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| United States Patent |
6,226,062
|
|
Gu
, et al.
|
May 1, 2001
|
Liquid crystal display with microlenses
Abstract
A liquid crystal display with a high transmittance and a low power
consumption rate, includes first and second transmittable substrates, a
plurality of gate and data bus lines formed on the first substrate, a
plurality of color filters formed on the second substrate, and a plurality
of microlenses formed on the first or second substrate corresponding to
the gate and data bus lines. The microlenses are formed at positions
corresponding to the gate and data bus lines which block incident lights,
so that most incident lights can be transmitted. Further, the
transmittance can be greatly improved by forming the microlenses at the
positions corresponding to storage capacitor lines as well as the gate and
data bus lines.
| Inventors:
|
Gu; Dong-Hyo (Kyunggi-do, KR);
Shin; Min-Cheol (Incheon-shi, KR)
|
| Assignee:
|
LG Electronics Inc. (Seoul, KR)
|
| Appl. No.:
|
889732 |
| Filed:
|
July 8, 1997 |
Foreign Application Priority Data
| Intern'l Class: |
G02F 001/133.5 |
| Field of Search: |
349/38,39,42,43,95,110,122,106
345/32,88
359/619,621,622
|
References Cited
U.S. Patent Documents
| 5101279 | Mar., 1992 | Kurematsu et al. | 349/95.
|
| 5187599 | Feb., 1993 | Nakanishi et al. | 349/95.
|
| 5693967 | Dec., 1997 | Park et al.
| |
| 5764318 | Jun., 1998 | Kuramatsu et al. | 349/95.
|
| 5811322 | Sep., 1998 | Robinson | 438/92.
|
| 5877040 | Mar., 1999 | Park et al. | 438/70.
|
| Foreign Patent Documents |
| 0366462A2 | May., 1990 | EP.
| |
| 0425266A3 | May., 1991 | EP.
| |
| 0425266A2 | May., 1991 | EP.
| |
| 0718665A2 | Dec., 1995 | EP.
| |
| 61-11788 | Jan., 1986 | JP.
| |
Other References
Japanese Abstract #JP-60262131A, Publication date: Dec. 25, 1985.
|
Primary Examiner: Parker; Kenneth
Assistant Examiner: Duong; Tai V.
Claims
What is claimed is:
1. A liquid crystal display comprising:
first and second transparent substrates;
a plurality of gate and data bus lines formed on the first substrate;
a color filter layer formed on the second transparent substrate; and
a plurality of microlenses formed on at least one of the first and second
transparent substrate at positions corresponding to the gate and data bus
lines.
2. The liquid crystal display according to claim 1, further comprising:
a black matrix formed on the gate and data bus lines.
3. The liquid crystal display according to claim 1, further comprising:
a light source located behind said at least one of the first and second
transparent substrates on which the microlenses are formed.
4. The liquid crystal display according to claim 1, wherein the microlenses
are formed on the color filter layer.
5. The liquid crystal display according to claim 2, wherein the microlenses
are formed on an inner surface of the second transparent substrate.
6. The liquid crystal display according to claim 5, further comprising:
an overcoat layer formed on the microlenses, the color filter layer being
formed on the overcoat layer.
7. The liquid crystal display according to claim 2, wherein the microlenses
are formed on an outer surface of the second transparent substrate.
8. The liquid crystal display according to claim 7, further comprising:
an overcoat layer formed on the microlenses.
9. The liquid crystal display according to claim 1, further comprising:
an overcoat layer formed on an outer surface of the second transparent
substrate,
wherein the microlenses are formed by etching an outer surface of the
overcoat layer.
10. The liquid crystal display according to claim 9, wherein spaces formed
by etching the outer surface of the overcoat layer are filled with at
least one of acrylic resin and benzocyclobutene.
11. The liquid crystal display according to claim 2, wherein the
microlenses are formed on an inner surface of the first transparent
substrate and are convex toward the gate and data bus lines.
12. The liquid crystal display according to claim 11, further comprising:
an overcoat layer formed on the microlenses.
13. The liquid crystal display according to claim 2, wherein the
microlenses are formed on an outer surface of the first transparent
substrate.
