U.S. patent application number 09/823370 was filed with the patent office on 2001-08-09 for liquid crystal display device.
Invention is credited to Hikiba, Masayuki, Konishi, Nobutake, Ohta, Masuyuki, Ohwada, Junichi.
Application Number | 20010012086 09/823370 |
Document ID | / |
Family ID | 18532306 |
Filed Date | 2001-08-09 |
United States Patent
Application |
20010012086 |
Kind Code |
A1 |
Ohta, Masuyuki ; et
al. |
August 9, 2001 |
Liquid crystal display device
Abstract
A liquid crystal display device includes a first substrate and a
second substrate facing the first substrate. A liquid crystal layer
is provided between the first and second substrates. First and
second gate lines are extending in a first direction, and first and
second drain lines are extending in a second direction. A pixel
area is defined by the gate lines and drain lines. A counter
electrode assigned to the pixel area and having a hollow portion is
provided adjacent to a solid portion. The hollow and solid portions
are extending in the second direction. One hollow portion is
provided after N number of the solid portions, the N being a number
equal to or greater than 3. A pixel electrode is assigned to the
pixel area and is opposing the counter electrode. The pixel
electrode has a connecting portion extending in the first direction
and first and second extending portions extending in the second
direction. The connection portion connects the first and second
extending portions, wherein the first extending portion is
vertically aligned to the hollow portion of the counter electrode
and the second extending portion is vertically aligned to the solid
portion of the counter electrode. An insulating layer is provided
between the counter and pixel electrodes.
Inventors: |
Ohta, Masuyuki; (Kariya,
JP) ; Ohwada, Junichi; (Mobara, JP) ; Konishi,
Nobutake; (Mobara, JP) ; Hikiba, Masayuki;
(Mobara, JP) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW
TWO EMBARCADERO CENTER
EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Family ID: |
18532306 |
Appl. No.: |
09/823370 |
Filed: |
March 30, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09823370 |
Mar 30, 2001 |
|
|
|
09760385 |
Jan 11, 2001 |
|
|
|
Current U.S.
Class: |
349/143 ;
349/42 |
Current CPC
Class: |
G02F 1/134363
20130101 |
Class at
Publication: |
349/143 ;
349/42 |
International
Class: |
G02F 001/136; G02F
001/1343 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 12, 2000 |
JP |
2000-003348 |
Claims
What is claimed is:
1. A liquid crystal display device comprising: a first substrate; a
second substrate facing the first substrate; a liquid crystal layer
provided between the first and second substrates; first and second
gate lines extending in a first direction; first and second drain
lines extending in a second direction; a pixel area defined by the
gate lines and drain lines; a counter electrode assigned to the
pixel area and having a hollow portion provided adjacent to a solid
portion, the hollow and solid portions extending in the second
direction, wherein one hollow portion is provided after N number of
the solid portions, the N being a number equal to or greater than
3; a pixel electrode assigned to the pixel area and opposing the
counter electrode, the pixel electrode having a connecting portion
extending in the first direction and first and second extending
portions extending in the second direction, the connection portion
connecting the first and second extending portions, wherein the
first extending portion is vertically aligned to the hollow portion
of the counter electrode and the second extending portion is
vertically aligned to the solid portion of the counter electrode;
and an insulating layer provided between the counter and pixel
electrodes.
2. The display device of claim 1, wherein the counter electrode has
a plurality of hollow portions and a plurality of solid portions,
and the pixel electrodes have more than two extending portions.
3. The display device of claim 1, wherein the hollow portion has a
first width, the solid portion has a second width, the first
extending portion has a third width, and the second extending
portion has a fourth width, wherein the first, second, third, and
fourth widths are distances in the first direction.
4. The display device of claim 3, wherein the first width of the
hollow portion is greater than the third and fourth widths of the
first and second extending portions.
5. The display device of claim 4, wherein the first and second
extending portions are separated by a first distance, and an edge
of the hollow portion extends beyond an edge of the first extending
portion by a second distance in the first direction, wherein the
first distance is greater than the second distance.
6. The display device of claim 5, wherein the second distance is as
great as possible without being greater than the first distance, in
order to obtain higher optical transmissivity.
