Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-04-28
2001-02-27
Malinowski, Walter J. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S126000
Reexamination Certificate
active
06195146
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to liquid crystal displays. Specifically, the present invention is directed to liquid crystal displays having at least one alignment layer which is exposed to a particle beam, such as an atomic or ion beam, so that the molecules of the liquid crystal material have a proper pretilt characteristic to form a liquid crystal display cell.
BACKGROUND OF THE INVENTION
Aligned liquid crystals are widely used in flat panel display technology. They are aligned by inducing anisotropy on the surface of a substrate. This surface is usually a polymer layer such as polyimide, coated on a glass substrate, as discussed in D.-S. Seo, H. Matsuda, J. Ishizaki, Y. Lamura and S. Kobayashi, SID Digest 1993, p. 953. Conventionally, there are a number of ways of introducing anisotropy on the surface. They include rubbing (see O. Kehmann (1906) and P. Chatelain (1943), cited by P. G. deGennes and J. Prost, “The Physics of Liquid Crystals,” Clarendon Press, Oxford (1993) p. 109, 161), stretching a polymer (as discussed in H. Aoyama, Y. Yamazaki, M. Matsuura, H. Mada and S. Kobayashi, Mol. Cryst. Liq. Cryst. 72, 127 (1981)), a Langmuir-Boldgett film (see H. Ikeno, A. Oshaki, M. Nitto, N. Ozaki, Y. Yokoyama, K. Kakaya and S. Kobayashi, Jpn. J. Appl. Phys., 27, L475, (1988)), a grating structure produced by microlithography (see M. Nakamura and M. Ura, J. Appl. Phys., 52, 210 (1981)), oblique angle deposition of SiOx (see J. lenuing, Appl. Phys. Lett., 21, 173 (1982)) and polarized UV radiation of polymer films (see M. Schadt, K. Suhmitt, V. Kozinkov and V. Chiqvinov, Jpn. J. Appl. Phys., 31, 2155 (1992)).
Most of these methods are impractical due to their complexity and/or cost for mass production. The pervasive method used in aligning liquid crystal displays available on the market today is the mechanical rubbing treatment (with, for example, a velvet cloth) of a polyimide film which is coated on the substrate. As discussed in S. Kobayashi and Y. limura, SPIE, 2175, 123 (1994), this method has several drawbacks. First, debris is left by the cloth during the rubbing process, damaging an otherwise clean room environment. Second, the vigorous rubbing may damage (e.g. scratch) the structure of the cell. Third, electrostatic discharging may influence the electronic circuitry below the thin polyimide film. Fourth, stability and consistency of pretilt angle are difficult to achieve and control. Finally, rubbing, being a macroscopic process, does not readily lend itself to aligning liquid crystals in different directions at the spatial size of a pixel, which is usually of the order of a hundred micrometers. This local alignment is desirable to obtain a multidomain structure, which significantly increases the angle of viewing of the display. The limited angle of viewing of current liquid crystal displays is one of the limitations of this technology.
It is an object of the present invention to provide a liquid crystal display cell produced by an improved method of providing a characteristic to a surface to which liquid crystal molecules align.
It is another object of the present invention to provide a liquid crystal display cell with such characteristic provided by using a particle beam, such as an atomic or ion beam.
SUMMARY OF THE INVENTION
The present invention provides liquid crystal display cells treated by a new non-contact method of aligning liquid crystals. These cells circumvent the problems posed by cells produced using the prior art methods of alignment, including the rubbing technique.
An aspect of the present invention is a liquid crystal display cell with an alignment layer or surface on which is generated an alignment direction by directing a particle beam at the alignment surface, wherein the particle beam is directed at the surface at an adjustable energy, at an adjustable angle with respect to the alignment surface and at an adjustable time to adjust the pretilt angle of a liquid crystal molecule with respect to the alignment surface.
The advantages of atomic beam induced alignment over the other alignment techniques are as follows. First, no contact is necessary for alignment. Second, a low energy beam ensures that only the surface layers are affected so that the number of radicals induced by broken bonds are a minimum This avoids charge build up when a voltage is applied across a liquid crystal cell. Third, large area uniform and parallel beams can be readily obtained. This is a problem with oblique deposition of SiOx. Fourth, atomic beams are well known to the electronics manufacturing community and are compatible with a clean room environment. Finally, atomic beams can be used to align both surfaces of a thin polymer film, which is self-supporting.
A liquid crystal display cell is provided including a first substrate; a second substrate; a liquid crystal layer of liquid crystal molecules disposed between the first substrate and the second substrate; a first alignment layer disposed between the first substrate and the liquid crystal layer; and a second alignment layer disposed between the second substrate and the liquid crystal layer; wherein a surface of at least one alignment layer is bombarded by a particle beam of an adjustable energy using a voltage less than 200 V so that the liquid crystal molecules proximate the surface are induced to a predetermined pretilt angle.
Preferably, the alignment layers comprise polymer films which are coated on the substrates. For homeotropic cell design, the film can be formed of homeotropic type material or, preferably, a homeotropic polyimide polymer film which is coated on the substrate. One or both alignment layers can have the film.
For homogeneous cell design, the liquid crystal can be formed of a homogeneous type material, preferably comprising twisted nematic liquid crystal molecules. One or both alignment layers can have a homogeneous polyimide film which is coated on the respective substrate.
Preferably, the particle beam is a beam of ion or neutral particles. The particle beam can be a beam of argon or oxygen particles. The particle beam can be an atomic beam, an ion beam, a molecular beam, an electron beam or an elementary beam.
It is preferable that the liquid crystal display be treated by a particle beam directed at an adjustable angle with respect to the surface of at least one of the alignment layers and at an adjustable time to adjust the pretilt angle of the liquid crystal molecules with respect to the surface of at least one of the alignment layers to which the liquid crystal molecules are aligned.
Preferably, the liquid crystal display cell is treated by a particle beam having a value of the adjustable energy, a value of the adjustable angle and a value of the adjustable time to result in the particle beam interacting only within a distance from the surface sufficient to result in an alignment direction but insufficient to introduce a substantial number of defects at or near the surface. The defects are, preferably, charge stored in the surface. The value of the adjustable energy is, preferably, greater than 25 eV. The value of the adjustable angle should range from about 0° to about 90°. Finally, the adjustable time preferably varies from five seconds to a few minutes.
REFERENCES:
patent: 5770826 (1998-06-01), Chaudhauri et al.
Chaudhari Praveen
Lacey James Andrew
Lien Shui-Chih Alan
International Business Machines - Corporation
Malinowski Walter J.
Shofi David M.
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