U.S. patent application number 09/841605 was filed with the patent office on 2001-11-15 for color liquid crystal projector having an improved optical system.
Invention is credited to Aoto, Katsuhide, Yanagawa, Kaoru.
Application Number | 20010040669 09/841605 |
Document ID | / |
Family ID | 18646215 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010040669 |
Kind Code |
A1 |
Aoto, Katsuhide ; et
al. |
November 15, 2001 |
Color liquid crystal projector having an improved optical
system
Abstract
A color liquid crystal projector has an optical system for color
splitting. The optical system includes a mirror for reflecting a
first primary-color light and transmitting second and third
primary-color lights in light from a light source; a first phase
plate for transmitting the second primary-color light from the
mirror with its polarization degree rotated through 90.degree., and
for transmitting the third primary-color light; a first prism for
transmitting the second primary-color light from the first phase
plate into a second liquid crystal display panel, and reflecting
the third primary-color light from the first phase plate into a
third liquid crystal display panel; a second prism for entering the
first primary-color light from the mirror into a first liquid
crystal display panel; and a dichroic prism for combining the
first, second and third primary-color lights reflected from the
liquid crystal display panels.
Inventors: |
Aoto, Katsuhide; (Mobara,
JP) ; Yanagawa, Kaoru; (Chosei, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
18646215 |
Appl. No.: |
09/841605 |
Filed: |
April 25, 2001 |
Current U.S.
Class: |
353/20 ;
348/E9.027; 353/31 |
Current CPC
Class: |
H04N 9/3105
20130101 |
Class at
Publication: |
353/20 ;
353/31 |
International
Class: |
G03B 021/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 11, 2000 |
JP |
2000-138630 |
Claims
What is claimed is:
1. A color liquid crystal projector including an optical system for
splitting light from a light source into first primary-color light,
second primary-color light and third primary-color light, first,
second and third reflection type liquid crystal display panels
corresponding to said first primary-color light, said second
primary-color light and said third primary-color light,
respectively, and a projection lens for projecting said first
primary-color light, said second primary-color light and said third
primary-color light from said optical system onto a screen, said
optical system comprising: a linear polarizer receiving the light
from the light source; a mirror for reflecting said first
primary-color light in the light from said linear polarizer and
transmitting said second primary-color light and said third
primary-color light in the light from said linear polarizer; a
first phase plate for rotating a direction of polarization of said
second primary-color light from said mirror through 90.degree. and
transmitting said second primary-color light, and for transmitting
said third primary-color light without changing a direction of
polarization thereof; a first prism for transmitting said second
primary-color light from said first phase plate and then entering
said second primary-color light into said second liquid crystal
display panel, and reflecting said third primary-color light from
said first phase plate and then entering said third primary-color
light into said third liquid crystal display panel; a second prism
for entering said first primary-color light from said mirror into
said first liquid crystal display panel; and a dichroic prism for
combining said first primary-color light, said second primary-color
light and said third primary-color light reflected from said first,
second and third liquid crystal display panels, respectively.
2. A color liquid crystal projector according to claim 1, wherein
said optical system further comprises a second phase plate disposed
between said dichroic prism and said first prism for rotating the
direction of polarization of said second primary-color light
through 90.degree. and transmitting said second primary-color
light, and transmitting said third primary-color light without
changing the direction of polarization thereof.
3. A color liquid crystal projector according to claim 1, wherein
said optical system further comprises a third phase plate disposed
between said second prism and said dichroic prism for rotating a
direction of polarization of said first primary-color light through
90.degree. and transmitting said first primary-color light.
4. A color liquid crystal projector according to claim 1, wherein
said optical system further comprises a glass plate disposed
between said second prism and said dichroic prism for equalizing
optical path lengths of said first, second and third primary-color
lights.
5. A color liquid crystal projector according to claim 1, wherein
said first phase plate, said first prism, said dichroic prism and
said second prism are cemented together.
6. A color liquid crystal projector comprising a light source and
an optical system for reflecting light from said light source by
reflection type liquid crystal display panels and projecting light
reflected from said reflection type liquid crystal display panels,
said optical system including: a mirror for reflecting a light of a
first wavelength of said light from said light source and
reflecting lights of second and third wavelengths of said light
from said light source; a first phase plate for rotating a
direction of polarization of said light of said second wavelength
through 90.degree. from said mirror and transmitting said light of
said second wavelength, and transmitting said light of said third
wavelength without changing a direction of polarization thereof; a
first prism for transmitting said light of said second wavelength
from said first phase plate and reflecting said light of said third
wavelength from said first phase plate; a first reflection type
liquid crystal display panel for reflecting said light of said
first wavelength from said mirror; a second reflection type liquid
crystal display panel for reflecting said light of said second
wavelength from said first prism; a third reflection type liquid
crystal display panel for reflecting said light of said third
wavelength from said first prism; and a dichroic prism for
combining lights from said first, second and third reflection type
liquid crystal display panels, each of said first, second and third
reflection type liquid crystal display panels being provided with
reflective electrodes for reflecting light entering a liquid
crystal layer thereof.
