Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
1999-11-12
2001-10-16
Sikes, William I. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S073000, C349S084000, C349S086000, C349S153000, C349S155000, C349S190000
Reexamination Certificate
active
06304309
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a liquid crystal display device and a method for fabricating the same. More specifically, the present invention relates to a liquid crystal display device which has a plurality of liquid crystal layers stacked on a substrate and provides bright color images even when it is a reflective type, and to a method for fabricating the same.
BACKGROUND OF THE INVENTION
First Prior Art
Widely used conventional liquid crystal display devices display images by combining twisted nematic liquid crystal and a polarizing plate so as to control penetrating light for each pixel. Conventional liquid crystal display devices for displaying color images have micro color filters corresponding to adjacent three pixels and penetrating red, green, and blue lights by the additive process.
However, in such a conventional liquid crystal display device a large amount of light absorption in the polarizing plate and the micro color filters causes the transmissivity in the entire liquid crystal display device to be about 10% or less, making it difficult to provide bright display images. In particular, in a reflective type liquid crystal display device which utilizes external light, the display is likely to be so dark as to make the colors unrecognizable.
Japanese Laid-open Patent Applications No. 61-238024 and No. 3-238424 show liquid crystal display devices which display bright color images even when they are used as reflective type because of a guest host mode for controlling the absorption and penetration of light for each color by using dichroic dyes. These liquid crystal display devices comprise a plurality of stacked panels each having a liquid crystal layer containing a dichroic dye different from each other. To be more specific, the three liquid crystal panels each comprise liquid crystal containing dichroic dyes of cyan, magenta, or yellow and sealed into between a pair of glass substrates. When all the panels absorb light, images are displayed in black; when all the panels penetrate light, images are displayed in white; and when one or two panels absorb light, images are displayed in colors. Not having a color filter or a polarizing plate for absorbing light, the display device with the guest host mode provides bright and clear color display and is suitable for a reflective type liquid crystal display device.
However, the liquid crystal display device comprising a plurality of stacked panels each having a pair of glass substrates has the following drawback. When the pixels are small, the thickness of the glass substrates composing each panel becomes relatively large as compared with the size of the pixels, and as a result, the parallax becomes so influential as to cause unevenness in color when display images are seen in a diagonal direction.
In order to solve the unevenness in color due to the parallax, a so-called polymer diffusion type liquid crystal display device has been proposed as in Japanese Laid-open Patent Application No. 6-337643.
FIG. 79
shows the polymer diffusion type liquid crystal display device, which comprises a substrate
1291
and liquid crystal layers
1295
-
1297
stacked thereonto by solidifying a resist material or polymeric material
1298
in which a guest host liquid crystal
1299
is dispersedly held. The display device further comprises driving electrodes
1292
-
1294
which correspond to the liquid crystal layers
1295
-
1297
, respectively and are connected with corresponding driving elements formed on the substrate
1291
. Such a structure requiring no glass substrate between adjacent ones of the liquid crystal layers
1295
-
1297
realizes a liquid crystal display device with a guest host mode which is freed of unevenness in color resulting from parallax.
However, in the polymer diffusion type liquid crystal display device, the guest host liquid crystal
1299
is dispersedly held in the resist material or polymeric material
1298
, so that the resist material or polymeric material
1298
makes up a large proportion of the liquid crystal layers
1295
-
1297
(the guest host liquid crystal
1299
makes up a small proportion of the liquid crystal layers
1295
-
1297
). This causes a problem that a substantial open area ratio becomes small, making it difficult to have a high contrast ratio.
Prior to the liquid crystal display device of the present invention, the inventors of the present invention have proposed a liquid crystal display device in Japanese Laid-open Patent Application No. 9-127057 which is shown in FIG.
80
. The liquid crystal display device comprises a substrate
1101
, film-like sealing plates
1113
-
1115
stacked on the substrate
1101
while being supported by supporting members (spacers)
1108
-
1110
, and liquid crystals
1125
-
1127
sealed into between the substrate
1101
and the sealing plate
1113
, between the sealing plates
1113
-
1114
, and between the sealing plates
1114
-
1115
, respectively. The use of the film-like sealing plates
1113
-
1115
supported by the supporting members
1108
-
1110
solves the unevenness in color due to parallax which is caused when glass substrates are used. Furthermore, the polymeric material which is used to hold liquid crystal in the above-mentioned polymer diffusion type liquid crystal display device is not required, so that the liquid crystal makes up a large proportion of the liquid crystal layers
1125
-
1127
disposed between adjacent ones of the sealing plates
1113
-
1115
. This makes it possible to increase a substantial open area ratio, thereby increasing the contrast ratio.
The supporting members
1108
-
1110
can be formed by applying a photosensitive resin onto each of the substrate
1101
and the sealing plates
1113
and
1114
and polymerizing and hardening parts of the photosensitive resin by mask exposure, where the supporting members
1108
-
1110
are formed, and then eliminating the remaining part of the photosensitive resin by development.
However, in the liquid crystal display device comprising the stacked film-like sealing plates
1113
-
1115
, each of the supporting members
1108
-
1110
must be formed exactly in the same position as each other in order to securely support the sealing plates
1113
-
1115
. For example, when the supporting members
1108
are formed in different positions from the supporting members
1109
as shown in FIG.
81
(
a
) due to low precision in positioning, these sealing plates are deformed as shown in FIG.
81
(
b
) by the pressure of bonding the sealing plate
1114
to the substrate
1101
. When the positional deviation between the supporting members
1108
and
1109
is large, the supporting member
1109
of a second display layer
1122
encroaches on a first display layer
1117
as shown in FIG.
81
(
c
) so as to destroy the first and second display layers
1117
and
1118
. In order to avoid this problem, the formation of the supporting members
1108
-
1110
by mask exposure requires mask alignment of high precision.
Since the supporting members
1108
and
1109
are in the region where the light transmissivity is not controlled, it is preferable to make the area for the supporting members
1108
-
1110
in pixels as small as possible in order to have a larger open area ratio. This requires higher precision in mask alignment. To be more specific, in the case where the supporting members
1109
are square pillars of 7 &mgr;m×7 &mgr;m, the positional deviation of 3 &mgr;m or more between the supporting members
1108
and
1109
damages the first display layer
1117
and other components as described above. Therefore, mask alignment must be performed so as to make the positional deviation less than 3 &mgr;m.
As a result, the device has a problem that the provision of a precision masking process leads to an increase in the production cost.
Second Prior Art
The inventors of the present invention previously filed Japanese Laid-open Patent Application No. 9-127057, which is about a liquid crystal display device successfully overcoming the problem of the liquid crystal display device shown in FIG.
79
Karasawa Takeshi
Kawaguri Mariko
Wakita Naohide
Yamanaka Yasuhiko
Yamazoe Hiroshi
Chowdhury Tarifur R.
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Sikes William I.
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