U.S. patent application number 13/935616 was filed with the patent office on 2013-11-07 for image display device.
The applicant listed for this patent is CHIMEI INNOLUX CORPORATION. Invention is credited to Mitsuru Ikezaki, Kaoru Kusafuka.
Application Number | 20130293813 13/935616 |
Document ID | / |
Family ID | 34735045 |
Filed Date | 2013-11-07 |
United States Patent
Application |
20130293813 |
Kind Code |
A1 |
Kusafuka; Kaoru ; et
al. |
November 7, 2013 |
IMAGE DISPLAY DEVICE
Abstract
An image display device includes a light source, an array
substrate having a display region and a peripheral region around
the display region, wherein the array substrate includes a first
light-shielding wiring layout arranged in the display region of the
array substrate, and a second light-shielding wiring layout
arranged in the peripheral region of the array substrate, an
occupied area per unit area of the second light-shielding wiring
layout in the peripheral region being equal to or greater than an
occupied area per unit area of the first light-shielding wiring
layout in the display region. The image display device further
includes an opposite substrate disposed on the array substrate, and
a liquid crystal layer comprising a plurality of liquid crystal
molecules and disposed between the array substrate and the opposite
substrate.
Inventors: |
Kusafuka; Kaoru;
(Kanagawa-ken, JP) ; Ikezaki; Mitsuru;
(Kanagawa-ken, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CHIMEI INNOLUX CORPORATION |
Miao-Li County |
|
TW |
|
|
Family ID: |
34735045 |
Appl. No.: |
13/935616 |
Filed: |
July 5, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11005874 |
Dec 7, 2004 |
8488083 |
|
|
13935616 |
|
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Current U.S.
Class: |
349/111 |
Current CPC
Class: |
G02F 1/133514 20130101;
G02F 1/1345 20130101; G02F 1/133512 20130101 |
Class at
Publication: |
349/111 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 12, 2003 |
JP |
2003415622 |
Claims
1. An image display device comprising: a light source; an array
substrate comprising a display region and a peripheral region
around the display region, wherein the array substrate comprises: a
first light-shielding wiring layout arranged in the display region
of the array substrate; and a second light-shielding wiring layout
arranged in the peripheral region of the array substrate, an
occupied area per unit area of the second light-shielding wiring
layout in the peripheral region being equal to or greater than an
occupied area per unit area of the first light-shielding wiring
layout in the display region; an opposite substrate disposed on the
array substrate; and a liquid crystal layer comprising a plurality
of liquid crystal molecules and disposed between the array
substrate and the opposite substrate; wherein a light transmittance
per unit area in the peripheral region of the array substrate is
equal to or less than a light transmittance per unit area in the
display region of the array substrate.
2. The image display device of claim 1, wherein the second
light-shielding wiring layout includes an electric line having a
line width, and the line width is enlarged and the occupied area
per unit area of the second light-shielding wiring layout to be
equal to or greater than the occupied area per unit area of the
first light-shielding wiring layout.
3. The image display device of claim 2, wherein the electric line
is a gate line.
4. The image display device of claim 2, wherein the electric line
is a signal line.
5. The image display device of claim 2, wherein the peripheral
region includes a plurality of input terminals for receiving
external electric signals and the electric line is extended to
connect one of the input terminals in the peripheral region.
6. The image display device of claim 1, wherein the second light
shielding wiring layout includes a plurality of electric lines, and
a line width of one of the electric lines is larger than that of
another electric lines, and the occupied area per unit area of the
second light shielding wiring layout to be equal to or greater than
the occupied area per unit area of the first light shielding wiring
layout.
7. The image display device of claim 1, wherein the array substrate
includes a sealant coating region, and the peripheral region is
positioned between the display region and the sealant coating
region.
8. The image display device of claim 1, wherein the second
light-shielding wiring layout includes a dummy pattern.
9. The image display device of claim 8, wherein a width of the
dummy pattern is equal to or greater than a line width of another
second light-shielding wiring layout.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of co-pending
application Ser. No. 11/005,874, filed Dec. 7, 2004 and entitled
"IMAGE DISPLAY DEVICE WITH LIGHT SHIELDING WIRINGS AND COLOR FILTER
HAVING RESISTIVITY RATIO", which claims the benefit of Japan
application Serial No. 2003415622, filed Dec. 12, 2003. These
related applications are incorporated herein by reference.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an image display device,
and more particularly, to an IPS (in-plane switching) mode LCD.
