Title: In-plane switching liquid crystal display unit having tinting compensation
Abstract: An in-plane-switching liquid crystal display unit has a two-dimensional matrix of pixel regions each including a first auxiliary region and a second auxiliary region. When no electric field is applied, liquid crystal molecules in the first and second auxiliary regions are directed in respective orientations that lie at 90° with respect to each other. When a voltage is applied, the liquid crystal molecules are rotated in the same direction while maintaining their orientations in the first and second auxiliary regions at 90° with respect to each other. Alternatively, the liquid crystal molecules in the first and second auxiliary regions are directed in the same orientation when no electric field is applied, and when a voltage is applied, the liquid crystal molecules are rotated opposite directions while maintaining their orientations in symmetric relationship.
Patent Number: 6,987,551 Issued on 01/17/2006 to Suzuki, et al.
| Inventors:
|
Suzuki; Teruaki (Tokyo, JP);
Nishida; Shinichi (Tokyo, JP);
Murai; Hideya (Tokyo, JP);
Suzuki; Masayoshi (Tokyo, JP);
Watanabe; Makoto (Tokyo, JP);
Hirai; Yoshihiko (Tokyo, JP)
|
| Assignee:
|
NEC Corporation (Tokyo, JP)
|
| Appl. No.:
|
350077 |
| Filed:
|
January 24, 2003 |
Foreign Application Priority Data
| Nov 06, 1996[JP] | 96/293897 |
| Mar 06, 1997[JP] | 97/051899 |
| Apr 28, 1997[JP] | 97/111160 |
| Current U.S. Class: |
349/141 |
| Current Intern'l Class: |
G02F 1/13.43 (20060101) |
| Field of Search: |
349/141
|
References Cited [Referenced By]
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| 5757455 | May., 1998 | Sugiyama et al.
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| 5793459 | Aug., 1998 | Toko.
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| 5831700 | Nov., 1998 | Li et al.
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| 5894361 | Apr., 1999 | Yamazaki et al.
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| 5907380 | May., 1999 | Lien.
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| 5977562 | Nov., 1999 | Hirakata et al.
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| 6266116 | Jul., 2001 | Ohta et al.
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| Foreign Patent Documents |
| 61-34134 | Mar., 1986 | JP.
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| 6-51321 | Feb., 1994 | JP.
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| 7-64119 | Mar., 1995 | JP.
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| 7-191336 | Jul., 1995 | JP.
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| 9-258269 | Oct., 1997 | JP.
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| 10-062802 | Mar., 1998 | JP.
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| 10-148833 | Jun., 1998 | JP.
| |
| WO 96/1077/5 | Apr., 1996 | WO.
| |
Other References
"Theoretical and Experimental Study of Nematic Liquid Crystal Display Cells Using
the In-Plane Switching Mode, Di Pasquale, et al., IEEE Transactions on Electron
Devices, vol. 46, No. 4, Apr. 1999.
Society for Information Display, Proceedings of the 16th International
Display Research Conference, Oct. 1-3, 1996, "LP-A: Display Characteristics of
In-Plane-Switching (IPS) LCDs and a Wide-Viewing-Angle 14.5-in. IPS TFT-LCD. Matsumoto,
et al.
|
Primary Examiner: Parker; Kenneth
Attorney, Agent or Firm: Sughrue Mion, PLLC
Parent Case Text
This is a divisional of application Ser. No. 08/965,619, filed Nov. 6, 1997
now U.S. Pat. No. 6,583,839; the disclosure of which is incorporated herein by reference.
Claims
What is claimed is:
1. An in-plane-switching liquid crystal display unit comprising a two-dimensional
matrix of pixel regions each including:
a first region having liquid crystal molecules directed in a first orientation
when no electric field is applied thereto;
a second region having liquid crystal molecules directed in a second orientation
which is the same as said first orientation when no electric field is applied thereto; and
electric field generating means for generating an in-plane electric field to
said liquid crystal molecules to rotate the liquid crystal molecules of the first
and second regions in opposite directions with respect to each other while maintaining
said first orientation and second orientation in symmetric relationship;
wherein said electric field generating means comprises a plurality of pairs of
confronting electrodes each having a longer arm and a shorter arm which extend
at a predetermined angle with respect to each other and define a rectangular region,
said pairs of confronting electrodes being inverted in said first region with respect
to those pairs in said second region.
2. An in-plane-switching liquid crystal display unit according to claim 1, wherein
the shorter arms of the electrodes are slightly tilted with respect to a direction
perpendicular to each of said first and second orientations of the liquid crystal
molecules when no electric field is applied.
3. A liquid crystal display device comprising:
a first substrate having a plurality of pixels each defined by adjacent ones
of a plurality of gate bus lines and adjacent ones of a plurality of data bus lines,
each of said pixels including a common electrode and an active element, said active
element having a gate electrode, a first electrode and a second electrode, said
gate electrode being connected to an associated one of said gate bus lines and
said first electrode being connected to an associated one of said data bus lines;
a second substrate; and
a liquid crystal sandwiched between said first and second substrates, rotation
of molecules of said liquid crystal being controlled by electric fields formed
between said second electrode and said common electrode;
said common electrode including a pair of first portions extending in a direction
of said gate bus lines, and at least one second portion extending in a direction
of crossing said gate bus lines to connect said pair of first portions to each
other said at least one second portion including a bend, said pair of first portions
being elongated over a plurality of pixels arranged in the direction of said gate
lines, and
said second electrode including at least one third portion cooperating with said
second portion of said common electrode to produce said electric field.