14. The liquid crystal display according to claim 13, further comprising:
an overcoat layer formed on the microlenses.
15. The liquid crystal display according to claim 1, further comprising:
an overcoat layer formed on an outer surface of the first transparent
substrate,
wherein the microlenses are formed by etching an outer surface of the
overcoat layer.
16. The liquid crystal display according to claim 15, wherein spaces formed
by etching the outer surface of the overcoat layer are filled with at
least one of acrylic resin and benzocyclobutene.
17. The liquid crystal display according to claim 1, wherein the color
filter layer includes a plurality of color filters, and the liquid crystal
display includes:
a black matrix formed between the color filters so that the black matrix
corresponds to the gate and data bus lines.
18. The liquid crystal display according to claim 17, wherein the
microlenses are formed by etching an outer surface of the second
transparent substrate.
19. The liquid crystal display according to claim 18, wherein spaces formed
by etching the outer surface of the second transparent substrate are
filled with acrylic resin.
20. The liquid crystal display according to claim 17, wherein the
microlenses are formed by etching the outer surface of the first
transparent substrate.
21. The liquid crystal display according to claim 20, wherein spaces formed
by etching the outer surface of the first transparent substrate are filled
with acrylic resin.
22. The liquid crystal display according to claim 1, further comprising:
a passivation layer formed between pixel electrodes and the gate and data
bus lines.
23. The liquid crystal display according to claim 22, wherein th e
passivation layer includes benzocyclobutene.
24. The liquid crystal display according to claim 23, further comprising:
a black matrix formed only on th e gate bus lines.
25. The liquid crystal display according to claim 1, wherein each of the
microlenses has a width of approximately 4-30 .mu.m and a height of
approximately greater than 0.5 .mu.m.
26. The liquid crystal display according to claim 1, wherein a border
between two of the microlenses is substantially aligned with a center of a
corresponding one of the gate and data bus lines.
27. The liquid crystal display according to claim 1, wherein the color
filter layer includes a plurality of color filters, and the microlenses
cover correspondingly the color filters.
28. The liquid crystal display according to claim 1, wherein the color
filter layer includes a plurality of color filters, and each of the
microlenses covers at least an area corresponding to each of the color
filters and includes a curved end portion and a substantially flat body
portion.
29. The liquid crystal display according to claim 1, wherein the
microlenses are made of organic materials.
30. The liquid crystal display according to claim 1, further comprising:
an overcoat layer made of at least one of acrylic resin and
benzocyclobutene, formed on the microlenses.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a transmissive-type display
device ("transmissive display device"). More particularly, the present
invention relates to a dot matrix type display device having a display
panel and multiple picture elements ("pixels") arranged in a matrix to
form a liquid crystal display ("LCD"), wherein the display panel is
provided with an array of microlenses.
2. Description of the Related Art
In general, LCDs are comprised of upper and lower substrates facing each
other as shown in FIG. 1. The lower substrate includes a plurality of
pixel electrodes 13 formed on a transparent glass substrate 10. Data bus
lines 12 are formed parallel to each other in a horizontal direction, and
gate bus lines 11 are formed parallel to each other in a vertical
direction. Between the data bus lines 12 and the gate bus lines 11, an
array of the pixel electrodes 13 are formed.
On the transparent substrate 10, switching elements such as thin film
transistors 15 ("TFTs") are disposed for the respective pixels at each
crossing area where the gate bus lines 11 and the data bus lines 12 cross
each other. The pixel electrodes 13 are electrically connected to the
output electrodes (e.g., drains) of the TFTs 15.
On the other hand, the upper substrate includes a color filter layer 21
formed on a transparent glass substrate 20 and common electrodes 22 formed
on the color filter layer 21. As shown in FIG. 2, the color filter layer
21 includes a red color filter 21R, a green color filter 21G, and a blue
color filter 21B successively formed on the substrate 20. Among the
different arrangements of color filters, the mosaic-array is employed in
an audio video (AV) mode and the striped array is used in an office
automation (OA) mode.