7. The display device of claim 5, wherein an edge of the solid
portion in the first direction is provided within a space between
the first and second extending portions to strengthen an electric
field substantially parallel to the first substrate and weaken an
electric field substantially perpendicular to the first
substrate.
8. The display device of claim 3, wherein the second width of the
solid portion is greater than the third and fourth widths of the
first and second extending portions.
9. The display device of claim 1, wherein the N is an integer.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present application is a continuation application of
U.S. Pat. No. 09/760,385, filed on Jan. 11, 2001, which claims
priority from Japanese Patent Application No. 2000-003348, filed
Jan. 12, 2000, the disclosures of which are incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a liquid crystal display
device and, more particularly, to a liquid crystal display device
which is called In-Plane Switching Mode.
[0003] Liquid crystal display device which is called In-Plane
Switching Mode has a construction in which a pixel electrode and a
counter electrode which causes an electric field (an in-plane
electric field) having a component parallel to transparent
substrates to be generated between the counter electrode and the
pixel electrode are formed in each liquid crystal-side pixel area
of one of the transparent substrates disposed in opposition to each
other with a liquid crystal interposed therebetween.
[0004] This type of liquid crystal display device is constructed so
that the amount of light to be transmitted through the area between
the pixel electrode and the counter electrode is controlled by the
driving of the liquid crystal to which the electric field is
applied.
[0005] Such a liquid crystal display device is known as a type
which is superior in so-called viewing angle characteristics and
enables a displayed image to be unchanged even when its display
surface is observed from an oblique direction.
[0006] The pixel electrode and the counter electrode have so far
been formed of a metal layer which does not transmit light
therethrough.
[0007] In recent years, a liquid crystal display device constructed
in the following manner has been known: a counter electrode made of
a transparent electrode is formed over the entire area of a pixel
area except the periphery thereof, and strip-shaped pixel
electrodes are formed on the counter electrode with an insulating
film interposed therebetween, in such a manner as to be extended in
one direction and to be juxtaposed in a direction traverse to the
one direction.
[0008] The liquid crystal display device having this construction
causes an in-plane electric field to be generated between each of
the pixel electrodes and the counter electrode, and is still
superior in viewing angle characteristics and is greatly improved
in aperture ratio.
[0009] Incidentally, this art is described, for example, in SID
(Society for Information Display) 99 DIGEST: pp. 202-205 and
Japanese Patent Laid-Open No. 202356/1999.
[0010] However, in the liquid crystal display device having this
construction, the occurrence of so-called horizontal smear is
visually observed on its display portion, and the occurrence of
image retention is also visually observed.
[0011] It has been found out that the cause of the occurrence of
horizontal smear is that the capacitance between the counter
electrode formed over the entire area of the pixel area except the
periphery thereof and the plural strip-shaped pixel electrodes
formed in juxtaposition on the counter electrode with the
insulating film interposed therebetween becomes larger than in
previous type and the charge of the pixel electrodes with signal
voltages becomes insufficient, and also the voltage of the counter
electrode is distorted and the time required for the distorted
voltage to be restored to its original state becomes long.
[0012] It has also been found out that the cause of the occurrence
of image retention is that an electric field other than an electric
field which has a component parallel to the substrate between the
pixel electrode and the counter electrode and contributes to the
control of the optical transmissivity of the liquid crystal, i.e.,
an electric field having a component perpendicular to the substrate
between the counter electrode and the pixel electrode, is
excessively strong.
SUMMARY OF THE INVENTION
[0013] The present invention has been made on the basis of the
above-described situations, and provides a liquid crystal display
device which can restrain the occurrence of horizontal smear.
[0014] The present invention also provides a liquid crystal display
device which can restrain the occurrence of image retention.
[0015] A representative aspect of the invention disclosed in the
present application will be described below in brief.
[0016] In one embodiment, a liquid crystal display device includes
a first substrate and a second substrate facing the first
substrate. A liquid crystal layer is provided between the first and
second substrates. First and second gate lines are extending in a
first direction, and first and second drain lines are extending in
a second direction. A pixel area is defined by the gate lines and
drain lines. A counter electrode assigned to the pixel area and
having a hollow portion is provided adjacent to a solid portion.