4. The device as claimed in claim 3, wherein said second portion of said common
electrode bends in a V-letter shape.
5. The device as claimed in claim 3, wherein said gate bus lines and said common
electrode are formed on said first substrate, and wherein said data bus lines,
said first electrode and said second electrode are formed on an insulating film
covering said gate bus line, said common electrode and said first substrate.
6. The device as claimed in claim 5, wherein said second electrode further comprises
a pair of fourth portions overlapping said pair of first portions with an intervention
of said second insulating film, and wherein said third portion is formed to connect
said pair of said fourth portions to each other.
7. A liquid crystal display device comprising:
a first substrate;
a plurality of gate bus lines formed over said first substrate in a first direction;
a plurality of pairs of common bus lines formed over said first substrate in
said first direction, each of said pairs of common bus lines being formed between
a corresponding adjacent two gate bus lines;
a plurality of sets of common electrodes formed over said first substrate, each
of said sets of common electrodes connecting an associated one of said pairs of
common bus lines to each other, said at least one of said common eletrodes including
a bend;
a plurality of data bus lines formed over said first substrate in a second direction
intersecting said first direction;
a plurality of active elements each provided at a corresponding one of intersections
of said gate bus lines and said data bus lines, each of said active elements having
a gate electrode connected to an associated one of said gate bus line, a first
electrode connected to an associated one of said data bus lines and a second electrode
cooperating with an associated one of said plurality sets of said common electrodes
to produce an electric field therebetween;
a second substrate; and
a liquid crystal sandwiched between said first and second substrate.
8. The device as claimed in claim 7, wherein said gate bus lines, said common
bus lines, said common electrodes and said gate electrode are made of a conductive
layer at a first level, and wherein said data bus lines, said first electrode and
said second electrode are made of a conductive layer at a second level that is
different from said first level.
9. The device as claimed in claim 8, wherein each of said common electrodes bends
in a V-letter shape at least once.
10. A liquid crystal display device comprising:
a first substrate having a plurality of pixels each defined by adjacent ones
of a plurality of gate bus lines and adjacent ones of a plurality of data bus lines,
each of said pixels including a common electrode and an active element, said active
element having a gate electrode, a first electrode and a second electrode, said
gate electrode being connected to an associated one of said gate bus lines and
said first electrode being connected to an associated one of said data bus lines;
a second substrate; and
a liquid crystal sandwiched between said first and second substrates, rotation
of molecules of said liquid crystal being controlled by electric fields formed
between said second electrode and said common electrode;
wherein one of said common electrode and said second electrode has first and
second portions extending in parallel to each other and first and second protrusions,
the other of said common electrode and said second electrode having a third portion
extending between said first and second portions in parallel thereto and having
third and fourth protrusions;
and wherein said pixel includes a first sub-area having first, second, third
and fourth sides and a second sub-area having fifth, sixth, seventh and eighth
sides, said first side being defined by said first portion, said second and fifth
sides being defined by said third portion, said sixth side being defined by said
second portion, two of said third, fourth, seventh and eighth sides being defined
by said first and second protrusions, and a remaining two of said third, fourth,
seventh and eighth sides being defined by said third and fourth protrusions;
wherein in said first sub-area an electric field is provided between said first
portion and said third portion, and in said second sub-area an electric field is
provided between said second portion and said third portion.
11. The device as claimed in claim 10, wherein each of said first, second, third
and fourth protrusions has a flat end side to define an associated side of said
first and second sub-areas.
12. The device as claimed in claim 10, wherein each of said first, second, third
and fourth protrusions has a slant end side to define an associated side of said
first and second sub-areas.
13. The device as claimed in claim 10, wherein each of said first, second and
third portions are bent at least once to respectively divide said first sub-area
into first and second segment areas and said second sub-area into third and fourth
segment areas, and wherein the molecules of said liquid crystal in said first and
third segment areas are rotated in one direction and the molecules of said liquid
crystal in said second and fourth segment areas are rotated in an opposite direction
in response to said electric fields.
14. An in-plane-switching liquid crystal display unit comprising a two-dimensional
matrix of pixel regions each including:
a first region having a plurality of first parallel pairs of electrodes;
a second region having a plurality of second parallel pairs of electrodes which
are not parallel to said first parallel pairs of electrodes; and
an electrode structure extending to a boundary portion between said first region
and said second region, said boundary portion including first boundary electrodes
connected to one electrode of said first parallel pairs of electrodes and second
boundary electrodes connected to another electrode of said first parallel pairs
of electrodes;
wherein said first boundary electrodes and said second boundary electrodes are
arranged alternately along said boundary portion.
15. The device as claimed in claim 3, wherein said bend is provided at a boundary
between a first region of said liquid crystal and a second region of said liquid crystal.
16. The device as claimed in claim 7, wherein said bend is provided at a boundary
between a first region of said liquid crystal and a second region of said liquid crystal.
17. The device as claimed in claim 10, further comprising a second electrode
structure extending to said boundary portion between said first region and said
second region, said second electrode structure being connected to another electrode
of said first parallel pairs of electrodes, and arranged at an obtuse angle with
said other electrode of said first parallel pairs of electrodes.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid crystal display unit, and more particularly
to an in-plane-switching (IPS) active-matrix liquid crystal display unit.
2. Description of the Related Art
Liquid crystal display (LCD) units are generally characterized by low-profile
shapes, lightweight structures, and low-power requirements. Particularly, active-matrix
liquid crystal display (AM-LCD) units which comprise a two-dimensional matrix of
pixels energizable by active devices are highly promising as high-image-quality
flat panel displays. Among those active-matrix liquid crystal display units which
are finding widespread use are thin-film-transistor liquid crystal display (TFT-LCD)
units which employ thin-film transistors (TFTs) used as active devices for switching
individual pixels.
