Title: Liquid crystal display device, method for producing the liquid crystal display device, and electronic apparatus
Abstract: The invention provides a transflective liquid crystal display device which can provide a display with good visibility, and a method of producing the same. A method of producing a liquid crystal display device in which a step of forming an inner polarizing layer of a transflective liquid crystal panel to perform a displaying operation in a transmission mode and a reflection mode includes making the direction of extension of openings, or through holes, formed in a reflective layer to reflect incident light and the direction of exerting stress to apply a material of the inner polarizing layer are the same when the material of the inner polarizing layer is applied while exerting a stress thereupon.
Patent Number: 6,914,652 Issued on 07/05/2005 to Iijima
| Inventors:
|
Iijima; Chiyoaki (Ina, JP)
|
| Assignee:
|
Seiko Epson Corporation (Tokyo, JP)
|
| Appl. No.:
|
435021 |
| Filed:
|
May 12, 2003 |
Foreign Application Priority Data
| May 15, 2002[JP] | 2002-140648 |
| Current U.S. Class: |
349/114; 349/114; 349/123; 349/96 |
| Intern'l Class: |
G02F 001/13.35 |
| Field of Search: |
349/96,114,123
|
References Cited [Referenced By]
U.S. Patent Documents
| 6320629 | Nov., 2001 | Hatano et al.
| |
| 6335773 | Jan., 2002 | Kamei et al.
| |
| 6686980 | Feb., 2004 | Ichihashi.
| |
| Foreign Patent Documents |
| A 2001-91747 | Apr., 2001 | JP.
| |
| A 2002-277636 | Sep., 2002 | JP.
| |
| WO 99/0814/0 | Feb., 1999 | WO.
| |
Primary Examiner: Kim; Robert H.
Assistant Examiner: Nguyen; (Nancy) Thanh-Nhan P
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
1. A method of producing a liquid crystal display device that includes a liquid
crystal layer disposed between a pair of opposing substrates and a plurality of
pixel including a transmissive display area and a reflective display area, a reflective
layer being disposed at the reflective display area and not the transmissive display
area, the method comprising:
forming the reflective layer on one of the pair of substrates; and
forming an inner polarizing layer which covers the reflective layer and the transmissive
display area, the forming the inner polarizing layer including applying a material
of the inner polarizing layer while exerting a stress thereupon in one direction,
the direction of exerting the stress being substantially the same as the direction
of extension of the transmissive display area.
2. A method of producing a liquid crystal display device that includes a liquid
crystal layer disposed between a pair of opposing substrates and a plurality of
pixels, each pixel including a transmissive display area, and a reflective display
area, a reflective layer being disposed at the reflective display area and not
the transmissive display area, the method comprising:
forming the reflective layer on one of the pair of substrates;
forming an alignment layer for an inner polarizing layer, the alignment layer
covering the reflective layer and the transmissive display area; and
forming the inner polarizing layer on the alignment layer;
the forming the alignment layer including forming the alignment layer so as to
cover the reflective layer and the transmissive display area and so as to be aligned,
the direction of performing the alignment operation being substantially the same
as the direction of extension of the transmissive display area in order to apply
the inner polarizing layer to the alignment layer.
3. A method of producing a liquid crystal display device that includes a liquid
crystal layer disposed between a pair of opposing substrates, the method comprising:
forming a stripe-shaped electrode on one of the pair of substrates, the electrode
being used to apply a voltage to the liquid crystal layer; and
forming an inner polarizing layer which covers the electrode, the forming the
inner polarizing layer including applying a material of the inner polarizing layer
while exerting a stress thereupon in one direction, the direction of exerting the
stress being substantially the same as the direction of extension of the electrode.
4. A method of producing a liquid crystal display device that includes a liquid
crystal layer disposed between a pair of opposing substrates, the method comprising:
forming a stripe-shaped electrode on one of the pair of substrates, the electrode
being used to apply a voltage directly to the liquid crystal layer;
forming an alignment layer for an inner polarizing layer, the alignment layer
covering the electrode; and
forming the inner polarizing layer on the alignment layer;
the forming the alignment layer including forming the alignment layer so as to
cover the electrode and so as to be aligned, the direction of performing the alignment
operation being substantially the same as the direction of extension of the electrode
in order to apply the inner polarizing layer to the alignment layer.
5. A liquid crystal display device produced by the method of producing a liquid
crystal display device of claim 1.
6. A liquid crystal display device, comprising:
a pair of opposing substrates;
a plurality of pixels,
a liquid crystal layer disposed between the pair of opposing substrates and the
plurality of pixels;
each pixel including a transmissive display area and
a reflective display area;
a reflective layer disposed at one of the pair of substrates and at the reflective
display area; and
an inner polarizing layer which covers the reflective layer and the transmissive
display area and which is formed of a material including a water-soluble dichromatic
dye, an alignment direction in the inner polarizing layer being substantially the
same as the direction of extension of the transmissive display area.
7. A liquid crystal display device, comprising:
a pair of opposing substrates;
a plurality of pixels;
a liquid crystal layer disposed between the pair of opposing substrates and the
plurality of pixels;
each of pixels including a transmissive display area and
a reflective display area;
a reflective layer disposed at one of the pair of substrates and at the reflective
display area;
an inner polarizing layer formed of a material including polymer liquid crystals;
and
an alignment layer for the inner polarizing layer, the alignment layer covering
the reflective layer and the transmissive display area, the alignment layer and
the inner polarizing layer being successively stacked upon each other, the direction
of performing an alignment operation on the alignment layer and the direction of
extension of the transmissive display area being substantially the same.
