U.S. patent application number 10/368191 was filed with the patent office on 2004-01-15 for liquid crystal device and electronic device.
Invention is credited to Maeda, Tsuyoshi, Okamoto, Eiji, Okumura, Osamu, Seki, Takumi.
Application Number | 20040008300 10/368191 |
Document ID | / |
Family ID | 26361060 |
Filed Date | 2004-01-15 |
United States Patent
Application |
20040008300 |
Kind Code |
A1 |
Maeda, Tsuyoshi ; et
al. |
January 15, 2004 |
Liquid crystal device and electronic device
Abstract
When a backlight 15 is turned on in a dark environment, white
light emerging from the surface of a light guide plate 15b passes
through a polarizer 12 and a retardation film 14, enters the
interior of the liquid crystal cell, passes through openings of
reflective electrodes 7, and is introduced into a liquid crystal
layer 3. The light introduced into the liquid crystal layer 3
passes through a color filter 5, emerges from the liquid crystal
cell, and passes through the retardation film 13 and the polarizer
11 towards the exterior. In a lighted environment, the light
incident on the polarizer 11 passes through the liquid crystal
layer 3, is reflected by the reflective electrode 7, and passes
through the polarizer 11 again and is emitted towards the
exterior.
Inventors: |
Maeda, Tsuyoshi; (Suwa,
JP) ; Okamoto, Eiji; (Suwa, JP) ; Seki,
Takumi; (Suwa, JP) ; Okumura, Osamu; (Suwa,
JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Family ID: |
26361060 |
Appl. No.: |
10/368191 |
Filed: |
February 18, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10368191 |
Feb 18, 2003 |
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09402557 |
Oct 4, 1999 |
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6628357 |
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09402557 |
Oct 4, 1999 |
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PCT/JP99/00311 |
Jan 26, 1999 |
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Current U.S.
Class: |
349/114 |
Current CPC
Class: |
G02F 2203/02 20130101;
G02F 1/133531 20210101; G02F 1/133528 20130101; G02F 1/133626
20210101; G02F 1/133555 20130101; G02F 1/134309 20130101; G02F
1/13439 20130101; G02F 2203/09 20130101; G02F 1/133784 20130101;
G02F 1/1336 20130101; G02F 1/134336 20130101; G02F 1/133707
20130101; G02F 1/134318 20210101; G02F 1/133504 20130101; G02F
1/133638 20210101; G02F 1/133615 20130101; G02F 1/13363
20130101 |
Class at
Publication: |
349/114 |
International
Class: |
G02F 001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 4, 1998 |
JP |
10-023656 |
Jun 5, 1998 |
JP |
10-157622 |
Claims
1. A liquid crystal device comprising: a pair of first and second
transparent substrates; a liquid crystal layer disposed between the
first and second substrates; a transparent electrode formed on a
face of the first substrate, contacting the liquid crystal layer; a
reflective electrode formed on a face of the second substrate and
having an oblong slit, the face contacting the liquid crystal
layer; and an illumination unit provided on an another face of the
second substrate, away from the liquid crystal layer.
2. A liquid crystal device according to claim 1, wherein the
reflective electrode comprises a plurality of stripe electrodes at
a predetermined gap and the slit extends in the longitudinal
direction of the reflective electrode.
3. A liquid crystal device according to claim 2, wherein the
transparent electrode comprises a plurality of stripe electrodes at
a predetermined gap in the direction perpendicular to the
reflective electrode and the slit extends to a position facing the
gap between the transparent electrodes.
4. A liquid crystal device according to claim 2, wherein the slit
extends over a plurality of pixels.
5. A liquid crystal device according to claim 4, wherein the slit
extends to the exterior of the image display region.
6. A liquid crystal device according to claim 2, wherein a width of
the slit is substantially equal to the gap between the two
reflective electrodes.
7. A liquid crystal device according to claim 1, wherein a width of
the slit is 4 .mu.m or less.
8. A liquid crystal device according to claim 1, wherein an angle
.xi. between the alignment direction of the liquid crystal
molecule, which is substantially the center between the transparent
electrode and the reflective electrode, and the longitudinal
direction of the slit is in a range of
-60.degree..ltoreq..xi..ltoreq.60.degree..
9. A liquid crystal device according to claim 1, wherein an angle 8
between the alignment direction of a liquid crystal molecule in the
vicinity of the reflective electrode and the longitudinal direction
of the slit is in a range of
-30.degree..ltoreq..delta..ltoreq.30.degree..
10. A liquid crystal device according to claim 1, wherein the
device is in a dim or black state when not driven.
11. A liquid crystal device according to claim 1, wherein a shading
layer is formed on at least one of the face of the first substrate,
contacting the liquid crystal layer and the face of the second
substrate, contacting the liquid crystal layer, so as to at least
partly cover the gap between the reflective electrodes.
12. A liquid crystal device according to claim 1, further
comprising a first polarizer provided on said another face of the
first substrate, away from the liquid crystal layer; and at least
one first retardation film disposed between the first substrate and
the first polarizer.
13. A liquid crystal device according to claim 1, further
comprising a second polarizer disposed between the second substrate
and the illumination unit; and at least a second retardation film
disposed between the second substrate and the second polarizer.
14. A liquid crystal device according to claim 1, wherein the
reflective electrode contains 95% by weight or more of aluminum and
has a thickness of 10 nm to 40 nm.
15. A liquid crystal device according to claim 1, further
comprising a color filter provided between the reflective electrode
and the first substrate.
16. A liquid crystal device according to claim 1, further
comprising a diffuser provided on said another face of the first
substrate, away from the liquid crystal layer.
17. A liquid crystal device according to claim 1, wherein the
reflective electrode has irregularities.
18. A liquid crystal device according to claim 1, wherein the
reflective electrode comprises a composite of a reflective layer
and a transparent electrode layer.
19. An electronic apparatus comprising a liquid crystal device
according to claim 1.
20. A liquid crystal device comprising: a pair of first and second
transparent substrates; a liquid crystal layer disposed between the
first and second substrates; a transparent electrode formed on a
face of the first substrate, contacting the liquid crystal layer; a
reflective electrode formed on a face of the second substrate,
contacting the liquid crystal layer and comprising a transflective
layer; an illumination unit provided on an another face of the
second substrate, away from the liquid crystal layer; a first
polarizer provided on said another face of the first substrate,
away from the liquid crystal layer; at least one first retardation
film disposed between the first substrate and the first polarizer;
a second polarizer disposed between the second substrate and the
illumination unit; and at least a second retardation film disposed
between the second substrate and the second polarizer.
21. A liquid crystal device according to claim 20, wherein the
device is in a dim or black state when not driven.
22. A liquid crystal device according to claim 20, wherein a
shading layer is formed on at least one of the face of the first
substrate, contacting the liquid crystal layer and the face of the
second substrate, contacting the liquid crystal layer, so as to at
least partly cover the gap between the reflective electrodes.
23. A liquid crystal device according to claim 20, wherein the
reflective electrode contains 95% by weight or more of aluminum and
has a thickness of 10 nm to 40 nm.
24. A liquid crystal device according to claim 20, further
comprising a color filter provided between the reflective electrode
and the first substrate.
25. A liquid crystal device according to claim 20, further
comprising a diffuser provided on said another face of the first
substrate, away from the liquid crystal layer.
26. A liquid crystal device according to claim 20, wherein the
reflective electrode has irregularities.
27. A liquid crystal device according to claim 20, wherein the
reflective electrode comprises a composite of a reflective layer
and a transparent electrode layer.
28. An electronic apparatus comprising a liquid crystal device
according to claim 20.
29. A liquid crystal device comprising: a pair of first and second
transparent substrates; a liquid crystal layer disposed between the
first and second substrates; a plurality of reflective electrodes
with a predetermined gap formed on a face of the second substrate,
contacting the liquid crystal layer; a transparent electrode formed
on a face of the first substrate, contacting the liquid crystal
layer, and opposing to the reflective electrodes and gaps between
the reflective electrodes; and an illumination unit provided on an
another face of the second substrate, away from the liquid crystal
layer.
30. A liquid crystal device according to claim 29, wherein an angle
.phi. between the alignment direction of liquid crystal molecules,
which is substantially the center between the transparent electrode
and the reflective electrodes, and the longitudinal direction of
the reflective electrodes is in a range of
-60.degree..ltoreq..phi..ltoreq.60.degree..
31. A liquid crystal device according to claim 29, wherein an angle
.psi. between the alignment direction of liquid crystal molecules
in the vicinity of the reflective electrodes and the longitudinal
direction of the reflective electrodes is in a range of
-30.degree..ltoreq..psi..ltore- q.30.degree..
32. A liquid crystal device according to claim 29, further
comprising a first polarizer provided on said another face of the
first substrate, away from the liquid crystal layer; and at least
one first retardation film disposed between the first substrate and
the first polarizer.
33. A liquid crystal device according to claim 29, further
comprising a second polarizer disposed between the second substrate
and the illumination unit; and at least a second retardation film
disposed between the second substrate and the second polarizer.
34. A liquid crystal device according to claim 29, wherein each of
the reflective electrodes contains 95% by weight or more of
aluminum and has a thickness of 10 nm to 40 nm.
35. A liquid crystal device according to claim 29, further
comprising color filters provided between the reflective electrodes
and the first substrate.
36. A liquid crystal device according to claim 29, further
comprising a diffuser provided on said another face of the first
substrate, away from the liquid crystal layer.
37. A liquid crystal device according to claim 29, wherein the
reflective electrodes have irregularities.
38. A liquid crystal device according to claim 29, wherein each of
the reflective electrodes comprises a composite of a reflective
layer and a transparent electrode layer.
39. An electronic apparatus comprising a liquid crystal device
according to claim 29.
40. A liquid crystal device comprising: a transflective liquid
crystal panel comprising a pair of first and second transparent
substrates; a liquid crystal layer disposed between the first and
second substrates; a transparent electrode comprising a
transflective layer formed on a face of the first substrate,
contacting the liquid crystal layer; a reflective electrode formed
on a face of the second substrate, contacting the liquid crystal
layer; and an illumination unit provided on an another face of the
second substrate, away from the liquid crystal layer; and a driving
means for driving the transparent electrode and the reflective
electrode; wherein the liquid crystal panel is in a dim or black
state when not driven.
41. A liquid crystal device according to claim 40, further
comprising a first polarizer provided on said another face of the
first substrate, away from the liquid crystal layer; and at least
one first retardation film disposed between the first substrate and
the first polarizer.
42. A liquid crystal device according to claim 40, further
comprising a second polarizer disposed between the second substrate
and the illumination unit; and at least a second retardation film
disposed between the second substrate and the second polarizer.
43. A liquid crystal device according to claim 40, wherein the
reflective electrode contains 95% by weight or more of aluminum and
has a thickness of 10 nm to 40 nm.
44. A liquid crystal device according to claim 40, further
comprising a color filter provided between the reflective electrode
and the first substrate.
45. A liquid crystal device according to claim 40, further
comprising a diffuser provided on said another face of the first
substrate, away from the liquid crystal layer.
46. A liquid crystal device according to claim 40, wherein the
reflective electrode has irregularities.
47. A liquid crystal device according to claim 40, wherein the
reflective electrode comprises a composite of a reflective layer
and a transparent electrode layer.
48. An electronic apparatus comprising a liquid crystal device
according to claim 40.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates to the technical field of
liquid crystal devices. In particular, the present invention
relates to a structure of a liquid crystal device which can change
a display mode between a reflective mode and a transmissive mode,
and to an electronic device using the liquid crystal device.
[0003] 2. Background Art
[0004] Reflective liquid crystal devices consuming small amounts of
electrical power have been widely used in portable devices and
display sections in various apparatuses. Since, however, the
display is performed by external light, an image is not visible in
dark environments. Thus, some proposed liquid crystal devices use
external light in a lighted environment as in general reflective
liquid crystal devices, and an internal light source in dark
environments so as to maintain a visible state. As disclosed in
Japanese Patent Application Laid-Open Nos. 57-049271, 57-049271,
and 57-049271, each device has a polarizer, a transflector, and a
backlight, in that order, at the outer face, away from the viewer,
in a liquid crystal panel. The liquid crystal device performs
reflective display using external light reflected by the
transflector in a lighted environment, and transmissive display
using light from the backlight, which is turned on so as to
maintain a visible state, transmitted through the transflector in
dark environments.
[0005] Another liquid crystal device having improved brightness in
a reflective display mode is disclosed in Japanese Patent
Application Laid-Open No. 8-292413. The liquid crystal device has a
transflector, a polarizer, and a backlight, in that order, at the
outer face, away from the viewer, of the liquid crystal panel. The
device performs reflective display using external light reflected
by the transflector when the environment is light, and transmissive
display using light from the backlight, which is turned on so as to
maintain a visible state, transmitted through the polarizer and the
transflector. Since the polarizer is not provided between the
liquid crystal cell and the transflector, brighter display is
achieved in a reflective mode compared to the above-mentioned
liquid crystal devices.
[0006] In the liquid crystal device disclosed in Japanese Patent
Application Laid-Open No. 8-292413, however, a transparent
substrate is disposed between a liquid crystal layer and the
transflector; hence, problems, such as double imaging and blurred
imaging, occur.
[0007] Color liquid crystal display has been required with recent
development of portable devices and office automation devices.
Apparatuses using reflective liquid crystal devices also require
color display. In a combination of the liquid crystal device
disclosed in the above patent application with a color filter, the
transflector is arranged behind the liquid crystal panel. Thus, the
thick transparent substrate lies between the liquid crystal layer
with the color filter and the transflector, resulting in occurrence
of double imaging or blurred imaging due to parallax and
insufficient coloring.
[0008] In order to solve the problems, Japanese Patent Application
Laid-Open No. 9-258219 discloses a reflective color liquid crystal
device in which a reflector is disposed so as to come into contact
with the liquid crystal layer. This liquid crystal device, however,
cannot display visible images in dark environments.
[0009] In addition, Japanese Patent Application Laid-Open No.
7-318929 discloses a transflective liquid crystal device in which a
pixel electrode functioning as a transflective film is provided on
the inner face of the liquid crystal cell. Since this liquid
crystal device has a transflective film such as a metallic thin
film having fine defects including pinholes, dimples, and fine
openings, an oblique electric field which is generated on the
periphery of the defects and openings causes unsatisfactory
orientation of the liquid crystal, producing many technical
problems which inhibit high-quality image display. That is, a high
contrast and brightness are not achieved, and coloring due to
wavelength dispersion of light inevitably occurs both in a
reflective display mode and a transmissive display mode.
Furthermore, it is difficult to achieve both prevention of
brightness defects at the gap between pixel electrodes or an
improvement in contrast and an improvement in brightness in a
reflective display mode. Furthermore, the production process
requires addition of a particular step; hence, the device satisfies
with great difficulty a typical demand for reduction in production
cost in this technical field.
