U.S. patent application number 10/176599 was filed with the patent office on 2002-12-26 for reflection plate, manufacturing method thereof, liquid crystal display device, and manufacturing method thereof.
This patent application is currently assigned to NEC CORPORATION. Invention is credited to Ikeno, Hidenori, Kikkawa, Hironori, Matuno, Fumihiko, Sakamoto, Michiaki, Watanabe, Takahiko, Yamaguchi, Yuichi.
Application Number | 20020196396 10/176599 |
Document ID | / |
Family ID | 19029065 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020196396 |
Kind Code |
A1 |
Sakamoto, Michiaki ; et
al. |
December 26, 2002 |
Reflection plate, manufacturing method thereof, liquid crystal
display device, and manufacturing method thereof
Abstract
A reflection plate is formed so as to have a wavy surface, and
to have uneven distribution of normal line directions of the
surface in terms of a specific azimuth angle. The wavy surface is
formed due to line-shaped protruding patterns and an insulation
film layer. The protruding patterns intersect with one another to
form concave portions each having a shape of a closed figure. The
protruding patterns are formed by patterning, such that they have
almost uniform thickness.
Inventors: |
Sakamoto, Michiaki; (Tokyo,
JP) ; Yamaguchi, Yuichi; (Tokyo, JP) ; Ikeno,
Hidenori; (Tokyo, JP) ; Watanabe, Takahiko;
(Tokyo, JP) ; Kikkawa, Hironori; (Tokyo, JP)
; Matuno, Fumihiko; (Tokyo, JP) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Assignee: |
NEC CORPORATION
TOKYO
JP
|
Family ID: |
19029065 |
Appl. No.: |
10/176599 |
Filed: |
June 24, 2002 |
Current U.S.
Class: |
349/113 |
Current CPC
Class: |
G02F 1/133553
20130101 |
Class at
Publication: |
349/113 |
International
Class: |
G02F 001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 2001 |
JP |
2001-190264 |
Claims
What is claimed is:
1. A reflection plate having concave and protruding portions on a
surface thereof, wherein: distribution of normal line directions on
said surface is uneven in terms of a specific azimuth angle; and
reflection light intensity is dependent upon azimuth angle.
2. The reflection plate according to claim 1. wherein distribution
of reflection light intensity in relation to polar angle at said
specific azimuth angle shows one or more local maximum values,
other than a normal reflection component.
3. The reflection plate according to claim 1, wherein: closed
figures are formed by said protruding portions of said concave and
protruding portions; and said concave portions of said concave and
protruding portions are enclosed by said closed figures.
4. The reflection plate according to claim 3, wherein said closed
figures are a polygon.
5. The reflection plate according to claim 4, wherein said polygon
is approximately a triangle, or approximately a trapezoid.
6. The reflection plate according to claim 4, wherein said polygon
is approximately a triangle having a flattening ratio of equal to
or greater than 0.5 and equal to or smaller than 0.8.
7. The reflection plate according to claim 3, wherein in each of
said closed figures, its length in a first direction in which
reflection light intensity becomes the largest, is smaller than its
length in a second direction which is perpendicular to said first
direction.
8. The reflection plate according to claim 3, wherein line shapes
formed by said protruding portions of said closed figures have
almost uniform width.
9. The reflection plate according to claim 3, wherein line shapes
formed by said protruding portions of said closed figures have
almost uniform thickness.
10. A liquid crystal display device having the reflection plate
recited in any one of claims 1 to 9.
11. The liquid crystal display device according to claim 10,
wherein when incident light is radiated to a display surface of
said liquid crystal display device from a direction of -30-degree
polar angle, the reflection light intensity reaches local maximum
in a range of polar angle of 0 to 10 degrees.
12. The liquid crystal display device according to claim 10,
wherein when incident light is radiated to a display surface of
said liquid crystal display device from a direction of -30-degree
polar angle, the reflection light intensity has a positive slope in
relation to polar angle in a range of polar angle of 10 to 20
degrees, said slope becomes smaller as polar angle becomes larger
in a range of polar angle of 10 to A degrees (10<A<20), and
said slope becomes larger as polar angle becomes larger in a range
of polar angle of A to 20 degrees.
13. A method of manufacturing a reflection plate, comprising:
coating an organic resin on a substrate, patterning said organic
resin with a line-shape mask, and thus forming a plurality of
line-shaped protruding patterns such that said protruding patterns
intersect with one another to form concave portions each having a
shape of a closed figure; and coating an interlayer film so as to
cover said line-shaped protruding patterns.
14. The method of manufacturing a reflection plate according to
claim 13, wherein said line-shape mask comprises mask lines whose
width at and about intersection portions of said mask lines is
narrower than that of portions other than said intersection
portions.
15. A method of manufacturing a reflection plate, comprising
forming a contact hole portion, and at a same time, concave and
protruding portions including a plurality of line-shaped protruding
portions which intersect with one another, and concave portions
enclosed by said protruding portions, by coating an organic resin
on a substrate, and exposing and developing said organic resin by
changing luminous exposure.
16. The method of manufacturing a reflection plate according to
claim 15, wherein said patterning of said contact hole portion and
said concave and protruding portions includes exposing said organic
resin using different masks and by different luminous exposures for
the two different portions.
17. The method of manufacturing a reflection plate according to
claim 16, wherein luminous exposure of said organic resin for
patterning said concave and protruding portions is 10 to 50% of
luminous exposure of said organic resin for patterning said contact
hole portion.
18. The method of manufacturing a reflection plate according to
claim 17, wherein said patterning of said contact hole portion and
said concave and protruding portions includes exposing said organic
resin by using a half tone mask having different light
transmittance for said contact hole portion and said concave and
protruding portions, respectively.
19. The method of manufacturing a reflection plate according to
claim 15, wherein a mask for forming said line-shaped protruding
portions comprises mask lines whose width at and about intersection
portions of said mask lines is narrower than that of portions other
than said intersection portions.
20. A method of manufacturing a liquid crystal display device,
comprising forming a reflection plate in accordance with a
manufacturing method recited in any one of claims 13 to 19.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a reflection plate
achieving a high contrast, a manufacturing method thereof, a liquid
crystal display device, and a manufacturing method thereof.
