JP2000193980A - Liquid crystal display element and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a vertical alignment liquid crystal display element in which a bright defect at voltages close to the threshold voltage is prevented and with which a high contrast display and excellent response characteristics are attained and a method for its manufacture. SOLUTION: The vertical alignment liquid crystal display element is provided with a pair of substrates 10, 11, placed opposite to each other with a specified gap and having electrodes formed on the respective surfaces and a liquid crystal layer interposed between the pair of the substrates 10, 11. Liquid crystal molecules are vertically aligned with respect to the surfaces of the substrates in the case no voltage is applied to the liquid crystal layer. A means is provided to generate an oblique electric field inclined with respect to the substrate surfaces between the pair of the substrates 10, 11 in the case a voltage is applied to the liquid crystal layer. The surfaces of the substrates 10, 11 in contact with the liquid crystal layer are subjected to an alignment treatment to provide a pretilt angle to the liquid crystal molecules in the liquid crystal layer in a direction different from the direction of the oblique electric field. The alignment direction of the liquid crystal molecules under voltage application is set by the directions of the oblique electric field and the pretilt.

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, and more particularly to a vertical alignment type liquid crystal display device having excellent display quality such as contrast characteristics and responsiveness, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Vertical alignment type electric field control based on birefringence E
CB (Electrically Control)
d Birefringence) operating in C mode
SH-LCD (Color Super Hoeotr)
opic liquid crystal display device) has high contrast display when combined with a polarizing plate having a crossed Nicols arrangement because liquid crystal molecules are oriented perpendicular to the upper and lower substrates when no voltage is applied.

FIGS. 6A and 6B are an enlarged plan view of a part (about one pixel) of a CSH-LCD and a cross-sectional view taken along line AA '. Two-dimensional directions x-
The y plane is a direction parallel to the glass substrate surface of the liquid crystal cell, the x axis matches the longitudinal direction of the segment electrode 62, and the y axis matches the longitudinal direction of the common electrode 63.

FIG. 6A is a plan view of an area corresponding to one pixel when applied to a simple matrix display device. FIG.
3A, the segment electrode 62 and the common electrode 6
One pixel region is formed in a region where 3 intersects. The pixel region has two left and right divided regions (domains) with the slit 67 as a boundary.

[0005] The structure is such that a pair of glass substrates 6 are arranged between polarizing plates (not shown) whose polarization axis directions p and d are orthogonal to each other.
0 and 61 are sandwiched, and a transparent electrode 6 is provided on each glass substrate.
2 and 63 and vertical alignment films 64 and 65 are formed, and a liquid crystal 66 having a negative dielectric anisotropy is sealed between the glass substrates. In this figure and other figures, the liquid crystal molecules are drawn as elongated ellipses in the direction of the director.

In the ECB mode, when voltage is applied, the liquid crystal molecules at the center between the upper and lower substrates of the cell begin to fall, and at the same time, the retardation of the liquid crystal layer changes and the transmissivity gradually increases. have.

In this CSH-LCD, as shown in FIG. 6A, a slit-shaped opening 67 is provided in the electrode,
A wider viewing angle characteristic is obtained by forming one pixel by two regions (division alignment structures) having different alignment directions. That is, the directionality of the liquid crystal molecules 66 that fall when a voltage is applied is controlled by the oblique electric fields 68a and 68b generated between the segment electrode 62 and the common electrode 63. FIG.
As shown in (B), the liquid crystal molecule director is divided into two by the oblique electric field from the left and right directions.

If there is no opening slit 67,
The liquid crystal molecule director collides at the center of the pixel due to the electric field in the left-right direction, and has a random direction. When the opening slit 67 is provided, the liquid crystal molecule director 66 is tilted in the left and right directions due to the oblique electric field. Therefore, as shown by arrows in FIG. It is effective to arrange them in the ° direction.

[0009]

However, this conventional C
In the SH-LCD, the liquid crystal molecule director at the electrode edge falls down in the horizontal direction at a lower voltage than the liquid crystal molecule director at the pixel center due to the oblique electric field. Therefore, when the polarizing axis angle of the polarizing plate is 45 ° / 135 °, o
There is a problem that light leakage occurs due to retardation at the ff voltage (near the threshold voltage), and the contrast is reduced.

When the polarizer angles p and d are arranged at 0 ° / 90 ° (overlap with the x and y axes), the liquid crystal molecule director and the polarizing axis direction of the polarizer are aligned. Dropout can be prevented. In this case, however, the ECB effect is reduced because the axial directions of the liquid crystal molecule director and the polarizing plate at the center of the pixel are aligned.