7. A color liquid crystal projector according to claim 6, wherein
said color liquid crystal projector further comprises a second
phase plate disposed between said dichroic prism and said first
prism for rotating the direction of polarization of said light of
said second wavelength through 90.degree. and transmitting said
light of said second wavelength, and transmitting said light of
said third wavelength without changing the direction of
polarization thereof.
8. A color liquid crystal projector according to claim 6, wherein
said color liquid crystal projector further comprises a second
prism for reflecting said light of said first wavelength from said
mirror and entering said light of said first wavelength into said
first reflection type liquid crystal display panel, and a third
phase plate disposed between said second prism and said dichroic
prism for rotating a direction of polarization of said light of
said first wavelength through 90.degree. and transmitting said
light of said first wavelength.
9. A color liquid crystal projector according to claim 6, wherein
said color liquid crystal projector further comprises a second
prism for reflecting said light of said first wavelength from said
mirror and entering said light of said first wavelength into said
first reflection type liquid crystal display panel, and a glass
plate disposed between said second prism and said dichroic prism
for equalizing optical path lengths of said lights of said first,
second and third wavelengths.
10. A color liquid crystal projector according to claim 6, wherein
said first phase plate and said first prism are cemented together.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a liquid crystal projector,
and in particular to a color liquid crystal projector having an
improved optical system.
[0002] The color liquid crystal projector is such that white light
from one light source is split into three primary colors of red
(R), green (G) and blue (B), then the three lights of the primary
colors are entered into the red-color, green-color and blue-color
liquid crystal display panels, respectively, and then the three
lights of the primary colors reflected from the respective liquid
crystal display panels are recombined and are projected onto a
screen via a projection lens.
[0003] Conventionally, a means for splitting white light from one
light source into three primary-color lights and for splitting and
combining the polarized light comprises three polarizing beam
splitters for the three primary colors, respectively, and a means
for combining the three primary-color lights uses a cross dichroic
prism.
SUMMARY OF THE INVENTION
[0004] In the liquid crystal projector of the above configuration,
the optical system for color splitting and color recombination is
large in size, and further, a problem has been pointed out that,
because two liquid crystal display panels face toward each other
with two of the three polarizing beam splitters and the cross
dichroic prism interposed therebetween, the contrast ratio of the
combined images is reduced by light reflections between the two
opposing liquid crystal display panels.
[0005] The present invention has been made in view of the above
situations, and therefore it is an object of the present invention
to provide a small and lightweight liquid crystal projector.
Further, it is another object of the present invention to a liquid
crystal projector featuring a good contrast ratio.
[0006] The following explains briefly an outline of representative
ones of the inventions disclosed in this specification.
[0007] In accordance with an embodiment of the present invention,
there is provided a color liquid crystal projector including an
optical system for splitting light from a light source into first
primary-color light, second primary-color light and third
primary-color light, first, second and third reflection type liquid
crystal display panels corresponding to the first primary-color
light, the second primary-color light and the third primary-color
light, respectively, and a projection lens for projecting the first
primary-color light, the second primary-color light and the third
primary-color light from the optical system onto a screen, the
optical system comprising: a linear polarizer receiving the light
from the light source; a mirror for reflecting the first
primary-color light in the light from the linear polarizer and
transmitting the second primary-color light and the third
primary-color light in the light from the linear polarizer; a first
phase plate for rotating a direction of polarization of the second
primary-color light from the mirror through 90.degree. and
transmitting the second primary-color light, and for transmitting
the third primary-color light without changing a direction of
polarization thereof; a first prism for transmitting the second
primary-color light from the first phase plate and then entering
the second primary-color light into the second liquid crystal
display panel, and reflecting the third primary-color light from
the first phase plate and then entering the third primary-color
light into the third liquid crystal display panel; a second prism
for entering the first primary-color light from the mirror into the
first liquid crystal display panel; and a dichroic prism for
combining the first primary-color light, the second primary-color
light and the third primary-color light reflected from the first,
second and third liquid crystal display panels, respectively.
[0008] In accordance with another embodiment of the present
invention, there is provided a color liquid crystal projector
comprising a light source and an optical system for reflecting
light from the light source by reflection type liquid crystal
display panels and projecting light reflected from the reflection
type liquid crystal display panels, the optical system including: a
mirror for reflecting a light of a first wavelength of the light
from the light source and reflecting lights of second and third
wavelengths of the light from the light source; a first phase plate
for rotating a direction of polarization of the light of the second
wavelength through 90.degree. from the mirror and transmitting the
light of the second wavelength, and transmitting the light of the
third wavelength without changing a direction of polarization
thereof; a first prism for transmitting the light of the second
wavelength from the first phase plate and reflecting the light of
the third wavelength from the first phase plate; a first reflection
type liquid crystal display panel for reflecting the light of the
first wavelength from the mirror; a second reflection type liquid
crystal display panel for reflecting the light of the second
wavelength from the first prism; a third reflection type liquid
crystal display panel for reflecting the light of the third
wavelength from the first prism; and a dichroic prism for combining
lights from the first, second and third reflection type liquid
crystal display panels, each of the first, second and third
reflection type liquid crystal display panels being provided with
reflective electrodes for reflecting light entering a liquid
crystal layer thereof.
