JP3386374B2 - Liquid crystal display - Google Patents

Abstract

A liquid crystal display device includes a first substrate; a second substrate; and a liquid crystal layer interposed between the first substrate and the second substrate and having liquid crystal molecules therein. The first substrate includes a first electrode facing the liquid crystal layer. The second substrate includes a second electrode facing the liquid crystal layer. The first electrode, the second electrode, and a region of the liquid crystal layer supplied with a voltage by the first electrode and the second electrode define a pixel region which is a unit for display. The pixel region includes a plurality of sub pixel regions, in each of which the liquid crystal molecules are aligned in an axial symmetrical manner. At least one of the first electrode and the second electrode includes a plurality of openings, which are regularly arranged, in the pixel region. The at least one of the first electrode and the second electrode having the openings include a plurality of polygonal sub electrode regions, each of which has at least a part of the plurality of openings at least one of at corners and along and overlapping sides thereof. The plurality of sub pixel electrodes are defined by the sub electrode regions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device used for a monitor such as a computer, a word processor, an in-vehicle navigation and a television.

[0002]

2. Description of the Related Art Currently, TN (Twis
Ted Nematic) type liquid crystal display devices are widely used.
In the liquid crystal layer of this TN type liquid crystal display device, the rubbing directions of the upper and lower two alignment films are changed so that the liquid crystal molecules are twisted (twist alignment) when no voltage is applied. TN
In the liquid crystal display device of the mode, there is a problem that the display quality largely depends on the viewing angle and that the gradation inversion phenomenon appears.

In order to solve such a problem, a method using a liquid crystal material having a negative dielectric anisotropy and a vertical alignment film (vertical alignment mode) has been proposed. In the vertical alignment mode, black display is performed when no voltage is applied. It is possible to obtain a good black display in an extremely wide viewing angle direction by roughly compensating for the birefringence due to the vertically aligned liquid crystal layer in the absence of voltage application by using a retardation plate having negative refractive index anisotropy. it can. Therefore, display with high contrast in a wide viewing angle direction is possible. However, in the vertical alignment mode, there is a problem that a gradation inversion phenomenon occurs when observed from the same direction as the tilted direction of the liquid crystal molecules in a voltage applied state.

[0004] JP-A 6-3 0 1036 No. discloses a configuration in which one opening in the central portion of the region facing the pixel electrode of the opposing electrode. As a result, the electric field generated perpendicularly to the electrode surface between the pixel electrode and the counter electrode can be inclined, so that in the vertical alignment mode, the liquid crystal molecules fall axially symmetrically when a voltage is applied, The viewing angle dependence is more averaged than when tilting in only one direction, and extremely good viewing angle characteristics can be obtained in all directions.

[0005]

[SUMMARY OF THE INVENTION However, the above-described, in JP-A-6-3 0 1036 of JP-configuration, it is difficult to generate uniform an oblique electric field to the pixel in the whole area, so that the voltage of the liquid crystal molecules There is a problem that a region in which the response to is delayed is generated in the pixel and an afterimage phenomenon appears.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a liquid crystal display device having a wide viewing angle characteristic and causing no afterimage phenomenon.

[0007]

A liquid crystal display device according to the present invention comprises a first substrate, a second substrate, and a liquid crystal layer sandwiched between the first substrate and the second substrate, The first substrate is connected to the plurality of scanning lines, the plurality of signal lines intersecting the plurality of scanning lines, and the plurality of scanning lines and the plurality of signal lines via switching elements, respectively. A plurality of picture element electrodes, the second substrate has a counter electrode facing the plurality of picture element electrodes, and each of the plurality of picture element electrodes,
The counter electrode and a region of the liquid crystal layer to which a voltage is applied by the pixel electrode and the counter electrode define a pixel region that is a display unit, and the pixel region is a liquid crystal of the liquid crystal layer. A liquid crystal display device having a plurality of sub-pixel regions in which molecules are oriented in axial symmetry , each of the pixel electrodes being in the pixel region.
A plurality of openings, and the plurality of openings are outside the pixel electrode.
The sub-pixel area includes a polygonal corner, including a shapeless one.
And a sub-electrode having the opening in at least one of the sides
It is defined by an area, which achieves the above objectives.

The polygons defining the plurality of sub picture element regions may be congruent with each other.

The polygon may have rotational symmetry, and the liquid crystal molecules of the liquid crystal layer may be oriented in axial symmetry with respect to the rotational symmetry axis of the polygon.

The liquid crystal layer is made of a liquid crystal material having a negative dielectric anisotropy, and liquid crystal molecules of the liquid crystal material are substantially perpendicular to the first substrate and the second substrate when no voltage is applied. You may orient to.

