U.S. patent application number 12/794986 was filed with the patent office on 2010-09-30 for liquid crystal display device.
Invention is credited to Atsushi Hasegawa, Toshio Miyazawa.
Application Number | 20100245739 12/794986 |
Document ID | / |
Family ID | 36261378 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100245739 |
Kind Code |
A1 |
Hasegawa; Atsushi ; et
al. |
September 30, 2010 |
Liquid Crystal Display Device
Abstract
The present invention provides a liquid crystal display device
which can reduce the difference in brightness between an image
obtained from a reflection region and an image obtained from a
transmission region. The liquid crystal display device includes a
pixel electrode and a counter electrode in each pixel region on a
liquid-crystal-side surface of one substrate out of respective
substrates which are arranged to face each other with liquid
crystal therebetween. The pixel region includes a transmission
region and a reflection region. A gap between the pixel electrode
and the counter electrode in the reflection region is set larger
than the gap between the pixel electrode and the counter electrode
in the transmission region.
Inventors: |
Hasegawa; Atsushi; (Togane,
JP) ; Miyazawa; Toshio; (Chiba, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
36261378 |
Appl. No.: |
12/794986 |
Filed: |
June 7, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12465748 |
May 14, 2009 |
7768614 |
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12794986 |
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11255107 |
Oct 21, 2005 |
7538845 |
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12465748 |
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Current U.S.
Class: |
349/113 |
Current CPC
Class: |
G02F 1/134363 20130101;
G02F 1/133555 20130101 |
Class at
Publication: |
349/113 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 2004 |
JP |
2004-316250 |
Claims
1-15. (canceled)
16. A liquid crystal display device comprising: a first substrate;
a second substrate; and liquid crystal sandwiched between the first
substrate and the second substrate, wherein the first substrate
includes a first electrode and a second electrode in the inside of
a pixel region, the liquid crystal is driven by an electric field
generated between the first electrode and the second electrode, at
least one of the first electrode and the second electrode is, as
viewed in a plan view, constituted of a reflecting conductive layer
and a light-transmitting conductive layer which is formed on at
least a periphery of the reflecting conductive layer, and the
reflecting conductive layer performs a reflection display by
reflecting light from a front surface side.
17. A liquid crystal display device according to claim 16, wherein
both of the first electrode and the second electrode are, as viewed
in a plan view, constituted of a reflecting conductive layer and a
light-transmitting conductive layer which is formed on at least a
periphery of the reflecting conductive layer.
18. A liquid crystal display device according to claim 16, wherein
the light-transmitting conductive layer is formed in a state that
the reflecting conductive layer is covered with the
light-transmitting conductive layer.
19. A liquid crystal display device according to claim 16, wherein
the first electrode includes at least one linear portion in the
inside of the pixel region, the second electrode includes at least
one linear portion in the inside of the pixel region, as viewed in
a plan view, the linear portion of the first electrode and the
liner portion of the second electrode are alternately arranged in
the inside of the pixel region, and the linear portion of at least
one of the first electrode and the second electrode is, as viewed
in a plan view, constituted of the reflecting conductive layer and
the light-transmitting conductive layer formed on at least a
periphery of the reflecting conductive layer.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a division of U.S. application Ser. No.
12/465,748, filed May 14, 2009 which is a division of U.S.
application Ser. No. 11/255,107, filed Oct. 21, 2005, now U.S. Pat.
No. 7,538,845, the contents of which are incorporated herein by
reference.
[0002] The present application claims priority from Japanese
application JP2004-316250 filed on Oct. 29, 2004, the content of
which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to a liquid crystal display
device, and more particularly to a liquid crystal display device
having pixel electrodes and counter electrodes in a pixel region
formed on a liquid-crystal-side surface of one substrate out of
respective substrates which are arranged to face each other in an
opposed manner with liquid crystal therebetween.
[0004] This kind of liquid crystal display device is referred to as
a so-called lateral electric field type (IPS type) liquid crystal
display device, for example, and is known as a display device which
has a so-called wide viewing angle characteristic compared to
liquid crystal display devices adopting other methods.
[0005] On the other hand, although the liquid crystal display
device is usually provided with a backlight or the like on a back
surface of a liquid crystal display panel, recently, in view of the
reduction of the power consumption, there has been known a liquid
crystal display device which allows the recognition of an image by
making use of an external light such as sun beams when
necessary.
[0006] The liquid crystal display device is of a type which forms a
so-called transmission region which allows light from the backlight
or the like to pass therethrough in a portion of the pixel region
and forms a reflection region which reflects light from sun beams
and returns the light frontward in a remaining portion. The latter
liquid crystal display device is provided with a reflector or a
means which has a function of the reflector.
[0007] Various types of liquid crystal display devices having such
a constitution have been disclosed in JP-A-2003-207795 (patent
document 1), JP-A-2003-15155 (patent document 2), JP-A-2001-343670
(patent document 3), JP-A-9-269508 (patent document 4) and the
like. However, in the patent document 1, a distance between
electrodes in the reflection region is narrower than a distance
between electrodes in a transmission region and hence, the liquid
crystal display device disclosed in the patent document 1 differs
from the liquid crystal display device of the present
invention.
[0008] Further, in the patent document 2, a potential from a second
signal line electrode 11 is supplied to a reflector provided to the
inside of a pixel (see FIG. 15 and FIG. 16 in the document) and
hence, the liquid crystal display device disclosed in the patent
document 2 differs from the liquid crystal display device of the
present invention.
[0009] Further, in the patent document 3, although a potential of a
video signal is supplied to a reflector which also functions as a
capacitance, the patent document 3 is directed to a so-called
vertical electric field type liquid crystal display device and
hence, the liquid crystal display device disclosed in the patent
document 3 differs from the liquid crystal display device of the
present invention.
[0010] Still further, in the patent document 4, a pair of
electrodes are respectively formed of a stacked body constituted of
a non-light-transmitting conductive layer and a light-transmitting
conductive layer. However, although the non-light-transmitting
conductive layer is provided with a light shielding function, the
non-light-transmitting conductive layer is not provided with a
reflection function and hence, the liquid crystal display device
disclosed in the patent document 4 differs from the liquid crystal
display device of the present invention.
SUMMARY OF THE INVENTION
[0011] With respect to the conventional liquid crystal display
devices, inventors of the present invention have found out that
there exists the difference in brightness between an image obtained
from the reflection region and an image obtained from the
transmission region and there arises a necessity to cope with such
difference in brightness.
[0012] Further, on the premise of the constitution of the lateral
electric field type liquid crystal display device, there also
arises a task with respect to the manner of forming reflectors in
the inside of a pixel region. That is, depending on the
constitution, there may arise a drawback that a parasitic
capacitance is generated.
[0013] Further, an optical path length of light in the inside of
the liquid crystal is approximately twice as long as an optical
path length of light in the reflection region and a change of a
phase of light attributed to the difference in the optical path
length of light brings about difference in image quality between
the transmission region and the reflection region whereby there
arises a necessity to cope with such difference in image
quality.
[0014] The present invention has been made under such circumstances
and it is an advantage of the present invention to provide a liquid
crystal display device which can reduce the difference in
brightness between an image obtained from a reflection region and
an image obtained from a transmission region.
[0015] Further, it is another advantage of the present invention to
provide a liquid crystal display device which can reduce a
parasitic capacitance.
[0016] Still further, it is another advantage of the present
invention to provide a liquid crystal display device which can
suppress the difference in image quality attributed to the
difference in optical path length in the inside of liquid
crystal.
[0017] To briefly explain the summary of typical inventions among
inventions disclosed in this specification, they are as
follows.
[0018] (1) In a liquid crystal display device which includes a
first substrate, a second substrate and liquid crystal sandwiched
between the first substrate and the second substrate,
[0019] the first substrate includes a first electrode having at
least one linear portion and a second electrode having at least one
linear portion in the inside of a pixel region,
[0020] as viewed in a plan view, the linear portion of the first
electrode and the linear portion of the second electrode are
alternately arranged in the inside of the pixel region,
[0021] the liquid crystal is driven by an electric field generated
between the first electrode and the second electrode,
[0022] the pixel region includes a transmission region which
performs a display by allowing light from a back surface side to
pass therethrough and a reflection region which performs a display
by reflecting light from a front surface side, and
[0023] as viewed in a plan view, a gap between the linear portion
of the first electrode and the linear portion of the second
electrode in the reflection region is larger than a gap between the
linear portion of the first electrode and the linear portion of the
second electrode in the transmission region.
