U.S. patent application number 09/911805 was filed with the patent office on 2001-12-20 for liquid crystal display device.
Invention is credited to Hirota, Syoichi, Matsumoto, Katsumi, Miyazawa, Toshio, Saito, Katsutoshi, Takemoto, Iwao.
Application Number | 20010052960 09/911805 |
Document ID | / |
Family ID | 16838477 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010052960 |
Kind Code |
A1 |
Saito, Katsutoshi ; et
al. |
December 20, 2001 |
Liquid crystal display device
Abstract
A method for forming a liquid crystal display device includes
forming a metal film over a drive substrate, and patterning the
metal film to form at least one pixel electrode and an optical
shield film. The optical shield film is provided outside of a pixel
electrode area and has a width greater than a width of each of the
pixel electrode. A resin is deposited over the patterned metal
film, and the resin is patterned to form at least one pole spacer
and strip spacer. The strip spacer surrounds the pixel electrode
area and has a width greater than a diameter of each of pole
spacer. Liquid crystal material is supplied into an inside space
which is surrounded by the strip spacer, and a sealing material is
filled at outer edges of the strip spacer for fixing the drive
substrate and a common substrate.
Inventors: |
Saito, Katsutoshi;
(Mobara-shi, JP) ; Hirota, Syoichi; (Hitachi-shi,
JP) ; Takemoto, Iwao; (Mobara-shi, JP) ;
Miyazawa, Toshio; (Chiba-shi, JP) ; Matsumoto,
Katsumi; (Mobara-shi, JP) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
16838477 |
Appl. No.: |
09/911805 |
Filed: |
July 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09911805 |
Jul 25, 2001 |
|
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|
09370245 |
Aug 9, 1999 |
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6304308 |
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Current U.S.
Class: |
349/155 |
Current CPC
Class: |
G02F 1/133512 20130101;
G02F 2203/02 20130101; G02F 1/13394 20130101 |
Class at
Publication: |
349/155 |
International
Class: |
G02F 001/1339 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 1998 |
JP |
10-226016 |
Claims
What is claimed is:
1. A method for forming a liquid crystal display device, comprising
the steps of: forming a metal film over a drive substrate;
patterning said metal film to form at least one pixel electrode and
an optical shield film, said optical shield film being provided
outside of a pixel electrode area and having a width greater than a
width of each of said pixel electrode; depositing a resin over said
patterned metal film; patterning said resin to form at least one
pole spacer and a strip spacer, said strip spacer surrounding said
pixel electrode area and having a width greater than a diameter of
each of said pole spacer and being formed over said optical shield
film; supplying liquid crystal material into an inside space which
is surrounded by said strip spacer; disposing a common substrate
over said drive substrate; and filling a sealing material at outer
edges of said strip spacer for fixing said drive substrate and
common substrates.
2. The method according to claim 1, wherein said resin depositing
is effected by spin coat.
3. The method according to claim 1, wherein said resin is a
photolithographically fabricated resist.
4. The method according to claim 1, wherein said pixel electrode is
a reflective pixel electrode.
5. A method for forming liquid crystal display device, comprising
the steps of: forming a metal film over a drive substrate;
patterning said metal film to form at least one pixel electrode and
an optical shield film, said optical shield film being provided
outside of a pixel electrode area and having a width greater than a
width of each of said pixel electrode; depositing a resin over said
patterned metal film; patterning said resin to form at least one
columnar spacer and a zonal spacer, said zonal spacer surrounding
said pixel electrode area and having a width greater than a
diameter of each of said columnar spacer and being formed over said
optical shield film; supplying liquid crystal material into an
inside space which is surrounded by said zonal spacer; disposing a
common substrate over said drive substrate; and filling a sealing
material at outer edges of said zonal spacer for fixing said drive
substrate and common substrates.
6. The method according to claim 5, wherein said resin depositing
is by effected spin coat.
7. The method according to claim 5, wherein said resin is a
photolithographically fabricated resist.
8. The method according to claim 5, wherein said pixel electrode is
a reflective pixel electrode.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a continuation of U.S. application Ser. No.
09/370,245, filed Aug. 9, 1999, the subject matter of which is
incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to liquid crystal
display devices; and, more particularly, the invention relates to a
liquid crystal display device that maintains a uniform gap for a
liquid crystal layer, to a liquid crystal display device that can
prevent optical leakage in the display area, and to a liquid
crystal display device that can prevent pollution in the liquid
crystal composite material by the seal agent.
[0003] Recently, display devices using a liquid crystal panel have
become more widely employed as display devices which are capable of
visually producing high-precision color images adaptable for use in
display devices of the projection type, in notebook personal
computers, in monitor units and in other similar visual
representation instruments.
[0004] Currently available display devices using such a liquid
crystal panel (liquid crystal display devices) typically include
those of the simple matrix type, which make use of a liquid crystal
panel having a liquid crystal layer sandwiched between a pair of
substrates with parallel electrodes formed on respective inner
surfaces in a mutual crossover fashion, and other panels of the
active matrix type which employ a liquid crystal element (referred
to also as "liquid crystal panel" hereinafter) that has switching
elements for selection in units of pixels on only one of the pair
of substrates.
[0005] Active-matrix liquid crystal display devices are generally
categorized into two groups: one group includes certain liquid
crystal display devices of the so-called vertical electric-field
type typically including the twisted nematic (TN) scheme (also
known as TN active-matrix liquid crystal display devices)
configured to include an ensemble of pixel selection electrodes
formed on each of a pair of upper and lower substrates, and a
second group includes the so-called "lateral electric-field" liquid
crystal display devices (generally called in-plane field type IPS
liquid crystal display devices) using a specific liquid crystal
panel with pixel select electrodes formed on only one of a pair of
upper and lower substrates.
[0006] Projection liquid crystal display devices are also known as
one type of liquid crystal display device application equipment.
Projection liquid crystal display devices include an optical system
for magnification of an image generated on a liquid crystal panel
of small size to provide an enlarged image which is then projected
onto a spaced-apart second screen of large size. Such projection
liquid crystal display devices include devices of the transmission
type and those of the reflection type, the former being designed
such that two separate dielectric substrates making up a liquid
crystal panel are both formed of transparent substrates, such as
glass substrates by way of example, for permitting rays of light to
be emitted from the back surface thereof to thereby cause resulting
modulated transmission light images to be projected with enlarged
sizes on an associative screen by use of an optical lens or
combination thereof. On the other hand, the reflective projectors
employ one of such dielectric substrates as a reflector plate for
emitting light from the surface side to thereby produce an image
which consists of modulated reflected light, which in turn is
projected by an optical system on a screen with a magnified
scale.
[0007] There are also display devices for use with notebook PCs or
direct view liquid crystal display devices for display monitors,
which are designed to employ as a reflector plate either one of the
dielectric substrates making up the liquid crystal panel and which
utilizes incoming light from the display surface side.
[0008] Typically, a liquid crystal panel constituting such a liquid
crystal display device is arranged so that a liquid crystal layer
made of a chosen liquid crystal material is sandwiched in a gap
between two separate dielectric substrates which are bonded
together, such as glass substrates, for example, and thereafter the
peripheral edges thereof are sealed using a chosen seal material.
The gap between two dielectric substrates is narrow and typically
will measure less than 4 to 7 micrometers (.mu.m) for instance,
which gap will be collectively referred hereinafter as a "cell
gap". One prior known method of retaining this cell gap is to
randomly distribute spherical spacers of substantially uniform
diameter, sometimes called beads, between the substrates.