At least one of the first and second substrates may have a columnar protrusion outside the picture element region for controlling the thickness of the liquid crystal layer.

The liquid crystal layer may contain a chiral agent, and the liquid crystal molecules of the liquid crystal layer may have a helical pitch that is approximately four times the thickness of the liquid crystal layer.

Further, there is further provided a pair of polarizing plates sandwiching the first substrate and the second substrate, and at least one negative refractive index is provided between the first and second substrates and the pair of polarizing plates. You may further have the uniaxial retardation plate which has anisotropy.

Further, there is further provided a pair of polarizing plates sandwiching the first substrate and the second substrate, and at least one positive refractive index is provided between the first and second substrates and the pair of polarizing plates. You may further have the uniaxial retardation plate which has anisotropy.

Further, a pair of polarizing plates sandwiching the first substrate and the second substrate are further provided, and at least one biaxial position is provided between the first and second substrates and the pair of polarizing plates. You may have a phase difference plate.

The operation will be described below.

In the liquid crystal display device of the present invention, the electrode for applying a voltage to the liquid crystal layer has an opening (a region without an electrode) in a pixel region which is a display unit. Since no electric field is generated from the opening, the electric field around the opening is an oblique electric field inclined from the direction normal to the electrode surface. For example, liquid crystal molecules having a negative dielectric anisotropy are oriented with their long axes perpendicular to the electric field, so that the liquid crystal molecules around the openings are oriented radially (axially symmetric) by the oblique electric field. As a result, the viewing angle dependence due to the refractive index anisotropy of the liquid crystal molecules is averaged in the azimuth direction.

By forming a sub-electrode area having an opening in at least one of a corner and a side of a polygon, a plurality of sub-picture element areas in which liquid crystal molecules are axially symmetrically aligned are stably formed in the picture element area. be able to. If the sub-picture element regions are defined by a plurality of congruent polygons, the symmetry of the arrangement of the sub-picture element regions is improved, and the uniformity of the viewing angle characteristics is improved.
Further, the polygonal shape has rotational symmetry, so that the viewing angle characteristics are further uniformized. In addition, at least one of the edges of the sub-electrode region is at least one of the edges of the pixel electrode.
When formed so as to be aligned with each other, a liquid crystal display device in which disclination is less likely to occur at the end of the pixel electrode is provided.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below by taking a transmissive active matrix type liquid crystal display device as an example.

(Embodiment 1) A sectional view of one picture element region of a liquid crystal display device 100 according to Embodiment 1 is schematically shown in FIG. The liquid crystal display device 100 has a liquid crystal layer 40 sandwiched between an active matrix substrate 20 and a counter substrate (color filter substrate) 30. Active matrix substrate 2
0 is the insulating film 2 on the surface of the transparent substrate 21 on the liquid crystal layer 40 side.
2. The pixel electrode 24 and the alignment film 26 are provided in this order. The active elements (typically TFTs) and wirings formed on the substrate 21 for applying a voltage to the pixel electrodes 24 are omitted for simplicity. Counter substrate (color filter substrate) 3
0 has a color filter layer 32, a counter electrode 34, and an alignment film 36 in this order on the surface of the transparent substrate 31 on the liquid crystal layer 40 side. In this example, the alignment films 26 and 36 are vertical alignment films, and the liquid crystal layer 40 is formed of a liquid crystal material having negative dielectric anisotropy.

The picture element electrode 24 of the liquid crystal display device 100 has a plurality of openings (portions without electrodes) 24a. As will be described later in detail, the plurality of openings 24a define the sub-electrode area 50 having the openings 24a at the corners or sides of the polygon, and the liquid crystal in the sub-picture element area 60 defined by the sub-electrode area 50. It acts to orient the molecules 40a in an axially symmetrical manner.

As shown in FIG. 1 (a), when no voltage is applied to the liquid crystal layer 40, the liquid crystal molecules 40a
Are aligned vertically with respect to the surfaces of the vertical alignment films 26 and 36 by the alignment control force of the vertical alignment films 26 and 36. As shown in FIG. 1B, in the state where a voltage is applied to the liquid crystal layer 40, the liquid crystal molecules 40 a having negative dielectric anisotropy are arranged such that the long axes of the molecules are perpendicular to the lines of electric force E. Orient to. The lines of electric force E around the opening 24a are inclined with respect to the surfaces of the substrate 21 and the substrate 31,
The liquid crystal molecules 40a around the opening 24a are
It is oriented so as to fall radially around the center. As a result, the liquid crystal molecules 40a in the sub picture element region 60 are aligned in an axially symmetrical manner.

FIG. 2 shows a top view of a region corresponding to one picture element of the active matrix substrate 20 used in the liquid crystal display device 100 of the present invention. FIG. 1 described above corresponds to a view of the liquid crystal display device as seen from a cross section taken along the line II ′ of FIG. 2.