[0024] (2) In a liquid crystal display device which includes a
first substrate, a second substrate and liquid crystal sandwiched
between the first substrate and the second substrate,
[0025] the first substrate includes a first electrode having at
least one linear portion and a second electrode having at least one
linear portion in the inside of a pixel region,
[0026] as viewed in a plan view, the linear portion of the first
electrode and the linear portion of the second electrode are
alternately arranged in the inside of the pixel region,
[0027] the liquid crystal is driven by an electric field generated
between the first electrode and the second electrode,
[0028] the pixel region includes a transmission region which
performs a display by allowing light from a back surface side to
pass therethrough and a reflection region which performs a display
by reflecting light from a front surface side, and
[0029] assuming a layer thickness of the liquid crystal in the
transmission region as dt and a layer thickness of the liquid
crystal in the reflection region as dr, a relationship
0.75dt.ltoreq.dr.ltoreq.1.1dt is established, and
[0030] as viewed in a plan view, a gap between the linear portion
of the first electrode and the linear portion of the second
electrode in the reflection region is larger than a gap between the
linear portion of the first electrode and the linear portion of the
second electrode in the transmission region.
[0031] (3) In the constitution (1) or (2), as viewed in a plan
view, with respect to at least either one of the linear portion of
the first electrode and the linear portion of the second electrode,
a width of the linear portion in the reflection region is smaller
than a width of the linear portion in the transmission region.
[0032] (4) In a liquid crystal display device which includes a
first substrate, a second substrate and a liquid crystal sandwiched
between the first substrate and the second substrate,
[0033] the first substrate includes a first electrode having a
plurality of linear portions and a second electrode having a planar
portion in the inside of a pixel region,
[0034] the liquid crystal is driven by an electric field generated
between the first electrode and the second electrode,
[0035] the linear portions of the first electrode are arranged
above the planar portion of the second electrode in an overlapped
manner by way of an insulation film,
[0036] the pixel region includes a transmission region which
performs a display by allowing light from a back surface side to
pass therethrough and a reflection region which performs a display
by reflecting light from a front surface side, and
[0037] as viewed in a plan view, a gap between the neighboring
linear portions of the first electrode in the reflection region is
larger than a gap of the neighboring linear portions of the first
electrode in the transmission region.
[0038] (5) In a liquid crystal display device which includes a
first substrate, a second substrate and a liquid crystal sandwiched
between the first substrate and the second substrate,
[0039] the first substrate includes a first electrode having a
plurality of linear portions and a second electrode having a planar
portion in the inside of a pixel region,
[0040] the liquid crystal is driven by an electric field generated
between the first electrode and the second electrode,
[0041] the linear portions of the first electrode are arranged
above the planar portion of the second electrode in an overlapped
manner by way of an insulation film,
[0042] the pixel region includes a transmission region which
performs a display by allowing light from a back surface side to
pass therethrough and a reflection region which performs a display
by reflecting light from a front surface side,
[0043] assuming a layer thickness of the liquid crystal in the
transmission region as dt and a layer thickness of the liquid
crystal in the reflection region as dr, a relationship
0.75dt.ltoreq.dr.ltoreq.1.1dt is established, and
[0044] as viewed in a plan view, a gap between the neighboring
linear portions of the first electrode in the reflection region is
larger than a gap of the neighboring linear portions of the first
electrode in the transmission region.
[0045] (6) In the constitution (4) or (5), as viewed in a plan
view, a width of the linear portion of the first electrode in the
reflection region is smaller than a width of the linear portion of
the first electrode in the transmission region.
[0046] (7) In a liquid crystal display device which includes a
first substrate, a second substrate and a liquid crystal sandwiched
between the first substrate and the second substrate,
[0047] the first substrate includes a pixel electrode to which a
video signal is applied and a counter electrode to which a signal
which is common with at least one of neighboring pixel regions and
becomes the reference with respect to the video signal is applied
in the inside of a pixel region,
[0048] the liquid crystal is driven by an electric field generated
between the pixel electrode and the counter electrode,
[0049] the pixel region includes a reflector which performs a
reflection display by reflecting light from the front surface side
on at least a portion of the pixel region,
[0050] the reflector has at least a portion thereof overlapped to
the pixel electrode and the counter electrode by way of an
insulation film, and
[0051] the reflector is formed independently for every pixel region
and a signal which is equal to a signal applied to the pixel
electrode is applied to the reflector.
[0052] (8) In the constitution (7), the first substrate includes
gate signal lines to which a scanning signal is applied, drain
signal lines to which the video signal is applied, thin film
transistors which are connected with the gate signal lines and are
driven in response to the scanning signal, and source electrodes to
which the video signal is applied by way of the thin film
transistors, and
[0053] the reflector is formed by extending the source
electrode.
[0054] (9) In the constitution (8), the liquid crystal display
device includes a capacitance signal line which is formed at a
position below the source electrode in an overlapped manner by way
of a second insulation film.
[0055] (10) In any one of the constitutions (7) to (9), the pixel
region includes a transmission region which performs a transmission
display by allowing light from a back surface side to pass
therethrough in at least a portion of the pixel region.
[0056] (11) In a liquid crystal display device which includes a
first substrate, a second substrate and liquid crystal sandwiched
between the first substrate and the second substrate,
[0057] the first substrate includes a pixel electrode to which a
video signal is applied and a counter electrode to which a signal
which is common with at least one of neighboring pixel regions and
becomes the reference with respect to the video signal is applied
in the inside of a pixel region,
[0058] the pixel region includes a reflector which performs a
reflection display by reflecting light from the front surface side
on at least a portion of the pixel region,
[0059] the pixel electrode and the reflector are formed below the
counter electrode and have at least portions thereof overlapped to
the counter electrode by way of an insulation film,
[0060] the reflector is independently formed for every pixel region
and a signal equal to the signal applied to the pixel electrode is
applied, and
[0061] the liquid crystal is driven by an electric field which is
generated between the pixel electrode which also functions as the
reflector and the counter electrode.
[0062] (12) In the constitution (11), the first substrate includes
gate signal lines to which a scanning signal is applied, drain
signal lines to which the video signal is applied, thin film
transistors which are connected with the gate signal lines and are
driven in response to the scanning signal, and source electrodes to
which the video signal is applied by way of the thin film
transistors, and
[0063] the reflector is formed by extending the source
electrode.
[0064] (13) In the constitution (12), the liquid crystal display
device includes a capacitance signal line which is formed at a
position below the source electrode in an overlapped manner by way
of a second insulation film.
[0065] (14) In any one of the constitutions (11) to (13), the pixel
region includes a transmission region which performs a transmission
display by allowing light from a back surface side to pass
therethrough in at least a portion of the pixel region.
[0066] (15) In the constitution (14), the pixel electrode includes
a light-transmitting conductive layer formed in the transmission
region.
[0067] (16) In a liquid crystal display device which includes a
first substrate, a second substrate and a liquid crystal sandwiched
between the first substrate and the second substrate,
[0068] the first substrate includes a first electrode and a second
electrode in the inside of a pixel region,
[0069] the liquid crystal is driven by an electric field generated
between the first electrode and the second electrode,
[0070] at least one of the first electrode and the second electrode
is, as viewed in a plan view, constituted of a reflecting
conductive layer and a light-transmitting conductive layer which is
formed on at least a periphery of the reflecting conductive layer,
and
[0071] the reflecting conductive layer performs a reflection
display by reflecting light from a front surface side.
[0072] (17) In the constitution (16), both of the first electrode
and the second electrode are, as viewed in a plan view, constituted
of a reflecting conductive layer and a light-transmitting
conductive layer which is formed on at least a periphery of the
reflecting conductive layer.
[0073] (18) In the constitution (16) or (17), the
light-transmitting conductive layer is formed in a state that the
reflecting conductive layer is covered with the light-transmitting
conductive layer.
[0074] (19) In any one of the constitutions (16) to (18), the first
electrode includes at least one linear portion in the inside of the
pixel region,
[0075] the second electrode includes at least one linear portion in
the inside of the pixel region,
[0076] as viewed in a plan view, the linear portion of the first
electrode and the liner portion of the second electrode are
alternately arranged in the inside of the pixel region, and
[0077] the linear portion of at least one of the first electrode
and the second electrode is, as viewed in a plan view, constituted
of the reflecting conductive layer and the light-transmitting
conductive layer formed on at least a periphery of the reflecting
conductive layer.
