Liquid crystal cells – elements and systems – Liquid crystal system – Projector including liquid crystal cell
Reexamination Certificate
2000-07-28
2004-11-30
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Projector including liquid crystal cell
Reexamination Certificate
active
06825889
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal device in which the liquid crystal sealed between a pair of substrates is twist-aligned between the substrates, and to a projection display device using the liquid crystal device as a light valve. More specifically, the present invention relates to a contrast improvement technology in a display device using a liquid crystal device.
2. Background Art
A liquid crystal device of a type in which the liquid crystal sealed between a pair of substrates (TN liquid crystal/liquid crystal of a twisted nematic mode) is twist-aligned between the substrates is installed in, for example, a projection display device as a light valve. In general, in the projection display device of this type, for example, lights of the three primary colors red, blue, and green pass through liquid crystal devices to form an image component for each color, these image components arc combined to create a desired color image, and the color image is projected.
The configuration of a conventional liquid crystal device used in such a display device will be described with reference to FIG.
27
.
FIG. 27
is an enlarged sectional view of an active matrix substrate, a counter substrate, and a bonding structure of these substrates.
As shown in
FIG. 27
, a liquid crystal device
1
is generally composed of an active matrix substrate
20
formed with a transparent pixel electrode
8
, an alignment layer
46
, a pixel-switching thin film transistor (hereinafter, referred to as a “TFT”) (not shown), a data line (not shown), a scanning line
91
, and a capacitor line
92
; a counter substrate
30
formed with a transparent counter electrode
32
and an alignment layer
47
; and liquid crystal
39
sealed and sandwiched between these substrates. As the liquid crystal
39
to be sealed, liquid crystal of a TN (twisted nematic) mode that is twist-aligned 90° by the alignment layers
46
and
47
between the substrates has been widely used. According to the thus-configured liquid crystal device
1
, in the active matrix substrate
20
, an alignment state of the liquid crystal
39
can be controlled between the pixel electrode
8
and the counter electrode
32
by image signals applied on the pixel electrode
8
from the data line via the TFT. Therefore, in the transmissive liquid crystal device
1
, light incident from the side of the counter substrate
30
enters the liquid crystal
39
from the side of the counter substrate after being arranged in predetermined linear polarized light beams by an incident-side polarizer (not shown). A linear polarized light beam passing through a certain area is emitted from the active matrix substrate
20
with a transmitted light polarization axis twisted, whereas a linear polarized light beam passing through another area is emitted from the side of the active matrix substrate
20
without twisting of a transmitted light polarization axis. Therefore, either one of the linear polarized light beam whose transmitted light polarization axis is twisted by the liquid crystal
39
, or the linear polarized light beam whose transmitted light polarization axis is not twisted by the liquid crystal
39
passes through an emitting-side polarizer (not shown). Thus, by controlling polarization states of these beams for every pixel, predetermined information can be displayed.
SUMMARY OF THE INVENTION
When the light incident from the side of the counter substrate
30
enters into a channel area of the TFT, or is reflected by the channel area of the TFT, not only does such light not contribute to display, but also a photoelectric current is generated by a photoelectric conversion effect, resulting in deterioration of transistor characteristics of the TFT. For this reason, the active matrix substrate
20
and the counter substrate
30
may be formed with a black matrix consisting of a metallic material, such as chrome, and a resin black, or a first light-shielding film
6
and a second light-shielding film
7
, called a black mask, in such a manner as to overlap areas between adjacent pixel electrodes
8
. When configured in this way, according to the liquid crystal device
1
, in either of the active matrix substrate
20
and the counter substrate
30
, light passes through only first and second opening areas
21
and
31
partitioned by the first light-shielding film
6
and the second light-shielding film
7
, and the light is intercepted by the first light-shielding film
6
and the second light-shielding film
7
in other areas. Therefore, it is possible to prevent intense light from entering or from being reflected by the channel area of the TFT
10
.
In the thus-configured liquid crystal device
1
, the first light-shielding film
6
of the active matrix substrate
20
and the second light-shielding film
7
of the counter substrate
30
are formed on nearly overlapping areas. For this reason, a center position
211
of the first opening area
2
of the active matrix substrate
20
coincides with the center position
311
of the second opening area
2
of the counter substrate
30
.
While it is not shown in the figure, in another example of a conventional liquid crystal device, the counter substrate
30
may be formed with a microlens to collect light incident on the liquid crystal device, thereby improving light utilization efficiency. That is, in the example shown in
FIG. 27
, a part of the incident light which is from the counter substrate
30
is intercepted by the second light-shielding film
7
and does not contribute to display. If the counter substrate
30
is formed with a microlens, however, light intercepted by the second light-shielding film
7
will enter the liquid crystal
39
, whereby the amount of light contributing to display is increased.
When the counter substrate
30
is formed with the microlens in this way, by forming the microlens in such a manner that an optical center position of the microlens is superimposed on the center positions
211
and
311
of the opening areas
21
and
31
of the active matrix substrate
20
and the counter substrate
30
, a decrease in the amount of light contributing to display can be avoided. Therefore, the liquid crystal device
1
which is highly reliable and is able to effect bright display can be formed.
In the thus-configured liquid crystal device
1
, as the alignment state of liquid crystal is schematically shown in
FIG. 28
, liquid crystal
39
is twist-aligned 90° between an active matrix substrate
20
and a counter substrate
30
. In order to show the directions of the substrates
20
and
30
, numerals corresponding to the time in a timepiece are assigned in FIG.
28
. In order to let the liquid crystal have such a twist of 90°, after forming polyimide layers and the like serving as alignment layers
46
and
47
on the surfaces of the substrates and
30
, rubbing treatment is applied to the pair of substrates in the directions perpendicular to each other, as rubbing directions are shown by an arrow A and an arrow and then the substrates
20
and
30
are bonded and the liquid crystal
39
is filled in a gap formed therebetween. As a result, the liquid crystal
39
is aligned with its major axis direction pointing in the rubbing directions of the alignment layers
46
and
47
, and the major axis direction of the liquid crystal
39
is twisted 90° between the pair of substrates
20
and
30
.
In the liquid crystal device
1
using the thus-twist-aligned liquid crystal
39
, contrast characteristics show directivity by the alignment state (the major axis direction and inclination of the major axis) of the liquid crystal
39
located in the middle of the substrates and
30
. That is, when the liquid crystal
39
is aligned as shown in
FIG. 28
, the contrast characteristics of the liquid crystal device
1
in the three o'clock-nine o'clock direction show characteristics of bilateral symmetry with respect to the six o'clock-twelve o'clock direction, as shown in FIG.
29
(A). In contrast, as shown in FIG.
29
(B), t
Inoue Ken
Saito Hiromi
Akkapeddi P. R.
Kim Robert H.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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