8. A liquid crystal display device, comprising:
a pair of opposing substrates;
a liquid crystal layer disposed between the pair of opposing substrates;
a striped-shaped electrode, disposed on one of the pair of substrates, to apply
a voltage to the liquid crystal layer;
a transmissive display area;
a reflective display area; and
an inner polarizing layer formed of a material including a water-soluble dichromatic
dye, an alignment direction in the inner polarizing layer and the direction of
extension of the electrode being substantially the same.
9. A liquid crystal display device, comprising:
a pair of opposing substrates;
a liquid crystal layer disposed between the pair of opposing substrates;
a striped-shaped electrode, disposed on one of the pair of substrates, to apply
a voltage to the liquid crystal layer;
a transmissive display area;
a reflective display area;
an inner polarizing layer formed of a material including polymer liquid crystals;
an alignment layer for the inner polarizing layer, the alignment layer and the
inner polarizing layer being successively stacked on the electrode, the direction
of performing an alignment operation on the alignment layer and the direction of
extension of the electrode being substantially the same.
10. An electronic apparatus, comprising:
the liquid crystal display device of claim 5 usable as a display section.
Description
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a liquid crystal display device and a method
of producing the liquid crystal display device. More particularly, the invention
relates to a transflective liquid crystal display device capable of providing a
sufficiently bright display even in a transmission mode, and a method of producing
the transflective liquid crystal display device.
2. Description of Related Art
The related art includes a transflective liquid crystal display device which
functions in both a reflection mode to display an image using external light, such
as natural light or illumination light, and a transmission mode to display an image
using an illuminator, such as a backlight, as a light source. One type of such
a transflective liquid crystal display device performs a displaying operation in
the transmission mode by transmitting light from the backlight through a though
hole. The through hole to transmit light is formed in a portion of a reflective
layer, disposed at the inner side or the outer side of a liquid crystal panel and
used to reflect external light.
SUMMARY OF THE INVENTION
In the related art transflective liquid crystal display device, when an image
is displayed in the reflection mode, light incident upon the liquid crystal panel
is reflected by the reflective layer and is transmitted through a liquid crystal
layer twice while the light exits towards the outside. Therefore, by reflecting
circularly polarized light by the reflective layer and reversing the direction
of rotation of its polarization axis, switching between pixels is carried out.
In this structure, in order to perform bright and dark displaying operations in
the transmission mode, it is necessary for light incident upon the liquid crystal
layer from a lower substrate to be circularly polarized light. As a result, light
incident upon a polarizer at the side of an upper substrate becomes circularly
polarized light or linearly polarized light, so that, when the bright displaying
operation is carried out, a portion (approximately half) of the incident circularly
polarized light is transmitted to display an image. In this way, since the light
incident upon the liquid crystal layer in the transmission mode is used with low
efficiency, sufficient luminance cannot be provided in the transmission mode.
The present invention addresses or solves the above and/or other problems, and
provides a liquid crystal display device which can provide a bright display in
the transmission mode. The invention also provides a method of producing the liquid
crystal display device.
In order to address or overcome the problem of the transflective liquid crystal
display device that a sufficient display luminance cannot be provided in the transmission
mode, a liquid crystal display device can be provided that includes a polarizing
layer which is disposed on the entire inner side of a substrate of a liquid crystal
panel and which has a function that is equivalent to the function of a polarizer.
FIG. 8 is a sectional view of the structure of this type of transflective liquid
crystal display device, which includes a liquid crystal panel 100 and a
backlight (illuminator) 130. In the liquid crystal panel 100, a liquid
crystal layer 104 is interposed between opposing upper and lower substrates
101 and 102 and sealed in by a sealant 105. The backlight
130 is disposed at the rear side (lower side in FIG. 8) of the liquid crystal
panel 100.
Color filter layers 111, a planarizing layer 112, a plurality
of electrodes 113 disposed in the form of stripes in plan view, and an alignment
layer 114 are disposed at the inner side (the side of the liquid crystal
layer 104) of the upper substrate 101 of the liquid crystal panel
100. A front diffuser 117, a retardation film 118, and a polarizer
119 are stacked upon each other in that order at the outer side (upper side
in FIG. 8) of the upper substrate 101.
On the other hand, a reflective layer 120, a polarizing layer 121,
a planarizing layer 122, a plurality of electrodes 123 disposed in
the form of stripes in plan view, and an alignment layer 124 are disposed
at the inner side (the side of the liquid crystal layer 104) of the lower
substrate 102 of the liquid crystal panel 100. A polarizer 129
is disposed at the outer side of the lower substrate 102. The direction
of extension of the electrodes 123 at the lower substrate 102 is
perpendicular to the direction of extension of the electrodes 113 at the
upper substrate 101. Through holes 110 are formed in portions of
the reflective layer 120. Light from the backlight 130 is incident
upon the liquid crystal layer 104 through the through holes 110.
FIG. 9 is a schematic that illustrates the principle of display of the transflective
liquid crystal display device having the above-described structure, and only shows
a significant portion of the liquid crystal display device shown in FIG. 8.
In FIG. 9, displaying operations in the reflection mode are illustrated on the
left, whereas displaying operations in the transmission mode are illustrated on
the right.
As shown in FIG. 9, in the liquid crystal display device shown in FIG. 8, when
a voltage is applied to the liquid crystal layer 104 (when the liquid crystal
layer 104 is set in an on state), dots are displayed darkly in both the
reflection and transmission modes. In contrast, when a voltage is not applied to
the liquid crystal layer 104 (when the liquid crystal layer 104 is
set in an off state), dots are displayed brightly in both the reflection and transmission modes.