[0003] 2. Description of the Related Art
[0004] There has been known a reflection type liquid crystal
display device, which reflects incident light coming from outside
with a reflection plate included therein, to use the light as the
light source for display. The reflection type liquid crystal
display device does not require backlight as a light source.
Therefore, the reflection type liquid crystal display device can be
more decreased in power consumption and more thinned than a
transmission type liquid crystal display device, and thus is used
in portable phones, etc.
[0005] The reflection type liquid crystal display device comprises
liquid crystal sealed in a liquid crystal cell, switching elements
for driving the liquid crystal, and a reflection plate which is
provided inside or outside the liquid crystal cell. The reflection
type liquid crystal display device is an active matrix type liquid
crystal display device employing thin film transistors as switching
elements, for example.
[0006] A liquid crystal display device, which comprises a
reflection plate on whose surface a reflection electrode having
uneven patterns is formed in order to increase light to be
scattered toward the normal line direction of the reflection plate
(toward the viewer) and thereby to improve the contrast, is
developed as a reflection type liquid crystal display device. Such
a liquid crystal display device is disclosed in Japanese Patent No.
2825713, and other publications.
[0007] In this liquid crystal display device, the wavy patterns are
formed by arranging a plurality of cylindrical protruding portions
made of resin, under a light reflection layer. This light
reflection layer is formed on the reflection plate on which the
protruding patterns arc formed, via an organic insulation film. As
illustrated in a plan view shown in FIG. 21, the plurality of
protruding patterns each having a circular-shaped cross section,
are arranged on the surface of the reflection plate independently
from one another. The protruding patterns having a circular-shaped
cross section have a high light scattering characteristic, and
reflect incident light almost uniformly toward the entire azimuth
angle.
[0008] The polar angle is an angle .theta.1 shown in FIG. 22
measured from the normal line direction of the reflection plate,
while the azimuth angle is an angle .theta.2 measured in the plane
parallel to thc reflection layer. Generally, reflection
characteristics (azimuth angle, polar angle, intensity) of a
reflection plate are observed by examining reflection light of
incident light coming from a direction of a -30-degree polar
angle.
[0009] A reflection plate acquiring a high reflection light
intensity toward the direction of a 0-degree polar angle (toward
the normal line direction) is demanded from a viewpoint of
improving the contrast of a liquid crystal display device when it
is used. However, a reflection plate having protruding patterns
like the one shown in FIG. 21 reflects light almost uniformly
toward the entire azimuth angle. Accordingly, the relationship
between the polar angle and the reflection light intensity shows a
state similar to normal distribution, as shown by a graph of FIG.
23. Therefore, there has existed a limit on how much the reflection
light intensity can be improved toward the direction of the
0-degree polar angle, with the use of such protruding patterns
having a circular-shaped cross section.
[0010] Not only the reflection type liquid crystal display device,
but a so-called semi-transparent liquid crystal display device,
such as disclosed in Japanese Patent No. 2955277, has the same
problem. This liquid crystal display device comprises pixel
electrodes having a transparent region and a reflection region, and
a reflection plate, and thus has both of the transmission function
and the reflection function. As having the reflection plate, this
type of liquid crystal display device cannot avoid the same
problem.
SUMMARY OF THE INVENTION
[0011] In view of the above circumstance, an object of the present
invention is to provide a reflection plate achieving a high
contrast, a manufacturing method thereof, a liquid crystal display
device, and a manufacturing method thereof.
[0012] Another object of the present invention is to provide a
reflection plate which can reflect light efficiently toward the
normal line direction of the reflection plate, a manufacturing
method thereof, a liquid crystal display device, and a
manufacturing method thereof.
[0013] To achieve the above objects, a reflection plate according
to a first aspect of the present invention has concave and
protruding portions on a surface thereof, wherein:
[0014] distribution of normal line directions on the surface is
uneven in terms of a specific azimuth angle; and
[0015] reflection light intensity is dependent upon azimuth
angle.
[0016] Distribution of reflection light intensity in relation to
polar angle at the specific azimuth angle may show one or more
local maximum values, other than a normal reflection component.
[0017] Closed figures may be formed by the protruding portions of
the concave and protruding portions.
[0018] The concave portions of the concave and protruding portions
may be enclosed by the closed figures.
[0019] The closed figures may be a polygon.
[0020] The polygon may be approximately a triangle, or
approximately a trapezoid.
[0021] The polygon may be approximately a triangle having a
flattening ratio of equal to or greater than 0.5 and equal to or
smaller than 0.8.
[0022] In each of the closed figures, its length in a first
direction in which reflection light intensity becomes the largest,
may be smaller than its length in a second direction which is
perpendicular to the first direction.
[0023] Line shapes formed by the protruding portions of the closed
figures may have almost uniform width.
[0024] The line shapes formed by the protruding portions of the
closed figures may have almost uniform thickness.
[0025] A liquid crystal display device according to a second aspect
of the present invention has the reflection plate described
above.
[0026] In this case, when incident light is radiated to a display
surface of the liquid crystal display device from a direction of
-30-degree polar angle, the reflection light intensity may reach
local maximum in a range of polar angle of 0 to 10 degrees.
[0027] When incident light is radiated to the display surface of
the liquid crystal display device from a direction of -30-degree
polar angle, the reflection light intensity may have a positive
slope in relation to polar angle in a range of polar angle of 10 to
20 degrees, the slope may become smaller as polar angle becomes
larger in a range of polar angle of 10 to A degrees
(10<A<20), and the slope may become larger as polar angle
becomes larger in a range of polar angle of A to 20 degrees.
[0028] A method of manufacturing a reflection plate according to a
third aspect of the present invention comprises:
[0029] coating an organic resin on a substrate, patterning the
organic resin with a line-shape mask, and thus forming a plurality
of line-shaped protruding patterns such that the protruding
patterns intersect with one another to form concave portions each
having a shape of a closed figure; and
[0030] coating an interlayer film So as to cover the line-shaped
protruding patterns.
[0031] The line-shape mask may comprise mask lines whose width at
and about intersection portions of the mask lines is narrower than
that of portions other than the intersection portions.