[0010] The present invention has been accomplished in view of the
above-mentioned problems and has an object to provide a
transflective liquid crystal device, which is changeably used both
in a reflective display mode and a transmissive display mode, does
not produce double imaging blurred imaging due to parallax, and can
display high-quality images, and to provide an electronic apparatus
using the liquid crystal device.
SUMMARY OF THE INVENTION
[0011] The object of the present invention is achieved by a first
liquid crystal device including a pair of first and second
transparent substrates; a liquid crystal layer disposed between the
first and second substrates; a transparent electrode formed on a
face of the first substrate, on the side of the liquid crystal
layer; a reflective electrode formed on a face of the second
substrate and having an oblong slit, the face contacting the liquid
crystal layer; and an illumination unit provided on another face of
the second substrate, on the opposite side of the liquid crystal
layer.
[0012] In accordance with the first liquid crystal device of the
present invention, the reflective electrode reflects external light
incident on the first substrate towards the liquid crystal layer in
a reflective display mode. Since the reflective electrode is
provided on the liquid crystal layer face of the second substrate,
no gap is substantially formed between the liquid crystal layer and
the reflective electrode and thus double imaging and blurred
imaging due to parallax do not occur. In a transmissive display
mode, illuminated light incident on the second substrate from the
illumination unit enters the liquid crystal layer through the
slits. Thus, the illuminated light enables bright display in dark
environments.
[0013] Since the reflective electrode has oblong slits, an oblique
electric field (hereinafter referred to as an "oblique electric
field due to the short sides of the slit") is applied to the liquid
crystal layer between the edges of each reflective electrode
defining short sides of a slit and opposingly disposed at a
relatively large distance (edges of each reflective electrode
opposing each other at each end of two long sides of a slit) and
the transparent electrode. An oblique electric field (hereinafter
referred to as an "oblique electric field due to the long sides of
the slit") is simultaneously applied to the liquid crystal layer
between edges of each reflective electrode defining long sides of a
slit and opposingly disposed at a relatively short distance (edges
of each reflective electrode opposing each other at each end of two
short sides of a slit) and the transparent electrode. The
components of the oblique electric field due to the short sides of
the slit and the same of the oblique electric field due to the long
sides of the slit are perpendicular to each other in the substrate
plane. When these two oblique electric fields interact with liquid
crystal molecules in the vicinity of the slit, the intensities of
these two oblique electric fields determine the direction of
movement of liquid crystal molecules. If the slit is a-square,
these two oblique electric fields are equivalent to each other.
Thus, the relationship between these intensities is reversed at
some positions. As a result, the directions of movement of liquid
crystal molecules are different at these positions, and
insufficient alignment of the liquid crystal appears as a
relatively large domain. That is, display defects occur in the
domain. Insufficient alignment is most noticeable when these two
oblique electric fields have the same intensity. If one is higher
than the other in a region, movement of liquid crystal molecules in
the region is controlled by the oblique electric field having a
higher intensity and thus becomes uniform. In the present
invention, the oblique electric field (the in-substrate-plane
component is parallel to the longitudinal direction of the slit)
due to the short sides of the slit is reduced in response to the
length of long sides of the slit. In contrast, the oblique electric
field (the in-substrate-plane component is perpendicular to the
longitudinal direction of the slit) due to the long sides of a slit
is relatively increased in response to the length of the short
sides of the slit. In the present invention, therefore, the oblique
electric field due to the long sides of the slit controls the
movement of liquid crystal molecules. Accordingly, insufficient
alignment is reduced in the vicinity of the slit and display
defects are reduced. Furthermore, electrical power consumed by the
liquid crystal device can be reduced by a reduced threshold
voltage, since the liquid crystal is partly driven using the
oblique electric field due to the long sides of the slit.
[0014] When a countermeasure is taken only for the oblique electric
field due to the long side of the slit, and no consideration is
given to the oblique electric field due to the short side of the
slit, overall insufficient alignment of the liquid crystal caused
by the oblique electric field can be reduced. Alternatively,
voluntary use of the oblique electric field (for example, setting
of various operational parameters for reducing adverse effects of
insufficient alignment of the liquid crystal caused by the oblique
electric field in practice or for satisfactorily driving of the
liquid crystal by the oblique electric field, setting of
specifications of constituents and parts, and device design)
facilitates satisfactory driving of the liquid crystal. If the slit
is square, countermeasures must be taken for two oblique electric
fields, resulting in very difficult design and production of the
liquid crystal device. Furthermore, voluntary use of these two
oblique electric fields is almost impossible in practice.
[0015] As materials for the reflective electrode, metals containing
aluminum as a primary component are used. Metals which can reflect
external visible light, such as chromium and silver, can also be
used without limitation. Since the reflective electrode has a
function of reflecting external light and a function of applying a
voltage to the liquid crystal, this device structure has advantages
in production and design and facilitates cost reduction compared to
a structure having independently formed reflective electrodes and
pixel electrodes.
[0016] Oblong slits can be readily formed by a photostep using a
resist, a development step, and then a peeling step. It means that
there is no need to increase the number of production processes
since the slits can be simultaneously formed when the reflective
electrodes are formed. The width of each slit is in a range of
preferably 0.01 .mu.m to 20 .mu.m, and is more preferably 1 .mu.m
to 5 .mu.m. Thus, a reflective display mode and a transmissive
display mode can be simultaneously achieved without deterioration
of image quality due to provision of the slit, since a viewer
cannot recognize such a structure. Preferably, the slit has an area
ratio of 5% to 30% with respect to the reflective electrode. Such a
ratio can moderate decreased brightness in a reflective display
mode, and achieves a transmissive display mode by light incident on
the liquid crystal layer via the slits of the reflective
electrodes.
[0017] The first liquid crystal device can be driven by various
conventional driving system, such as a passive matrix driving
system, a thin film transistor (TFT) active matrix driving system,
a thin film diode (TFD) active matrix driving system, or a segment
driving system.
[0018] In an embodiment of the first liquid crystal device in
accordance with the present invention, the reflective electrode
comprises a plurality of stripe electrodes at a predetermined gap
and the slit extends in the longitudinal direction of the
reflective electrode.
[0019] According to this embodiment, a countermeasure for the
oblique electric field caused by the long sides of the slit is
effective for the oblique electric field caused by gaps between the
reflective electrodes. Furthermore, the reflective electrodes and
the slits can be simultaneously formed, and the design of the mask
used in the formation can be simplified. Thus, this embodiment has
advantages in a structure, production, and design of the
device.
[0020] In this embodiment in which the stripe reflective electrodes
are formed in stripe, the transparent electrode may comprise a
plurality of stripe electrodes at a predetermined gap in the
direction perpendicular to the reflective electrode and the slit
may extend to a position facing the gap between the transparent
electrodes.
[0021] In such a structure, edges of each reflective electrode
defining short sides of each slit and opposingly disposed at a
relatively large distance lie in a position in which the
transparent electrode is not formed. That is, the edges lie distant
from a portion of the reflective electrode in which a voltage is
applied between the transparent electrode and the reflective
electrode. Thus, the effect of the oblique electric field due to
the short side of the slit can be significantly reduced.
[0022] In this embodiment in which the reflective electrodes are
formed in stripe, the slit may extend over a plurality of
pixels.
[0023] In such a structure, each pixel does not have edges of
reflective electrodes defining short sides of slits opposingly
disposed at a relatively large distance; hence, the effect of the
oblique electric field which is applied to the liquid crystal layer
between the edges of the reflective electrode and the transparent
electrode due to the short side (a shorter side is preferable) of
the slit can be significantly reduced.
[0024] In this case, the slit may extend to the exterior of the
image display region.
[0025] In such a structure, each pixel does not have edges of
reflective electrodes defining short sides of slits opposingly
disposed at a relatively large distance; hence, the effect of the
oblique electric field due to the short side (a shorter side is
preferable) of the slit can be almost completely reduced.
[0026] In this embodiment in which electrodes are formed in stripe,
the width of a slit may be substantially equal to a gap between
reflective electrodes.
[0027] In such a structure, a countermeasure for or voluntary use
of, the oblique electric field due to the long side of the slit is
also effective as a countermeasure for or voluntary use of, the
oblique electric field due to the gap between the reflective
electrodes. Furthermore, the slits can be simultaneously formed
when the reflective electrodes are formed and design of the
photomask is simplified; hence this structure has significant
advantages in production and design of the device. Herein
"substantially equal" means that the width of a slit is almost
equal to the gap between the reflective electrodes so that the
effect of the oblique electric field due to the long side of the
slit and the effect of the oblique electric field caused by the gap
between the reflective electrodes appear equally, or almost equal
enough that they can be formed utilizing photomasks having the same
width.
[0028] In another embodiment of the first liquid crystal device in
accordance with the present invention, the width of the slit is 4
.mu.m or less.
[0029] As a result of experiments and research by the present
inventors, the variation of the threshold voltage of the liquid
crystal with the width of the slit was elucidated. Specifically,
when the slit width is larger than 4 Am, the threshold voltage of
the liquid crystal significantly differs between the reflective
display mode and the transmissive display mode; hence, it is
difficult or impossible to set a driving voltage enabling a
satisfactory contrast and a variation of density in both display
modes. When the width of the slit is larger than 4 Am, a high
intensity electric field would likely be necessary to drive the
liquid crystal facing the slit. Since the width of the slit is 4
.mu.m or less in this embodiment, the threshold voltage of the
liquid crystal can be set to be substantially the same in both the
reflective display mode and the transmissive display mode. For
example, when the width of the slit is 2 .mu.m and the width of the
reflective electrode is 10 .mu.m, a driving voltage facilitating a
high contrast and a large change in density can be readily set.
[0030] In another embodiment of the first liquid crystal device in
accordance with the present invention, an angle .xi. between the
alignment direction of the liquid crystal molecule substantially in
the center between the transparent electrode and the reflective
electrode and the longitudinal direction of the slit is in a range
of -60.degree..ltoreq..xi..ltoreq.60.degree..
[0031] According to this embodiment, the angle between the
alignment direction of liquid crystal molecules, which lie
substantially in the center between the transparent electrode and
the reflective electrode and have the highest mobility, and the
longitudinal direction of the slit shifts by 30.degree. or more
from a right angle. Thus, when a voltage is applied between the
transparent electrode and the reflective electrode, the alignment
state of the liquid crystal molecules changes satisfactorily with
almost no formation of a tilt domain. Thus, the threshold voltage
during driving of the liquid crystal can be reduced, resulting in
reduced power consumption of the liquid crystal device.
Furthermore, display defects, such as disclination due to the tilt
domain in the liquid crystal layer, are avoidable. A significant
tilt domain is generated if the angle .xi. is outside the range of
-60.degree..ltoreq..xi..ltoreq.60.degree., because the alignment
direction of the liquid crystal molecules is perpendicular to the
longitudinal direction of the slit. Thus, the driving voltage
increases. The above advantage is particularly noticeable in a
range of -30.degree..ltoreq..xi..ltoreq.30.degree.. The tilt domain
is the same as the phenomenon described in "Liquid Crystal Device
Handbook", p. 254, edited by Committee 142 in Japan Society for the
Promotion of Science, and published by The Daily Industrial News.
The tilt domain in the present invention, however, is generated by
the direction of the applied voltage, not by the pretilt angle.
[0032] In another embodiment of the first liquid crystal device of
the present invention, an angle .xi. between the alignment
direction of a liquid crystal molecule in the vicinity of the
reflective electrode and the longitudinal direction of the slit is
in a range of -30.degree..ltoreq..xi..ltoreq.30.degree..
[0033] According to this embodiment, the alignment direction of the
liquid crystal molecule in the vicinity of the reflective electrode
having a predetermined pretilt angle is nearly parallel to, rather
than perpendicular to, the longitudinal direction of the slit.
Thus, there is substantially no possibility of the liquid crystal
molecule at the substrate interface being reverse-tilted by the
effect of the oblique electric field. Display defects such as
disclination due to the reverse tilt domain are, therefore,
avoidable. Thus, the threshold voltage during driving of the liquid
crystal can be reduced, resulting in reduced power consumption of
the liquid crystal device. If the angle .xi. is in a range outside
-30.degree..ltoreq..xi..ltoreq.30.degree., the liquid crystal
molecule at the substrate interface is noticeably reverse-titled by
the effect of the oblique electric field causing display defects.
Furthermore, the driving voltage increases, resulting in increased
power consumption. The above advantage is particularly noticeable
in a range of -10.degree..ltoreq..xi..ltoreq.10.degree..
[0034] In another embodiment of the first liquid crystal device in
accordance with the present invention, the device is in a dim or
black state when not driven.
[0035] Since the device is in a dim or black state when not driven
in this embodiment, optical leakage from boundaries between
non-driven liquid crystal pixels or dots can be reduced in a
transmissive display mode, resulting in transmissive display having
a high contrast. Furthermore, undesirable reflection at boundaries
between pixels or dots can be reduced in a reflective display mode,
resulting in a display having a high contrast.
[0036] In another embodiment of the first liquid crystal device in
accordance with the present invention, a shading layer is formed on
at least one of the face of the first substrate, on the side of the
liquid crystal layer and the face of the second substrate, on the
side of the liquid crystal layer, so as to at least partly cover
the gap between the reflective electrodes.
[0037] According to this embodiment, optical leakage from
boundaries between non-driven liquid crystal pixels or dots can be
reduced in a transmissive display mode, resulting in transmissive
display having a high contrast. Furthermore, undesirable reflection
at boundaries between pixels or dots can be reduced in a reflective
display mode, resulting in a display having a high contrast.
[0038] In another embodiment of the first liquid crystal device in
accordance with the present invention, the device further includes
a first polarizer provided on another face of the first substrate,
on the opposite side of the liquid crystal layer, and at least one
first retardation film disposed between the first substrate and the
first polarizer.
[0039] According to this embodiment, the first polarizer primarily
achieves satisfactory display control in both the reflective and
transmissive display modes, and the first retardation film
primarily reduces effects on tonality, such as coloring, due to the
wavelength dispersion of light.
[0040] In another embodiment of the first liquid crystal device in
accordance with the present invention, the device further includes
a second polarizer disposed between the second substrate and the
illumination unit, and at least a second retardation film disposed
between the second substrate and the second polarizer.
[0041] According to this embodiment, the second polarizer primarily
achieves satisfactory display control in the transmissive display
mode, and the second retardation film primarily reduces effects on
tonality, such as coloring, due to the wavelength dispersion of
light.
[0042] In another embodiment of the first liquid crystal device in
accordance with the present invention, the reflective electrode
contains 95% by weight or more of aluminum and has a thickness of
10 nm to 40 nm.
[0043] According to this embodiment, a thin transflective type
reflective electrode is formed. According to experiments, the
transflective reflective electrode has a transmittance of 1% to 40%
and a reflectance 50% to 95% within the above thickness range.
