JPH11183907A - Liquid crystal display device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable liquid crystal display device having a wide viewing angle characteristic, high display uniformity and high contrast, and a method of manufacturing the same. SOLUTION: By irradiating light to an array substrate 1 having a pixel electrode 9 and a common electrode 10 having a step in a pixel, an alignment film for generating uniaxial alignment is formed, and an alignment process is performed by non-contact. When an electric field is generated between the electrode 9 and the common electrode 10, the orientation of the liquid crystal molecules 4a is changed on a plane parallel to the array substrate 1. By manufacturing a panel from the array substrate 1 and the counter substrate, a uniform alignment state can be obtained over the entire surface of the panel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid crystal display device having a wide viewing angle and a method for manufacturing the liquid crystal display device.

[0002]

2. Description of the Related Art Liquid crystal display elements are thin, lightweight, and low power consumption display elements, and are therefore widely used in image display devices such as televisions and videos, and office automation equipment such as word processors and personal computers. . In particular, most of the active matrix type liquid crystal display elements in which a large number of switching elements are arranged on an array substrate among liquid crystal display elements have a twisted nematic (TN) mode structure in which the orientation direction of liquid crystal is twisted by about 90 °. It is being used and is being developed as a display capable of high-speed response and high-definition display.

However, the TN mode liquid crystal display element has a major problem that the color tone and the contrast are different depending on the viewing angle of the panel sandwiching the liquid crystal, since the display is performed using the optical rotation of the liquid crystal. In order to solve these problems, a compensation method using a retardation film, a pixel division method having a plurality of different orientation regions in a pixel, an orientation division method, and the like are used. However, in the TN mode, the viewing angle range in which good display can be obtained is still narrower than that of a cathode ray tube (CRT), and display performance equal to or higher than that of a CRT has not yet been realized.

In order to realize a viewing angle characteristic closer to that of a CRT, there is a display system in which liquid crystal molecules are moved in a direction substantially horizontal to the substrate surface, and the light transmittance is controlled by the birefringence effect of electric field control. For example, a method of forming a comb-shaped electrode on a substrate has been proposed by RASoref (J. App.
l.Phys. 45, 5446 (1974)). According to this display method,
The liquid crystal molecules are always viewed from the side (short axis direction),
Even if the viewing direction is different, there is almost no difference in the refractive index, and the viewing angle dependency of the contrast can be extremely reduced.

However, since this display system utilizes birefringence, when the panel is viewed at an angle close to the horizontal direction,
Depending on the viewing direction, blue and yellow are slightly colored. Furthermore, in order to eliminate this coloring, the electrodes in the pixels are bent in, for example, a "<" shape so as to have regions having different directions in which the orientation direction of the liquid crystal molecules changes, thereby compensating for each other's coloring. The method has been adopted.

[0006]

However, if a rubbing process is performed on a substrate having an electrode having a step in a pixel, the substrate is not rubbed well in the vicinity of the electrode, causing light to escape and leading to a decrease in contrast. In addition, when the electrode shape is bent in the shape of a ku, the bristles of the rubbing cloth flow along the electrode shape, and the liquid crystal molecules that should originally be arranged in the rubbing direction near the bending point are different from that. When the voltage is not applied, a deviation from the polarization axis or the absorption axis of the polarizing plate occurs when the voltage is not applied.

In view of the above-mentioned conventional problems, the present invention provides a uniform orientation even when a substrate having an electrode having a step in a pixel is used, and even when the electrode is bent. It is an object of the present invention to provide a liquid crystal display device having a high contrast, a wide viewing angle, and no coloring, and a method of manufacturing the same.

[0008]

In order to achieve the above object, in a liquid crystal display device and a method of manufacturing the same according to the present invention, a substrate having a comb-shaped electrode having a step in a pixel is provided with an alignment that produces uniaxial alignment by light irradiation. By providing the film, a liquid crystal display element having wide viewing angle characteristics, high contrast, and no coloring can be obtained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION
A 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 in the pixel on the substrate having the active element. A liquid crystal display element in which the arrangement of liquid crystal molecules changes in a horizontal direction with respect to the substrate surface when a voltage is applied between the two electrodes, wherein at least the substrate having the active element is irradiated with light. In which an alignment film for providing uniaxial alignment with liquid crystal molecules is provided.

[0010] With this configuration, the uniaxial orientation of the liquid crystal molecules is provided by the alignment film, so that the alignment treatment is performed also in the vicinity of the electrodes, so that light leakage hardly occurs.
Uniform orientation can be obtained, and high contrast can be obtained.

According to a second aspect of the present invention, in the liquid crystal display element of the first aspect, the linear pixel electrode and the common electrode are bent in a substantially rectangular shape.

