JP3207374B2 - Liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an IPS mode active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art Liquid crystal display devices are thin, lightweight, and low power consumption display devices, and are therefore widely used in image display devices such as televisions and videos, and OA equipment such as word processors and personal computers. .

[0003] Among liquid crystal display elements, an active matrix type liquid crystal display element in which a number of switching elements are arranged on an array substrate generally has an orientation azimuth of liquid crystal of about nine.
The display uses a twisted nematic (TN) mode twisted by 0 ° for display, and is being developed as a display capable of high-speed response and high definition.

[0004]

However, the TN mode liquid crystal display element has a drawback that the color tone and the contrast are different depending on the angle at which the panel is viewed, since the display is performed using the optical rotation of the liquid crystal. In order to solve this drawback, a method of compensating color tone and contrast using a retardation film, a pixel division method in which a plurality of different alignment regions are provided in a pixel, an alignment division method, and the like are performed.

[0005] However, even if the above method is used, the viewing angle range in the TN mode is limited by a cathode ray tube (CRT).
There is a problem that the viewing angle range is narrower in the case where is used. In order to solve such a problem, even in the TN mode, C
In order to achieve a viewing angle characteristic close to RT, a liquid crystal molecule is moved in a direction substantially horizontal to the substrate surface, and a display method (hereinafter referred to as “IPS”) in which light transmittance is controlled by an electric field control birefringence effect
Mode ". ) Has been proposed.

As the IPS mode, for example, RASore
f. Method of forming a comb-shaped electrode on a substrate proposed by f (Journal of the Japan Society of Applied Physics J. Appl. Phys. 45, 5446 (197
4)). According to this method, since the liquid crystal molecules are always viewed substantially from the side (the short axis direction), there is almost no difference in the refractive index even when the viewing direction is different, and the viewing angle dependence of the contrast is extremely reduced. Becomes possible.

In the above method, it is preferable that the tilt angle of the liquid crystal molecules is as low as possible from the viewpoint of the symmetry of the viewing angle characteristics. Therefore, a low pretilt type alignment film is used. However, when a low pre-tilt film is used as an alignment film in order to obtain a low tilt angle, there is a problem that the voltage holding ratio is generally low and burn-in easily occurs due to charge accumulation.

As described above, a low pretilt film is used as an alignment film in the IPS mode. However, in a conventional TN mode active matrix panel, the orientation of active elements and step portions of wiring is higher than 3 mm. Since a pretilt angle is required, a high pretilt film is used as an alignment film.

Therefore, when the IPS mode and TN mode liquid crystal display panels are manufactured on the same manufacturing line, the alignment film cannot be shared, and there is a problem that the productivity is low and the cost is high.

The present invention solves the above-mentioned problems, and the liquid crystal display panel of the IPS mode can share the alignment film having a high pretilt angle for the conventional TN mode, and has a wide viewing angle and a high response speed. Realization of display element, IP
It is possible to fabricate a liquid crystal display panel in the S mode and TN mode on the same production line, good productivity, there is provided a liquid crystal display element that allows the cost.

[0011]

A liquid crystal display device according to the present invention is characterized in that liquid crystal molecules between the two substrates are aligned with a splay distortion.

According to the present invention, a liquid crystal display device having a wide viewing angle characteristic and good symmetry can be obtained, and a conventional high pretilt film for a TN mode can be used as an alignment film.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The liquid crystal display device according to claim 1 is
Liquid crystal is sandwiched between a pair of substrates, an active element is arranged for each pixel on one of the substrates, and a pair of or more linear pixel electrodes and a common electrode are formed on the substrate having the active elements. Formed in a pixel and shared with the pixel electrode
When a voltage is applied between the electrodes, the liquid crystal molecules
A liquid crystal display device to direct the rubbing direction of the substrates, whereupon co in the same direction and substantially parallel
Next, the liquid crystal molecules existing near the interface between the pair of substrates are projected.
It is characterized in that the retilt angles are different from each other .

According to this configuration, when a voltage is applied between the electrodes, the liquid crystal molecules are aligned with the splay distortion between the two substrates, and the liquid crystal molecules in the midplane are substantially parallel to the substrates. The tilt component of the liquid crystal molecules is offset as a whole in the thickness direction, so that the viewing angle is wide and the symmetry is improved.

A liquid crystal display device according to a second aspect of the present invention comprises a pair of substrates.
Liquid crystal is sandwiched between the plates, and one of the substrates has
The active element is arranged in the
A pair of linear pixel electrodes and a common electrode
Formed in the pixel, the pixel electrode and the common electrode
When a voltage is applied between the substrates, the liquid crystal molecules are aligned between the two substrates.
Rubbing method of the alignment film of both substrates
Directions are almost parallel and the same direction,
The alignment films of the substrates are made of different materials .