[0044] In another embodiment of the first liquid crystal device in
accordance with the present invention, the device further includes
a color filter provided between the reflective electrode and the
first substrate.
[0045] According to this embodiment, reflective color display by
external light and transmissive color display using an illumination
unit are available. Preferably, the color filter has a
transmittance of 25% or more for light of any wavelength within a
range of 380 nm to 780 nm. Bright reflective and transmissive color
display is thereby achieved.
[0046] In another embodiment of the first liquid crystal device in
accordance with the present invention, the device further includes
a diffuser on another face of the first substrate, on the opposite
side of the liquid crystal layer.
[0047] According to this embodiment, the diffuser makes the mirror
face of the reflective electrode look as a diffusing face (white
surface). Diffusion by the diffuser enables display with a wide
view angle. The diffuser may be disposed at any position above the
face of the first substrate, on the opposite side of the liquid
crystal layer. Preferably, the diffuser is disposed between the
polarizer and the first substrate in consideration of the effect of
back scattering (scattering of the external light towards the
incident side of it). The back scattering not contributing to the
display of the liquid crystal device causes a decreased contrast in
a reflective display mode. When the diffuser is disposed between
the polarizer and the first substrate, the polarizer can reduce the
quantity of light of back scattering to approximately one-half.
[0048] In another embodiment of the first liquid crystal device in
accordance with the present invention, the reflective electrode has
irregularities.
[0049] According to this embodiment, the irregularities eliminate
the mirroring on the face of the reflective electrode and make the
mirror face look as a diffusing face (white face). Diffusion by the
irregularities enables display with a wide view angle. The
irregularities may be formed by-forming a photosensitive acrylic
resin layer under the reflective electrode, or by roughening the
underlying glass substrate with aqueous hydrogen fluoride. It is
preferable in order to achieve satisfactory alignment of the liquid
crystals that a transparent planarization film be formed on the
irregular surface of the reflective electrode so that the surface
contacting the liquid crystal layer (the surface on which an
alignment film is formed) is planarized.
[0050] In another embodiment of the first liquid crystal device in
accordance with the present invention, the reflective electrode is
a composite of a reflective layer and a transparent electrode
layer.
[0051] According to this embodiment, even if the reflective
electrode with slits is not composed of a reflective and conductive
single film, the reflective electrode can be obtained by making the
reflective layer reflect external light, and the transparent
electrode layer apply a driving voltage to the liquid crystal.
[0052] The above-mentioned object of the present invention is also
achieved by a first electronic apparatus provided with the first
liquid crystal device.
[0053] The first electronic apparatus in accordance with the
present invention uses a transflective liquid crystal device or a
color transflective liquid crystal device without double imaging
and blurred imaging due to parallax, and can change a display mode
between a reflective mode and a transmissive mode. Thus, the
electronic apparatus can display high-quality images in any lighted
or dark environment regardless of the level of ambient or external
light.
[0054] The object of the present invention is also achieved by a
second liquid crystal device including a pair of first and second
transparent substrates; a liquid crystal layer disposed between the
first and second substrates; a transparent electrode formed on a
face of the liquid crystal layer side of the first substrate; a
reflective electrode formed on a face of the liquid crystal layer
side of the second substrate; an illumination unit provided on
another face of the second substrate, on the opposite side of the
liquid crystal layer; a first polarizer provided on another side of
the first substrate, on the opposite side of the liquid crystal
layer; at least one first retardation film disposed between the
first substrate and the first polarizer; a second polarizer
disposed between the second substrate and the illumination unit;
and at least a second retardation film disposed between the second
substrate and the second polarizer.
[0055] According to the second liquid crystal device of the present
invention, the reflective electrode reflects external light
incident on the first substrate towards the liquid crystal layer in
a reflective display mode. Since the reflective electrode is
provided on the face of the second substrate, contacting the liquid
crystal layer, no gap is substantially formed between the liquid
crystal layer and the reflective electrode. Thus, double imaging
and blurred imaging due to parallax do not occur. On the other
hand, the reflective electrode comprising a transflective layer
transmits light which emerges from the illumination unit and is
incident on the second substrate towards the liquid crystal layer
in a transmissive display mode. Thus, light from the light source
achieves bright display in a dark environment. The transflective
layer may be a reflective film having oblong slits or square fine
openings so that light partly passes through the film, as in the
above-mentioned first liquid crystal of the present invention, a
thin metal transflective film having fine defects, such as pinhole
defects or dimples, or a film which shows overall transflective
characteristics. Alternatively, the layer may be composed of a
plurality of stripes or island reflective electrodes formed with a
predetermined gap.
[0056] Since the second liquid crystal device has the first
polarizer, the first retardation film, the second polarizer, and
the second retardation film, the first and the second polarizers
satisfactorily control display in both the reflective and
transmissive display modes. The first retardation film reduces
effects on tonality, such as coloring, due to the wavelength
dispersion of light in a reflective display mode, whereas the
second retardation film reduces effects on tonality, such as
coloring, due to the wavelength dispersion of light in a
transmissive display mode. The second liquid crystal device can be
driven by various conventional driving system, such as a passive
matrix driving system, a TFT active matrix driving system, a TFD
active matrix driving system, or a segment driving system.
[0057] In an embodiment of the second liquid crystal device of the
present invention, the device is in a dim or black state when not
driven.
[0058] Since the device is in a dim or black state when not driven
in this embodiment, optical leakage from boundaries between
non-driven liquid crystal pixels or dots can be reduced in a
transmissive display mode, resulting in transmissive display having
a high contrast. Furthermore, undesirable reflection at boundaries
between pixels or dots can be reduced in a reflective display mode,
resulting in a display having a high contrast.
[0059] In another embodiment of the second liquid crystal device in
accordance with the present invention, a shading layer is formed on
at least one of the face of the first substrate, on the side of the
liquid crystal layer and the face of the second substrate,
contacting the liquid crystal layer so as to at least partly cover
the gap between the reflective electrodes.
[0060] According to this embodiment, optical leakage from
boundaries between non-driven liquid crystal pixels or dots can be
reduced in a transmissive display mode, resulting in transmissive
display having a high contrast. Furthermore, undesirable
reflection, which does not contribute to the display, at boundaries
between pixels or dots can be reduced in a reflective display mode,
resulting in a display having a high contrast.
[0061] In another embodiment of the second liquid crystal device in
accordance with the present invention, the reflective electrode
contains 95% by weight or more of aluminum and has a thickness of
10 nm to 40 nm.
[0062] According to this embodiment, a thin transflective type
reflective electrode is formed. According to experiments, the
transflective type reflective electrode has a transmittance of 1%
to 40% and a reflectance 50% to 95% within the above thickness
range.
[0063] In another embodiment of the second liquid crystal device in
accordance with the present invention, the device further includes
a color filter provided between the reflective electrode and the
first substrate.
[0064] According to this embodiment, reflective color display by
external light and transmissive color display using an illumination
unit are available. Preferably, the color filter has a
transmittance of 25% or more for light of any wavelength within a
range of 380 nm to 780 nm. Bright reflective and transmissive color
displays are thereby achieved.
[0065] In another embodiment of the second liquid crystal device in
accordance with the present invention, the device further includes
a diffuser on another face of the first substrate, on the opposite
side thereof the liquid crystal layer.
[0066] According to this embodiment, the diffuser makes the mirror
face of the reflective electrode look as a diffusing face (white
surface). Diffusion by the diffuser enables display with a wide
view angle. The diffuser may be disposed at any position above the
face of the first substrate, on the opposite side of the liquid
crystal layer. Preferably, the diffuser is disposed between the
polarizer and the first substrate in consideration of the effect of
back scattering (scattering of the external light towards the
incident side of it). The back scattering not contributing to the
display of the liquid crystal device causes a decreased contrast in
a reflective display mode. When the diffuser is disposed between
the polarizer and the first substrate, the polarizer can reduce the
quantity of light of back scattering to approximately one-half.
[0067] In another embodiment of the second liquid crystal device in
accordance with the present invention, the reflective electrode has
irregularities.
[0068] According to this embodiment, the irregularities eliminate
the mirroring on the face of the reflective electrode and render
the mirror face into a diffusing face (white face). Diffusion by
the irregularities enables display with a wide view angle. The
irregularities may be formed by forming a photosensitive acrylic
resin layer under the reflective electrode, or by roughening the
underlying glass substrate with aqueous hydrogen fluoride. It is
preferable in order to achieve satisfactory alignment of the liquid
crystals that a transparent planarization film be formed on the
irregular surface of the reflective electrode so that the surface
facing to the liquid crystal layer (the surface on which an
alignment film is formed) is planarized.
[0069] In another embodiment of the second liquid crystal device in
accordance with the present invention, the reflective electrode is
a composite of a reflective layer and a transparent electrode
layer.
[0070] According to this embodiment, the reflective layer reflects
external light, and the transparent electrode layer applies a
driving voltage to the liquid crystal even if the reflective
electrode is not composed of a reflective and conductive single
film.
[0071] The above-mentioned object of the present invention is also
achieved by a second electronic apparatus provided with the second
liquid crystal device.
[0072] The second electronic apparatus in accordance with the
present invention uses a transflective liquid crystal device or a
color transflective liquid crystal device without double imaging
and blurred imaging due to parallax, and can change a display mode
between a reflective mode and a transmissive mode. Thus, the
electronic apparatus can display high-quality images in any lighted
or dark environment regardless of the level of ambient or external
light.
[0073] The object of the present invention is also achieved by a
third liquid crystal device including a pair of first and second
transparent substrates; a liquid crystal layer disposed between the
first and second substrates; a plurality of reflective electrodes
with a predetermined gap formed on a face of the second substrate,
on the side of the liquid crystal layer; a transparent electrode
formed on a face of the first substrate, on the side of the liquid
crystal layer, and opposing to the reflective electrodes and gaps
between the reflective electrodes; and an illumination unit
provided on an another face of the second substrate, on the
opposite side of the liquid crystal layer.
[0074] According to the third liquid crystal device of the present
invention, the reflective electrode reflects external light
incident on the first substrate towards the liquid crystal layer in
a reflective display mode. Since the reflective electrode is
provided on the face of the second substrate, on the side of the
liquid crystal layer, no gap is substantially formed between the
liquid crystal layer and the reflective electrode. Thus, double
imaging and blurred imaging due to parallax do not occur. On the
other hand, light which is incident on the second substrate passes
through a gap between the reflective electrodes and is incident on
the liquid crystal layer in a transmissive display mode. Herein, an
oblique electric field generated between a portion of the
transparent electrode facing the gap between the reflective
electrodes, and the reflective electrode can drive the liquid
crystal. Thus, light from the light source which passes through the
gap between the reflective electrodes is driven by the oblique
electric field to facilitate bright display. Whitening by
non-driven liquid crystal portions facing the gap between the
reflective electrodes can be simultaneously prevented, and thus
display defects due to the gap between the reflective electrodes
can be reduced. Since covering the gap between the reflective
electrodes with a shading film (called a "black matrix" or a "black
mask") is not necessary, this structure has advantages in
production and design of the device.
[0075] The third liquid crystal device can be driven by various
conventional driving system, such as a passive matrix driving
system, a TFT active matrix driving system, a TFD active matrix
driving system, or a segment driving system. Thus, the reflective
electrodes may be composed of a plurality of stripe electrodes or a
plurality of rectangular electrodes depending on the applied
driving system.
[0076] The width of the gap between the reflective electrodes is in
a range of preferably 0.01 .mu.m to 20 .mu.m, and is more
preferably 1 .mu.m to 5 .mu.m. A reflective display mode and a
transmissive display mode can be simultaneously achieved without
deterioration of image quality due to provision of the gap, since a
viewer cannot recognize such a structure. Preferably, the gap has
an area ratio of 5% to 30% with respect to the reflective
electrode. Such a ratio can moderate decreased brightness in a
reflective display mode, and achieves a transmissive display mode
by light incident on the liquid crystal layer via the gap between
the reflective electrodes. In the transmissive display mode, bright
high-quality display by the liquid crystal at the gap portion is
achieved by increasing luminance of the light source in the
illumination unit, even if only a small portion of the overall
liquid crystal is driven by the oblique electric field.
[0077] In an embodiment of the third liquid crystal in accordance
with the present invention, a plurality of long reflective
electrodes is formed, and an angle .phi. between the alignment
direction of liquid crystal molecules, which lie substantially in
the center between the transparent electrode and the reflective
electrodes, and the longitudinal direction of the reflective
electrodes is in a range of -60.degree..ltoreq..phi..lt-
oreq.60.degree..
[0078] According to this embodiment, long reflective electrodes,
such as stripe- or rectangular-reflective electrodes, are formed,
and the angle between the alignment direction of liquid crystal
molecules, which lie substantially in the center between the
transparent electrode and the reflective electrode and have the
highest mobility, and the longitudinal direction of the reflective
electrode shifts by 30.degree. or more from a right angle. When a
voltage is applied between the transparent electrode and the
reflective electrode, the alignment state of the liquid crystal
molecules changes satisfactorily without formation of a tilt
domain. Thus, the threshold voltage during driving of the liquid
crystal can be reduced, resulting in reduced power consumption of
the liquid crystal device. Furthermore, display defects, such as
disclination, due to the tilt domain in the liquid crystal layer,
are avoidable. A significant tilt domain is generated if the angle
4 is outside the range of
-60.degree..ltoreq..phi..ltoreq.60.degree., because the alignment
direction of the liquid crystal molecules is perpendicular to the
longitudinal direction of the reflective electrode. Thus, the
driving voltage increases. The above advantage is particularly
noticeable in a range of
-30.degree..ltoreq..phi..ltoreq.30.degree..
[0079] In another embodiment of the third liquid crystal device of
the present invention, an angle .psi. between the alignment
direction of a liquid crystal molecule in the vicinity of the
reflective electrode and the longitudinal direction of the
reflective electrode is in a range of
-30.degree..ltoreq..psi..ltoreq.30.degree..
[0080] According to this embodiment, the alignment direction of the
liquid crystal molecule in the vicinity of the reflective electrode
having a predetermined pretilt angle is nearly parallel to, rather
than perpendicular to, the longitudinal direction of the reflective
electrode. Thus, there is substantially no possibility of the
liquid crystal molecule at the substrate interface being
reverse-tilted by the effect of the oblique electric field. Display
defects such as disclination due to the reverse tilt domain are,
therefore, avoidable. Thus, the threshold voltage during driving of
the liquid crystal can be reduced, resulting in reduced power
consumption of the liquid crystal device. If the angle .psi. is in
a range outside -30.degree..ltoreq..psi..ltoreq.30.degree., the
liquid crystal molecule at the substrate interface is noticeably
reverse-titled by the effect of the oblique electric field to cause
display defects. Furthermore, the driving voltage increases,
resulting in increased power consumption. The above advantage is
particularly noticeable in a range of
-10.degree..ltoreq..psi..ltoreq.10.degree..