[0009] Although controllability of the cell gap may readily be
enhanced by increasing the requisite number of beads that are
distributed, the distribution amount has generally been set at 150
pieces per square millimeter in view of the fact that random
distribution of such beads inherently lacks uniformity thereby
making it very difficult to completely prevent some beads from
locally crowding together at a location. This can result in an
increase in the number of optical dot-like dislocations, and the
random bead distribution also causes an adverse reaction, such as
creation of an undesired disturbance in the alignment of the liquid
crystals near or around such beads, which would result in a
contrast reduction becoming greater locally.
[0010] While the beads may be made of an organic polymer or quartz,
use of quartz beads can cause destruction of any one of the
protective films, the electrodes, and the switching elements, such
as TFTs, which are fabricated on a dielectric substrate at a
press-machining step for establishment of the cell gap, or
alternatively result in unwanted creation of air holes or "bubbles"
with a change in temperature due to a difference in the thermal
expansion coefficient between the beads and a liquid crystal
material being used. For this reason organic polymer beads are
employed in most cases.
[0011] In direct-view liquid crystal display devices, the beads
which are distributed often attempt to move or "drift" upon
application of a stress to the dielectric substrate. In this
respect, it will be desirable for the liquid crystal layer to be
kept at negative pressures relative to the atmospheric; however,
presently available manufacturing technologies make it difficult to
constantly maintain such a state in which the liquid crystal panel
products are constantly held in a negative pressure condition.
[0012] On the other hand, small size liquid crystal display devices
for use in projector equipment are burdened with a problem in that
certain beads distributed between dielectric substrates of its
liquid crystal panel, which reside in the panel's display area, can
unintentionally be projected on a screen as a magnified shadow
image, which in turn results in a decrease in the quality of the
picture images being displayed. One prior known approach to
avoiding such image quality reduction is to employ what is called a
"beads-less" scheme which uses a limited number of beads or fibers
only at the periphery of the liquid crystal panel's display area to
thereby retain the intended cell gap at such periphery only.
Unfortunately, this beads-less approach suffers from a difficulty
in maintaining the cell gap in the display area at a predetermined
value, which can result in a decrease in the production yield and
in image quality.
[0013] Further, in recent years, high-speed image displayability
has been demanded, which in turn calls for establishment of
so-called "narrow gap" designs for further reduction of cell gaps
with increased gap control accuracies of 0.1 .mu.m or below. As
such narrow-gap designs are becoming more important, a need is felt
to further increase the bead-spacer machining accuracy, which
however is very difficult, especially in prior art reflective
liquid crystal panels, wherein achievement of such high machining
accuracy remains extremely difficult due to the fact that the cell
gaps are nearly half the size of those in the devices of the
transmission type.
[0014] One proposed approach to avoiding the cell-gap problem is to
form, by photolithography techniques, columnar or pillar-shaped
spacers (referred to hereinafter as "pole-like spacers") on a
dielectric substrate at selected locations (certain portions that
do not affect displayability, such as portions between adjacent
pixels or alternatively those immediately underlying a black
matrix) in the display area thereof, which spacers provide support
between the two dielectric substrates stacked over each other to
thereby render the cell gap uniform.
[0015] Use of such pole-like spacers eliminates local crowding and
unwanted drift movement of distributed beads. Furthermore, as the
fabrication accuracy of photolithography is significantly greater
than the machining accuracy of beads by one order of magnitude or
greater, the height of the pole spacers is simply determinable
depending upon the thickness of the deposited photoresist film
constituting these pole spacers, which in turn makes it possible to
noticeably improve the cell gap accuracy.
SUMMARY OF THE INVENTION
[0016] Unfortunately, currently available photoresist materials can
dissolve into a liquid crystal material, so as to undesirably
reduce the electrical resistivity of the liquid crystal layer,
which would result in a decrease in co-useability or "congeniality"
with respect to the liquid crystal materials. Alternative use of
inorganic materials therefor can result in a mismatch of the
thermal expansion coefficient with the liquid crystal layer. All in
all, no optimal materials adaptable for use in fabricating the
intended spacers have been reported to date.
[0017] One typical prior known approach to controlling the cell gap
is to mix either fibers or beads made of organic polymer or quartz
as a filler into a seal material being deposited at the outer
periphery of a display area. However, this approach also creates a
problem in that the use of a quartz filler(s) can result in
destruction of the lead terminal electrodes and/or switching
circuitry, as in the case of employing beads distributed within the
display area. While it is also considered effective to coat a seal
material at specific portions lying outside of a switching
circuitry formation region of the display area, this inherently
creates a serious problem in that the resulting liquid crystal
panel increases in size due to a need to reserve an extra area for
seal portions. Another problem encountered in the prior art is
difficultly in improving the accuracy of the cell gap because of
the fact that organic polymer beads are readily collapsible; and,
in view of this, it is a general approach to employ fibers for the
seal portions.
[0018] A known sealing method includes the steps of coating, by use
of screen printing techniques or using dispensers or the like, one
of two dielectric substrates with a filler-mixed seal material in a
selected region along the outer periphery of its display area,
laminating the other dielectric substrate over the seal
material-coated substrate, pressing these substrates together at
increased pressures to permit the seal material sandwiched
therebetween to sheet against the substrate surface for
establishment of the intended cell gap, and then hardening the seal
material sheet. A disadvantage of this method is that it remains
impossible, or at least greatly difficult, to attain the required
accuracy of position alignment at the seal edge portions, which
results in the seal portions becoming irregular in shape. An
optical blocking or shielding means must be additionally provided
to preclude unintentional visualization of such an irregular seal
edge shape. Especially with small size liquid crystal panels, use
of such optical shield means can result in an increase in the
surface area for use in sealing.
[0019] An object of the present invention is to provide an improved
liquid crystal display device which is capable of eliminating
display irregularities by avoiding random behavior (either local
crowing or drift movement) of beads in a display area which can
occur when using beads, as well as destruction of switching
elements and electrodes or the like due to presence of fillers
contained in beads or seal materials, along with cell gap
differences in the liquid crystal panel occurring in the display
area and at sealed portions, while at the same time enabling
achievement of high-quality displayability by precluding
contamination of a liquid crystal material due to unwanted contact
between the seal material and the liquid crystal layer.
[0020] To attain the foregoing object the present invention, spaces
are formed photolithographically both in a display surface area of
one dielectric substrate of a liquid crystal panel constituting the
liquid crystal display device and at sealed portions thereof at the
same time. The spacers formed within the display area are comprised
of columnar or pole-like spacers while those formed at the sealed
portions consists of a zonal or band-shaped spacer which has a
width which is greater than the diameter of such pole spacers. A
chosen sealing material containing no fillers therein is deposited
or coated at the outer periphery of this zonal spacer, which
material is later hardened, thus allowing both substrates to be
tightly bonded together.
[0021] With regard to the embodiments disclosed herein, some
representative aspects of the invention will be summarized
below.
[0022] A liquid crystal display device in accordance with the
instant invention is arranged to include a first substrate having
thereon a great number of pixel electrodes in the form of a matrix,
a second substrate opposing said first substrate with a predefined
gap defined between them, a liquid crystal layer made of a liquid
crystal composition material sealed into the gap between said first
and second substrates, and an optical alignment film formed on at
least one of said first and second substrates in contact with said
liquid crystal layer for controlling the optical orientation or
alignment of said liquid crystal material, wherein the device
further includes a plurality of columnar or pole-like spacers
formed in the display surface area of said first substrate for
retaining the size of said gap between said first and second
substrates at a preselected value, while also including a zonal or
band-shaped spacer made of the same material as that of said
pole-like spacers for surrounding said display area and having a
width greater than the diameter of said pole-like spacers, with a
seal material being filled at the outer periphery of said
strip-like spacer for tightly bonding said first and second
substrates together. Note that providing the band spacer avoids the
necessity for the seal material to contain therein beads or fibers
or any equivalents thereto for use in controlling the gap between
the two substrates.