Conventional AM-LCD units utilize a twisted-nematic (TN) electrooptical
effect, and comprise a liquid crystal layer sandwiched between two substrates.
The liquid crystal layer is activated when an electric field is applied substantially
perpendicularly to the substrates.
U.S. Pat. No. 3,807,831 discloses an in-plane-switching liquid crystal display
unit having a liquid crystal layer which is activated when an electric field is
applied substantially parallel to two substrates which sandwich the liquid crystal
layer therebetween, the liquid crystal display unit including interleaved arrays
of alternate parallel electrodes.
Japanese patent publication No. 21907/88 reveals an AM-LCD unit based on
a TN electrooptical effect and including interleaved or interdigitating arrays
of alternate parallel electrodes for the purpose of reducing parasitic capacitance
between a common electrode and a drain bus line or between a common electrode and
a gate bus line.
FIG. 1 of the accompanying drawings shows a conventional in-plane-switching
liquid crystal display unit. The illustrated conventional liquid crystal display
unit comprises a liquid crystal layer sandwiched between two glass substrates
11,
12, and interdigitating arrays of alternate parallel electrodes
70
mounted on one of the glass substrates
11. When a voltage is applied between
the electrodes
70, a liquid crystal activating electric field E
1
is generated parallel to the glass substrates
11,
12 and perpendicularly
to the interdigitating teeth of the electrodes
70 for thereby changing the
orientation of liquid crystal molecules
21. Therefore, the application of
the voltage between the electrodes
70 is effective to control the transmittance
of light through the liquid crystal layer. The term "the orientation of liquid
crystal molecules" used in this specification means the direction of the longer
axis of liquid crystal molecules.
With the in-plane-switching liquid crystal display unit shown in FIG. 1, it
is necessary that when the voltage is applied, the liquid crystal molecules be
rotated in a certain direction in order to achieve stable displays. To meet such
a requirement, it is customary to initially orient the liquid crystal molecules
in a direction that is slightly shifted from a direction perpendicular to the liquid
crystal activating electric field. Specifically, the liquid crystal molecules are
initially oriented at an angle of φ
LCO (<90°) with respect
to a direction perpendicular to the parallel pairs of the interdigitating teeth
of the electrodes. In the specification, the direction of the electric field and
the orientation of the liquid crystal molecules will be described in the range
of from -90° to 90° (the counterclockwise direction being positive) with
respect to a reference direction (φ=0) which is perpendicular to the parallel
pairs of the interdigitating teeth of the electrodes. As described later on, in
order to accomplish sufficient display contrast, it is necessary to rotate the
liquid crystal molecules 45° from the initial orientation. Therefore, it is
preferable to orient the liquid-crystal molecules at an angle of φ
LCO
in the range of 45°≦φ
LCO<90°. In the
in-plane-switching liquid crystal display unit shown in FIG. 1, the initial orientation
of the liquid crystal molecules is slightly shifted clockwise (as viewed from the
upper substrate
12) from the parallel pairs of the interdigitating teeth
of the electrodes. When the voltage is applied, therefore, the liquid crystal molecules
are rotated clockwise as indicated by the arrows.
The transmittance T of light passing through the liquid crystal cell shown in
FIG. 1 which is sandwiched between two confronting polarizers whose axes of polarization
transmission (directions of polarization) are perpendicular to each other is expressed
by the following equation (1):
##EQU1##
where φ
LC represents the orientation of the liquid crystal
molecules when a voltage is applied thereto, φ
P the direction
of the axis of transmission of the polarizer on which the light falls, Δn
the refractive index anisotropy of the liquid crystal layer, d the thickness of
the cell (the thickness of the liquid crystal layer, and λ the wavelength
of the light. The direction φ
A of the axis of transmission of
the polarizer from which the light exits is expressed by φ
A=φ
P+90°
or φ
A=φ
P-90°. It is possible to control
the transmittance of the light by varying the orientation φ
LC of
the liquid crystal molecules with a liquid crystal activating electric field parallel
to the substrates based on the above equation (1). If the direction of the axis
of transmission of one of the polarizers and the initial orientation of the liquid
crystal molecules are in agreement with each other (φ
LCO=φ
P
or φ
LCO=φ
A), then the liquid crystal display
unit is brought into a dark display state when no voltage is applied. If the orientation
of the liquid crystal molecules is rotated substantially 45° under a liquid
crystal activating electric field, then the transmittance becomes highest, and
the liquid crystal display unit is brought into a bright display state. Of course,
the polarizers may be so arranged that the liquid crystal display unit will be
brought into a dark display state when a voltage is applied.
It has been assumed for the sake of brevity that the liquid crystal molecules
in the liquid crystal layer between the upper and lower substrates are uniformly
rotated. Discussions based on such a simplified model do not essentially affect
the principles of the present invention. Actually, however, those liquid crystal
molecules which are held in contact with the surfaces of the upper and lower substrates
are relatively firmly fixed in position, and do not basically change their orientation,
whereas those liquid crystal molecules which are positioned nearly intermediate
between the upper and lower substrates change their orientation to a greater extent.
In view of these practical considerations, the in-plane angle φ
LC
through which the liquid crystal molecules rotate under an applied electric field
is represented as a function of coordinates in the transverse direction of the
liquid crystal layer.