With this configuration, even if the electrode shape is made substantially rectangular in order to suppress coloring due to the viewing angle, light leakage near the electrode is suppressed, and even in the vicinity of the inflection point, no misalignment of the orientation occurs. Is obtained.

According to a third aspect of the present invention, in the liquid crystal display device of the first aspect, the light to be irradiated is ultraviolet light linearly polarized.

According to this configuration, since the orientation can be regulated in a more constant direction, the orientation of the liquid crystal molecules can be improved, and a higher contrast can be obtained.

According to a fourth aspect of the present invention, in the liquid crystal display device according to the first aspect, the alignment film has a uniaxial alignment property due to a molecular chain of a polymer constituting the film being cut by light irradiation. It is characterized by being.

According to this configuration, since the molecular design of the alignment film material is easy, the adjustment of the sensitivity to irradiation light is also easy, and a higher uniaxial orientation can be obtained.

According to a fifth aspect of the present invention, in the liquid crystal display device according to the first aspect, the alignment film has a uniaxial alignment property due to a molecular chain of a polymer constituting the film being bonded by light irradiation. There is a feature.

According to this configuration, the molecular weight of the alignment film is increased by light irradiation, and the alignment film is stabilized against external factors such as heat, and the reliability is further improved.

According to a sixth aspect of the present invention, there is provided a method of manufacturing a liquid crystal display device according to the first aspect, wherein an alignment film having uniaxial alignment by light is formed on at least a substrate having an active element. The alignment film is irradiated with light, and then the substrate is bonded to an opposing substrate.

According to this method, uniaxial orientation can be imparted without contact after forming the orientation film.
Since there is no contamination due to the rubbing treatment, a high voltage holding ratio can be secured, and a highly reliable liquid crystal display device can be obtained.

According to a seventh aspect of the present invention, in the method for manufacturing a liquid crystal display element according to the sixth aspect, after irradiating the alignment film on the substrate with light, the substrate is washed, and the substrate is bonded to the opposing substrate. Features.

By this method, decomposition products and the like generated by light irradiation are removed, so that a higher voltage holding ratio can be secured and reliability is further improved.

According to an eighth aspect of the present invention, in the method for manufacturing a liquid crystal display element according to the sixth aspect, after irradiating the alignment film on the substrate with light, the substrate is heat-treated, and the substrate is bonded to the opposing substrate. Features.

According to this method, the transistor characteristics changed by the light irradiation can be returned to an appropriate state.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an exploded perspective view showing a configuration common to each embodiment in the liquid crystal display device of the present invention, and FIG. 2 is a thin film transistor (TFT) array in the liquid crystal display device for describing the first embodiment of the present invention. FIG. 3 is a plan view illustrating a schematic configuration of a TFT pixel portion of a substrate.

In FIG. 1, the liquid crystal display element has alignment films 3a and 3b formed on an array substrate 1 and a counter substrate 2 disposed opposite to the array substrate 1, respectively. The liquid crystal display device includes a liquid crystal layer 4 interposed therebetween, and polarizing plates 5a and 5b disposed outside the array substrate 1 and the counter substrate 2, respectively. Both polarizing plates 5a, 5b
Are arranged such that their polarization axes are orthogonal to each other.

The array substrate 1 shown in FIG. 2 has a plurality of signal lines 6 and a plurality of scanning lines 7 arranged in a matrix.
At least one switching element 8 provided in each pixel corresponding to the intersection, a comb-shaped pixel electrode 9 connected to the switching element 8, and a comb-shaped bit formed to engage with the pixel electrode 9. And the common electrode 10. Each of the pixel electrode 9 and the common electrode 10 has a width of 5
μm and the interval is kept at 12 μm.

In the figure, reference numeral 4a denotes a liquid crystal molecule, 11 denotes a storage capacitor portion, and 20 and 21 denote regions in which the arrangement of the liquid crystal molecules 4a changes in different directions.

In this example, an alignment film (polyimide alignment film) for aligning the liquid crystal molecules 4a in a direction orthogonal to the polarization direction by polarized ultraviolet light on the array substrate 1.
3a is offset-printed with a varnish having a solid concentration of 4%,
It was formed by heating at 200 ° C. for 1 hour. The thickness of the alignment film 3a was about 600 °. Then, the entire surface of the alignment film 3a was irradiated with ultraviolet rays from a Hg lamp through a polarizing prism. The direction of polarization of the irradiated ultraviolet rays is set to a direction inclined by 10 ° from the direction parallel to the scanning wiring 7, and as a result, the orientation of the liquid crystal molecules 4 a is shifted by 10 ° from the direction parallel to the signal wiring 6. Was. The irradiation amount is 2
The irradiation time was controlled so as to be 800 mJ / cm ^{2 at} 54 nm.