[0023] With such an arrangement, the spacer's inherent random
behavior within the display area may be suppressed or eliminated,
thereby retaining a more uniform resultant cell gap. Another
advantage is that the seal material will no longer come into
contact with the liquid crystal layer thus precluding contamination
of the liquid crystal material due to the presence of seal
material, which in turn makes it possible to avoid destruction of
the electrodes and the like due to the beads in the display area or
alternatively destruction of electrode extension leads and the like
at the sealed portions due to presence of fillers mixed into the
seal material, thus improving the production yields and the
reliability.
[0024] A further advantage is that the pole spacers stay equal in
height to the band spacer with an increased accuracy to thereby
enable the cell gap to be well controlled to a high accuracy over
almost all regions of the display area, which in turn makes it
possible to eliminate visualization irregularities during
displaying of on-screen images, including flutter, moire,
streaking, and pixel jitter at certain intensities.
[0025] Additionally the present invention should not be limited
only to the above-noted arrangements and may alternatively be
modified and altered in a variety of different forms without
departing from the technical concept of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a diagram illustrating, in cross-section, a liquid
crystal panel of a liquid crystal display device in accordance with
one embodiment of the present invention.
[0027] FIG. 2 is a diagram depicting a plan view of the liquid
crystal panel shown in FIG. 1 for explanation of a layout of
columnar spacers and a zonal spacer thereon.
[0028] FIG. 3 is a microphotograph-based pictorial representation
of a plan view of one typical columnar spacer in accordance with
the invention.
[0029] FIG. 4 is a diagram showing a plan view of a liquid crystal
panel of a liquid crystal display device in accordance with a
second embodiment of the invention, for explanation of a layout of
columnar spacers and a zonal spacer thereon.
[0030] FIG. 5 is a diagram showing a plan view of a liquid crystal
panel of a liquid crystal display device in accordance with a third
embodiment of the invention, for explanation of a layout of
columnar spacers and a zonal spacer thereon.
[0031] FIG. 6A is a plan view and FIG. 6B is a cross-section on
line VIB-VIB in FIG. 6A, showing an overall configuration of a
projection-type liquid crystal display device incorporating an
actually implemented-liquid crystal display device of the
invention.
[0032] FIG. 7 is a diagram schematically depicting one exemplary
structure of the projection liquid crystal display device employing
the liquid crystal display device shown in FIG. 6.
[0033] FIG. 8 is a plan view diagram of a liquid crystal panel
constituting an active-matrix liquid crystal display device also
incorporating the principles of the invention.
[0034] FIG. 9 is an enlarged partial plan view diagram of the
liquid crystal panel shown in FIG. 8 showing the upper left part
thereof and its nearby portions with a seal section SL provided
thereon.
[0035] FIGS. 10A, 10B and 10C are diagram showing in cross-section
main parts of a liquid crystal panel constituting the active-matrix
liquid crystal display device embodying the invention.
[0036] FIG. 11 is an exploded perspective view of a direct-view
liquid crystal display apparatus employing a liquid crystal display
device of the invention.
[0037] FIG. 12 is a perspective view of a notebook computer for
explanation of one embodiment of the liquid crystal display device
of FIG. 11.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] Preferred embodiments of the present invention will be
explained in detail with reference to the accompanying
drawings.
[0039] Referring now to FIG. 1, there is illustrated in schematic
cross section a liquid crystal panel in accordance with one
embodiment of the instant invention. This liquid crystal panel is a
reflective liquid crystal panel adaptable for use in projection
liquid crystal display devices, wherein reference character "USUB"
designates an upper-side substrate (opposed substrate) representing
a first substrate; DSUB denotes a lower-side substrate (drive
substrate) representing a second substrate; LC indicates a liquid
crystal layer made of a chosen liquid crystal composition material;
SUB2 represents the glass substrate making up the opposed
substrate; ITO-C specifies a transparent electrode (common
electrode, or alternatively opposed electrode); ORI2 shows an
upper-side optical orientation or "alignment" film; SUB1 is a
single-crystalline silicon substrate constituting the drive
substrate; AL-P denotes pixel electrodes; ORI1 denotes a lower
alignment film; TM denotes a terminal section; PSV1 denotes a
protective film; SPC-P denotes columnar or pole-like spacers; SPC-S
denotes zonal or band strip-shaped spacers; SL denotes a sealing
material; and SHF denotes a light shield film.
[0040] It should be noted that the illustrated liquid crystal panel
is assumed to be of the active matrix type, and that this panel
also includes switching elements for pixel selection and storage
capacitors or the like, not shown, on the drive substrate DSUB
along with the pixel electrodes AL-P shown in FIG. 1.
[0041] The liquid crystal layer LC is sealed and sandwiched between
the opposed substrate USUB with the opposed electrodes ITO-C and
alignment film ORI2 formed thereon and the drive substrate DSUB on
which the pixel electrodes AL-P and protective film PSV1 plus
alignment film ORI1 are formed. The drive substrate DSUB is
associated with the columnar or pole-like spacers SPC-P which are
formed on the protective film PSVl at selected locations excluding
those of the pixel electrodes and also with the zonal or band
strip-shaped spacer SPC-S that is placed at the bonding periphery
the both substrates; that is, along the outer peripheral sides of a
display surface area with the pixel electrodes AL-P and the like
formed therein. The strip-like spacer SPC-S is designed to have a
predefined width that is greater in size or dimension than the
diameter of the pole spacers SPC-P to thereby receive the
compressive pressures which are applied when the two substrates are
bonded and pressed together during assembly for accurately
retaining a cell gap between the substrates at the periphery
thereof while controlling the cell gap of the display area, so that
the gap is held at a predefined value in cooperation with the pole
spacer SPC-P.
[0042] More specifically, upon pressing both substrates together,
the resultant gap space, i.e. the cell gap of the liquid crystal
layer, may be accurately controlled by the height of the pole
spacers SPC-P and strip spacer SPC-S. And, sealing the liquid
crystal layer into the display area or region may be achieved by a
method that includes the steps of dripping a liquid crystal
composition into the display region prior to lamination of the
substrates and then pressing the laminated substrates when bonding
them together while permitting outward draining of any extra liquid
crystal material; or, alternatively, by another method including
the steps of forming in advance or "preforming" an opening at part
of the strip spacer SPC-S, superposing the substrates over each
other, coating a chosen seal material containing therein no fillers
along the outer edges of the strip spacer SPC-S, irradiating
ultraviolet rays for effecting half-hardening thereof, injecting a
liquid crystal material from the opening, while setting the
atmosphere at a negative pressure, and thereafter effectuating
pressing and thermal treatment for complete hardening of the seal
material SL to thereby establish the required cell gap.
[0043] Note that, although not specifically illustrated in the
drawing, in the case of a projection liquid crystal display device,
the terminal section TM is connected to those terminals of a
flexible printed circuit board for use in coupling electrical
signals for driving the involved switching elements.
[0044] FIG. 2 is a diagram showing a plan view of the liquid
crystal panel shown In FIG. 1 for explanation of the planar layout
pattern of the pole spacers and strip spacer. The layout of these
spacers is indicated in positional relation with respect to the
pixel electrodes associated therewith.
[0045] The pole spacers SPC-P that are to be formed in the display
area are provided at crossover locations among the pixel electrodes
AL-P. In this embodiment, providing the pole spacers SPC-P in the
spaces between adjacent pixel electrodes precludes significant
reduction of the aperture ratio. In addition, since it is possible
to provide the pole spacers SPC-P one by one in all the spaces
among pixel electrodes, the resulting setup number of such spacers
is increased by one order of magnitude or greater when compared to
the case of using beads to thereby permit achievement of enhanced
cell gap controllability, which in turn guarantees that any
positional deviation or misalignment will no longer take place
between the two substrates.