[0081] In another embodiment of the third liquid crystal device in
accordance with the present invention, the device further includes
a first polarizer provided on another face of the first substrate,
away from the liquid crystal layer, and at least one first
retardation film disposed between the first substrate and the first
polarizer.
[0082] According to this embodiment, the first polarizer primarily
achieves satisfactory display control in both the reflective and
transmissive display modes, and the first retardation film
primarily reduces effects on tonality, such as coloring, due to the
wavelength dispersion of light.
[0083] In another embodiment of the third liquid crystal device in
accordance with the present invention, the device further includes
a second polarizer disposed between the second substrate and the
illumination unit, and at least a second retardation film disposed
between the second substrate and the second polarizer.
[0084] According to this embodiment, the second polarizer primarily
achieves satisfactory display control in the transmissive display
mode, and the second retardation film primarily reduces effects on
tonality, such as coloring, due to the wavelength dispersion of
light.
[0085] In another embodiment of the third liquid crystal device in
accordance with the present invention, the reflective electrode
contains 95% by weight or more of aluminum and has a thickness of
10 nm to 40 nm.
[0086] According to this embodiment, a thin transflective type
reflective electrode is formed. According to experiments, the
transflective type reflective electrode has a transmittance of 1%
to 40% and a reflectance 50% to 95% within the above thickness
range.
[0087] In another embodiment of the third liquid crystal device in
accordance with the present invention, the device further includes
a color filter provided between the reflective electrode and the
first substrate.
[0088] According to this embodiment, reflective color display by
external light and transmissive color display using an illumination
unit are available. Preferably, the color filter has a
transmittance of 25% or more for light of any wavelength within a
range of 380 nm to 780 nm. Bright reflective and transmissive color
displays are thereby achieved.
[0089] In another embodiment of the third liquid a crystal device
in accordance with the present invention, the device further
includes a diffuser on another face of the first substrate, on the
opposite side of the liquid crystal layer.
[0090] According to this embodiment, the diffuser makes the mirror
face of the reflective electrode look as a diffusing face (white
surface). Diffusion by the diffuser enables display from a wide
view angle. The diffuser may be disposed at any position above the
face of the first substrate, on the opposite side of the liquid
crystal layer. Preferably, the diffuser is disposed between the
polarizer and the first substrate in consideration of the effect of
back scattering (scattering of external light towards the incident
side of it). The back scattering not contributing to the display of
the liquid crystal device causes a decreased contrast in a
reflective display mode. When the diffuser is disposed between the
polarizer and the first substrate, the polarizer can reduce the
quantity of light of back scattering to approximately one-half.
[0091] In another embodiment of the third liquid crystal device in
accordance with the present invention, the reflective electrode has
irregularities.
[0092] According to this embodiment, the irregularities eliminate
the mirroring on the face of the reflective electrode and render
the mirror face into a diffusing face (white face). Diffusion by
the irregularities enables display with a wide view angle. The
irregularities may be formed by forming a photosensitive acrylic
resin layer under the reflective electrode, or by roughening the
underlying glass substrate with aqueous hydrogen fluoride. It is
preferable in order to achieve satisfactory alignment of the liquid
crystals that a transparent planarization film be formed on the
irregular surface of the reflective electrode so that the surface
facing the liquid crystal layer (the surface on which an alignment
film is formed) is planarized.
[0093] In another embodiment of the third liquid crystal device in
accordance with the present invention, the reflective electrode is
a composite of a reflective layer and a transparent electrode
layer.
[0094] According to this embodiment, the reflective layer of the
transflective electrode reflects external light, and the
transparent electrode layer applies a driving voltage to the liquid
crystal even if the reflective electrode is not composed of a
reflective and conductive single film.
[0095] The above-mentioned object of the present invention is also
achieved by a third electronic apparatus provided with the third
liquid crystal device.
[0096] The third electronic apparatus in accordance with the
present invention uses a transflective liquid crystal device or a
color transflective liquid crystal device without double imaging
and blurred imaging due to parallax, and can change a display mode
between a reflective mode and a transmissive mode. Thus, the
electronic apparatus can display high-quality images in any lighted
or dark environment regardless of the level of ambient or external
light.
[0097] The object of the present invention is also achieved by a
fourth liquid crystal device including (i) a transflective liquid
crystal panel comprising a pair of first and second transparent
substrates; a liquid crystal layer disposed between the first and
second substrates; a transparent electrode formed on a face of the
first substrate facing the liquid crystal layer; a reflective
electrode formed on a face of the second substrate facing the
liquid crystal layer; and an illumination unit provided on an
another face of the second substrate, on the opposite side of the
liquid crystal layer; and (ii) a driving means for driving the
transparent electrode and the reflective electrode; wherein the
liquid crystal panel is in a dim or black state when not
driven.
[0098] According to the fourth liquid crystal device of the present
invention, the reflective electrode reflects external light
incident on the first substrate towards the liquid crystal layer in
a reflective display mode. Since the reflective electrode is
provided on the face of the second substrate facing the liquid
crystal layer, no gap is substantially formed between the liquid
crystal layer and the reflective electrode. Thus, double imaging
and blurred imaging due to parallax do not occur. On the other
hand, the reflective electrode comprising a transflective layer
transmits light which emerges from the illumination unit and is
incident on the second substrate towards the liquid crystal layer
in a transmissive display mode. Thus, light from the light source
achieves bright display in a dark environment. The transflective
layer may be a reflective film having oblong slits or square fine
openings so that light partly passes through the film, as in the
above-mentioned first liquid crystal of the present invention, a
thin metal transflective film having fine defects, such as pinhole
defects or dimples, or a film which shows overall transflective
characteristics. Alternatively, the layer may be composed of a
plurality of stripes or island reflective electrodes formed with a
predetermined gap.
[0099] In the fourth liquid crystal device, the liquid crystal
panel driven between the transparent electrode and the reflective
electrode by a driving means is a dim state when not driven. That
is, it is driven by a normally black mode. Thus, optical leakage
from boundaries between non-driven liquid crystal pixels or dots
can be reduced in a transmissive display mode, resulting in
transmissive display having a high contrast. Furthermore,
undesirable reflection at boundaries between pixels or dots can be
reduced in a reflective display mode, resulting in a display having
a high contrast. Accordingly, an improved contrast is achieved in
both a transmissive display mode and a reflective display mode
without covering the gap between the reflective electrodes with a
shading film (called a "black matrix" or a "black mask"). Since no
shading film is provided, brightness does not decrease in a
reflective display mode.
[0100] The fourth liquid crystal device can be driven by various
conventional driving system, such as a passive matrix driving
system, a TFT active matrix driving system, a TFD active matrix
driving system, or a segment driving system.
[0101] In another embodiment of the fourth liquid crystal device in
accordance with the present invention, the device further includes
a first polarizer provided on another face of the first substrate,
on the opposite side of the liquid crystal layer, and at least one
first retardation film disposed between the first substrate and the
first polarizer.
[0102] According to this embodiment, the first polarizer primarily
achieves satisfactory display control in both the reflective and
transmissive display modes, and the first retardation film
primarily reduces effects on tonality, such as coloring, due to the
wavelength dispersion of light.
[0103] In another embodiment of the fourth liquid crystal device in
accordance with the present invention, the device further includes
a second polarizer disposed between the second substrate and the
illumination unit, and at least a second retardation film disposed
between the second substrate and the second polarizer.
[0104] According to this embodiment, the second polarizer primarily
achieves satisfactory display control in the transmissive display
mode, and the second retardation film primarily reduces effects on
tonality, such as coloring, due to the wavelength dispersion of
light.
[0105] In another embodiment of the fourth liquid crystal device in
accordance with the present invention, the reflective electrode
contains 95% by weight or more of aluminum and has a thickness of
10 nm to 40 nm.
[0106] According to this embodiment, a thin transflective type
reflective electrode is formed. According to experiments, the
transflective type reflective electrode has a transmittance of 1%
to 40% and a reflectance 50% to 95% within the above thickness
range.
[0107] In another embodiment of the fourth liquid crystal device in
accordance with the present invention, the device further includes
a color filter provided between the reflective electrode and the
first substrate.
[0108] According to this embodiment, reflective color display by
external light and transmissive color display using an illumination
unit are available. Preferably, the color filter has a
transmittance of 25% or more for light of any wavelength within a
range of 380 nm to 780 nm. Bright reflective and transmissive color
display is thereby achieved.
[0109] In another embodiment of the fourth liquid crystal device in
accordance with the present-invention, the device further includes
a diffuser on another face of the first substrate, on the opposite
side of the liquid crystal layer.
[0110] According to this embodiment, the diffuser makes the mirror
face of the reflective electrode a diffusing face (white surface).
Diffusion by the diffuser enables display with a wide view angle.
The diffuser may be disposed at any position above the face of the
first substrate, on the opposite side of the liquid crystal layer.
Preferably, the diffuser is disposed between the polarizer and the
first substrate in consideration of the effect of back scattering
(scattering of external light towards the incident side of it). The
back scattering not contributing to the display of the liquid
crystal device causes a decreased contrast in a reflective display
mode. When it is disposed between the polarizer and the first
substrate, the polarizer can reduce the quantity of light of back
scattering to approximately one-half.
[0111] In another embodiment of the fourth liquid crystal device in
accordance with the present invention, the reflective electrode has
irregularities.
[0112] According to this embodiment, the irregularities eliminate
the mirroring on the face of the reflective electrode and render
the mirror face into a diffusing face (white face). Diffusion by
the irregularities enables display with a wide view angle. The
irregularities may be formed by forming a photosensitive acrylic
resin layer under the reflective electrode, or by roughening the
underlying glass substrate with aqueous hydrogen fluoride. It is
preferable in order to achieve satisfactory alignment of the liquid
crystals that a transparent planarization film be formed on the
irregular surface of the reflective electrode so that the surface
facing to the liquid crystal layer (the surface on which an
alignment film is formed) is planarized.
[0113] In another embodiment of the fourth liquid crystal device in
accordance with the present invention, the reflective electrode is
a composite of a reflective layer and a transparent electrode
layer.
[0114] According to this embodiment, the reflective layer of the
transflective electrode reflects external light, and the
transparent electrode layer applies a driving voltage to the liquid
crystal even if the reflective electrode is not composed of a
reflective and conductive single film.
[0115] The above-mentioned object of the present invention is also
achieved by a fourth electronic apparatus provided with the fourth
liquid crystal device.
[0116] The fourth electronic apparatus in accordance with the
present invention uses a transflective liquid crystal device or a
color transflective liquid crystal device without double imaging
and blurred imaging due to parallax, and can change a display mode
between a reflective mode and a transmissive mode. Thus, the
electronic apparatus can display high-quality images in any lighted
or dark environment regardless of the level of ambient or external
light.
BRIEF DESCRIPTION OF THE DRAWINGS
[0117] FIG. 1a is a longitudinal cross-sectional view of an outline
structure in a first embodiment and a second embodiment of a liquid
crystal device in accordance with the present invention.
[0118] FIG. 1b is a plan view of an outline structure in the first
embodiment and the second embodiment.
[0119] FIG. 2 includes a schematic illustration of the relationship
among a polarizer, a retardation film, and a rubbing direction of a
liquid crystal cell, and a characteristic graph between the driving
voltage and the reflectance R/transmittance T in the liquid crystal
device.
[0120] FIG. 3 is an enlarged cross-sectional view of an outline
structure of a second transparent substrate in a third embodiment
of a liquid crystal device in accordance with the present
invention.
[0121] FIG. 4 is a longitudinal cross-sectional view of an outline
structure in a fourth embodiment of a liquid crystal device in
accordance with the present invention.
[0122] FIG. 5a is a longitudinal cross-sectional view of an outline
structure in a fifth embodiment of a liquid crystal device in
accordance with the present invention.
[0123] FIG. 5b is a plan view of an outline structure in a fifth
embodiment of a liquid crystal device in accordance with the
present invention.
[0124] FIG. 6 is a plan view of a reflective electrode provided
with slits in a sixth embodiment of a liquid crystal device in
accordance with the present invention.
[0125] FIG. 7 is a plan view of another reflective electrode
provided with slits in the sixth embodiment.
[0126] FIG. 8 is a plan view of still another reflective electrode
provided with slits in the sixth embodiment.
[0127] FIG. 9 is a plan view of a further reflective electrode
provided with slits in the sixth embodiment.
[0128] FIG. 10 is a plan view of a still further reflective
electrode provided with slits in the sixth embodiment.
[0129] FIG. 11 is a plan view of another reflective electrode
provided with slits in the sixth embodiment.
[0130] FIG. 12 is a plan view of still another reflective electrode
provided with slits in the sixth embodiment.
[0131] FIG. 13 is a conceptual view for illustrating the alignment
direction of a liquid crystal in the center between substrates in a
seventh embodiment and a ninth embodiment in accordance with the
present invention.
[0132] FIG. 14 is a longitudinal cross-sectional view of an outline
liquid crystal device in an eighth embodiment in accordance with
the present invention.
[0133] FIG. 15 is a plan view of a reflective electrode structure
in the eighth embodiment.
[0134] FIG. 16 is a plan view of another reflective electrode
structure in the eighth embodiment.
[0135] FIG. 17 is a plan view of still another reflective electrode
structure in the eighth embodiment.
[0136] FIG. 18 is a plan view of a further reflective electrode
structure in the eighth embodiment.
[0137] FIG. 19 is a table showing contrasts in a reflective display
mode and a transmissive display mode when the angle .phi. is varied
in a ninth embodiment in accordance with the present invention.
[0138] FIG. 20 is a table showing contrasts in a reflective display
mode and a transmissive display mode when the angle .psi. is varied
in the ninth embodiment.
[0139] FIG. 21a is a schematic plan view of a TFD driving element
and a pixel electrode in a tenth embodiment in accordance with the
present invention.
[0140] FIG. 21b is a cross-sectional view taken along line B-B' in
FIG. 21a.
[0141] FIG. 22 is an equivalent circuit diagram of a liquid crystal
device and a driving circuit in the tenth embodiment.
[0142] FIG. 23 is a partially broken isometric view for
schematically showing the liquid crystal device in the tenth
embodiment.
[0143] FIG. 24 is an equivalent circuit diagram of various elements
and lead lines in a plurality of pixels formed in a matrix which
constitutes an image display region in a liquid crystal device in
an eleventh embodiment in accordance with the present
invention.
[0144] FIG. 25 is a plan view of a plurality of adjacent pixels on
a transparent substrate provided with data lines, scanning lines
and pixel electrodes in the eleventh embodiment.
[0145] FIG. 26 is a cross-sectional view taken along line C-C' in
FIG. 25.
