U.S. patent application number 11/878579 was filed with the patent office on 2008-01-31 for liquid crystal display device.
This patent application is currently assigned to EPSON IMAGING DEVICES CORPORATION. Invention is credited to Tomohide Onogi, Yasuo Segawa.
Application Number | 20080024416 11/878579 |
Document ID | / |
Family ID | 38985665 |
Filed Date | 2008-01-31 |
United States Patent
Application |
20080024416 |
Kind Code |
A1 |
Onogi; Tomohide ; et
al. |
January 31, 2008 |
Liquid crystal display device
Abstract
This invention offers a liquid crystal display device according
to FFS technology, which is capable of sufficiently providing a
common electrode with common electric potential and improving an
aperture ratio of pixels to obtain a bright display. A pixel
electrode is formed of a first layer transparent electrode. A
common electrode made of a second layer transparent electrode is
formed above the pixel electrode interposing an insulation film
between them. The common electrode in an upper layer is provided
with a plurality of slits. The common electrode extends over all
the pixels in a display region. An end of the common electrode is
disposed on a periphery of the display region and connected with a
peripheral common electric potential line that provides a common
electric potential Vcom. There is provided neither an auxiliary
common electrode line nor a pad electrode, both of which are
provided in a liquid crystal display device according to a
conventional art.
Inventors: |
Onogi; Tomohide;
(Azumino-shi, JP) ; Segawa; Yasuo; (Azumino-shi,
JP) |
Correspondence
Address: |
MORRISON & FOERSTER LLP
1650 TYSONS BOULEVARD, SUITE 400
MCLEAN
VA
22102
US
|
Assignee: |
EPSON IMAGING DEVICES
CORPORATION
Azumino-shi
JP
|
Family ID: |
38985665 |
Appl. No.: |
11/878579 |
Filed: |
July 25, 2007 |
Current U.S.
Class: |
345/92 ; 345/87;
349/139 |
Current CPC
Class: |
G02F 1/134372 20210101;
G02F 2202/103 20130101; G02F 2202/104 20130101; G02F 2201/40
20130101; G02F 1/13439 20130101; H01L 29/78669 20130101; G02F
2201/123 20130101; G02F 1/133345 20130101; G02F 1/134336 20130101;
G02F 1/136295 20210101; G02F 1/133357 20210101; H01L 29/78678
20130101; H01L 27/1244 20130101; G02F 1/136286 20130101; H01L
27/1222 20130101; G02F 1/1368 20130101; G02F 2201/121 20130101;
G02F 1/136227 20130101; G02F 1/134363 20130101 |
Class at
Publication: |
345/92 ; 345/87;
349/139 |
International
Class: |
G09G 3/36 20060101
G09G003/36; G02F 1/1343 20060101 G02F001/1343 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 27, 2006 |
JP |
2006-204624 |
Claims
1. A liquid crystal display device comprising: a substrate
comprising a display region and a periphery region surrounding the
display region; a plurality of pixels disposed in the display
region, each of the pixels comprising a pixel electrode; a
peripheral common electric potential line provided with a common
electric potential and disposed on the periphery region; and a
common electrode disposed on the pixel electrodes so as to cover
the display region and so as to extend over and be in contact
electrically with the peripheral common electric potential line,
wherein the common electrode has a plurality of slits at each of
the pixels.
2. The liquid crystal display device of claim 1, wherein an
intersection angle between the peripheral common electric potential
line and a longitudinal direction of the slits is larger than 45
degrees and equal to or smaller than 90 degrees.
3. The liquid crystal display device of claim 1, further comprising
a display signal line control circuit that provides the pixels with
a display signal or a gate line control circuit that provides the
pixels with a gate signal, wherein the peripheral common electric
potential line surrounds the display region and the display signal
line control circuit or the gate line control circuit is disposed
between the display region and the peripheral common electric
potential line.
4. The liquid crystal display device of claim 1, further comprising
a display signal line that provides the pixels with a display
signal, wherein the peripheral common electric potential line is
part of a wiring layer that is common to the display signal
line.
5. The liquid crystal display device of claim 1, further comprising
a thin film transistor that is connected with the pixel
electrode.