[0046] The strip spacer SPC-S is formed to overlie the optical
shield film SHF at the outer periphery of the display area. The
optical shield film SHF is formed by the same layer as the pixel
electrode. This strip spacer SPC-S is so formed as to surround the
outer periphery of the display area while its width is greater than
the diameter of the pole spacers SPC-P. And, this strip spacer
SPC-S has the function of sealing the liquid crystal layer LC while
allowing the seal material, this has traditionally been disposed in
contact with the liquid crystal layer to be coated at the outer
periphery of the strip spacer SPC-S.
[0047] An explanation will next be given of a method of forming the
pole spacers and the strip spacer in the illustrated
embodiment.
[0048] In the embodiment, the pole spacers and the strip spacer are
made of a chosen material, such as, for example, the chemical
amplification negative-type resist "BPR-113" (trade name)
manufactured by Kabushiki Kaisha JRS. This resist material is
comprised of a specific material which is very similar to those
materials which have been employed for bead spacers in prior art
liquid crystal panels, in that the material will hardly attempt,
after having hardened, to dissolve into the liquid crystal
material, nor exhibit imbibition or swelling activities. while
simultaneously offering increased adaptability or congeniality with
such liquid crystal material, with the machinability also being
enhanced.
[0049] FIG. 3 is a pictorial representation of the shape of a
typical one of the pole spacers used in the embodiment, which has
been prepared by illustrative duplication to mimic a corresponding
microphotograph thereof. The pole spacer shown herein has been
fabricated into a good shape at a crossing point or "intersection"
of the spacers SSP between the pixel electrodes AL-P.
[0050] The "BPR-113" that becomes the material of the pole spacers
and strip spacer is deposited by spin coat techniques on the
protective film PSV1 (see FIG. 1) of the drive substrate DSUB with
the pixel electrodes AL-P formed thereon; then, the resultant
structure is irradiated with i-rays; and next, development for
fabrication is effected.
[0051] The liquid crystal material is injected into the space
surrounded by the strip spacer SPC-S of the drive substrate DSUB
with the pole spacers and strip spacer formed thereon. In the case
where the strip spacer SPC-S has the shape as shown in FIG. 2, the
liquid crystal material dropped into the space. The common
substrate USUB is positioned while preventing it from coming into
contact with the upper part of this drive substrate DSUB; and then,
de-gas processing is carried out. After having removed any gases,
both substrates are laminated over each other and are then
processed together at increased pressures for tight contact with
each other. At this time, any extra components of the liquid
crystal material behave to overflow or extrude out of the strip
spacer SPC-S. These extra extruded liquid crystal material
components are washed out; then, the seal material SL that contains
no fillers is deposited along the outer edges of the strip spacer
SPC-S and between both substrates and is then hardened.
[0052] In the illustrative embodiment, use of the pole spacers
SPC-P and the strip spacer SPC-S fabricated under the same
conditions ensures that the cell gap in the display area is equal
to that at the sealed portions, which in turn makes it possible to
eliminate undesired creation of display image irregularities
otherwise occurring due to any possible cell gap differences. In
addition, the liquid crystal material constituting the liquid
crystal layer LC will no longer come in direct contact with the
seal material being used, which in turn enables preclusion of
contamination of the liquid crystal material due to the presence of
a non-hardened or uncured part of the seal material; and in
addition, it is no longer required that the seal material contain
fillers therein, which guarantees that the electrode extension
terminals are hardly open-circuited, while minimizing the risks of
destruction of other thin-films.
[0053] FIG. 4 depicts a plan view of a liquid crystal panel used in
a liquid crystal display device in accordance with a second
embodiment of this invention, which panel has on its surface pole
spacers and a strip spacer formed into a planar pattern as shown
herein. This embodiment is arranged so that a gap is provided at
part of the strip spacer SPC-S formed at the outer periphery of the
display area for use as a liquid crystal injection port INJ. The
remaining arrangement of the embodiment is similar to that of said
first embodiment and thus a further explanation thereof will be
omitted herein. A manufacturing method of the liquid crystal panel
of this embodiment will be explained below.
[0054] Fabrication of the drive substrate DSUB may be similar in
principle to--that of said first embodiment except that a process
step is added of providing the liquid crystal injection port INJ in
the strip spacer SPC-S. The opposed substrate USUB is bonded to
this drive substrate DSUB; and then, the substrate are pressed
together at high pressures to thereby bring these substrates into
tight contact with each other. Under this condition, the atmosphere
is pressure-reduced for gas removal; and then, the liquid crystal
material is injected thereinto from the liquid crystal injection
port INJ. Thereafter, a chosen seal material is deposited along the
outer edges of the strip spacer SPC-S including the liquid crystal
injection port INJ; and then, it is allowed to harden.
[0055] Alternatively, a similar seal material may be deposited at
the liquid crystal injection port INJ for sealing prior to
deposition of the seal material at the outer edges of the strip
spacer SPC-S. Note that the liquid crystal injection port INJ may
be replaced with an array of two or more liquid crystal injection
ports INJ where appropriate. The present embodiment is capable of
attaining similar effects and advantages to those of said first
embodiment.
[0056] It is noted that, although in both of the respective
embodiments referred to above, the drive substrate DSUB has been
described to be of the reflection type using a single-crystalline
silicon substrate, a similar arrangement may also be achieved
either in the case of liquid crystal display devices of the
transparent type with both substrates formed as glass substrates or
in the case of direct-view liquid crystal display devices with
large display screen areas.
[0057] FIG. 5 is a plan view of a liquid crystal panel used in a
liquid crystal display device in accordance with a third embodiment
of this invention, for explanation of the layout of pole spacers
and a strip spacer thereon. This embodiment is arranged such that a
built-in driver circuit DCT is directly mounted on the drive
substrate DSUB at a location outside of the display surface area
thereon, while letting the strip spacer SPC-S be formed overlying
this driver circuit DCT. The pole spacers SPC-P are similar in
nature to those in the first embodiment.
[0058] With this embodiment the same effects and advantages as
those of the above-noted respective embodiments are obtainable; and
additionally, it is possible to achieve a small-area liquid crystal
display device as a whole because of the fact that a space for
driver circuitry to be mounted externally of the liquid crystal
panel may be omitted.
[0059] An explanation will next be given of some examples which are
obtainable by implementation of each embodiment stated supra.
[0060] FIGS. 6A and 6B show an overall arrangement of a liquid
crystal display device of the projection type employing an actually
implemented example of the liquid crystal display device in
accordance with the invention, wherein FIG. 6A is a partly cutaway
plan view, whereas FIG. 6B is a cross-section taken along line
VIB-VIB of FIG. GA.
[0061] As shown in the drawing, this projection liquid crystal
display device is arranged to have on its second substrate DSUB
multiple pole-like spacers SPC-P and a strip spacer SPC-S With a
liquid crystal layer LC sandwiched between a first substrate USUB
and the second substrate DSUB for controlling the required cell gap
using the pole spacers SPC-P and the strip spacer SPC-S. The
reflective liquid crystal panel having a seal material SL coated
along outer edges of the strip spacer SPC-S, which is then hardened
for tightly bonding both substrates together, is received inside of
the cavity of a package PCG. The package PCG may preferably be
constituted from a mold-machined product made of resin materials,
and a flexible printed circuit board FPC for use in supplying one
or more signals along with electrical power to one edge thereof is
connected thereto at its one end. The package PCG is provided with
a surface glass WG employed for covering the cavity to thereby
provide a sealed environment therein.