[0146] FIG. 27 is a graph showing transmittance of individual color
layers in a color filter in the first or fifth embodiment.
[0147] FIG. 28 includes outline isometric views of various
electronic apparatuses in a twelfth embodiment in accordance with
the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0148] A best mode in each embodiment for carrying out the present
invention will now be described with reference to the drawings.
[0149] A first embodiment of a liquid crystal device in accordance
with the present invention will be described with reference to
FIGS. 1a and 1b. FIG. 1a is a longitudinal cross-sectional view of
an outline structure in the first embodiment of the present
invention. FIG. 1b is an outline plan view of the first embodiment
shown in FIG. 1a. In FIG. 1b, a color filter and a black matrix
layer shown in FIG. 1a are omitted so that the electrode
arrangement is readily visible, and only three vertical and three
horizontal stripe electrodes are depicted, although many stripe
electrodes are provided in an actual liquid crystal device.
Although the first embodiment fundamentally relates to a passive
matrix liquid crystal device, it is also applicable to an active
matrix device, a segment-type device, and other types of liquid
crystal devices.
[0150] As shown in FIGS. 1a and 1b, in the first embodiment, a
liquid crystal cell is formed in which a liquid crystal layer 3 is
disposed between two transparent substrates 1 and 2 and sealed by a
sealing frame 4. The liquid crystal layer 3 is composed of a
nematic liquid crystal having a predetermined twist angle. A color
filter 5 is formed on an inner surface of the front transparent
substrate 1, and the color filter 5 is provided with three red (R),
green (G), and blue (B) coloring layers which are arranged in a
predetermined pattern. The surface of the color filter 5 is covered
with a transparent protective film 10, and a plurality of stripe
transparent electrodes 6 composed of, for example, indium tin oxide
(ITO) is formed on the surface of the protective film 10. An
alignment film 9 is formed on the transparent electrodes 6, and is
previously subjected to rubbing treatment in a predetermined
direction.
[0151] A plurality of stripe reflective electrodes 7, which is
formed corresponding to coloring layers of the color filter 5, is
arranged on the inner face of the rear transparent substrate 2 so
as to cross the transparent electrodes 6. In an active matrix
device provided with TFD elements and TFT elements, each reflective
electrode 7 is rectangular, and is connected to a lead line through
an active element. The reflective electrode 7 is composed of
chromium or aluminum, and has a reflective surface which reflects
light incident on the transparent substrate 1. An alignment film 19
is formed on the reflective electrode 7 as described above. Each
reflective electrode 7 has many openings 7b having a diameter of 2
.mu.m (see FIG. 1b), and the openings 7b have a total area
corresponding to approximately 10% of the total area of the
reflective electrode 7.
[0152] A polarizer 11 is disposed above the outer face of the front
transparent substrate 1, and a retardation film 13 is disposed
between the polarizer 11 and the transparent electrode 1. At the
rear side of the liquid crystal cell, a retardation film 14 is
provided behind the transparent substrate 2, and a polarizer 12 is
provided behind the retardation film 14. A backlight 15 provided
with a fluorescent tube 15a emitting white light and a light guide
plate 15b having an incident end face along the fluorescent tube
15a is arranged behind the polarizer 12. The light guide plate 15b
is composed of a transparent body, such as an acrylic resin plate,
having an entire rough surface for scattering or a printed layer
for scattering. It receives light from the fluorescent tube 15a as
a light source at the end face, and emerges substantially uniform
light from the top face in the drawing. Examples of other usable
backlights include a light emitting diode (LED) and an
electroluminescent (EL) lamp.
[0153] In the first embodiment, a black matrix layer 5a as a
shading layer is formed between two coloring layers of the color
filter 5 in such manner that the black matrix layer 5a is provided
substantially corresponding to the region 7a, when viewing from the
top, between two reflective electrodes 7, so that the black matrix
layer prevents optical leakage from the region 7a in a transmissive
display mode. The black matrix layer 5a is formed of a coated
chromium layer or a photosensitive black resin layer.
[0154] The operation of the first embodiment having the above
structure will now be described.
[0155] First, a reflective display mode will be described. External
light, in FIG. 1, transmitted through the polarizer 11, the
retardation film 13, the color filter 5, and then passing through
the liquid crystal layer 3, is reflected by each reflective
electrode 7, and emerges again from the polarizer 11. The polarizer
11 is controlled to a transmissive state (lighted state), an
absorbed state (dim state), or an intermediate brightness state
therebetween in response to a voltage applied to the liquid crystal
layer 3.
[0156] Next, a transmissive display mode will be described. Light
from the backlight 15 is converted to a predetermined polarized
light beam by the polarizer 12 and the retardation film 14, enters
the liquid crystal layer 3 through openings 7b of each reflective
electrode 7, passes though the liquid crystal layer 3, and then is
transmitted through the color filter 5 and the retardation film 13.
Brightness of the polarizer 11 is controlled to a transmissive
state (lighted state), an absorbed state (dim state), or an
intermediate state therebetween in response to a voltage applied to
the liquid crystal layer 3.
[0157] This embodiment can provide a color liquid crystal device
without double imaging and blurred imaging, and which can change a
display mode between a reflective mode and a transmissive mode.
[0158] In the first embodiment, the polarizer 11 as a first
polarizer, the retardation film 13 as a first retardation film, the
polarizer 12 as a second polarizer, and the retardation film 14 as
a second retardation film, are provided; hence, the polarizers 11
and 12 can satisfactorily control display in both the reflective
display mode and the transmissive display mode. The retardation
film 13 moderates effects on tonality such as coloring due to
wavelength dispersion of light in the reflective display mode (the
retardation film 13 optimizes display in the reflective mode).
Also, the retardation film 14 moderates effects on tonality such as
coloring due to wavelength dispersion of light in the transmissive
display mode (the retardation film 14 optimizes display in the
transmissive mode, under the condition of the optimization by the
retardation film 13 in the reflective display mode). Although one
retardation film is used in this embodiment regarding each of the
retardation film 13 and the retardation film 14, a plurality of
retardation films may be provided at positions for correcting
coloring of the liquid crystal cell and for correcting the view
angle. Use of a plurality of retardation films further facilitates
optimization of correction of the coloring and the view angle.
[0159] The openings 7b provided in each reflective electrode 7 in
the first embodiment are composed of square fine openings or oblong
slits which are regularly arranged in the plane of the reflective
electrode 7, or composed of fine defects, such as pinholes and
dimples, dotted in the reflective electrode 7. These openings
transmit light. The structure of such openings 7b will be described
in subsequent sixth to eighth embodiments in detail with reference
to FIGS. 7 to 11, and thus detailed description is omitted in this
embodiment.
[0160] Transmissive display is performed by light emerging from the
backlight 15 through the openings 7b provided in the reflective
electrode 7 in the first embodiment. Also, in a structure for
performing transmissive display in which light is introduced
through openings 7a in the reflective electrode 7 (see the
thirteenth embodiment described below), a combination of a
polarizer 11 with a retardation film 13 and a combination of a
polarizer 12 and a retardation film 14 can provide satisfactory
display in a reflective display mode and a transmissive display
mode, respectively, and can moderate coloring due to wavelength
dispersion of light.
[0161] A second embodiment of a liquid crystal device in accordance
with the present invention will now be described with reference to
FIGS. 1a and 1b. The fundamental structure in the second embodiment
is the same as that in the first embodiment. In the second
embodiment, materials for and properties of the liquid crystal, the
reflective electrode, the alignment film, and the polarizer are
specifically limited. Although the second embodiment fundamentally
relates to a passive matrix liquid crystal display device, it is
also applicable to an active matrix device, a segment-type device,
and other types of liquid crystal devices.
[0162] With reference to FIGS. 1a and 1b, in the second embodiment,
rubbing treatment in a predetermined direction is performed on the
alignment film 9 formed on the transparent electrode 6 so that
liquid crystal molecules in the liquid crystal layer 3 have a
pretilted angle of approximately 85 degrees in the rubbing
direction. The above-described alignment film 19 is formed on the
reflective electrode 7, but is not subjected to rubbing treatment.
As the reflective electrode 7, a metal film with a thickness of 25
nm is used in which aluminum containing 1.0 percent by weight of
neodymium is sputtered. The aluminum used has a purity of 95
percent by weight, and the thickness is set to be in a range of 10
nm to 40 nm. Such a reflective electrode 7 may also be used in the
first embodiment. Quarter-wavelength plates are used as retardation
films 13 and 14.
[0163] In the second embodiment, the polarization axes P1 and P2 of
the polarizers 11 and 12 are set in the same direction, as shown in
FIG. 2(a). The slow axes C1 and C2 of the retardation films 13 and
14 (the quarter-wavelength plates) are set in the direction
rotating clockwise by .theta.=45 degrees from the polarization axes
P1 and P2 of the polarizers 11 and 12, respectively. The rubbing
direction R1 of the alignment film 9 on the inner face of the
transparent substrate 1 also agrees with the slow axes C1 and C2 of
the retardation films 13 and 14 (the quarter-wavelength plates).
The rubbing direction R1 determines the tilted direction of the
liquid crystal layer 3 when a voltage is applied. A nematic liquid
crystal having negative 2 is used as the liquid crystal layer
3.
[0164] FIG. 2(b) shows a driving voltage versus a reflectance R
relationship in a reflective display mode and a driving voltage
versus a transmittance T relationship in a transmissive display
mode in the second embodiment. The display state when no voltage is
applied is dim or black. That is, the liquid crystal device is
driven by a normally black mode. Since such a driving mode
suppresses optical leakage and unnecessarily reflected light from a
gap 7a between reflective electrodes 7 with respect to a non-driven
liquid crystal, formation of a black matrix layer 5a is
unnecessary.
[0165] The operation of the second embodiment having the above
structure will now be described.
[0166] First, a reflective display mode will be described. External
light, in FIG. 1, is transmitted through the polarizer 11, the
retardation film 13, and the color filter 5, then passing through
the liquid crystal layer 3, and is reflected by each reflective
electrode 7, and still further emerges from the polarizer 11.
Brightness of the polarizer 11 is controlled to a transmissive
state (lighted state), an absorbed state (dim state), or an
intermediate state therebetween in response to a voltage applied to
the liquid crystal layer 3.
[0167] Next, a transmissive display mode will be described. Light
from the backlight 15 is converted into a predetermined polarized
light beam by the polarizer 12 and the retardation film 14
(circularly polarized light, elliptically polarized light, or
linearly polarized light), enters the liquid crystal layer 3
through openings 7b of each reflective electrode 7, and passes
though the liquid crystal layer 3, then is transmitted through the
color filter 5 and the retardation film 13, respectively.
Brightness of the polarizer 11 is controlled to a transmissive
state (lighted state), an absorbed state (dim state), or an
intermediate state therebetween in response to a voltage applied to
the liquid crystal layer 3.
[0168] This embodiment can provide a color liquid crystal device
without double imaging and blurred imaging, and which can change a
display mode between a reflective mode and a transmissive mode.
[0169] A third embodiment of a liquid crystal device in accordance
with the present invention will now be described with reference to
FIG. 3. FIG. 3 is an enlarged cross-sectional view of a structure
on the inner face of a transparent substrate in the third
embodiment.
[0170] In the third embodiment, as shown in FIG. 3, a reflective
electrode 17 is provided in place of the reflective electrode 7 in
the first embodiment, and other structures are the same as those in
the first embodiment. Although the third embodiment fundamentally
relates to a passive matrix liquid crystal device, it is also
applicable to an active matrix device, a segment-type device, and
other types of liquid crystal devices.
[0171] In the third embodiment, the reflective electrode 17 is
provided with irregularities having a height of, for example,
approximately 0.8 .mu.m. The irregularities remove the mirror face
of the reflective electrode 17 and impart a scattering face (a
white face) thereto. Scattering caused by the irregularities
permits display with a wider view angle.
[0172] A method for making the reflective electrode 17 will now be
described.
[0173] A photosensitive resist for the reflective electrode 17 is
applied to the inner face of the transparent substrate 2 shown in
FIG. 1 by spin coating or the like, and is exposed to light in
which the amount of the light is adjusted by a mask having fine
openings. The photosensitive resist is fired, if necessary, and is
developed. Portions corresponding to the openings of the mask are
selectively removed by the development to form a supporting layer
16 having a wavy cross-sectional shape as shown in the drawing. A
wavy cross-sectional shape as in the supporting layer 16 shown in
the drawing may be formed by selective removing or remaining at the
portions corresponding to the openings of the mask by the
photolithographic process, and then by smoothing the irregular
shape by etching or heating. Alternatively, another layer may be
deposited on the surface of the formed supporting layer to smooth
the surface.
[0174] Next, a metallic thin film is vapor-deposited on the surface
of the supporting layer 16 by sputtering or the like to form a
reflective electrode 17 with a reflective surface. Examples of
metals used include Al, CrAg, and Au. Since the shape of the
reflective electrode 17 reflects the wavy surface shape of the
supporting layer 16, its overall surface has irregularities. A
planarization film 18 composed of a transparent resin may be formed
thereon, if necessary, and then an alignment film 19 is formed
thereon.
[0175] Such provision of the reflective electrode 17 can prevent
direct reflection of external light in a reflective display mode,
and improved visibility is achieved without diminished display
brightness.
[0176] In this case, a reflective layer having the same shape as
that of the reflective electrode 17 may be formed and then a
transparent electrode may be formed thereon. When the reflective
electrode consists of a composite of the reflective layer and the
transparent electrode layer so that the reflective layer reflects
external light, and the transparent electrode layer applies a
liquid crystal driving voltage, the reflective electrode having
irregularities functions as a transflective layer.
[0177] A fourth embodiment of a liquid crystal device in accordance
with the present invention will now be described with reference to
FIG. 4. FIG. 4 is a longitudinal cross-sectional view of an outline
structure in the fourth embodiment in accordance with the present
invention. In FIG. 4, the same elements as in the first embodiment
shown in FIG. 1a are referred to by the same reference numerals,
without further description.
[0178] As shown in FIG. 4, in the fourth embodiment, a transmissive
optical diffuser 21 is disposed between the retardation film 13 and
the transparent substrate 1, in addition to the structure shown in
the first embodiment. The optical diffuser 21 may be of an internal
diffusion type in which transparent particles are dispersed in a
transparent substrate such as an acrylic resin having a different
refractive index, or of a surface diffusion type in which the
surface of a transparent substrate is roughened (to form a mat).
The other structures are the same as those in the first
embodiment.
[0179] The optical diffuser 21 can also prevent direct reflection
of external light on the reflective electrode 7 in a reflective
display mode, resulting in improved visibility. The position of the
optical diffuser 21 is not limited to that shown in FIG. 4, as long
as it is disposed forward the reflective layer. For example, the
optical diffuser may be formed on the reflective electrode or the
reflective layer.