[0032] A method of manufacturing a reflection plate according to a
fourth aspect of the present invention comprises forming a contact
hole portion, and at a same time, concave and protruding portions
including a plurality of line-shaped protruding portions which
intersect with one another, and concave portions enclosed by the
protruding portions, by coating an organic resin on a substrate,
and exposing and developing the organic resin by changing luminous
exposure.
[0033] The patterning of the contact hole portion and the concave
and protruding portions may include exposing the organic resin
using different masks and by different luminous exposures for the
two different portions.
[0034] Luminous exposure of the organic resin for patterning the
concave and protruding portions may be 10 to 50% of luminous
exposure of the organic resin for patterning the contact hole
portion.
[0035] The patterning of the contact hole portion and the concave
and protruding portions may include exposing the organic resin by
using a half tone mask having different light transmittance for the
contact hole portion and the concave and protruding portions,
respectively.
[0036] A mask for forming the line-shaped protruding portions may
comprise mask lines whose width at and about intersection portions
of the mask lines is narrower than that of portions other than the
intersection portions.
[0037] A method of manufacturing a liquid crystal display device
according to a fifth aspect of the present invention comprises
forming a reflection plate in accordance with the manufacturing
method described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] These objects and other objects and advantages of the
present invention will become more apparent upon reading of the
following detailed description and the accompanying drawings in
which:
[0039] FIG. 1 is a diagram showing the cross section of a
reflection type liquid crystal display device according to an
embodiment of the present invention;
[0040] FIGS. 2A and 2B are diagrams illustrating light to be
reflected;
[0041] FIGS. 3A to 3F are diagrams showing steps of manufacturing a
lower substrate shown in FIG. 1;
[0042] FIG. 4 is a diagram showing a mask pattern;
[0043] FIGS. 5A to 5C are expanded diagrams of an intersection of a
mask pattern;
[0044] FIG. 6A is an expanded diagram of a basic figure, and FIGS.
6B to 6D are cross sections of FIG. 6A when it is cut along a line
A-A;
[0045] FIGS. 7A and 7B are graphs showing the relationship between
reflection light intensity and azimuth angle and polar angle,
regarding a reflection plate according to the embodiment;
[0046] FIG. 8 shows a protruding pattern having an equilateral
triangle basic figure;
[0047] FIG. 9 is a graph showing the relationship between line
width and thickness of side;
[0048] FIG. 10 is a graph showing the relationship between polar
angle and reflectivity at an azimuth angle of 180 degrees;
[0049] FIGS. 11A and 11B are graphs showing the relationship
between polar angle and reflectivity in a case where line width is
varied;
[0050] FIGS. 12A to 12C are graphs showing the relationship between
polar angle and reflectivity in a case where length of side is
varied;
[0051] FIGS. 13A and 13B are graphs showing the relationship
between polar angle and reflectivity in a case where flattening
ratio is varied;
[0052] FIG. 14 shows a protruding pattern having an isosceles
triangle basic figure;
[0053] FIGS. 15A and 15B are graphs showing the relationship
between polar angle and reflectivity in a case where randomness is
varied;
[0054] FIGS. 16A and 16B are graphs showing the relationship
between polar angle and reflectivity in a case where different mask
patterns are used;
[0055] FIG. 17 is a graph showing the relationship between azimuth
angle and reflectivity in a case where the thickness of the organic
insulation layer is varied;
[0056] FIGS. 18A to 18C arc diagrams showing steps of manufacturing
a lower substrate according to the second embodiment of the
invention;
[0057] FIG. 19 is a graph showing the relationship between azimuth
angle and reflectivity in a case where luminous exposure is
varied;
[0058] FIG. 20 shows a semi-transparent type liquid crystal display
device according to the other embodiment of the invention.
[0059] FIG. 21 is a plan view showing conventional protruding
patterns;
[0060] FIG. 22 is a diagram for explaining a polar angle and an
azimuth angle; and
[0061] FIG. 23 is a graph showing the relationship between polar
angle and reflection light intensity in a case where the protruding
patterns shown in FIG. 21 arc used.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0062] An embodiment of the present invention will be explained
below with reference to the drawings. The embodiment to be
described below is one embodiment of the present invention, and not
intended to limit the scope of the present invention.
First Embodiment
[0063] A reflection type liquid crystal display device according to
this embodiment is an active matrix type liquid crystal display
device having a switching element such as a thin film transistor
(TFT) in each pixel.
[0064] FIG. 1 is a cross section of a unit pixel area of the
reflection type liquid crystal display device according to this
embodiment. As shown in FIG. 1, the reflection type liquid crystal
display device 10 comprises a lower substrate 11, an opposing
substrate 12 which is set opposite from the lower substrate 11, and
a liquid crystal layer 13 which is sandwiched between the lower
substrate 11 and the opposing substrate 12.
[0065] The lower substrate 11 includes an insulation substrate 14,
an insulation protection film 15, a TFT 16, a first insulation
layer 17, protruding patterns 18, a second insulation layer 19, and
a reflection electrode 20.
[0066] The insulation protection film 15 made of an inorganic or
organic insulation material is deposited on the insulation
substrate 14. The TFT 16 which serves as a switching element is
formed on the insulation protection film 15.
[0067] The TFT 16 comprises a gate electrode 16a formed on the
insulation substrate 14, a semiconductor layer 16b which is laid
just above the gate electrode 16a via the insulation protection
film 15, and a drain electrode 16c and a source electrode 16d
respectively connected to a drain area and a source area in a
non-illustrated semiconductor layer.
[0068] Transistors other than a TFT, a diode such as MTM may be
used as the switching element.
[0069] The first insulation layer 17 is made of an inorganic or
organic insulation material, and is formed to have predetermined
patterns on the insulation protection film 15 on which the TFT 16
is formed.
[0070] The protruding patterns 18 are made of a resin material, and
are formed on the first insulation layer 17 and the source
electrode 16d. The protruding patterns 18 are formed into a
plurality of line-shaped patterns, as will be described later.
[0071] The second insulation layer 19 is formed to cover the
protruding patterns 18. The second insulation layer 19 is made of a
resin material. A contact hole 21, at the bottom of which the
source electrode 16d is exposed, is formed in the second insulation
layer 19. The surface of the second insulation layer 19 is wavy
(uneven) due to the protruding patterns 18 thereunder.