[0078] Here, the present invention is not limited to the
above-mentioned constitutions and various modifications can be made
without departing from the technical concept of the present
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0079] FIG. 1 is a plan view showing one embodiment of the
constitution of a pixel of a liquid crystal display device
according to the present invention;
[0080] FIG. 2 is a cross-sectional view taken along a line A-A' in
FIG. 1;
[0081] FIG. 3 is a cross-sectional view taken along a line B-B' in
FIG. 1 and also is a drawing which shows the constitution of a
pixel electrode and a counter electrode of the liquid crystal
display device according to the present invention;
[0082] FIG. 4 is an explanatory view of the pixel of the liquid
crystal display device according to the present invention which has
a transmission region and a reflection region;
[0083] FIG. 5 is an equivalent circuit diagram showing one
embodiment of the constitution of the pixel of the liquid crystal
display device according to the present invention;
[0084] FIG. 6 is a plan view showing another embodiment of the
constitution of the pixel of the liquid crystal display device
according to the present invention;
[0085] FIG. 7 is a cross-sectional view taken along a line A-A' in
FIG. 6;
[0086] FIG. 8 is an equivalent circuit diagram showing another
embodiment of the constitution of the pixel of the liquid crystal
display device according to the present invention;
[0087] FIG. 9 is a plan view showing another embodiment of the
constitution of the pixel of the liquid crystal display device
according to the present invention;
[0088] FIG. 10 is a cross-sectional view taken along a line A-A' in
FIG. 9;
[0089] FIG. 11 is a cross-sectional view showing another embodiment
in which a modification of the constitution shown in FIG. 10 is
described;
[0090] FIG. 12 is a plan view showing the constitution of a
comparison example for explaining an advantageous effect of the
constitution shown in FIG. 9;
[0091] FIG. 13 is an equivalent circuit diagram showing a parasitic
capacitance generated in the constitution shown in FIG. 12;
[0092] FIG. 14 is a cross-sectional view showing a parasitic
capacitance generated in the constitution shown in FIG. 12;
[0093] FIG. 15 is a plan view showing another embodiment of the
constitution of the pixel of the liquid crystal display device
according to the present invention;
[0094] FIG. 16 is a plan view showing another embodiment of the
constitution of the pixel of the liquid crystal display device
according to the present invention;
[0095] FIG. 17A and FIG. 17B are graphs showing B-V
characteristics, wherein FIG. 17A is the graph showing the B-V
characteristics of a reflection region and a transmission region in
a state that a gap between a pair of electrodes is equal and FIG.
17B is the graph showing the B-V characteristic of the reflection
region and the transmission region in a state that a gap between a
pair of electrodes is different;
[0096] FIG. 18 is a plan view showing another embodiment of the
constitution of the pixel of the liquid crystal display device
according to the present invention;
[0097] FIG. 19 is a cross-sectional view taken along a line B-B' in
FIG. 18;
[0098] FIG. 20 is a cross-sectional view taken along a line A-A' in
FIG. 18;
[0099] FIG. 21 is a plan view showing another embodiment of the
constitution of the pixel of the liquid crystal display device
according to the present invention;
[0100] FIG. 22 is a cross-sectional view taken along a line B-B' in
FIG. 21;
[0101] FIG. 23 is a plan view showing another embodiment of the
constitution of the pixel of the liquid crystal display device
according to the present invention;
[0102] FIG. 24 is a plan view showing another embodiment of the
constitution of the pixel of the liquid crystal display device
according to the present invention; and
[0103] FIG. 25 is a cross-sectional view taken along a line B-B' in
FIG. 24.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0104] Embodiments of a liquid crystal display device according to
the present invention are explained in conjunction with attached
drawings hereinafter.
Embodiment 1
[0105] FIG. 5 is a graph showing one embodiment of an equivalent
circuit showing one pixel of the liquid crystal display device
according to the present invention, wherein a common signal line
CTL runs at a portion corresponding to an upper side of a region of
the pixel formed in a rectangular shape, a gate signal line
(scanning signal line) GL runs at a portion corresponding to a
lower side of the region of the pixel, and a drain signal line
(video signal line) DL runs at a portion corresponding to a left
side.
[0106] Other pixels which are arranged close to the pixel in the
left, right, upper and lower directions have the substantially same
constitution, wherein the common signal line CTL and the gate
signal line GL are used in common with respect to other pixels
which are arranged close to the pixel in the lateral direction, and
the drain signal line DL is used in common with respect to other
pixels which are arranged close to the pixel in the vertical
direction.
[0107] Further, the gate signal line GL is connected to respective
gate electrodes of two switching elements TFT1, TFT2, wherein the
respective switching elements TFT1, TFT2 are turned on in response
to a scanning signal supplied from the gate signal line GL.
[0108] A video signal from the drain signal line DL is supplied to
the pixel electrode PX through the respective switching elements
TFT1, TFT2 which are turned on, wherein the video signal is
supplied to one switching element TFT2 from one switching element
TFT1.
[0109] The pixel electrode PX is constituted of a group of
electrodes formed of a plurality of (two pieces in the drawing)
electrodes which extend in the running direction of the drain
signal line DL and are arranged in parallel on the running
direction side of the gate signal line GL in the inside of the
pixel region.
[0110] Further, the pixel includes a counter electrode CT which
generates an electric field between the pixel electrode PX and the
counter electrode CT, wherein the counter electrode CT is also
constituted of a group of electrodes formed of a plurality of
(three pieces in the drawing) electrodes which extend in the
running direction of the drain signal line DL and are arranged in
parallel on the running direction side of the gate signal line GL,
and the respective electrodes of the counter electrode CT are
alternately arranged with respective electrodes of the pixel
electrode PX.
[0111] One ends of respective electrodes of the counter electrode
CT are connected to the common signal lien CTL, and a signal which
becomes the reference with respect to the video signal is applied
to the respective electrodes of the counter electrode CT by way of
the common signal line CTL.
[0112] Here, although two switching elements are used in the
above-mentioned equivalent circuit diagram, the present invention
is not limited to such a case and it is needless to say that the
pixel includes one switching element, for example.
[0113] FIG. 1 is a plan view showing the constitution of the pixel
region which embodies the equivalent circuit shown in FIG. 5 and
the constitution is substantially geometrically equal to the
equivalent circuit. Further, FIG. 2 shows a cross-sectional view
taken along a line A-A' in FIG. 1. Here, the switching elements
TFT1, TFT2 are formed of so-called thin film transistors TFT1,
TFT2.
[0114] In FIG. 1, on a main surface of a substrate not shown in the
drawing, first of all, a poly-silicon layer PS which forms
semiconductor layers of the thin film transistors TFT1, TFT2 is
formed. Since the pixel includes two switching elements as
described above, the poly-silicon layer PS is formed to wind
through a region where the gate signal line GL is formed one time
thus forming two intersecting portions with the gate signal line
GL. Here, a background layer (not shown) may be formed between the
substrate not shown in the drawing and the poly-silicon layer PS.
Further, although an example which uses poly-silicon as a material
of the semiconductor layer is explained in this embodiment,
amorphous silicon may be used as the material of the semiconductor
layer. Further, semiconductor other than silicon may be used.
[0115] On the substrate, an insulation film GI (see FIG. 2) is
formed in a state that the insulation film GI also covers the
poly-silicon layer PS. The insulation film GI also functions as a
gate insulation film in regions where thin film transistors TFT1,
TFT2 are formed.
[0116] The gate signal line GL is formed on an upper surface of the
insulation film GI, and a first interlayer insulation film INS1
(see FIG. 2) is also formed on the substrate in a state that the
first interlayer insulation film INS1 covers the gate signal line
GL. For example, MoW is used as a material of the gate signal line
GL.
[0117] On an upper surface of the first interlayer insulation film
INS1, the drain signal line DL and first source electrodes ST1 of
the thin film transistors TFT2 (electrodes which are connected with
the pixel electrodes PX described later) are formed.
[0118] The drain signal lines DL and the first source electrodes
ST1 are constituted of a conductive film having the three-layered
structure in which a MoW layer, an Al layer and a MoW layer are
sequentially stacked, for example. It is because that, as will be
described explicitly later, to establish the connection with the
poly-silicon layer PS or the pixel electrode PX, the first source
electrode ST1 at least requires a buffer layer made of MoW or the
like at least on a connection surface thereof. Accordingly, for
example, Ag or the like can be also selected besides MoW as the
material of the buffer layer. Here, when materials which can obtain
a favorable contact are selected as metal which is used as the
material of the first source electrode ST1 and another conductive
film connected to the first source electrode ST1, the buffer layer
may be omitted.