[0062] A heat release or heat sink plate PPB made of a chosen metal
is disposed on the back surface of the package PCG in a manner such
that the heat sink has its peripheral portions embedded therein at
four lower sides of the package main body PCG while letting the
liquid crystal panel be received With a comparatively elastic or
resilient heat radiator sheet DPH placed between it and the heat
sink PPB. Accordingly, the back surface of the liquid crystal panel
comes into tight contact with the heat sink PPB via the heat
radiator sheet DPH to thereby provide the intended structure with
enhanced heat radiation effects.
[0063] The liquid crystal panel that is housed inside of the cavity
of the package PCG is fixed by adhesive ADH to a step-like portion
on the back side of the first substrate USUB thereof, which portion
is formed at the inner periphery on the bottom of this package PCG,
while the surface glass WG is adhered to a space plate SPB for
fixing the package PCG and flexible printed circuit board FPC
together. Note here that the space plate SPB is bonded to the
flexible printed circuit board FPC by adhesive, not shown.
[0064] FIG. 7 is a pictorial representation for explanation of one
exemplary configuration of a projection liquid crystal display
device using the liquid crystal display device that has been
explained in conjunction with FIG. 6, which includes housing, CAS a
liquid crystal display device (liquid crystal module) MOD,
illumination light source LSS, illumination lens system LNS, first
optical polarizer plate POL1, reflection mirror MIL, focusing lens
system FLN, second optical polarizer plate POL2, optical diaphragm
or iris ILS, and image-projection optical system PLN.
[0065] Illumination light from the light source device LSS is
guided by the illumination lens system LNS and first polarizer
plate POLI plus reflection mirror MIL to the surface of the liquid
crystal panel PNL constituting the liquid crystal display device
MOD. Light which arrives at the liquid crystal panel PNL is then
subjected to modification in a way corresponding to an image signal
at the pixel electrode of the liquid crystal panel PNL to thereby
provide refection light which is magnified for projection onto the
screen SCN by way of the focussing lens system FLN and second
polarizer plate Pd2 plus iris ILS as well as projection optical
system PLN.
[0066] An explanation will next be given of an example which
applies the invention to a direct-view liquid crystal display
device in terms of an active-matrix liquid crystal display
device.
[0067] FIG. 8 is a diagram showing a plan view of a liquid crystal
panel constituting the active-matrix liquid crystal display device,
which depicts a main part around a matrix AR of a liquid crystal
panel PNL including upper and lower transparent glass substrates
SUB2 (color filter substrate), SUB1 (active-matrix substrate) which
constitute the first and second substrates; and FIG. 9 is an
enlarged plan view of part near a seal section corresponding to the
upper left corner portion of the liquid crystal panel shown in FIG.
8.
[0068] In addition, FIGS. 10A, 10B and 10C are diagrams showing in
cross-section main portions of the liquid crystal panel, wherein
FIG. 10A is a sectional view taken along line 19a-19a of FIG. 9,
FIG. 10B is a sectional view of a TFT section, and FIG. 10C is a
sectional view near an external connection terminal DTM to which
image signal line driver circuitry is to be connected.
[0069] In the manufacture of this liquid crystal panel, if it is of
small size, then a single glass substrate is subject to
simultaneous processing of a plurality of panels at one time and is
the substrate then separated into plural pieces for throughput
improvement; alternatively, if it is large in size, then a specific
glass substrate having its size standardized for common use with a
variety of types of products is employed which is so processed and
then made smaller into a proper size accommodating respective types
of products for purposes of shared use of the production facility;
in either case, the glass substrate is cut after having completed a
series of specified process steps.
[0070] FIGS. 8 and 10 show the state after having completed a
cut-off process of the upper and lower substrates SUB2, SUB1;
whereas, FIG. 9 shows the state prior to the cutoff process,
wherein LN designates the edge of a cut line of such glass
substrate, and CT1 and CT2 denote certain positions at which the
glass substrates SUB1, SUB2 are to be cut, respectively.
[0071] In either case, the finally manufactured state is such that
at those portions whereat external connection terminal groups Tg,
Td (suffix omitted) are located, the upper-side glass substrate
SUB2 is limited in size so that it exists inside of the lower-side
glass substrate SUB1 to thereby allow the terminal groups to be
exposed to the outside.
[0072] The external connection terminal groups Tg, Td are such that
a plurality of components consisting essentially of scan circuit
connection terminals GTM and image signal circuit connection
terminals DTM along with electrical extension leads associated
therewith are organized into a group in units of tape carrier
packages with driver circuits mounted thereon. Those extension
leads of each group extending from the matrix section up to the
external connection terminal unit are so designed as to become
slanted or tilted as they come closer to both ends. This is aimed
at positional alignment of the terminals DTM, GTM of the liquid
crystal panel PNL with the connection terminal pitch at respective
tape carrier packages.
[0073] Pole spacers SPC-P are formed in the display area AR between
the transparent glass substrates SUB1, SUB2 whereas a strip spacer
SPC-S is formed in the seal section thereof along its edges,
excluding the liquid crystal seal injecting portion INJ, in a such
a manner as to seal the liquid crystal LC. And, a seal material SL
is coated at the outer edges of the strip spacer SPC-S. This seal
material is made of an epoxy resin, for example. Note that the pole
spacers SPC-P are not visible in FIG. 10 because they are formed at
the boundaries of pixels.
[0074] A common transparent pixel electrode IT02 on the upper
transparent glass substrate SUB2 is connected by a silver paste
material SGP at least at one portion; here, at four corner edges of
the liquid crystal panel to an extension lead INT that is formed on
the lower transparent glass substrate SUB 1. This extension lead
INT is fabricated simultaneously during formation of gate terminals
GTM and drain terminals DTM.
[0075] Respective layers of alignment films ORI1, ORI2 and
transparent pixel electrodes ITO1 plus common transparent pixel
electrodes ITO2 are formed inside of the strip spacer SPC-S.
Polarizer plates POL1, POL2 are formed on outer surfaces of the
lower transparent glass substrate SUB1 and upper transparent glass
substrate SUB2, respectively.
[0076] Liquid crystal LC is sealed in the display area AR which is
partitioned by the strip spacer SPC-S between the lower alignment
film ORI1 and upper alignment film ORI2. The lower alignment film
ORIL is formed on a protective film PSV1 on the side of the lower
transparent glass substrate SUB1.
[0077] This liquid crystal panel PNL is assembled through process
steps of individually stacking various layers over each other on
each side of the transparent glass substrate SUB1 and transparent
glass substrate SUB2, laminating the lower transparent glass
substrate SUB1 and the upper transparent glass substrate SUB2 over
each other, injecting a chosen liquid crystal material via the
opening INJ (liquid crystal seal injection port) of the strip
spacer SPC-S, thereafter sealing using the seal material SL, and
then cutting the upper and lower transparent glass substrates.
[0078] A thin-film transistor TFT as shown in FIGS. 10A, 10B and
10C operates in a way such that, upon application of a positive
bias to its gate electrode GT, the channel resistivity between the
source and drain thereof decreases; alternatively, the source-drain
resistivity increases when the bias is set at zero.
[0079] The thin-film transistor TFT of each pixel is divided into
two portions (plural parts) within the pixel. In FIG. 10B only one
of them is depicted. Each of the two thin-film transistors TFT is
arranged to have substantially the same size (equal in channel
length and in channel width). Each of such divided thin-film
transistors TFT has a gate electrode GT, gate insulation film GI,
i-type semiconductor layer AS made of intrinsic amorphous silicon
(Si) with no conductivity type determination impurities doped
therein, and a pair of source electrode SD1 and drain electrode
SD2. Note here that the source and drain are inherently determined
depending on the bias polarity between them, and that such polarity
will possibly be inverted in this liquid crystal display device so
that the source and drain are interchangeable in nature. In the
following explanation however, one of them is fixedly represented
by the source with the other called the drain for purposes of
convenience in the discussion herein.