In order to accomplish sufficient display contrast, the orientation of the liquid
crystal molecules may be rotated substantially 45° in the entire liquid crystal
layer. However, for the reasons described above, the liquid crystal molecules which
are positioned nearly intermediate between the upper and lower substrates are actually
rotated more than 45°.
Published Japanese translation No. 505247/93 of a PCT international publication
(International publication No. WO91/10936) describes improvements of angle of view
characteristics, which have been poor in TN liquid crystal display devices, achieved
by the in-plane-switching liquid crystal display unit. Because of their excellent
angle of view characteristics, in-plane-switching active-matrix liquid crystal
display units have recently been considered as a candidate for large-size display monitors.
FIG. 2 of the accompanying drawings shows the transmittance of the liquid crystal
display unit shown in FIG. 1 as it varies when the applied voltage is changed,
with respect to various observational directions in which the liquid crystal display
unit is observed. The observational directions are defined as φ
obs
and θ
obs where φ
obs is an angle of orientation
with respect to a direction perpendicular to the direction of the electrodes and
θ
obs is an angle of tilt from a direction perpendicular to the
substrates. A sample liquid crystal cell used in obtaining the measurements shown
in FIG. 2 was arranged such that φ
LC=85°, φ
P=85°,
and φ
A=-5°. The sample liquid crystal cell had interdigitating
arrays of alternate parallel electrodes, including interdigitating teeth each having
a width of 5 μm with adjacent ones of the interdigitating teeth being spaced
15 μm from each other. The sample liquid crystal cell had a liquid crystal
material whose refractive index anisotropy Δn is 0.067. The sample liquid
crystal cell had a thickness of 4.9 μm. It can be seen from FIG. 2 that the
transmittance does not change largely depending on the observational direction.
Therefore, the in-plane-switching liquid crystal display unit shown in FIG. 1 has
excellent angle of view characteristics.
However, the in-plane-switching liquid crystal display unit shown in FIG.
1 suffers a problem in that displayed images may look bluish or reddish to a viewer
depending on the observational direction.
FIG. 3 of the accompanying drawings shows the transmittance of the liquid crystal
display unit shown in FIG. 1 as it varies with the wavelength with respect to various
observational directions when the liquid crystal display unit is brought into a
bright display state. The measurements shown in FIG. 3 were obtained from the same
liquid crystal cell as the one used to obtain the measurements shown in FIG. 2.
In the liquid crystal cell, the orientation φ
LC of the liquid
crystal molecules is 40° because when the liquid crystal cell is brought into
a bright display state, i.e., when a voltage is applied, the orientation φ
LC
changes about 45° from the initial orientation φ
LCO=85°.
It can be understood from FIG. 3 that when the liquid crystal cell is brought into
a bright display state, the peak of the transmission spectrum at the observational
direction φ
obs=40° is shifted toward shorter wavelengths,
making displayed images bluish, and the peak of the transmission spectrum at the
observational direction φ
obs
=-50° is shifted toward longer wavelengths, making displayed images
reddish. The same tendency was observed at those observational directions which
are 180° spaced from the above observational directions.
As described above, while the in-plane-switching liquid crystal display unit
has
much better characteristics than the conventional TN liquid crystal display units
with regard to display contrast and freedom from gradation reversal, it suffers
the problem of tilts depending on the observational direction.
In the above liquid crystal cell, the liquid crystal molecules are directed at
the initial orientation φ
LCO=85° in the absence of any applied
voltage. When a voltage is applied to bring the liquid crystal cell into a bright
display state, the orientation φ
LC of the liquid crystal molecules
is 40° because the orientation φ
LC changes about 45°
from the initial orientation φ
LCO=85°. The direction in which
displayed images look bluish to the viewer corresponds to this orientation φ
LC
of the liquid crystal molecules, and the direction in which displayed images
look reddish to the viewer corresponds to the orientation perpendicular to the
orientation φ
LC. In a display mode based on birefringence, as
achieved by the above liquid crystal cell, light having a wavelength which satisfies
the relationship of Δn·d=λ/2 passes most efficiently through the
liquid crystal cell, as can be seen from the equation (1). The tinting depending
on the angle of view, i.e., the angle at which the liquid crystal cell is observed,
is caused by the dependency of the birefringence (Δn·d) of the liquid
crystal layer on the angle of view.
The dependency of the birefringence of the liquid crystal layer on the angle
of view will be described in detail below.
It is assumed that the angle formed between the direction of travel of light
and
the longitudinal direction of liquid crystal molecules is represented by θ
2,
the refractive index with respect to an ordinary ray of light which is vibrated
(polarized) in a direction perpendicular to a direction called the optic axis of
crystal is represented by n
o, and the refractive index with respect
to an extraordinary ray of light which is vibrated (polarized) parallel to the
optic axis is represented by n
e. Effective refractive index anisotropy
Δn′ when light is obliquely applied to the liquid crystal cell is
given by the following equation (2):
##EQU2##
When light is applied perpendicularly to the liquid crystal cell, since θ
2=90°,
the effective refractive index anisotropy Δn′ is given as Δn′=n
e-n
o.
In the direction in which displayed images look bluish to the viewer, because the
angle of view is tilted to the longitudinal direction of liquid crystal molecules,
the angle θ
2 becomes θ
2<90° and Δn′
becomes smaller. In the direction in which displayed images look reddish to the
viewer, because the angle of view is tilted to a direction perpendicular to the
longitudinal direction of liquid crystal molecules, the angle θ
2 remains
θ
2=90° and Δn′=Δn. FIGS. 4A and 4B illustrate
the refractive index anisotropy as it varies with the angle of view.