The array substrate 1 is placed on the opposite substrate 2 on which an alignment film 3b is formed and subjected to alignment processing in the same manner as the array substrate 1 so that the liquid crystal molecules 4a have the same orientation. (Not shown) and bonded together via 4 μm beads.

In the panel composed of the array substrate 1 and the counter substrate 2, Δn is 0.075 and the NI point is 95 ° C.
Was sealed by a vacuum injection method, and the panel thus obtained was annealed for 1 hour at 120 ° C. higher than the NI point of the liquid crystal.

As a result, a uniform alignment state was obtained over the entire panel. Furthermore, as a result of observing the microscopic alignment state of this panel under a polarizing microscope, no light leakage near the electrodes was observed. Moreover, there was no line-like unevenness as in the case where the rubbing treatment was performed, and the state was very uniform over the entire panel.

The polarizing plates 5a and 5b were adhered to both sides of the liquid crystal panel prepared as described above so as to be in a crossed Nicols state, and a normally black mode liquid crystal display device was obtained. At this time, the method of attaching the polarizing plates 5a and 5b is as follows.
The alignment direction A of the liquid crystal molecules 4a on the array substrate 1 side and the polarizing plate 5
The polarization axes of a and 5b were set to be parallel.

When a lighting image inspection of this liquid crystal display element was performed, it was confirmed that the viewing angle was wide. Further, the luminance during black display and white display was measured, and the contrast ratio was calculated to be as high as 200.

In order to compare and examine the effects of the liquid crystal display device according to the first embodiment, Comparative Example 1 will be described below.

In the first embodiment, the alignment films 3a and 3b formed on the array substrate 1 and the counter substrate 2, respectively, are irradiated with light to cause uniaxial alignment. And the counter substrate are not uniaxially oriented by light, that is, a varnish of ordinary polyimide (for example, Optmer AL-5442: manufactured by Nippon Synthetic Rubber Co., Ltd.) is offset-printed,
Heating was performed for a time to form an alignment film. Then, using an array substrate with rayon cloth, the direction parallel to the
The rubbing treatment was performed in the same direction as the liquid crystal molecules so as to show the angle of ゜. On the other hand, the opposing substrate was subjected to a rubbing treatment so as to be substantially parallel and in the same direction when bonded to the array substrate.

Except for this, a liquid crystal panel was manufactured in the same manner as in the first embodiment. As a result of observing the alignment state of this liquid crystal panel under a polarizing microscope, a non-aligned region was formed in a portion of the rubbing cloth on both sides near the electrode where the hair did not touch, and light leakage was observed. Polarizing plates were attached to both sides of the panel so as to be in a crossed Nicols state, and a normally black mode liquid crystal display device was obtained. As a result of measuring the contrast ratio of this liquid crystal display element, it was 180.

Normally, when a stepped portion is rubbed with a rubbing cloth, it is difficult to eliminate the non-aligned area due to the relationship between the length of the bristle of the cloth and the height of the step. Although light leakage near the peripheral wiring could be hidden by the black matrix on the counter substrate side, hiding light leakage in the pixel is not practical because it leads to a decrease in aperture ratio. Therefore, by adopting the configuration of the liquid crystal display element as in the first embodiment, the viewing angle is widened and the contrast ratio is improved.

Further, in order to compare the voltage holding ratios of the first embodiment and the comparative example 1, a substrate having only comb-shaped electrodes without TFT elements was used in place of the array substrate, and each of the alignment treatment methods was used. Make a cell, 80 ℃
As a result, the voltage holding ratio was 98% in the configuration of the first embodiment and 96% in the configuration of Comparative Example 1.

FIG. 3 shows a thin film transistor (TFT) in a liquid crystal display device for explaining a second embodiment of the present invention.
FIG. 4 is a plan view illustrating a schematic configuration of a TFT pixel portion of an array substrate. In FIG. 3, members common to the first embodiment described with reference to FIGS. 1 and 2 are denoted by the same reference numerals, and description thereof is omitted. Then, particularly different parts will be described.

In the second embodiment, the pixel electrode 9 and the common electrode 10 on the array substrate 1 are not parallel to the signal wiring 6, and each central portion is about 10 ° in a direction parallel to the signal wiring 6. At an angle of approximately. The alignment film 3 having such a property that the molecular chains of the alignment film 3a are bonded to the array substrate 1 by polarized ultraviolet light, and the liquid crystal molecules 4a are aligned in the same direction as the transmission axis.
a is formed, and polarized ultraviolet rays having a polarization axis in a direction parallel to the signal wiring 6 are irradiated. On the other hand, the opposite substrate 2 is similarly subjected to an alignment treatment.