In the reflection mode, as shown on the left side in FIG. 9, external light incident
upon the liquid crystal panel 100 is converted into linearly polarized light
that is parallel to the sheet plane of FIG. 9 by the polarizer 119 having
a polarization axis that is parallel to the sheet plane of FIG. 9 and impinges
upon the liquid crystal layer 104. Here, when the liquid crystal layer 104
is set in an on state, the light that has impinged upon the liquid crystal layer
104 is incident upon the polarizing layer 121 as linearly polarized
light parallel to the sheet plane of FIG. 9 and is absorbed by the polarizing
layer 121 having a polarization axis perpendicular to the sheet plane of
FIG. 9. Therefore, the dots are darkly displayed. In contrast, when the
liquid crystal layer 104 is set in an off state, the light that has impinged
upon the liquid crystal layer 104 is converted into linearly polarized light
that is perpendicular to the sheet plane of FIG. 9 by the action of the liquid
crystal layer 104. The converted light impinges upon and is transmitted
through the polarizing layer 121. Then, the light is reflected by the reflective
layer 120, is transmitted through the polarizing layer 121 again,
and impinges upon the liquid crystal layer 104. Thereafter, the light is
converted into linearly polarized light parallel to the sheet plane of FIG. 9 by
the action of the liquid crystal layer 104, is transmitted through the polarizer
119, and exits away from the upper substrate 101. In this way, dots
are brightly displayed.
In the transmission mode, as shown on the right side in FIG. 9, light from the
backlight 130 is converted into linearly polarized light that is perpendicular
to the sheet plane of FIG. 9 by the polarizer 129. Then, the light transmits
through the through holes 110 of the reflective layer 120, impinges
upon and is transmitted through the polarizing layer 121 having a polarization
axis perpendicular to the sheet plane of FIG. 9, and impinges upon the liquid crystal
layer 104. Here, when the liquid crystal layer 104 is set in an on
state, the light impinges upon the polarizer 119 at the upper substrate
101 as linearly polarized light perpendicular to the sheet plane of FIG.
9 without being subjected to the action of the liquid crystal layer 104,
and is absorbed by the polarizer 119 having a polarization axis that is
parallel to the sheet plane of FIG. 9, so that dots are darkly displayed. In contrast,
when the liquid crystal layer 104 is set in an off state, the incident light
is converted into linearly polarized light parallel to the sheet plane of FIG.
9 by the action of the liquid crystal layer 104, and impinges upon the polarizer
119. Then, the light is transmitted through the polarizer 119 and
exits therefrom, so that dots are brightly displayed.
Accordingly, in the liquid crystal display device shown in FIG. 8 having
the polarizing layer 121 disposed at the inner sides of the substrates 101
and 102, the light incident upon the polarizer 119 from the liquid
crystal layer 104 is linearly polarized light when a bright display is provided
in the transmission mode. Therefore, there is almost no light absorbed by the polarizer
119. Consequently, the liquid crystal display device makes it possible to
address or overcome the problem of the luminance being insufficient in the transmission
mode, which is a problem in related art transflective liquid crystal display devices,
and can provide a bright display.
In the liquid crystal display device shown in FIG. 8, since, structurally speaking,
the light incident upon the liquid crystal layer 104 can be maximally used
for a display operation, the display luminance in the transmission mode may be
made up to approximately twice that of related art liquid crystal display devices.
However, the display luminance in the transmission mode cannot be actually made
up to approximately twice that of related art liquid crystal display devices. Therefore,
there are still differences between the display luminances in the transmission
and reflection modes.
In order to address or overcome the problem of the luminance being insufficient
in the transmission mode in the transflective liquid crystal display device having
the structure shown in FIG. 8, the inventor repeatedly conducted research, and
discovered that the insufficient luminance is caused by the polarization function
in a transmissive display area of the polarizing layer 121 (the level area
of the through holes 110 of the reflective layer 120) at the inner
side of the liquid crystal panel 100 being less than the polarization function
in its reflective display area (the area where the reflective layer 120
is provided). In other words, the light incident upon the through holes 110
from the backlight 130 is attenuated by the polarizing layer 121,
so that, in the transmission mode, the light source is used with lower efficiency.
As a result, sufficient luminance cannot be provided.
The polarization function of portions of the polarizing layer 121 at the
through holes 110 of the reflective layer 120 is reduced due to the
method of forming the polarizing layer 121. FIGS. 10 and 11 illustrate alignment
states of liquid crystal molecules in a portion of the polarizing layer 121
in the reflective layer 120 and in a portion of the polarizing layer 121
on the top portion of the reflective layer 120. The parts required to illustrate
the alignment states of the liquid crystal molecules of the polarizing layer 121
are only shown. FIG. 10 is a partial plan view of these parts, and FIG. 11 is a
partial sectional view of these parts. In FIGS. 10 and 11, parts common to ones
shown in FIG. 8 are given the same reference numerals. As shown in FIG. 10, the
polarizing layer 121 is formed by applying what are called lyotropic liquid
crystals (an aqueous solution of a liquid crystal material including, for example,
water-soluble dichromatic dye) to the reflective layer 120 and letting it
dry and harden. In order to determine the direction of the polarization axis of
the polarizing layer 121, the polarizing layer 121 is formed by stretching
the material while exerting stress thereupon in one direction as indicated by the
arrow shown in FIG. 10. When this method is used, the liquid crystals are
properly aligned on the level reflective layer, so that good polarization properties
can be provided. However, as shown in FIG. 11, unaligned portions 140 where
liquid crystal molecules L of the polarizing layer 121 are not aligned are
formed at steps 110
a formed by the reflective layer 120 and
the through hole 110. The unaligned portions 140 give rise to differences
between the polarization functions in the polarizing layer 121. In particular,
the polarization function at the steps 110
a at the peripheries of
the inner sides of the through holes is reduced. Therefore, the light entering
the through hole 110 from the lower substrate 102 is attenuated.