[0004] 2. Description of the Prior Art
[0005] An image display device is an optoelectronic device able to
transfer electric signals into visible images so that human beings
can see the information contained in the electronic signals. These
days, the typical image display device is commonly an LCD, and
other display devices, such as a PDP (plasma display panel)
display, an EL (electro luminescence) display, an FED (field
emission display), and a DMD (deformable mirror device)
display.
[0006] Among all those image display devices, an active matrix LCD,
which utilizes thin film transistors as switching elements, is
popular due to its small size, light weight, and low power
consumption. The LCD substantially includes two glass substrates, a
liquid crystal layer disposed between the two substrates, and two
alignment films respectively disposed on two opposite surfaces of
the two substrates for orientating liquid crystal molecules in
predetermined directions. The liquid crystal molecules arranged in
predetermined directions are rotated when an electric filed is
applied, and thus images are displayed via light transmittance
changes through the liquid crystal layer.
[0007] For known art, a TN (twisted nematic) mode LCD has been in
use for a long time. In the TN mode LCD, the liquid crystal
molecules are rotated in a vertical direction with respect to the
substrate. However, this leads to problems of narrow viewing angles
and color distortions.
[0008] In order to solve these problems, Japanese patent
(publication No. 07-36058) has proposed an IPS mode LCD. In the
Japanese patent, the IPS mode LCD includes a plurality of pixel
electrodes and a plurality of common electrodes arranged in
parallel to the pixel electrodes in an array substrate. A voltage
is applied between the pixel electrode and the common electrode so
that a parallel electric field, which rotates the liquid crystal
molecules, is generated above the array substrate. Since the liquid
crystal molecules are rotated in a plane approximately parallel to
the array substrate, the problems of color distortions and narrow
viewing angles are reduced. Therefore, the IPS mode LCD is suitable
for use in large-sized displays.
[0009] For the IPS mode LCD, however, an uneven brightness defect
occurs when a large-sized screen with fine image qualities is
desired. Presumably, the uneven brightness defect results from the
existence of impurity ions. FIG. 14 is a schematic diagram
illustrating an image display condition of a conventional LCD. As
shown in FIG. 14, when a white image is displayed in a display
region 102, red color unevenness defects 104 appears around the
display region 102. These red color unevenness defects 104 degrade
the image quality of the IP.S mode LCD.
SUMMARY OF INVENTION
[0010] It is therefore a primary object of the claimed invention to
provide an image display device to prevent the aforementioned
uneven brightness problem.
[0011] According to claim 1, an image display device is provided.
The image display device includes a light source, an array
substrate including a display region and a peripheral region around
the display region, a color filter substrate including a plurality
of color filters having different transmissivities, a liquid
crystal layer including a plurality of liquid crystal molecules,
and an alignment film for aligning the liquid crystal molecules.
Characteristically, a light transmittance per unit area in the
peripheral region is equivalent to or less than a light
transmittance per unit area in the display region.
[0012] By virtue of the image display device recited in claim 1,
the light transmittance per unit area in the peripheral region is
equivalent to or less than a light transmittance per unit area in
the display region, so as to inhibit impurity ions from traveling
from the peripheral region to the display region. Consequently, the
uneven brightness problem is reduced.
[0013] According to claim 2, the array substrate recited in claim 1
includes a first light-shielding wiring layout arranged in the
display region, and a second light-shielding wiring layout arranged
in the peripheral region. Characteristically, an occupied area per
unit area of the second light-shielding wiring layout in the
peripheral region is equivalent to or greater than an occupied area
per unit area of the first light-shielding wiring layout in the
display region.
[0014] According to claim 3, the image display device recited in
claim 2, wherein the first light-shielding wiring layout and the
second light-shielding wiring layout comprise at least one of an
active element, a passive element, and a wiring.
[0015] According to claim 4, an image display device is disclosed.
The image display device includes a light source, an array
substrate including a display region and a peripheral region around
the display region, a color filter substrate including a plurality
of color filters having different transmissivities, a liquid
crystal layer including a plurality of liquid crystal molecules,
and an alignment film for aligning the liquid crystal molecules.
Characteristically, a resistivity ratio of the color filter having
a highest resistivity to the color filter having a lowest
resistivity is set according to a difference between a light
transmittance per unit area in the peripheral region and a light
transmittance per unit area in the display region.