The liquid crystal display device according to the third aspect is the first aspect.
Or 2) liquid crystal molecules existing near the interface of the substrate
Has a pretilt angle of 3 ° or more . According to this configuration, since the pretilt angle is high, the conventional TN
Using high pretilt film for mode as alignment film
Can be. This alignment film has good voltage holding ratio and burn-in
Of IPS mode and TN mode
Display panels can be manufactured on the same line,
Productivity is improved, and costs can be reduced.

According to a fourth aspect of the present invention, there is provided a liquid crystal display device.
4. The method according to claim 3, wherein the alignment film is polyimide. According to this configuration, by using a polyimide alignment film having excellent alignment stability, the alignment stability of liquid crystal molecules is improved, and a liquid crystal display device with high display quality can be obtained.

The liquid crystal display element according to the fifth aspect is the first aspect.
5. The liquid crystal display device according to claim 4, wherein the liquid crystal is a fluorine-based liquid crystal. According to this configuration, it becomes difficult to take in impurity ions at the time of liquid crystal injection or from a surrounding material,
The lowering of the voltage holding ratio is eliminated, and burn-in hardly occurs.

[0019]

[0020]

An embodiment of the present invention will be described below with reference to FIGS. (Embodiment) FIGS. 1 and 2 show (embodiment) of the present invention.

FIG. 1 is a plan view of a substrate used in the liquid crystal display panel of the present invention, and FIG. 2 is a sectional view of the liquid crystal display panel. As shown in FIG.
a, a plurality of gate electrodes 1 and source electrodes 2 are arranged in a grid pattern, and a common electrode 6 is arranged in parallel with the source electrode 2.
Are short-circuited by the extraction electrode 5 provided at the end of the first electrode.

A U-shaped linear pixel electrode 7 is disposed in a portion surrounded by the gate electrode 1 and the source electrode 2, and one end of each pixel electrode 7 intersects the gate electrode 1. A thin film transistor element (hereinafter, referred to as a “TFT”) 4 as an active element is provided in such a manner. TF
A drain electrode 3 is provided at a connection between T4 and the pixel electrode 7.

As shown in FIG. 2, the liquid crystal display panel of this embodiment has an alignment film 9a between the glass substrate 8a and each electrode. Similarly, an alignment film 9b is provided on one surface of the glass substrate 8b.

The glass substrates 8a and 8b provided with the alignment films 9a and 9b are rubbed in opposite directions, respectively, so that the rubbing directions are substantially parallel and the same when the glass substrates 8a and 8b are bonded to face each other. Is rubbed.

Rubbed glass substrates 8a, 8b
A spacer is interposed between the glass substrates 8a and 8b to keep the distance between the glass substrates 8a and 8b constant.
After the bonding of 8b, the space therebetween is filled with a liquid crystal (not shown).

In such a liquid crystal display panel, when a voltage is applied to the common electrode 6 and the pixel electrode 7, an electric field is generated in the horizontal direction with respect to the surface of the glass substrate 8a, and the liquid crystal molecules cause a splay distortion. As a result, the liquid crystal display element is aligned, the viewing angle is widened, and a liquid crystal display element having good symmetry can be obtained.

Specific examples of the liquid crystal display device in the above (embodiment) are shown below. (Example 1) In the above (embodiment), the pixel electrode 7
Was connected to the drain electrode 3 in parallel with the common electrode 6 and at a distance of 15 μm.

The glass substrate 8a and the glass substrate 8
The alignment films 9a and 9b provided on one surface of b are offset-printed with a soluble polyimide varnish having a solid content of 6% by weight (for example, Optmer AL-5442: manufactured by Nippon Synthetic Rubber Co., Ltd.), and heated at 170 ° C. for 1 hour. Alignment films 9a, 9
b was formed. At this time, the thickness of each of the alignment films 9a and 9b was about 800 °.

The glass substrate 8a is made of rayon cloth, and the arrow 1 is shown so as to show an angle of about 10 ° with the direction parallel to the electrode wiring.
Rubbing was performed in the direction of 0. The other glass substrate 8b was subjected to a rubbing treatment in a direction opposite to the glass substrate 8a so as to be substantially parallel and in the same direction when bonded to the glass substrate 8a.

Then, the substrates 8a and 8b are opposed to each other so that the alignment films 9a and 9b face each other.
Then, they were bonded via m beads 11. Δn
Is 0.075, and a fluorine-based nematic liquid crystal having an NI point of 95 ° C. is sealed by a vacuum injection method, and the obtained liquid crystal display panel is annealed at 120 ° C. higher than the NI point for 1 hour. I did it. As a result, a uniform alignment state of liquid crystal molecules was obtained over the entire surface of the liquid crystal panel.