The active matrix substrate 20 includes a TFT 70 for controlling the voltage applied to the pixel electrode 24 and a TFT.
A gate wiring (scanning line) 72 that supplies a scanning signal to the gate of 70, a source line (signal line) 74 that supplies a data signal to the source of the TFT 70, and an auxiliary capacitance common wiring 76 that has the same potential as the pixel electrode 24. And have. In this example, a so-called Cs On Common structure in which the auxiliary capacitance is formed by using the auxiliary capacitance common wiring 76 is illustrated, but a Cs On Gate structure in which the auxiliary capacitance is formed by using the gate wiring may be used, The auxiliary capacity may be omitted.

The picture element electrode 24 has a plurality of openings 24a. The opening 24a is provided not only inside the pixel electrode 24 (for example, in the lower right corner of the sub electrode region 50a), but also because the outer shape of the pixel electrode 24 is lacking within the sub electrode region (for example, the sub electrode region). Lower left corner, upper left corner and upper right corner of electrode region 50a). The plurality of openings 24a have sub-electrode regions 50a to 50i whose openings are located at corners.
Stipulate. The sub-electrode area can be defined by a polygon formed by a line connecting the centers of the closest openings 24a, and the sub-electrode area in this example is nine quadrangles. The sub-electrode regions 50a, 50b, 50c and 50d are congruent squares (having a rotation axis of 4 times in the center), and the sub-pixel electrode regions 50e and 50d.
f is a rectangle (having a rotation axis twice at the center). The rectangles of the sub picture element electrode regions 50e and 50f share one side with the sub electrode regions 50c, 50d, 50g and 50h, respectively.

In the active matrix substrate 20 shown in FIG. 2, the edge side of the sub electrode region coincides with the edge side of the pixel electrode 24. In this way, the opening 24a is formed in the pixel electrode 24.
By providing the distances d and d ′ between the edge of the pixel electrode 24 and the opening 24a shown in the comparative example below.
(See FIG. 6A), it is possible to prevent the disclination that occurs at the end of the pixel electrode from occurring easily. By aligning the edges of the sub-electrode region with the edges of the pixel electrode 24, the alignment of the liquid crystal molecules from the center of the pixel electrode 24 in the edge direction, that is, in the direction A of FIG. 1B. It is possible to change continuously.

The liquid crystal display device 100 of this embodiment can be manufactured, for example, as follows. In the known process of making an active matrix substrate,
In the step of patterning the pixel electrodes, by using the pattern in which the openings 24a shown in FIG. 2 are formed, the active matrix substrate used in this embodiment can be used without increasing the number of steps in the conventional process. 20 can be formed. Known processes can be used for the other steps. The counter substrate 30 can also be manufactured using a known method. Picture element electrode 24 and counter electrode 3
4 is ITO (indium tin oxide) with a thickness of about 50 nm
It was formed of the film.

Polyimide vertical alignment films 26 and 36 (for example, JALS-204: manufactured by Nippon Synthetic Rubber Co., Ltd.) were applied to the obtained active matrix substrate 20 and counter substrate 30 by a printing method. As the vertical alignment films 26 and 36, materials having vertical alignment such as octadecylethoxysilane and lecithin can be widely used other than the above. Next, plastic beads having a diameter of about 4.5 μm were dispersed on the active matrix substrate 20. On the counter substrate 30, a seal portion made of epoxy resin mixed with glass fiber was formed around the display area by screen printing. Both of the substrates 20 and 30 were attached and heat-cured. A liquid crystal material (Δε =) having a negative dielectric anisotropy is formed in the gap between the active matrix substrate 20 and the counter substrate 30 by using a vacuum impregnation method.
-4.0, Δn = 0.08) was injected. Thus, the liquid crystal display device 100 was obtained. In the present embodiment, the example in which the opening 24a is formed in the pixel electrode 24 is shown, but the opening may be formed in the counter electrode. In any case, a plurality of openings may be formed in the electrode in the picture element area which is a display unit. In particular, the opening 24a is formed in the pixel electrode 24.
Then, the conductive film is patterned to form the pixel electrode 24.
Since the opening 24a can be formed at the same time in the step of forming the, the number of steps is not increased.

FIG. 3 shows a result of observing one picture element region 100a under a crossed Nicols with a polarization microscope in a state where a halftone voltage is applied to the liquid crystal display device 100. Picture element area 100
a has sub-picture element regions 60a to 60i. The sub-pixel regions 60a to 60i are defined by the sub-electrode regions 50a to 50i of FIG. 2, respectively. TFT
70, the gate line 72, the source line 74, a portion formed of a material that does not transmit light (or a portion where a black matrix is formed) and the opening 24a are observed to be black (the auxiliary capacitance common wiring 76 is transparent). Formed of electrodes). In this example, the pitch in the long side direction of the picture element region is about 300 μm, and the pitch in the short side direction is about 100 μm.
The diameter of the opening 24a is about 10 μm.