The hollow and solid portions are extending in the second
direction. One hollow portion is provided after N number of the
solid portions, the N being a number equal to or greater than 3. A
pixel electrode is assigned to the pixel area and is opposing the
counter electrode. The pixel electrode has a connecting portion
extending in the first direction and first and second extending
portions extending in the second direction. The connection portion
connects the first and second extending portions, wherein the first
extending portion is vertically aligned to the hollow portion of
the counter electrode and the second extending portion is
vertically aligned to the solid portion of the counter electrode.
An insulating layer is provided between the counter and pixel
electrodes.
[0017] In one embodiment, a liquid crystal display device according
to the present invention includes a pair of substrates, a liquid
crystal layer interposed between the pair of substrates, a
plurality of pixel parts being constructed with a plurality of gate
lines and a plurality of drain lines arranged in a matrix on one of
the pair of substrates, at least one pair of the first electrodes
and the second electrodes provided for each pixel part between one
of the pair of substrates and the liquid crystal layer, wherein the
first electrode and the second electrode being disposed with an
insulating film interposed therebetween, and the second electrode
is transparent electrode formed in a rectangular shape and having a
slit formed in a portion which is superposed on the first
electrodes.
[0018] In the liquid crystal display device constructed in this
manner, the selected ones of the plural electrodes of the other
electrode (for example, pixel electrodes) are formed not to be
superposed on the one of the pair of electrodes (for example, a
counter electrode).
[0019] Accordingly, it is possible to decrease the capacitance
occurring between the pixel electrode and the counter electrode,
whereby it is possible to restrain the occurrence of horizontal
smear.
[0020] In addition, it is possible to weaken an electric field
other than an electric field which contributes to the control of
the optical transmissivity of the liquid crystal, i.e., an electric
field having a component perpendicular to the substrate between the
counter electrode and the pixel electrode, from among electric
fields occurring between the pixel electrode and the counter
electrode, whereby it is possible to restrain the occurrence of
image retention.
[0021] Moreover, since the holes formed in the other-side electrode
are disposed with respect to one-side electrodes that are not
adjacent to one another, the holes are formed with a comparatively
large space, whereby the holes have the advantage of being easily
worked.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The present invention will be more apparent from the
following detailed description, when taken in conjunction with the
accompanying drawings, in which:
[0023] FIG. 1 is a plan view showing one embodiment of a pixel of a
liquid crystal display device according to the present
invention;
[0024] FIG. 2 is a cross-sectional view taken along line 2-2 of
FIG. 1;
[0025] FIG. 3 is a cross-sectional view taken along line 3-3 of
FIG. 1;
[0026] FIG. 4 is a cross-sectional view take along line 4-4 of FIG.
1;
[0027] FIG. 5 is an explanatory view showing the positional
relationship between pixel electrodes and holes formed in a counter
electrode of the liquid crystal display device according to the
present invention;
[0028] FIG. 6 is a plan view showing one embodiment of the whole of
the liquid crystal display panel of the liquid crystal display
device according to the present invention;
[0029] FIG. 7 is a view showing the equivalent circuit of the
liquid crystal panel according to the present invention;
[0030] FIG. 8 is a cross-sectional view showing another embodiment
of the liquid crystal display device according to the present
invention; and
[0031] FIG. 9 is a plan view showing another embodiment of the
liquid crystal display device according to the present
invention.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0032] Preferred embodiments of the liquid crystal display device
according to the present invention will be described below.
[0033] [Embodiment 1]
[0034] <<Construction of Pixel>>
[0035] FIG. 1 is a plan view showing the construction of a pixel
area of a liquid crystal display device (panel) according to the
present invention as viewed from the liquid-crystal side of one of
transparent substrates disposed in opposition to each other with a
liquid crystal interposed therebetween.
[0036] FIG. 2 is a cross-sectional view taken along line 2-2 of
FIG. 1, FIG. 3 is a cross-sectional view taken along line 3-3 of
FIG. 1, and FIG. 4 is a cross-sectional view take along line 4-4 of
FIG. 1.
[0037] Referring first to FIG. 1, gate signal lines GL are disposed
to be extended in the x-direction of FIG. 1 and to be juxtaposed in
the y-direction of FIG. 1, and the gate signal lines GL are formed
of, for example, chromium (Cr). These gate signal lines GL form a
rectangular area together with drain signal lines DL which will be
described below, and the area constitutes a pixel area.