[0009] The liquid crystal projectors of the above configuration are
capable of being made smaller in size than the conventional liquid
crystal projector requiring a prism for each of the liquid crystal
display panels, because the two liquid crystal display panels can
be disposed with the above-described prism interposed
therebetween.
[0010] The mirror is used instead of the prisms, as an element for
reflecting a first primary-color light in white light from the
light source and transmitting a second primary-color light and a
third primary-color light, and consequently, the liquid crystal
projector is capable of being made lightweight.
[0011] Two of the three required liquid crystal display panels are
capable of being disposed at the two sides of the prism
perpendicular to each other, respectively, and consequently, they
do not need to be disposed to face each other with the prism
interposed therebetween. As a result, light incident on one of the
three liquid crystal display panels does not enter another of the
three liquid crystal display panels, and therefore the display
contrast ratio is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] In the accompanying drawings, in which like reference
numerals designate similar components throughout the figures, and
in which:
[0013] FIG. 1 is an illustration of an embodiment of the liquid
crystal projector in accordance with the present invention;
[0014] FIGS. 2A and 2B are schematic illustrations for operation of
a reflection type liquid crystal display panel of a
single-polarizer twisted-nematic mode (SPTN) which is one of
electrically controlled birefringent modes, in the field-off and
field-on states, respectively;
[0015] FIG. 3 is a schematic plan view of a driving circuit
substrate having a reflective electrodes thereon in an embodiment
in accordance with the present invention;
[0016] FIG. 4 is a schematic cross-sectional view for explaining an
embodiment in accordance with the present invention;
[0017] FIG. 5 is a perspective view of a driving circuit substrate
superposed with a transparent substrate in an embodiment in
accordance with the present invention;
[0018] FIG. 6 is a plan view of a liquid crystal display panel
having a flexible printed wiring board connected thereto;
[0019] FIG. 7 is an exploded view in perspective of major elements
of a liquid crystal display device in an embodiment in accordance
with the present invention; and
[0020] FIG. 8 is a plan view of a liquid crystal display device in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] An embodiment of the liquid crystal projector in accordance
with the present invention will be explained with reference to the
drawings.
[0022] FIG. 1 illustrates a configuration of an embodiment of the
liquid crystal projector in accordance with the present invention
including optical paths therein.
[0023] A dichroic mirror 3 is disposed to the right of a light
source 1 with an illuminating optical system 2 and a polarizer 21
interposed therebetween, and the mirror plane of the dichroic
mirror 3 is oriented at 45.degree. to the x axis in a system of
rectangular co-ordinates in FIG. 1.
[0024] A first polarizing beam splitter 4 is disposed adjacently to
and above the dichroic mirror 3 with its reflective plane oriented
at -45.degree. to the x axis. A blue-color liquid crystal display
panel DB for a blue color display is disposed adjacently to and to
the left of the first polarizing beam splitter 4.
[0025] A second polarizing beam splitter 9 is disposed adjacently
to and to the right of the dichroic mirror 3 with its reflective
plane oriented at -45.degree. to the x axis. Disposed adjacently to
the second polarizing beam splitter 9 are a first phase plate 6 to
on the dichroic-mirror 3 side thereof, a green-color liquid crystal
display panel DG for a green color display below the second
polarizing beam splitter 9, and a red-color liquid crystal display
panel DR for a red color display to the right of the second
polarizing beam splitter 9.
[0026] A dichroic prism 5 is disposed above the second polarizing
beam splitter 9 (to the right of the first polarizing beam splitter
4) with its reflective plane oriented at 45.degree. to the x axis.
A second phase plate 10 is disposed between the second polarizing
beam splitter 9 and the dichroic prism 5. A projection lens 7 is
disposed above the dichroic prism 5.
[0027] In the liquid crystal projector having the above optical
system, light from the light source 1 enters the illuminating
optical system 2 and the polarizer 21, is collimated, and produces
so-called s-polarized light having a homogenized distribution. The
light from the illuminating optical system 2 enters the dichroic
mirror 3, then a blue light LB of the light is reflected at
90.degree. from the x axis, and the yellow light of the light is
transmitted. Here, although, instead of the dichroic mirror 3, a
dichroic prism similar to the dichroic prism 5 explained
subsequently can be used, this embodiment uses the dichroic mirror
3 for weight reduction of the liquid crystal projector.