As is apparent from FIG. 3, the sub-picture element region 6
A cross extinction pattern is observed within 0a to 60i, which shows that the liquid crystal molecules are oriented in axial symmetry.
In the sub-picture element regions 60a to 60d defined by the square sub-electrode regions 50a to 50d, the extinction pattern having the four-time rotation axis is rectangular sub-electrode regions 50e, 50d.
In the sub-picture element regions 60e and 60f defined by f, an extinction pattern having a twice rotating axis is observed.

As described above, according to this embodiment, it is possible to form a region in which liquid crystal molecules are oriented in axial symmetry over the entire pixel region. Therefore, the display characteristics of this liquid crystal display device have wide viewing angle characteristics without depending on the azimuth angle in the viewing angle direction. When no voltage was applied, all liquid crystal molecules stood perpendicular to the substrate surface, and a good black display was shown. Further, the rising response time was about 20 msec, and good white display could be obtained. Even in the halftone display, the axisymmetric orientation was formed without being disturbed, the response speed was sufficiently fast, and the afterimage phenomenon was not observed. The obtained axisymmetric orientation was extremely stable, and no orientation failure occurred in the repeated operation test.

In the above example, the rectangular sub electrode region 50 is formed.
Although a to 50i are formed, the shape of the sub electrode region is not limited to these. Any polygon may be used as long as it has an opening in at least one of a corner and a side of the polygon. Although it may be a triangle, in order to make the azimuth dependence of the viewing angle uniform,
A square or more is preferable. Further, since the square has a higher rotational symmetry than the rectangle, the effect of making the viewing angle characteristics uniform is excellent. A pixel electrode 2 having a rectangular sub-electrode region 50
Another example of No. 4 is shown in FIGS. Further, the pixel electrode 2 including the polygonal sub-electrode regions 50 of pentagon or more
4 is shown in FIGS. 5 (a) to 5 (c). For example, in FIG.
As shown in (a), the openings 24a may be arranged at the corners of the hexagon, or as shown in FIG. 5 (b), the openings 24a may be further formed at the center of the hexagon. . When the picture element electrode 24 of FIG. 5B is used, the sub picture element region in which the liquid crystal molecules are oriented in axial symmetry becomes a triangle. In addition, FIG.
As shown in, the rectangular opening 24a may be arranged on the side of the octagon. The shape of the opening 24a is not limited to a circle or a rectangle, and may be any shape. Since the sub-picture element region is preferably a polygon having high rotational symmetry (closest to a circle), it is preferably a regular polygon. Since it is preferable that the plurality of sub-picture element regions are also arranged to have rotational symmetry, it is preferable to regularly arrange congruent regular polygons. In any case, at least one of the side edges of the sub-electrode region may match at least one of the side edges of the pixel electrode.

The size of the sub picture element region 60 is about 20 μm.
A uniform axial symmetry can be stably formed in the range of about 50 μm square. When the opening 24a has a circular shape, the diameter thereof is preferably about 5 μm to about 20 μm. Since the pixel aperture ratio decreases when a large number of openings 24a are formed, the arrangement (shape of the sub-electrode regions) and the number of the openings 24a are considered in consideration of the balance between the viewing angle characteristics and the display brightness according to the application of the display device. Should be set appropriately.

Comparative Example 1 FIG. 6A shows a top view of a region corresponding to one picture element of the active matrix substrate used in the liquid crystal display device of the comparative example. The pixel electrode 24 has a plurality of openings 24a. In this example, the sub electrode region is three quadrangles 50a, 50c, and 50e.
FIG. 6B shows a result of observing one picture element region 100b under a crossed Nicols with a polarization microscope in a state where a halftone voltage is applied to the liquid crystal display device. The picture element area 100b has sub picture element areas 60a, 60c, and 60e. The sub picture element regions 60a, 60c, 60e are defined by the sub electrode regions 50a, 50c, 50e of FIG. 6A, respectively. In FIG. 6A, the distances d and d ′ from the edge of the pixel electrode 24 to the opening 24a are about 5 μm.
When the opening is formed at least 2 μm away from the edge of the pixel electrode, the horizontal electric field generated by the bus line electrode near the edge of the pixel electrode for connecting the active element causes the liquid crystal molecules to move. It is possible to obtain the effect that it is possible to prevent the orientation from becoming unstable.