To address or overcome the problem of the polarization function being reduced
in the transmission display area, according to one aspect of the present invention,
there is provided a method of producing a liquid crystal display device that includes
a liquid crystal layer disposed between a pair of opposing substrates, a transmissive
display area, and a reflective display area, a reflective layer being disposed
at the reflective display area and having an opening which transmits light and
which defines the transmissive display area. The method includes forming the reflective
layer having the opening on one of the pair of substrates; and forming an inner
polarizing layer which covers the reflective layer and the opening. In the forming
of the inner polarizing layer, a material of the inner polarizing layer is applied
while exerting a stress thereupon in one direction, the direction of exerting the
stress being substantially the same as the direction of extension of the opening
of the reflective layer.
The inner polarizing layer produced by the method of the present invention is
such that the direction in which stress is exerted during the application thereof
is substantially the same as the direction of extension of the opening defined
by a step formed by the opening and the reflective layer, so that the fraction
of a portion at the step that extends in a direction intersecting the direction
in which the stress is exerted is reduced, so that nonalignment in the material
of the inner polarizing layer can be reduced or minimized. This makes it less likely
for a reduction in the property of the inner polarizing layer caused by the non-alignment
to occur, so that a light source can be used with higher efficiency. Therefore,
a liquid crystal display device that provides a bright transmissive display can
be provided.
According to another aspect of the present invention, there is provided
a method of producing a liquid crystal display device comprising a liquid crystal
layer disposed between a pair of opposing substrates, a transmissive display area,
and a reflective display area, a reflective layer being disposed at the reflective
display area and having an opening which transmits light and which defines the
transmissive display area. The method includes forming the reflective layer having
the opening on one of the pair of substrates; forming an alignment layer for an
inner polarizing layer, the alignment layer covering the reflective layer and the
opening; and forming the inner polarizing layer on the alignment layer. In the
forming of the alignment layer, the alignment layer is formed so as to cover the
reflective layer and the opening and is aligned, the direction of performing the
alignment operation being substantially the same as the direction of extension
of the opening of the reflective layer in order to apply the inner polarizing layer
to the alignment layer.
According to this method of the present invention, in forming an inner
polarizing layer, an alignment layer for the inner polarizing layer aligned in
the same direction as the direction of extension of the opening of the reflective
layer is first formed. Then, the inner polarizing layer is formed on the alignment
layer for the polarizing layer. Therefore, by interposing the alignment layer for
the inner polarizing layer between the reflective layer and the inner polarizing
layer, the degree of non-alignment in a portion of the inner polarizing layer at
the opening of the reflective layer can be reduced. In addition, since the alignment
layer for the polarizing layer is aligned in the same direction as the direction
of extension of the opening of the reflective layer, alignment properties at the
boundary between a step and a level portion of the reflective layer do not change,
so that the alignment layer for the inner polarizing layer has acceptable alignment
properties. Further, since the inner polarizing layer is formed on the alignment
layer having acceptable alignment properties, the degree of non-alignment in the
inner polarizing layer can be further reduced. As a result, it is possible to reduce
attenuation of light in the inner polarizing layer, so that a light source can
be used with greater efficiency. Therefore, it is possible to provide a liquid
crystal display device that provides a bright transmissive display.
According to still another aspect of the present invention, there is provided
a method of producing a liquid crystal display device that includes a liquid crystal
layer disposed between a pair of opposing substrates. The method includes forming
a stripe-shaped electrode on one of the pair of substrates, the electrode being
used to apply a voltage to the liquid crystal layer, and forming an inner polarizing
layer which covers the electrode. In the forming of the inner polarizing layer,
a material of the inner polarizing layer is applied while exerting a stress thereupon
in one direction, the direction of exerting the stress being substantially the
same as the direction of extension of the electrode.
According to the method of producing a liquid crystal display device of
the present invention, by making the direction of extension of the stripe-shaped
electrode and the direction of exerting stress upon the inner polarizing layer
the same, the percentage of a portion at a step, which corresponds to an edge of
the electrode, extending in a direction intersecting the direction of exerting
stress is reduced, so that the degree of non-alignment in the material of the inner
polarizing layer due to the step at the electrode can be reduced. As a result,
attenuation of light in the inner polarizing layer can be reduced, thereby making
it possible to provide a liquid crystal display device which can provide a display
with high luminance. In this structure, the reflective layer in the present invention
is not a necessary structural element, so that the present invention is effective
not only in a transflective liquid crystal display device, but also in a transmissive
liquid crystal display device.
According to still another aspect of the present invention, there is provided
a method of producing a liquid crystal display device that includes a liquid crystal
layer disposed between a pair of opposing substrates. The method includes forming
a stripe-shaped electrode on one of the pair of substrates, the electrode being
used to apply a voltage to the liquid crystal layer; forming an alignment layer
for an inner polarizing layer, the alignment layer covering the electrode; and
forming the inner polarizing layer on the alignment layer. In the forming of the
alignment layer, the alignment layer is formed so as to cover the electrode and
aligned, the direction of performing the alignment operation being substantially
the same as the direction of extension of the electrode in order to apply the inner
polarizing layer to the alignment layer.