[0016] By virtue of the image display device recited in claim 4,
the resistivity ratio of the color filter having the highest
resistivity to the color filter having the lowest resistivity is
set according to the difference between the light transmittance per
unit area in the peripheral region and the light transmittance per
unit area in the display region, so as to inhibit impurity ions
from traveling from the peripheral region to the display region.
Consequently, the uneven brightness problem is reduced.
[0017] According to claim 5, the relation between the resistivity
ratio of the color filter having the highest resistivity to the
color filter having the lowest resistivity and the difference
between the light transmittance per unit area in the peripheral
region and the light transmittance per unit area in the display
region is expressed by
p max p min<10.sup.(4100/(If-Ip)+0.05)
wherein p max is the highest resistivity having units of .OMEGA.
cm; [0018] p min is the lowest resistivity having units of .OMEGA.
cm; [0019] I.sub.f is the light transmittance in the peripheral
region having units of cd/mm; and [0020] Ip is the light
transmittance in the display region having units of cd/mm.
[0021] According to claim 6, an image display device is provided.
The image display device includes a light source, an array
substrate including a display region and a peripheral region around
the display region, a color filter substrate including a plurality
of color filters having different transmissivities, a liquid
crystal layer including a plurality of liquid crystal molecules,
and an alignment film for aligning the liquid crystal molecules.
Characteristically, the alignment film is only positioned in the
display region.
[0022] By virtue of the image display device recited in claim 6,
the alignment film is only positioned in the display region, so
that the uneven brightness problem due to the contamination of
impurity ions coming from the peripheral region is prevented.
[0023] According to claim 7, the image display device is an IPS
mode LCD.
[0024] The image display device reduces electric filed deviations
due to impurity ions by means of controlling the extension of
impurity ions. As a result, the image display device is able to
exhibit high quality images without suffering the red color
unevenness phenomenon.
[0025] These and other objectives of the present invention will no
doubt become obvious to those of ordinary skill in the art after
reading the following detailed description of the preferred
embodiment that is illustrated in the various figures and
drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0026] FIG. 1 is a top view of an array substrate of an LCD
according to Embodiment 1.
[0027] FIG. 2 is a schematic diagram of a wiring layout in an area
A shown in FIG. 1.
[0028] FIG. 3 is a cross-sectional view of the LCD of Embodiment
1.
[0029] FIG. 4 is a schematic diagram illustrating variations of
electric field magnitude of the conventional LCD.
[0030] FIG. 5 is a schematic diagram illustrating whether the red
color unevenness defect happens to LCDs having different ratios of
occupied area Sr to occupied area Sp while displaying a white
image.
[0031] FIG. 6 is a cross-sectional view of an LCD according to
Embodiment 2.
[0032] FIG. 7 is a schematic diagram illustrating whether the red
color unevenness defect happens to LCDs having different light
transmittance differences (Ir-Ip) and different resistivity ratios
while displaying a white image.
[0033] FIG. 8 is a schematic diagram illustrating areas being
heated and shielded in the display region.
[0034] FIG. 9 is a schematic diagram illustrating a relation
between the volume resistivity and time in the R pixels, G pixels,
and B pixels of a conventional LCD at a humidity of 85%.
[0035] FIG. 10 is a schematic diagram illustrating variations of
electric field magnitude of the conventional LCD.
[0036] FIG. 11 is a cross-sectional view of an LCD according to
Embodiment 3.
[0037] FIG. 12 is a schematic diagram illustrating an array
substrate of a conventional LCD with an alignment printed
region.
[0038] FIG. 13 is a schematic diagram illustrating the array
substrate shown in FIG. 12.
[0039] FIG. 14 is a schematic diagram illustrating an image display
condition of a conventional LCD.
DETAILED DESCRIPTION
[0040] Please refer to the drawings of the present invention. In
the embodiments, an IPS mode LCD is merely an example, but not a
limitation to the present invention. In the drawings, like elements
are denoted by like numerals. In addition, the drawings are
schematic diagrams, and therefore the dimensions and ratios of
components may not be identical to real ones.
Embodiment 1
[0041] In Embodiment 1, an occupied area per unit area of wirings
in the peripheral region is either approximately equivalent to or
greater than an occupied area per unit area of wirings in the
display region for adjusting the light transmittance passing
through the display region and the peripheral region. This inhibits
the movement of impurity ions that is presumed to cause the uneven
brightness defect.
