Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-04-11
2004-09-07
Nguyen, Dung T. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S123000, C349S114000, C349S155000
Reexamination Certificate
active
06788375
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly, it relates to a liquid crystal display device having a wide viewing angle characteristic and high display quality.
Recently, a thin and light liquid crystal display device is used as a display device for a display of a personal computer or a display unit of portable information terminal equipment. Conventional twist nematic (TN) or super twist nematic (STN) liquid crystal display devices have, however, a disadvantage of a narrow viewing angle, and a variety of techniques have been developed for overcoming this disadvantage.
A typical technique to improve the viewing angle characteristic of a TN or STN liquid crystal display device is a method of additionally providing an optical compensator. Another technique is a lateral field method of applying, through a liquid crystal layer, an electric field in a lateral direction to the substrate surface. Liquid crystal display devices of the lateral field method are recently mass-produced and regarded as promising devices. A still another technique is DAP (deformation of vertical aligned phase) in which a nematic liquid crystal material with negative dielectric anisotropy is used as a liquid crystal material and a vertical alignment film is used as an alignment film. The DAP is a kind of an electrically control birefringence (ECB) method, in which the transmittance is controlled by utilizing the birefringent property of the liquid crystal molecules.
Although the lateral field method is one of the effective methods for attaining a wide viewing angle, the production margin is very small in the production process as compared with that of a general TN liquid crystal display device, and hence, there is a difficulty in stable production of this type of liquid crystal display devices. This is because gap irregularity between substrates and shift of the transmission axis of a polarizing plate (polarization axis) from the orientation axis of a liquid crystal molecule largely affect the luminance and the contrast ratio of display. In order to stably produce the liquid crystal display devices of the lateral field method by highly precisely controlling these factors, the technique should be further highly developed.
Furthermore, in order to produce an even display free from display unevenness by a liquid crystal display device of the DAP method, it is necessary to control orientation. For controlling the orientation, an alignment treatment is carried out by rubbing the surface of an alignment film. When the surface of a vertical alignment film is subjected to a rubbing treatment, however, rubbing streaks are easily caused in a displayed image. Therefore, this treatment is not suitable to mass-production.
On the other hand, for controlling the orientation without the rubbing treatment, a method for controlling the orientation directions of liquid crystal molecules by an inclined electric field generated by forming a slit (opening) in an electrode has been proposed (as described in, for example, Japanese Laid-Open Patent Publication Nos. 6-301036 and 2000-47217). However, the present inventors have found the following as a result of examination: The orientation state of a portion of a liquid crystal layer corresponding to the opening of the electrode is not specified in the methods disclosed in these publications, and the continuity of the orientation of the liquid crystal molecules is not sufficient. Therefore, it is difficult to obtain a stable orientation state over an entire picture element, and hence, a displayed image becomes disadvantageously uneven.
SUMMARY OF THE INVENTION
The present invention was devised to overcome the aforementioned disadvantages, and an object of the invention is providing a liquid crystal display device having a wide viewing angle characteristic and high display quality.
The liquid crystal display device of this invention includes a first substrate; a second substrate; a liquid crystal layer disposed between the first substrate and the second substrate; and a plurality of picture element regions each defined by a first electrode provided on a surface of the first substrate facing the liquid crystal layer and a second electrode provided on a surface of the second substrate facing the liquid crystal layer, and the first substrate has, on the surface thereof facing the liquid crystal layer, at least one first protrusion with an inclined side face correspondingly to each of the plurality of picture element regions, and a portion of the liquid crystal layer included in each of the plurality of picture element regions is in a substantially vertical orientation state under application of no voltage, and includes at least a part of a first liquid crystal domain placed in a radially-inclined orientation state about the at least one first protrusion under voltage application, for producing a display by changing an orientation state of the liquid crystal layer in accordance with an applied voltage. Thus, the aforementioned object can be achieved.
The at least one first protrusion may be formed within each of the plurality of picture element regions.
The at least one first protrusion may be plural in number, and the portion of the liquid crystal layer included in each of the plurality of picture element regions may include a plurality of first liquid crystal domains all placed in the radially-inclined orientation state under voltage application.
The first electrode may include at least one first opening, and the at least one first protrusion may be formed within the at least one first opening.
Preferably, the second substrate has, on the surface thereof facing the liquid crystal layer, at least one second protrusion with an inclined side face correspondingly to each of the plurality of picture element regions, and the portion of the liquid crystal layer included in each of the plurality of picture element regions includes, under voltage application, at least a part of a second liquid crystal domain placed in a radially-inclined orientation state about the at least one second protrusion, so that inclination directions of liquid crystal molecules in the first liquid crystal domain can be continuous with inclination directions of liquid crystal molecules in the second liquid crystal domain.
The second electrode may have at least one second opening, the portion of the liquid crystal layer included in each of the plurality of picture element regions may include, under voltage application, a second liquid crystal domain placed in a radially-inclined orientation state about the at least one second opening, so that inclination directions of liquid crystal molecules in the first liquid crystal domain can be continuous with inclination directions of liquid crystal molecules in the second liquid crystal domain.
The second electrode may have at least one second opening, and the at least one second protrusion may be formed within the at least one second opening.
The at least one second protrusion may include a plurality of second protrusions formed out of each of the plurality of picture element regions.
A cross-section, taken along a surface of the first substrate, of the at least one first protrusion is preferably in a shape having rotational symmetry.
Alternatively, the cross-section, taken along the surface of the first substrate, of the at least one first protrusion may be in a substantially circular shape.
Alternatively, the cross-section, taken along the surface of the first substrate, of the at least one first protrusion may be in a substantially cross shape consisting of crossing lines extending along a first direction and a second direction crossing each other at substantially right angles.
The liquid crystal display device may further include a pair of polarizing plates respectively provided on outer surfaces of the first substrate and the second substrate, so that the pair of polarizing plates may be disposed in such a manner that a polarization axis of one of the pair of polarizing plates is parallel to the first d
Kubo Masumi
Ogishima Kiyoshi
Nguyen Dung T.
Nixon & Vanderhye P.C.
Qi Mike
Sharp Kabushiki Kaisha
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