Manufacture of flat panel displays

Radiation imagery chemistry: process – composition – or product th – Holographic process – composition – or product

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Details

430 2, 430313, 430319, 356363, 359 12, 359 15, 313309, G03H 100

Patent

active

056269919

DESCRIPTION:

BRIEF SUMMARY
This invention relates to the manufacture of flat panel displays for use as flat screens for TV or for video or computer displays.
Large-size flat panel displays for use as TV, video or computer screens are being developed and comprise a flat transparent (typically glass) substrate with a matrix of liquid crystal elements formed on one surface of the substrate. Hitherto flat panel active-matrix liquid crystal displays have involved the formation of a very large number of transistors and liquid crystal elements on the surface of the substrate in a photo-imaging and etching process corresponding to that used to form integrated circuits on semiconductor wafers, but the process has involved "stepping" from area-to-area of the panel in order to cover its full size.
I have now devised a method in which an image with the required pattern can be formed onto a photo sensitive surface of the panel without the need for "stepping", the image being of high precision and high resolution.
In accordance with this invention, there is provided a method of forming a flat panel display, which includes forming a volume holographic image on a recording medium by interference between an object beam of coherent light after passage through a mask and a reference beam of coherent light which is totally internally reflected at a surface on which the recording medium is disposed, then replacing the mask by a flat panel which has a coating of photosensitive substance and forming an image of the holographic recording on the photosensitive coating using a second reference beam replayed in the opposite direction from the first reference beam.
Preferably the holographic image is recorded on the recording medium in one apparatus and the holographic recording is replayed onto the flat panel in a separate, corresponding apparatus.
The first reference beam may be provided by a laser, but the second or conjugate reference beam may be provided either by a laser or by a light source having a distinct spectral line, close to the wavelength of the first reference beam, in which case filters are used to filter out light of other wavelengths emitted by the light source.
It is necessary for the recording medium to be a photosensitive, variable refractive index material which exhibits negligible light scatter during the course of recording the holographic image. Suitable recording media are photopolymeric materials and dichromated gelatin, which exhibit negligible scatter and light absorption and do not shrink or distort during exposure and provide for a high resolution recorded image.
The method in accordance with this invention may be used in forming various types of flat panel displays, including active-matrix liquid crystal displays, electroluminescent displays, plasma displays and vacuum microelectronic displays. In particular the method can be used for forming images on the flat panel corresponding to the required patterns of pixels (e.g. liquid crystal or electroluminescent elements), thin film transistors and electrical conductors which must be formed on the panel, involving multiple applications of photoresist coatings, exposure and etching.
An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawings, in which:
FIG. 1 is a schematic diagram of an apparatus used for recording a holographic image onto a recording medium and then for replaying the holographic recording onto a flat panel in the manufacture of a flat panel display; and
FIG. 2 shows arrangements for automatically focussing the replayed image onto the flat panel.
Referring to FIG. 1 of the drawing, the apparatus includes a source of coherent light 10 from which an object beam OB is derived by a collimating lens 12. This beam OB is directed perpendicularly towards a surface X of a prism 14. The apparatus further comprises a second source of coherent light 16 from which a reference beam RB1 is derived by a collimating lens 18. This beam RB1 is directed perpendicular to one of the inclined faces Y of the prism. Preferably

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