[0119] The drain signal line DL is connected with a drain region of
one thin film transistor TFT1 via a contact hole CH1 formed in the
first interlayer insulation film INS1 and the insulation film
GI.
[0120] The first source electrode ST1 is connected with the source
region of another thin film transistor TFT2 via a contact hole CH2
formed in the first interlayer insulation film INS1 and the
insulation film GI.
[0121] On an upper surface of the first interlayer insulation film
INS1, a second interlayer insulation film INS2 (see FIG. 2) is
formed in a state that the second interlayer insulation film INS2
also covers the drain signal lines DL and the first source
electrodes ST1, while on an upper surface of the second interlayer
insulation film INS2, a protective film PAS (see FIG. 2) is formed.
The protective film PAS is constituted of an organic material layer
which is formed by coating, for example. The protective film PAS is
provided for leveling a surface.
[0122] In portions of the protective film PAS, contact holes CH3
which also penetrate the second interlayer insulation film INS2
arranged below the protective film PAS are formed. The contact hole
CH3 is formed to expose a portion of the first source electrode ST1
thus establishing the connection of the pixel electrode PX
described later and the first source electrode ST1 via the contact
hole CH3.
[0123] On an upper surface of the protective film PAS, the pixel
electrodes PX, the counter electrodes CT and the common signal
lines CTL which are connected with the counter electrodes CT are
formed.
[0124] Here, these pixel electrodes PX, counter electrodes CT and
common signal liens CTL which are connected with the counter
electrodes CT are formed of the two-layered structure in which a
reflecting conductive film made of, for example, Al, MoW, Ag or the
like and a light-transmitting conductive film made of ITO (Indium
Tin Oxide) are sequentially stacked.
[0125] The pixel electrode PX includes at least one linear portion.
In FIG. 1, two linear portions of the pixel electrode PX have one
ends thereof on the thin film transistors TFT1, TFT2 side connected
with each other, and the connecting portions are arranged to cover
the contact hole CH3. Due to such a constitution, the connection
between the pixel electrode PX and the first source electrode ST1
is established.
[0126] The counter electrode CT includes at least one linear
portion. In FIG. 1, three linear portions of the counter electrode
CT are connected with each other using the common signal line CTL.
Here, among these three linear portions, two linear portions on
both sides are used in common by the neighboring pixel and hence,
these two linear portions also function as the counter electrodes
CT of the neighboring pixel regions. Among respective electrodes of
the linear portions of the counter electrode CT, the electrodes
which are arranged close to the drain signal line DL are formed in
a state that the electrodes sufficiently cover the drain signal
line DL. That is, the electrode and the drain signal line DL are
arranged in a state that a center line of the electrode is
substantially aligned with a center line of the drain signal line
DL and, at the same time, a width of the electrode is set larger
than a width of the drain signal line DL. Due to such a
constitution, lines of electric force attributed to the signal from
the drain signal line DL are terminated to the electrode side thus
obviating the termination of the electric lines of force to the
pixel electrode PX side whereby an image is prevented from
generating noises.
[0127] The linear portions of the pixel electrode PX and the linear
portions of the counter electrode CT are alternately arranged in
the inside of the pixel region.
[0128] Here, the linear portions of the pixel electrode PX and the
linear portions of the counter electrode CT are not always formed
of a straight line. In this specification, the linear portion is
not limited to the straight line and includes a curve or a line
which is bent in a midst portion thereof.
[0129] Although orientation films are formed on surfaces of the
pair of substrates which are directly brought into contact with the
liquid crystal, these orientation films are omitted from the
drawing. Further, although a backlight is arranged on a back
surface side (a side opposite to a viewer) of the liquid crystal
display panel, the backlight is omitted from the drawing.
[0130] FIG. 3 is a view showing cross sections of the counter
electrode CT and the pixel electrode PX taken along a line B-B' in
FIG. 1.
[0131] As described above, the counter electrode CT and the pixel
electrode PX are respectively formed of the two-layered structure
in which the reflecting conductive layer and the light-transmitting
conductive layer are sequentially stacked.
[0132] Here, with respect to the counter electrode CT, a portion
thereof which is formed of the reflecting conductive layer is
referred to as a counter electrode CT1 and a portion thereof which
is formed of the light-transmitting conductive layer is referred to
as a counter electrode CT2, while with respect to the pixel
electrode PX, a portion thereof which is formed of the reflecting
conductive layer is referred to as a pixel electrode PX1 and a
portion thereof which is formed of the light-transmitting
conductive layer is referred to as a pixel electrode PX2.
[0133] As a material of the light-transmitting conductive layer,
besides the above-mentioned ITO, ITZO (Indium Tin Zinc Oxide), IZO
(Indium Zinc Oxide), SnO.sub.2 (Tin Oxide), In.sub.2O.sub.3 (Indium
Oxide) or the like can be also selected.
[0134] As a material of the reflective conductive layer, Al, MoW,
Ag or the like can be used. It is desirable that the reflectance is
50% or more. It is more desirable that the reflectance is 70% or
more. For example, since the reflectance of Al is approximately
95%, Al is suitable as the material of the reflecting conductive
layer.
[0135] Here, when Al is used as a material of the reflecting
conductive layer, an electrical contact with the light-transmitting
conductive layer is not favorable and hence, it is desirable to
connect the reflecting conductive layer with the light-transmitting
conductive layer by way of a buffer layer not shown in the drawing
at least one portion. When MoW, Ag or the like is used as the
material of the reflecting conductive layer, the reflecting
conductive layer exhibits the favorable electric contact with the
light-transmitting conductive layer and hence, the buffer layer may
be omitted.
[0136] In FIG. 3, for example, the pixel electrode PX1 has side
wall surfaces of respective sides thereof formed in a tapered shape
with a width thereof expanding toward a distal end thereof, and the
pixel electrode PX2 is formed so as to cover the pixel electrode
PX1.
[0137] That is, a center axis which is arranged in the extending
direction of the pixel electrode PX1 is substantially aligned with
a center axis of the pixel electrode PX2, while a width of the
pixel electrode PX2 is set larger than a width of the pixel
electrode PX1. In other words, the pixel electrode PX2 is
configured to project outwardly from surroundings (peripheries) of
the pixel electrode PX1.
[0138] Such a constitution is also adopted by the counter electrode
CT, wherein the counter electrode CT1 has side wall surfaces of
respective sides thereof formed in a tapered shape with a width
thereof expanding toward a distal end thereof, and the counter
electrode CT2 is formed so as to cover the counter electrode
CT1.
[0139] That is, a center axis which is arranged in the extending
direction of the counter electrode CT1 is substantially aligned
with a center axis of the counter electrode CT2, while a width of
the counter electrode CT2 is set larger than a width of the counter
electrode CT1. In other words, the counter electrode CT2 is
configured to project outwardly from surroundings (peripheries) of
the counter electrode CT1.
[0140] In the pixel region which includes the pixel electrode PX
and the counter electrode CT having such a constitution, so-called
reflection regions RT and so-called transmission regions TT are
formed. The reflection regions RT are regions where the counter
electrodes CT1 and the pixel electrodes PX1 are formed. The
transmission regions TT are remaining regions and also include
portions where the counter electrodes CT2 and the pixel electrodes
PX2 are formed.
[0141] When the pixel region is viewed in a plan view, with respect
to a layer surface on which the pixel electrode PX and the counter
electrode CT are formed, the regions where the reflecting
conductive layer is formed function as the reflection regions RT,
while the remaining regions excluding the regions where the
reflecting conductive layer is formed and including regions where
the light-transmitting conductive layer is formed and regions where
the light-transmitting conductive layer is not formed function as
the transmission region TT.
[0142] Next, advantageous effects of the present invention are
explained.
[0143] FIG. 4 shows a transmission optical path TLP and a
reflection optical path RLP which pass through the inside of the
liquid crystal LC in a state that an electric field (or electric
lines of force) is generated between the counter electrode CT and
the pixel electrode PX and the liquid crystal LC is activated in
response to the electric field.
[0144] The transmission optical path TLP is formed of a path along
which light passes through between the counter electrode CT1 and
the pixel electrode PX1, while the reflection optical path RLP is
formed of a path along which light irradiated to the counter
electrode CT1 or the pixel electrode PX1 is reflected on the
counter electrode CT1 or the pixel electrode PX1.
[0145] In this case, an optical path length of the reflecting light
which passes through the liquid crystal is twice as long as an
optical path length of the transmitting light since the reflecting
light reciprocates. Assuming that the behavior of the liquid
crystal is at the substantially same level between the transmission
region TT and the reflection region RT when the liquid crystal is
driven by the electric field, the influence (phase shift or the
like) which is applied to the light when the light passes through
the liquid crystal in the reflection region RT becomes
approximately twice as large as the corresponding influence in the
transmission region TT. Accordingly, there arises a drawback that
the brightness differs between the transmission regions TT and the
reflection regions RT.