According to the method of producing a liquid crystal display device of
the present invention, prior to forming an inner polarizing layer, an alignment
layer for the inner polarizing layer aligned in the same direction as the direction
of extension of the stripe-shaped electrode is formed, so that it is possible to
prevent the alignment properties of the inner polarizing layer from becoming degraded
due to the step at the electrode. Therefore, an inner polarizing layer having good
alignment properties can be formed. As a result, it is possible to provide a liquid
crystal display device which can provide a high-quality display.
According to still another aspect of the present invention, there is provided
a liquid crystal display device that includes a liquid crystal layer disposed between
a pair of opposing substrates; a transmissive display area; and a reflective display
area. At one of the pair of substrates, a reflective layer is disposed at the reflective
display area and has an opening which transmits light and which defines the transmissive
display area. The liquid crystal display device also includes an inner polarizing
layer which covers the reflective layer and the opening and which is formed of
a material including or consisting essentially of a water-soluble dichromatic dye.
An alignment direction in the inner polarizing layer is substantially the same
as the direction of extension of the opening of the reflective layer.
According to still another aspect of the present invention, there is provided
a liquid crystal display device that includes a liquid crystal layer disposed between
a pair of opposing substrates; a transmissive display area; and a reflective display
area. At one of the pair of substrates, a reflective layer is disposed at the reflective
display area and has an opening which transmits light and which defines the transmissive
display area. The liquid crystal display device further includes an alignment layer
for an inner polarizing layer, the alignment layer covering the reflective layer
and the opening; and the inner polarizing layer formed of a material including
or consisting essentially of polymer liquid crystals. The alignment layer and the
inner polarizing layer are successively stacked upon each other. The direction
of performing an alignment operation on the alignment layer and the direction of
extension of the opening of the reflective layer are substantially the same.
According to still another aspect of the present invention, there is provided
a liquid crystal display device that includes a liquid crystal layer disposed between
a pair of opposing substrates; a striped-shaped electrode, disposed on one of the
pair of substrates, to apply a voltage to the liquid crystal layer; a transmissive
display area; a reflective display area; and an inner polarizing layer formed of
a material including or consisting essentially of a water-soluble dichromatic dye.
An alignment direction in the inner polarizing layer and the direction of extension
of the electrode are substantially the same.
According to still another aspect of the present invention, there is provided
a liquid crystal display device that includes a liquid crystal layer disposed between
a pair of opposing substrates; a striped-shaped electrode, disposed on one of the
pair of substrates, to apply a voltage to the liquid crystal layer; a transmissive
display area; a reflective display area; an alignment layer for an inner polarizing
layer; and the inner polarizing layer formed of a material including or consisting
essentially of polymer liquid crystals. The alignment layer and the inner polarizing
layer are successively stacked on the electrode. The direction of performing an
alignment operation on the alignment layer and the direction of extension of the
electrode are substantially the same.
The liquid crystal display device of the present invention is produced by any
one of the aforementioned methods of producing a liquid crystal display device.
According to this structure, since the alignment properties of the material of
the inner polarizing layer are not degraded by a step at an underlying layer, the
liquid crystal display device includes an inner polarizing layer having good polarization
properties. When the liquid crystal display device includes such an inner polarizing
layer having good polarization properties, it provides a bright transmissive display
and has excellent visibility.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial sectional view of the structure of a liquid crystal display
device of an exemplary embodiment of the present invention;
FIG. 2 is a schematic plan view of a reflective layer of the liquid crystal
display device shown in FIG. 1;
FIG. 3 is a schematic plan view of an inner polarizing layer of the liquid crystal
display device shown in FIG. 1;
FIG. 4 is a schematic that illustrates the principle of operation of the liquid
crystal display device shown in FIG. 1;
FIG. 5 is a schematic plan view of electrodes of the liquid crystal display
device shown in FIG. 1;
FIG. 6 is a schematic perspective view of a step in a first method of producing
the liquid crystal display device of the present invention;
FIG. 7 is a schematic perspective view of a step in a second method of producing
the liquid crystal display device of the present invention;
FIG. 8 is a partial sectional view of a liquid crystal display device including
a polarizing layer at the inner surface of a substrate;
FIG. 9 is a schematic that illustrates the principle of operation of the liquid
crystal display device shown in FIG. 8;
FIG. 10 is a schematic plan view of the polarizing layer in the liquid crystal
display device shown in FIG. 8;
FIG. 11 is a partial schematic sectional view of a reflective layer and the
polarizing layer in the liquid crystal display device shown in FIG. 8;
FIG. 12 is a schematic that illustrates an example of an electronic apparatus
of the present invention;
FIG. 13 is a schematic that illustrates another example of an electronic apparatus
of the present invention;
FIG. 14 is a schematic that illustrates still another example of an electronic
apparatus of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A description of an exemplary embodiment of the present invention is provided
below
with reference to the relevant drawings.
FIG. 1 is a partial sectional view of the structure of an exemplary embodiment
of a liquid crystal display device produced by a method of producing a liquid crystal
display device of the present invention.
The liquid crystal display device shown in FIG. 1 generally includes a liquid
crystal panel
10 and a backlight (illuminator)
30 disposed at the
rear side (lower side in FIG. 1) of the liquid crystal panel
10. In the
exemplary embodiment, the case where the present invention is applied to a passive
matrix transflective liquid crystal display device is described. In order to make
it easier to view the figures that are referred to below, the elements are illustrated
with different film thicknesses, dimensions, etc., as appropriate.