[0028] After having changed its optical path, the blue light LB
enters the first polarizing beam splitter 4, then changes its
optical path through an angle of 90.degree. and enters the
blue-color liquid crystal display panel DB disposed adjacently to
the first polarizing beam splitter 4.
[0029] The blue-color liquid crystal display panel DB comprises an
envelope formed of two opposing transparent substrates with a
spacing therebetween, liquid crystal sandwiched between the two
substrates and a large number of pixel electrode formed in a matrix
fashion between inner surfaces of the two substrates, and light
transmission through the liquid crystal in each of the pixels is
controlled by external video signals.
[0030] The liquid crystal display panel DB in this embodiment is of
the reflection type. Light from the first polarizing beam splitter
4 passes through the liquid crystal the light transmission through
which is controlled in the respective pixels, then is reflected by
a reflective plate (or a reflective film) provided to the liquid
crystal display panel DB, then the reflected light is modulated by
the liquid crystal and enters the first polarizing beam splitter 4
again.
[0031] The liquid crystal projector of this embodiment includes the
red-color liquid crystal display panel DR and the green-color
liquid crystal display panel DG as subsequently described, in
addition to the blue-color liquid crystal display panel DB, and the
red-color and blue-color liquid crystal display panels DR, DG are
similar in configuration to the blue-color liquid crystal display
panel DB. The three liquid crystal display panels DB, DG, DR are
driven by video signals of corresponding colors, respectively,
supplied simultaneously.
[0032] The reflected light from the blue-color liquid crystal
display panel DB enters the dichroic prism 5 after passing through
the first polarizing beam splitter 4. The dichroic prism 5 changes
the optical path of the blue light LB into a direction at an angle
of 90.degree. with respect to the x axis, and passes red light LR
and green light LG therethrough.
[0033] The blue light LB entered into the dichroic prism 5 is
directed toward the projection lens 7 by the dichroic prism 5, and
then is projected onto a screen 8 positioned separately from the
liquid crystal projector by the projection lens 7.
[0034] The yellow light having passed through the dichroic mirror 3
passes through the first phase plate 6, and is split into the green
light LG and the red light LR by the first phase plate 6. The first
phase plate 6 rotates the direction of polarization of wavelengths
in the region of red only through 90.degree..
[0035] The red light LR enters the second polarizing beam splitter
9, passes through it, then enters the red-color liquid crystal
display panel DR disposed adjacently to it, then is reflected by
the red-color liquid crystal display panel DR, and then enters the
second polarizing beam splitter 9 again.
[0036] The path of the red light LR modulated by the liquid crystal
of the red-color liquid crystal display panel DR is changed by an
angle of 9.degree. with respect to the x axis by the second
polarizing beam splitter 9, and then the direction of the
polarization of the red light is rotated through 90.degree. by the
second phase plate 10, and then the red light LR passes through the
dichroic prism 5.
[0037] The red light LR passing through the dichroic prism 5 is
combined with the already explained blue light LB, and then
projected onto the screen 8 via the projection lens 7.
[0038] The green light LG passes unchanged through the first phase
plate 6, then its path is changed by an angle of -90.degree. with
respect to the x axis by the second polarizing beam splitter 9,
then the green light LG enters the green color liquid crystal
display panel DG disposed adjacently to the second polarizing beam
splitter 9, then is reflected by the liquid crystal display panel
DG, and then enters the second polarizing beam splitter 9. The
green light LG reflected by the green color liquid crystal display
panel DG has been modulated by the green color liquid crystal
display panel DG, then passes through the second polarizing beam
splitter 9, then passes through the second phase plate 10, and
passes through the dichroic prism 5.
[0039] The green light LG passing through the dichroic prism 5 is
combined the already described blue and red lights LB, LR is
projected onto the screen 8 via the projection lens 7.
[0040] In the above configuration, in combining the three color
lights, it is conceivable to use a mirror similar to the dichroic
mirror 3 instead of the dichroic prism 5. However, it was confirmed
that it is not desirable to use such a mirror as the output stage
of the optical system because coma is liable to occur.
[0041] As is apparent from the above explanation, in the
above-described liquid crystal projector, two liquid crystal
display panels DG, DR can be disposed with the second polarizing
beam splitter 9, and consequently, the liquid crystal projector of
the above configuration is capable of being made smaller in size
than the conventional liquid crystal projector requiring a
polarizing beam splitter for each of the liquid crystal display
panels.
[0042] The dichroic mirror 3 is used instead of a dichroic prism,
for reflecting the blue light LB, for example, in light from the
light source 1 and transmitting the green light LG and the red
light LR, and consequently, the liquid crystal projector is capable
of being made lightweight. In this case, there is possibility that
the dichroic mirror causes aberration, unlike the prism, but the
aberration at the input stage of the optical system causes no
particular problems.