[0038] A counter electrode CT which generates an electric field
between the counter electrode CT and pixel electrodes PX which will
be described below are formed in this pixel area. This counter
electrode CT is formed in the central portion of the pixel area
except the periphery thereof, and is made of, for example, ITO1
(Indium-Tin-Oxide) which forms a transparent conductive layer.
[0039] As will be described later in detail, the plural pixel
electrodes PX are formed in juxtaposition, and the counter
electrode CT is formed in such a manner as to be superposed on the
plural pixel electrodes PX with an insulating film GI interposed
therebetween. Holes CTH are respectively formed in the portions of
the counter electrode CT that are superposed on every other one of
the pixel electrodes PX.
[0040] A counter voltage signal line CL is formed to be connected
to the counter electrode CT in such a manner as to border the
entire periphery thereof. This counter voltage signal line CL is
formed integrally with counter voltage signal lines CL which are
similarly formed at the respective counter electrodes CT in the
right and left pixel areas as viewed in FIG. 1 (i.e., the
corresponding one of the pixel areas arrayed along the gate signal
lines GL).
[0041] In this case, the counter voltage signal lines CL are
connected to one another at each of locations above and below the
pixel areas. This construction is intended to minimize the portion
of superposition of each of the counter voltage signal lines CL and
the adjacent one of the drain signal lines DL which will be
described later, thereby reducing the capacitance generated
therebetween.
[0042] Each of these counter voltage signal lines CL is formed of
an opaque material made of, for example, chromium (Cr). In this
case, even if an electric field which acts as noise is generated
between any of the drain signal lines DL which will be described
later and the periphery of the adjacent one of the counter
electrodes CT and the optical transmissivity of the liquid crystal
is not obtained as desired, that portion is shielded by the counter
voltage signal line CL, whereby it is possible to solve a problem
in terms of display quality.
[0043] This also means that it is possible to solve a problem due
to an electric field (noise) which is generated between any of the
gate signal lines GL and the periphery of the adjacent one of the
counter electrodes CT.
[0044] In addition, as described above, since the material of the
counter voltage signal lines CL is identical to that of the gate
signal lines GL, the counter voltage signal lines CL and the gate
signal lines GL can be formed in the same process, whereby it is
possible to avoid an increase in the number of manufacturing
steps.
[0045] It goes without saying that the material of the counter
voltage signal lines CL is not limited to Cr and the counter
voltage signal lines CL may be formed of, for example, Al or a
material which contains Al.
[0046] In this case, it is effective to position the counter
voltage signal lines CL as a layer which overlies the counter
electrodes CT. This is because Al is easily melted by an etching
solution (for example, HBr) for selectively etching an ITO film
which constitutes the counter electrodes CT.
[0047] Furthermore, it is effective to interpose a high melting
point metal such as Ti, Cr, Mo, Ta or W at least the interface
between each of the counter voltage signal lines CL and the
adjacent one of the counter electrodes CT.. This is because ITO
which constitutes the counter electrodes CT oxidizes Al of the
counter voltage signal lines CL and generates a high-resistance
layer.
[0048] For this reason, as one example, if the counter voltage
signal lines CL made of Al or a material which contains Al are to
be formed, it is preferable to form each of the counter voltage
signal lines CL as a multilayered structure having a first layer
made of the high melting point metal.
[0049] In this manner, the counter electrodes CT, the counter
voltage signal lines CL and the gate signal lines GL are formed
over the transparent substrate, and the insulating film GI made of,
for example, SiN is formed over the transparent substrate in such a
manner as to cover all of the counter electrodes CT, the counter
voltage signal lines CL and the gate signal lines GL.
[0050] The insulating film GI has the function of an interlayer
insulating film for insulating the drain signal lines DL from the
counter voltage signal lines CL and the gate signal lines GL. The
insulating film GI also has the function of a gate insulating film
in each area in which a thin film transistor TFT which will be
described below is formed, as well as the function of a dielectric
film in each area in which a capacitance element Cstg which will be
described below is formed.