When light is applied obliquely to the liquid crystal cell, since the substantial
thickness d′ of the liquid crystal layer is given by d′=d/cos θ
obs,
the substantial thickness d′ becomes larger independent of the direction
in which the angle of view is tilted.
Because of changes of both the refractive index anisotropy and the thickness
of the liquid crystal layer, the birefringence (Δn′·d′)
varies, changing the tint depending on the angle of view.
Table 1 shown below contains details of the tinting.
| |
TABLE 1 |
| |
|
| |
Δn |
d |
Δn · d |
Remarks |
| |
|
| |
| Bluish tint |
Reduced |
Increased |
Reduced |
* |
| Reddish tint |
Unchanged |
Increased |
Increased |
** |
|
| *The longitudinal direction of the liquid crystal molecules when the liquid
crystal cell is in a bright display state. |
| **The direction perpendicular to the longitudinal direction of the liquid crystal molecules. |
As described above, the conventional in-plane-switching liquid crystal display
units cannot avoid tinting of displayed images in certain directions.
In view of the experimental data and considerations described above, the inventors
have made the present invention in efforts to suppress tinting in in-plane-switching
active-matrix liquid crystal display units.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an in-plane-switching
liquid crystal display unit which suffers minimum tinting of displayed images due
to changes in the angle of view and can display high-quality images.
According to a first aspect of the present invention, there is provided
an in-plane-switching liquid crystal display unit comprising a two-dimensional
matrix of pixel regions each including two auxiliary regions capable of compensating
for tinting characteristics of each other. With this arrangement, the directions
in which displayed images look bluish and reddish compensate for each other, thereby
suppressing tints of the displayed images due to changes in the angle of view,
i.e., the angle at which the liquid crystal display unit is observed.
According to a second aspect of the present invention, there is provided
an in-plane-switching liquid crystal display unit comprising a two-dimensional
matrix of pixel regions each including a first auxiliary region having liquid crystal
molecules directed in a first orientation when no electric field is applied thereto,
a second auxiliary region having liquid crystal molecules directed in a second
orientation extending at 90° with respect to the first orientation when no
electric field is applied thereto, and electric field generating means for generating
an in-plane electric field in a liquid crystal sealed layer and applying the in-plane
electric field to the liquid crystal molecules to rotate the liquid crystal molecules
in one direction while maintaining the first orientation and the second orientation
at 90° with respect to each other. With this arrangement, when the liquid
crystal display unit changes from a dark display state to a bright display state,
the directions in which displayed images look bluish and reddish compensate for
each other, thereby suppressing tints of the displayed images due to changes in
the angle of view.
According to a third aspect of the present invention, in the liquid crystal
display unit according to the second aspect, the electric field generating means
comprises a plurality of parallel pairs of electrodes disposed in the first auxiliary
region and the second auxiliary region, the electrodes disposed in the first auxiliary
region extending at 90° with respect to the electrodes disposed in the second
auxiliary region. When a voltage is applied, the liquid crystal molecules are rotated
in one direction while their first and second orientations are maintained at 90°
with respect to each other. Consequently, the directions in which displayed images
look bluish and reddish compensate for each other, thereby suppressing tints of
the displayed images due to changes in the angle of view.
According to a fourth aspect of the present invention, in the liquid crystal
display unit according to the second aspect, the electric field generating means
comprises a plurality of parallel pairs of electrodes, the electrodes extending
straight in the first auxiliary region and the second auxiliary region, and wherein
the liquid crystal molecules are oriented at 45° with respect to a direction
in which the electrodes extend in the first auxiliary region and the second auxiliary
region when no electric field is applied thereto. This arrangement is also effective
in suppressing tints of the displayed images due to changes in the angle of view.
According to a fifth aspect of the present invention, the liquid crystal
display unit according to the second aspect further comprises a front substrate
and a rear substrate, the pixel regions being disposed between the front substrate
and the rear substrate, the liquid crystal molecules have a substantially nil pretilt
angle with respect to the front substrate and the rear substrate. With this arrangement,
the liquid crystal molecules in the first auxiliary region and the second auxiliary
region operate stably.
According to a sixth aspect of the present invention, the liquid crystal
display unit according to the second aspect further comprises a front substrate
and a rear substrate, the pixel regions being disposed between the front substrate
and the rear substrate, wherein the liquid crystal molecules have pretilt angles
in a spray-type pattern with respect to the front substrate and the rear substrate,
and the pretilt angles of liquid crystal molecules near the front substrate and
the rear substrate are different from those of other liquid crystal molecules.
With this arrangement, the liquid crystal molecules in the first auxiliary region
and the second auxiliary region operate stably.
According to a seventh aspect of the present invention, there is provided
an in-plane-switching liquid crystal display unit comprising a two-dimensional
matrix of pixel regions each including a first auxiliary region having liquid crystal
molecules directed in a first orientation when no electric field is applied thereto,
a second auxiliary region having liquid crystal molecules directed in a second
orientation which is the same as the first orientation when no electric field is
applied thereto, and electric field generating means for generating an in-plane
electric field in a liquid crystal sealed layer and applying the in-plane electric
field to the liquid crystal molecules to rotate the liquid crystal molecules in
opposite directions while maintaining the first orientation and the second orientation
in symmetric relationship. With this arrangement, when the liquid crystal display
unit is in a bright display state, since the liquid crystal molecules in the first
and second auxiliary regions are rotated in opposite directions through substantially
45° with respect to their initial orientations, the orientations of the liquid
crystal molecules in the first and second auxiliary regions lie at 90° with
respect to each other. Consequently, the directions in which displayed images look
bluish and reddish compensate for each other, thereby suppressing tints of the
displayed images due to changes in the angle of view. The orientations of the liquid
crystal molecules in the first and second auxiliary regions lie at 90° with
respect to each other only when the liquid crystal display unit is fully in a bright
display state. However, even when the liquid crystal display unit displays intermediate
gradations, the tinting compensation is partly achieved to reduce tints of the
displayed images much better as compared with the conventional liquid crystal display
unit. Furthermore, the liquid crystal display unit can be manufactured relatively
simply because the initial orientations of the liquid crystal molecules are not
required to be different from each other in the first and second auxiliary regions.