6. A liquid crystal display device comprising: a substrate
comprising a display region and a periphery region surrounding the
display region; a plurality of pixels disposed in the display
region, each of the pixels comprising a pixel electrode having a
plurality of slits; a peripheral common electric potential line
provided with a common electric potential and disposed on the
periphery region; and a common electrode disposed between the
substrate and the pixel electrodes so as to cover the display
region and so as to extend over and be in contact electrically with
the peripheral common electric potential line.
7. The liquid crystal display device of claim 6, wherein an
intersection angle between the peripheral common electric potential
line and a longitudinal direction of the slits is larger than 45
degrees and equal to or smaller than 90 degrees.
8. The liquid crystal display device of claim 6, further comprising
a display signal line control circuit that provides the pixels with
a display signal or a gate line control circuit that provides the
pixels with a gate signal, wherein the peripheral common electric
potential line surrounds the display region and the display signal
line control circuit or the gate line control circuit is disposed
between the display region and the peripheral common electric
potential line.
9. The liquid crystal display device of claim 6, further comprising
a display signal line that provides the pixels with a display
signal, wherein the peripheral common electric potential line is
part of a wiring layer that is common to the display signal
line.
10. The liquid crystal display device of claim 6, further
comprising a thin film transistor that is connected with the pixel
electrode.
Description
CROSS-REFERENCE OF THE INVENTION
[0001] This application claims priority from Japanese Patent
Application No. 2006-204624, the content of which is incorporated
herein by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a liquid crystal display device,
specifically to a liquid crystal display device in which an
alignment direction of liquid crystal molecules is controlled by a
lateral electric field generated between a pixel electrode and a
common electrode.
[0004] 2. Description of the Related Art
[0005] As a way to achieve a wide viewing angle of the liquid
crystal display device, a method has been developed to realize a
light switching function by rotating the liquid crystal molecules
in a plane parallel to a substrate with a lateral electric field
generated between the electrodes on the same substrate. In-Plane
Switching (hereafter referred to as IPS) technology and
Fringe-Field Switching (hereafter referred to as FFS) technology,
which is an improved IPS technology, are known as examples of these
technologies.
[0006] A manufacturing process of the liquid crystal display device
according to the FFS technology will be explained referring to the
drawings. FIGS. 18A through 20B show the manufacturing process of
one pixel in the liquid crystal display device according to the FFS
technology. FIGS. 18A, 19A and 20A are plan views of a part of a
display region in the liquid crystal display device. Each of FIGS.
18B, 19B and 20B is a cross-sectional view showing a section A-A in
each of FIGS. 18A, 19A and 20A, respectively. Although a large
number of pixels are disposed in a matrix form in the display
region in the actual liquid crystal display device, only three
pixels are shown in each of the plan views.
[0007] A buffer layer 11, which is made of a silicon dioxide
(SiO.sub.2) film or a silicon nitride (SiNx) film, and an amorphous
silicon layer are successively formed by CVD (Chemical Vapor
Deposition) on a TFT substrate 10, which is made of a glass
substrate or the like, as shown in FIG. 18B. The amorphous silicon
layer is crystallized and transformed into a polysilicon layer by
excimer laser annealing. The polysilicon layer is patterned to form
a U-shaped active layer 12 of a thin film transistor 1 (hereafter
referred to as TFT 1).
[0008] After that, a gate insulation film 13 is formed to cover the
active layer 12. A gate line 14 made of chromium, molybdenum or the
like is formed on the gate insulation film 13 overlapping the
active layer 12. The gate line 14 extends in a row direction, and
intersects the active layer 12 at two locations. A gate signal that
controls turning on/off of the TFT 1 is applied to the gate line
14. On the other hand, an auxiliary common electrode line 15, that
is made of the same material as the gate line 14 and is for
providing a common electric potential Vcom, is formed parallel to
the gate line 14.
[0009] Next, there is formed an interlayer insulation film 16 that
covers the TFT 1 and the auxiliary common electrode line 15. And
contact holes CH1 and CH2, which expose a source region 12s and a
drain region 12d in the active layer 12, respectively, are formed
in the interlayer insulation film 16. Also, a contact hole CH3,
that exposes the auxiliary common electrode line 15, is formed in
the interlayer insulation film 16.