[0051] The thin film transistor TFT is formed to be superposed on a
portion of the gate signal line GL (the bottom left portion of FIG.
1), and in this portion, a semiconductor layer AS made of, for
example, amorphous silicon (a-Si) is formed on the insulating film
GI.
[0052] A source electrode SD1 and a drain electrode SD2 are formed
on the upper surface of the semiconductor layer AS, whereby an
inverted staggered structure MIS transistor is formed which uses a
portion of the gate signal line GL as its gate electrode. The
source electrode SD1 and the drain electrode SD2 are formed at the
same time as the drain signal line DL.
[0053] Specifically, the drain signal lines DL which are disposed
to be extended in the y-direction of FIG. 1 and to be juxtaposed in
the x-direction of FIG. 1 are formed, and a portion of an adjacent
one of the drain signal lines DL is extended to the surface of the
semiconductor layer AS and constitutes the drain electrode SD2 of
the thin film transistor TFT.
[0054] During the formation of the adjacent drain signal line DL,
the source electrode SD1 is formed, and this source electrode SD1
is extended to the inside of the pixel area, thereby integrally
forming a contact portion which provides connection between the
thin film transistor TFT and the pixel electrode PX which will be
described below.
[0055] As shown in FIG. 3, a contact layer d0 which is doped with,
for example, an n type impurity is formed at the interface between
the source electrode SD1 and the drain electrode SD2 of the
semiconductor layer AS.
[0056] This contact layer d0 is formed by forming an n type
impurity-doped layer over the entire surface of the semiconductor
layer AS, and, after forming the source electrode SD1 and the drain
electrode SD2, etching the n type impurity-doped layer on the
portion of the surface of the semiconductor layer AS that is
exposed between these electrodes SD1 and SD2, by using each of
these electrodes SD1 and SD2 as a mask.
[0057] In Embodiment 1, the semiconductor layer AS is formed not
only in the area in which the thin film transistor TFT is formed,
but also at the intersection of the drain signal line DL and the
gate signal line GL and at the intersection of the drain signal
line DL and the counter voltage signal line CL. This construction
is intended to strengthen the function of the interlayer insulating
film.
[0058] A protective film PSV covers the thin film transistor TFT
formed over the surface of a transparent substrate SUB1 on which
the thin film transistor TFT is formed. The protective film is
generally made of a dielectric material, for example, SiN. The
protect film prevents the thin film transistor TFT from coming into
direct contact with the liquid crystal LC.
[0059] Furthermore, the pixel electrode PX which is made of a
transparent conductive film are formed over the upper surface of
the protective film PVS. The pixel electrode PX is generally made
of a conductive material, for example, Indium-Tin-Oxide (ITO).
[0060] In Embodiment 1, five pixel electrodes PX are formed to be
superposed on an area in which the counter electrode CT is formed,
and are also formed to be extended in the y direction of FIG. 1 and
to be equidistantly spaced apart from one another. Both ends of
each of the five pixel electrodes PX are connected to the
respective ends of the adjacent one by layers made of the same
material which is formed to be extended in the x direction of FIG.
1.
[0061] In this construction, three pixel electrodes PX which are
respectively disposed at the first, third and fifth positions as
viewed from the left side of FIG. 1 are positioned in the
respective holes CTH formed in the counter electrode CT.
[0062] Specifically, within a substantial pixel area, i.e., within
the aperture of a black matrix, each of the first, third and fifth
pixel electrodes PX is formed without being superposed on the
counter electrode CT, and the other pixel electrodes PX which are
respectively disposed at the second and fourth positions as viewed
from the left side of FIG. 1 are formed to be superposed on the
counter electrode CT.
[0063] In the case where the pixel electrodes PX are formed in this
manner, since the area of superposition of the pixel electrodes PX
and the counter electrodes CT can be decreased, the capacitance
between the pixel electrodes PX and the counter electrodes CT can
be decreased, whereby it is possible to decrease the occurrence of
so-called horizontal smear.
[0064] In this construction, the holes CTH are formed in the
counter electrode CT in such a manner as to correspond to every
other one of the pixel electrodes PX. This construction is intended
to facilitate the working of the holes CTH by increasing the spaces
between the adjacent holes CTH.