According to an eighth aspect of the present invention, in the liquid crystal
display unit according to the seventh aspect, the electric field generating means
comprises a plurality of parallel pairs of electrodes, the electrodes extending
in the first auxiliary region and the second auxiliary region and being bent to
a V shape at a boundary between the first auxiliary region and the second auxiliary
region. With this arrangement, the boundary where the electrodes are bent to the
V shape divides the two auxiliary regions where the liquid crystal molecules are
rotated in opposite directions.
According to a ninth aspect of the present invention, in the liquid crystal
display unit according to the seventh aspect, the electric field generating means
comprises a plurality of pairs of confronting electrodes each having a longer arm
and a shorter arm which extend at a predetermined angle with respect to each other
and define a rectangular region, the pairs of confronting electrodes being inverted
in the first auxiliary region and the second auxiliary region. The pairs of confronting
electrodes each having a longer arm and a shorter arm define a rectangular region
such as an elongate rectangular region, a parallelogrammatic region, or a trapezoidal
region. Therefore, it is possible to generate an electric field slightly tilted
with respect to the shorter arms in the regions surrounded by the electrode pairs.
Since the direction in which the electric field is tilted is determined by the
layout of the electrode pairs, the liquid crystal molecules are rotated in opposite
directions in the two auxiliary regions by inverting the layout of the electrode
pairs in the auxiliary regions.
According to a tenth aspect of the present invention, in the liquid crystal
display unit according to the ninth aspect, the shorter arms of the electrodes
are slightly tilted with respect to a direction perpendicular to each of the first
and second orientations of the liquid crystal molecules when no electric field
is applied. With this arrangement, the direction of rotation of the liquid crystal
molecules is stable even in the vicinity of the shorter arms, making the liquid
crystal display unit operate stably, and increasing an allowable range of registration
errors in a process of manufacturing the liquid crystal display unit.
According to an eleventh aspect of the present invention, in the liquid
crystal display unit according to the seventh aspect, the electric field generating
means comprises a plurality of parallel pairs of electrodes disposed in the first
auxiliary region and the second auxiliary region, the electrodes disposed in the
first auxiliary region extending at 90° with respect to the electrodes disposed
in the second auxiliary region, and wherein each of the first and second orientations
extends parallel to a direction bisecting an angle formed between a direction in
which the electrodes of the parallel pairs extend in the first auxiliary region
and a direction in which the electrodes of the parallel pairs extend in the second
auxiliary region. This arrangement is also effective in suppressing tints of the
displayed images due to changes in the angle of view.
According to a twelfth aspect of the present invention, in the liquid crystal
display unit according to the seventh aspect, wherein each of the first and second
orientations is substantially the same as a direction in which a liquid crystal
material flows when the liquid crystal material is introduced into the first and
second auxiliary regions. With this arrangement, a period of time required to introduce
the liquid crystal material can be reduced, and an orientation defect called a
flow orientation which would otherwise occur after the liquid crystal material
is introduced is minimized.
According to a thirteenth aspect of the present invention, the liquid crystal
display unit according to the seventh aspect further comprises a front substrate
and a rear substrate, the pixel regions being disposed between the front substrate
and the rear substrate, the liquid crystal molecules have a substantially nil pretilt
angle with respect to the front substrate and the rear substrate. With this arrangement,
the liquid crystal molecules in the first and second auxiliary regions operate stably.
According to a fourteenth aspect of the present invention, the liquid crystal
display unit according to the seventh aspect further comprises a front substrate
and a rear substrate, the pixel regions being disposed between the front substrate
and the rear substrate, wherein the liquid crystal molecules have pretilt angles
in a spray-type pattern with respect to the front substrate and the rear substrate,
and the pretilt angles of liquid crystal molecules near the front substrate and
the rear substrate are different from those of other liquid crystal molecules.
This arrangement is also effective to operate the liquid crystal molecules stably
in the first and second auxiliary regions.