[0042] FIG. 1 is a top view of an array substrate of an LCD
according to Embodiment 1. As shown in FIG. 1, an array substrate 1
includes a display region 2 composed of a plurality of pixels (not
shown) and a peripheral region 3 having a plurality of input
terminals (not shown) for receiving external electric signals. The
array substrate 1 further includes a sealant coating region 4 in
which a sealant is coated thereon. The peripheral region 3 is
positioned between the display region 2 and the sealant coating
region 4.
[0043] FIG. 2 is a schematic diagram of wirings disposed in an area
A shown in FIG. 1. As shown in FIG. 2, gate lines 5 and signal
lines 6 are arranged in a matrix, and each pixel includes a TFT 8.
Since the LCD is an ISP mode LCD, the LCD includes a plurality of
pixel electrodes (not shown) and a plurality of common electrodes 7
positioned in line with the pixel electrodes. In addition, the gate
lines 5 are extended to connect input terminals (not shown) in the
peripheral region 3. Besides, there is a plurality of dummy
patterns 9 in the peripheral region 3. The dummy patterns 9 are
used to adjust the occupied area of the wirings so that the
occupied area of the wirings per unit area in the peripheral region
3 (hereinafter referred to as Sr) is approximately equivalent to or
greater than the occupied area of the wirings per unit area in the
display region 2 (hereinafter referred to as Sp). The wirings
include not only the gate lines 5, the signal lines 6, the common
electrodes 7, and the pixel electrodes, but also the TFTs 8,
passive elements (e.g. capacitors), and the dummy patterns 9. The
function of the dummy patterns 9 is to adjust the occupied areas Sr
and Sp, thus the dummy patterns 9 are light shielding, and the line
width of the dummy patterns 9 is not necessarily identical to other
wirings disposed in the peripheral region 3.
[0044] FIG. 3 is a cross-sectional view of the LCD of Embodiment 1.
As shown in FIG. 3, an array substrate 1 and a CF (color filter)
substrate 11 are bonded together with a sealant 12. A liquid
crystal layer 16 including liquid crystal molecules is filled
between the array substrate 1 and the CF substrate 11. The CF
substrate 11 includes a BM (black matrix) layer 13, a color filter
layer 14 including a plurality of color filters having different
transmissivities, and a passivation layer 15. The LCD further
includes two alignment films 17 respectively positioned on the
surface of the array substrate 1 and the surface of the CF
substrate 11 in contact with the liquid crystal molecules, so as to
orientate the liquid crystal molecules. The array substrate 1
includes a plurality of common electrodes 7, signal lines 6, and
pixel electrodes 10 in the display region 2. By applying a voltage
to the common electrode 7 and the pixel electrode 10, an electric
field parallel to the array substrate 1 is generated between the
common electrodes 7 and the pixel electrodes 10. Consequently, the
liquid crystal molecules of the liquid crystal layer 16 rotate. In
addition, the array substrate 1 further includes gate lines 5 and
dummy patterns 9 in the peripheral region 3.
[0045] Generally, the light coming from a light source of a
backlight unit (not shown) evenly enters the liquid crystal layer
16 through the array substrate 1. With the dummy patterns 9, that
make the occupied area S.sub.f approximately equivalent to or
larger than the occupied area S.sub.p, disposed in the peripheral
region 3, a light transmittance per unit area in the peripheral
region 3 (hereinafter referred to as I.sub.f) is equivalent to or
less than a light transmittance per unit area in the display region
2 (hereinafter referred to as I.sub.p). By making I.sub.f equal to
or smaller than I.sub.p, the uneven brightness defect due to the
movement of impurity ions towards the display region 2 is
inhibited. The reason for the reduction of the uneven brightness
defect is detailed in the following.
[0046] The red color unevenness defect is inferred to be from
impurity ions while the LCD is operating. Specifically, the
emission of the impurity ions from the peripheral region to the
liquid crystal layer is driven by backlight unit illumination. The
higher the light transmittance is, the more impurity ions enter the
liquid crystal layer. The accumulation of the impurity ions in the
display region leads to the red color unevenness defect.
[0047] Therefore, upon close inspection of the cause of the red
color unevenness defect, an experimental result is obtained. Please
refer to Table 1. Table 1 shows an experimental result of a
conventional LCD in sequence from 1 to 3 after applying a voltage
to each wiring or/and lighting up the light source to examine if
the red color unevenness defect appears in the display region when
displaying a white image. It is important to note that the
conventional LCD does not include dummy patterns in the peripheral
region, and therefore the occupied area Sr is smaller than the
occupied area Sp. In addition, all results are from experiments at
50 degrees Celsius for 100 hours. In Experiment 1, each wiring is
applied with a voltage, and the light source is off. Subsequently,
the voltage applied to the wirings is ceased, and the light source
is on for Experiment 2. Following that, a voltage is applied to
each wiring again, and the backlight is off for Experiment 3.