[0080] The gate electrode GT is designed to extend beyond
respective active regions of the thin-film transistor TFT while
respective gate electrodes GT of the thin-film transistors TFT are
formed continuously. Here, the gate electrode GT is formed of a
single-layer second conductive film g2. The second conductive film
g2 may be made for example of an aluminum (Al) film as formed by
sputtering techniques to a predetermined thickness ranging from
1,000 to 5,500 Angstroms (A). In addition, an anodized film AOF of
aluminum is provided on the gate electrode GT.
[0081] This gate electrode GT is formed to have a slightly larger
size than the i-type semiconductor layer AS to thereby completely
cover it (when looking from the lower side thereof). Accordingly,
in case a backlight BL, such as a fluorescent tube, is attached to
the lower part of the lower transparent glass substrate SUB1, the
gate electrode GT consisting of such opaque aluminum film serves to
block rays of light emitted from the backlight BL thus preventing
the light from falling onto the i-type semiconductor layer AS,
which in turn makes it possible to minimize the possibility of
conduction phenomena due to light irradiation, i.e. reduction of
the turn-off characteristics of the thin-film transistor TFT.
Additionally, the inherent size of the gate electrode GT is such
that it has a width minimally required to allow the gate electrode
to span or "bridge" between the source electrode SD1 and drain
electrode SD2 (also including margins for position alignment
between the gate electrode GT and the source and drain electrodes
SD1, SD2) whereas the depth thereof which determines the resultant
channel width W is determinable depending on how the ratio of it to
a distance (channel length) L between the source electrode SD I and
drain electrode SD2; namely a factor W/L determining the mutual
conductance or transconductance gm is designed. Obviously the
actual size of the gate electrode GT in this liquid crystal display
device is made greater than the inherent size noted above.
[0082] Scan signal lines are constituted from a second conductive
film g2. This second conductive film g2 of such scan signal lines
is fabricated simultaneously during formation of the second
conductive film g2 of gate electrodes GT while allowing the former
to be integral with the latter. An anodized film AOF of aluminum is
also provided overlying the scan signal lines.
[0083] A dielectric film GI is employed to function as the gate
insulation film of each of the thin-film transistors TFT, and is
formed to overlie the gate electrodes GT and scan signal lines. The
dielectric film GI is made for example of a silicon nitride film
fabricated by plasma chemical vapor deposition (CVD) techniques to
a thickness of from 1,200 to 2,700 .ANG. (preferably 2,000 .ANG. in
this liquid crystal(display device). As shown in FIG. 9, the gate
insulation film GI is so formed as to entirely surround a matrix
section AR with its peripheral portions removed away thus allowing
the external connection terminals DTM, GTM to be exposed to the
outside.
[0084] The i-type semiconductor layer AS is used as a channel
formation region of each of two thin-film transistors TFT. The
i-type semiconductor layer AS is formed of either an amorphous
silicon film or a polycrystalline silicon film of about 200 to 220
.ANG. in thickness (about 200 .ANG. thick in this liquid crystal
display device).
[0085] This i-type semiconductor layer AS is fabricated
continuously to effect formation of the dielectric film GI made of
Si.sub.2N.sub.4 for use as the gate insulation films while varying
feed gas components in the same plasma CVD equipment without
causing external exposure from such plasma CVD equipment.
[0086] In addition, an N(+) type semiconductor layer do with a
chosen impurity for ohmic contact such as phosphorus (P) doped
therein at 2.5% is also formed continuously to a thickness ranging
from 200 to 500 .ANG. (about 300 .ANG. in this liquid crystal
display device). Thereafter, the lower transparent glass substrate
SUB1 is removed from the CVD apparatus to the outside to carry out
photolithographical patterning processes so that the N(+) type
semiconductor layer do and i-type semiconductor layer AS are
patterned into several independent islands.
[0087] The i-type semiconductor layer AS is also provided between
both intersections (crossover portions) of the scan signal lines
with respect to image signal lines associated therewith. The i-type
semiconductor layer AS at the intersections acts to reduce
electrical short-circuiting between the scan signal lines and the
image signal lines at such intersections.
[0088] A transparent pixel electrode ITO1 (corresponding to AL-P in
FIG. 1) constitutes one of those pixel electrodes of the liquid
crystal panel. The transparent pixel electrode ITO1 is connected to
the source electrode SDl of each of the two thin-film transistors
TFT. Due to this, even where a defect occurs at any one of such two
thin-film transistors TFT, the operation reliability may be
guaranteed in a way such, that if such defect can result in
secondary operation failures or malfunction, then an appropriate
portion is cut away, such as by laser light, otherwise no
particular actions will be taken due to the fact that the remaining
thin-film transistor TFT is operating normally. Additionally, it
will rarely happen that both of two thin-film transistors TFT
experience defects at the same time, so that use of the redundancy
scheme makes it possible to greatly reduce the possibility of
occurrence of point defects and/or line defects.
[0089] The transparent pixel electrode ITO1 is comprised of a first
conductive film dl. This first conductive film dl is made of a
transparent conductive film (indium-tin-oxide or ITO film, or Nesa
film) that was formed by sputtering techniques to a thickness of
from 1,000 to 2,000 .ANG. (about 1,400 .ANG. in this liquid crystal
display device).
[0090] The source electrode SD1 and drain electrode SD2 of each of
the two thin-film transistors TFT are provided so as to be spaced
apart from each other on the i-type semiconductor layer AS.
[0091] The individual one of the source electrode SD1 and drain
electrode SD2 is arranged by sequentially laminating or stacking a
second conductive film d2 and third conductive film d3, as seen
from the lower layer side, in contact with the N(+) type
semiconductor layer do. The second conductive film d2 and third
conductive film d3 of the source electrode SD1 are fabricated at
the same process step or steps during formation of the second
conductive film d2 and third conductive film d3 of the drain
electrode SD2.
[0092] The second conductive film d2 may be a chromium (Cr) film
that is formed to a thickness of 500 to 1,000 .ANG. (approximately
600 .ANG. in this liquid crystal display device). The Cr film is
adapted for use as a so-called barrier layer to be described later,
which prevents unwanted outdiffusion of aluminum Al of the third
conductive film d3 into the N(+) type semiconductor layer do. The
second conductive film d2 may be made of, in the alternative, a Cr
film, a film of high-melting-point metal (Mo, Ti, Ta, W, and the
like), a layer of high-melting-point suicide (MoSi.sub.2,
Tisi.sub.2, TaSi.sub.2, WSi.sub.2 or else), or any other similar
suitable materials.
[0093] The third conductive film d3 is formed by sputtering of
aluminum Al to a thickness of from 3,000 to 5,000 .ANG. (about
4,000 .ANG. in this liquid crystal panel). Aluminum Al films are
less in stress than chromium Cr films and for this reason are
capable of formation to large film thicknesses while being arranged
to reduce the electrical resistance values of the source electrode
SDl and drain electrode SD2, as well as the image signal lines DL.
The third conductive film d3 may alternatively be made from, other
than ordinary aluminum, an aluminum containing therein silicon or
copper (Cu) as additive materials.
[0094] After completion of the intended patterning processing of
the second conductive film d2 and third conductive film d3 using
the same mask pattern, the N(+) type semiconductor layer do is
removed by using the same mask or alternatively using the second
conductive film d2 and third conductive film d3 as a mask therefor.