[0010] There are formed a source electrode 17 that is connected
with the source region 12s through the contact hole CH1, a display
signal line 18 that is connected with the drain region 12d through
the contact hole CH2, and a pad electrode 19 that is connected with
the auxiliary common electrode line 15 through the contact hole
CH3. The source electrode 17, the display signal line 18 and the
pad electrode 19 are made of metal including aluminum or aluminum
alloy or the like. Next, a planarization film 20 is formed over the
entire surface. Contact holes CH4 and CH5, that expose the source
electrode 17 and the pad electrode 19 respectively, are formed in
the planarization film 20.
[0011] And there is formed a pixel electrode 21 that is connected
with the source electrode 17 through the contact hole CH4 and
extends over the planarization film 20, as shown in FIGS. 19A and
19B. The pixel electrode 21 is made of a first layer transparent
electrode such as ITO (Indium Tin Oxide), and is applied a display
signal Vsig from the display signal line 18 through the TFT 1.
[0012] After that, an insulation film 22 is formed to cover the
pixel electrode 21, as shown in FIG. 20B. A contact hole CH6, that
exposes the pad electrode 19, is formed by etching the insulation
film 22. A common electrode 23, that has a plurality of slits S, is
formed on the pixel electrode 21 through the insulation film 22.
The common electrode 23 is made of a second layer transparent
electrode such as ITO, and is connected with the pad electrode 19
through the contact hole CH6.
[0013] A counter substrate 30 made of a glass substrate or the like
is disposed facing the TFT substrate 10. A polarizing plate 31 is
attached to the counter substrate 30. Also, a polarizing plate 32
is attached to a back surface of the TFT substrate 10. The
polarizing plates 31 and 32 are disposed in a way that their
polarization axes are perpendicular to each other. A liquid crystal
40 is sealed-in between the TFT substrate 10 and the counter
substrate 30.
[0014] In the liquid crystal display device described above, an
average alignment direction (hereafter simply referred to as
"alignment direction") of major axes of the liquid crystal
molecules of the liquid crystal 40 is parallel to the polarization
axis of the polarizing plate 32 when a display voltage is not
applied to the pixel electrode 21 (no voltage state). In this case,
linearly polarized light passing through the liquid crystal 40 does
not go through the polarizing plate 31 because its polarization
axis is perpendicular to the polarization axis of the polarizing
plate 31. That is, black is displayed.
[0015] When the display voltage is applied to the pixel electrode
21, on the other hand, there is generated a lateral electric field
from the pixel electrode 21 toward the common electrode 23 through
the slits S. The electric field is perpendicular to a longitudinal
direction of the slits S on the plan view, and the liquid crystal
molecules are rotated along a line of electric force of the
electric field. At that time, the linearly polarized incident light
to the liquid crystal 40 is turned into elliptically polarized
light by birefringence to have a component of linearly polarized
light that passes through the polarizing plate 31. In this case,
white is displayed. The liquid crystal display device according to
the FFS technology is disclosed in Japanese Patent Application
Publication Nos. 2001-183685 and 2002-296611.
[0016] In general, when the common electrode 23 is insufficiently
provided with the common electric potential Vcom because of an
influence of electric resistance, the voltage applied to the liquid
crystal 40 is reduced to cause degradation in quality of display
such as reduced contrast. Since the common electrode 23 is formed
of the transparent electrode such as ITO that has higher sheet
resistivity than ordinary metal, the degradation in the quality of
display is prone to be caused. This problem becomes evident
particularly as a panel size of the liquid crystal display device
becomes larger. Therefore, in order to provide the common electrode
23 with the common electric potential Vcom sufficiently, the
auxiliary common electrode line 15 that supplies the common
electric potential Vcom is disposed within the display region and
the auxiliary common electrode line 15 is connected with the common
electrode 23 in each of the pixels in the conventional liquid
crystal display device.
[0017] When the auxiliary common electrode line 15 is disposed
within the display region, however, there is a problem that its
wiring portion makes a light-shielding region to reduce an aperture
ratio of the pixels. This invention is directed to offer a liquid
crystal display device capable of securely providing the common
electrode with the common electric potential sufficiently and
improving the aperture ratio of the pixels to obtain a bright
display.