[0146] However, due to the provision of the above-mentioned
constitutions, the present invention can obtain advantageous
effects to suppress such a drawback.
[0147] That is, as can be readily understood from the distribution
of the electric lines of force shown in FIG. 4, at locations in the
vicinity of the center right above the counter electrode CT and the
pixel electrode PX (right above the counter electrode CT1 and the
pixel electrode PX1), components of the electric field
substantially parallel to the substrate are small and hence, it is
possible to suppress the behavior of the liquid crystal at the
portions to a level substantially one half of a level of the
behavior of the liquid crystal in the vicinity of the portions.
[0148] Accordingly, even when the reflecting light having the long
optical path length in the inside of the liquid crystal receives
the phase shift corresponding to the optical path length, the level
of the phase shift eventually becomes equal to the phase shift of
light which the transmitting light having the short optical path
length receives.
[0149] Accordingly, it is possible to reduce the drawback that the
image display attributed to the transmitting light and the image
display attributed to the reflecting light differ from each
other.
[0150] Further, the counter electrode CT and the pixel electrode PX
are not formed of only the reflecting conductive layer but are
formed of the sequential two-layered structure formed of the
reflecting conductive layer and the light-transmitting conductive
layer and, at the same time, the light-transmitting conductive
layer projects outwardly from the reflecting conductive layer and
hence, it is possible to obtain following advantageous effects.
[0151] That is, assuming that the counter electrode CT and the
pixel electrode PX are formed of only the reflecting conductive
layer (only the counter electrode CT1, the pixel electrode PX1),
the regions where these respective electrodes are formed are all
constituted as the reflection region and hence, a distance between
the electrode and other electrode arranged close to the electrode
is increased. In this case, the electric field between the
respective electrodes becomes weak and the display in the
transmission regions TT is deteriorated.
[0152] To cope with such a drawback, it may be possible to narrow
the distance between the counter electrode CT1 and the pixel
electrode PX1. In this case, however, it is necessary to increase
the number of electrodes in the pixel region and hence, an area
which the transmission region TT occupies becomes small.
[0153] To the contrary, by adopting the constitution in which the
counter electrode CT and the pixel electrode PX are formed of the
sequential two-layered structure formed of the reflecting
conductive layer and the light-transmitting conductive layer and,
at the same time, the light-transmitting conductive layer projects
outwardly from the reflecting conductive layer, it is possible to
ensure the sufficient area which the transmission regions TT occupy
while maintaining the intensity of the electric field in the
transmission regions TT by setting the distance of the gap between
the respective electrodes (the counter electrode CT2 and the pixel
electrode PX2 in this case), to a proper value. Further, the
molecules of the liquid crystal LC exhibit the larger degree of
behavior in peripheral portions of the counter electrode CT and the
pixel electrode PX (the projecting portions of the counter
electrode CT2 and the pixel electrode PX2) than the center portions
of the counter electrode CT and the pixel electrode PX (right above
the counter electrode CT1 and the pixel electrode PX1) and hence,
when the constitution is used in the reflection display, there
arises a drawback that the phase shift of light in the portion
becomes excessively large. However, since a certain amount of the
behavior of the liquid crystal is ensured in the portion, it is
possible to obtain the phase shift of light to an extent which
allows the constitution to be used in the transmission display.
Accordingly, by using such a portion as the transmission regions
TT, it is possible to further enhance the brightness of the
transmission regions TT while reducing the influence attributed to
the above-mentioned drawback.
[0154] As described above, according to the present invention, it
is possible to establish the balance between the reflectance and
the transmissivity as a whole and, at the same time, it is possible
to realize the bright display.
[0155] Further, in this embodiment, the reflecting conductive layer
(CT1, PX1) formed of the metal layer is sufficiently covered with
the light-transmitting conductive layer (CT2, PX2) and hence, it is
possible to obtain the advantageous effect that the direct contact
of the reflecting conductive layer with the liquid crystal or the
contact of the reflecting conductive layer with the liquid crystal
by way of the orientation film not shown in the drawing can be
obviated. This is because that assuming the reflecting conductive
layer is brought into contact with the liquid crystal, a specific
resistance of the liquid crystal is changed due to substances which
are dissolved from the conductive layer and the substances
ill-affect the image quality.
[0156] Accordingly, it is needless to say that when a barrier layer
or the like which interrupts the intrusion of the dissolved
substances in the liquid crystal is formed above the pixel
electrode PX and the counter electrode CT by forming an insulation
film or the like, for example, it is not always necessary to
sufficiently cover the reflecting conductive layer (CT1, PX1) with
the light transmitting conductive layer (CT2, PX2). It is also
possible to overlap the reflecting conductive layer and the
light-transmitting conductive layer with an insulation film
interposed therebetween.
[0157] Here, in this embodiment, the sequential stacked body formed
of the reflecting conductive layer and the light-transmitting
conductive layer is also applied to the common signal line CTL. In
general, the light-transmitting conductive layer exhibits the large
electric resistance and hence, the electric resistance of the
common signal line CTL is reduced by connecting the
light-transmitting conductive layer with the reflecting conductive
layer which exhibits the low electric resistance.
[0158] Here, although both of the pixel electrode PX and the
counter electrode CT adopt the sequential stacked body formed of
the reflecting conductive layer and the light-transmitting
conductive layer, either one of the pixel electrode PX and the
counter electrode CT may adopt the sequential stacked body.
Embodiment 2
[0159] FIG. 6 is a plan view showing another embodiment of the
liquid crystal display device according to the present invention
and corresponds to FIG. 1. The liquid crystal display device has an
equivalent circuit substantially equal to the equivalent circuit
shown in FIG. 5. Further, FIG. 7 is a cross-sectional view taken
along a line A-A' in FIG. 6.
[0160] The constitution which makes this embodiment different from
the embodiment shown in FIG. 1 lies, first of all, in that the
above-mentioned first metal layers (CT1, PX1) in the counter
electrode CT and the pixel electrode PX are formed of the
two-layered structure in which, for example, a MoW layer (indicated
by symbol PX11 in the drawing) and an Al layer (indicated by symbol
PX12 in the drawing) are sequentially stacked.
[0161] Al exhibits the high reflectance (approximately 95%) and
hence, it is desirable to adopt the region formed of the Al layer
as the reflection region RT.
[0162] Accordingly, for example, the pixel electrode PX is formed
of the three-layered structure including the uppermost pixel
electrode PX2 thus providing the constitution in which the
conductive layers made of MoW, Al and ITO from the lowermost layer
are sequentially stacked.
[0163] Further, the first source electrode ST1 of the thin film
transistor TFT is formed of the two-layered structure in which an
MoW layer (indicated by symbol ST11 in the drawing) and an Al layer
(indicated by symbol ST12 in the drawing) are sequentially
stacked.
[0164] In this case, the connection of the first source electrode
ST1 and the pixel electrode PX in the contact hole CH3 can ensure
the favorable electric connection since Al of the first source
electrode ST1 and MoW of the pixel electrode PX are brought into
contact with each other.
[0165] However, in the pixel electrode PX, the electric connection
between ITO of the uppermost layer and Al of the lower layer is
relatively unfavorable and hence, a contact hole CH4 is formed in
Al in the vicinity of the contact hole CH3 thus ensuring the
electric connection between ITO of the uppermost layer and MoW of
the lowermost layer. This is because that the connection of ITO and
MoW can improve the electric connection.
[0166] The materials which are exemplified in this embodiment are
only examples and the materials can be suitably changed. For
example, Al is replaceable with other material provided that the
material can form the reflecting conductive layer, ITO is
replaceable with other material provided that the material can form
the light-transmitting conductive layer, and MoW is replaceable
with other material provided that the material can function as a
buffer layer when two conductive layers are electrically connected
with each other.
Embodiment 3
[0167] In the above-mentioned embodiments, the portion which
functions as the pixel electrode PX and the counter electrode CT is
provided with the pixel electrode PX1 and the counter electrode CT1
which are formed of the reflecting conductive layer. In other
words, in the inside of the substantial pixel region (for example,
in an aperture region of a black matrix), the transmission region
and the reflection region are substantially uniformly arranged.