In single terms, certain portions of the N(+) type semiconductor
layer d0 which reside on the i-type semiconductor layer AS other
than those on the second conductive film d2 and third conductive
film d3 will be removed in a self-align fashion. At this time the
N(+) type semiconductor layer d0 will be etched away so that its
thickness portions are all removed so that the i-type semiconductor
layer AS will likewise be etched away at the surface portion
thereof; however, the degree of such etching treatment may be
controlled based on the length of the etching processing time.
[0095] The source electrode SD1 is connected to the transparent
pixel electrode ITO1. The source electrode SD1 is arranged along
the i-type semiconductor layer AS's step-like difference portion (a
step-like surface configuration corresponding to a film thickness
equivalent to the total sum of the film thickness of the second
conductive film d2 and the film thickness of the anodized film AOF
plus the film thickness of the i-type semiconductor layer AS as
well as the film thickness of the N(+) type semiconductor layer
d0). Practically, the source electrode SD1 consists of the second
conductive film d2, formed along the step-like difference of the
i-type semiconductor layer AS, and the third conductive film d3
formed to overlie this second conductive film d2. The third
conductive film d3 of the source electrode SD1 is arranged to
permit climbing over the i-type semiconductor layer AS in view of
the fact that the Cr film of the second conductive film d2 is
incapable of being made thicker due to an increase in stress and
also is incapable of climbing over the step-like difference of the
i-type semiconductor layer AS. In other words, thickening the third
conductive film d3 improves the step coverage. Since the third
conductive film d3 is capable of formation to increased
thicknesses, this significantly contributes to reduction of the
resistance value of the source electrode SD1 (the same goes with
the drain electrode SD2 and/or image signal lines DL).
[0096] A protective film PSV1 is provided so as to overlie the
thin-film transistors TFT and transparent pixel electrodes ITO. The
protective film PSVl is formed in order to protect mainly the
thin-film transistors TFT against moisture; to this end, the one
that is high in transparency and has good resistance to humidity
must be used therefor. The protective film PSV1 is made, for
example, of a silicon oxide film or silicon nitride film which is
formed by plasma CVD apparatus to a thickness of about 1 .mu.m.
[0097] As shown in FIG. 9, the protective film PSV1 is formed to
surround the entire matrix section AR, with its peripheral portions
remove so as to allow the external connection terminals DTM, GTM to
be exposed to the outside and also with those portions removed
which are used to connect a common electrode COM (corresponding to
the transparent electrode ITO-C of FIG. 1) of the upper transparent
glass substrate SUB2 to an external connection terminal extension
lead INT of the lower transparent glass substrate SUB1 using silver
paste. With regard to the thickness relationship of the protective
film PSV1 versus the gate insulation film GI, the former is made
thicker in light of protection effect enhancement, whereas the
latter is made thinner in view of the transconductance gm of the
transistors. Accordingly, as shown in FIG. 9. the protective film
PSV1, which is high in protection effects, is fabricated so that it
is larger in size than the gate insulation film GI to ensure that
its periphery offers enhanced protectability over an extended area
that is as wide as possible.
[0098] On the side of the upper transparent glass substrate SUB2,
an optical shield film BM is provided to prevent unwanted entry or
incidence of incoming external light into the i-type semiconductor
layer AS that is used as the channel formation region.
[0099] The optical shield film BM is made of either an aluminum
film or chromium film or any equivalents thereof, which, is high in
optical blocking ability. In this liquid crystal display device,
the chromium film is formed by sputtering to a thickness of 1,300
.ANG., more or less. Additionally this shield film is different
from the shield film SHF in FIG. 1.
[0100] Consequently, the i-type semiconductor layer AS of thin-film
transistor TFT is sandwiched between the overlying shield film BM
and the underlying gate electrode GT of slightly larger size so
that such portion will no longer receive any externally attendant
natural light nor any rays of backlight. As indicated by hatching
in FIG. 19, the shield film BM is formed around a pixel; in other
words, the shield film BM is formed to have a lattice or grid-like
pattern (known as black matrix), which grid defines by partition
the effective or net display area of a single pixel. Use of such
shield film BM makes the contour of each pixel clear and "crisp" to
thereby improve the contrast. In summary, the shield film BM
functions to offer optical shielding with respect to the i-type
semiconductor layer AS while simultaneously serving as the black
matrix for improvement of the contrast by providing partitions
between color filters FIL (R), FIL (G), FIL (B).
[0101] In addition, since part of the transparent pixel electrode
ITO1 which opposes the root-side edge portion in the rubbing
direction is optically blocked or "shuttered" by the shield film
BM, any domains that can occur at such part are invisible, which in
turn ensures that the display characteristics are free from any
possible degradation.
[0102] Where necessary, the backlight may alternatively be attached
to the upper transparent glass substrate SUB2 while allowing the
lower transparent glass substrate SUB1 to be on the observation
side (external exposure side).
[0103] The shield film BM is also formed at the peripheral section
to have a flat rectangular frame-like pattern which resembles a
window frame in planar shape and is formed continuously with the
pattern of the matrix section that has a plurality of openings or
apertures in the form of dots. The shield film at this part is
similar in function to the shield film SHF. The shield film BM at
the periphery is extended beyond the strip spacer SPC-S toward the
outside of the seal material SL, thereby precluding undesired
entrance or "invasion" of leakage light, such as reflection light
otherwise occurring in actually implemented equipment, such as
personal computers or the like. On the other hand, this shield film
BM is forced to reside inside of the edge of the upper transparent
glass substrate SUB2 by approximately 0.3 to 1.0 mm and is formed
to avoid passing through cut regions of the upper transparent glass
substrate SUB2.
[0104] The color filters FIL(R), FIL(G), FIL(B) are comprised of a
dyeing or stain base made of a resin material such as acrylic resin
or the like with color development effected thereto using dyestuff.
Note that the color filter FIL(B) is not depicted in FIGS. 10A, 10B
or 10C. These color filters FIL(R), FIL(G), FIL(B) are formed at
specified positions corresponding to pixels to have a stripe shape,
and are individually colored into respective colors of red (R),
green (G) And Blue (B). The color filters FIL(R), FIL(G), FIL(B)
are formed to have a predefined size large enough to cover all of
the transparent pixel electrodes ITO1 whereas the shield film BM is
formed inside of the peripheral edges of such transparent pixel
electrodes ITO1 to thereby overlap those edge portions of the
transparent pixel electrodes ITO1.
[0105] The color filters FIL(R), FIL(G), FIL(B) may alternatively
be formed in the following way. First, a chosen dyeing base is
formed on the surface of the upper transparent glass substrate
SUB2; then, certain portions of the dyeing base residing in
specified regions other than the red-color filter formation regions
are photolithographically removed. Thereafter, the dyeing base is
dyed with red dyestuff and then fixing or sticking treatment is
carried out thus forming the red color filters FIL(R). Next,
similar treatment processes are performed to sequentially form the
green color filters FIL(G) and blue color filters FIL(B).
[0106] A protective film PSV2 is provided for preventing the
dyestuff used to dye the color filters FIL(R), FIL(G), FIL(B) ]into
different colors from attempting to leak into the liquid crystal
layer LC. This protective film PSV2 is made of transparent resin
materials typically including acrylic resin or epoxy resin or the
like.
[0107] A common transparent pixel electrode IT02 opposes
transparent pixel electrodes ITO1 that are provided on the lower
transparent glass substrate SUB1 in units of pixels, wherein the
optical state of the liquid crystal layer LC varies or changes in
response to a voltage potential difference (electric field) between
each pixel electrode ITO1 and common transparent pixel electrode
ITO2. This common transparent pixel electrode ITO is arranged to
receive a common voltage Vcom as applied thereto. Although the
common voltage Vcom is set here at an intermediate potential
between a low-level drive voltage Vdmin and high-level drive
voltage Vdmax applied to the image signal lines, if the power
supply voltage of an integrated circuit for use in image signal
line drive circuitry is required to decrease down to about half
then an AC voltage may be applied thereto. Additionally, part of
the planar shape of the common transparent pixel electrode ITO2 is
shown in FIG. 9.