SUMMARY OF THE INVENTION
[0018] A liquid crystal display device of this invention includes a
substrate; a plurality of pixels disposed in a display region on
the substrate, each of the pixels including a pixel electrode and a
common electrode having a plurality of slits and disposed on the
pixel electrode through an insulation film and extending over the
plurality of the pixels; and a peripheral common electric potential
line provided with a common electric potential and disposed on a
periphery of the display region, wherein an end of the common
electrode is connected with the peripheral common electric
potential line.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a plan view showing a portion of a display region
in a liquid crystal display device according to a first embodiment
of this invention.
[0020] FIG. 2 is a cross-sectional view showing a section X1-X1 in
FIG. 1.
[0021] FIG. 3 shows a first layout of the liquid crystal display
device according to the first embodiment of this invention.
[0022] FIG. 4 shows a second layout of the liquid crystal display
device according to the first embodiment of this invention.
[0023] FIG. 5 shows a third layout of the liquid crystal display
device according to the first embodiment of this invention.
[0024] FIG. 6 shows a fourth layout of the liquid crystal display
device according to the first embodiment of this invention.
[0025] FIG. 7 shows a fifth layout of the liquid crystal display
device according to the first embodiment of this invention.
[0026] FIG. 8 shows a sixth layout of the liquid crystal display
device according to the first embodiment of this invention.
[0027] FIG. 9 is a plan view showing a portion of a display region
in a liquid crystal display device according to a second embodiment
of this invention.
[0028] FIG. 10 is a cross-sectional view showing a section X2-X2 in
FIG. 9.
[0029] FIG. 11 is a cross-sectional view showing a section Y1-Y1 in
FIG. 9.
[0030] FIG. 12 is a plan view showing a portion of a display region
in a liquid crystal display device according to a third embodiment
of this invention.
[0031] FIG. 13 is a cross-sectional view showing a section X3-X3 in
FIG. 12.
[0032] FIG. 14 is a cross-sectional view showing a section Y2-Y2 in
FIG. 12.
[0033] FIG. 15 is a plan view showing a portion of a display region
in a liquid crystal display device according to a fourth embodiment
of this invention.
[0034] FIG. 16 is a cross-sectional view showing a section X4-X4 in
FIG. 15.
[0035] FIG. 17 is a cross-sectional view showing a section Y3-Y3 in
FIG. 15.
[0036] FIGS. 18A and 18B are for explanation of a structure and a
manufacturing method of a liquid crystal display device according
to a conventional art.
[0037] FIGS. 19A and 19B are for explanation of the structure and
the manufacturing method of the liquid crystal display device
according to the conventional art.
[0038] FIGS. 20A and 20B are for explanation of the structure and
the manufacturing method of the liquid crystal display device
according to the conventional art.
DETAILED DESCRIPTION OF THE INVENTION
[0039] A liquid crystal display device according to a first
embodiment of this invention will be explained referring to the
drawings. FIG. 1 is a plan view showing a portion of a display
region in the liquid crystal display device. FIG. 2 is a
cross-sectional view showing a section X1-X1 in FIG. 1. Although a
large number of pixels are disposed in a matrix form in the display
region 70 in the actual liquid crystal display device, only three
pixels are shown in the plan view.
[0040] A pixel electrode 21 is formed of a first layer transparent
electrode. A common electrode 23A made of a second layer
transparent electrode is formed above the pixel electrode 21
interposing an insulation film 22 between them. The common
electrode 23A in an upper layer is provided with a plurality of
slits S. The structures described above are generally common to the
structure shown in FIGS. 20A and 20B. In the embodiment, however,
the common electrode 23A extends over all the pixels in the display
region 70. An end of the common electrode 23A is disposed on a
periphery of the display region 70 and connected with a peripheral
common electric potential line 50 that provides a common electric
potential Vcom.
[0041] A cross-sectional structure of the connecting portion is
shown in FIG. 2. The peripheral common electric potential line 50
is formed of a layer same as a layer forming a display signal line
18 and is made of metal including aluminum or aluminum alloy or the
like. The peripheral common electric potential line 50 is formed on
an interlayer insulation film 16. The common electrode 23A is
connected with the peripheral common electric potential line 50
through a contact hole CH7 that is formed in a planarization film
20 and the insulation film 22 formed on the peripheral common
electric potential line 50. The peripheral common electric
potential line 50 is connected with a terminal (not shown) on a TFT
substrate 10. The common electric potential Vcom is supplied from
an IC or the like outside the TFT substrate 10 through the
terminal.