TABLE-US-00001 TABLE 1 Red color Experiments Voltage Light source
unevenness defect 1 On Off No 2 Off On No 3 On Off Yes
[0048] As shown in Table 1, the red color unevenness defect while
displaying a white image does not appear in Experiment 1. In
Experiment 1, a voltage is applied to the wirings for generating an
electric filed, and the light source is off. Presumably the
electric filed is not the cause of the red color unevenness defect.
The red color unevenness defect while displaying a white image also
does not appear in Experiment 2. In Experiment 2, the light source,
which is inferred to cause the emission of impurity ions, is on,
however, the red color unevenness does not appear. The explanation
for this experimental result is that the amount of impurity ions
may not cause the red color unevenness defect in the display
region.
[0049] On the other hand, the red color unevenness defect does
appear while displaying a white image in Experiment 3. Thus, the
presence of the red color unevenness defectis inferred to be caused
by the movement of impurity ions induced in Experiment 2 into the
display region under the effect of the electric filed. In the
conventional LCD, the occupied area Sr is less than the occupied
area Sp, meaning the light transmittance Ir is greater than the
light transmittance Ip. Therefore, In Experiment 2, the majority of
the impurity ions due to the backlight exist in the peripheral
region. In Experiment 3, the electric filed drives the impurity
ions to move into the display region. FIG. 4 is a schematic diagram
illustrating variations of electric field magnitude of the
conventional LCD. As shown in FIG. 4, impurity ions emitted from a
peripheral region 3a slowly move to a display region 2a, and
accumulate on the surface of the CF substrate 11 facing the array
substrate 1. These accumulated impurity ions result in electric
deflections, and disturb the electric filed while displaying an
image. For instance, if the electric filed has a desired magnitude
of A1 as shown in FIG. 4, the accumulated impurity ions disturb the
electric field, making the electric field have an actual magnitude
of A2. The disorder of the electric field further deranges the
alignment of the liquid crystal molecules of the liquid crystal
layer 16. Consequently, the brightness is partially reduced, and
the red color unevenness defect therefore appears when displaying a
white image.
[0050] In Embodiment 1, the occupied area S.sub.f is either
equivalent to or greater than the occupied area S.sub.p. In the
case that the occupied area S.sub.f is equivalent to the occupied
area S.sub.p, the light transmittance I.sub.f is approximately
equivalent to the light transmittance I.sub.p. Namely, the emitted
impurity ions are about equal in the display region 2 and in the
peripheral region 3. Therefore, the distributions of impurity ions
in the display region 2 and the peripheral region 3 are
approximately equal. In other words, few impurity ions travel from
the peripheral region 3 towards the display region 2, and thus
electric deflections do not occur. In addition, in the case that
the occupied area S.sub.f is greater than the occupied area
S.sub.p, the light transmittance Iris less than the light
transmittance I.sub.p. This means the emitted impurity ions in the
peripheral region 3 are even fewer than in the display region 2. In
that case, the impurity ions in the peripheral region 3 do not move
towards the display region 2 even when a voltage is applied to each
wiring. Consequently, the electric deflections do not show up.
[0051] In Embodiment 1, the variations of the electric field never
happens even though a voltage is applied to the common electrodes 7
and the pixel electrodes 10 and the light source is turned on. As a
result, high-quality display images without the occurrence of the
red color unevenness defect is realized when displaying a white
image.
[0052] FIG. 5 is a schematic diagram illustrating whether the red
color unevenness defect happens to LCDs having different ratios of
occupied area S.sub.f to occupied area S.sub.p while displaying a
white image. In FIG. 5, the longitudinal axis represents a product
of light transmittance and pixel numbers per inch. The higher the
product is, the higher the difference between the occupied area
S.sub.p and the occupied area S.sub.f is. Samples a to g are ranked
by the ratio of the occupied area S.sub.f to the occupied area
S.sub.p, in which samples a and b have an occupied area S.sub.f
less than an occupied area S.sub.p, and samples c, d, e, f, and g
have an occupied area S.sub.f equivalent to or greater than an
occupied area S.sub.p.