In the liquid crystal panel
10, an upper substrate
1 and a lower
substrate
2 are disposed so as to oppose each other, and a liquid crystal
layer
4 is interposed between the substrates
1 and
2 and sealed
in by a sealant
5.
A plurality of color filters
11, a planarizing layer
12, a plurality
of electrodes
13, and an alignment layer
15 are formed at the inner
side (liquid crystal layer
4 side) of the upper substrate
1. The
plurality of color filters
11 are arranged and formed in a matrix in plan
view. The planarizing layer
12 is formed so as to cover the color filters
11. The plurality of electrodes
13 are formed of transparent electrically
conductive materials, such as indium tin oxide (ITO), and are disposed on the planarizing
layer
12 in the form of stripes in plan view. The alignment layer
15
is formed so as to cover the electrodes
13. A front diffuser
17,
a retardation film
18, and a polarizer
19 are stacked upon each other
at the outer side of the upper substrate
1.
A reflective layer
20, openings
21, an inner polarizing layer
22,
a plurality of electrodes
23, and an alignment layer
24 are formed
at the inner side (liquid crystal layer
4 side) of the lower substrate
2.
The reflective layer
20 is a thin metal layer having high reflectivity such
as an Al or Ag layer. The openings
21 are formed in the reflective layer
to pass transmission light from the backlight
30 (described later). The
inner polarizing layer
22 is formed so as to cover the reflective layer
20 and the openings
21. The electrodes
23 are formed of transparent
electrically conductive materials, such as ITO, and are disposed in the form of
stripes in plan view on the inner polarizing layer
22. The alignment layer
24 is formed so as to cover the electrodes
23. A polarizer
29
is disposed on the outer surface of the lower substrate
2.
A reflective layer
31, which is a metal layer having high reflectivity
such
as an Al layer or an Ag layer, is disposed on the outer surface (that is, the side
opposite to the liquid crystal panel
10) of the backlight
30.
FIG. 2 is a schematic plan view of a surface of the reflective layer
20
of the liquid crystal panel
10 shown in FIG.
1. The openings
21
pass through the reflective layer
20 formed on the lower substrate
2.
Light from the backlight
30 can pass through the openings
21. Although,
in the exemplary embodiment, each opening
21 is rectangular, each opening
21 in the liquid crystal display device of the present invention is not
limited thereto and may have other shapes such as stripe shapes or elliptical shapes.
The inner polarizing layer
22 is formed on the reflective layer
20
having the openings
21 so as to cover them. The direction of alignment of
liquid crystals of the inner polarizing layer
22 is the same as the direction
of the long sides of each rectangular shape of each opening
21, that is,
the direction of extension of each opening
21. This direction is indicated
by the arrow shown in FIG.
2.
The material of the inner polarizing layer
22 is not particularly limited
as long as it polarizes transmission light without attenuating it. However, it
is desirable that the material is formed of the material including or consisting
essentially of water-soluble liquid crystals because of its polarization properties
and easiness of production. For example, a material consisting essentially of lyotropic
liquid crystals (produced by OPTIVA and disclosed in International Publication
No. WO99/08140). This material is a liquid crystal material which becomes a lyotropic
liquid crystal material when it is in an aqueous state. In applying the liquid
crystal material as an aqueous solution to the reflective layer
20, when
the liquid crystal material is spread on the openings
21 and the reflective
layer
20 while exerting a stress thereupon, an inner polarizing layer
22
having a polarization axis in a predetermined direction can be formed with a predetermined
thickness. In addition, when applying the liquid crystal material, by making the
direction of exerting stress the same as the direction of extension of the openings
21, liquid crystal molecules can be aligned in one direction. In other words,
by making drops of the liquid crystal solution fall onto the reflective layer
20
and moving a Meyer rod (wire bar) or the like at a predetermined speed in the direction
of extension of the openings
21, the liquid crystal aqueous solution can
be applied while exerting stress thereupon in a constant direction, so that the
inner polarizing layer
22 having a predetermined polarization axis can be produced.
As shown in FIG. 3, since the inner polarizing layer
22 formed in this
way is formed of a liquid crystal material whose molecules are aligned in the same
direction as the direction of extension of the openings
21, unaligned portions
140 in which the molecules of the liquid crystal material are out of alignment
at steps formed by the reflective layer
20 and the openings
21 exist
in an inclined manner only at the peripheral portions of the steps at the short
sides of the openings
21, so that the areas of the unaligned portions
140
are considerably smaller than those in the related art. Therefore, not only can
the polarization properties of the entire inner polarizing layer
22 be enhanced,
but also attenuation of transmission light can be reduced, so that the display
luminance in a transmission mode can be increased.
A liquid crystal material including or consisting essentially of thermotropic
polymer
liquid crystals containing dichromatic dye may also be used as the material of
the inner polarizing layer
22. In this case, an alignment layer for the
inner polarizing layer is formed so as to cover the reflective layer
20
and the openings
21, and is rubbed in a predetermined direction. Then, the
thermotropic polymer liquid crystal material containing dichromatic dye is applied
to the alignment layer for the inner polarizing layer, is heated to make it isotropic,
cooled to rearrange the liquid crystal molecules, and hardened by, for example,
photopolymerization. By this, the inner polarizing layer
22 can be formed.
The alignment layer for the inner polarizing layer may be a polymer material layer,
formed of, for example, polyimide, that has been subjected to a predetermined rubbing
operation (alignment operation).
By interposing the alignment layer for the inner polarizing layer between the
reflective layer
20 and the inner polarizing layer
22, not only are
the unaligned portions
140 of the inner polarizing layer
22 less
often produced, but also the alignment properties of the inner polarizing layer
22 can be further enhanced, so that a high-quality display can be provided.
