Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1998-03-09
2001-01-16
Parker, Kenneth (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S088000
Reexamination Certificate
active
06175397
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display apparatus in which high polymer is mixed in liquid crystal, a liquid crystal projector using the liquid crystal apparatus, and a method of manufacturing the liquid crystal display apparatus.
2. Related Background Art
In recent years, liquid crystal display apparatuses have been widely used in various devices because of their advantages of thin sizes, low voltage driving ability, and saved power consumption, and the like, as is representatively known from a display of a direct view type having a diagonal size exceeding 10 inches. Also, liquid crystal projectors which realize display on a larger screen by providing a liquid crystal display panel together with an optical system have come to be introduced as practically useful commercial products having high resolution and brightness, as computers have spread popularly.
Liquid crystal used in those liquid crystal panels is generally TN (Twisted Nematic) liquid crystal which achieves higher response speed and contrast in comparison with STN (Super Twisted Nematic) liquid crystal used mainly in conventional panels, so that images of higher quality can be displayed.
However, in a display apparatus using TN liquid crystal, loss of light is largely due to a polarizing plate and the brightness is therefore limited. Particularly, the drawback of the TN liquid crystal display apparatus is remarkable in case of a projection type liquid crystal display apparatus which requires high brightness.
As countermeasures against the drawback, proposals have been made as to liquid crystal display apparatuses using various liquid crystal, such as “PNLC (Polymer Network Liquid Crystal)” in which TN liquid crystal is dispersed in a liquid crystal continuous phase or a sponge-like polymer network, a “high-polymer/liquid crystal composite film” capable of forming a display of a large screen by using an electro-optic effect accompanying light diffusion without using a polarizing plate, or “polymer dispersed liquid crystal” having a structure in which spherical liquid crystal grains are dispersed in a high-polymer matrix between transparent electrode and liquid crystal molecules are oriented along a wall surface of the high-polymer matrix within the grains in the following manner. Specifically, incident light is diffused when a difference exists between the average refractive index of the liquid crystal grains and the refractive index of the high-polymer matrix. As the refractive indexes is increased when a voltage is applied to the high-polymer dispersed cell, liquid crystal is released from restrictions from the wall surface of the high-polymer matrix, to be oriented to be vertical to the surfaces of the transparent electrodes. When the refractive index of the high-polymer matrix is close to the refractive index of the liquid crystal molecules in the short-axis direction of the molecules, incident light is transmitted without being dispersed.
The PNLC is provided as a type of liquid crystal in which light is transmitted at a high transmit rate by making the refractive index of TN liquid crystal be substantially equal to the refractive index of the polymer network when a voltage is applied, while incident light is diffused to produce black by a difference between the refractive index of the TN liquid crystal oriented randomly and the refractive index of the polymer network when no voltage is applied. A display apparatus using the PNLC does not use a polarizing plate, and therefore essentially realizes display with a higher light use efficiency, i.e., brighter display than a TN liquid crystal display apparatus. These phenomena and applications are common to the “high-polymer/liquid crystal composite film” and the “polymer dispersed liquid crystal”.
In order to more advantageously use the high light use efficiency of the “polymer network liquid crystal” and the like, it is effective that the active matrix substrate is of a reflective type. Since a reflective type substrate can be embedded below a reflective electrode to shield light, the aperture can be increased to be close to 100%, resulting in a potential that the light use efficiency is not decreased unlike a transparent type even when the pixel size is reduced.
In case of manufacturing a liquid crystal display apparatus using “high-polymer/liquid crystal composite film”, “polymer dispersed liquid crystal”, or “polymer network liquid crystal” of a reflective type, an active element is embedded below a reflective electrode with respect to a reflective type substrate and high-polymer, and liquid crystal are injected and sealed between the substrate and a transparent electrode. Thereafter, ultraviolet light (UV) is irradiated thereon, and thus, a liquid crystal panel is prepared.
In particular, a method of manufacturing the (polymer dispersed liquid crystal” is described in Japanese Patent Laid-open Application No. 5-61016. According to this publication, an acrylate-based ultraviolet-polymerized composite material (using a light-polymerization starting agent of DAROQUA (phonetic translation) 1116 available from Merck & Co., Inc.) and a liquid crystal composite material (E8 available from BDH-SHA (phonetic translation)) are uniformly dissolved and injected into glass cell having an ITO electrode. Thereafter, ultraviolet light is irradiated thereon (at 1 mW for 500 seconds), thereby to prepare the polymer dispersed liquid crystal (PDLC) cell. The grain diameter of the liquid crystal composite material in the PDLC material is set to 0.1 to 10 &mgr;m which is adjusted by the content of the liquid crystal composite material. That is, a liquid crystal composite material of 65 to 75 weight % is used with respect to a total weight of the high-polymer matrix and the liquid crystal composite material, to mix samples having different grain diameters.
However, in case of a conventional liquid crystal panel using ultra-violet irradiation, it has been found that uneven display occurs. Particularly, in case of irradiating ultra-violet light of parallel light onto the entire surface of liquid crystal area, there appears a phenomenon that the reflection light amount decreases concentrically from the center portion of the liquid crystal panel to the peripheral portion thereof, i.e., the transmittance rate decreases. In case of a color three-plate type, irregular color appears concentrically. These drawbacks are caused by unevenness of the polymerization condition or unevenness of liquid crystal grain diameters, and are estimated to be due to a stress during polymerization. Another factor is estimated to be that an influence from a seal differs in accordance with a distance from the seal during polymerization.
In addition, it has been found that there is a problem concerning the stability of liquid crystal. That is, the liquid crystal phase lacks the stability because of an existence of a non-reactive liquid crystal phase exists during preparation using ultraviolet light.
A liquid crystal display apparatus into which liquid crystal has been injected will be explained with reference to a cross-section shown in FIG.
5
. The applicant filed Japanese Patent Application No. 7-186473 concerning a method of manufacturing an active matrix substrate. The active matrix substrate is constructed as follows. A lower portion of liquid crystal
214
is comprised of an n-type silicon semiconductor substrate
201
having an impurity density of 10
15
cm
−3
or less, LOCOS
202
, a PWL
203
as a p-type impurity region having an impurity density of about 10
16
cm
−3
, an NLD
206
as an n-type impurity region having an impurity density of about 10
16
cm
−3
, source and drain regions
207
and
207
′ having an impurity density of about 10
19
cm
−3
, an AI electrode
209
, a PSG
211
, an SiN
210
, and a pixel electrode
213
.
Next, an upper portion of the liquid crystal
214
is comprised of a transparent substrate
220
, a color filter
221
, a black matrix
222
, and a common electrode consisting o
Inoue Shunsuke
Mizuno Hiroshi
Sekine Yasuhiro
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Parker Kenneth
Qi Mike
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