Once the upper and lower substrates are individually formed, it is
necessary to join them for injecting liquid crystal 24 therebetween. The
upper substrate and the lower substrate may be joined so that the color
filter layer 21 faces the pixel electrodes 13 formed on the transparent
glass substrate 10.
Additionally, a black matrix 14 is formed over the gate bus lines 11 and
the data bus lines 12 corresponding to the border of the each color filter
21R, 21G and 21B. The black matrix 14 shields light which may have leaked
from the gaps formed between the bus lines and the pixel electrodes 13,
and improves the contrast of the LCD by making the borders of the color
filters more clear.
Generally, the size of the black matrix 14 is larger than that of each bus
line because of the misalignment arising from joining the upper substrate
with the lower substrate. The gate bus lines 11 and the data bus lines 12
are approximately 15 .mu.m-40 .mu.m and 10 .mu.m-25 .mu.m wide,
respectively. Therefore, the black matrix 14 is slightly wider than the
bus lines.
In the conventional LCDs having the above described elements, a light
source is located at the backside of the transparent glass substrate 20.
The black matrix 14 is formed on the transparent glass substrate 10 to
cover the gate bus lines 11 and data bus lines 12. The light from the
light source, as depicted with a straight line in FIG. 2, is transmitted
through the transparent glass substrate 20, the color filters 21R, 21G and
21B, the common electrodes 22 and the liquid crystal 24, sequentially.
This light passes through the portion of transparent glass substrate 10
having the pixel electrodes 13 thereon. But, the light impinging on the
gate and data bus lines 11 and 12 are blocked by the black matrix 14. As a
result, the aperture ratio of the LCD and the brightness of the device is
reduced.
The aperture ratio is expressed by "the effective area of all the pixels"
divided by "the total display area". The aperture ratio equals the ratio
of the recoverable light to all incident light (recoverable and
unrecoverable light). (The unrecoverable light is the light blocked by the
untransmissive portion of the display panel, and does not contribute to
displaying.) As the size of the untransmissive portion increases, the
aperture ratio decreases. The reduced aperture ratio leads to reproduction
of dark pictures and poor image quality.
The LCDs may include a storage capacitor for assisting the cell capacitance
of the LCDs. There are two types of storage capacitors. One is a
storage-on-common type in which the storage capacitor is formed
separately. The other is a storage-on-gate type in which a portion of gate
line functions as a storage capacitor electrode. The former has a smaller
effective area for forming the pixels than the latter. Therefore, the
aperture ratio of such LCDs and the brightness of the display device is
reduced.
In order to refine pictures on the display, the brightness of the backlight
must be increased and the size of the untransmissive portion must be
minimized. To increase the brightness of the backlight, more electricity
(power) is required; however, such is undesirable because it is costly.
Many different methods have been developed to improve the aperture ratio of
the LCDs, e.g., enlarging the area of pixel electrodes or enlarging the
pixel size. To enlarge the pixel size, however, the other elements of the
LCD such as gate bus lines, source bus lines, TFTs and so on, need to be
minimized. But, photo-lithography and etching has a limit on minimizing
these elements. Further, the width of bus lines cannot be reduced below a
certain level. Therefore, it is difficult to manufacture LCDs with an
improved aperture ratio. But, even if the pixel size were increased by the
above methods, the aperture ratio is generally 40% or 50% at best.
To solve the problems described above, an LCD with a different structure
has been proposed in which the display panel with an array of microlenses
are formed on one side or both sides of the panel. Such a structure is
disclosed in Japanese Laid-Open Patent Publications No. 60-262131 and No.
61-11788. Referring to FIG. 3, one of the advantages of such known display
devices is that the light rays incident onto the portion of display panel
which does not contribute to displaying, are focused on the pixel
electrodes using elements 31 and pass through elements 32. As a result,
the transmittance of the LCD having the same aperture ratio is increased.
Another proposal for further enhancing the above mentioned device is
disclosed in U.S. Pat. No. 5,187,599. Referring to FIG. 4, such a display
device comprises a first array of microlenses 31' disposed on the incident
side of the display panel, and a second array of microlenses 32' disposed
on the incident side of the other display panel, each microlens being
disposed according to the respective pixels. The focal points of the first
array of microlenses are identical with those of the second array of
microlenses, and the focal length of each microlens in the first array is
greater than that of the second array. Therefore, the light rays incident
on the untransmissive portion of the display panel is redirected by
condensing the diverging rays.