[0065] In Embodiment 1, the number of pixel electrodes PX per pixel
area is five, but there actually are cases in which dozens of pixel
electrodes are formed per pixel area. In such a case, the holes CTH
may be formed at positions which correspond to not only every other
one of the pixel electrodes PX but also every third one, every
fourth one and so on, whereby it is possible to achieve far easier
working of the holes CTH.
[0066] FIG. 8 is a view which shows such a construction and
corresponds to FIG. 2. In the construction shown in FIG. 8, the
holes CTH are formed in the counter electrode CT which underlies
the juxtaposed multiple pixel electrodes PX, at positions which
correspond to every fourth one of the pixel electrodes PX.
[0067] In addition, in this embodiment, the central axis of every
fourth one of the pixel electrodes PX agrees with that of the
corresponding one of the holes CTH formed in the counter electrode
CT, and each of the holes CTH is formed to have a width larger than
the corresponding one of the pixel electrodes PX.
[0068] FIG. 5 is a cross-sectional view (which corresponds to the
cross-sectional view of FIG. 2) showing the positional relationship
between the pixel electrodes PX and the holes CTH formed in the
counter electrode CT.
[0069] As can be seen from FIG. 5, each of the counter electrodes
CT which are separated by the formation of the holes CTH (but are
connected for electrical connection at their opposite peripheral
ends) is formed to be superposed on pixel electrodes PX(2) adjacent
to a pixel electrode PX(1) which is one of the pixel electrodes PX,
and to be extended to the area between each of the pixel electrodes
PX(2) and the pixel electrode PX(1) as viewed in the direction of
juxtaposition of the pixel electrodes PX. Thus, each of the counter
electrodes CT is formed to have an area superposed on the pixel
electrode PX(1) and widths W.
[0070] The widths W are mainly determined from the point of view of
decreasing an electric field other than an electric field which
contributes to the control of the optical transmissivity of the
liquid crystal between the pixel electrode PX and the counter
electrode CT, that is to say, an electric field which has a
component perpendicular to the substrate between the counter
electrode CT and the pixel electrode PX. Accordingly, it is
appropriate to make each of the widths W smaller than the
separation distance between the pixel electrode PX(1) and each of
the pixel electrodes PX(2) adjacent to the pixel electrode
PX(1).
[0071] The widths W are preferably as wide as possible, but
slightly smaller than the respective separation distances.
[0072] In other words, the peripheral outline portion of the
counter electrode CT has only to lie at the intermediate position
between the pixel electrode PX(1) and each of the pixel electrodes
PX(2) adjacent to the pixel electrode PX(1), and the counter
electrode CT has to be wider than the pixel electrode PX(1),
preferably slightly wider.
[0073] The reason for this is that the existence of the widths W
makes it possible to strengthen an electric field having a
component approximately parallel to the transparent substrate in
each pixel area and to decrease an electric field which occurs in a
direction perpendicular to the substrate and adversely affects the
phenomenon of image retention. In addition, as the widths W are
made larger, the absorption loss of light due to transparent
electrodes becomes smaller and higher optical transmissivity can be
obtained.
[0074] The bottom-end same-material layer of each of the pixel
electrodes PX which are formed in this manner is connected to a
contact portion of the source electrode SD1 of the thin film
transistor TFT through a contact hole formed in the protective film
PSV. The top-end same-material layer is formed to be superposed on
the counter voltage signal line CL.
[0075] In the case of this construction, a capacitance element Cstg
which uses as a dielectric film a stacked film made of the
insulating film GI and the protective film PSV is formed in the
portion of superposition of the counter electrode CT and each of
the pixel electrodes PX.
[0076] This capacitance element Cstg is formed for purposes such as
storing a video signal in the pixel electrode PX for a
comparatively long period even if the thin film transistor TFT is
turned off after the video signal from the drain signal line DL is
applied to the pixel electrode PX via the thin film transistor
TFT.
[0077] An alignment film ORI1 which covers the pixel electrodes PX
is formed over the surface of the transparent substrate SUB1 over
which the pixel electrodes PX are formed in the above-described
manner. This alignment film ORI1 is a film which is in direct
contact with the liquid crystal LC and determines the initial
alignment direction of the liquid crystal LC.