[0043] Two liquid crystal display panels DG and DR are capable of
being disposed at the two mutually perpendicular sides of the
polarizing beam splitter 9, respectively, and consequently, they do
not need to be disposed to face each other with the polarizing beam
splitter 9 interposed therebetween. As a result, light incident on
one of the two liquid crystal display panels does not enter the
other of the two liquid crystal display panels, and therefore the
display contrast ratio is improved.
[0044] If a phase plate 20 is disposed between the first polarizing
beam splitter 4 and the dichroic prism 5 for rotating the
polarization direction of the light passing therethrough through
90.degree. as indicated by a broken line in FIG. 1, the polarized
light is converted into the s-polarized light, and as a result, the
blue light LB is efficiently reflected by the dichroic prism 5 and
the light utilization efficiency is improved.
[0045] Insertion of the phase plate 20 or a glass plate between the
first polarizing beam splitter 4 and the dichroic prism 5 can
equalize the optical path lengths of the lights emergent from the
liquid crystal display panels DR, DG and DB.
[0046] Unwanted reflections in the optical paths can be reduced by
cementing together the first polarizing beam splitter 4, the phase
plate 20 or the glass plate, the dichroic prism 5, the second phase
plate 10, the second polarizing beam splitter 9 and the first phase
plate 6, and consequently, the display contrast ratio can be
improved.
[0047] The above-described liquid crystal projector uses the
reflection type liquid crystal display panel, but the present
invention is not limited to the reflection type liquid crystal
display panel, and the present invention can utilize the
transmission type liquid crystal display panel. When the
transmission type liquid crystal display panel is used in the
present invention, the above-described basic configuration is the
same except for some modifications in the optical system.
[0048] As is apparent from the above explanation, the liquid
crystal projector in accordance with the present invention realizes
reduction of its size and its weight.
[0049] The following explains the liquid crystal display panel used
in the liquid crystal projector in accordance with the present
invention.
[0050] FIGS. 2A and 2B are schematic illustrations for operation of
a reflection type liquid crystal display panel of a
single-polarizer twisted-nematic mode (SPTN) which is one of
electrically controlled birefringent modes. For the sake of
clarity, FIG. 2 illustrates the configuration of the liquid crystal
display panel 100 schematically. Details of the liquid crystal
display panel 100 will be described subsequently. Structures
related to splitting and combining of colors are omitted in FIGS.
2A and 2B.
[0051] In FIGS. 2A and 2B, reference numeral 105 denotes a
reflective electrode formed on one substrate (not shown), 106 is a
counter electrode formed on the other substrate (not shown), and
103 is a liquid crystal composition. Reference numeral 109 denotes
a polarizing beam splitter which divides an incident light L1 from
a light source (not shown) into two polarized lights, and a
linearly polarized one L2 of the two.
[0052] In FIGS. 2A and 2B, a light having passed through the
polarizing beam splitter 109, which is a p-polarized light, is
entered into the liquid crystal display panel 100, but a light
reflected by the polarizing beam splitter 109, which is an
s-polarized light, can be entered into the liquid crystal display
panel 100 instead.
[0053] The liquid crystal composition 103 is a nematic liquid
crystal material having positive dielectric anisotropy.
Longitudinal axes of the liquid crystal molecules are oriented in
parallel with the major surfaces of the reflective electrode 105
and the counter electrode 106, and the liquid crystal molecules are
twisted across the liquid crystal layer by about 90.degree. by the
orientation films formed on the reflective electrode 105 and the
counter electrode 106 when a voltage is not applied between the
reflective electrode 105 and the counter electrode 106.
[0054] FIG. 2A illustrates a case where no voltage is applied
between the reflective electrode 105 and the counter electrode 106.
The light L2 entering the liquid crystal display panel 100 is
converted into elliptically polarized light by birefringence of the
liquid crystal composition 103, and then becomes circularly
polarized light on the reflective electrode 105. The light
reflected by the reflective electrode 105 passes through the liquid
crystal composition 103 again, thereby becomes elliptically
polarized light again, and then returns to linearly polarized light
again when it leaves the liquid crystal display panel 100. The
emergent linearly polarized light L3 is s-polarized light having
its direction of polarization rotated through an angle of
90.degree. with respect to that of the incident light L2, enters
the polarizing beam splitter 109 again, and then is reflected by an
internal interface of the polarizing beam splitter 109 to become
emergent light L4 which is projected onto a screen or the like to
provide a display. This configuration is of the so-called normally
white (normally open) type which emits light when a voltage is not
applied across the liquid crystal layer.
[0055] FIG. 2B illustrates a case where a voltage is applied
between the reflective electrode 105 and the counter electrode 106.
When an electric field is applied to the liquid crystal composition
103, the liquid crystal molecules align in a direction of the
electric field and consequently, the influence of birefringence of
the liquid crystal molecules weakens. As a result, the linearly
polarized light L2 entering the liquid crystal display panel 100 is
reflected by the reflective electrode 105 without undergoing
changes, and then the light L5 emergent from the liquid crystal
display panel 100 has the same direction of polarization as that of
the incident light L2. The emergent light L5 passes through the
polarizing beam splitter 109, and returns to the light source such
that no light is projected onto the screen and a black display is
provided on the screen.