In order to increase adherence between the reflective layer
20 and the
inner polarizing layer
22, for example, an adherence layer (formed of a
silane coupling agent, SiO
2, or the like) may be interposed. When such
an adherence layer is provided, the adherence between the reflective layer
20
and the inner polarizing layer
22 is increased, so that double refraction
and non-alignment at the boundary of these layers occur less frequently.
A description of the principle of operation of the liquid crystal display device
having the above-described structure is provided below. FIG. 4 illustrates the
principle of operation of the liquid crystal display device, and shows only the
main portion of the liquid crystal display device shown in FIG.
1. In FIG.
4, operations in a reflection mode are illustrated on the left side, whereas operations
in the transmission mode are illustrated on the right sides. In the description
below, when a voltage is applied to the liquid crystal layer
4 (that is,
when it is set in an on state), the liquid crystal molecules are aligned substantially
perpendicular to the direction of the surfaces of the upper substrate
1
and the lower substrate
2, whereas, when a voltage is not applied to the
liquid crystal layer
4 (that is, when it is set in an off state), the liquid
crystal molecules are aligned substantially parallel to the direction of the surfaces
of the upper substrate
1 and the lower substrate
2. Therefore, when
the liquid crystal layer
4 is in an on state, light incident upon the liquid
crystal layer
4 is transmitted through the liquid crystal layer
4
almost without being subjected to the action of the liquid crystal layer
4,
whereas, when the liquid crystal layer
4 is in an off state, the light incident
upon the liquid crystal layer
4 is transmitted through the liquid crystal
layer
4 while being subjected to the action of the liquid crystal layer
4. The action of the liquid crystal layer
4 refers to polarization
conversion action including optical rotation and double refraction of polarized
light incident upon the liquid crystal layer.
In the reflection mode, external light incident upon the liquid crystal panel
10 is converted into linearly polarized light parallel to the sheet plane
of FIG. 4 by the polarizer
19 having a polarization axis parallel to the
sheet plane of FIG. 4, and impinges upon the liquid crystal layer
4. Here,
when the liquid crystal layer
4 is set in an on state, the light that has
impinged upon the liquid crystal layer
4 is incident upon the inner polarizing
layer
22 as linearly polarized light parallel to the sheet plane of FIG.
4 and is absorbed by the inner polarizing layer
22 having a polarization
axis perpendicular to the sheet plane of FIG.
4. Therefore, dots are darkly
displayed. In contrast, when the liquid crystal layer
4 is in an off state,
the incident light is converted into linearly polarized light perpendicular to
the sheet plane of FIG. 4 by optical rotation by the liquid crystal layer
4,
impinges upon the inner polarizing layer
22, is transmitted through the
inner polarizing layer
22 having a polarization axis perpendicular to the
sheet plane of FIG. 4, and impinges upon the reflective layer
20. Then,
the light is reflected by the reflective layer
20, is re-transmitted through
the inner polarizing layer
22, and impinges upon the liquid crystal layer
4 from the side of the lower substrate
2. At this time, since the
liquid crystal layer
4 is in an off state, the light transmitted through
the liquid crystal layer
4 is linearly polarized light parallel to the sheet
plane of FIG. 4 due to the optical rotation by the liquid crystal layer
4.
Thereafter, the light is transmitted through the polarizer
19 having a polarization
axis parallel to the sheet plane of FIG.
4 and exits therefrom, so that
dots are brightly displayed.
In the transmission mode, as shown on the right side of FIG. 4, light from the
backlight
30 is converted into linearly polarized light perpendicular to
the sheet plane of FIG. 4 by the polarizer
29. Then, the converted light
passes through the openings
21 (which are through holes formed in the reflective
layer
20) and the inner polarizing layer
22, and impinges upon the
liquid crystal layer
4. Here, when the liquid crystal layer
4 is
in an on state, the incident light impinges upon the polarizer
19 at the
upper substrate
1 as linearly polarized light perpendicular to the sheet
plane of FIG. 4 without being subjected to the action of the liquid crystal layer
4, and is absorbed by the polarizer
19 having a polarization axis
parallel to the sheet plane of FIG. 4, so that dots are darkly displayed. In contrast,
when the liquid crystal layer
4 is in an off state, the incident light is
converted into linearly polarized light parallel to the sheet plane of FIG. 4 by
the action of the liquid crystal layer
4, and impinges upon the polarizer
19. Then, the light is transmitted through the polarizer
19 and exits
therefrom, so that dots are brightly displayed.
Light reflected by the outer side (that is, the lower substrate
2 side)
of the reflective layer
20 after being emitted from the backlight
30
and transmitted through the polarizer
29 is linearly polarized light perpendicular
to the sheet plane of FIG. 4 due to the action of the polarizer
29, so that
the light is transmitted through the polarizer
29 and impinges upon the
backlight
30 again. Then, the light is reflected by the reflective layer
31 provided on the outer surface of the backlight
30, and travels
towards the liquid crystal panel
10 again. In this way, the light reflected
by the outer surface of the reflective layer
20 is repeatedly reflected
between the reflective layer
20 and the reflective layer
31 at the
backlight
30. As the light is repeatedly reflected, it impinges upon the
openings
21 of the reflective layer
20, and is used for display.
Therefore, in the liquid crystal display device of the exemplary embodiment, almost
all of the light from the backlight
30 can be used for a display operation
in the transmission mode, so that the light source is used with greater efficiency.
Therefore, a bright display can be provided.