However, in the active matrix substrate of FIG. 6A, between the edge of the pixel electrode and the opening,
Since a region in which the orientation of liquid crystal molecules changes discontinuously is formed, the disclination line 42 is formed at the end of the pixel electrode.
Occurs. Such disclination line 4
When 2 occurs, the tilting direction of the liquid crystal molecules is not constant due to the electric field, which causes a problem that the display is rough and the display quality is deteriorated.

(Embodiment 2) In Embodiment 1 described above, plastic beads are used as spacers for controlling the thickness of the liquid crystal layer 40 and are dispersed on the active matrix substrate. As shown in FIG. 7, if the plastic beads 92 are present in the pixel region 100c, some of the axially symmetric orientations in the pixel region 100c may be disturbed. In order to prevent the disorder of the orientation due to the plastic beads, in the second embodiment, the columnar protrusions made of a polymer are formed in the region that does not affect the display by using the photolithography technique.

Similar to the first embodiment, after forming the active matrix substrate 20, a photocurable resin (eg, OM) is used.
R83: manufactured by Tokyo Ohka Co., Ltd.) was applied to about 4 μm. This photo-curable resin film is exposed and developed so that the columnar protrusions 94 having a diameter of about 20 μm remain on the wiring around the picture element region, and FIG.
The columnar protrusions 94 made of the polymer shown in (a) were formed. Further, as shown in FIG. 8B, when the auxiliary capacitance common electrode 76 is formed of a material such as a metal material that does not transmit light, the columnar protrusion 94 is formed on the auxiliary capacitance common electrode 76. May be.

Thereafter, a liquid crystal display device was formed in the same manner as in the first embodiment. As a result of observing the pixel region 100d with a polarizing microscope in a state where a halftone voltage was applied to the obtained liquid crystal display device, as shown in FIG.
Liquid crystal molecules fall radially corresponding to a, and the pixel region 100
It was confirmed that a plurality of axisymmetric orientations were formed in d. Similar to the liquid crystal display device 100 of the first embodiment, the liquid crystal display device of the second embodiment has a wide viewing angle characteristic, a sufficiently fast response speed, and no afterimage phenomenon was observed. Furthermore, since the plastic beads were not sprayed, no disturbance of the axisymmetric orientation when they were in the picture element was observed. In addition, the in-plane uniformity of the thickness of the liquid crystal layer was improved, and the display quality was improved.

(Embodiment 3) Embodiments 1 and 2 above
In the above, as the material of the liquid crystal layer 40, a nematic liquid crystal material having negative dielectric anisotropy (for example, S811: manufactured by Merck) was used. In this embodiment, a chiral agent is added to the liquid crystal material. A chiral agent was added so that the helical pitch in the liquid crystal layer 40 was about 18 μm. The reason for adding the chiral agent so that the twist angle is 90 °, that is, the pitch is approximately four times the cell thickness, is as follows. First, by adopting a 90 ° twist structure when an electric field is applied, it is possible to optimize the light utilization efficiency and the white display color balance as in the conventional TN mode liquid crystal display device. If the added amount of the chiral agent is too small, the twist alignment when the electric field is applied may become unstable, and if the added amount of the chiral agent is too large, the vertical alignment may become unstable when no voltage is applied. .

A liquid crystal display device was manufactured in the same manner as in Embodiment 1 except that the chiral agent was added to the liquid crystal material as described above. When the picture element region 100e is observed with a polarization microscope in a state where a halftone voltage is applied to the obtained liquid crystal display device, as shown in FIG.
Liquid crystal molecules fall radially corresponding to a, and the pixel region 100
It was confirmed that a plurality of axisymmetric orientations were formed in e. Similar to the liquid crystal display device 100 of the first embodiment, the liquid crystal display device of the third embodiment has a wide viewing angle characteristic, a sufficiently fast response speed, and no afterimage phenomenon was observed. Further, as compared with the liquid crystal display device 100 of the first embodiment using the liquid crystal layer to which the chiral agent is not added, the dark field portion is reduced and the brightness of the liquid crystal display device is improved. According to the present embodiment, it is possible to improve the decrease in the transmittance of the liquid crystal display device when a large number of openings 24a are formed in the pixel electrode 24 or when large openings 24a are formed.

(Fourth Embodiment) In the fourth embodiment,
An example will be described in which the viewing angle is further expanded by combining the liquid crystal display devices of Embodiments 1 to 4 described above with an appropriate retardation plate.

Of the pair of polarizing plates 102a and 102b provided in the liquid crystal display device 100, the absorption axis direction of the polarizing plate 102b on the backlight side is the x axis, and the direction perpendicular to the absorption axis direction on the display surface is the y axis. The direction normal to the display surface is the z axis.