[0056] In the single-polarizer twisted nematic type, the direction
of orientation of the liquid crystal molecules is parallel with the
major surfaces of the substrates carrying the reflective electrode
105 and the counter electrode 106, and therefore usual methods of
orientating the liquid crystal molecules can be employed and
stability in manufacturing process is high. The normally white mode
operation is preventive of defective displays occurring at low
voltage levels. The reason is that, in the normally white mode, a
dark level (a black display) is provided when a high voltage is
applied across the liquid crystal layer, and in this state, almost
all the liquid crystal molecules are orientated in the direction of
the electric field which is perpendicular to the major surfaces of
the substrates, and consequently, a display of the dark level does
not depend very much upon the initial conditions of orientation of
the liquid crystal molecules having a low electric field applied
thereto.
[0057] The human eye perceives non-uniformity in luminance based
upon the ratio of luminances, is responsive approximately to the
logarithm of luminance, and consequently, is sensitive to
variations in dark levels.
[0058] Because of the above reasons, the normally white mode has
advantages with respect to prevention of non-uniformity in
luminance caused by initial conditions of orientation of the liquid
crystal molecules.
[0059] The electrically controlled birefringence mode requires a
highly precise cell gap between the substrates of the liquid
crystal display panel. The electrically controlled birefringence
mode utilizes a phase difference between ordinary rays and
extraordinary rays caused while they pass through the liquid
crystal layer, and therefore the intensity of the light
transmission through the liquid crystal layer depends upon the
retardation .DELTA.n.multidot.d between the ordinary and
extraordinary rays, where .DELTA.n is a birefringence and d is a
cell gap established by spacers between the substrates of the
liquid crystal display panel.
[0060] In this embodiment, considering non-uniformity in a display,
the manufacturing tolerance of the cell gap is chosen to be
.+-.0.05 .mu.m.
[0061] In the reflection type liquid crystal display panel, light
entering the liquid crystal layer is reflected by the reflective
electrode, and then passes through the liquid crystal layer.
Therefore, if liquid crystal compositions having the same
birefringence .DELTA.n are used, the cell gap d of the reflection
type is set to be half that of the transmission type. In the usual
transmission type liquid crystal display panels, the cell gap is
about 5 .mu.m to about 6 .mu.m, and therefore the cell gap in this
embodiment is about 2 .mu.m.
[0062] In this embodiment, to secure the smaller and high-precision
cell gap, column-like spacers are used instead of using a
conventional method of dispersing beads between the substrates.
[0063] FIG. 3 is a schematic plan view of a driving circuit
substrate 101 having the reflective electrodes 105 thereon. On the
driving circuit substrate 101 is disposed the reflective electrodes
105 and the spacers 104. The spacers 104 are disposed in a matrix
fashion over the entire driving circuit substrate 101 to ensure the
high precision cell gap. Each of the reflective electrodes 105
forms a minimum pixel for forming an image on the liquid crystal
display panel. For the sake of simplicity, FIG. 3 illustrates an
array of five columns by four rows of pixels.
[0064] In FIG. 3, the array of five columns by four rows of pixels
forms a display area, in which a display by the liquid crystal
display panel is formed. Dummy pixels 110 are disposed around the
display area, a peripheral frame 111 made of the same material as
that of the spacers 4 is disposed around the dummy pixels 110, and
a sealing member 112 is coated around the peripheral frame 111 on
the driving circuit substrate 101. Reference numeral 113 denotes
terminals for external connections which are used for supplying
external signals to the liquid crystal display panel 100.
[0065] The spacers 104 and the peripheral frame 111 are formed of
resin material which is a negative photoresist of the chemically
sensitized type "BPR-113" (trade name) manufactured by JSR Co. Ltd.
(Japan), for, example. The photoresist material is coated on the
driving circuit substrate 101 having the reflective electrodes 105
thereon by spin coating, or the like, then the photoresist coating
is exposed to form patterns of the spacers 104 and the peripheral
frame 111 through a mask and by a light source, and then the
photoresist coating is developed to form the spacers 104 and the
peripheral frame 111 by using a remover.
[0066] The spacers 104 and the peripheral frame 104 made of the
photoresist material or the like can be fabricated with high
precision because their height can be controlled by the thickness
of the coating. The positions of the spacers 104 are determined by
the pattern of the mask, and consequently, the spacers 104 are
capable of being positioned at their desired positions with
accuracy.
[0067] In the liquid crystal projector, if the spacers 104 are
present in the pixels, a problem arises that the shadows of the
spacers 104 appear in an enlarged projected image. The spacers 104
fabricated by exposure through the pattern mask and subsequent
development are capable of being disposed so as not to interfere
with a displayed image.