The above suggested structure of the LCD are. to increase the transmittance
of the light and to acquire the effect of having an increased aperture
ratio, without actually increasing the aperture ratio. Each microlens
covers the entire pixel electrode. The height of the microlenses need to
be greater than 50 .mu.m to cover the dimension of each pixel electrode
having generally 100 .mu.m.times.300 .mu.m. However, in practice, it is
difficult to form the LCD having microlenses greater than 50 .mu.m in
height, resulting relatively flat lenses. Accordingly, the transmittance
of conventional LCDs cannot be effectively improved.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an LCD which has an
improved transmittance.
Another object of the present invention is to provide a brighter LCD with
low power consumption.
Still another object of the present invention is to provide an LCD which
has an improved contrast ratio.
Still another object of the present invention is to provide an LCD which
overcomes the disadvantages and problems encountered in the conventional
LCDs.
In order to achieve the above and other objects, an LCD according to the
present includes multi-microlenses corresponding to the border of the
untransmissive portions of the LCD. More particularly, the LCD according
to the embodied invention includes first and second transparent substrates
facing each other, a plurality of gate and data bus lines formed on the
first substrate, a plurality of color filters formed on the second
substrate, and a plurality of microlenses formed corresponding to the gate
and data bus lines. In case that storage capacitor lines including storage
capacitors are formed on the first substrate for storage capacitance, it
is desirable to have a plurality of microlenses at the position
corresponding to the storage capacitor lines in order to improve the
transmittance.
These and other objects of the present application will become more readily
apparent from the detailed description given hereinafter. However, it
should be understood that the detailed description and specific examples,
while indicating preferred embodiments of the invention, are given by way
of illustration only, since various changes and modifications within the
spirit and scope of the invention will become apparent to those skilled in
the art from this detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed
description given hereinbelow and the accompanying drawings which are
given by way of illustration only, and thus are not limitative of the
present invention and wherein:
FIG. 1 is a three-dimensional view showing a structure of a conventional
LCD;
FIG. 2 is a partial, cross-sectional view showing a light path in the
conventional LCD of FIG. 1;
FIG. 3 is a cross-sectional view showing a light path in a conventional
LCD;
FIG. 4 is a cross-sectional view showing a light path in another
conventional LCD.
FIGS. 5A-5B, 6A-6B, and 7A-7B are cross-sectional views showing examples of
different configurations and shapes of microlenses for an LCD according to
the embodiments of the present invention;
FIG. 8 is a cross-sectional view of an LCD according to a first example of
a first embodiment of the present invention;
FIG. 9 is a cross-sectional view of an LCD according to a second example of
the first embodiment of the present invention.
FIG. 10 is a cross-sectional view of an LCD according to a third example of
the first embodiment of the present invention;
FIG. 11 is a cross-sectional view of an LCD according to a fourth example
of the first embodiment of the present invention;
FIG. 12 is a cross-sectional view of an LCD according to a first example of
a second embodiment of the present invention.
FIG. 13 is a cross-sectional view of an LCD according to a second example
of the second embodiment of the present invention;
FIG. 14 is a cross-sectional view of an LCD according to a third example of
the second embodiment of the present invention;
FIG. 15 is a cross-sectional view of an LCD according to a first example of
a third embodiment of the present invention;
FIG. 16 is a cross-sectional view of an LCD according to a second example
of the third embodiment of the present invention; and
FIG. 17 is a cross-sectional view of an LCD according to an example of a
fourth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The LCDs according to the preferred embodiments of the present invention
will be described with reference to FIGS. 5 through 17. The LCD according
to the first through fourth embodiments of the present invention includes
a plurality of microlenses for effectively redirecting light from a light
source all onto the pixel electrodes of the LCD, with simplicity.
Generally, a path of light is depicted in the Figures by a line with
arrow.