[0078] Incidentally, in Embodiment 1, the initial alignment
direction is made 75.degree. with respect to the direction of
application of an electric field. The initial alignment direction
is not limited to 75.degree., and may be greater than 0.degree. and
less than 90.degree., preferably 10.degree.0 to 80.degree. so that
high-speed responses (drivable at low voltages) can be
achieved.
[0079] In the above-described embodiment, the gate signal lines GL,
the counter voltage signal lines CL and the drain signal lines DL
are formed of chromium (Cr). However, it goes without saying that
another high melting point metal such as Mo, W, Ti or Ta or an
alloy of two or more kinds of such metals or a stacked film made of
two or more kinds of such metals may also be used.
[0080] Moreover, although in the above description the transparent
conductive film is made of ITO, it goes without saying that similar
advantages can be obtained even with IZO (Indium-Zinc-Oxide).
[0081] The transparent substrate constructed in this manner is
called a TFT substrate, and a transparent substrate disposed in
opposition to this TFT substrate with the liquid crystal LC
interposed therebetween is called a filter substrate.
[0082] <<Filter Substrate>>
[0083] As shown in FIG. 2, on the liquid crystal-side surface of
the filter substrate, a black matrix BM is formed to separate the
pixel areas from one another, and a filter FIL is formed to cover
each aperture of the black matrix BM that determines a substantial
pixel area.
[0084] An overcoat layer OC made of, for example, a resin layer is
formed to cover the black matrix BM and the filter FIL, and an
alignment layer 0RI2 is formed on the overcoat layer OC.
[0085] The alignment direction of the alignment layer ORI2 is
selected to be the same as that of the alignment film ORI1 when the
alignment film ORI1 is superposed on the alignment layer ORI1. That
is to say, the alignment of the molecules of the liquid crystal LC
is made homogeneous.
[0086] <<Liquid Crystal Layer>>
[0087] In Embodiment 1, a liquid crystal having a dielectric
anisotropy .DELTA..epsilon. of, for example, -5 is used, whereby it
is possible to obtain a high optical transmissivity. This is
because the directors of the liquid crystal molecules of a liquid
crystal of negative .DELTA..epsilon. do not greatly change due to
an electric-field component perpendicular to a substrate
surface.
[0088] Embodiment 1 uses a liquid crystal of negative
.DELTA..epsilon., but even if a liquid crystal of positive
.DELTA..epsilon. is used, the effects and advantages of the present
invention can similarly be obtained.
[0089] Since the liquid crystal of positive .DELTA..epsilon. is
large in .DELTA..epsilon. and low in viscosity compared to the
liquid crystal of negative .DELTA..epsilon., the liquid crystal of
positive .DELTA..epsilon. has the advantage of being drivable at
lower voltages and at higher response speeds.
[0090] <<Entire Construction of Liquid Crystal Display
Panel>>
[0091] FIG. 6 is a view of the entire construction of the liquid
crystal display panel, showing a display area AR constructed of an
assembly of pixel areas arranged in matrix form.
[0092] A transparent substrate SUB2 is formed to be slightly
smaller than the transparent substrate SUB1, and the right and
bottom sides (as viewed in FIG. 6) of the transparent substrate
SUB2 are disposed to be approximately in flush with the
corresponding sides of the transparent substrate SUB1.
[0093] Accordingly, areas which are not covered with the
transparent substrate SUB2 are respectively formed along the left
and top sides (as viewed in FIG. 5) of the transparent substrate
SUB1, and gate signal terminals Tg and drain signal terminals Td
are formed in the respect areas. The gate signal terminals Tg are
formed for supplying scanning signals to the respective gate signal
lines GL, while the drain signal terminals Td are formed for
supplying video signals to the respective drain signal lines
DL.
[0094] The transparent substrate SUB2 is secured to the transparent
substrate SUB1 by a sealing material SL formed along the periphery
of the transparent substrate SUB2, and this sealing material SL
also has the function of a sealing material for sealing the liquid
crystal LC between the transparent substrates SUB1 and SUB2.
[0095] A liquid crystal filling port INJ is disposed in a portion
of the sealing material SL, and after the gap between the
transparent substrates SUB1 and SUB2 has been filled with the
liquid crystal LC through the liquid crystal filling port INJ, the
liquid crystal filling port INJ is sealed by a liquid crystal
sealing material (not shown).