[0072] The reflection electrode 20 is made of a conductive material
such as aluminum, and is formed on the second insulation layer 19
including the contact hole 21. The reflection electrode 20 is
connected to the source electrode 16d of the TFT 16 through the
contact hole 21, so as to function as a pixel electrode and a light
reflection layer. The surface of the reflection electrode 20 is
also wavy, due to the protruding patterns 18 and the second
insulation layer 19.
[0073] In a terminal area around the periphery of the lower
substrate 11, a gate terminal 22 is formed on the insulation
substrate 14, and a drain terminal 23 is formed on the insulation
protection film 15 which covers the gate terminal 22.
[0074] The opposing substrate 12 includes a color filter 25 and a
transparent electrode 24 which are sequentially deposited on one
surface of a transparent insulation substrate 26. A polarizing
plate 27 is formed on the other surface of the insulation substrate
26.
[0075] The liquid crystal layer 13 is formed using a TN (Twisted
Nematic) method, an STN (Super Twisted Nematic) method, a one
polarizing plate method, a GH (Guest Host) method, a PDLC (Polymer
Dispersed Liquid Crystal) method, a cholesteric method, or the
like. The liquid crystal layer 13 is provided with a predetermined
orientation.
[0076] The operation of the reflection type liquid crystal display
device 10 having the above described structure will now be
explained.
[0077] In a white mode, incident light Li coming from outside of
the opposing substrate 12 through the polarizing plate 27 goes
through the insulation substrate 26, the color filter 25, the
transparent electrode 24, and the liquid crystal layer 13, and
finally reaches the surface of the reflection electrode 20.
[0078] The surface of the reflection electrode 20 is wavy due to
the protruding patterns 18, thus the incident light Li is reflected
in accordance with a directivity influenced by the waves. The
reflection light Lr returns to the outside as display light, going
back through the liquid crystal layer 13, the transparent electrode
24, the color filter 25, the insulation substrate 26, and the
polarizing plate 27.
[0079] On the contrary, in a black mode, although the incident
light Li coming from outside of the opposing substrate 12 is
reflected on the reflection electrode 20 likewise in the white
mode, the reflected light is prevented by the polarizing plate 27
from being externally emitted. In this way, the reflection type
liquid crystal display device 10 is switched ON and OFF.
[0080] The distributions of reflection direction and reflection
light intensity of the reflection light Lr depend upon the
distributions of tilt angle and normal line direction of the wavy
surface patterns formed on the surface of the reflection electrode
20. FIG. 2A is a diagram exemplarily showing the incident light Li,
and the reflection light Lr to be perceived by the viewer. The
angles respectively formed by the incident light Li from the light
source and the light Lr reflected on the opposing substrate 12 with
respect to the normal line direction of the opposing substrate 12
are defined incident angle Ti and reflection angle Tr,
respectively. Since the incident light Li is reflected on the wavy
surface of the reflection electrode 20, the incident angle Ti and
the reflection angle Tr take different values.
[0081] FIG. 23 is a diagram exemplarily showing reflection of the
incident light Li' coming to a point A which exists on wavy surface
of the reflection electrode 20. In the case where the incident
light Li' comes to the point A, the light is reflected on the
contact plane at the point A of the reflection electrode 20. Thus,
the reflection light Lr' is reflected in a direction determined by
the normal line direction at the point A as a symmetry axis to have
the same angle as that of the incident light Li' with respect to
the symmetry axis. Here, it is assumed that an angle formed by the
contact plane of the reflection electrode 20 at the point A and the
lower substrate 11 is defined as a tilt angle .theta. at the point
A. The distributions of reflection direction and reflection light
intensity of the reflection light Lr depend upon the distributions
of the tilt angle .theta. and normal line direction of the convex
and concave patterns of the reflection electrode 20.
[0082] Next, a method of manufacturing the above described
reflection type liquid crystal display device 10 will be explained.
FIGS. 3A to 3F are explanatory diagrams showing manufacturing steps
of the reflection type liquid crystal display device 10 shown in
FIG. 1, or the lower substrate 11 in particular.
[0083] The TFT serving as a switching element is formed on the
insulation substrate 14 first. Specifically, the gate electrode 16a
is formed on the insulation substrate 14, and then the insulation
protection film 15 is formed so as to cover the insulation
substrate 14 and the gate electrode 16a. Next, the semiconductor
layer 16b having a drain area and source area (not illustrated) is
formed on the insulation protection film 15 by etching, impurity
implantation, etc. (FIG. 3A). Then, the drain electrode 16c and the
source electrode 16d which are to be connected respectively to the
drain area and the source area are formed on the insulation
protection film 15. Further, the first insulation layer 17 is
formed on the TFT 16 (FIG. 3B).
[0084] Then, after organic resin is coated on the first insulation
layer 17, the resin is patterned using a predetermined
photolithography technique and an etching technique. By this
patterning, the protruding patterns 18 are formed, as shown in FIG.
3C. After the patterning, a baking process is applied to the
protruding patterns 18. The shapes of the protruding patterns 18
are rounded by the baking process, as shown in FIG. 3D.
[0085] The protruding patterns 18 are formed into a shape of line.
Adjacent protruding patterns 18 form a concave portion having a
shape of a basic figure, especially, a closed figure such as a
triangle. The formation of the line-shaped protruding patterns 18
is carried out with the use of a mask pattern as shown in FIG. 4. A
reflection plate having such line-shaped protruding patterns 18 is
disclosed in the Japanese Patent Application No. 2001-55229 filed
by the applicant of the present patent application.
[0086] By forming the line-shaped protruding patterns 18 so as to
form a concave portion having a shape of a basic figure, the
reflection electrode 20 to be formed in a later step will have
concave and protruding portions of a predetermined shape on its
surface. As a result, there will be provided the lower substrate
11, which achieves reflection light intensity that depends upon the
azimuth angle, and which enables a highly directional light
reflection with increasing the light to be reflected toward a
specific direction.
[0087] In the mask pattern shown in FIG. 4, the pattern of an
intersection (shown in FIG. 5A) of some line-shaped protruding
portion forming portions may be replaced with modified mask
patterns shown in FIGS. 5B and 5C. With the use of such modified
mask patterns, it is possible to reduce the difference in film
thickness between the vertex and side of the basic figure.