The above and other objects, features, and advantages of the present invention
will become apparent from the following description with references to the accompanying
drawings which illustrate examples of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary perspective view of a conventional in-plane-switching
liquid crystal display unit;
FIG. 2 is a graph showing how the transmittance of the in-plane-switching liquid
crystal display unit shown in FIG. 1 varies with the applied voltage in various
observational directions;
FIG. 3 is a graph showing how the transmittance of the in-plane-switching liquid
crystal display unit shown in FIG. 1 varies with the wavelength in various observational
directions when the in-plane-switching liquid crystal display unit is in a bright
display state;
FIGS. 4A and 4B are diagrams illustrative of the refractive index anisotropy
as it varies with the angle of view;
FIGS. 5A through 5E are schematic cross-sectional views of various basic forms
of a liquid crystal display unit according to the present invention;
FIG. 6A is a sectional plan view of a liquid crystal display unit according
to a first embodiment of the present invention;
FIG. 6B is a cross-sectional view taken along line 6B—6B
of FIG. 6A;
FIG. 7 is a sectional plan view of a liquid crystal display unit according to
a second embodiment of the present invention;
FIG. 8 is a sectional plan view of a liquid crystal display unit according to
a third embodiment of the present invention;
FIG. 9 is a sectional plan view of a liquid crystal display unit according to
a fourth embodiment of the present invention;
FIG. 10 is a sectional plan view of a liquid crystal display unit according
to a fifth embodiment of the present invention;
FIG. 11 is a sectional plan view of a liquid crystal display unit according
to a sixth embodiment of the present invention;
FIG. 12 is a sectional plan view of a liquid crystal display unit according
to a seventh embodiment of the present invention;
FIG. 13 is an enlarged fragmentary sectional plan view of the liquid crystal
display unit shown in FIG. 12;
FIG. 14 is an enlarged fragmentary sectional plan view of a liquid crystal display
unit according to an eighth embodiment of the present invention; and
FIGS. 15A and 15B are schematic views of a liquid crystal display unit according
to a ninth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Various basic forms of a liquid crystal display unit according to the present
invention will be described below with reference to FIGS. 5A through 5E.
The liquid crystal display unit of the first form shown in FIG. 5A has two auxiliary
regions
1,
2 disposed in a pixel region and having liquid crystal
molecules
21 whose respective initial orientations lie at 90° with
respect to each other. Electrodes
70 disposed in the auxiliary regions
1,
2, which provide parallel electrode pairs for generating electric fields
E
1 to activate the liquid crystal molecules
21, extend in respective
directions that lie at 90° with respect to each other. When a voltage is applied
to the liquid crystal display unit, the liquid crystal molecules
21 are
rotated in the same direction, clockwise in FIG. 5A, while their orientations remain
90° spaced from each other. Therefore, the directions in which displayed images
look bluish and reddish compensate for each other, thereby suppressing tints of
the displayed images due to changes in the angle of view, i.e., the angle at which
the liquid crystal display unit is observed.
The liquid crystal display unit of the second form shown in FIG. 5B has two auxiliary
regions
1,
2 disposed in a pixel region and having liquid crystal
molecules
21 whose respective initial orientations lie in the same direction,
i.e., parallel to each other. The liquid crystal molecules
21 are activated
by an electric field E
1 generated by parallel electrode pairs of electrodes
70 which are bent to a V shape at the boundary between the auxiliary regions
1,
2. When a voltage is applied to the liquid crystal display unit,
the liquid crystal molecules
21 are rotated counterclockwise in the auxiliary
region
1, and clockwise in the auxiliary region
2. When the liquid
crystal display unit is in a bright display state, since the liquid crystal molecules
21 are rotated substantially 45° from their initial orientation in
each of the auxiliary regions
1,
2, the orientations of the liquid
crystal molecules
21 in the auxiliary regions
1,
2 lie at
90° with respect to each other. Consequently, the directions in which displayed
images look bluish and reddish compensate for each other, thereby suppressing tints
of the displayed images due to changes in the angle of view. The orientations of
the liquid crystal molecules
21 in the auxiliary regions
1,
2
lie at 90° with respect to each other only when the liquid crystal display
unit is fully in a bright display state. However, even when the liquid crystal
display unit displays intermediate gradations, the tinting compensation is partly
achieved to reduce tints of the displayed images much better as compared with the
conventional in-plane-switching liquid crystal display unit.
The liquid crystal display unit of the third form shown in FIG. 5C has two auxiliary
regions
1,
2 disposed in a pixel region and having liquid crystal
molecules
21 whose respective initial orientations lie in the same direction,
i.e., parallel to each other. The liquid crystal molecules
21 are activated
by an electric field E
1 generated by parallel electrode pairs of electrodes
70 each having a longer arm and a shorter arm which extend substantially
perpendicularly to each other, such that each pair of electrodes
70 defines
an elongate rectangular region therebetween. The electrode pairs in the auxiliary
regions
1,
2 are reversed, i.e., turned upside down, with respect
to each other.
In each of the elongate rectangular regions surrounded by the electrode pairs
shown in FIG. 5C, the electrode pair generates an electric field which is slightly
tilted to the direction of the shorter arms of the electrodes
70. The direction
in which the electric field which is slightly tilted depends on the layout of the
electrode pairs. For example, if the electrode pairs are arranged such that each
of the electrodes of the electrode pairs is of an L shape, then the in-plane electric
field is tiled slightly counterclockwise (see the auxiliary region
2 in
FIG. 5C) with respect to the direction of the shorter arms of the electrodes
70.
If the electrode pairs are arranged such that each of the electrodes of the electrode
pairs is of an inverted L shape, then the in-plane electric field is tiled slightly
clockwise (see the auxiliary region
1 in FIG. 5C) with respect to the direction
of the shorter arms of the electrodes
70. For these reasons, when a voltage
is applied to the liquid crystal display unit, the liquid crystal molecules
21
are rotated counterclockwise in the auxiliary region
1, and clockwise in
the auxiliary region
2. Consequently, the directions in which displayed
images look bluish and reddish compensate for each other, thereby suppressing tints
of the displayed images due to changes in the angle of view.
Whether the electrode layout shown in FIG. 5C is able to generate an electric
field tilted sufficiently to rotate the liquid crystal molecules
21 in desired
directions in the auxiliary regions
1,
2 is determined by the ratio
of the length of the longer arms to the length of the shorter arms of the electrodes.