[0108] It should be noted that the gate terminals GTM are composed
of a chromium Cr layer g1 having excellent adhesiveness with a
silicon oxide SIO layer and having a higher resistance to
electrolytic corrosion than aluminum Al, and a transparent
conductive layer d1 lying at the same level as the pixel electrodes
ITO1 (same layer, simultaneous fabrication) while protecting the
surface of the former. Also note that conductive layers d2 and d3
that are formed on the gate insulation film GI and sidewalls
thereof are the ones which reside as a result of coverage of such
regions by a photoresist to preclude the conductive layers g2 and
g1 from being etched away due to presence of pinholes during
etching of such conductive layers d2 and d3. Additionally the ITO
layer d1 that is designed to extend in the right direction beyond
the gate insulation film GI is for further enhancing such similar
remedy.
[0109] As shown in FIG. 9, the drain terminals DTM constitute a
terminal group Td (suffix omitted), which terminals are arranged to
further extend beyond a cut line CT1 of the lower transparent glass
substrate SUB1 and all of which are electrically short-circuited
together by a lead SHd in order to prevent electrostatic breakdown
or destruction during the manufacturing processes.
[0110] The drain terminals DTM are each formed of two layers
including a chromium Cr layer g1 and ITO layer d1 for the same
reasons as in the gate terminals GTM and are connected to an image
signal line DL at a specified part from which the gate insulation
film GI has been removed away. The semiconductor layer AS is formed
to overlie the edge of the gate insulation film GI for image-signal
etching the edge of the gate insulation film GI into a tapered
shape. Of course, the protective film PSV1 for providing
interconnection with external circuitry has been removed at
locations overlying the drain terminals DTM.
[0111] FIG. 11 is an exploded perspective view of the overall
structure of a direct-view liquid crystal display device employing
the liquid crystal display device in accordance with the present
invention.
[0112] The liquid crystal display device shown herein represents
one actually implemented structure of a liquid crystal display
device (liquid crystal display module) with its liquid crystal
panel and circuit boards plus backlight unit along with other
components associated therewith assembled together integrally.
[0113] In FIG. 11, "SHD", designates an upper frame (also known as
a shield casing, or metal frame) made of a metal plate; WD denotes
a display window; INS1-3 indicate dielectric sheets; PCB1-3
represent printed circuit boards (PCB1 is a drain-side circuit
board for use as an image signal line driver circuit board, PCB2 is
a gate-side circuit board, and PCB3 is an interface circuit board);
JN1-3 are joiners for electrical connection among the circuit
boards PCB1-3; TCP.sub.1, TCP2 are tape carrier packages; PNL
denotes a liquid crystal panel using the pole spacers and strip
spacer that have been described in the embodiment for setup of a
prespecified cell gap; POL denotes upper polarizer plate; GC
denotes a rubber cushion; ILS denotes an optical shielding spacer
(corresponding to the shield film SHF in FIG. 1); PRS denotes a
prism sheet; SPS denotes a diffuser sheet; GLB denotes a light
guide plate; RFS denotes a reflection sheet; MCA denotes a lower
frame formed by all-at-a time machining of resin (also called a
lower casing, or mold frame); MO denotes an opening or aperture of
the MCA; BAT denotes both-side adhesive tape, wherein diffuser
plate members are laminated over one another to assemble the liquid
crystal display device MDL. In addition, a light source assembly
consisting of a fluorescent tube LP and reflector sheet LS is
disposed along one side of the light guide plate GLB, which is
electrically fed from a backlight power supply unit, not shown, via
a lamp cable LPC that is extended from the rubber cushion GC
portion as provided at the edge of the fluorescent tube LP. The
light guide plate GLB and the light source assembly makes up the
backlight BL. Additionally, the light source assembly may
alternatively be provided along two sides or four sides of the
light guide plate GLB.
[0114] This liquid crystal display device (liquid crystal display
module MDL) has an enclosure or housing that consists essentially
of two kinds of receiving/retainment members, which constitute the
lower frame MCA and upper frame SHD, and is arranged so that the
dielectric sheets INS1-3 and circuit boards PCB 1-3 plus liquid
crystal panel PNL are immovably received therein while engaging
with the upper frame SHD and the lower frame MCA with the backlight
including the light guide plate GLB and others.
[0115] Mounted on the image signal line driver circuit board PCB1
are several electronics components including but not limited to
integrated circuit chips for use in driving respective pixels on
the liquid crystal panel PNL, whereas the interface circuit board
PCB3 mounts thereon integrated circuit chips for use in receiving
image signals from an external host computers) and also for
receiving control signals such as timing signals and the like, more
than one timing converter (TCON) for generation of a clock signal
or signals by processing the timing, one or more low-voltage
differential signal chips, and other electronic parts or components
typically including capacitors and resistors or any equivalents
thereto.
[0116] A clock signal which is generated and issued from the timing
converter is then supplied to built-in driver circuit chips
(integrated circuit chips) mounted on the image signal line driver
circuit board PCB 1.
[0117] The interface circuit board PCB3 and image signal line
driver circuit board PCB1 are multilayer printed circuit boards,
wherein the clock signal lines CLL are formed as inner leads of the
interface circuit board PCB3 and image signal line driver circuit
board PCB1.
[0118] It is noted that the drain-side circuit board PCB1 for use
in driving the TFTs and the gate-side circuit board PCB2 plus
interface circuit board PCB3 are connected by the tape carrier
packages TCP1, TCP2 to the liquid crystal panel PNL while using the
joiners JN1, 2, 3 to connect between respective circuit boards.
[0119] With this liquid crystal display device, it becomes possible
to obtain high-quality image displayability with on-screen visual
irregularities being suppressed or minimized.
[0120] FIG. 12 depicts a perspective view of a notebook personal
computer (PC) also embodying the invention, which employs the
liquid crystal display device shown in FIG. 11.
[0121] This notebook computer (handheld or mobile PC) consists
essentially of a keyboard unit (main body) and a display unit as
foldably coupled via hinges to the keyboard unit. The keyboard unit
has a keyboard on its top faceplate and contains therein a host
(host computer) along with signal generation functions achieved by
a microprocessor such as a CPU or the like, while the display unit
has the liquid crystal panel PNL assembled together with a PCB
mounting thereon driver circuit boards FPC1, FPC2 and controller
chip TCON as well as an inverter power supply board IV used as the
backlight power supply, which are received near or around the
liquid crystal panel PNL.
[0122] Each of the electronic equipment with the liquid crystal
display device built therein is capable of offering enhanced
displayability of high-quality images with visual irregularities
greatly suppressed or eliminated because of the fact that its
liquid crystal panel's cell gap has less variation.
[0123] As apparent from the foregoing, according to the present
invention, it is possible to provide a high-quality liquid crystal
display device with reliability increased, wherein since the
columnar or pole-like spacers are provided at selected positions
excluding the pixel electrodes in a display area while at the same
time providing the zonal or band strip-shaped spacer at the sealing
portions around the display area between two insulative substrates
for permitting deposition or coating of a seal material at outer
edges of this strip spacer which is later hardened, it is possible
to uniformly control the cell gap over almost the entire screen
area. In addition, because a liquid crystal material constituting
the liquid crystal layer will no longer come into contact with the
seal material being used, contamination of the liquid crystal
material due to such seal material may be eliminated. Furthermore,
use of no fillers for the seal material makes it possible to avoid
damage such as undesired open-circuiting of electrode extension
leads.
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