[0042] The liquid crystal display device according to the
embodiment is provided with neither the auxiliary common electrode
line 15 nor the pad electrode 19, which is provided in the
conventional liquid crystal display device. As a result, the
aperture ratio of the pixel is improved. Also the common electric
potential Vcom is sufficiently supplied to the common electrode 23A
through a low resistance, since the common electrode 23A extends
over all the pixels in the display region 70 and its end is
connected with the peripheral common electric potential line
50.
[0043] The peripheral common electric potential line 50 is disposed
on the periphery of the display region 70 along a side of the
rectangular display region 70 in a first layout shown in FIG. 3. In
order to supply the common electric potential Vcom to the common
electrode 23A through even lower resistance, it is preferable that
the peripheral common electric potential line 50 is disposed along
each of two sides of the display region 70 facing each other and
that the peripheral common electric potential line 50 on each side
is connected with each end of the common electrode 23A,
respectively, as in a second layout shown in FIG. 4. In this case,
the peripheral common electric potential line 50 may be disposed
along each of two adjacent sides of the display region 70, as in a
third layout shown in FIG. 5.
[0044] In order to supply the common electric potential Vcom to the
common electrode 23A through further lower resistance, it is
preferable that the peripheral common electric potential line 50 is
disposed along each of three sides of the display region 70 and
that the peripheral common electric potential line 50 on each side
is connected with each end of the common electrode 23A, as in a
fourth layout shown in FIG. 6. Or it is preferable that the
peripheral common electric potential line 50 is disposed along each
of four sides of the display region 70 and that the peripheral
common electric potential line 50 on each side is connected with
each end of the common electrode 23A, as in a fifth layout shown in
FIG. 7.
[0045] However, with the fifth layout shown in FIG. 7, in which the
display region 70 is surrounded by the peripheral common electric
potential line 50, it is necessary that a gate line 14 and the
display signal line 18 are drawn out across the peripheral common
electric potential line 50. That is required in order to connect
each of the gate line 14 and the display signal line 18 with a
corresponding signal source, respectively.
[0046] When the peripheral common electric potential line 50 and
the display signal line 18 are formed of the same layer, it is
necessary that either the layer forming the peripheral common
electric potential line 50 or the layer forming the display signal
line 18 is partially modified to form a bridge at an intersection
of the peripheral common electric potential line 50 and the display
signal line 18 in order to avoid a short circuit, as shown in a
portion surrounded by a dashed line in FIG. 7. For example, the
display signal line 18 is modified into the same layer as the gate
line 14 at the intersection. The gate line 14 crosses the
peripheral common electric potential line 50 without causing a
short circuit, because it is formed of the layer different from the
layer forming the peripheral common electric potential line 50.
[0047] The bridge and the crossing as described above can be
avoided by disposing circuits serving as the signal sources in a
region surrounded by the peripheral common electric potential line
50, as shown in FIG. 8. That is, a display signal line control
circuit 61 that provides the display signal line 18 with the
display signal and a gate line control circuit 62 that provides the
gate line 14 with the gate signal are disposed in a region between
the display region 70 and the peripheral common electric potential
line 50.
[0048] A liquid crystal display device according to a second
embodiment of this invention will be explained referring to the
drawings. FIG. 9 is a plan view showing a portion of a display
region in the liquid crystal display device. FIG. 10 is a
cross-sectional view showing a section X2-X2 in FIG. 9. FIG. 11 is
a cross-sectional view showing a section Y1-Y1 in FIG. 9. Although
a large number of pixels are disposed in a matrix form in the
display region in the actual liquid crystal display device, only
three pixels are shown in the plan view.
[0049] A relationship between vertical locations of the pixel
electrode 21 and the common electrode 23A in the liquid crystal
display device according to the first embodiment is reversed in the
liquid crystal display device according to the second embodiment. A
common electrode 23B is formed of the first layer transparent
electrode and a pixel electrode 21B is formed of the second layer
transparent electrode above it interposing the insulation film 22
between them. The pixel electrode 21B in an upper layer is provided
with a plurality of slits S.
