Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2001-09-12
2004-04-06
Chowdury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S096000, C349S132000, C349S117000, C345S087000
Reexamination Certificate
active
06717645
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a horizontal orientation liquid crystal layer.
2. Description of the Prior Art
A liquid crystal display device (also referred to by the abbreviation “LCD”) is a flat panel display device having desirable characteristics such as a small thickness, a small weight, and a small power consumption. However, TN (Twisted Nematic) type LCDs, which are widely used in the art, have a problem in that the display quality varies depending on the direction from which they are observed (viewing angle), i.e., have poor viewing angle characteristics. Particularly, the display characteristics vary significantly when the viewing angle is changed in the orientation axis direction defined by the azimuth direction of the orientation direction of liquid crystal molecules (the direction of the long axis of the liquid crystal molecules in the plane of the liquid crystal layer) that are near the center of the liquid crystal cell in the thickness direction thereof (also referred to as “the orientation axis direction of the intermediate layer of the liquid crystal cell”). Specifically, when the angle at which the LCD is observed is changed in the orientation axis direction of the intermediate layer of the liquid crystal cell, the display characteristics (e.g., the contrast ratio) become asymmetric about the normal direction (the direction normal to the display plane). Moreover, in an intermediate gray level display, there occurs a display brightness (gray level) inversion phenomenon. In an intermediate gray level display, when the viewing angle direction is inclined from the direction normal to the display plane (viewing angle è=0°) toward one direction (e.g., upwardly) in the orientation axis direction of the intermediate layer of the liquid crystal cell (i.e., when the viewing angle è is increased from 0°), the display brightness once increases and then decreases after a certain angle. When the viewing angle direction is inclined toward the opposite direction (e.g., downwardly) in the orientation axis direction of the intermediate layer of the liquid crystal cell, the display brightness once decreases and then increases after a certain angle.
Various techniques have been developed in the art to improve the viewing angle characteristics of the TN type LCD. For example, Japanese Laid-Open Patent Publication No. 7-43719 discloses a liquid crystal display device having electrooptical characteristics of a normally white mode, in which at least one of a pair of electrodes for applying an electric field across the liquid crystal layer is provided with slits whose long side is parallel to the average orientation direction of the liquid crystal molecules being projected onto the substrate (substantially the same as the orientation axis direction of the intermediate layer of the liquid crystal cell). With this configuration, an inclined electric field is produced in the liquid crystal layer in each pixel. As a result, a plurality of regions where liquid crystal molecules rise in respectively different directions are formed in each pixel, thereby improving the viewing angle characteristics.
However, according to a study conducted by the present inventors, although the technique disclosed in Japanese Laid-Open Patent Publication No. 7-43719 is effective in reducing the change in the brightness occurring as the viewing angle is changed in the orientation axis direction of the intermediate layer of the liquid crystal cell, it falls short of solving the asymmetry of the display characteristics about the normal direction and the inversion phenomenon. Moreover, with this technique, the display contrast ratio as viewed from the normal direction is lower than that of other conventional TN type LCDs.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a liquid crystal display device having desirable viewing angle characteristics.
The object is achieved by a liquid crystal display device as set forth below. A liquid crystal display device of the present invention is a liquid crystal display device having a normally black mode electrooptical characteristics and including: a liquid crystal cell having a pair of substrates, a horizontal orientation liquid crystal layer provided between the pair of substrates and including liquid crystal molecules having a positive dielectric anisotropy, and a plurality of pixels each being defined by a pair of electrodes opposing each other via the liquid crystal layer therebetween; and a pair of polarizers and at least one phase difference compensator provided outside the liquid crystal cell, wherein: the pair of polarizers and the at least one phase difference compensator are arranged so that the transmittance is lower in the absence of an electric field applied across the liquid crystal layer than in the presence of an electric field applied across the liquid crystal layer; and the pair of electrodes produce a transverse electric field component parallel to the plane of the liquid crystal layer in the presence of an applied voltage therebetween, and an orientation axis direction, which is defined by the azimuth angle of the orientation direction of liquid crystal molecules near the center of the liquid crystal layer in the thickness direction thereof, is changed by the transverse electric field component.
The liquid crystal display device of the present invention has desirable viewing angle characteristics. Since the liquid crystal display device of the present invention uses a horizontal orientation liquid crystal layer, there is provided a wide variety of materials to choose from, and the liquid crystal display device can be manufactured by using a reliable material. Moreover, since the transverse electric field component for improving the viewing angle dependence of the brightness can be produced only by providing an opening in a conventional electrode, the liquid crystal display device can be easily manufactured by using a conventional manufacturing method.
The pair of polarizers may be arranged so that polarization axes thereof are orthogonal to each other.
The liquid crystal layer may be a homogenous alignment type liquid crystal layer. Preferably, the azimuth angle direction of the orientation direction of the liquid crystal molecules of the liquid crystal layer in the presence of an applied voltage varies depending on the position in the thickness direction of the liquid crystal layer.
Preferably, the liquid crystal layer includes, in each of the plurality of pixels, a plurality of domains whose orientation axis directions differ from one other.
Preferably, the plurality of domains include domains whose orientation axis directions differ from each other by 180°.
Preferably, the pair of electrodes produce transverse electric field components of different directions in the presence of an applied voltage. More preferably, the transverse electric field components of different directions include transverse electric field components of directions differing from each other by 180°.
Preferably, the liquid crystal layer includes, in each of the plurality of pixels, a plurality of regions whose orientation axis directions change in different directions in the presence of an applied voltage, and the plurality of regions have an equal area and are arranged symmetrically.
Preferably, the direction of the transverse electric field component produced by the pair of electrodes is at an angle of 60° to 90° with respect to the orientation axis direction of the liquid crystal layer in the absence of an applied voltage.
At least one of the pair of electrodes may be a conductive layer including openings therein, thereby producing the transverse electric field component.
Preferably, the liquid crystal display device further includes another phase difference compensator for compensating for the retardation of the liquid crystal layer in the absence of an applied voltage for light incident from a
Shimoshikiryou Fumikazu
Watanabe Keizo
Yoshida Keisuke
Chowdury Tarifur R.
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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