As shown in FIGS. 11A and 11B,
When the refractive index of the retardation plate is (nx, ny, nz),
A retardation plate having a relationship of nx = ny> nz was provided between the polarizing plate and the glass substrate of the liquid crystal display device 100.

As shown in FIG. 11A, when one retardation plate 104a is provided between the polarizing plate 102a and the substrate of the liquid crystal display device 100, the retardation of the retardation plate 104a = film thickness. (Dp) × {(nx + ny) /
2-nz} is the retardation of the liquid crystal layer = thickness of the liquid crystal layer ×
The viewing angle characteristics were improved by setting the value to be approximately 1/2 to 3/2 of (ne-no). Similar effects were obtained when one retardation plate was provided between the polarizing plate 102b and the liquid crystal display device 100.

As shown in FIG. 11B, the polarizing plate 10
When the retardation plates 104a and 104b are provided between the glass substrates 2a and 102b, respectively, the retardations of the respective retardation plates 104a and 104b are summed up to about 1/2 of the retardation of the liquid crystal layer. 3 /
By setting the value to be 2, the viewing angle characteristic was improved.

The effect of the liquid crystal display device provided with the retardation films 104a and 104b shown in FIGS. 11A and 11B will be described with reference to FIG. The retardation of the liquid crystal layer is 3
60 nm (liquid crystal layer thickness 4.5 μm, ne = 1.55,
FIG. 12 (a) shows the viewing angle dependence of the transmittance in the black display state when the retardation plates 104a and 104b having various retardations are used for no = 1.47). The horizontal axis θ in FIG. 12A indicates the viewing angle (angle formed with the normal to the display surface) in the 45 ° direction with the polarization axis, and the vertical axis represents the transmittance (value normalized with the transmittance of air being 1). Indicates. FIG. 14B shows the result of plotting the transmittance value at the viewing angle θ of 60 ° in FIG. 12A against the retardation.

As can be seen from FIG. 12A, when the phase difference plates 104a and 104b are not provided (0 nm), the viewing angle is inclined in the 45 ° direction with the polarization axis (θ becomes large).
As a result, the transmittance increases (light leakage occurs) and good black display cannot be obtained. Retardation plate 104a (and / or 104b)
And its retardation (dp × (nx + ny) /
2-nz) to the appropriate value,
As shown in (b), the transmittance can be reduced. In particular, the retardation of the retardation plate is about 180 nm
(1/2 of retardation of liquid crystal layer) to about 540 nm
Within the range of (3/2 of the retardation of the liquid crystal layer),
The increase in the transmittance when θ is 60 ° can be reduced to less than half that in the case where the retardation plate is not provided.

As described above, in the case where there is no retardation plate, in the black display when no voltage is applied, the black display is good when observed from the front (the direction normal to the display surface), but the diagonal display At the viewing angle (direction tilted from the normal direction), due to the phase difference of the liquid crystal layer, light leakage occurs and good black display cannot be performed (black floating). Since the above retardation plate compensates for the retardation of the liquid crystal layer at an oblique viewing angle, it is possible to provide a good black display in a wide viewing angle. That is, it is possible to display a high contrast in a wide viewing angle. Furthermore, FIG.
As shown in (a) and (b), retardation plates 106a and / or 106b having a relationship of nx> ny = nz were provided between the polarizing plates 102a and / or 102b and the glass substrate. By setting the retardation {dp × (nx− (ny + nz) / 2} of the retardation plates 106a and 106b to a value of about 1/10 to about 7/10 of the retardation value of the liquid crystal layer in total, good display characteristics can be obtained. By providing this retardation plate, the absorption axis of the polarizing plate and the
The effect was to improve the black display when viewed from the azimuth angle of 5 °.

The effect of the liquid crystal display device provided with the retardation films 106a and 106b shown in FIGS. 13A and 13B will be described with reference to FIG. The retardation of the liquid crystal layer is 360 nm (the thickness of the liquid crystal layer is 4.5 μm, ne = 1.5).
5, no = 1.47), the viewing angle of the transmittance in the black display state when the retardation plates 106a and 106b having different retardations (dp × (nx− (ny + nz) / 2) in the polarization axis direction are used. The dependency is shown in FIG.
In addition, the retardation (dp ×
(Nx + ny) / 2-nz) was fixed at 250 nm.
The horizontal axis θ in FIG. 14A indicates the viewing angle (angle formed with the normal to the display surface) in the 45 ° direction with the polarization axis, and the vertical axis indicates the transmittance (value normalized with the transmittance of air being 1). Indicates. Figure 1
FIG. 14B shows the result of plotting the transmittance value at a viewing angle θ of 60 ° in FIG.

