WO1999024865A1

WO1999024865A1 - Process for producing an electro-optical display

Info

Publication number: WO1999024865A1
Application number: PCT/DE1998/003232
Authority: WO
Inventors: Joachim Glueck
Original assignee: Robert Bosch Gmbh
Priority date: 1997-11-07
Filing date: 1998-11-05
Publication date: 1999-05-20
Also published as: DE19749189A1

Abstract

A passivation layer (17) for colour filter structures (14-16, 19) is applied at low temperatures for producing coloured liquid crystal displays. This makes it possible to use brighter colour filters which nevertheless are heat-sensitive. This passivation layer can be applied as a transparent film or by means of plasma polymerisation.

Description

Process for the production of an electro-optical display

State of the art

The invention relates to a method for producing an electro-optical display according to the type of the independent claim. A process for producing a liquid crystal display is already known from the publication “Simplest Process Color TFT-LCDs” in the conference reports on the ASIA Display'95, p. 697. To produce a liquid crystal display, a liquid crystal cell is provided with backlighting. The liquid crystal cell in turn consists of two glass plates, which are fixed parallel to each other at a short distance, and a liquid crystal is inserted in the space between the two glass plates, which functions as an optical switch.

In order to be able to display colored images with the aid of the liquid crystal display, the display is divided into individual pixels, so-called pixels. Each pixel can be controlled by a pair of electrodes, one electrode being attached to each of the first and second glass plates. These electrodes are made of indium tin oxide, a conductive and transparent material. Furthermore, every Pi Provide xel with a color filter, which is made from photoemulsion with color pigments. This colored layer is comparable to the coating of color films that are used for photography.

An essential part of the photo emulsion is gelatin. However, gelatin is sensitive to various environmental influences, both moisture and mechanical influences, such as notches or scratches. For this reason, the color filter must be protected by an additional protective layer or passivation layer.

This passivation layer is applied according to the prior art in a so-called spin coating

Processes as is known, for example, from the application of photoresist to a wafer in microelectronic production. Here, the coating material in the liquid or semi-liquid state is applied approximately centrally to the body to be coated. The body to be coated is then set into rapid rotation, as a result of which the coating material forms a thin layer on the body to be coated.

A disadvantage of the method according to the prior art is a very high material consumption, since approximately 95% of the material used is thrown off and cannot be reprocessed. Furthermore, high process temperatures are often required to harden the spun material, which impair the properties of the photoemulsion. Advantages of the invention

In contrast, the method according to the invention with the characterizing features of the independent claim has the advantage that the material for the passivation layer is used much more efficiently. This is the reason for a significant cost advantage. Furthermore, this also results in significant reductions in the environmental impact, since the solvent content in the materials to be spun on i. d. R. are not dangerous substances.

Another advantage is that the process temperatures in the manufacture of the liquid crystal cell can be kept significantly lower, which makes the production of the color filter much easier.

Another advantage is that, due to the lower process temperatures, more brilliant, but less heat-resistant color pigments can also be used. The measures listed in the dependent claims allow advantageous developments and improvements of the method specified in the independent claims.

It is particularly advantageous to produce the passivation layer from thin glass, since glass forms a very good starting point for an indium tin oxide layer to be applied later.

drawing

Exemplary embodiments of the invention are shown in the drawing and are described in more detail in the following description. purifies. 1 shows a liquid crystal display according to the prior art, FIG. 2 shows a color filter according to the invention.

description

Figure 1 shows a liquid crystal display according to the prior art. The liquid crystal display consists of an illumination unit 30 and a liquid crystal cell 31, which are arranged one above the other. The liquid crystal cell 31 has two substrate plates, the first substrate plate 10 and the second substrate plate 11, which are designed, for example, as thin glass plates. The first substrate plate 10 and the second substrate plate 11 are arranged parallel to one another at a short distance. Between the first substrate plate 10 and the second substrate plate 11 there are an abs holder 2, which is formed for example by short fragments of a glass fiber. The two substrate plates are connected to one another by adhesive 3.

The two substrate plates are preferably designed as approximately rectangular plates, and the adhesive 3 connects the two substrate plates all around in the edge region.

The liquid crystal 4 is introduced in the space between the first substrate plate 10 and the second substrate plate 11. The lighting unit 30 essentially consists of a waveguide plate 7, which is made of a transparent material and has approximately the shape of a flat, rectangular plate, with four narrow ones

End faces and two large cover areas. An approximately rod-shaped lamp 5 runs parallel to one of the end faces A reflector 6 is located on the side of the lamp 5 facing away from the end face of the waveguide plate 7.

The lamp 5 emits light, which is either reflected by the reflector 6 onto the end face of the waveguide plate 7, or is radiated directly from the lamp 5 onto the end face. The light 1 penetrates the waveguide plate 7 through the end face. The light is reflected or scattered in the waveguide plate 7 until it is finally coupled out of the top surface of the waveguide plate 7 and enters the liquid crystal cell. Various decoupling mechanisms are known for this from the prior art.

In order to achieve a colored display, the first substrate plate 10 is coated with a color filter made of photoemulsion, which is not shown in FIG. 1.

FIG. 2 shows the cross section through the first substrate plate 10 and the first substrate plate 10 has a glass plate 13 on which a color filter 19 is applied. The color filter 19 is designed as a coating with photoemulsion, the photoemulsion having gelatin and colored pigments as important constituents. In order to form pixels of different colors, the color filter has yellow zones 16, magenta zones 15, and cyan zones 14 which are arranged next to one another. A passivation 17 is applied to the color filter, which is in the form of a thin glass plate which has been laminated on. On the side of the thin glass plate facing away from the color filter, which is used as passivation 17, there is one thin transparent conductive coating 18, which consists for example of indium tin oxide.