FIGS. 8-11 show cross-sectional views of examples of an LCD according to
the first embodiment of the present invention.
As shown in FIG. 8, the first example of the LCD according to the first
embodiment of the present invention includes a plurality of microlenses
131 formed on a color filter layer 121 containing color filters 121R, 121G
and 121B. The color filter layer 121 is formed on a second transparent
glass substrate 120. The microlenses 131 are covered with an overcoat
material, such as acrylic resin to form an overcoat layer 132. Common
electrodes 122 are formed on the overcoat layer 132 and constitute a
transparent conductive layer made of ITO. Pixel electrodes 113 are formed
on a first transparent glass substrate 110, and a black matrix 114 is
formed to cover gaps between the pixel electrodes 113 and data bus lines
112 and gaps between the pixel electrodes 113 and gate bus lines.
As shown in FIG. 9, the second example of the LCD according to the first
embodiment of the present invention includes a plurality of microlenses
231 formed directly on a second glass substrate 220 and covered with an
overcoat layer 232 made of acrylic resin. A color filter layer 221 having
red, blue, and green filters 221R, 221B, 221G is then formed on the
overcoat layer 232. On the color filter layer 221, common electrodes 222
are formed. Other elements, such as the data bus lines 112, pixel
electrodes 113, black matrix 114 and gate bus lines are formed on the
first substrate 110 in a manner similar to the LCD of FIG. 8.
As shown in FIG. 10, the third example of the LCD according to the first
embodiment of the present invention includes a plurality of microlenses
331 formed on the outer surface of a second transparent glass substrate
320. The microlenses 331 are covered with an overcoat layer 332 made of
acrylic resin. On the inner surface of the second substrate 320, a color
filter layer 321 having red, blue, and green filters 321R, 321B, 321G is
formed. Then on the color filter layer 321, common electrodes 322 are
formed. Other elements, such as the data bus lines 112, pixel electrodes
113, black matrix 114 and gate bus lines are formed on the first substrate
110, in a manner similar to the LCDs of FIG. 8 and 9.
As shown in FIG. 11, the fourth example of the LCD according to the first
embodiment of the present invention includes a plurality of microlenses
431 formed by selectively etching the outer surface portion of an overcoat
layer 432 formed on a second transparent glass substrate 420. The spaces
formed by etching the overcoat layer 432 are filled with a material
different from the material constituting the overcoat layer 432 in
refraction index. For example, the overcoat layer 432 may be formed of
acrylic resin and the microlenses 431 may be formed of an organic
material, such as benzocyclobutene ("BCB"). Similarly the overcoat layer
432 may be formed of BCB and the microlenses 431 may be formed of acrylic
resin.
On the inner surface of the second substrate 420, a color filter layer 421
having red, blue and green filters 421R, 421B, 421G is formed. Then on the
color filter layer 421, common electrodes 422 are formed. Other elements,
such as the data bus lines 112, pixel electrodes 113, black matrix 114 and
gate bus lines are formed on the first substrate 110, in a manner similar
to the LCDs of FIG. 8, 9 and 10.
The microlenses 131, 231, 331 and 431 are preferred to be about 6 .mu.m in
width and about 3 .mu.m in height, in view of the distance between the
color filter layer and data bus lines 112 (or gate bus lines), and in view
of the width of each bus line and the refraction index of the microlenses.
According to the first embodiment, the light from the backlight, which is
shielded by the bus lines in the conventional LCDs, is refracted when
arriving at the surface of each microlens 131, 231, 331 and 431, and
passes through the pixel electrodes 113 and first transparent glass
substrate 110. As a result, almost all incident light can be transmitted,
increasing the transmittance substantially.
In these cases, a micro black matrix whose width is narrower than that of
bus lines can be additionally disposed between the color filters on the
second transparent substrate, in order to further emphasize the color
difference with clear boundaries.
Furthermore, according to the first embodiment of the present invention,
the microlenses 131, 231, 331, and 431 are formed on the second substrate
corresponding to the edge portions of the pixel electrodes and to cover
the bus lines and the gaps between the bus lines and pixel electrodes. The
middle portions of the pixel electrodes 113 may not be covered by the
microlenses.