As can be seen from FIG. 14A, when the phase difference plates 106a and 106b are not provided (0 nm), the viewing angle is inclined in the 45 ° direction with the polarization axis (θ becomes large).
As a result, the transmittance increases (light leakage occurs) and good black display cannot be obtained. Retardation plate 106a (and / or 106b)
And its retardation (dp × (nx− (ny +
By setting nz) / 2) to an appropriate value,
As shown in 4 (b), the transmittance can be reduced. Especially, the retardation of the retardation plate is about 36 nm.
(1/10 of retardation of liquid crystal layer) to about 252 nm
In the range of (7/10 of the retardation of the liquid crystal layer), the transmittance is less than about 0.03, so that θ is 60.
The increase in the transmittance at ° can be made lower than that without the retardation plate.

The above-mentioned two types of phase difference plates 104a and 104
b and 106a and 106b may be used in combination as shown in FIG. Not limited to the example shown in FIG. 15A, two kinds of retardation plates can be used in any combination. Furthermore, FIGS. 15 (b) and 15 (c)
As shown in FIG. 2, a biaxial retardation plate 110 having a refractive index anisotropy almost equivalent to that when two types of retardation plates are combined is used.
Similar viewing angle performance could be obtained using a and / or 110b. Instead of two uniaxial retardation plates, one 2
The manufacturing process can be reduced by using the axial retardation plate.

In the above-described embodiment, the example using the liquid crystal layer in the vertical alignment mode has been described, but the present invention is not limited to this, and the same effect can be obtained in the horizontal alignment mode (TN mode, STN mode, etc.). . Further, although the present invention has been described in the above embodiment by taking a transmissive active matrix liquid crystal display device as an example, the present invention is not limited to this, and is widely applied to a reflective liquid crystal display device and a simple matrix liquid crystal display device. Applicable.

[0053]

As described above, according to the present invention, there is provided a liquid crystal display device in which disclination is less likely to occur at the ends of the picture element electrodes. Further, according to the present invention, there is provided a liquid crystal display device having a wide viewing angle characteristic and causing no afterimage phenomenon. Since the liquid crystal display device of the present invention uniformly and stably forms a plurality of axially symmetric orientations for each pixel region, it has a wide viewing angle with excellent display quality and a high-speed response. Further, the liquid crystal display device of the present invention can be manufactured without increasing the number of processes in the conventional manufacturing method, so that the cost does not increase.

The liquid crystal display device of the present invention is a computer,
It is preferably used for monitors such as word processors and in-vehicle navigations, and liquid crystal display devices for televisions.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a cross-sectional view of one picture element region of a liquid crystal display device according to the present invention. (A) is a state in which no voltage is applied,
(B) shows a halftone voltage application state, respectively.

FIG. 2 is a top view of a region corresponding to one picture element of an active matrix substrate used in the liquid crystal display device according to the present invention.

FIG. 3 is a diagram showing a result of observing one picture element region with a polarization microscope under a crossed Nicols in a state where a halftone voltage is applied to the liquid crystal display device of the first embodiment.

FIG. 4 is a top view showing another example of the pixel electrode used in the liquid crystal display device of the present invention.

FIG. 5 is a top view showing another example of the pixel electrode used in the liquid crystal display device of the present invention.

FIG. 6A is a top view of a region corresponding to one picture element of an active matrix substrate used in a liquid crystal display device of a comparative example, and FIG. 6B is a halftone voltage applied to the liquid crystal display device of the comparative example. It is a figure which shows the result of having carried out the polarization microscope observation of 1 picture element area | region under orthogonal Nicols in the state which it did.

FIG. 7 is a diagram showing the result of polarization microscope observation of one pixel region under a crossed Nicols showing the disorder of the axially symmetrical orientation in the pixel region due to the plastic beads.

FIG. 8 is a top view of an active matrix substrate having columnar protrusions made of a polymer. (A) shows an example in which columnar protrusions are formed on the gate wiring, and (b) shows an example in which columnar protrusions are formed on the auxiliary capacitance common wiring.

FIG. 9 is a diagram showing a result of observing one picture element region with a polarization microscope under a crossed Nicols in a state where a halftone voltage is applied to the liquid crystal display device of the second embodiment.

FIG. 10 is a diagram showing a result of observing one picture element region under a crossed Nicols with a polarization microscope in a state where a halftone voltage is applied to the liquid crystal display device of the third embodiment.

FIG. 11 is a cross-sectional view schematically showing the configuration of the liquid crystal display device of Embodiment 4.

FIG. 12A is a graph showing the viewing angle dependence of the transmittance in the black display state of the liquid crystal display device having the retardation plates 104a and 104b of the fourth embodiment. (B) is
It is a graph which shows the relationship of the transmittance | permeability and the retardation of a phase difference plate in the case where the viewing angle (theta) of (a) is 60 degrees.