[0053] As shown in FIG. 5, the red color unevenness defect occurs
when displaying a white image in samples a and b having occupied
area S.sub.f less than occupied area S.sub.p. On the other hand,
the red color unevenness defect does not occur when displaying a
white image in samples c, d, e, f, and g having occupied area
S.sub.f equivalent to or greater than occupied area S.sub.p. This
result is consistent with the assumption recited earlier. For cases
in which the occupied area S.sub.f is equivalent to or greater than
the occupied area S.sub.p, the distributions of impurity ions in
the display region 2 and the peripheral region 3 are approximately
equal, and few impurity ions travel from the peripheral region 3
towards the display region 2. Thus, the electric deflections, which
incur the red color unevenness defect, do not occur.
[0054] Accordingly, Embodiment 1 modifies the light transmittance
I.sub.f to be approximately equal to or less than the light
transmittance I.sub.p by virtue of adjusting the occupied area
S.sub.f approximately to be equal to or greater than the occupied
area S.sub.p. Consequently, the amount of the impurity ions
traveling from the peripheral region 3 to the display region 2 due
to light irradiation is inhibited. In this case, the red color
unevenness defect when displaying a white image, and the uneven
brightness problem are both reduced. This enables the LCD according
to Embodiment 1 to display high-quality images.
[0055] According to Embodiment 1, the dummy patterns 9 are
positioned in the peripheral region 3 so that the occupied area
S.sub.f is equal to or greater than the occupied area S.sub.p.
However, the present invention is not limited to Embodiment 1, and
the occupied area S.sub.f can also be modified by enlarging the
line width of the gate lines 5 or the signal lines 6 in the
peripheral region 3. In this case, the light transmittance Iris
also equivalent to or less than the light transmittance I.sub.p, so
as to inhibit impurity ions from moving from the peripheral region
3 to the display region 2. Accordingly, the red color unevenness
defect when displaying a white image is reduced.
Embodiment 2
[0056] In Embodiment 1, the movement of the impurity ions from the
peripheral region towards the display region is prohibited by
virtue of adjusting the occupied area S.sub.f in the peripheral
region and the occupied area S.sub.p in the display region. In
Embodiment 2, on the other hand, a resistivity ratio of the color
filter layer is modified to prevent the impurity ions in the
display region from partially deviating, so that the red color
unevenness defect is reduced.
[0057] FIG. 6 is a cross-sectional view of an LCD according to
Embodiment 2. As shown in FIG. 6, dummy patterns are not provided
in the peripheral region 3. Therefore, the light transmittance Ir
in the peripheral region 3 is greater than the light transmittance
I.sub.p in the display region 2. In addition, the color filter
layer includes a plurality of R (red) color filters 24r having a
resistivity r, G (green) color filters 24g having a resistivity g,
and B (blue) color filters 24b having a resistivity b. In
Embodiment 2, a resistivity ratio of the lowest resistivity color
filter to the highest resistivity color filter (hereinafter
referred to as resistivity ratio) is set in view of the difference
of the light transmittance Ip and the light transmittance Ir as
shown in the following equation (1):
p max p min<10.sup.(4100/(If-Ip)+0.05) (1)
wherein p max is the highest resistivity having units of .OMEGA.
cm;
[0058] p min is the lowest resistivity having units of .OMEGA.
cm;
[0059] FIG. 7 is a schematic diagram illustrating whether the red
color unevenness defect happens to LCDs having different light
transmittance differences (I.sub.f-I.sub.p) and different
resistivity ratios while displaying a white image. In FIG. 7,
sample groups h to l represent LCDs having different light
transmittance differences (I.sub.r-I.sub.p) and different
resistivity ratios. As shown in FIG. 7, with regard to sample group
h, the difference between I.sub.f and I.sub.p is negative, and the
red color unevenness defect does not occur when displaying a white
image. This supports the conclusion of Embodiment 1 that the
movement of impurity ions from the peripheral region to the display
region is inhibited when the light transmittance I.sub.f is less
than the light transmittance I.sub.p.
[0060] As for sample groups i, j, k, and l, each of these has a
positive light transmittance difference. In addition, curve 1a is a
boundary: the red color unevenness defect occurs over curve 1a, and
it does not occur under curve 1a. In conclusion, to inhibit the red
color unevenness defect, the relation between the light
transmittance difference and the resistivity ratio has to fulfill
equation (1).