[0050] With the pixels structured as described above, it is
possible to obtain a liquid crystal display device having a wide
viewing angle by generating lateral electric field between the
pixel electrode 21B and the common electrode 23B and controlling
the alignment direction of the liquid crystal molecules.
[0051] The pixel electrodes 21B are separated from each other and
each of the pixel electrodes 21Bis connected with a source
electrode 17 of a TFT 1 in the same pixel. The common electrode 23B
extends over all the pixels in the display region 70 as in the
liquid crystal display device according to the first embodiment. An
end of the common electrode 23B is disposed on a periphery of the
display region 70 and connected with a peripheral common electric
potential line 50 that provides a common electric potential
Vcom.
[0052] A cross-sectional structure of the connecting portion is
shown in FIG. 10. The peripheral common electric potential line 50
is formed of the same layer as a display signal line 18 and is made
of metal including aluminum or aluminum alloy or the like. The
peripheral common electric potential line 50 is formed on an
interlayer insulation film 16. The common electrode 23B is
connected with the peripheral common electric potential line 50
through a contact hole CH8 that is formed in a planarization film
20 and the insulation film 22 formed on the peripheral common
electric potential line 50. The peripheral common electric
potential line 50 is connected with a terminal (not shown) on a TFT
substrate 10. The common electric potential Vcom is supplied from
an IC or the like outside a TFT substrate 10 through the
terminal.
[0053] Other structures are generally the same as those in the
liquid crystal display device according to the first embodiment.
That is, the layouts shown in FIG. 3 through FIG. 8 can be applied
to a layout of the peripheral common electric potential line 50 and
the common electrode 23B to obtain the same effects.
[0054] A liquid crystal display device according to a third
embodiment of this invention will be explained referring to the
drawings. The TFT 1 in the pixel in the liquid crystal display
device according to the first and second embodiments is a
polysilicon TFT that has an active layer made of polysilicon.
Instead, an amorphous silicon TFT 1a (hereafter referred to as
aSi-TFT 1a) that has an active layer made of amorphous silicon is
used in the liquid crystal display device according to the third
embodiment.
[0055] FIG. 12 is a plan view showing a portion of a display region
in the liquid crystal display device. FIG. 13 is a cross-sectional
view showing a section X3-X3 in FIG. 12. FIG. 14 is a
cross-sectional view showing a section Y2-Y2 in FIG. 12. Although a
large number of pixels are disposed in a matrix form in the display
region in the actual liquid crystal display device, only three
pixels are shown in the plan view.
[0056] Agate line 114 of the aSi-TFT 1a is formed on aTFT substrate
100. The gate line 114 is formed of chromium, molybdenum or the
like. A common electrode 123B extending over a plurality of pixels
is formed in a shape of stripes in regions except for the gate line
114. The common electrode 123B is made of a first layer transparent
electrode such as ITO. A gate insulation film 101 is formed to
cover the gate line 114 and the common electrode 123B. An amorphous
silicon layer 102 is formed on the gate insulation film 101 to
cover the gate line 114. And a display signal line 118 (drain
electrode) and a source electrode 103 are formed in contact with
the amorphous silicon layer 102.
[0057] An interlayer insulation film 104 is formed over the entire
surface and the interlayer insulation film 104 on the source
electrode 103 is selectively etched to form a contact hole CH12.
There is formed a pixel electrode 121B that is connected with the
source electrode 103 through the contact hole CH12. The pixel
electrode 121B is made of a second layer transparent electrode such
as ITO and has a plurality of slits S. The pixel electrode 121B is
formed above the common electrode 123B, interposing the gate
insulation film 101 and the interlayer insulation film 104 between
them.
[0058] With the pixels using the aSi-TFT 1a and structured as
described above, it is possible to obtain a liquid crystal display
device having a wide viewing angle by generating lateral electric
field between the pixel electrode 121B and the common electrode
123B and controlling the alignment direction of the liquid crystal
molecules.