FIGS. 12-14 show cross-sectional views of examples of an LCD according to
the second embodiment of the present invention. In the second embodiment,
microlenses are disposed on the lower substrate and the backlight is
disposed behind the lower substrate.
As shown in FIG. 12, the first example of the LCD according to the second
embodiment of the present invention includes a plurality of microlenses
155 formed on the inner surface of a first transparent glass substrate
150. The microlenses 155 are covered with an overcoat layer 156 made of
acrylic resin. On the overcoat layer 156, other elements, such as the data
bus lines 152, pixel electrodes 153, a black matrix 154 and gate bus lines
are formed.
In the upper substrate, a color filter layer 121' having red, blue and
green filters 121R', 121B' and 121G' is formed on a second transparent
glass substrate 120'. On the color filter layer 121', common electrodes
122' are formed.
Further, the backlight is disposed behind the first transparent substrate
150 and directs the light toward the second transparent substrate 120'.
The incident light is focused by the microlenses 155 SO that it is
directed to the pixel electrodes 153 and not to the data and gate bus
lines. As a result, the microlenses 155 redirect light which would have
been blocked and scattered by the bus lines onto the edge portions of the
pixel electrodes 153. Accordingly, the transmittance is increased and the
LCD with an increased brightness and increased power efficiency is
produced.
As shown in FIG. 13, the second example of the LCD according to the second
embodiment of the present invention includes a plurality of microlenses
165 formed on the outer surface of a first transparent glass substrate
160. These microlenses 165 are covered with an overcoat layer 166 made of
benzocyclobutene or acrylic resin. On the inner surface of the first
transparent substrate 160, other elements, such as data bus lines 162,
pixel electrodes 163, a black matrix 164 and gate bus lines are formed.
In the upper substrate, common electrodes 122', a color filter layer 121'
having color filters 121R', 121B', 121G', and a second transparent glass
substrate 120' are formed in a manner similar to the upper substrate of
the LCD in FIG. 12.
As shown in FIG. 14, the third example of the LCD according to the second
embodiment of the present invention includes a plurality of microlenses
175 formed by selectively etching the outer surface portion of an overcoat
layer 176 formed on a first transparent glass substrate 170. The spaces
formed by etching the overcoat layer 176 may be filled with a material
such as acrylic resin or BCB. For example, if the overcoat layer 176 is
made of acrylic resin, the spaces may be filled with BCB. If the overcoat
layer 176 is made of BCB, the spaces may be filled with acrylic resin. On
the inner surface of the first transparent substrate 170, other elements,
such as data bus lines 172, pixel electrodes 173, a black matrix 174 and
gate bus lines are formed.
In the upper substrate, common electrodes 122', a color filter layer 121'
having color filters 121R', 121B', 121G', and a second transparent glass
substrate 120' are formed in a manner similar to the LCDs of FIGS. 12 and
13.
According to the second embodiment of the present invention, the light
source is positioned at the backside of the first transparent glass
substrate 150, 160 and 170. When the light from the light source hits the
surface of the microlenses 155, 165 and 175, it is refracted. That is, the
light which is blocked by the gate and data bus lines in the conventional
LCDs is refracted as it passes through the microlenses. The refracted
light then passes through the pixel electrodes 153, 163 and 173 and the
second transparent substrate 120'. As a result, almost all incident light
can be transmitted and the transmittance is consequently increased.
In these cases, a micro black matrix whose width is less than that of the
bus lines can be additionally disposed between the color filters on the
second transparent substrate, to emphasize the different colors.
FIGS. 15 and 16 show cross-sectional views of examples of an LCD according
to the third embodiment of the present invention.
As shown in FIG. 15, the first example of the LCD according to the third
embodiment of the present invention includes a plurality of microlenses
531 formed by selectively etching the outer surface portion of a second
transparent glass substrate 520. The spaces formed by etching the second
substrate 520 may be filled with a material 532, such as acrylic resin.
