Patent
1982-10-05
1984-06-26
Corbin, John K.
350339R, 350339D, G02F 113
Patent
active
044563361
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a reflector for a liquid crystal display and the method of fabricating the reflector.
BACKGROUND OF THE INVENTION
Liquid crystal displays, particularly those based on guest host or dye switching effects, in general comprise a cell having at least two spaced plates having electrodes selectively disposed on the inner surfaces of the two plates and a liquid crystal composition, such as doped with dyes, filled in the space between the plates. The display device includes means for selectively applying an electric field across the liquid crystal composition through the electrodes to modify the light absorption in the liquid crystal composition when the electric field exceeds a threshold value. The front plate through which the display is to be viewed, of course, is transparent, whereas the back plate typically employs a white reflector located outside the liquid crystal cell. This reflector, in many cases, is a thin layer of white material, such as barium sulfate, that has nearly 100 percent reflectivity and perfect Lambertian scattering providing for excellent off-axis viewing. However, since the reflector is located behind the liquid crystal layer at a distance at least equal to the back plate thickness, the image provided by the display is always accompanied by a slightly offset shadow.
Since liquid crystal display devices such as those utilizing various dye switching effects require scattering reflectors for adequate off-axis viewing, many researchers have tried depositing aluminum or other metallic reflectors over a glass surface uniformly frosted by chemical etching or fine polishing. Although they have been capable of achieving a reflective surface with optical properties very close to those of a standard white material, the shiny aluminum reflector appears darker when a layer of liquid crystal is placed on it. Thus, when the liquid crystal display device is fabricated with a metallic reflector deposited over a frosted back glass plate, it has very low brightness and does not perform well.
Recently, a liquid crystal device has been reported which includes a reflector formed by a thick film silver compound screened and fired on a back glass plate. This reflector, which also is the back electrode of the liquid crystal device, has good brightness, but the resolution obtained in the device is restricted by the coarse patterns achievable by a thick film process. See for example T. J. Scheffer and J. Nehring, "Guest-Host Displays", the Physics and Chemistry of Liquid Crystal Devices, Edited by G. J. Sprokel, Plenum Press, N.Y., 1980.
In the art of reflector design, there are surfaces known as spreading surfaces (see, for example, William B. Elmer, "The Optical Design of Reflectors," 2nd edition, John Wiley & Sons, N.Y., page 27 and following), the optical properties of which are excellent for a reflector placed inside a liquid crystal display. However, a typical spreading surface is generated by impressing or molding carefully designed patterns on a smooth surface. The most commonly used pattern is the positive or negative spherical segment having controlled depth and diameter such as result from peening. Many spreading reflectors are made this way on metals and plastic materials. Unfortunately, it is impractical according to such prior art methods to form such surfaces on a glass plate for a liquid crystal display device.
Clearly, there remains a need for an improved liquid crystal display devices including reflectors which provide high brightness over extended viewing angles.
SUMMARY OF THE INVENTION
Simply stated, the present invention comprises a liquid crystal display which includes a reflector comprising a substrate having a micro-lenticular surface, a layer of reflective material, such as aluminum of silver overlying the micro-lenticular surface, and including a light transparent organic layer having a low index of refraction, i.e., an index of refraction below that of SiO.sub.2 overlying and in optical contract with the reflective layer.
The presen
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patent: 2911682 (1959-11-01), Ewald
patent: 3912366 (1975-10-01), Sprokel
patent: 4097131 (1978-06-01), Nishiyama
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Levi, L., Applied Optics, vol. 2, (John Wiley & Sons 1980), pp. 918-921.
T. J. Scheffer and J. Nehring, "Guest-Host Displays", the Physics and Chemistry of Liquid Crystal Devices, Edited by G. J. Sprokel, Plenum Press N.Y., 1980.
William B. Elmer, "The Optical Design of Reflectors", 2nd Edition, John Wiley & Sons, N.Y., p. 27.
Minoru Hosokawa et al., "Dichroic Guest-Host Active Matrix Video Display", SID 81 Digest, Apr. 19, 1981.
Chung Chi H.
Chung David B.
Lu Sun
Barte William B.
Corbin John K.
Gallivan Richard
Minnesota Mining and Manufacturing Company
Sell Donald M.
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