[0180] A fifth embodiment of a liquid crystal device in accordance
with the present invention will now be described with reference to
FIGS. 5a and 5b. FIG. 5a is a longitudinal cross-sectional view of
an outline structure in a fifth embodiment in accordance with the
present invention, and FIG. 5b is an outline plan view in the fifth
embodiment. In FIG. 5b, a color filter and a black matrix layer
shown in FIG. 5a are not depicted to facilitate a view of an
electrode arrangement, and only three vertical stripe electrodes
and three horizontal stripe electrodes are indicated for
simplicity. An actual liquid crystal device has many more stripe
electrodes. In FIGS. 5a and 5b, the same elements as in the first
embodiment shown in FIGS. 1a and 1b are referred to by the same
reference numerals, without further description. Although the fifth
embodiment fundamentally relates to a passive matrix liquid crystal
device, it is also applicable to an active matrix device, a
segment-type device, and other types of liquid crystal devices.
[0181] As shown in FIGS. 5a and 5b, in the fifth embodiment,
reflective electrodes 17' each having many fine pores 17'a are
provided in place of the reflective electrodes 7 in the first
embodiment, and the other structures are the same. Light from the
backlight 15 passes through fine pores 17'a of the reflective
electrodes 17' in a transmissive display mode so that display on
the liquid crystal is visible. After the reflective electrodes 17'
are formed by vapor evaporation or sputtering, a resist layer
having openings is formed by photolithography, and then the fine
pores 17'a are formed by etching.
[0182] In the fifth embodiment, the fine pores 17'a ensure bright
display in a transmissive display mode, and prevents reflection of
external light in a reflective display mode as in the third
embodiment.
[0183] (Sixth Embodiment)
[0184] A sixth embodiment of a liquid crystal device in accordance
with the present invention will now be described with reference to
FIGS. 6 and 12. The fundamental structure in the sixth embodiment
is the same as that in the first embodiment, but the structure
relating to the reflective electrode 7 in the first embodiment is
specified in the sixth embodiment. FIGS. 6 to 12 are plan views of
reflective electrodes provided with various slits. Although the
sixth embodiment fundamentally relates to a passive matrix liquid
crystal device, it is also applicable to an active matrix device, a
segment-type device, and other types of liquid crystal devices.
[0185] In the sixth embodiment shown in FIG. 6, a plurality of
transparent electrodes 801 functioning as scanning lines are formed
on the inner surface of the transparent substrate 1 (see FIG. 1) in
a stripeed pattern, in which the transparent electrode 801 is an
example of the transparent electrode 6. Reflective electrodes 802
as data lines are formed on the inner surface of the transparent
substrate 2 (see FIG. 1), in which the reflective electrode 802 is
an example of the reflective electrode 7. Each reflective electrode
(data line) 802 is provided with slits 803 as an example of the
openings 7b. Each reflective electrode 802 allotted to any one of
red (R), green (G), and blue (B) forms one dot at a region
overlapping one transparent electrode 801, and adjacent three R, G
and B dots constitute one substantially square pixel. In each dot,
each reflective electrode 802 has four slits 803.
[0186] Since each reflective electrode 802 has oblong slits 803 in
the sixth embodiment, an oblique electric field caused by a short
side 803a of each slit 803 (the in-substrate component is parallel
to the longitudinal direction of the slit 803) is moderated
depending the length of the long side 803b of the slit 803. That
is, an oblique electric field caused by the long side 803b of the
slit 803 (the in-substrate component is perpendicular to the
longitudinal direction of the slit 803) controls,movement of liquid
crystal molecules in the vicinity of the slit. Thus, such a
structure can suppress insufficient alignment of the liquid crystal
which is caused by disagreement between the oblique electric field
due to the short side 803a and the oblique electric field due to
the long side 803b of the slit 803, and thus can suppress overall
insufficient alignment of the liquid crystal caused by the oblique
electric fields by the slit 803. Also, the oblique electric field
due to the long side 803b can be voluntarily used for driving the
liquid crystal.
[0187] In accordance with the sixth embodiment, display defects can
be reduced, and electrical power consumed by the liquid crystal
device can be simultaneously reduced by a reduced threshold voltage
when the liquid crystal is driven. When a countermeasure is taken
only for the oblique electric field due to the long side 803b of
the slit 803, and no consideration is given to the oblique electric
field due to the short side 803a of the slit 803, overall
insufficient alignment of the liquid crystal caused by the oblique
electric field can be reduced. Alternatively, voluntary use of the
oblique electric field due to the long side 803b of the slit 803
facilitates overall effective use of the oblique electric field due
to the slit 803.
[0188] Such oblong slits 803 can be readily formed by a photostep
using a resist, a development step, and then a peeling step. Thus,
the slits 803 can be simultaneously formed when the reflective
electrodes 802 are formed. The width of each slit 803 is in a range
of preferably 0.01 .mu.m to 20 .mu.m, and more preferably 4 .mu.m
or more. Since a viewer cannot recognize such a structure, a
reflective display mode and a transmissive display mode can be
simultaneously achieved without deterioration of image quality due
to the slit 803. Preferably, the slit 803 has an area ratio of 5%
to 30% with respect to the reflective electrode 802. Such a ratio
can moderate decreased brightness in a reflective display mode, and
achieves a transmissive display mode by light incident on the
liquid crystal layer via the slits 803 of the reflective electrodes
802.
[0189] In the sixth embodiment, a plurality of stripe reflective
electrodes 802 is formed at a predetermined gap, and slits 803
extend in the longitudinal direction of the reflective electrodes
802 (the longitudinal direction in FIG. 6). Thus, a countermeasure
for the oblique electric field caused by the slits 803 is effective
for the oblique electric field caused by gaps 802b between the
reflective electrodes 802. Furthermore, the reflective electrodes
802 and the slits 803 can be simultaneously formed; hence, the
design of the mask used in the formation can be simplified. That
is, a photomask for forming the reflective electrodes 802 may
include a pattern for the slits 803, without providing an
additional step for forming the slits 803.
[0190] In the sixth embodiment, each slit 803 extends to a position
facing a gap 801b between the transparent electrodes 801. Thus,
edges of each reflective electrode 802, which define short sides
803a of each slit 803 and are opposingly disposed at a relatively
large distance, lie in a gap 801b between transparent electrodes
801. Namely, since the edge is distant from a region in which a
voltage is applied between the transparent electrode 801 and the
reflective electrode 802, the effect of the oblique electric field
due to the short side 803a of the slit 803 causing insufficient
alignment of the liquid crystal can be significantly and
effectively reduced.
[0191] As a modification of the sixth embodiment, in consideration
of this, as shown in FIG. 7, the slit 803 may extend over a
plurality of pixels or may extend towards the exterior of the image
display region. In such a structure, each pixel does not have or
the image display area does not include the edges of reflective
electrodes 802 defining short sides 803 (as not shown in FIG. 7) of
slits 803 opposingly disposed at a relatively large distance;
hence, the effect of the oblique electric field due to the short
side 803a of the slit 803 causing insufficient alignment of the
liquid crystal can be significantly and effectively reduced.
[0192] Possible further modifications of the oblong slit 803 in the
sixth embodiment include two slits 803 for one dot as shown in FIG.
8; two slits 703 for one dot, each slit having a long side in the
direction perpendicular to the reflective electrode 702 (parallel
to the transparent electrode 701) as shown in FIG. 9; one slit 903
for one dot, each slit having a long side in the direction slant to
the reflective electrode 902 (slant to the transparent electrode
901) as shown in FIG. 10; and a slit 1003 consisting of a plurality
of oblong slit elements having long sides in directions parallel to
and perpendicular to the reflective electrode 1002 (parallel to and
perpendicular to the transparent electrode 1001) as shown in FIG.
11.
[0193] In the sixth embodiment, as shown in FIG. 12, a width of a
slit 1202 provided in a reflective electrode 1201 may be
substantially equal to a gap (an interdot region) 1203 between two
reflective electrodes 1201. When L1 is nearly equal to L2, wherein
L1 is the width of the gap 1203 and L2 is the width of the slit
1020, a photomask does not require high design accuracy and thus
can be readily designed. Furthermore, provision of such slits
causes slightly increased cost.
[0194] As in the second to fourth embodiments, the sixth embodiment
can include normally black mode driving, provision of a diffuser,
or a reflective electrode with irregularities. In the normally
black mode driving, the black matrix layer 5a may be omitted.
[0195] (Seventh Embodiment)
[0196] A seventh embodiment of a liquid crystal device in
accordance with the present invention will now be described
with-reference to FIGS. 13 and 6 to 10.
[0197] In the seventh embodiment, attention is paid to the
alignment direction of the liquid crystal molecules in the center
of the liquid crystal layer disposed between the two transparent
substrates in a liquid crystal device which is similar to that in
the sixth embodiment.
[0198] FIG. 13 is a longitudinal cross-sectional view for
illustrating the alignment direction of a liquid crystal in the
center between the substrates. A liquid crystal 503 is in a
predetermined twist-alignment state between two substrates 501 and
502. The long axis direction of a liquid crystal molecule 504 lying
substantially in the center between the substrates is defined as an
alignment direction 505.
[0199] In the seventh embodiment, with reference to FIG. 6
described above, a potential difference generated between a
reflective electrode (data line) 802 and a transparent electrode
(scanning line) 801 forms an oblique electric field which drives a
liquid crystal on an oblong slit 803 to achieve transmissive
display. As shown in FIG. 6, an angle between the longitudinal
direction of the slit 803 of the reflective electrode 802 (the y
direction in FIG. 6) and the alignment direction 804 of the liquid
crystal molecule in the center between the substrates is defined as
.xi.. Display defects (disclination) due to a reverse tilt domain
occur in a range of -90.degree..ltoreq..xi..ltoreq.-60.degree. or
60.degree..ltoreq..xi..ltoreq.90.degree., and thus bright,
high-quality transmissive display is not achieved. A possible
reason is formation of a tilt domain by orthogonal crossing of the
alignment direction of the liquid crystal molecule in the center
between the substrates and the longitudinal direction of the
reflective electrode. The display defects formed in the region
causes an inevitable increase in the threshold voltage during
driving of the liquid crystal. Display defects such as disclination
due to the reverse tilt domain are avoidable in a range of
-60.degree..ltoreq..xi..ltoreq.60.degree., and thus bright,
high-quality transmissive display is achieved. Since the display
defects barely occur, the threshold voltage during driving of the
liquid crystal can be reduced, resulting in reduced power
consumption of the liquid crystal device. The above advantage is
particularly noticeable in a range of
-30.degree..ltoreq..xi..ltoreq.30.degree..
[0200] In cases of oblong slits 803 shown as modifications of the
sixth embodiment in FIGS. 7 and 8, the longitudinal direction is
parallel to the reflective electrode 802 as in FIG. 6, and bright,
high-quality transmissive display is achieved in a range of
-60.degree..ltoreq..xi..lt- oreq.60.degree.. The above advantage is
particularly noticeable in a range of
-30.degree..ltoreq..xi..ltoreq.30.degree..
[0201] Also, in the slits 703 and 903, as modifications of the
sixth embodiment, shown in FIG. 9 and 10, an angle between the
longitudinal direction of the slit 703 of the reflective electrode
702 (the X direction in the drawings) and the alignment direction
704 of the liquid crystal molecule in the center between the
substrates is defined as .xi., and an angle between the
longitudinal direction 904 of the slit 903 of the reflective
electrode 902 and the alignment direction 905 of the liquid crystal
molecule in the center between the substrates is defined as .xi.. A
preferable angle is in a range of -60.degree..ltoreq..xi..ltor-
eq.60.degree.. The above advantage is particularly noticeable in a
range of -30.degree..ltoreq..xi..ltoreq.30.degree..
[0202] The effects of the present invention described in the
seventh embodiment can be further ensured by specifying the
alignment direction 506 of the liquid crystal molecule in the
vicinity of the substrate 502 in FIG. 13. That is, in FIG. 6, an
angle between the alignment direction 805 of the liquid crystal
molecule in the vicinity of the lower substrate and the
longitudinal direction (the Y direction in FIG. 6) of the slit 703
is defined as .delta.. A preferable angle is in a range of
-30.degree..ltoreq..delta..ltoreq.30.degree.. In a range outside
-30.degree..ltoreq..delta..ltoreq.30.degree., the liquid crystal
molecule at the substrate interface is reverse-titled by the effect
of the oblique electric field to cause display defects. Limitation
of the angle in a range of
-30.degree..ltoreq..delta..ltoreq.30.degree. can reduce the
threshold voltage during driving of the liquid crystal, resulting
in reduced power consumption of the liquid crystal device. The
above advantage is particularly noticeable in a range of
-10.degree..ltoreq..delta..ltoreq.10.degree..
[0203] Also, in modifications shown in FIGS. 7 to 10, an angle
between the alignment direction of the liquid crystal molecule in
the vicinity of the lower substrate and the longitudinal direction
of the slit is defined as .delta.. A preferable angle is in a range
of -30.degree..ltoreq..delta..l- toreq.30.degree.. Limitation of
the angle in a range of
-30.degree..ltoreq..DELTA..ltoreq.30.degree. can reduce the
threshold voltage during driving of the liquid crystal, resulting
in reduced power consumption of the liquid crystal device. The
above advantage is particularly noticeable in a range of
-10.degree..ltoreq..delta..ltoreq.1- 0.degree..
[0204] As in the second to fourth embodiments, the sixth embodiment
can include normally black mode driving, provision of a diffuser,
or a reflective electrode with irregularities. In the normally
black mode driving, the black matrix layer 5a may be omitted.
[0205] (Eighth Embodiment)
[0206] An eighth embodiment of a liquid crystal device in
accordance with the present invention will now be described with
reference to FIGS. 14 to 18. FIG. 14 is a longitudinal
cross-sectional view of an outline structure in the eighth
embodiment in accordance with the present invention. In FIG. 14,
the same elements as in the first embodiment shown in FIG. 1a are
referred to by the same reference numerals, without further
description. FIGS. 15 to 17 are plan views of concrete reflective
electrode structures, and FIG. 18 is a plan view of a modification
of the reflective electrode.
[0207] As shown in FIG. 14, each reflective electrode 107 in the
eighth embodiment is one size smaller than each respective
transparent electrode 6, as compared with the first embodiment. In
an active matrix device provided with TFD elements and TFT
elements, the reflective electrode 114 has a rectangular shape, and
is connected to a lead line via an active element. The other
structures are the same as those in the first embodiment.
[0208] In the eighth embodiment, a reflective electrode 107 having
a smaller area than that of a transparent electrode 6 on the inner
face of a transparent substrate 1 is formed on the inner face of a
transparent substrate 2 so that an oblique electric field generated
between the two electrodes partly drives the liquid crystal layer 3
facing a gap 107b in which a reflective electrode 107 is not
provided (thus, the gap transmits light from the backlight 15).