FIG. 3 is a schematic diagram showing a state of alignment of liquid crystal molecules in the liquid crystal panel when no voltage is applied, cut by a cross section parallel to the rubbing direction 10. The liquid crystal molecules 12 are oriented with splay distortion between the upper and lower substrates as shown in FIG. 3, and are parallel to the substrates 8a and 8b in the midplane. A homogeneous cell having a gap of 20 μm was prepared from the same liquid crystal material and alignment film as used for this liquid crystal panel, and the pretilt angle was measured by a crystal rotation method. As a result, the pretilt angle was 4 °.

A polarizing plate was attached to both sides of the liquid crystal panel manufactured as described above so as to be in a crossed Nicols state, and a normally black mode liquid crystal display element was obtained. At this time, the polarizing plate was attached such that the rubbing direction 10 on the glass substrate 8a side was parallel to the absorption axis of the polarizing plate.

FIG. 4 is a view showing the viewing angle dependence of a portion where the contrast (CR) is 100 in this liquid crystal display device. Since the rubbing direction was shifted by 10 ° with respect to the electrode, the axis was shifted by 10 ° in the vertical and horizontal directions, but the shape was almost symmetric and very wide.

As described above, the obtained liquid crystal display element had a wide viewing angle and good symmetry. (Comparative example 1) is shown below in order to compare and study the effects of the liquid crystal display element obtained in the above (Example 1).

(Comparative Example 1) In the above (Example 1), when the glass substrates 8a and 8b are bonded, the rubbing treatment is performed so that the rubbing directions of the respective glass substrates 8a and 8b are parallel and the same. In this (Comparative Example 1), when the glass substrates 8a and 8b were bonded to each other, the rubbing treatment was performed so that the rubbing directions of the glass substrates 8a and 8b were parallel and opposite to each other.

Otherwise, a liquid crystal display device was manufactured in the same manner as in the above (Example 1). FIG. 5 schematically illustrates the orientation state of liquid crystal molecules when no voltage is applied to the liquid crystal panel.

The liquid crystal molecules 12 are aligned in parallel with a certain inclination between the upper and lower substrates. Polarizing plates were attached to both sides of this panel so as to be in a crossed Nicols state, and a normally black mode liquid crystal display device was obtained.

FIG. 6 shows the viewing angle dependence of the contrast of the liquid crystal display device. As is clear from FIG. 6, the viewing angle dependence of the liquid crystal molecules 12 aligned as shown in FIG. 5 was quite asymmetrical in the vertical, horizontal, and horizontal directions, and the liquid crystal display element had a narrow viewing angle.

Further, in (Example 1) and (Comparative Example 1), the contrast is represented by the ratio of the luminance of white display to the luminance of black display, and the magnitude of the value is greatly affected by the luminance of black. In the black mode, a black display is obtained when no voltage is applied, so that the alignment states of the liquid crystal molecules at this time will be compared.

In the first embodiment, as shown in FIG. 3, the liquid crystal molecules 12 are oriented with splay distortion, so that the liquid crystal molecules 12 are almost parallel to the substrate at the center of the liquid crystal layer. . Therefore, the liquid crystal molecules 12 are almost symmetrical when viewed from obliquely above either the left or right, and the inclination of the liquid crystal molecules 12 near the interface between the glass substrates 8a and 8b is a direction in which the liquid crystal molecules vertically cancel each other.

On the other hand, in (Comparative Example 1), as shown in FIG. 5, since the liquid crystal molecules 12 are aligned with a uniform inclination, the liquid crystal molecules 12 are also present at the center of the liquid crystal layer. I have. In addition, when viewed from the upper right of FIG. 5, the liquid crystal molecules are viewed from a direction close to the major axis, and light tends to escape and the contrast is reduced.

As a result, in the case of (Comparative Example 1), the range of the contrast 100 is narrower in the upper part than in the lower part of the liquid crystal display panel, and the isocontrast curve is asymmetric especially in the vertical direction.

In the above (Example 1), the glass substrate 8
The pretilt angle of the liquid crystal molecules 12 near the interface between a and 8b is 4
However, in the present invention, if the pretilt angle is 3 ° or more, it is possible to use a high plethystic alignment film used for a normal TN mode, which leads to an improvement in productivity and a reduction in cost.

(Embodiment 2) In the above (Embodiment 1), the alignment films 9a and 9b of both substrates are made of the same material. However, in (Embodiment 2), the alignment films 9a and 9b of both substrates are formed. Were manufactured using different materials.

With such a configuration, the glass substrate 8
Although the pretilt angles near the interface a and 8b are different from each other, an equal contrast region wider than the contrast region of FIG. 4 in the above (Example 1) is obtained.