[0088] In the case where the protruding patterns are formed using
the mask pattern shown in FIG. 5A, the vertexes of the basic figure
(triangle) will become broadened and rounded as shown in FIG. 6A,
due to an error in the resolution of exposure and the resolution of
a resist. Further, as shown in a cross section shown in FIG. 6B
along a line A-A of FIG. 6A, heights (film thickness) of the
patterns will not be uniform, such that the vertex portion is
higher than the side portion.
[0089] In the case where the second insulation layer 19 is
deposited on the protruding patterns 18 where the heights of the
vertex portions and the side portions are not uniform, if the areas
around the vertex portions are designed to be provided with
appropriate tilt angles, the second insulation layer 19 may be flat
in the areas near the side portions (FIG. 6C). On the other hand,
if the areas near the side portions are designed to be provided
with appropriate tilt angles, the vertex portions may project from
the second insulation layer 19 (FIG. 6D). Therefore, if there is
difference in the heights of the protruding patterns 18, efficient
light reflection cannot be obtained, and unevenness of light
reflection may be caused.
[0090] In the mask pattern shown in FIG. 5B, the protruding portion
forming portions have, at the intersection thereof, narrower width
of line. For example, in the mask pattern shown in FIG. 5A, the
line width of the protruding portion forming portions is set to
about 4 .mu.m along the entire line, while in the mask pattern
shown in FIG. 5B, the line width is set to about 2 .mu.m at and
near the intersections. In the mask pattern shown in FIG. 5C, the
lines are removed at and near the intersections. By narrowing the
line width of the protruding patterns 18 at the vertex portions, or
by removing the lines at the vertex portions, it is possible to
reduce or eliminate the unevenness in the height (film thickness)
between the vertexes and sides of the basic figure. Accordingly,
efficient light reflection can be obtained.
[0091] The explanation will return to FIG. 3D. Successively, an
interlayer film made of organic resin is coated over the protruding
patterns 18, so that the surface becomes mildly wavy. Then, the
contact hole 21 is opened using a photolithography technique.
Afterwards, baking is applied to the interlayer film to form the
second insulation layer 19 (FIG. 3E).
[0092] Then, an aluminum (Al) thin film is formed on the second
insulation layer 19 including the contact hole 21. After this, the
reflection electrode 20 as a reflection pixel electrode is formed
by patterning (FIG. 3F). Thus, the lower substrate 11 as a
reflection plate is completed.
[0093] Spacers (not illustrated) are placed between thus formed
lower substrate 11 and the opposing substrate 12 formed by
depositing the color filter 25, etc. on the insulation substrate
26. A space (cell) formed by the spacers is filled with resin and
sealed. Thereafter, the polarizing plate 27 is adhered onto the
surface of the opposing substrate 12 to complete the reflection
type liquid crystal display device 10 shown in FIG. 1.
[0094] As described above, in the reflection type liquid crystal
display device 10 having the above structure including the
line-shaped protruding patterns 18, the reflection light intensity
depends upon the azimuth angle, and thus light to be reflected
toward a specific direction can be increased.
[0095] FIG. 7 shows a result of a research to test the azimuth
angle and reflection light intensity when light is radiated on the
lower substrate 11 (reflection plate) having the above structure,
from a direction of -30-degree polar angle. Here, the polar angle
is the angle .theta.1 shown in FIG. 22 measured from the normal
line direction of the reflection plate, and the azimuth angle is
the angle .theta.2 measured in the plane parallel to the reflection
layer.
[0096] When considering an ordinary usage situation of a liquid
crystal display device, it can be considered that when incident
light Li is radiated onto the display surface from a direction of
-30 degree polar angle (0 degree azimuth angle), the viewer best
perceives light Lr reflected from a direction of 0 to 20 degree
polar angle (180 degree azimuth angle), preferably from direction
of 0 to 10 or 10 to 20 polar angle (180 degree azimuth angle).
Accordingly, high contrast may be realized on a liquid crystal
display device having a reflection plate which reflects light Lr in
the above direction more than the other directions, when incident
light Li is radiated from the above described direction.
[0097] FIG. 7A and FIG. 7B respectively show the relationship
between polar angle and reflection light intensity and the
relationship between the azimuth angle and reflection light
intensity, which are obtained when light is radiated to the lower
substrate 11 (reflection plate) having the above described
structure from a direction of -30 degree polar angle. As shown in
FIG. 22, the polar angle is an angle .theta.1 measured from the
normal line direction of the reflection plate, and the azimuth
angle is an angle .theta.2 measured in the plane parallel to the
reflection plate.
[0098] Closed figure patterns made of equilateral triangle basic
figures arc formed on the lower substrate 11, as shown in FIG.
8.
[0099] As shown in FIG. 7A, the reflection light intensity shows a
peak near the polar angle of 0 to 10 degrees, other than in the
normal reflection direction (polar angle of 30 degrees). As shown
in FIG. 7B, the reflection light intensity changes regularly, in
response to the change of azimuth angle. Especially, the reflection
light intensity shows peaks at the polar angles of 0 degree, 60
degrees, and 120 degrees. And as the polar angle becomes larger,
for example, from 10 degrees to 20 degrees, the peak becomes
lower.
[0100] The reason why the reflection light intensity becomes
stronger toward a direction of a specific angle is that there is
unevenness in the distribution of normal line directions on the
wavy surface of the lower substrate 11.
[0101] It can be considered that the reflection characteristic near
the polar angle Of 0 to 10 degrees is mainly caused by the side
portions of the triangles, and the reflection characteristic of the
component near the normal reflection equal to or larger than 20
degrees is, due to the flat portion near the center of the
triangles. Accordingly, it can be considered that it is effective
to increase the number of sides orthogonal to the measuring
direction, in order to improve the reflectivity near the polar
angle of 0 to 30 degrees when the azimuth angle is at 180 degrees
(when the azimuth angle faces toward the front).
EXAMPLE 1
[0102] FIG. 9 shows the relationship between the line width of the
basic figure (triangle) and the thickness of the vertex and side
portions, in a case where the basic figure is formed by coating a
resin film having 2.35 .mu.m thickness, patterning the film with
the use of the mask patterns shown in FIGS. 5A and 5B, and baking
the film.
