other metal is of course usable in particular silicon or boron. A mixture of nitrides may also be used.

p00222 barrier thickness greater than about 50 nanometers is adequate to prevent yellowing.

p0023The glass substrate 1 may, for example, be soda-lime type (known in the literature as the Anglo-Saxon name of float glass). This substrate 1 may be optionally annealed, polished or shaped. Other types of flat glass can of course be used, for example borosilicate or aluminosilicate.

p0024Deposit 3 based on silver can be achieved in conventional manner by photoetching screen printing and then be subjected to baking at a temperature higher than 400 ° as previously described.

p0025The thickness of the deposit 3 based on silver may be about 7 micrometers. Usually the thickness of the silver based coating is between 3 to 12 micrometers.