On the other hand, in order to increase the contrast under multiplex driving conditions, a chiral agent is added to a liquid crystal material. Also in this case, the polarization axis angle is typically 45 ° / 135 °, but this is 0 ° / 90 °.
The light leakage at the off voltage can be suppressed by setting the angle to the same degree as in the case where the chiral agent is not added.

In the case of adding a chiral agent, since the liquid crystal molecule director is twisted, the ECB effect is not reduced as described above, and a high contrast can be obtained. However, in this arrangement, the response is extremely slow (response time is about 10 times), which is not practical.

An object of the present invention is to provide a vertical alignment type liquid crystal display device which can obtain high contrast display by suppressing light leakage near a threshold voltage and has good responsiveness, and a method of manufacturing the same. .

[0014]

In a vertical alignment type liquid crystal display device according to the present invention, electrodes are formed on a surface, respectively, and a pair of substrates arranged opposite to each other at a predetermined interval, and are disposed between the pair of substrates. A liquid crystal layer, wherein the liquid crystal molecules are vertically aligned with respect to the substrate surface in a state where no voltage is applied to the liquid crystal layer, wherein when applying a voltage to the liquid crystal layer, Means for generating an oblique electric field inclined with respect to the substrate surface is provided between the pair of substrates, and the surface of the substrate in contact with the liquid crystal layer is applied to liquid crystal molecules of the liquid crystal layer in a direction different from the direction of the oblique electric field. An orientation process for giving a pretilt angle is performed, and the orientation direction of the liquid crystal molecules when a voltage is applied is set by the oblique electric field and the direction of the pretilt.

The method of manufacturing a vertical alignment type liquid crystal display device according to the present invention comprises the steps of: preparing a pair of substrates on which an alignment process is performed so that liquid crystal molecules are vertically aligned and an electrode having an opening is formed on the surface; A step of subjecting the surface of the substrate to an alignment treatment for giving a pretilt angle to the liquid crystal molecules in a predetermined direction with respect to the edge of the opening, and applying a voltage to the liquid crystal layer;
An oblique electric field inclined with respect to the substrate surface is generated between the opening and the substrate facing the opening, and the pair of substrates are separated at a predetermined interval so that the direction of the oblique electric field and the direction of the pretilt are different. And injecting a liquid crystal material between the substrates.

The direction of the liquid crystal director when voltage is applied is determined by the direction of the combined vector of the alignment force vector due to the oblique electric field and the alignment force vector due to the pretilt. By setting the direction of the pretilt so that the direction of the composite vector and the direction of the polarization axis of the polarizing plate have a specific relationship, for example, 45 °, a high-contrast display can be obtained.

[0017]

1A and 1B are an enlarged plan view of a portion (about one pixel) of a CSH-LCD according to an embodiment of the present invention and a cross-sectional view taken along the line BB '. .
The structure is such that a pair of glass substrates 10 and 11 are sandwiched between polarizing plates (not shown) whose polarization axis directions p and d are orthogonal to each other, and transparent electrodes 12 and 13 are provided on each glass substrate. Vertical alignment films 14 and 15 are formed, and liquid crystal 16 having negative dielectric anisotropy is sealed between glass substrates. In the figure, the liquid crystal molecules 16 are drawn as ellipses elongated in the direction of the director.

Also in this CSH-LCD, similarly to FIG. 6A, a slit-shaped opening 17 is provided in the electrode, and one pixel is formed of two regions (division alignment structures) having different alignment directions from each other. To obtain a wider viewing angle characteristic. That is, the directionality of the liquid crystal molecules 16 that fall down when a voltage is applied is controlled by the oblique electric field generated between the segment electrode 12 and the common electrode 13.

In this embodiment, in order to suppress light leakage at the off voltage, the angle of the polarizing plate is set as shown in FIG.
The arrangement is 0 ° / 90 °. As described in the paragraph of the problem to be solved by the invention, the polarizing plate angle is set to 0 ° / 90 °.
In order to solve this problem, the ECB effect is reduced. Therefore, the direction of the liquid crystal molecule director is tilted (inclined) in the direction of 45 ° with respect to the x-axis in the substrate plane. That is, the pre-tilt process is performed on the vertical alignment films 14 and 15 by performing a rubbing process in the x-axis direction or the like.

As a result, the orientation vector e due to the oblique electric field
And the resultant vector d of the orientation vector t by the pretilt process becomes the direction of the liquid crystal molecule director.
This means that it is inclined in the direction of 45 ° with respect to the x-axis.