[0059] An end of the common electrode 123B is disposed on a
periphery of the display region 70 and connected with a peripheral
common electric potential line 150 that provides a common electric
potential Vcom. A cross-sectional structure of the connecting
portion is shown in FIG. 13. The peripheral common electric
potential line 150 is formed of the same layer as a display signal
line 118 and is made of metal including aluminum or aluminum alloy
or the like. The peripheral common electric potential line 150 is
formed on the gate insulation film 101. The common electrode 123B
is connected with the peripheral common electric potential line 150
through a connection wiring 119 that is made of the second layer
transparent electrode and extending through a contact hole CH13
formed in the gate insulation film 101 and the interlayer
insulation film 104 above the common electrode 123B and a contact
hole CH14 formed in the interlayer insulation film 104 above the
peripheral common electric potential line 150.
[0060] The peripheral common electric potential line 150 is
connected with a terminal (not shown) on the TFT substrate 100. The
common electric potential Vcom is supplied from an IC or the like
outside the TFT substrate 100 through the terminal.
[0061] Other features such as that the counter substrate is
disposed so as to face the TFT substrate 100 and that the liquid
crystal is sealed-in between the TFT substrate 100 and the counter
substrate are the same as in the first and second embodiments, and
detailed explanations are omitted.
[0062] Neither the auxiliary common electrode line 15 nor the pad
electrode 19 is provided in the liquid crystal display device
according to the third embodiment, as in the liquid crystal display
devices according to the first and second embodiments. As a result,
the aperture ratio of the pixel is improved. Also the common
electric potential Vcom is sufficiently supplied to the common
electrode 123B through a low resistance, since the common electrode
123B extends over all the pixels in the display region 70 and its
end is connected with the peripheral common electric potential line
150. Also, the layouts shown in FIG. 3 through FIG. 8 can be
applied to a layout of the peripheral common electric potential
line 150 and the common electrode 123B to obtain the same
effects.
[0063] A liquid crystal display device according to a fourth
embodiment of this invention will be explained referring to the
drawings. FIG. 15 is a plan view showing a portion of a display
region in the liquid crystal display device. FIG. 16 is a
cross-sectional view showing a section X4-X4 in FIG. 15. FIG. 16 is
a cross-sectional view showing a section Y3-Y3 in FIG. 15. Although
a large number of pixels are disposed in a matrix form in the
display region in the actual liquid crystal display device, only
three pixels are shown in the plan view.
[0064] A relationship between vertical locations of the pixel
electrode 121B and the common electrode 123B in the liquid crystal
display device according to the third embodiment is reversed in the
liquid crystal display device according to the fourth embodiment. A
pixel electrode 121A is formed of a first layer transparent
electrode and a common electrode 123A is formed of a second layer
transparent electrode above it interposing a gate insulation film
101 and an interlayer insulation film 104 between them in the
liquid crystal display device according to the fourth embodiment.
The common electrode 123A in an upper layer is provided with a
plurality of slits S.
[0065] An end of the common electrode 123A is disposed on a
periphery of the display region 70 and connected with a peripheral
common electric potential line 150 that provides a common electric
potential Vcom. A cross-sectional structure of the connecting
portion is shown in FIG. 16. The peripheral common electric
potential line 150 is formed of the same layer as a display signal
line 118 and is made of metal including aluminum or aluminum alloy
or the like. The peripheral common electric potential line 150 is
formed on the gate insulation film 101. The common electrode 123A
is connected with the peripheral common electric potential line 150
through a contact hole CH15 formed in the interlayer insulation
film 104 above the peripheral common electric potential line 150.
Other structures are the same as those in the liquid crystal
display device according to the third embodiment.
[0066] Note that the slits S may extend over a plurality of pixels
although the slits S in the common electrode 23A or 123A are formed
within a single pixel in the liquid crystal display devices
according to the first through fourth embodiments. Also, the pixel
electrodes 21B and 121B may have a comb-shaped slit S that is open
at one end.
[0067] With the liquid crystal display devices according to the
embodiments of this invention, the auxiliary common electrode line
in the display region can be removed to improve the aperture ratio
of the pixel, since the common electrode is provided with the
common electric potential through the peripheral common electric
potential line disposed on the periphery of the display region. In
addition, the common electrode can be sufficiently provided with
the common electric potential through the low resistance, because
the common electrode is disposed to extend over the plurality of
pixels and connected with the peripheral common electric potential
line.
* * * * *