On the inner surface of the second transparent substrate 520, a color
filter layer 521 having red, blue and green filters 521R, 521B and 521G is
formed. Between these color filters, a black matrix 514 having a width
larger than the width of each bus line is formed, in accordance with the
joining margin of the second transparent substrate 520 and a first
transparent glass substrates 510. On the color filter layer 521, common
electrodes 522 are formed.
In the lower substrate, data bus lines 512, pixel electrodes 513, and gate
bus lines are formed on the first transparent glass substrate 510.
Here, a backlight is located behind the second substrate 520. The light
which would have been blocked by the black matrix 514 is redirected onto
the color filter layer 521 and passes through the pixel electrodes 513.
As shown in FIG. 16, the second example of the LCD according to the third
embodiment of the present invention includes a plurality of microlenses
631 formed in the lower substrate. By selectively etching the outer
surface portion of the first transparent glass substrate 610, the
microlenses 631 are shaped. The spaces formed by etching the first
substrate 610 may be filled with a material 632, such as an acrylic resin.
On the inner surface of the first transparent substrate 610, data bus lines
612, pixel electrodes 613, and gate bus lines are formed. In the upper
substrate, a color filter layer 621 having red, blue and green filters
621R, 621B and 621G is formed on a second transparent glass substrate 620.
Between these color filters, a black matrix 614 having a width larger than
the width of each bus line is formed, in accordance with the joining
margin of the first and second transparent substrates 610 and 620. On the
color filter layer 621, common electrodes 622 are formed.
Here, the backlight is located behind the first substrate 610. The light
which would have been blocked by the black matrix 614 is redirected onto
the color filter layer 621 and passes through the pixel electrodes 613.
Therefore, according to the third embodiment of the present invention, the
transmittance and aperture ratio of the LCD is increased with increased
power efficiency.
FIG. 17 shows a cross-sectional view of an LCD according to the fourth
embodiment of the present invention.
The LCDs according to the first and second embodiments comprise a BM (black
matrix) formed on arrays of TFTs formed on a first substrate. The
transmittance can be increased by enlarging the size of pixel electrodes,
avoiding the BM-on-array structure. The LCD according to the fourth
embodiment of the present invention is formed with enlarged pixel
electrodes, which includes pixel electrodes formed on a passivation layer
made of benzocyclobutene.
The LCD according to the fourth embodiment further includes microlenses
formed at each pixel border area of the color filter layer corresponding
to the gate bus lines and the data bus lines. The microlenses 731 are
covered with an overcoat layer 732 made of an organic film such as BCB or
acrylic resin. The overcoat layer is formed to enhance stability in
rubbing and to improve leveling. The overcoat layer may not be necessary
if stability in rubbing and improvement in leveling are already obtained.
This embodiment provides pixel electrodes 713 larger than those of an LCD
comprising a typical BM-on-array structure.
As shown in FIG. 17, the LCD includes a plurality of microlenses 731 formed
on the inner surface of a color filter layer 721. The color filter layer
having red, green and blue filters 721R, 721G and 721B is formed on the
inner surface of a second transparent glass substrate 720. On the
microlenses 731, an overcoat layer 732 made of benzocyclobutene is formed,
and common electrodes 722 are formed thereon.
In the lower substrate, a passivation layer 715 made of an organic
material, such as benzocyclobutene is formed between data bus lines 712
and pixel electrodes 713, so that larger pixel electrodes can be formed. A
black matrix is formed only on the gate bus lines formed on a first
transparent glass substrate 710.
In the fourth embodiment of the present invention, a light from the
backlight travels straight through the second substrate 720 and is
refracted at the surface of the microlenses 731. The refracted light
impinges on the pixel electrodes 713, but not on the gate and data bus
lines. Consequently, most of the light from the light source is
transmitted through the first transparent glass substrate 710.
According to the first through fourth embodiments of the present invention,
when the microlenses (131, 155, 165, 175, 231, 331, 431, 531, 631 and 731)
are formed at the positions corresponding to the gate and source bus
lines, almost no incident light is lost. Consequently, the aperture ratio
is improved up to 90%, compared to at most 70% in the conventional LCDs.
Therefore, an LCD which is driven by a low power and has a high
transmittance is obtained.