Therefore, in this embodiment, a combination of a slit electrode for generating an oblique electric field, a polarizing plate arranged at 0 ° / 90 °, and a pretilt treatment of a vertical alignment film is employed.
High contrast can be obtained. The responsiveness is improved by adding a chiral agent.

The pretilt method is as follows.
In addition to the method of rubbing the vertical alignment film as described above, a method of irradiating ultraviolet light to the vertical alignment film in an oblique direction with respect to the substrate normal, or a method of sputtering a SiO ₂ film in a transparent electrode shape from an oblique direction. A method of forming a film and forming a vertical alignment film on the SiO ₂ film can be used.

[0023]

EXAMPLES (Example 1) An example of a method for manufacturing a CSH-LCD according to the present invention and experimental results of its display performance will be further described.

A vertical alignment film (SE1211, Nissan Chemical Co., Ltd.) is formed on two glass substrates in which the segment electrode and the common electrode having the patterns shown in FIGS. 6A and 6B are formed of ITO (indium tin oxide). Co., Ltd.) was applied by spin coating and baked at 200 ° C.

The alignment film on the substrate obtained in the above step was rubbed with a cotton cloth. That is, in the direction of arrow r _s in FIG. 2 for the segment electrode substrate 12, for the common electrode substrate 13 is rubbed in the direction of the arrow r _c 1
It gave pretilt angle theta _p as shown by (B). The pretilt angle θ _p was 89.9 ° as measured by the crystal rotation method.

The value of the pretilt angle θ _p is 89.9.
It is desirably in the range of ° to 80 °.

A sealant of an epoxy-based adhesive is printed on one of the two glass substrates subjected to the orientation treatment in the above process, and silica beads (SW3) as a gap control material for controlling the thickness between cells are printed on the other substrate. .8 μm, manufactured by Catalyst Chemicals Co., Ltd.).
An empty cell was produced by superposing the substrates so that the pretilt directions of the substrates were antiparallel.

A liquid crystal material having a negative dielectric anisotropy, to which a chiral agent (CB15) is added, is injected into each empty cell obtained in the above process by using a vacuum injection method, and the injection port (not shown) is provided. Was sealed. In the injected liquid crystal material, the relationship between the value of the natural twist pitch p of the liquid crystal and the value of the cell thickness d is d / p =
The concentration of the chiral agent was adjusted to 0.7.

The completed liquid crystal cell is sandwiched between two polarizing plates (SQ1852, manufactured by Sumitomo Chemical Co., Ltd.) having orthogonal Nicols, and their polarization axes are 0 ° / 90 ° as in FIG. 1A.
It was arranged. A square wave is applied to this liquid crystal cell, and a voltage −
When the light transmittance characteristics were measured, the results as shown in FIG. 3 were obtained. At this time, a vertical alignment type cell according to the prior art as shown in FIG. 6 which was not subjected to pretilt treatment and had a polarization axis arrangement of 45 ° / 135 ° was similarly produced and used for comparison. It was measured.

FIG. 3 shows the voltage-light transmittance characteristics obtained as a result of the measurement experiment.
Table 1 shows the contrast values when multiplex driving was performed with a bias voltage of (/11.95)V.

[0031]

[Table 1]

From the measurement results shown in FIG. 3, it can be seen that in the cell according to the prior art, light leakage occurs near the threshold voltage (4.5 to 5.2 V) due to the oblique electric field caused by the electrode edge, and the transmittance of the cell according to the present invention is reduced. It turns out that it is higher than the cell of the example. Conversely, according to the embodiment of the present invention, 0 ° / 90 °
Since a pretilt is provided by a rubbing process using a polarizing plate arranged at an angle, light leakage near the threshold voltage is suppressed. Further, as is clear from Table 1, the contrast value is improved as compared with the conventional one. In addition, a display with a wide viewing angle was obtained by two-division alignment by an oblique electric field at the electrode slit.

(Example 2) CSH-LCD according to the present invention
A further example of the manufacturing method of the present invention and experimental results of its display performance will be further described. FIGS. 4A and 4B show an enlarged plan view of a part (about one pixel) of the CSH-LCD according to the second embodiment and a cross-sectional view taken along CC '.

The segment electrode 22 and the common electrode 23 having the same pattern as in the first embodiment are formed by ITO.
Vertical alignment films 24 and 25 (S
E1211, manufactured by Nissan Chemical Industries, Ltd.) was applied by spin coating and baked at 200 ° C.