For example, if the elongate rectangular region surrounded by an electrode pair
were too slender, then such an electrode layout would not be preferable because
an in-plane electric field is generated in a direction transverse to the longer
arms of the electrodes.
As shown in FIG. 5C, each of the electrode pairs for generating the electric
field
E
1 to activate the liquid crystal molecules
21 comprises two confronting
electrodes which jointly define an elongate rectangular region therebetween and
each comprise a longer arm and a shorter arm that extend substantially perpendicularly
to each other. However, the region defined by each of the electrode pairs in surrounding
relation to the liquid crystal molecules
21 may be of any shape insofar
as the electrodes are capable of generating an electric field slightly tilted with
respect to a direction perpendicular to the initial orientation of the liquid crystal
molecules
21 within that region. For example, the region defined by each
of the electrode pairs may be of a quadrilateral shape such as a parallelogrammatic
shape, a trapezoidal shape, or the like other than the elongate rectangular shape
as shown in FIG. 5C. Therefore, the angle between the longer and shorter arms of
each of the electrodes
70 is not limited to a 90°, but any of various
other angles including obtuse angles. The shorter arm of each of the electrodes
70 may be of a curved shape.
The liquid crystal display unit of the fourth form shown in FIG. 5D has two auxiliary
regions
1,
2 disposed in a pixel region and having liquid crystal
molecules
21, and electrodes
70 for activating the liquid crystal
molecules
21, the electrodes
70 extending in the same direction,
i.e., parallel to each other. The liquid crystal molecules
21 in the auxiliary
regions
1,
2 have respective initial orientations that lie at 90°
with respect to each other. In the auxiliary regions
1,
2, the liquid
crystal molecules
21 are aligned such that they are inclined 45° to
the direction of the electrodes
70. With the liquid crystal display unit
shown in FIG. 5D, the auxiliary regions
1,
2 compensate for each
other with respect to their angle of view characteristics thereby to suppress tints
of displayed images.
The liquid crystal display unit of the fifth form shown in FIG. 5E has two auxiliary
regions
1,
2 disposed in a pixel region and having liquid crystal
molecules
21 whose respective initial orientations lie in the same direction,
i.e., parallel to each other. Electrodes
70 disposed in the auxiliary regions
1,
2, which provide parallel electrode pairs for generating electric
fields E
1 to activate the liquid crystal molecules
21, extend in
respective directions that lie at 90° with respect to each other. The liquid
crystal molecules
21 are oriented parallel to a direction which bisects
the angle formed between the direction of the electrodes
70 of the electrode
pairs in the auxiliary region
1 and the direction of the electrodes
70
of the electrode pairs in the auxiliary region
2. Specifically, the liquid
crystal molecules
21 are oriented uniformly at 45° with respect to
the direction of the electrodes
70 in each of the auxiliary regions
1,
2. With the liquid crystal display unit shown in FIG. 5E, the auxiliary
regions
1,
2 compensate for each other with respect to their angle
of view characteristics thereby to suppress tints of displayed images.
Detailed embodiments of the liquid crystal display unit according to the
present invention will be described below with reference to FIGS. 6A,
6B
through
15A,
15B. Those parts shown in FIGS. 6A,
6B through
15A,
15B which are identical to those shown in FIGS. 5A through 5E
are denoted by identical reference characters.
A liquid crystal display unit according to a first embodiment will be described
below with reference to FIGS. 6A and 6B.
As shown in FIG. 6A, the liquid crystal display unit according to the first embodiment
comprises a plurality of horizontal gate bus lines
55 and a plurality of
vertical drain bus lines
56 which jointly surround pixel regions arranged
in a two-dimensional matrix. Active devices
54 are positioned respectively
in the vicinity of the points of intersection of the gate bus lines
55 and
the drain bus lines
56 and associated with the pixel regions, respectively.
Each of the pixel regions has first and second auxiliary regions
1,
2.
A source electrode
71 and a common electrode
72 are each of a planar
shape comprising a combination of vertical and horizontal ladder structures. Specifically,
the vertical ladder structures of the source electrode
71 and the common
electrode
72 are disposed in the first auxiliary region
1, and the
horizontal ladder structures of the source electrode
71 and the common electrode
72 are disposed in the second auxiliary region
2. The source electrode
71 and the common electrode
72 have crosspieces positioned alternately
with each other. The source electrode
71 and the common electrode
72
are partly superimposed one over the other through an interlayer insulating film
57 (see FIG. 6B). The superimposed region of the source electrode
71
and the common electrode
72 provides an added capacitance. In order to prevent
line breaks, the common electrode
72 extend over pixels which are disposed
adjacent to each other in the direction in which the gate bus lines
55 extend,
with two upper and lower lines a, b shown in FIG. 6A.
As shown in FIG. 6B, the common electrode
72, the source electrode
71,
and the drain bus lines
56 are disposed on a first substrate
11.
The common electrode
72 is insulated from the source electrode
71
and the drain bus lines
56 by the interlayer insulating film
57.
Although not shown in FIGS. 6A and 6B, the gate bus lines
55 are also insulated
from the source electrode
71 and the drain bus lines
56 by the interlayer
insulating film
57. The above structure disposed on the first substrate
11 is covered with a protective insulating film
59. On the surface
of an active matrix substrate which is of the structure described above, there
is disposed an alignment film
31 comprising an insulative organic polymeric
film for aligning the surface of the active matrix substrate.
Color filters (not shown) of three primaries R, G, B are disposed in association
with the pixel regions on a second substrate (front substrate)
12 which
confronts the active matrix substr