FIG. 13 is a cross-sectional view schematically showing the configuration of another liquid crystal display device of Embodiment 4.

FIG. 14A is a graph showing the viewing angle dependence of the transmittance in the black display state of the liquid crystal display device having the retardation plates 106a and 106b of the fourth embodiment. (B) is
It is a graph which shows the relationship of the transmittance | permeability and the retardation of a phase difference plate in the case where the viewing angle (theta) of (a) is 60 degrees.

FIG. 15 is a cross-sectional view schematically showing the configuration of another liquid crystal display device of Embodiment 4.

[Explanation of symbols]

20 active matrix substrate 21, 31 substrate 22 insulating film 24 picture element electrode 24a openings 26, 36 alignment film 30 counter substrate (color filter substrate) 32 color filter layer 34 counter electrode 40 liquid crystal layer 40a liquid crystal molecules 50, 50a, 50b, 50c Sub-electrode regions 60, 60a, 60b, 60c Sub-pixel regions 70 TFT 72 Gate wiring 74 Source wiring 76 Auxiliary capacitance common wiring 92 Plastic beads 94 Columnar protrusion 100 Liquid crystal display devices 100a, 100b, 100c, 100d, 100e
Pixel area

─────────────────────────────────────────────────── --- Continuation of front page (56) References JP-A-9-22025 (JP, A) JP-A-6-43461 (JP, A) JP-A-1-291215 (JP, A) JP-A-10- 186330 (JP, A) JP 10-90708 (JP, A) JP 10-142591 (JP, A) JP 6-294962 (JP, A) JP 3-103822 (JP, A) JP-A 8-190101 (JP, A) JP-A 64-42631 (JP, A) JP-A 8-15714 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/1343 G02F 1/1337 G02F 1/1362

Claims (9)

(57) [Claims] 1. A first substrate, a second substrate, and a liquid crystal layer sandwiched between the first substrate and the second substrate, the first substrate including a plurality of scanning lines. A plurality of signal lines intersecting the plurality of scanning lines, and a plurality of pixel electrodes respectively connected to the plurality of scanning lines and the plurality of signal lines via switching elements, The two substrates have counter electrodes facing the plurality of picture element electrodes, and a voltage is applied to each of the plurality of picture element electrodes, the counter electrodes, and the picture element electrodes and the counter electrodes. A liquid crystal display device, wherein a region of a liquid crystal layer defines a pixel region which is a display unit, and the pixel region has a plurality of sub-pixel regions in which liquid crystal molecules of the liquid crystal layer are oriented in axial symmetry. , Each of the picture element electrodes has a plurality of openings in the picture element region.
And the plurality of openings lack the outer shape of the pixel electrode.
And the sub-pixel region is at least one of the corners and sides of the polygon.
Liquid crystal surface defined by a sub-electrode region having the opening on one side
Indicating device. 2. The liquid crystal display device according to claim 1, wherein the polygons defining the plurality of sub-picture element regions are congruent with each other. 3. The liquid crystal display device according to claim 2, wherein the polygon has rotational symmetry, and the liquid crystal molecules of the liquid crystal layer are oriented in axial symmetry with respect to the rotational symmetry axis of the polygon. . 4. The liquid crystal layer is formed of a liquid crystal material having a negative dielectric anisotropy, and liquid crystal molecules of the liquid crystal material are formed on the first substrate and the second substrate when no voltage is applied. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is aligned substantially vertically. 5. The liquid crystal display device according to claim 1, wherein at least one of the first and second substrates has a columnar protrusion that controls the thickness of the liquid crystal layer, outside the pixel region. 6. The liquid crystal display device according to claim 1, wherein the liquid crystal layer contains a chiral agent, and the liquid crystal molecules of the liquid crystal layer have a spiral pitch that is approximately four times the thickness of the liquid crystal layer. 7. A pair of polarizing plates sandwiching the first substrate and the second substrate is further provided, and at least one negative plate is provided between the pair of polarizing plates of the first substrate and the second substrate. The liquid crystal display device according to claim 1, further comprising a uniaxial retardation plate having a refractive index anisotropy. 8. A pair of polarizing plates sandwiching the first substrate and the second substrate is further provided, and at least one positive plate is provided between the pair of polarizing plates of the first substrate and the second substrate. The uniaxial retardation plate having a refractive index anisotropy is further included.
The liquid crystal display device according to item 1. 9. A pair of polarizing plates sandwiching the first substrate and the second substrate is further provided, and at least one biaxial plate is provided between the pair of polarizing plates of the first substrate and the second substrate. The liquid crystal display device according to claim 1, which has a retardation film.