The substrate obtained in the above process has a wavelength of 254.
irradiates ultraviolet rays of 45 nm obliquely to the substrate surface,
Pretilt treatment was applied. That is, in the direction of arrow v _s in Figure 4 for the segment electrode substrate 22 (B), as shown in FIG. 4 (B) with respect to the common electrode substrate 23 is irradiated with ultraviolet rays in the direction of arrow v _c such was given a pre-tilt angle θ _p. The pretilt angle θ _p was 89.9 ° as measured by the crystal rotation method.

A sealing agent such as an epoxy-based adhesive is printed on one of the two glass substrates subjected to the orientation treatment in the above process, and silica beads (SW3) as a gap control material for controlling the thickness between cells are printed on the other substrate. 0.8 μm, manufactured by Catalyst Chemicals Co., Ltd.), and the two substrates were overlapped so that the pretilt directions of the two substrates were parallel to each other as shown in FIG.

A liquid crystal material having a negative dielectric anisotropy, to which a chiral agent (CB15) is added, is injected into each of the empty cells obtained in the above process by using a vacuum injection method. Was sealed. In the injected liquid crystal material, the relationship between the value of the natural twist pitch p of the liquid crystal and the value of the cell thickness d is d / p =
The concentration of the chiral agent was adjusted to 0.7.

The completed liquid crystal cell is sandwiched between two polarizing plates (SQ1852, manufactured by Sumitomo Chemical Co., Ltd.) having orthogonal Nicols, and their polarization axes are 0 ° / 90 ° as in FIG. 1A.
It was arranged. A square wave is applied to this liquid crystal cell, and a voltage −
When the light transmittance characteristics were measured, the results as shown in FIG. 5 were obtained.

It should be noted that a vertical alignment type cell according to the prior art as shown in FIG. 6 which was not subjected to pretilt treatment by ultraviolet rays and had a polarization axis arrangement of 45 ° / 135 ° was similarly manufactured and used for comparison. Measured for.

FIG. 5 shows a voltage-light transmittance characteristic obtained as a result of the measurement experiment. At 1/120 duty (1
(V / 11.95) The contrast value when multiplex driving was performed with a V bias voltage is shown in Table 2. Table 2
In the above, a cell of the prior art having a polarization axis arrangement of 0 ° / 90 ° is also described as a comparative object.

[0041]

[Table 2]

From the measurement results shown in FIG. 5, it can be seen from this result that light leakage near the threshold voltage was not obtained in the prior art because a polarizing plate arranged at 0 ° / 90 ° was used and pretilt was applied by ultraviolet irradiation. It is much lower than that.
Further, as is apparent from Table 2, the contrast value is improved as compared with any conventional polarization axis arrangement. Furthermore, it can be seen that the response time is faster than that of the prior art having a 0 ° / 90 ° polarization axis arrangement despite the addition of the chiral agent.

In the embodiment described above, the pretilt direction is set in an anti-parallel or parallel relationship between the upper and lower substrates. However, the present invention is not limited to this, and the pretilt direction is in the range of 0 ° to 360 °. The pretilt directions of the upper and lower substrates can be set as desired.

Further, the generation of the oblique electric field is not limited to the one in the elongated slit opening as in the above embodiment, but may be an electrode of another shape.

Although the present invention has been described with reference to the embodiments, the present invention is not limited to these embodiments. Also,
It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made.

[0046]

According to the present invention, in a vertical alignment type liquid crystal display device, means for generating an oblique electric field inclined with respect to the substrate surface is provided between a pair of substrates, and a surface of the substrate which is in contact with the liquid crystal layer is provided. By performing an alignment process for giving a pretilt angle to liquid crystal molecules in a direction different from the direction of the oblique electric field, the orientation direction of the liquid crystal molecules when a voltage is applied is set by the oblique electric field and the direction of the pretilt. That is, the direction of the liquid crystal director when voltage is applied is determined by the direction of the combined vector of the alignment force vector due to the oblique electric field and the alignment force vector due to the pretilt. By setting the pretilt direction so that the direction of the composite vector and the polarization axis direction of the polarizing plate have a specific relationship, light leakage near the threshold voltage is suppressed, and high-contrast display and responsiveness are achieved. A good vertical alignment type liquid crystal display device and a method for manufacturing the same can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view and a cross-sectional view of almost one pixel of a vertical alignment type CSH-LCD subjected to a pretilt process according to an embodiment of the present invention.