With respect to forming the microlenses, a discussion on how large the
scale of microlenses is and where the microlenses are formed is provided
below.
In order to design the microlenses for condensing or dispersing the
incident light, the relationship between the incident angle and the
refracted angle of the light is considered. The refraction angle of the
light is calculated from the following equation (1) known as the Snell's
law, which shows the relationship between refraction indices and
refraction angles.
n.sub.2 /n.sub.1 =sin .theta..sub.1 /sin .theta..sub.2 (1)
According to the equation (1), the refraction angle .theta..sub.2 of
incident light at an angle .theta..sub.1 to the normal line of each
microlens is determined by the refraction index of the material (n.sub.1)
of the microlens and the refraction index of the material (n.sub.2) being
in contact with the microlens.
In the present invention, considering the effects of the microlenses and
easiness of making them, microlenses having the width of 4 .mu.m-30 .mu.m
and the height of greater than 0.5 .mu.m are suggested.
The microlenses according to the embodiments of the present invention are
formed at the positions according to the gate bus lines and the data bus
lines so as to obtain the best effect. In a case where the light source is
positioned at the backside of the second substrate having a color filter
layer, it is desirable to form the microlenses on the outer or inner side
of the second substrate. In a case where the light source is positioned at
the backside of the first substrate having pixel electrodes, it is
desirable to form the microlenses on the outer or inner side of the first
substrate. However, the position of the microlenses is not restricted to
the above. That is, as long as the microlenses function to focus and
redirect the light which travels to the gate bus lines and the data bus
lines, the shape of microlenses can be varied.
FIGS. 5A-7B are cross-sectional and plan views showing examples of
different configurations and shapes of microlenses for the LCDs according
to the present invention. These examples are applicable to the first
through fourth embodiments of the present invention. Each of the
microlenses of the present invention can be formed to be equal to or
greater (e.g., more than 30 .mu.m) than each line width at the positions
corresponding to the gate data lines and data bus lines.
As shown in FIGS. 5A and 5B, the microlenses (141) cover each data bus line
142 and each gate bus line 144.
The microlenses 141 are positioned so that the border therebetween is
substantially aligned with the center of each bus line (shown by the
dotted line). In FIGS. 6A and 6B, moreover, the microlenses (145) can also
be formed at any position in the LCD panel, including where the pixel
electrodes 143 are.
As shown in FIGS. 7A and 7B, the microlens (146) having the same size as
the color filter layer can be formed at a position corresponding to each
color filter layer, covering the corresponding array of pixel electrodes
143. The microlens 146 includes edge portions which are curved and which
cover the area in which the color filter layer overlaps the gate bus lines
141 and data bus lines 142. These edge portions correspond to a light
shielding area (non-transmissive portion), such as gate and data bus
lines, a black matrix, and storage capacitor lines. The shape of the edge
portions allows the incident light to be focused onto the transmissive
portion. The microlens 146 further includes a substantially flat portion
for allowing the light to pass straight through the pixel electrodes 143.
The microlenses according to the first through fourth embodiments of the
present invention can be made of a different material or can be formed by
patterning LCD elements such as a color filters, pixel electrodes,
insulating layers, a transparent glass substrate, etc. into the shape of a
lens. As described above, an overcoat layer is formed on the microlenses
for increased stability in rubbing and upgrading the uniformity of the
substrate surface.
According to the present invention, although the amount of an incident
light is not increased, the amount of the transmitted light is increased.
In other words, though the aperture ratio, namely the size of transmissive
portion, is not increased, the same effect of having an increased aperture
ratio is achieved.
The effect of the present invention is increased when it is applied to the
LCD structures, in which the pixel electrodes overlap the data bus lines
and an organic insulator such as BCB is inserted between the pixel
electrodes and the bus lines, for increasing the size of the pixels. The
effect is also increased by forming a black matrix (BM-on-array) on the
first transparent glass substrate.
The invention being thus described, it will be obvious that the same may be
varied in many ways. Such variations are not to be regarded as a departure
from the spirit and scope of the invention, and all such modifications as
would be obvious to one skilled in the art are intended to be included
within the scope of the following claims.
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