[0068] The peripheral frame 111 is fabricated simultaneously with
the spacers 104, and as a result, the liquid crystal composition
103 can be filled into a space between the driving circuit
substrate 101 and a transparent substrate 102 (see FIG. 4) by
dropping a small quantity of the liquid crystal composition 103 on
the driving circuit substrate 101 and then attaching the
transparent substrate 102 to the driving circuit substrate 101 and
sealing them together.
[0069] When the liquid crystal display panel 100 is assembled after
interposing the liquid crystal composition 103 between the driving
circuit substrate 101 and the transparent substrate 102, the liquid
crystal composition 103 is held within a region surrounded by the
peripheral frame 111.
[0070] The sealing member 112 is coated around the outside of the
peripheral frame 111 and confines the liquid crystal material 103
within the liquid crystal display panel 100.
[0071] As described above, the peripheral frame 111 is fabricated
by using the pattern mask, and therefore it is fabricated on the
driving circuit substrate 101 with high positional accuracy, and
consequently, the border of the liquid crystal composition 103 can
be defined with high accuracy. Further, the peripheral frame 111
can define the border of the sealing member 112 with high
accuracy.
[0072] The sealing member 112 serves to fix the driving circuit
substrate 101 and the transparent substrate 102 together, and also
serves to prevent materials harmful to the liquid crystal
composition 103 from penetrating thereinto. When the fluid sealing
member 112 is applied, the peripheral frame 111 serves as a stopper
against the sealing member 112. By disposing the peripheral frame
111 as the stopper against the sealing member 112, the design
margin at the border of the liquid crystal composition 103 and that
at the border of the sealing member 112 can be made smaller, and
consequently, the region between the display area and the
peripheral sides of the liquid crystal display panel 100 can be
reduced, resulting in the reduction of the peripheral border around
the display area.
[0073] The peripheral frame 111 is fabricated to surround the
display area, and as a result, a problem arises in that, in
performing a rubbing treatment on the surface of the driving
circuit substrate 101 for orientating the liquid crystal molecules,
the peripheral frame 111 impedes the rubbing treatment of the
surface in the vicinity of the peripheral frame 111. In this
embodiment, a liquid crystal molecule orientation film (not shown)
is coated on the driving circuit substrate 101 after the spacers
104 and the peripheral frame 111 are fabricated on the driving
circuit substrate 101, and then the rubbing treatment is performed
by rubbing the liquid crystal molecule orientation film with a
cloth or the like such that the rubbed orientation film orients the
liquid crystal molecules of the liquid crystal composition 103 in a
specified direction.
[0074] In the rubbing treatment, because the peripheral frame 111
is raised above the surface of the driving circuit substrate 101,
the orientation film in the vicinity of the peripheral frame 111 is
not rubbed sufficiently because of the step formed by the
peripheral frame 111, and consequently, non-uniformity in
orientation of the liquid crystal molecules is apt to occur in the
vicinity of the peripheral frame 111. In order to make
inconspicuous non-uniformity in a display caused by defective
orientation of the liquid crystal molecules, some of the pixels
immediately inside the peripheral frame 111 are made dummy pixels
110 which do not contribute to a display.
[0075] However, if the dummy pixel electrodes 110 are supplied with
signals like the pixels 105 are supplied with signals, a problem
arises in that displays produced by the dummy pixels 110 are also
observed by the viewer because of presence of the liquid crystal
composition 103 between the dummy pixels 110 and the transparent
substrate 102. In the liquid crystal display panel of the normal
white type, the dummy pixels 110 appear white when a voltage is not
applied across the liquid crystal layer, and consequently, the
border of the display area becomes ill-defined and the quality of a
display is deteriorated. It is conceivable to mask the dummy pixels
110, but it is difficult to fabricate a light-blocking frame at the
border of the display area accurately because of a spacing of a few
microns between the pixels, and therefore the dummy electrodes 110
are supplied with such a voltage that the dummy electrodes 110
display black images which appear as a black peripheral frame
surrounding the display area.
[0076] Next, a pixel area in a liquid crystal display device in
accordance with the present invention will be explained by
reference to FIG. 4. FIG. 4 is a schematic cross-sectional view for
explaining an embodiment in accordance with the present invention.
In FIG. 4, reference numeral 100 denotes the liquid crystal display
panel, 101 is the driving circuit substrate, 102 is the transparent
substrate, 103 is the liquid crystal composition, and 104 are the
spacers. The spacers 104 establish a fixed cell gap d between the
driving circuit substrate 101 and the transparent 102. The liquid
crystal composition 103 is confined in the cell gap d. Reference
numeral 105 are reflective electrodes formed on the driving circuit
substrate 101. Reference numeral 106 is the counter electrode which
serves to apply a voltage across the layer of the liquid crystal
composition 103 in cooperation with the reflective electrodes 105.
Reference numerals 107 and 108 are orientation films which serve to
orient the liquid crystal molecules in a specified direction.
Reference numeral 30 are active elements for supplying a voltage to
the reflective electrodes 105.