[0168] However, when it is necessary to allow the transmission
region to ensure an area sufficiently larger than an area of the
reflection region, it is needless to say that the pixel region is
imaginarily divided and one half is configured to possess both of
the reflection region RT and the transmission region TT and another
half does not possess the reflection region RT and possesses only
the transmission region TT.
[0169] FIG. 15 is a plan view of the pixel electrode having such a
constitution and corresponds to FIG. 1.
[0170] As can be readily understood from FIG. 15, using an
imaginary line segment which passes through the substantially
center of the pixel region and is arranged parallel to the gate
signal line GL as a boundary, the pixel electrode PX and the
counter electrode CT in the thin-film-transistor-TFT side region
are only constituted of the pixel electrode PX2 and the counter
electrode CT2 formed of the light-transmitting conductive layer and
the pixel electrode PX1 and the counter electrode CT1 formed of the
reflecting conductive layer are not formed.
[0171] Accordingly, with respect to the imaginary line segment,
only the pixel electrode PX and the counter electrode CT (and the
common signal line CTL) on the side opposite to the thin film
transistor TFT are constituted of the sequential stacked body
formed of the reflecting conductive layer and the
light-transmitting conductive layer.
[0172] However, it is needless to say that such a constitution
merely constitutes one example and shows the constitution in which
an area ratio between the reflection region RT and the transmission
region TT can be freely set and the mode of division can be
arbitrarily set.
Embodiment 4
[0173] FIG. 8 is an equivalent circuit diagram showing another
embodiment of the constitution of the pixel of the liquid crystal
display device according to the present invention and corresponds
to FIG. 5.
[0174] The constitution which makes this embodiment different from
the embodiment shown in FIG. 5 lies in that the pixel of this
embodiment includes a capacitance signal line CDL and a capacitive
element Cst is formed between the capacitance signal line CDL and
the pixel electrode PX or the electrode (first source electrode ST1
or the like) having a potential equal to a potential of the pixel
electrode PX. The capacitive element Cst is provided for storing
the video signal supplied to the pixel electrode PX for a long
time. Here, the capacitance signal line CDL is also formed in
common with pixels which are arranged on both left and right sides
of the pixel electrode PX. A given potential (for example, a
potential equal to a potential of the counter electrode CT) is
applied to the capacitance signal line CDL.
[0175] FIG. 9 is a plan view showing a case in which the equivalent
circuit shown in FIG. 8 is applied to the constitution of the
pixel. Further, a cross-sectional view taken along a line A-A' in
FIG. 9 is shown in FIG. 10. Here, the explanation is made
hereinafter by focusing on only points which make this embodiment
different from the embodiments described heretofore and the
explanation of parts which are common with the parts of the
embodiments described heretofore is omitted.
[0176] On an upper surface of the insulation film GI, gate signal
lines GL and capacitance signal lines CDL are formed. The gate
signal lines GL and the capacitance signal lines CDL are formed in
a same step and MoW is selected as a material of the gate signal
lines GL and the capacitance signal lines CDL.
[0177] Further, a first interlayer insulation film INS is formed on
the upper surface of the insulation film GI in a state that the
first interlayer insulation film INS also covers the gate signal
lines GL and the capacitance signal lines CDL (see FIG. 10).
[0178] On an upper surface of the first interlayer insulation film
INS1, drain signal lines DL and first source electrodes ST1 of thin
film transistors TFT2 are formed.
[0179] The drain signal line DL and the first source electrode ST1
are, for example, constituted of the three-layered structure
conductive film in which a MoW layer, an Al layer and a MoW layer
are sequentially stacked. Here, the MoW layers are formed as buffer
layers and may be formed of other material. Further, the MoW layers
may be omitted when unnecessary.
[0180] Here, the first source electrode ST1 is configured to
function also as a reflector in a reflection region of the pixel.
That is, using an imaginary line segment which passes through the
substantially center of the pixel region and is arranged parallel
to the gate signal line GL as a boundary, the first source
electrode ST1 is formed on a region of a side on which a thin film
transistor TFT is formed in a state that the first source electrode
ST1 is extended over a substantially whole area of the region, and
the reflector is constituted at the portion where the thin film
transistor TFT is formed. Here, the reflector is not limited to the
size, the shape and the position illustrated in the drawing and
they can be arbitrarily changed corresponding to a ratio between
the reflection region and the transmission region.
[0181] Further, the capacitance signal line CDL is formed below the
first source electrode ST1 which also functions as the reflector by
way of a first interlayer insulation film INS and a capacitance Cst
which uses the first interlayer insulation film INS as a dielectric
film is formed in an overlapped portion of the capacitance signal
line CDL and the first source electrode ST1.
[0182] Further, as shown in the drawing, a poly-silicon layer PS is
expanded to a position where the poly-silicon layer PS is
overlapped to the capacitance signal line CDL thus forming a second
capacitance which uses the insulation film GI as a dielectric
layer.
[0183] On an upper surface of a protective film PAS, pixel
electrodes PX, counter electrodes CT and common signal lines CTL
which are connected with the counter electrodes CT are formed.
[0184] Here, the pixel electrodes PX, the counter electrodes CT and
the common signal lines CTL which are connected with the counter
electrodes CT are formed of a light-transmitting conductive layer
(only one layer in this embodiment) made of ITO (Indium Tin
Oxide).
[0185] In this manner, on at least the portion of the pixel region,
the reflector which performs the reflection display by reflecting
light from a front surface side is formed. The reflector is
configured to have at least a portion thereof overlapped to the
pixel electrode PX and the counter electrode CT by way of an
insulation film (for example, a protective film PAS or the
like).
[0186] In a portion of a contact hole CH3, a buffer layer BL made
of MoW or the like, for example, is interposed between the pixel
electrode PX and the first source electrode ST1 thus establishing
the reliable electric connection between the pixel electrode PX and
the first source electrode ST1.
[0187] Here, in this embodiment, either one of the buffer layer BL
and an uppermost MoW layer of the first source electrode ST1 which
functions as a buffer layer may be omitted. Here, to take the fact
that the first source electrode ST1 is allowed to function as the
reflector into consideration, it is preferable to eliminate the
uppermost MoW layer of the first source electrode ST1 to expose the
Al layer for enhancing the reflectance.
[0188] FIG. 11 is a cross-sectional view showing another embodiment
which is a partial modification of the above-mentioned constitution
and corresponds to FIG. 10.
[0189] The constitution which makes this embodiment different from
the embodiment shown in FIG. 10 lies in that a first source
electrode ST1 which also functions as a reflector is constituted of
a sequential stacked body formed of a MoW layer (indicated by
symbol ST11 in the drawing) and an Al layer (indicated by symbol
ST12 in the drawing), and an MoW layer which constitutes a buffer
layer BL is selectively formed in a region of the sequential
stacked body where the contact hole CH3 is formed and in the
vicinity of the region. Due to such a constitution, the Al layer is
exposed and hence, the reflectance of the first source electrode
ST1 as the reflector is further enhanced.
[0190] Further, in the contact hole CH3, a pixel electrode PX which
is connected with the first source electrode ST1 is formed of an
ITO layer having a single layer.
[0191] Next, advantageous effects of the embodiments explained in
conjunction with FIG. 9 to FIG. 11 are explained in comparison with
comparison examples shown in FIG. 12 to FIG. 14.
[0192] In the embodiments explained in conjunction with FIG. 9 to
FIG. 11, the first source electrode ST1 of the thin film transistor
TFT is extended and the first source electrode ST1 is allowed to
ensure the large area so as to also function as the reflector in
the reflection region. The reflector is formed independently for
every pixel region. Further, since the first source electrode ST1
also functions as a source electrode, a video signal which is
applied to the pixel electrode PX is also applied to the first
source electrode ST1. Due to such a constitution, it is possible to
realize the reflector which can reduce a parasitic capacitance
between the first source electrode ST1 and the drain signal line DL
or the gate signal line GL.
[0193] For example, with respect to variations of the reflector, as
comparison examples, it may be possible to consider constitutions
shown in FIG. 12 to FIG. 14 where a common signal line CTL' also
functions as a reflector. Here, the common signal line CTL' is
provided separately from the common signal line CTL and is formed
of a metal layer or the like which exhibits the high
reflectance.
[0194] FIG. 12 is a plan view which shows the constitution of the
pixel provided with the common signal line CTL' which also
functions as a reflector. The common signal line CTL' is formed
between a second interlayer insulation film INS2 and a protective
film PAS and a line width thereof is set relatively large to allow
the common signal line CTL' to be formed in a state that the common
signal line CTL' occupies a reflection region.
