Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-05-25
2001-03-13
Dudek, James A. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
Reexamination Certificate
active
06201592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method for producing the same. In particular, the present invention relates to an LCD device having broad viewing angle characteristics, and a method for producing the same.
2. Description of the Related Art
The inventors of the present invention have disclosed in Japanese Laid-Open Publication No. 7-120728 a display mode designated “ASM mode” (axially symmetric aligned microcell mode), in which liquid crystal molecules are allowed to be twisted across the interspace between a pair of substrates and yet be axially-symmetrically oriented within each pixel region.
This method amounts to a technique of aligning liquid crystal molecules in an axially symmetrical orientation by utilizing phase separation from a mixture of liquid crystal and a photocurable resin. This mode is a so-called normally-white mode, where the liquid crystal molecules in an axially symmetrical orientation are aligned along a normal direction of the substrates in response to an applied voltage.
This conventional ASM mode LCD device employs a liquid crystal material having a positive dielectric anisotropy &Dgr;&egr;. Although this display mode provides excellent display characteristics in all directions because of the axially symmetrical orientation of liquid crystal molecules, it has a problem in that a black matrix having relatively large light-shielding portions must be employed in order to prevent the unwanted passage of light in the absence of an applied voltage. This has posed practical constraints on the upper limit of the aperture ratio. Furthermore, the conventional ASM mode utilizes a phase separation step, which requires complex temperature control to achieve an axially symmetrical orientation of liquid crystal molecules. In addition, it is difficult to produce a conventional ASM mode LCD device because it requires high-precision positioning of a pair of substrates, i.e., a color filter substrate and an active matrix substrate.
In view of the above problems, the inventors have proposed in Japanese Laid-Open Publication No. 8-341590 an ASM mode LCD device which is relatively easy to produce.
In accordance with the LCD device proposed in the 8-341590 application, the liquid crystal molecules within a liquid crystal layer interposed between a pair of substrates have a negative dielectric anisotropy (i.e., &Dgr;&egr;<0), and a negative phase plate having refractive index anisotropy is provided on the inside of a pair of polarizing plates. In the absence of an applied voltage, the liquid crystal molecules are aligned generally perpendicularly with respect to the substrate plane, so that a black state is attained regardless of the viewing angle. Furthermore, since the liquid crystal molecules are aligned so as to be axially-symmetrical within each pixel region, this device functions so as to compensate for the retardation which the light outgoing from the liquid crystal layer in any oblique direction is subjected to in a TN (twisted nematic) LCD device.
However, the above-described conventional LCD device has a problem in that it provides a very gentle voltage-transmittance characteristic curve so that a high voltage is incurred at the time of saturation. As a result, it is difficult to drive the conventional LCD device with a low voltage, resulting in large power consumption.
The above-described conventional LCD device attains an excellent black state in the absence of an applied voltage regardless of the direction of observation, thereby providing viewing angle characteristics with an excellent contrast ratio. However, when an intermediate gray scale image displayed on the LCD device is observed in the direction of e.g., about 45° with respect to the absorption axis of a polarization plate, the contrast may greatly deteriorate, and the gray scale characteristics may even be inverted in a certain range of viewing angles (e.g., about 35° to about 50°) due to the retardation caused by the ASM liquid crystal cell and the characteristics of the polarization plate.
Moreover, in accordance with the LCD device proposed in the 8-341590 application, the step of attaching the pair of substrates to each other still requires highly precise positioning and use of plastic beads or the like for controlling the cell thickness, as in the case of other conventional LCD devices.
SUMMARY OF THE INVENTION
A liquid crystal display device according to the present invention includes: a first substrate and a second substrate; a liquid crystal layer interposed between the first substrate and the second substrate, the liquid crystal layer including liquid crystal molecules having a negative dielectric anisotropy; a plurality of first convex members formed on the first substrate along a first direction; and a plurality of second convex members formed on the second substrate along a second direction which is different from the first direction, the plurality of first convex members partially overlapping the plurality of second convex members, the plurality of first convex members and the plurality of second convex members defining liquid crystal regions, and, under an applied voltage, the liquid crystal molecules in each liquid crystal region are aligned in an axially symmetrical or radial orientation; and, in the absence of an applied voltage, the liquid crystal molecules in each liquid crystal region are aligned substantially perpendicularly to the first substrate and the second substrate.
In one embodiment of the invention, the plurality of first convex members and the plurality of second convex members are formed in continuous stripes.
In another embodiment of the invention, the plurality of first convex members and the plurality of second convex members are formed in disrupted stripes.
In still another embodiment of the invention, the liquid crystal layer has a thickness (d
in
) within the liquid crystal regions and a thickness (d
out
) in between or around the liquid crystal regions, the thickness (d
in
) being larger than the thickness (d
out
), and a vertical alignment layer is provided on a side of at least one of the first substrate and the second substrate facing the liquid crystal layer.
In still another embodiment of the invention, the plurality of first convex members have substantially the same height with one another, and the plurality of second convex members have substantially the same height with one another; and an interspace between the first substrate and the second substrate is retained by intersections between the plurality of first convex members and the plurality of second convex members.
In still another embodiment of the invention, no chiral dopant is mixed in the liquid crystal layer; and at least one convex member among the plurality of first convex members and the plurality of second convex members has a face tilted with respect to a direction perpendicular to the substrate plane.
In still another embodiment of the invention, a chiral dopant is mixed in the liquid crystal layer.
In still another embodiment of the invention, the liquid crystal molecules in the liquid crystal layer have twist angles in the range of about 80° to about 120°.
In still another embodiment of the invention, &Dgr;n×d is in the range of about 300 to about 550 nm, where &Dgr;n is a refractive index anisotropy of the liquid crystal molecules, and d is a thickness of the liquid crystal layer.
In still another embodiment of the invention, a first polarization plate is provided on a side of the first substrate opposite the side facing the liquid crystal layer, and a second polarization plate is provided on a side of the second substrate opposite the side facing the liquid crystal layer, the first polarization plate and the second polarization plate being placed in a crossed Nicol state; and a first phase plate is provided between the first polarization plate and the first substrate, the first phase plate having in-plane primary refractive indices nx and ny and a primary refractive index nz along
Kouzaki Shuichi
Terashita Shin-ichi
Dudek James A.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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