[0103] As shown in FIG. 9, in the case of using the unmodified mask
pattern shown in FIG. 5A, the thickness of the vertex portion is
1.90 .mu.m. On the other hand, in the case of using the mask
pattern shown in FIG. 5B where the line width at the intersection
is narrowed, the thickness of the vertex portion is 1.60 .mu.m. It
is turned out from this result that in the case where the modified
mask pattern is used, difference in the thickness between the
vertex and the side can be reduced.
[0104] Further, it is apparent that the larger the line width
becomes, the thicker the side portion becomes Therefore, it can
preferably be said that the larger the line width of the side
portion is, the smaller the difference in the thickness between the
side portion and the vertex portion becomes. Especially, it is
apparent that the line width should be preferably set to about 5
.mu.m, so that the thickness of the side portion can be about 1.3
.mu.m.
EXAMPLE 2
[0105] Light is radiated from a direction of -30-degree polar angle
onto the lower substrate 11 in which the protruding patterns 18 are
formed so as to constitute triangle-shaped concave portions, in
order to measure the relationship between polar angle and
reflection light intensity at all azimuth angle of 180 degrees,
which is counter to the light source.
[0106] In this measurement, a spectrophotometer IMUC (LCD7000) made
by Otsuka Electronics Co., Ltd. is used. Further in this
measurement, the incident light is caused to be radiated onto one
vertex of the triangle, which is the basic figure. And the
spectrophotometer is placed horizontally to one side of the
triangle. The measurement result at the 180-degree azimuth angle is
shown in FIG. 10.
[0107] It is apparent from the result shown in FIG. 10 that the
reflection light intensity (reflectivity) reaches local maximum
twice near the polar angle of 30 degrees and the polar angle of 5
degrees. The fact that alternation of the reflection light
intensity shows a plurality of local maximum values in accordance
with the polar angle, proves the fact that the lower substrate 11
has the directivity shown in FIGS. 7A and 7B, regarding the azimuth
angle.
[0108] The reflection light intensity at the 0-degree polar angle
is stronger than the reflection light intensity at the 90-degree
azimuth angle (not shown by the data). The reason for this is
considered to be that in case of the 180-degree azimuth angle,
local maximum of the reflection light intensity appears near the
5-degree polar angle, due to azimuth-angle-dependent light
reflection as shown in FIGS. 7A and 7B. The reflection light
intensity at the 0-degree polar angle can be strengthened if the
local maximum of the reflection light intensity appears near 0 to
10 degrees.
EXAMPLE 3
[0109] In order to maximize the reflection light intensity at an
azimuth angle of 180 degrees and at a polar angle of 0 degree,
parameters with regard to the protruding patterns 18 will be
considered.
EXAMPLE 3-1
[0110] FIGS. 11A and 11B respectively show results of measuring the
relationship between polar angle and reflection light intensity at
an azimuth angle of 180 degrees, where the line width of the basic
figure is set to 3 .mu.m in FIG. 11A, and 4 .mu.m in FIG. 11B. The
conditions for measurement are the same as those in the example 2.
The film thickness of the protruding patterns 18 at the sides of
the basic figure is 1.3 .mu.m after being baked. The film thickness
of the second insulation layer 19 is 1.5 .mu.m, and the length of
the sides of the basic figure is 24 .mu.m on the average.
[0111] The reflection light intensity has a plurality of local
maximum values, in each of the graphs shown in FIG. 11A and 11B.
From FIG. 11A, it is known that the reflection light intensity
reaches local maximum near the polar angle of 15 degrees in the
case where the line width is 3 .mu.m. On the other hand, it is
known from FIG. 11B that the reflection light intensity reaches
local maximum near the polar angle of 0 degree in addition to the
polar angle of 15 degrees, in the case where the line width is 4
.mu.m. Since the reflection light intensity reaches local maximum
near the polar angle of 0 degree, it is turned out that the
reflection light intensity at the polar angle of 0 degree is
stronger, in the case where the line width is 4 .mu.m.
EXAMPLE 3-2
[0112] FIGS. 12A to 12C respectively show results of measuring the
relationship between polar angle and reflection light intensity,
where the length of a side of a triangle (basic figure) is 24 .mu.m
in FIG. 12A, 20 .mu.m in FIG. 12B, and 16 .mu.m in FIG. 12C. The
conditions for measurement are the same as those in the example 2.
The film thickness of the protruding patterns 18 at the sides of
the basic figure is 1.3 .mu.m after being baked. The film thickness
of the second insulation layer 19 is 1.5 .mu.m, and the line width
of the basic figure is 5 .mu.m.
[0113] The reflection light intensity has a plurality of local
maximum values, in each of the graphs shown in FIGS. 12A to 12C. By
comparing FIGS. 12A to 12C, it is apparent that the larger the
length of the side is, the polar angle, at which the local maximum
of the reflection light intensity appears, becomes closer to 0
degree. That is, it is turned out that the larger the length of the
side is, the stronger the reflection light intensity at the polar
angle of 0 degree becomes.
EXAMPLE 3-3
[0114] FIGS. 13A and 13B respectively show results of measuring the
relationship between polar angle and reflection light intensity,
where the flattening ratio of a triangle is 1.0 in FIG. 13A, and
0.8 in FIG. 13B. Here, it is defined that ratio between base and
altitude of an equilateral triangle represents a flattening ratio
of 1.0 (as illustrated in FIG. 8), and the ratio between base and
altitude of an isosceles triangle having an altitude of 0.8 times
as high as that of an isosceles triangle represents a flattening
ratio of 0.8 (as illustrated in FIG. 14). The conditions for
measurement are the same as those in the example 2. The film
thickness of the protruding patterns 18 at the sides of the
triangle is 1.3 .mu.m after being baked. The film thickness of the
second insulation layer 19 is 1.5 .mu.m, the length of the sides of
the triangle is 24 .mu.m on the average, and the line width is 5
.mu.m.
[0115] The reflection light intensity has a plurality of local
maximum values, in each of the graphs shown in FIGS. 13A and 13B.