The transparent, conductive coating 18 serves as one of the two electrodes in order to be able to expose the liquid crystal 4 from FIG. 1 to an electrical field and thus to use it as an optical switch for the light.

By executing the passivation 17 as a thin glass plate, the photoemulsion is optimally protected against environmental influences. The thin glass plate used as passivation 17 is advantageously applied by lamination. Here, the thin glass plate is coated either over an entire surface or at least in the edge area with an adhesive which is largely transparent in the visible spectral range. At the same time, the adhesive should be curable by irradiation with ultraviolet light.

Such an adhesive is available, for example, under the name NOA 68 from Norland Optics. The thin glass plate coated with the adhesive layer is then applied with the adhesive side onto the glass plate 13 coated with the color filter 19, pressed on and irradiated with ultraviolet light. This will cause the adhesive to harden.

To avoid parallax effects, the laminated glass must be thin. The entire process of laminating takes place almost without increasing the temperature. A slight increase in temperature can only occur through absorption of the light, which, however, is neither intended is still necessary. However, it is usually sufficiently small so that it does not adversely affect the color filter.

At the same time, the glass layer creates a very hard passivation layer, so that the spacers 2 cannot be pressed into the color filter 19.

In a next step, indium tin oxide is applied to the passivation 17 as a transparent conductive coating 18. Glass is also ideally suited for this step, since it is a good base for indium tin oxide.

In a second exemplary embodiment, the passivation 17 is formed from plasma polymers. For this purpose, the first substrate plate 10 provided with the color filters is placed in a gas-tight vessel which can be subjected to positive or negative pressure. The vessel is also called the reactor below. Together with the first substrate plate 10 to be coated, a process gas is introduced into the reactor, which is then sealed. In the exemplary embodiment described here, the process gas used is HMDSO (hexamethyldisiloxane), which is liquid at atmospheric pressure, but assumes vapor form at lower ambient pressures. After the reactor has been sealed in a gastight manner, a negative pressure is generated in it, the size of which is suitable for converting the process gas, which is liquid by atmospheric pressure, into the previous vapor state. The individual molecules of the process gas are also called monomers. A high-frequency electromagnetic wave, for example a microwave, is then radiated into the interior of the reactor. The electromagnetic wave is already in the Process gas in the vapor state is ionized so that the individual monomer molecules are present as charged particles. These individual charged particles are also called radicals and are also known from other areas of chemistry. They are characterized by a particularly high reactivity. The vapor containing monomers, ionized monomer molecules, and radicals is also called plasma. Individual components of the plasma can now react and form so-called oligomers as reaction products. These are, for example, clusters of molecular fragments and monomer radicals. These so-called oligomers condense on the surface of the first substrate plate 10. The intensity of the electromagnetic wave, the conditions in the reactor and the temperature of the first substrate plate 10 are to be selected such that they condense on the first substrate plate

Oligomers are crosslinked on the surface of the first substrate plate, although under certain circumstances the ultraviolet radiation from the plasma and ion or electron bombardment from the plasma do not necessarily promote the connection of the oligomers to polymers. Because of the high reactivity of the oligomers, a highly cross-linked polymeric top layer forms on the first substrate plate. This process is also called plasma polymerization.

A further plasma-induced polymerization can optionally take place parallel to the plasma polymerization, in which the monomer molecules are deposited directly on the surface of the first substrate plate, where they polymerize through the action of environmental influences, such as temperature, particle influence, radiation with ultraviolet radiation. The advantage of the method according to the invention is that the first substrate plate does not have to be heated above 100 ° C. This makes it possible to use sensitive color filters, which nevertheless have very desirable color properties. Plasma polymer layers produced in this way are very resistant, so that a very thin layer is sufficient to achieve suitable protection for the color filter. Due to the high reactivity in the plasma, very high deposition rates can be achieved for the passivation layer. In conjunction with the small layer thickness required, a very high process speed can be achieved.

In both exemplary embodiments, the passivation is applied at a low temperature and thus enables the use of color filters which contain gelatin.

Claims

Expectations

1. A method for producing an electro-optical display with a first substrate plate and a second substrate plate, the first substrate plate being provided with a color filter which is produced from a photoemulsion, the photoemulsion being provided with a protective layer, characterized in that the Protective layer is applied by placing a transparent thin plate, which at least covers the photoemulsion, on the photoemulsion and is at least partially connected to the photoemulsion and / or the first substrate plate.

2. The method according to claim 1, characterized in that the transparent thin plate consists of glass.

3. A method for producing an electro-optical display with a first substrate plate and a second substrate plate, the first substrate plate being provided with a color filter which is produced from a photoemulsion, the photoemulsion being provided with a protective layer, characterized in that the protective layer is applied - Is brought by coating the photoemulsion with plasma polymers.

4. The method according to claim 3, characterized in that the first substrate plate is introduced into a vessel, that a monomer is introduced into the vessel, that the vessel is pressurized with a vacuum, so that part of the monomer passes into the gas phase that high-frequency electromagnetic waves are introduced into the vessel so that a polymer film is formed on the surface of the first substrate plate, which also contains molecules of the monomer.

5. The method according to claim 4, characterized in that the first substrate plate is heated.

6. The method according to claim 5, characterized in that the first substrate plate is heated to 60-90 degrees Celsius.

7. The method according to claim 3 to 6, characterized in that hexamethyldisiloxane is used as the monomer.

8. A method for producing an electro-optical display according to one of the preceding claims, characterized in that a transparent conductive coating is applied to the protective layer.