However, in order to obtain more symmetric viewing angle characteristics, it is preferable that the alignment films of both substrates are made of the same material, or that the pretilt angles are the same even if different alignment films are used.

(Embodiment 3) In the above (Embodiment 1), a fluorine-based liquid crystal is used as a liquid crystal material. Was used.

With such a configuration, substantially the same effects as the above (Embodiment 1) were obtained. However, a liquid crystal material such as a cyano-based material tends to take in impurities, resulting in a lower voltage holding ratio than a fluorine-based material. In an active matrix liquid crystal display element, since a reduction in voltage holding ratio leads to a reduction in display quality, it is preferable to use a fluorine-based liquid crystal composition.

[0050]

As described above, according to the liquid crystal display device of the present invention, the rubbing directions of the alignment films on both substrates are substantially parallel and the same direction, and the vicinity of the interface between the pair of substrates is improved.
Since the pretilt angles of the liquid crystal molecules existing in the liquid crystal molecules are different from each other , when a voltage is applied between the electrodes, the liquid crystal molecules are aligned with splay distortion. Therefore, the liquid crystal molecules in the midplane are substantially parallel to the substrate, and the tilt components of the liquid crystal molecules at the interface of the substrate are optically almost canceled vertically, whereby a liquid crystal display device having a wide viewing angle characteristic and good symmetry can be provided. In addition, the rubbing directions of the alignment films on both substrates are almost parallel.
And the alignment films of the two substrates are
Similar effects can be obtained by using different materials
Is obtained.

Further, when the pretilt angle at the substrate interface is 3 ° or more, it is possible to use a normal alignment film for the TN mode, and a panel for both the IPS mode and the TN mode can be used on the same production line. Even in the case of manufacturing, it is not necessary to change the alignment film, which leads to an improvement in productivity and a reduction in cost.

Further, by making the pretilt angles of the upper and lower substrates the same, the tilt component at the interface between the upper and lower substrates is completely canceled, and the symmetry of the viewing angle characteristic is further improved. Further, when the alignment film is made of polyimide, the alignment stability becomes good, and a liquid crystal display device with high display quality can be obtained.

Further, by using a fluorine-based liquid crystal, it becomes difficult to take in impurities at the time of injection or from a peripheral material, so that a decrease in the voltage holding ratio is eliminated.

[Brief description of the drawings]

FIG. 1 is a plan view of a substrate in Embodiment 1;

FIG. 2 is a cross-sectional view of a liquid crystal display panel in Embodiment 1;

FIG. 3 is a schematic view of an alignment state of liquid crystal molecules in (Example 1).

FIG. 4 shows equal contrast characteristics of a liquid crystal display device in (Example 1).

FIG. 5 is a schematic diagram of an alignment state of liquid crystal molecules in (Comparative Example 1).

FIG. 6 shows equal contrast characteristics of a liquid crystal display element in Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Source electrode 2 Gate electrode 3 Drain electrode 4 Thin film transistor element 5 Leader electrode 6 Common electrode 7 Pixel electrode 8a, 8b Glass substrate 9a, 9b Alignment film 10 Rubbing direction 11 Bead 12 Liquid crystal molecule

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/1343

Claims (5)

(57) [Claims] A liquid crystal is sandwiched between a pair of substrates, an active element is arranged for each pixel on one of the substrates, and at least one pair of linear pixel electrodes is provided on the substrate having the active elements. Forming a common electrode in the pixel ;
When a voltage is applied between the pixel electrode and the common electrode
A liquid crystal display element in which liquid crystal molecules are aligned between the two substrates, wherein the rubbing directions of the alignment films of the two substrates are substantially parallel and in the same direction, and are present near an interface between the pair of substrates.
Liquid crystal display with different pretilt angles of rotating liquid crystal molecules
element. 2. A liquid crystal is sandwiched between a pair of substrates , and an active element is arranged for each pixel on one of the substrates.
And, on the substrate having this active element,
Forming a linear pixel electrode and a common electrode in the pixel;
When a voltage is applied between the pixel electrode and the common electrode
A liquid crystal display device that aligns liquid crystal molecules between the two substrates.
Te, the rubbing direction of the substrates, the mutually substantially parallel
And the alignment films of the two substrates are different from each other.
Liquid crystal display device made of a material. 3. The method according to claim 1 , wherein liquid crystal molecules existing near the interface of the substrate are blocked.
3. The liquid crystal display device according to claim 1 , wherein a retilt angle is 3 [deg.] Or more . 4. The liquid crystal display device according to claim 1, wherein the alignment film is made of polyimide. 5. The liquid crystal display device according to claim 1, wherein the liquid crystal is a fluorine-based liquid crystal.