Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1995-12-27
2001-01-30
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S049000, C349S051000, C349S100000, C349S110000, C349S069000, C205S477000, C420S124000
Reexamination Certificate
active
06181396
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a reflective liquid crystal display apparatus and, more particularly, to an improvement in a reflective plate of a reflective liquid crystal display apparatus.
2. Description of the Prior Art
A reflective liquid crystal display apparatus does not require a back light as a light source because light obtained by reflecting external incident light by a reflective plate positioned inside the liquid crystal display apparatus is used as a display light source. This apparatus is considered to be an effective system for achieving a decrease in power consumption, a decrease in thickness, and a light weight, compared to a transparent liquid crystal display apparatus. The basic structure of a conventional reflective liquid crystal display apparatus comprises a liquid crystal of a TN (Twisted Nematic) scheme, an STN (Super Twisted Nematic) scheme, a GH (Guest Host) scheme, a PDLC (macromolecular dispersion) scheme, or the like, elements (e.g., thin film transistors or diodes) for switching the liquid crystal, and a reflective plate arranged on the inner or outer side of the elements.
The display performance of the reflective liquid crystal display apparatus is required to provide a bright, white display in a liquid crystal transmissive state. To realize this display performance, it is important to control the reflective properties of the reflective plate.
The surface of a conventional reflective plate is corrugated to reflect light incident at all angles by a reflective surface in a target direction (display direction).
Well-known corrugation shapes on the surfaces of reflective plates are as follows.
{circle around (1)} The pitch of corrugations falls within a range of 1 &mgr;m to 100 &mgr;m, the corrugation height falls within a range of 0.1 &mgr;m to 10 &mgr;m, the corrugation inclination angle is 0° to 30° with respect to the horizontal surface of a substrate, and intervals between the projecting portions of the corrugations are irregular (disclosed in Japanese Examined Patent Publication No. 61-6390).
{circle around (2)} The corrugation height exhibits the Gaussian distribution, and the average inclination angle of corrugations at this time is 10° (disclosed in Tohru Koizumi and Tatsuo Uchida, Proceedings of the SID, Vol. 29, 157, 1988).
{circle around (3)} The surface of a reflective electrode has a plurality of projecting portions arrayed irregularly (disclosed in Japanese Unexamined Patent Publication No. 6-75237).
{circle around (
4
)} The surface of a reflective plate is a smooth corrugated surface, and the average inclination angle of corrugations is selected from 4° to 15° (disclosed in Japanese Unexamined Patent Publication No. 6-175126).
{circle around (
5
)} At least two or more projecting portions having different heights are formed on the surface of a reflective plate (disclosed in Japanese Unexamined Patent Publication No. 6-27481).
A conventional method of corrugating a reflective plate uses photolithography and etching which are performed to an organic film to uniformly corrugate a large-area substrate without causing any damage. To obtain a reflective plate having desired reflective properties, a corrugation shape on the surface of the reflective plate must be optimally designed.
In the above references of the reflective liquid crystal display apparatuses, the average inclination angle of corrugations is designated to optimize a corrugation shape. As for practical reflective performance, however, a flat region is included in the corrugation shape on the entire surface of the reflective plate, or corrugated surfaces having various inclination angles except for the inclination angle designated in the reference are present on the entire surface of the reflective plate. For this reason, it is difficult to obtain a bright reflective liquid crystal display apparatus having a reflective plate by designating only the average inclination angle described in the references.
In the above references, the surface of the reflective plate is irregularly corrugated. However, these references are insufficient for defining a corrugated structure on the surface of the reflective plate having optimum reflective performance because designation of a detailed irregular shape is indefinite, and irregularity from a regular structure is not defined.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation in the conventional techniques, and has as its object to provide a reflective liquid crystal display apparatus with a reflective plate having a corrugated structure which is required for obtaining optimum reflective properties.
To achieve the above object, according to the present invention, there is provided a reflective liquid crystal display apparatus having a structure in which a liquid crystal layer is sandwiched between an insulating substrate having a corrugated reflective plate as a pixel electrode and an insulating substrate having a transparent electrode, wherein the reflective plate is a reflective plate having an irregularly corrugated structure and satisfies any one of {circle around (1)} to {circle around (6)} in order to obtain a reflective plate having excellent scattering performance. That is,
{circle around (1)} a value obtained by standardizing a full-width at half maximum in a distribution graph of distances between adjacent projecting or recessed portions with an average of the distances between the adjacent projecting or recessed portions falls within a range of 0.3 to 0.9;
{circle around (2)} an average of distances between adjacent projecting or recessed portions falls within a range of 1 &mgr;m to 80 &mgr;m;
{circle around (3)} a value obtained by standardizing a full-width at half maximum in a distribution graph of heights of projecting or recessed portions with an average of the heights is 0.2 or more;
{circle around (4)} a maximum height of corrugations on a surface of the reflective plate falls within a range of 0.1 &mgr;m to 5 &mgr;m;
{circle around (5)} a region having an inclination angle of 0° with respect to a horizontal surface of the insulating substrate inside a surface of the pixel electrode as the reflective plate occupies 20% or less of an entire region inside the surface of the pixel electrode, and an average inclination angle of corrugations in the entire surface is 5° to 10° in all azimuths on the pixel electrode as the reflective plate; and
{circle around (6)} the reflective plate which satisfies at least one of the conditions described in {circle around (1)} to {circle around (5)} has six or more projecting or recessed portions inside the surface of the pixel electrode.
According to the present invention, a corrugated reflective plate can be formed which is rarely affected by the use environment or can most efficiently utilize incident light for reflected light when the use environment is set.
With this reflective plate, a bright, high-quality reflective liquid crystal display apparatus can be provided. In addition, this reflective plate can be applied to not only a liquid crystal display apparatus but also various display apparatuses and the like.
The above and other advantages, features and additional objects of the present invention will become manifest to those versed in the art upon making reference to the following detailed description and accompanying drawings in which preferred structural embodiments incorporating the principle of the present invention are shown by way of illustrative example.
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patent: 5734455 (1998-03-01), Yoshida et al.
patent: 5805252 (1998-09-01), Sh
Kanoh Hiroshi
Mizobata Eishi
NEC Corporation
Ngo Julie
Sikes William L.
Young & Thompson
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