[0209] The operation of the eighth embodiment having the above
structure will now be described.
[0210] First, a reflective display mode will be described. External
light, in FIG. 14, is transmitted through a polarizer 11, a
retardation film 13, a color filter 5, and passes the liquid
crystal layer 3, and then is reflected by each reflective electrode
107, and emerges from the polarizer 11. Brightness of the polarizer
11 is controlled to a transmissive state (lighted state), an
absorbed state (dim state), or an intermediate state therebetween
in response to a voltage applied to the liquid crystal layer 3.
[0211] Next, a transmissive display mode will be described. Light
from the backlight 15 is converted into a predetermined polarized
light beam by a polarizer 12 and the retardation film 14, enters
the liquid crystal layer 3 through each gap 107b in which a
reflective electrode 107 is not formed, passes though the liquid
crystal layer 3, and is transmitted through the color filter 5 and
the retardation film 13. The liquid crystal layer 3 is driven by an
oblique electric field between the reflective electrode 107 and the
transparent electrode 6, having different sizes, and thus
brightness of the polarizer 11 is controlled to a transmissive
state (lighted state), an absorbed state (dim state), or an
intermediate state therebetween in response to a voltage applied to
the liquid crystal layer 3.
[0212] This embodiment can provide a color liquid crystal device
without double imaging and blurred imaging, and which can change a
display mode between a reflective mode and a transmissive mode.
[0213] In the eighth embodiment, actual structures of the
transparent electrode 6 and the reflective electrode 107 which
generate such an oblique electric field will be described in FIGS.
15 to 17.
[0214] FIG. 15 shows a structure in which the present invention is
applied to a TFD active matrix liquid crystal device. Scanning
lines 202 are formed on the inner face of a lower substrate, and a
TFD element 203 and a reflective electrode 204 are formed
corresponding to each dot. Transparent electrodes 201 as data lines
are formed on the inner face of an upper substrate. The transparent
electrode 201 has a larger area than that of the reflective
electrode 204 in each pixel, and extends to the opposing region in
which the reflective electrode 204 is not formed. When a driving
voltage is applied to the liquid crystal, an oblique electric field
is generated at the gap 205 (an edge of the reflective electrode
204) in which the reflective electrode 204 is not formed, by a
potential difference between the reflective electrode 204 and the
transparent electrode 201. The oblique electric field drives the
liquid crystal in the vicinity of the reflective electrode 204, and
transmissive display is achieved.
[0215] FIG. 16 is a structure when the present invention is applied
to a simple or passive matrix liquid crystal device. Reflective
electrodes 302 as data lines are formed on the inner face of a
lower substrate. A plurality of transparent electrodes 301 as
scanning lines is formed on the inner face of an upper electrode in
a striped pattern. When a potential difference is generated between
a reflective electrode 302 and a transparent electrode 301 at a gap
303 between reflective electrodes 302 in which the transparent
electrode (scanning line) 301 is formed on the upper substrate, an
oblique electric field is formed. The oblique electric field drives
the liquid crystal facing the gap 303, and transmissive display is
achieved.
[0216] FIG. 17 shows a structure when the present invention is
applied to a TFT active matrix liquid crystal device. Gate lines
403 and scanning lines 402 are formed on the inner face of a lower
substrate, and a TFT element 404 and a reflective electrode 405 are
formed corresponding to each dot. A transparent electrode 401 as a
common electrode (a counter electrode) is formed on the inner face
of an upper substrate. The transparent electrode 401 has a larger
area than that of the reflective electrode 405 in each pixel, and
extends to the opposing region in which the reflective electrode
405 is not formed. Thus, an oblique electric field is generated at
the gap 406 (an edge of the reflective electrode 405) in which the
reflective electrode 405 is not formed, by a potential difference
between the reflective electrode 405 and the transparent electrode
401. The oblique electric field drives the liquid crystal in the
vicinity of the reflective electrode 405, and transmissive display
is achieved.
[0217] As a modification of the eighth embodiment, as shown in FIG.
18, openings 603 may be provided in each reflective electrode 602
and transparent electrodes 601 may be provided in regions facing
the openings 603. Also, in such a structure, a potential difference
between the reflective electrode 602 and the transparent electrode
601 generates an oblique electric field, and the oblique electric
field drives the liquid crystal at the openings 603, and
transmissive display is achieved.
[0218] As in the second to fourth embodiments, the eighth
embodiment can include normally black mode driving, provision of a
diffuser, or a reflective electrode with irregularities. In the
normally black mode driving, the black matrix layer 5a may be
omitted.
[0219] A ninth embodiment of a liquid crystal device in accordance
with the present invention will now be described with reference to
FIGS. 13 to 17.
[0220] In the ninth embodiment, attention is paid to the alignment
direction of the liquid crystal molecules in, the center of the
liquid crystal layer disposed between the two transparent
substrates in a liquid crystal device which is similar to that in
the eighth embodiment.
[0221] When an electrode arrangement shown in FIG. 15 in the ninth
embodiment is employed, an angle between the longitudinal direction
of the reflective electrode 204 (the Y direction in FIG. 15) and
the alignment direction 206 of the liquid crystal molecule in the
center between the substrates is defined as .phi.. Display defects
(disclination) due to a reverse tilt domain occur in a range of
-90.degree..ltoreq..phi..ltoreq.-60.degree. or
60.degree..ltoreq..phi..lt- oreq.90.degree., and thus bright,
high-quality transmissive display is not achieved. A possible
reason is formation of a tilt domain by orthogonal crossing of the
alignment direction of the liquid crystal molecule in the center
between the substrates and the longitudinal direction of the
reflective electrode. The display defects formed in the region
causes an inevitable increase in the threshold voltage during
driving of the liquid crystal.
[0222] A table shown in FIG. 19 shows a contrast in a reflective
display mode (the ratio of a reflectance at a white display mode to
a reflectance at a black display mode) and a contrast in a
transmissive display mode (the ratio of a transmittance at a white
display mode to a transmittance at a black display mode) when the
above-defined angle .phi. is varied. In this case, the liquid
crystal mode is left-twisted by 255 degrees. As shown in the table
in FIG. 19, an angle in a range of
-60.degree..ltoreq..phi..ltoreq.60.degree. is essential for
achieving a contrast of 10 or more which is necessary for
high-quality image display in a reflective display mode and for
simultaneously achieving a contrast of 5 or more which is necessary
for high-quality image display in a transmissive display mode.
Display defects such as disclination due to the reverse tilt domain
are avoidable in a range of
-60.degree..ltoreq..phi..ltoreq.60.degree., and thus bright,
high-quality transmissive display is achieved. Since the display
defects barely occur, the threshold voltage during driving of the
liquid crystal can be reduced, resulting in reduced power
consumption of the liquid crystal device. The above advantage is
particularly noticeable in a range of
-30.degree..ltoreq..phi..ltoreq.30.degree..
[0223] When an electrode arrangement shown in FIG. 16 is employed,
an angle between the longitudinal direction of the reflective
electrode 302 (the Y direction in FIG. 16) and the alignment
direction 304 of the liquid crystal molecule in the center between
the substrates is defined as 4. Display defects (disclination) due
to a reverse tilt domain occur in a range of
-90.degree..ltoreq..phi..ltoreq.-60.degree. or 60.degree. C.
.ltoreq..phi..ltoreq.90.degree., and thus bright, high-quality
transmissive display is not achieved. A possible reason is
formation of a tilt domain by orthogonal crossing of the alignment
direction of the liquid crystal molecule in the center between the
substrates and the longitudinal direction of the reflective
electrode. The display defects formed in the region causes an
inevitable increase in the threshold voltage during driving of the
liquid crystal. Display defects such as disclination due to the
reverse tilt domain are avoidable in a range of
-60.degree..ltoreq..phi..ltoreq.60.degree., and thus bright,
high-quality transmissive display is achieved. Since the display
defects barely occur, the threshold voltage during driving of the
liquid crystal can be reduced, resulting in reduced power
consumption of the liquid crystal device. The above advantage is
particularly noticeable in a range of
-30.degree..ltoreq..phi..ltoreq.30.degree..
[0224] When an electrode arrangement shown in FIG. 17 is employed,
an angle between the longitudinal direction of the reflective
electrode 405 (the Y direction in FIG. 17) and the alignment
direction 407 of the liquid crystal molecule in the center between
the substrates is defined as .phi.. Display defects (disclination)
due to a reverse tilt domain occur in a range of
-90.degree..ltoreq..phi..ltoreq.-60.degree. or 60.degree. C.
.ltoreq..phi..ltoreq.90.degree., and thus bright, high-quality
transmissive display is not achieved. A possible reason is
formation of a tilt domain by orthogonal crossing of the alignment
direction of the liquid crystal molecule in the center between the
substrates and the longitudinal direction of the reflective
electrode. The display defects formed in the region causes an
inevitable increase in the threshold voltage during driving of the
liquid crystal. Display defects such as disclination due to the
reverse tilt domain are avoidable in a range of
-60.degree..ltoreq..phi..ltoreq.60.degree., and thus bright,
high-quality transmissive display is achieved. Since the display
defects barely occur, the threshold voltage during driving of the
liquid crystal can be reduced, resulting in reduced power
consumption of the liquid crystal device. The above advantage is
particularly noticeable in a range of
-30.degree..ltoreq..phi..ltoreq.30.degree..
[0225] The effects of the present invention described in the ninth
embodiment can be further ensured by specifying the alignment
direction 506 of the liquid crystal molecule in the vicinity of the
substrate 502 in FIG. 13. That is, in FIG. 15, an angle between the
alignment direction 207 of the liquid crystal molecule in the
vicinity of the lower substrate (TFD substrate) and the
longitudinal direction of the reflective electrode 204 is defined
as .psi.. A preferable angle is in a range of
-30.degree..ltoreq..psi..ltoreq.30.degree.. In a range outside
-30.degree..ltoreq..psi..ltoreq.30.degree., the liquid crystal
molecule at the substrate interface is reverse-titled by the effect
of the oblique electric field to cause display defects.
[0226] A table shown in FIG. 20 shows a contrast in a reflective
display mode (the ratio of a reflectance at a white display mode to
a reflectance at a black display mode) and a contrast in a
transmissive display mode (the ratio of a transmittance at a white
display mode to a transmittance at a black display mode) when the
above-defined angle .psi. is varied. In this case, the liquid
crystal mode is left-twisted by 70 degrees. As shown in the table
in FIG. 20, an angle in a range of
-30.degree..ltoreq..psi..ltoreq.30.degree. is essential for
achieving a contrast of 10 or more which is necessary for
high-quality image display in a reflective display mode and for
simultaneously achieving a contrast of 5 or more which is necessary
for high-quality image display in a transmissive display mode.
Display defects due to reverse tilt caused by the liquid crystal
molecules at the substrate interface are avoidable in a range of
-30.degree..ltoreq..psi..ltoreq.30.degree.. Also, in FIGS. 16 and
17, display defects such as disclination due to a tilt domain are
avoidable when the angle .psi. between the alignment directions 305
and 408 of the liquid crystal molecules at the substrate interfaces
and the longitudinal directions of the reflective electrodes 302
and 405 is in a range of -30.degree. to 30.degree.. The threshold
voltage during driving of the liquid crystal can be reduced,
resulting in reduced power consumption of the liquid crystal
device. The above advantage is particularly noticeable in a range
of -10.degree..ltoreq..psi..ltoreq.10.- degree..
[0227] As in the second to fourth embodiments, the ninth embodiment
can include normally black mode driving, provision of a diffuser,
or a reflective electrode with irregularities. In the normally
black mode driving, the black matrix layer 5a may be omitted.
[0228] A tenth embodiment of a liquid crystal device in accordance
with the present invention will now be described with reference to
FIGS. 21a to 23. The tenth embodiment includes a TFD active matrix
liquid crystal device in accordance with the present invention.
[0229] A structure in the vicinity of a TFD driving element, as an
example of a diode-type nonlinear element used in this embodiment,
will now be described with reference to FIGS. 21a and 21b. FIG. 21a
is a schematic plan view of a TFD driving element and a pixel
electrode, and FIG. 21b is a cross-sectional view taken along line
B-B' in FIG. 21a. In FIG. 21b, individual layers and elements are
depicted at different scales so that these layers and elements are
visible in the drawing.
[0230] In FIGS. 21a and 21b, A TFD driving element 40 is formed on
an underlying insulating film 41 formed on a transparent substrate
2, is composed of a first metal film 42, an insulating layer 44,
and a second metal film 46, in that order from the side of the
insulating film 41, and has a thin film diode (TFD) or
metal-insulator-metal (MIM) structure. The first metal film 42 is
connected to a scanning line 61 formed on the transparent substrate
2, and the second metal film 46 is connected to a pixel electrode
62 composed of a-conductive reflective film as another embodiment
of the reflective electrode. In place of the scanning line 61, a
data line (described below) may be formed on the transparent
substrate 2, and be connected to the pixel electrode 62, and the
scanning line 61 may be provided on a counter substrate.
[0231] The transparent substrate 2 is composed of an insulating
transparent substrate, for example, glass or plastic. The
underlying insulating film 41 is composed of, for example, tantalum
oxide. The main purpose of the formation of the insulating film 41
is to prevent separation of the first metal film 42 from the
underlying layer and diffusion of impurities from the underlying
layer into the first metal film 42 during heat treatment performed
after deposition of the second metal film 46. When the transparent
substrate 2 is composed of, for example, a quartz substrate having
high thermal resistance and high purity which does not cause such
separation and diffusion, the insulating film 41 can be omitted.
The first metal film 42 is a conductive metal thin film composed
of, for example, elemental tantalum or a tantalum alloy. The
insulating film 44 is composed of, for example, an oxide film which
is formed on the first metal film 42 by anodic oxidation in a
chemical solution. The second metal film 46 is a conductive metal
thin film composed of, for example, elemental chromium or a
chromium alloy.
[0232] In this embodiment, the pixel electrode 62 has regions
permitting optical transmittance, such as oblong or square slits or
fine openings, as described in the above embodiments.
Alternatively, each pixel is smaller than the transparent electrode
on the counter electrode so that light passes through a gap
therebetween.
[0233] A transparent insulating film 29 is provided on a side (the
upper face in the drawing) facing the liquid crystal, such as the
pixel electrode 62, the TFD driving element 40, and the scanning
line 61. An alignment film 19 which is composed of an organic thin
film such as a polyimide thin film and was subjected to alignment
treatment such as rubbing is provided thereon.
[0234] Some examples of a TFD driving element as a diode-type
nonlinear element have been described above. A diode-type nonlinear
element having bi-directional diode characteristics, such as a zinc
oxide (ZnO) varistor, a metal semi-insulator (MSI) driving element
or a ring diode (RD), is also applicable to the reflective liquid
crystal device in this embodiment.