[0096] Polarizers are respectively stuck to the outside surfaces of
the transparent substrates SUB1 and SUB2 in such a manner that the
transparent substrates SUB1 and SUB2 are interposed between the
polarizers.
[0097] <<Equivalent Circuit>>
[0098] FIG. 7 is a view showing the equivalent circuit of the
liquid crystal panel as well as the external circuits of the liquid
crystal panel.
[0099] Scanning signals (voltage signals) are sequentially supplied
to the individual gate signal lines GL disposed to be extended in
the x-direction of FIG. 7 and to be juxtaposed in the y-direction
of FIG. 7, by a vertical scanning circuit V.
[0100] The thin film transistors TFT in the respective pixel areas
arranged along the one of the gate signal lines GL to which a
scanning signal is supplied are turned on by the scanning
signal.
[0101] At this timing, video signals are supplied to the individual
drain signal lines DL from a video signal driver circuit H, and
these video signals are applied to the respective pixel electrodes
PX via the thin film transistors of the corresponding pixel
areas.
[0102] In the respective pixel areas, counter voltages are applied
to the counter electrodes CT formed together with the pixel
electrodes PX via the counter voltage signal lines CL, so that
electric fields can be generated between the pixel electrodes and
the counter electrodes CT.
[0103] The optical transmissivity of the liquid crystal LC is
controlled by the ones (in-plane electric fields) of these electric
fields each of which has a component parallel to the transparent
substrate SUB1.
[0104] Incidentally, in FIG. 7, the symbols R, G and B shown in the
individual pixel areas represent that a red filter, a green filter
and a blue filter are formed in the respective pixel areas.
[0105] <<Other Embodiments>>
[0106] In the above-described embodiment, the counter electrodes CT
are formed below the pixel electrodes PX with the insulating film
GI interposed therebetween. However, the present invention is not
limited to this construction, and it goes without saying that the
pixel electrodes PX are formed below the counter electrodes CT with
the insulating film GI interposed therebetween.
[0107] In the above-described embodiment, the pixel electrodes PX
formed in juxtaposition are formed as rectilinear strip-shaped
electrodes in the respective pixel areas.
[0108] However, the present invention is not limited to this
construction, and it goes without saying that each of the pixel
electrodes PX may be an element having one or more bent portions in
the direction of extension of the pixel electrode PX.
[0109] Such an electrode is called a multi domain scheme in which
the direction of an electric field generated between the electrode
and the counter electrode CT is made different to provide the
advantage of canceling a difference in the optical transmissivity
of a liquid crystal when a display area is viewed in any direction
different from the direction normal to its front surface.
[0110] Even in this case, the holes CTH can be formed in the
counter electrode CT at locations corresponding to the bent
extended portion of the pixel electrode PX.
[0111] FIG. 9 is a plan view which corresponds to FIG. 1, showing
an example to which the multi domain scheme is applied.
[0112] Each of the pixel electrodes PX has, for example, a zigzag
pattern along its extension direction, and the holes CTH each
having a zigzag shape along the zigzag pattern are respectively
formed in the counter electrodes CT which are superposed on some of
the pixel electrodes PX (for example, every other one of the pixel
electrodes PX).
[0113] The extension direction of the pixel electrodes PX is along
the y-direction of FIG. 9, but the present invention is not limited
to this construction and can, of course, be applied to a
construction in which the extension direction of the pixel
electrodes PX is along the x-direction of FIG. 9.
[0114] In the above-described embodiment, an electrode which is
formed over nearly the whole of the central portion of the pixel
area except the periphery thereof serves as the counter electrode
CT, while plural strip-shaped electrodes which are juxtaposed in
one direction serve as the pixel electrodes PX. However, an
electrode which is formed over the central portion of the pixel
area except the periphery thereof may be used as the pixel
electrode PX, while plural strip-shaped electrodes which are
juxtaposed in one direction may be used as the counter electrode
CT.
[0115] As is apparent from the foregoing description, in accordance
with the liquid crystal display device according to the present
invention, it is possible to prevent the occurrence of horizontal
smear and image retention.
* * * * *