By comparing FIGS. 13A and 13B, it is apparent that the reflection
light intensity at the polar angle of 0 degree is stronger in a
case where a triangle having a flattening ratio of 0.8 is formed,
than in a case where a triangle having a flattening ratio of 1.0 is
formed. As explained above, the reason for this result is
considered to be that there are more line-shaped protruding
patterns 18 that are arranged horizontally to the spectrophotometer
within a specific area in the case of the flattening ratio of 0.8
than in the case of the flattening ratio of 1.0.
[0116] However, if the flattening ratio is less than 0.5, the
reflection light might cause interference, and thus the
characteristic of the reflection plate might be deteriorated.
Therefore, it is found that the flattening ratio is preferably 0.5
to 0.8.
EXAMPLE 3-4
[0117] FIGS. 15A and 15B respectively show results of measuring the
relationship between polar angle and reflection light intensity,
where the randomness when arranging the basic figures is 0.5 in
FIG. 15A, and 0.75 in FIG. 15B. Here, it is assumed that in a case
where all the basic figures are arranged parallel to one another,
this state is defined as having randomness of 0.0, while in a case
where all the basic figures arc arranged completely randomly, this
state is defined as having randomness of 1.0. The conditions for
measurement are the same as those in the example 2. The film
thickness of the protruding patterns 18 at the sides of the basic
figure is 1.3 .mu.m after being baked. The film thickness of the
second insulation layer 19 is 1.5 .mu.m, the length of the sides of
the basic figure is 24 .mu.m on the average, and the line width is
5 .mu.m.
[0118] The reflection light intensity has a plurality of local
maximum values, in each of the graphs shown in FIGS. 15A and 15B.
By comparing FIGS. 15A and 15B, it is apparent that the reflection
light intensity at the polar angle of 0 degree is stronger in a
case where the randomness is 0.5, than in a case where the
randomness is 0.75. The reason for this result is considered to be
that the number of the line-shaped protruding patterns 18 that are
arranged horizontally to the spectrophotometer is smaller in a case
where the randomness is large. However, if the randomness is
reduced too much, the reflection light might cause interference,
and thus the characteristic of the reflection plate might be
deteriorated
EXAMPLE 3-5
[0119] FIGS. 16A and 16B respectively show results of measuring the
relationship between polar angle and reflection light intensity,
where the modified mask pattern shown in FIG. 5B is applied to the
vertexes of the basic figure in FIG. 16A, and the unmodified mask
pattern shown in FIG. 5A is applied to the vertexes of the basic
figure in FIG. 16B. The conditions for measurement are the same as
those in the example 2. The film thickness of the protruding
patterns 18 at the sides of the basic figure is 1.3 .mu.m after
being baked The film thickness of the second insulation layer 19 is
1.5 .mu.m, the length of the sides of the basic figure is 24 .mu.m
on the average, and the line width is 5 .mu.m.
[0120] The reflection light intensity has a plurality of local
maximum values, in each of the graphs shown in FIGS. 16A and 16B.
By comparing FIGS. 16A and 16B, it is apparent that the reflection
light intensity at the polar angle of 0 degree is stronger in the
case where the modified mask pattern shown in FIG. 5B is used, than
in the case where the unmodified mask pattern is used. By narrowing
the line width at the vertexes of the basic figure, the difference
in height between the vertex and side portions of the protruding
patterns 18 is reduced. Thus, it is considered that the shape of
the vertexes is prevented from being circular as shown in FIG. 21,
when viewed in a plan, and the directivity (anisotropy) of the
reflection light intensity is enhanced toward the direction of
azimuth angle.
EXAMPLE 3-6
[0121] The relationship between polar angle and reflection light
intensity will be considered by changing the thickness of the
second insulation layer 19. The conditions for measurement are the
same as those in the example 2. FIG. 17 shows the result when the
coating thickness of the second insulation layer 19 is 1.5 .mu.m,
2.0 .mu.m or 3.0 .mu.m, on the condition that the basic figure is a
triangle, the flattening ratio is 0.8, the line width is 0.4 .mu.m,
the length of a side is 28 .mu.m, the thickness of the protruding
pattern 18 is 2.0 .mu.m and the randomness is 0.75.
[0122] From FIG. 17, it is known that as the second insulation
layer 19 becomes thicker, peak appearing near the azimuth angle of
0 degree shifts to near 20 degrees and finally disappears. It can
be considered that this is because the sides of the triangles are
flattened by the second insulation layer 19.
[0123] In the case where the thickness of the second insulation
layer 19 is 1.5 .mu.m, the reflection light intensity reaches local
maximum near the polar angle of 0 to 10 degrees. Accordingly, when
the display device is used in this range of angles, high
reflectivity can be obtained if the reflection plate is designed in
this way.
[0124] Also it is known that in the case where the thickness of the
second insulation layer 19 is 2.0 .mu.m, the change of the
reflection light intensity has a positive slope in the range of
polar angle of 10 to 20 degrees. And in the range of polar angle of
10 to A degrees (10<A<20), the slope of the change of the
reflection light intensity becomes smaller, as the polar angle
becomes larger. Further, in the range of polar angle of A to 20
degrees, the slope of the change of the reflection light intensity
becomes larger, as the polar angle becomes larger. Accordingly, in
the case where the display device is used in this range of polar
angle, high reflectivity can be obtained if the reflection plate is
designed in this way.
[0125] The same consideration will be made (not shown by data) by
using three materials having different melting characteristics when
being baked, as the material for the second insulation layer 19.
From the result of the measurement, a material which has a poor
melting characteristic and thus a poor tendency to change in its
shape, achieves the strongest reflection light intensity at the
polar angle or 0 degree.
[0126] As described in the above examples, the reflection light
intensity is changed by the protruding patterns 18 which form the
basic figure, in accordance with the azimuth angle. Therefore, it
has been made sure that the alteration of the reflection light
intensity in relation to the polar angle takes a plurality or local
maximum values, and the reflection light intensity at the polar
angle of 0 degree can be strengthened, if one of such local maximum
values appears near the polar angle of 0 to 10 degrees. Thus, the
lower substrate 11 (reflection plate) can increase the amount of
light to be reflected toward the direction of 0-degree polar angle,
i.e., toward the viewer, and thus can improve the contrast.
[0127] Specifically, by changing the line width, length of a side,
and film thickness of the protruding patterns 18, and the film
thickness of the second insulation layer 19, it is possible to form
the protruding and concave portions, so as to maximize the
anisotropy of the reflection plate and the reflection light
intensity toward the normal line direction of the reflection plate.