[0061] In practice, sometimes the resistivity ratio of the color
filter layer is higher if different materials are adopted. For a
higher resistivity ratio, the light transmittance difference must
be set in accordance with equation (1), so as to inhibit the red
color unevenness defect. Therefore, Table 2 illustrates the
occupied area difference (S.sub.f-S.sub.p) and the light
transmittance difference (I.sub.f-I.sub.p) of sample groups h, i,
j, k, and l.
TABLE-US-00002 TABLE 2 Light transmittance difference Occupied area
difference [cd/m.sup.2] Sample group h -0.17 -930 -0.13 -730 Sample
group i 0.09 730 0.12 800 0.14 950 Sample group j 0.32 2300 Sample
group k 0.39 3500 Sample group l 0.46 3800
[0062] Accordingly, the occupied area difference and the light
transmittance difference are roughly proportional. Therefore, for a
known resistivity ratio, the occupied area difference, which
represents the light transmittance difference, can be modified to
meet equation (1), so as to reduce the red color unevenness defect.
In addition, even though the light transmittance difference is
inevitably higher due to circuit design requirements, the red color
unevenness defect when displaying a white image still can be
reduced by selecting different materials for the color filter
layer.
[0063] The relation between the resistivity ratio, the light
transmittance difference, and the occurrence of the red color
unevenness defect is detailed in the following. For ensuring
variations of brightness in each pixel, which is assumed to be the
cause of the red color unevenness defect, the display region of a
conventional LCD is first heated and shielded in predetermined
areas. FIG. 8 is a schematic diagram illustrating areas heated and
shielded from light in the display region 2. In FIG. 8, an area A
is heated to a temperature ranging from 55 to 75 degrees Celsius,
and the area outside the area A is maintained at a temperature
ranging from 25 to 35 degrees Celsius. In addition, an area B is a
light-shielded area. Therefore, an area C where the area A and the
area B overlap is heated and light-shielded. Subsequently, the
brightness in the area A and the area C of R pixels, G pixels, and
B pixels are measured. In the G pixels, a brightness reduction is
observed. Table 3 shows the brightness Y G of the area A and the
area C in the G pixels.
TABLE-US-00003 TABLE 3 Brightness Y.sub.G Area Light-shielded
Heated [cd/m.sup.2] A No Yes 133 C Yes Yes 150
[0064] As shown in Table 3, compared to the area C that is heated
and light-shielded, a brightness Y G reduction in the area A is
observed. This result shows that the impurity ions caused by the
backlight particularly accumulate in the G pixels, rather than in
the R pixels and the B pixels. As a result, the brightness Y G in
the G pixels is reduced, causing the red color unevenness defect
while displaying a white image.
[0065] Therefore, to determine the differences between the R
pixels, B pixels, and G pixels, volume resistivities of the R
pixels, G pixels, and B pixels can be measured to reveal a
significant difference. FIG. 9 is a schematic diagram illustrating
a relation between the volume resistivity and time in the R pixels,
G pixels, and B pixels of a conventional LCD at a humidity of 85%.
Volume resistivity is the resistivity divided by the thickness of
the color filter layer in cm. Curves I.sub.R and I.sub.R'
illustrate the variations of an R color filter with time. Curves
I.sub.G and I.sub.G' illustrate the variations of a G color filter
with time. Curves I.sub.B and I.sub.B' illustrate the variations of
a B color filter with time. Curves I.sub.R, I.sub.G, and I.sub.B
are measured at 70 degrees Celsius, and curves I.sub.R', I.sub.G',
and I.sub.B' are measured at 50 degrees Celsius. As illustrated by
curves I.sub.G and I.sub.G', the G color filter is irrelevant to
the atmosphere. In addition, compared to the R color filter and the
B color filter, the volume resistivity of the G color filter is one
tenth that of the R color filter or the B color filter. Since the
thickness of each color filter is about equal, and so is the area
of each pixel, the resistivity of the G color filter, compared to
that of the R color filter and the B color filter, is dramatically
reduced.
[0066] As shown in FIG. 9, due to the accumulation of impurity
ions, the resistivity of the G color filter, compared to that of
the R color filter and the B color filter, is reduced greatly.
Therefore, it is assumed that the accumulated impurity ions are
relevant to the resistivity of the pixel having the accumulated
impurity ions therein. Specifically, the impurity ions tend to
accumulate in pixels with low resistivity. FIG. 10 is a schematic
diagram illustrating variations of electric field magnitude of the
conventional LCD.