Since the inner polarizing layer
22 used in the present invention is
aligned in the same direction as the direction of extension of the openings
21
of the reflective layer
20, the production of unaligned portions by the
steps at the openings
21 can be reduced or minimized, so that attenuation
of light can be reduced. Therefore, it is possible to provide a bright display
in the transmission mode, as a result of which a liquid crystal display device
having excellent visibility can be provided.
Although the liquid crystal display device of this exemplary embodiment
of the present invention is described taking a passive matrix liquid crystal display
device as an example, the present invention is not limited to the above-described
structure. Therefore, as long as the liquid crystal display device is a transflective
liquid crystal display device having openings, which are through holes, in the
reflective layer, the present invention may be applied to any type of liquid crystal
display device regardless of the method of driving the liquid crystals. For example,
the present invention may also be applied to an active matrix liquid crystal display
device without any problem.
FIG. 5 is a schematic plan view showing another example of the inner polarizing
layer
22 in the present invention, which is used in the liquid crystal panel
10 shown in FIG.
1. The inner polarizing layer
22 shown in
FIG. 5 is formed on the electrodes
23 formed with stripe shapes above the
lower substrate
2, and is applied to the electrodes
23 while applying
stress thereupon in the same direction as the direction of extension of the electrodes
23, that is, in the same direction as the direction of the arrow in FIG.
5. According to the method of forming the inner polarizing layer
22
of the present invention, even if an underlying portion for forming the inner polarizing
layer
22 is not level, by making the direction of extension of the steps
at the underlying portion and the direction of application of the inner polarizing
layer
22 the same, non-alignment in the material of the inner polarizing
layer
22 at areas near the steps can be reduced or minimized. By this, it
is possible for the inner polarizing layer
22 to have good polarization
properties with little attenuation of light. Here, each electrode
23 has
a terminal
23a. Although there are portions of the terminals
23a
that do not extend in the same direction as the direction of application of
the inner polarizing layer
22, these portions are eventually removed from
the inner polarizing layer
22 or disposed outside the display area, so that
non-alignment in these portions do not affect the displaying operation. In the
example shown in FIG. 5, an alignment layer for the inner polarizing layer may
be interposed between the electrodes
23 and the inner polarizing layer
22.
By such a structure, it is possible to further enhance the alignment properties
of the material of the inner polarizing layer
22. In order to increase adherence
between the electrodes
23 and the inner polarizing layer
22, for
example, an adherence layer (formed of a silane coupling agent, SiO
2,
or the like) may be interposed therebetween.
Hereunder, methods for producing the liquid crystal display device of
the present invention will be described with reference to the relevant drawings.
In the exemplary embodiment, two types of methods including different production
steps and structures are described below. In the production methods described below,
only the step of forming an inner polarizing layer at the inner surface of the
lower substrate, which is a distinctive feature of the present invention, is described
in detail. A detailed description of the steps of forming electrodes and an alignment
layer on a lower substrate and the step of forming an upper substrate are not provided.
These parts may be formed by steps of a related method of producing a liquid crystal panel.
The liquid crystal display devices that are produced by these production methods
have optically equivalent functions. If a reflective layer having through holes
is provided, the liquid crystal display devices can be operated based on the principle
of operation illustrated in FIG.
4.
The first method of producing the liquid crystal display device of the present
invention is carried out as follows. First, a lower substrate
2 formed of
glass or transparent resin is provided. Then, a metallic material, such as Al or
Ag, is deposited onto the lower substrate
2 to form a reflective layer
20
entirely on the lower substrate
2. After forming the reflective layer
20,
openings
21 are formed through predetermined locations of the reflective
layer
20 by photolithography, and needless portions of the reflective layer
20 at, for example, the peripheral portions of the substrate
2 are
removed. Next, when the openings
21 have been formed, an inner polarizing
layer
22 is formed so as to cover the reflective layer
20 and the
openings
21. The inner polarizing layer
21 may be formed by, for
example, the method illustrated in FIG.
6. In this method, an aqueous solution
L of a water-soluble liquid crystal material consisting essentially of water-soluble
dichromatic dye, that is, what are called lyotropic liquid crystals are applied
to the reflective layer
20 and the openings
21 while exerting stress
thereupon in a predetermined direction by a Meyer rod R or the like. Here, by making
the direction of extension of the openings
21 and the direction of exerting
stress upon the inner polarizing layer
22 the same (as indicated by the
arrow shown in FIG.
6), an inner polarizing layer
22 having a polarization
axis parallel to the direction of exerting stress can be formed. In other words,
by making the sliding direction of the Meyer rod R and the direction of extension
of the openings
21 the same during the application of the liquid crystals,
the liquid crystal molecules of the inner polarizing layer
22 align themselves
in the same direction as the direction of exerting stress, so that the inner polarizing
layer
22 having a polarization axis that is parallel to the direction of
exerting stress can be provided.
Next, after forming transparent electrodes
23 having stripe shapes in
plan view on the inner polarizing layer
22, an alignment layer
24
is formed so as to cover the transparent electrodes
23, thereby defining
the lower substrate
2. With the lower substrate
2 and a separately
provided upper substrate
1 disposed in an opposing manner, the inner surfaces
of peripheral ends of the substrates are sealed in by a sealant
5 having
a substantially frame shape in plan view. Then, a space defined by the sealant
5 and both of the substrates
1 and
2 is filled with liquid
crystals. As a result, a liquid crystal panel
1 is formed. Thereafter, a
polarizer
19, a front diffuser
17, etc., are disposed at the outer
surface of the liquid crystal panel, whereby the liquid crystal displa