FIG. 2 is a plan view of almost one pixel of a rubbed vertical alignment type CSH-LCD according to an embodiment of the present invention.
is there.

FIG. 3 is a voltage-light transmittance characteristic diagram of the liquid crystal cell according to the embodiment of FIG. 2;

FIG. 4 is a plan view and a cross-sectional view of almost one pixel of a vertical alignment type CSH-LCD subjected to an ultraviolet irradiation process according to another embodiment of the present invention.

FIG. 5 is a voltage-light transmittance characteristic diagram of the liquid crystal cell according to the embodiment of FIG.

FIG. 6 is a plan view and a cross-sectional view of almost one pixel of a vertical alignment type CSH-LCD according to a conventional technique.

[Explanation of symbols]

 10, 11 Glass substrate 12 Segment electrode 13 Common electrode 14, 15 Vertical alignment film 16 Liquid crystal molecule 17 Electrode opening (slit) 20, 21 Glass substrate 22 Segment electrode 23 Common electrode 24, 25 Vertical alignment film 26 Liquid crystal molecule 27 Electrode opening Part (slit)

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[Procedure amendment]

[Submission date] January 26, 1999 (1999.1.2
6)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] All figures

[Correction method] Change

[Correction contents]

FIG. 2

FIG. 3

FIG.

FIG. 4

FIG. 5

FIG. 6

Claims (8)

[Claims] An electrode is formed on a surface of the substrate, and the substrate has a pair of substrates disposed to face each other at a predetermined interval, and a liquid crystal layer disposed between the pair of substrates. A voltage is applied to the liquid crystal layer. In a vertical alignment type liquid crystal display device in which liquid crystal molecules are vertically aligned with respect to a substrate surface in a state where the liquid crystal layer is not placed, an oblique electric field inclined with respect to the substrate surface between the pair of substrates when a voltage is applied to the liquid crystal layer. The surface of the substrate that is in contact with the liquid crystal layer is subjected to an orientation treatment for giving a pretilt angle to the liquid crystal molecules of the liquid crystal layer in a direction different from the direction of the oblique electric field. A vertical alignment type liquid crystal display element in which the alignment direction of the liquid crystal molecules when voltage is applied is set according to the direction of the pretilt and the pretilt direction. 2. The means for generating an oblique electric field includes an electrode opening provided on at least one of the pair of substrates,
2. The vertical alignment type liquid crystal display device according to claim 1, wherein when a voltage is applied to the liquid crystal layer, an oblique electric field inclined with respect to a substrate surface is generated between an edge of the electrode opening and a substrate facing the opening. . 3. The electrode opening has a left-right symmetric rectangular edge, and is oriented so as to pretilt the liquid crystal molecules in a long side direction of the rectangular opening. Vertical alignment type liquid crystal display device. 4. The method according to claim 1, wherein the pretilt angle is 8 with respect to the substrate surface.
4. The vertical alignment type liquid crystal display device according to claim 3, wherein the angle is in the range of 9.9 ° to 80 °. 5. The method according to claim 1, wherein the direction of the pretilt angle in the plane of the substrate and the direction of the oblique electric field are in a relationship of 90 °.
5. The vertical alignment type liquid crystal display device according to any one of items 4 to 4. 6. The vertical alignment type liquid crystal display according to claim 1, wherein the directions of the pretilt between the one substrate and the other substrate are set in a range of 0 ° to 360 °. element. 7. A liquid crystal layer comprising a pair of polarizing plates sandwiching the pair of substrates, wherein the polarizing axes of the pair of polarizing plates are arranged to be substantially orthogonal to each other, and the polarizing axes of the pair of polarizing plates and the liquid crystal layer. 2. The vertical alignment type liquid crystal display device according to claim 1, wherein the liquid crystal molecules at the central portion thereof are arranged such that the alignment directions thereof when voltage is applied intersect at substantially 45 degrees. 8. A step of preparing a pair of substrates on which liquid crystal molecules are aligned so that liquid crystal molecules are vertically aligned, and on which an electrode having an opening is formed. Performing an alignment treatment for giving a pretilt angle to the liquid crystal molecules in a predetermined direction, and when applying a voltage to the liquid crystal layer, the liquid crystal layer is inclined with respect to the substrate surface between the opening and the substrate facing the opening. Generating an oblique electric field, arranging the pair of substrates facing each other at a predetermined interval so that the direction of the oblique electric field is different from the direction of the pretilt, and injecting a liquid crystal material between the substrates. A method for manufacturing a display element.