[0195] Further, it is necessary to form the common signal line CTL'
in common with the neighboring pixels and hence, it is necessary to
form the common signal line CTL' in a state that the common signal
line CTL' runs while intersecting the drain signal line DL or the
gate signal line GL (In FIG. 12, the common signal line CTL'
intersects the drain signal line DL).
[0196] Here, in the case shown in FIG. 12, there arises a drawback
that a parasitic capacitance Ca which is generated between the
common signal line CTL' and the drain signal line DL is increased
to a level that the parasitic capacitance Ca cannot be ignored. The
same goes for a case in which the common signal line CTL' is
arranged to intersect the gate signal line GL.
[0197] FIG. 13 shows the parasitic capacitance Ca in an equivalent
circuit of the constitution of the pixel shown in FIG. 12 and FIG.
14 shows the parasitic capacitance Ca which is generated between
the drain signal line DL and the common signal line CTL' in a
cross-sectional view taken along a line B-B' in FIG. 12.
[0198] Although a given potential (for example, a potential equal
to a potential of the counter electrode CT) is applied to the
common signal line CTL' which also functions as a reflector, when a
potential of the drain signal line DL is changed to write a video
signal into other pixel, the potential of the common signal line
CTL' is also changed due to the influence from the parasitic
capacitance Ca and hence, there arises a drawback that a display in
a reflection region is changed correspondingly.
[0199] To the contrary, according to the present invention, the
reflector does not intersect the drain signal line DL and the gate
signal line GL and hence, it is possible to obtain an advantageous
effect that the parasitic capacitance can be reduced.
[0200] Further, in the present invention, the reflector can be used
in combination with the capacitance signal line CDL. In this case,
the first source electrode ST1 may be constituted as one electrode
of the capacitance Cst. However, since the combination of the
reflector with the capacitance signal line CDL is an additional
matter, the combined use of the capacitance signal line CDL and the
reflector is arbitrary.
[0201] Here, the capacitance signal line CDL is applicable to the
inventions described in the embodiment 1, the embodiment 3 and the
embodiment 5 and the embodiments succeeding the embodiment 5. Since
the capacitance signal line CDL is readily applicable to these
embodiments by modifying the first embodiment by reference to FIG.
9 and the like, the illustration and the detailed explanation of
such applications are omitted.
Embodiment 5
[0202] FIG. 16 is a plan view of another embodiment of the
constitution of the pixel of the liquid crystal display device
according to the present invention and corresponds to FIG. 9. Here,
the explanation is made hereinafter by focusing on only points
which make this embodiment different from the embodiments described
heretofore and the explanation of parts which are common with the
parts of the embodiments described heretofore is omitted.
[0203] The constitution which makes this embodiment different
compared with the embodiment shown in FIG. 9 lies in that a pixel
electrode PX and a counter electrode CT in a reflection region have
widths which are smaller than widths of the pixel electrode PX and
the counter electrode CT in a transmission region.
[0204] Accordingly, a width of a gap between the pixel electrode PX
and the counter electrode CT in the reflection region is set larger
than a width of a gap between the pixel electrode PX and the
counter electrode CT in the transmission region.
[0205] To be more specific, as viewed in a plan view, a gap between
a linear portion of the counter electrode CT and a linear portion
of the pixel electrode PX in the reflection region is larger than a
gap between the linear portion of the counter electrode CT and the
linear portion of the pixel electrode PX in the transmission
region.
[0206] To realize such a constitution, as viewed in a plan view,
with respect to at least one of the linear portion of the counter
electrode CT and the linear portion of the pixel electrode PX (both
linear portions in the case shown in FIG. 16), the width of the
linear portion in the reflection region is set smaller than the
width of the linear portion in the transmission region.
[0207] Here, although FIG. 16 shows the constitution which is not
provided with the capacitance signal line CDL, the capacitance
signal line CDL may be provided.
[0208] FIG. 17A shows characteristics of a potential difference (V)
between the counter electrode CT and the pixel electrode and the
brightness (B) of the pixel attributed to the potential difference
in a state that widths of the counter electrode CT and the pixel
electrode PX are set equal in the respective transmission
reflection regions thus setting a spaced-apart distance between the
counter electrode CT and the pixel electrode PX equal in the
respective transmission and reflection regions.
[0209] As can be readily understood from FIG. 17A, the B-V
characteristic of the transmission region and the B-V
characteristic of the reflection region differ largely from each
other, wherein the transmission region exhibits the characteristic
in which the brightness is increased corresponding to the elevation
of the potential difference, while the reflection region exhibits
the characteristic that the brightness is increased with the small
potential difference and, thereafter, the brightness is lowered
when the potential difference is elevated.
[0210] To the contrary, as shown in FIG. 16, FIG. 17B shows the
characteristics of the potential difference (V) between the counter
electrode CT and the pixel electrode PX and the brightness (B) of
the pixel attributed to the potential difference in a state that
the spaced-apart distance between the counter electrode CT and the
pixel electrode PX in the reflection region is set larger than the
corresponding spaced-apart distance in the transmission region. In
FIG. 17B, in the same manner as the case shown in FIG. 17A, in the
B-V characteristic (RT) in the reflection region, there exists a
range where the brightness is lowered when the potential difference
is largely elevated. However, the B-V characteristic (RT) in the
reflection region substantially equally follows the B-V
characteristic (TT) in the transmission region until the potential
difference is largely elevated. Accordingly, it is understood that
the respective B-V characteristics can be set substantially equal
within a relatively large range of the change of the potential
difference and hence, the characteristics are improved.
[0211] In this manner, by increasing the width of the gap between
the electrodes in the reflection region so as to weaken the
electric field of the reflection region than the electric field in
the transmission region, it is possible to stretch the B-V
characteristic in the reflection region in the V direction thus
realizing the substantial alignment of the B-V characteristics of
both regions.
[0212] Accordingly, by adopting the constitution shown in FIG. 16,
it is possible to obtain an advantageous effect that the difference
in image quality can be reduced in both of the reflection mode and
the transmission mode.
[0213] Here, such an advantageous effect on the improvement of
image quality can be increased when a layer thickness of the liquid
crystal in the transmission region and a layer thickness of the
liquid crystal in the reflection region are set as close as
possible to each other. To be more specific, assuming the layer
thickness of the liquid crystal in the transmission region as dt
and the layer thickness of the liquid crystal in the reflection
region as dr, it is desirable that a relationship
0.75dt.ltoreq.dr.ltoreq.1.1dt is established. It is more desirable
that a relationship 0.9dt.ltoreq.dr.ltoreq.1.1dt is established.
However, the layer thicknesses of the liquid crystal in the
transmission region and the reflection region are not required to
strictly satisfy the above-mentioned relationships or ranges and
the application of the present invention in ranges other than the
above-mentioned ranges is not restricted.
[0214] Here, these numerical ranges have been explained with
respect to the inventions on the gap between electrodes in the
reflection region explained in this embodiment and hence, other
inventions are not limited to these numerical ranges.
[0215] Further, the above-mentioned relationship between the layer
thickness dt of the liquid crystal in the transmission region and
the layer thickness dr of the liquid crystal in the reflection
region implies that, when the spaced-apart distance between the
counter electrode CT and the pixel electrode PX in the reflection
region is set larger than the corresponding spaced-apart distance
in the transmission region, it is unnecessary to provide the large
difference in height with respect to the substrate between the
transmission region and the reflection region in the layer
structure which is formed on a liquid-crystal-side surface of each
one of respective substrates with the liquid crystal sandwiched
therebetween.
[0216] Conventionally, an attempt has been made to reduce the
difference in the optical path length of the light between the
transmission region and the reflection region due to the stepped
portion of the layer structure. In this embodiment, it is possible
to obtain an advantageous effect that surfaces which are brought
into contact with the liquid crystal can be substantially leveled
due to the reduction of the stepped portion. This advantageous
effect also brings about an advantageous effect that the rubbing
treatment can be reliably performed in the formation of orientation
films, for example.
[0217] In view of the above, the above-mentioned relationship
between the layer thickness dt of the liquid crystal in the
transmission region and the layer thickness dr of the liquid
crystal in the reflection region can be grasped as an advantageous
effect which can be obtained by setting the spaced-apart distance
between the counter electrode CT and the pixel electrode PX in the
reflection region larger than the corresponding spaced-apart
distance in the transmission region. Accordingly, it is not always
necessary to grasp the above-mentioned relationship between the
layer thickness dt of the liquid crystal in the transmission region
and the layer thickness dr of the liquid crystal in the reflection
region as the constitutional feature of the present invention.