[0077] Reference numeral 34 denotes drain regions, 35 are source
regions, 36 are gate electrodes, 38 is an insulating film, 39 are
field oxide films for electrically separating adjacent transistors
from each other, and 40 are retaining electrodes which form
capacitances with the driving circuit substrate 1 with the
insulating film 38 therebetween. Reference numeral 41 denotes a
first interlayer film, 42 is a first conductive film, 43 is a
second interlayer film, 44 is a first light-blocking film, 45 is a
third interlayer film, 46 is a second lightblocking film, 47 is a
fourth interlayer film, and 48 are second conductive films forming
the reflective electrodes 5.
[0078] The liquid crystal display panel of this embodiment is of
the reflection type. Light projected to the liquid crystal display
panel 100 enters the transparent substrate 102 (at the top of FIG.
4), passes through the liquid crystal composition 103, then is
reflected by the reflective electrodes, and again passes through
the liquid crystal composition 103, passes through the transparent
substrate 102, and exits from the liquid crystal display panel
100.
[0079] In a liquid crystal display panel of the reflection type,
when the reflective electrode 105 is disposed on the surface of the
driving circuit substrate 101 on the liquid crystal composition 103
side thereof, an opaque substrate such as a silicon substrate can
be used as the driving circuit substrate 101, and further, the
active elements 30 and wiring can be disposed below the reflective
electrodes 105, and consequently, the advantage is obtained that
the area of the respective reflective electrodes 105 which serve as
pixels is made larger and therefore the so-called high aperture
ratio is realized. Another advantage is that heat generated by the
light projected to the liquid crystal display panel 100 is radiated
from the rear surface of the driving circuit substrate 101.
[0080] FIG. 5 is a perspective view of the driving circuit
substrate 101 superposed with the transparent substrate 102. Formed
at the periphery of the driving circuit substrate 101 is the
peripheral frame 111, and the liquid crystal composition 103 is
confined in a space surrounded by the peripheral frame, the driving
circuit substrate 101 and the transparent substrate 102. The
sealing member 112 is coated around the outside of the peripheral
frame 111 between the superposed driving circuit substrate 101 and
transparent substrate 102. The driving circuit substrate 101 and
the transparent substrate 102 are fixed together by the sealing
member 112 to form the liquid crystal display panel 100.
[0081] Next, as shown in FIG. 6, a flexible printed wiring board 80
is connected to the terminals 113 for external connections which
are used for supplying external signals to the liquid crystal
display panel 100. Two outermost terminals on opposite sides of one
end of the flexible printed wiring board 80 are made longer than
the remainder of terminals, are connected to the counter electrode
106 formed on the transparent substrate 102, and thereby serve as
counter-electrode terminals 81. In this way, the flexible printed
wiring board 80 is connected to both of the driving circuit
substrate 101 and the transparent substrate 102.
[0082] Conventionally, a flexible printed wiring board is connected
to terminals for external connections disposed on the driving
circuit substrate 101 only, and therefore the wiring to the counter
electrode 106 from the flexible printed wiring board is made via
the driving circuit substrate 101.
[0083] The transparent substrate 102 in this embodiment of the
present invention is provided with connecting portions 82 to be
connected to the flexible printed wiring board 80 such that the
flexible printed wiring board 80 is connected directly to the
counter electrode 105. The liquid crystal display panel 100 is
formed by superposing the transparent substrate 102 on the driving
circuit substrate 101. The transparent substrate 102 is superposed
on the driving circuit substrate 101 such that a peripheral portion
of the transparent substrate 102 extends beyond the outside edges
of the driving circuit substrate 101 and provides the connecting
portions 82 where the flexible printed wiring board 80 is connected
to the counter electrode 106.
[0084] FIGS. 7 and 8 illustrate a configuration of the liquid
crystal display device 200. FIG. 7 is an exploded view in
perspective of the major elements of the liquid crystal display
device 200, and FIG. 8 is a plan view of the liquid crystal display
device 200.
[0085] As shown in FIG. 7, the liquid crystal display panel 100
having the flexible printed wiring board 80 connected thereto is
disposed on the heat-radiating plate 62 with a cushion member 61
interposed therebetween. The cushion member 61 is highly
heat-conductive, and fills a gap between the heat-radiating plate
62 and the liquid crystal display panel 100 for heat from the
liquid crystal display panel 100 to conduct to the heat-radiating
plate 62 easily. Reference numeral 63 denotes a mold, which is
fixed to the heat-radiating plate 62 with an adhesive.
[0086] As shown in FIG. 8, the flexible printed wiring board 80 is
passed between the mold 63 and the heat-radiating plate 62, and
then is brought out of the mold 63. Reference numeral 65 denotes a
light-blocking plate which prevents light from a light source from
entering the unintended portions of the liquid crystal display
device 200, and 66 is a light-blocking frame which defines the
display area of the liquid crystal display device 200.
* * * * *