[0067] As shown in FIG. 10, in the conventional LCD, the light
transmittance I.sub.f is greater than the light transmittance
I.sub.p, and impurity ions generated in the peripheral region tend
to move to the display region of the G color filter, which has a
low resistivity 204g, instead of the R color filter having a higher
resistivity 204r or the B color filter having a higher resistivity
204b. In that case, when a voltage is applied to each wiring for
generating an electric field, the electric field in a B pixel has a
magnitude A.sub.3, while the electric field in a G pixel has an
actual magnitude A.sub.4 under the influence of the impurity ions.
Impurity ions lead to disorder in the liquid crystal molecules,
thereby causing brightness reduction and the red color unevenness
defect. Based on the above assumption, the accumulation of impurity
ions can be reduced by diminishing the resistivity ratio of the
color filters.
[0068] In Embodiment 2, the light transmittance difference and the
resistivity ratio have the relation as expressed in equation (1).
Therefore, to prevent the accumulation of impurity ions in the
display region 2, reducing the resistivity ratio is a useful
approach. Accordingly, the local brightness reduction problem is
improved, and so is the red color unevenness defect. In addition,
if the resistivity ratio is inevitably high due to the material
characteristics of the color filters, adjusting the occupied area
difference of the wirings to meet equation (1) is another approach
to reduce the red color unevenness defect. In conclusion,
high-quality images without the red color unevenness defect can be
obtained by adjusting the resistivity ratio and the occupied area
difference according to Embodiment 2.
[0069] Furthermore, the relation between the resistivity ratio and
the light transmittance difference is defined by equation (1) in
Embodiment 2, but the present invention is not limited by equation
(1) if different materials are adopted for making the LCD. The
essence of the present invention is to reduce the red color
unevenness defect while displaying a white image either by
adjusting the resistivity ratio according to the light
transmittance difference, or adjusting the light transmittance
difference according to the resistivity ratio.
Embodiment 3
[0070] In both Embodiment 1 and Embodiment 2, the red color
unevenness defect is reduced by inhibiting the move and the
accumulation of the impurity ions. In Embodiment 3, on the other
hand, the red color unevenness defect is reduced by reducing
emissions of the impurity ions.
[0071] FIG. 11 is a cross-sectional view of an LCD according to
Embodiment 3. As shown in FIG. 11, alignment films 37a and 37b are
only formed in a display region 2, rather than in a peripheral
region 3. FIG. 12 is a schematic diagram illustrating an array
substrate 1 of a conventional LCD with an alignment printed region
38a. As shown in FIG. 12, an alignment film (not shown) is printed
within the alignment film printed region 38a, which covers the
display region 2 and the peripheral region 3, on an array substrate
1. Red color unevenness defects 39a to 39d occur around the display
region 2. FIG. 13 is a schematic diagram illustrating the array
substrate 1 shown in FIG. 12. As shown in FIG. 13, the alignment
film printed region 38a is shifted leftward, forming a new
alignment film printed region 38b. In addition, a CF substrate (not
shown) also includes a corresponding alignment film printed region
(not shown). It can seen in FIG. 13 that the red color unevenness
defects 39b, 39c, and 39d occur in the upper, lower, and left
sides, but not in the right side of the display region 2.
Therefore, the alignment film is construed as a cause of the
emission of impurity ions.
[0072] The alignment films 37a and 37b, which are assumed to be the
cause of the emission of impurity ions, are only formed in the
display region 2 in Embodiment 3, so as to inhibit the emission of
impurity ions. This is different from Embodiment 1 and Embodiment 2
in which the impurity ions are inhibited from moving from the
peripheral region 3 towards the display region 2. Therefore, the
LCD has a reduction in the uneven brightness problem and the red
color unevenness defect.
[0073] In summary, the LCDs of Embodiment 1, Embodiment 2, and
Embodiment 3 of the present invention inhibit the movement,
accumulation, or generation of impurity ions, and thus reduce the
red color unevenness defect due to the brightness reduction in
green pixels being prevented. Furthermore, the brightness reduction
in red pixels and blue pixels can also be avoided. Consequently,
high-quality images without uneven brightness can be achieved.
[0074] Those skilled in the art will readily observe that numerous
modifications and alterations of the device and method may be made
while retaining the teachings of the invention. Accordingly, the
above disclosure should be construed as limited only by the metes
and bounds of the appended claims.
* * * * *