Embodiment 6
[0218] FIG. 18 is a plan view showing another embodiment of the
constitution of the pixel when the width of the pixel electrode PX
or the counter electrode CT is made different between the
transmission region and the reflection region. Further, FIG. 19 is
a cross-sectional view taken along a line B-B' in FIG. 18 and FIG.
20 is a cross-sectional view taken along a line A-A' in FIG. 19.
Here, the explanation is made hereinafter by focusing on only
points which make this embodiment different from the embodiments
described heretofore and the explanation of parts which are common
with the parts of the embodiments described heretofore is
omitted.
[0219] On an upper surface of the first interlayer insulation film
INS1, drain signal lines DL and first source electrodes ST1 of thin
film transistors TFT2 are formed.
[0220] The drain signal lines DL and the first source electrodes
ST1 are formed of a conductive film having the three-layered
structure in which, for example, a MoW layer, an Al layer and a MoW
layer are sequentially stacked. The first source electrode ST1 is
connected with a poly-silicon layer PS or the pixel electrode PX
and hence, it is necessary to form a buffer layer made of MoW or
the like at least on a connection surface of the first source
electrode ST1. Accordingly, it is possible to select an Ag layer as
a buffer layer, for example, besides the MoW layer.
[0221] Here, the first source electrode ST1 is configured to
function also as a reflector in the reflection region of the
pixel.
[0222] Further, the pixel electrode PX made of ITO, for example, is
formed at least on the transmission region of the pixel, and the
pixel electrode PX is connected with the first source electrode
ST1. Accordingly, the pixel electrode PX is formed on a whole area
or on a portion of an upper surface of the first source electrodes
ST1 in an overlapped manner, and the pixel electrode PX may be
extended to the transmission region.
[0223] In this embodiment, the pixel electrode PX is formed above
the first source electrode ST1. However, the embodiment is not
limited to such a constitution and it is possible to obtain the
substantially equal advantageous effect by forming the pixel
electrode PX below the first source electrode ST1.
[0224] Further, the pixel electrode PX and the first source
electrode ST1 may be overlapped to each other by way of an
insulation film. In this case, it is possible to electrically
connect the pixel electrode PX and the first source electrode ST1
by forming a contact hole or the like in the insulation film.
[0225] On an upper surface of the first interlayer insulation film
INS1, a second interlayer insulation film INS2 (see FIG. 19, FIG.
20) is formed in a state that the second interlayer insulation film
INS2 also covers the drain signal lines DL, the first source
electrodes ST1 and the pixel electrodes PX. Further, on an upper
surface of the second interlayer insulation film INS2, a protective
film PAS (see FIG. 19, FIG. 20) is formed. The protective film PAS
is, for example, formed of an organic material layer which is
formed by coating.
[0226] On an upper surface of the protective film PAS, counter
electrodes CT and common signal lines CTL which are connected with
the counter electrodes CT are formed.
[0227] Here, the counter electrodes CT and the common signal lines
CTL which are connected with the counter electrodes CT are formed
of a light-transmitting conductive film (only a single layer in
this embodiment) such as an ITO (Indium Tin Oxide) film.
[0228] The counter electrode CT is constituted of a plurality of
electrodes which are extended along the direction of the drain
signal lines DL, for example. Among these electrodes, the
electrodes which are positioned in the reflection region have a
smaller electrode width compared to an electrode width of the
electrodes which are positioned in the transmission region as
mentioned above.
[0229] This embodiment is also directed to a kind of lateral
electric field type liquid crystal display device which generates
an electric field between the pixel electrode PX and the counter
electrode CT so as to drive the liquid crystal.
[0230] In this embodiment, one electrode has linear portions and
another electrode has a planar portion, wherein at least portions
of both electrodes are overlapped to each other by way of the
insulation film.
Embodiment 7
[0231] FIG. 21 is a plan view showing another embodiment which
modifies the constitution shown in FIG. 18. The constitution which
makes this embodiment different from the embodiment shown in FIG.
18 lies in counter electrodes CT. FIG. 22 is a cross-sectional view
taken along a line B-B' in FIG. 21.
[0232] While the counter electrode CT shown in FIG. 18 has a
comb-teeth-shaped pattern which uses a common signal line CTL as a
proximal portion, the counter electrode CT of this embodiment
adopts a pattern in which distal end portions of the comb teeth are
connected in common. In other words, a portion of the counter
electrode CT is formed in a pattern which has slit-like openings
(slits). Here, a portion which is sandwiched by two slits is
considered as a kind of linear portion.
[0233] Accordingly, even a portion of the contact hole CH2 is
covered with a conductive layer made of a material equal to a
material of the counter electrode CT. However, it is not always
necessary to cover the contact hole CH2 with the conductive
layer.
[0234] Here, the embodiments 6, 7 are also modifications of the
embodiment 4. This is because that the first source electrode ST1
also functions as a reflector. Further, in the embodiments 6, 7,
the pixel electrode PX and the reflector are formed below the
counter electrode CT and, at the same time, at least a portion
thereof are overlapped to the counter electrode CT by way of an
insulation film (a protective film PAS or the like). The reflector
also functions as a source electrode and hence, the reflector is
independently formed for every pixel region and a signal equal to a
signal applied to the pixel electrode PX is applied to the
reflector. Accordingly, the reflector also plays a role of the
pixel electrode PX. Further, the liquid crystal is driven by an
electric field generated between the pixel electrode PX which also
functions as the reflector and the counter electrode CT.
Embodiment 8
[0235] FIG. 23 is a plan view showing another embodiment in which
the present invention is applied to the above-mentioned
constitution shown in FIG. 12.
[0236] To allow the common signal line CTL' formed of a reflecting
conductive layer to function as a reflector, the common signal line
CTL' is formed as a reflection region at a portion where the common
signal line CTL' in the pixel region runs.
[0237] Further, the respective widths of the pixel electrode PX and
the counter electrode CT which are arranged in the inside of the
reflection region are set narrower than the respective widths of
the pixel electrode PX and the counter electrode CT which are
arranged in the inside of the transmission region.
Embodiment 9
[0238] FIG. 24 is a plan view showing another embodiment which
modifies the constitution shown in FIG. 18. The constitution which
makes this embodiment different from the embodiment shown in FIG.
18 lies in that the constitutions of the counter electrode CT and
the pixel electrode PX are reversed. FIG. 25 is a cross-sectional
view taken along a line B-B' in FIG. 24.
[0239] In this embodiment, the counter electrode CT is formed of an
electrode having a planar portion and the pixel electrode PX is
formed of an electrode having linear portions and both electrodes
have at least portions thereof overlapped to each other by way of
an insulation film INS.
[0240] This embodiment is also directed to a kind of lateral
electric field type liquid crystal display device which generates
an electric field between the pixel electrode PX and the counter
electrode CT so as to drive the liquid crystal.
[0241] A reflector MET is formed on a portion of the pixel region
and the reflector MET is connected with the counter electrode
CT.
[0242] In this embodiment, a gap between the pixel electrodes PX in
the reflection region is set larger than a gap between the pixel
electrodes PX in the transmission region. Further, a width of the
pixel electrode PX in the reflection region is set smaller than the
width of the pixel electrode PX in the transmission region.
[0243] Here, in FIG. 24, thin film transistors TFT1, TFT2 which are
driven by a gate signal line GL, a first source electrode ST1 which
is provided for supplying a video signal from the drain signal line
DL to the pixel electrode PX by way of the thin film transistors
TFT1, TFT2, a contact hole CH2 (or a contact hole CH3) which is
necessary for connecting the first source electrodes ST1 and the
pixel electrode PX and the like are omitted from the drawing.
However, it is needless to say that the liquid crystal display
device is provided with these parts in a suitably modified manner
as explained in the above-mentioned respective embodiments. This is
because that, in the inside of the pixel, the constitutional
feature of this embodiment lies in a constitutional portion shown
in FIG. 24 and the constitution of the whole pixel can be readily
understood by explaining the portion mainly.
Embodiment 10
[0244] The counter electrode CT shown in FIG. 18 and FIG. 21 or the
pixel electrode PX shown in FIG. 24 can be also constituted by
sequentially stacking the reflecting conductive layer and the
light-transmitting layer as explained in conjunction with the
embodiment 1. Here, to focus on only the advantageous effects of
the embodiment 1, it is arbitrary to adopt the invention on the
electrode gap explained in conjunction with FIG. 5.
[0245] The above-mentioned respective embodiments may be used in a
single form or in combination. This is because that the
advantageous effects of the respective embodiments can be achieved
independently or synergistically.
* * * * *