[0235] The structure and the operation of a TFD active matrix
driving-type transflective liquid crystal device provided with TFD
driving elements in accordance with the tenth embodiment will now
be described with reference to FIGS. 22 and 23. FIG. 22 is an
equivalent circuit diagram of a liquid crystal device and a driving
circuit, and FIG. 23 is a partially broken isometric view for
schematically showing the liquid crystal device.
[0236] With reference to FIG. 22, in the TFD active matrix
driving-type transflective liquid crystal device, a plurality of
scanning lines 61 arranged on a transparent substrate 2 is
connected to a Y driver circuit 100 constituting a scanning line
driving circuit, and a plurality of data lines 60 arranged on a
counter substrate is connected to an X driver circuit 110
constituting a data line driving circuit. The Y driver circuit 100
and the X driver circuit 110 may be formed on a transparent
substrate 2 or a counter substrate. In such a case, the
transflective liquid crystal device is of a driving
circuit-integrated type. Alternatively, the Y driver circuit 100
and the X driver circuit 110 are composed of external ICs which may
be independent of the transflective liquid crystal device, and be
connected to the scanning lines 61 and the data lines 60 via
predetermined lead lines. In this case, the transflective liquid
crystal device does not have these driving circuits.
[0237] In each of pixel regions arranged in a matrix, the scanning
line 60 is connected to one terminal of the TFD driving element 40
(See FIGS. 21a and 21b), and the data line 60 is connected to the
other terminal of the TFD driving element 40 via the liquid crystal
layer 3 and the pixel electrode 62. In each pixel region, when
scanning signals are supplied to the respective scanning line 61
while data signals are supplied to the respective data line 60, the
TFD driving element 40 in the pixel region is turned on so that a
driving voltage is applied to the liquid crystal layer 3 between
the pixel electrode 62 and the data line 60 via the TFD driving
element 40. Reflective display is performed by reflection of
external light by the pixel electrode 62 in a lighted environment,
whereas transmissive display is performed by transmission of light
from a backlight as a light source through slits in the pixel
electrode 62 in a dark environment.
[0238] In FIG. 23, the transflective liquid crystal device is
provided with a transparent substrate 2 and a transparent substrate
(counter substrate) 1 opposingly arranged thereto. The transparent
substrate 1 is composed of, for example, a glass substrate. The
transparent substrate 2 is provided with pixel electrodes 62
arranged in a matrix, and each pixel electrode 62 is connected to a
scanning line 61. The transparent substrate 1 is provided with a
plurality of rectangular data lines 60 as transparent electrodes
extending in the direction perpendicular to the scanning line 61.
The data line 60 is composed of, for example, a transparent
conductive thin film, such as an indium tin oxide (ITO) film. An
alignment film 9 which is composed of an organic thin film such as
a polyimide thin film and was subjected to alignment treatment such
as rubbing is provided below the data line 60. A color filter (not
shown in the drawing) composed of color films arranged in a
stripeed, mosaic, or triangle pattern according to use is provided
on the transparent substrate 1.
[0239] As described above, the tenth embodiment can provide a color
liquid crystal device without double imaging and blurred imaging,
and which can change a display mode between a reflective mode and a
transmissive mode. In particular, the transflective liquid crystal
device can be driven in a normally black mode by voltage control in
the X driver circuit 110 and the Y driver circuit 100 as an example
of driving means.
[0240] An eleventh embodiment of a liquid crystal device in
accordance with the present invention will now be described with
reference to FIGS. 24 to 26. The eleventh embodiment includes a TFT
active matrix liquid crystal device as a preferable application in
accordance with the present invention. FIG. 24 is an equivalent
circuit diagram of various elements and lead lines in a plurality
of pixels formed in a matrix which constitutes an image display
region in a liquid crystal device. FIG. 25 is a plan view of a
plurality of adjacent pixels on a transparent substrate provided
with data lines, scanning lines and pixel electrodes, and FIG. 26
is a cross-sectional view taken along line C-C' in FIG. 25. In FIG.
26, individual layers and elements are depicted at different scales
so that these layers and elements are visible in the drawing.
[0241] In the TFT active matrix transflective liquid crystal device
in accordance with the eleventh embodiment shown in FIG. 24, a
plurality of TFTs 130 is formed in a matrix and controls pixel
electrodes 62 as another example of reflective electrodes arranged
in a matrix. Data lines 135 for supplying image signals are
electrically connected to sources of TFTs 130. Image signals S1,
S2, . . . , Sn may be sequentially supplied to the data lines 135,
or may be simultaneously supplied to each group consisting of a
plurality of adjacent data lines 135. The gates of the TFTs 130 are
electrically connected to scanning lines 131, and pulse scanning
signals G1, G2, . . . , Gm are sequentially supplied to the
scanning lines 131 at a given timing. Each pixel electrode 62 is
electrically connected to the drain of the TFT 130. The switch of
the TFT 130 as a switching element is turned off for a
predetermined term so as to input the image signals S1, S2, . . . ,
Sn supplied from the data lines 135 for a predetermined timing. The
image signals S1, S2, . . . , Sn which are inputted to the liquid
crystal via the pixel electrodes 62 and have given levels are
maintained between the pixel electrode 62 and a counter electrode
(described below) formed on a counter electrode (described below)
for a predetermined period. A storage capacitor 170 is provided
parallel to the liquid crystal capacitor formed between the pixel
electrode 62 and the counter electrode in order to prevent leakage
of the stored image signals.
[0242] In FIG. 25, pixel electrodes 62 (the contour 62a is shown by
dotted lines in the drawing) composed of reflective films are
provided in a matrix array on a transparent substrate 2 as a TFT
array substrate. Data lines 135, scanning lines 131 and capacitor
lines 132 are provided along horizontal and vertical boundaries
between the pixel electrodes 62. Each data line 135 is electrically
connected to a source region in a semiconductor layer 81a composed
of a polysilicon film via a contact hole 85. Each pixel electrode
62 is electrically connected to a drain region in the semiconductor
layer 81a via a contact hole 88. Each capacitor line 132 is
arranged so as to oppose a first capacitor electrode extending from
the drain region in the semiconductor layer 1a with an insulating
film provided therebetween to form a storage capacitor 170. Each
scanning line 131 is arranged so as to oppose a channel region
81a', shown by a shaded region in the drawing, in the semiconductor
layer 81a, and functions as a gate electrode. As described above, a
TFT 130 with a scanning line 131 as a gate electrode opposing a
channel region 81a' is provided at a crossing of a scanning line
131 and a data line 135.
[0243] As shown in FIG. 26, the liquid crystal device has a
transparent substrate 2, and a transparent electrode (counter
substrate) 1 opposing thereto. These transparent substrates 1 and 2
are insulating and transparent substrates composed of quartz,
glass, or plastic.
[0244] In this embodiment, the pixel electrode 62 has regions
permitting optical transmittance, such as oblong or square slits or
fine openings, as described in the above embodiments.
Alternatively, each pixel is smaller than the transparent electrode
on the counter substrate so that light passes through a gap
therebetween.
[0245] A transparent insulating film 29 is provided on a side (the
upper face in the drawing) facing the liquid crystal of the pixel
electrode 62 and the TFT 40. An alignment film 19 which is composed
of an organic thin film such as a polyimide thin film and was
subjected to alignment treatment such as rubbing is provided
thereon.
[0246] The entire face of the transparent substrate 1 is provided
with a counter electrode 121 as another example of the transparent
electrode, and a second shading film 122 called a black mask or
black matrix is provided in the unopened region of each pixel. An
alignment film 9 which is composed of an organic thin film such as
a polyimide film and was subjected to a given alignment treatment
such as rubbing treatment is provided under the counter electrode
121. A color filter (not shown in the drawing) composed of color
films arranged in a stripeed, mosaic, or triangle pattern according
to use is provided on the transparent substrate 1.
[0247] A pixel-switching TFT 130 for controlling by switching each
pixel electrode 62 is provided at a position adjacent to the pixel
electrode 62 on the transparent substrate 2.
[0248] As in the first embodiment, a gap surrounded by a sealant
between the pair of first and second substrates 1 and 2 which are
disposed so that each pixel electrode 62 and the counter electrode
121 are opposing each other is filled with a liquid crystal to form
a liquid crystal layer 3.
[0249] A first insulating interlayer 112 is provided below the
plurality of pixel-switching TFTs 30. The first insulating
interlayer 112 is formed on the entire transparent substrate 2, and
functions as an underlying film for the pixel-switching TFTs 30.
The first insulating interlayer 112 is composed of, for example, a
high insulating glass, such as nondoped silicate glass (NSG),
phosphosilicate glass (PSG), borosilicate glass (BSG), or
borophosphosilicate glass (BPSG); silicon oxide; or silicon
nitride.
[0250] In FIG. 26, the pixel-switching TFT 130 includes a source
region connected to a data line 135 via a contact hole 85, a
channel region 81a' opposing a scanning line 131 and a gate
insulating film therebetween, and a drain region connected to the
pixel electrode 62 via a contact hole 88. The data line 131 is
composed of a light-shading and conductive thin film such as a low
resistance metal film, e.g., aluminum, or an alloy film such as
metal silicide. A second insulating interlayer 114 provided with
contact holes 85 and 88 is formed thereon, and a third insulating
interlayer 117 provided with a contact hole 88 is formed thereon.
The second and third insulating interlayers 114 and 117 are also
composed of a high-insulating glass, such as NSG, PSG, BSG, or
BPSG, silicon oxide or silicon nitride, as in the first insulating
interlayer 112.
[0251] The pixel-switching TFT 130 may have a LDD structure, an
offset structure, or a self-aligned structure. The TFT 130 may have
a dual gate structure or a triple gate structure, in addition to a
single gate structure.
[0252] According to the TFT active matrix driving-type
transflective liquid crystal device of the eleventh embodiment, as
described above, an electric field is sequentially applied to a
liquid crystal portion at each pixel electrode 62 between the pixel
electrode 62 and the counter electrode 121 to control the alignment
state at the liquid crystal portion. Thus, reflective display is
performed by reflection of external light by the pixel electrode 62
in a lighted environment, whereas transmissive display is performed
by transmission of light from a backlight as a light source through
slits in the pixel electrode 62 in a dark environment. Accordingly,
a color liquid crystal device without double imaging and blurred
imaging, and which can change a display mode between a reflective
mode and a transmissive mode is achieved. In particular, electrical
power is supplied to each pixel electrode 62 via the respective TFT
130; hence, crosstalk between pixel electrodes 62 can be reduced
and high-quality images can be displayed.
[0253] The counter electrode on the transparent substrate 1 may be
omitted, and driving may be performed by a transverse electric
field, parallel to the substrate 1, between pixel electrodes 62 on
the transparent substrate.
[0254] Color layers of the color filter 5 used in the first to
eleventh embodiments will now be described with reference to FIG.
27. FIG. 27 is a graph showing transmittance characteristics of
individual color layers in the color filter 5. In a reflective
display mode in each embodiment, incident light is transmitted
through any one coloring layer of the color filter 5, passes
through the liquid crystal layer 3, and is reflected by the
reflective electrode 7, 17, or 17', passes through the liquid
crystal layer 3 again, and is then emitted. Thus, light passes
through the color filter two times, unlike in general transmissive
liquid crystal devices. Use of a general color filter, therefore,
causes dim display and a reduced contrast. Accordingly, in each
embodiment, colors of the R, G, and B coloring layers in the color
filter 5 are lighted so as to have a minimum transmittance 61 of 25
to 50% in a visible light region, as shown in FIG. 27. Color
lighting of the coloring layers can be achieved by reducing the
thickness of the coloring layers or by reducing the pigment or dye
contents in the coloring layers. Brightness in a reflective display
mode is, thereby, not lowered.
[0255] In a transmissive display mode, light passes through the
light color filter 5 only one time, and thus the displayed image
has a lighted color. Since the reflective electrode in each
embodiment shades a large amount of light from the backlight, color
lighting of the color filter 5 is advantageous to securing display
brightness.
[0256] A twelfth embodiment of the present invention will be
described with reference to FIG. 28. The twelfth embodiment
pertaining to electronic apparatuses including
[0257] liquid crystal device according to any one of the first to
eleventh embodiments. That is, the twelfth embodiment includes
various electronic apparatuses each using a liquid crystal device
shown in any one of the first to eleventh embodiments as a display
section of the portable apparatuses requiring low power consumption
under various environment. FIG. 28 shows three electronic
apparatuses in accordance with the present invention.
[0258] FIG. 28(a) shows a portable phone having a display section
72 provided on the upper front of a body 71. Portable phones are
used in various environments including the interior and the
exterior. They are frequently used in automobiles, but the interior
of the automobile is significantly dark at night. A preferable
display device used in a portable phone is a transflective liquid
crystal device which is primarily used in a reflective display mode
having low power consumption and is operable in a transmissive
display mode using auxiliary light, if necessary. Use of a liquid
crystal device according to any one of the first to eleventh
embodiments as a display section 72 of a portable phone yields a
portable phone having higher brightness and a high contrast in both
of reflective display mode and transmissive
[0259] display mode.
[0260] FIG. 28(b) shows a watch having a display section 74
provided in the center 73 of the body. An important point in use of
the watch is a feeling of luxury. Use of liquid crystal device
according to any one of the first to eleventh embodiments of the
present invention as a display section 74 of a watch achieves
higher brightness and a high contrast, and reduced coloring due to
a small change in properties with the wavelength of light. Thus,
color display with a very a luxurious feeling is achieved compared
to conventional watches.
[0261] FIG. 28(c) shows a portable information apparatus having a
display section 76 at the upper section and an input section 77 at
the lower section of a body 75. In most cases, touch keys are
provided on the front face of the display section 76. Since
conventional touch keys have high surface reflectance, it is
difficult to see the display. Thus, many conventional portable
apparatuses use transmissive liquid crystal devices as a display
section. Since the transmissive liquid crystal device uses a
backlight, a large amount of power is consumed and a battery has a
shortened life. Use of a liquid crystal device according to any one
of the first to eleventh embodiments as a display section 76 of a
portable information apparatus produces a portable information
apparatus having high brightness and clarity in any of reflective,
transflective, and transmissive display modes.
[0262] The liquid crystal device of the present invention is not
limited to the above embodiments, and can be appropriately modified
within the gist and concept of the present invention in view of
claims and the overall specification. The modified liquid crystal
device is also included in the technical scope of the present
invention.
[0263] Industrial Applicability
[0264] The liquid crystal device in accordance with the present
invention can be used as various display devices which can display
bright high-quality images in both of dark and lighted
environments, and as display sections of various electronic
apparatuses. Electronic apparatuses using such liquid crystal
devices include liquid crystal televisions, view finder-type and
monitor-viewing-type videotape recorders, automobile navigation
systems, electronic notebooks, portable calculators,
wordprocessors, portable phones, videophones, POS terminals, and
touch panels.
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