Further, by narrowing the line width of the line-shaped protruding
patterns 18 at the intersections, it is possible to make the
thickness of the protruding patterns 18 almost uniform. Thus, the
difference in height between at the vertexes and at the sides of
the basic figure can be reduced.
[0128] With the reduction of the difference in height,
deterioration of light reflection efficiency due to projection of
the protruding patterns 18 from the second insulation layer 19 can
be prevented. Moreover, since the thickness of the second
insulation layer 19 can freely be set to some extent, it is
possible to select the thickness of the second insulation layer 19,
so that the light reflection intensity toward the normal line
direction (direction of 0-degree polar angle) can be
strengthened.
Second Embodiment
[0129] FIG. 18C shows the structure of a reflection plate (lower
substrate 11) according to a second embodiment. The lower substrate
11 according to the second embodiment forms the wavy surface of the
reflection electrode 20, by the waves formed on one interlayer
insulation film 30, unlike the first embodiment.
[0130] The interlayer insulation film 30 is made of photosensitive
resin, and its concave and protruding patterns are formed at the
same time as the contact hole 21 is formed, by changing the
luminous exposure of ultra violet rays (UV), as will be described
later.
[0131] A method of manufacturing the lower substrate 11 according
to the second embodiment will be explained below with reference to
FIGS. 18A to 18C. This manufacturing method is disclosed in
Unexamined Japanese Patent Application KOKAI Publication No.
2000-250025.
[0132] First, as shown in FIG. 18A, an organic resin layer 31 made
of, for example, positive photosensitive resin is formed by coating
on the first insulation layer 17 and the like in the state shown in
FIG. 3B.
[0133] Then, the organic resin layer 31 is exposed and developed to
form the contact hole 21, and at the same time, concave and
protruding patterns are formed on the surface of the organic resin
layer 31, as shown in FIG. 18B. That is, the area where the contact
hole 21 is formed, and the areas where the concave and protruding
patterns are formed, are exposed by using different masks and by
different luminous exposures. Preferably, the luminous exposure
(UV1) for the areas for the concave and protruding patterns is 10
to 50% of the luminous exposure (UV2) of the area for the contact
hole.
[0134] The dissolution speed of a positive photosensitive resin
depends largely upon the decomposition ratio of a photosensitive
agent. Using this characteristic, by changing the decomposition
ratios for the areas for the concave and protruding patterns and
the area for the contact hole, it is possible to generate a
difference in dissolution speed between the resins of the both
areas. Accordingly, it is possible to form the deep contact hole 21
and the shallow patterns, by developing the organic resin layer 31
during a period of time enough to dissolve (resolve) the layer to
form the contact hole 21.
[0135] Patterning of the organic resin layer 31 may be carried out
by using a same mask, if the mask is a so called half tone mask,
that is, if the mask has different light transmittance for the area
for the contact hole 21, and the areas for the concave and
protruding patterns.
[0136] After the organic resin layer 31 is patterned, it is baked
to form an interlayer insulation film 30. Then, a metal film made
of aluminum or the like is formed, and then patterned. Thus, a
reflection electrode 20 is formed. As a result, the lower substrate
11 shown in FIG. 18C is completed.
[0137] FIG. 19 shows results obtained when the film thickness of
the organic resin layer 31 is unchanged, and the luminous exposure
for the areas for the concave and protruding patterns is set to
25%, 20%, and 15% of the luminous exposure of the area for the
contact hole. The conditions for measurement are the same as those
in the above example 3-6.
[0138] As known from FIG. 19, as the luminous exposure is reduced,
the peak of the reflection light intensity near the 0 degree angle
shifts to near the 20 degree angle, and at last disappears. This
may be because the sides of the triangles are flattened by the
interlayer insulation film 30.
[0139] When the luminous exposure is 25% of that of the contact
hole area, the reflection light intensity reaches local maximum
near the polar angle of 0 to 10 degrees. Accordingly, if the
display device is used in this range of polar angle, high
reflectivity can be obtained if the lower substrate is designed as
described above.
[0140] When the luminous exposure is 20% of that of the contact
hole area, the change of the reflection light intensity has a
positive slope in the range of polar angle of 10 to 20 degrees. And
in the range of polar angle of 10 to A degrees (10<A<20), the
slope of the change of the reflection light intensity becomes
smaller, as the polar angle becomes larger. Further, in the range
of polar angle of A to 20 degrees, the slope of the change of the
reflection light intensity becomes larger, as the polar angle
becomes larger. Accordingly, if the display device is used in this
range of polar angle, high reflectivity can be obtained if the
lower substrate is designed as described above.
[0141] As explained, the reflection plate having the concave and
protruding patterns according to the first and second embodiments
achieves reflection light intensity which is dependent upon azimuth
angle. And the change of the reflection light intensity in relation
to the polar angle shows a plurality of local maximum values. High
reflection light intensity at the polar angle of 0 degree is
realized when the local maximum appears near the polar angle of 0
to 10 degrees.
[0142] Various embodiments and changes may be made thereunto
without departing from the broad spirit and scope of the invention.
The above-described embodiments are intended to illustrate the
present invention, not to limit the scope of the present invention.
The scope of the present invention is shown by the attached claims
rather than the embodiments. Various modifications made within the
meaning of an equivalent of the claims of the invention and within
the claims are to be regarded to be in the scope of the present
invention.
[0143] In the above described embodiments, examples where the
present invention is applied to a reflection type liquid crystal
display device, are explained. However, the present invention can
be applied to a so-called semi-transparent type liquid crystal
display device, as disclosed in Japanese Patent No. 2955277. For
example, the present invention can be applied to a liquid crystal
display device shown in FIG. 20, which comprises a transparent
electrode including a transparent region and a reflection region,
and a reflection plate, and thus has the function of a transparent
liquid crystal display device and the function of a reflection type
liquid crystal display device.
[0144] This application is based on Japanese Patent Application No.
2001-190264 filed on Jun. 22, 2001 and including specification,
claims, drawings and summary. The disclosure of the above Japanese
Patent Application is incorporated herein by reference in its
entirety.
* * * * *