Then, a panel was prepared from the array substrate 1 and the counter substrate 2 in the same manner as in the first embodiment, and the alignment state was observed under a polarizing microscope. Polarizing plates 5a and 5b are provided on both sides of this panel.
By pasting so that it becomes cross Nicole,
A normally black mode liquid crystal display device was obtained. At this time, the alignment direction A of the liquid crystal molecules 4a and 4b on the side of the array substrate 1 and the polarization axes of the polarizing plates 5a and 5b were set to be parallel.

In this liquid crystal display device, since the pixel electrode 9 and the common electrode 10 are bent in a substantially rectangular shape, the pixel electrode 9
When a voltage is applied between the electrodes 9 and 10,
The liquid crystal molecules 4a and 4b in the first and second display regions 20 and 21 located on both sides of the central wiring portion 10a of the electric field in a direction substantially orthogonal to the longitudinal direction of
The alignment directions A move so as to be aligned with the direction of the electric field, and are opposite to each other.

As a result, color changes with respect to the viewing angle are compensated for each other. When a lighting image inspection of this liquid crystal display element was performed,
It was confirmed that a liquid crystal display device having a wide viewing angle, high contrast, and excellent images without coloring was obtained.

The alignment films 3a, 3 used in this liquid crystal display element
Since the molecular chain of b is bonded by polarized ultraviolet rays, the stability of the orientation in the surrounding environment such as heat and long-term use is also ensured.

In the second embodiment, the common electrode 10 and the pixel electrode 9 have only one inflection point in one pixel. However, as long as the areas of different regions in the direction in which the arrangement changes are the same. It may be bent a plurality of times because the color change is compensated.

In the above-described embodiment, the uniaxial alignment is generated by irradiating the alignment film with polarized ultraviolet light. However, this light may not be ultraviolet light. The same effect can be obtained if it is combined with an orientation film that can be oriented in the direction.

Further, in the above-described embodiment, the same alignment film material that produces uniaxial alignment by polarized ultraviolet light is used for the array substrate 1 and the counter substrate 2. The same high contrast can be obtained, but by using a film that generates uniaxial orientation by light irradiation as the counter substrate, alignment treatment can be performed in a non-contact manner, so that incorporation of impurities is suppressed and a higher voltage holding ratio is obtained. Since it can be realized, the array substrate 1 and the opposing substrate 2
In both substrates, it is preferable to use a film that generates uniaxial orientation by light.

A comparative example 2 will be described below in order to compare and examine the effects of the liquid crystal display device according to the second embodiment.

In Comparative Example 2, the array substrate 1 used in the second embodiment was used, and an alignment process was performed by rubbing in the same manner as in Comparative Example 1 to produce a panel. Then, as a result of observing the alignment state under a polarizing microscope, light leakage was observed in the vicinity of the common electrode and the pixel electrode, and a slight deviation of the alignment direction near the bending point was also confirmed. By attaching a polarizing plate to this panel as in the second embodiment, a normally black mode liquid crystal display device was obtained. A lighting image inspection is performed on this liquid crystal display element,
As a result of measuring the contrast, it was 140.

In Comparative Example 2, when an electrode having a stepped shape bent in a V-shape was rubbed with a rubbing cloth, the rubbing cloth was caused to flow along the shape of the electrode. Rubbing in different directions, further reducing the contrast.

Next, a manufacturing method according to a third embodiment of the present invention will be described.

In the first embodiment, the array substrate 1 is irradiated with polarized ultraviolet light, and then bonded to the counter substrate 2. In the third embodiment, after the irradiation, ultrasonic cleaning with pure water is performed. After drying, the substrate was bonded to the counter substrate. Although the same effect was obtained by this method, a cell for evaluating the voltage holding ratio was manufactured and evaluated. As a result, the voltage holding ratio was 9%.
9%. As a result of removing impurities such as decomposition products of organic substances generated by ultraviolet irradiation by washing, such a high voltage holding ratio was realized.

In the third embodiment, cleaning with pure water is performed, but an organic solvent such as IPA which does not destroy the uniaxial orientation may be used. In addition, the same effect can be obtained regardless of whether ultrasonic cleaning or shower cleaning is performed as long as impurities are removed.

Next, a manufacturing method according to a fourth embodiment of the present invention will be described.

In the first embodiment, after irradiating the array substrate 1 with polarized ultraviolet light, the array substrate 1 was annealed at 220 ° C. for 2 hours, and then bonded to the counter substrate 2. However, when the TFT element is irradiated with ultraviolet light, there is a problem in display because the transistor characteristics are changed.

Therefore, in the method of the fourth embodiment, by performing the heat treatment after the light irradiation, the changed transistor characteristics can be almost returned to the original, and a liquid crystal display element having no problem in characteristics can be obtained.

[0059]

As described above, according to the present invention,
An alignment film that generates uniaxial alignment by light is formed on a substrate having a step between a linear common electrode and a pixel electrode parallel to a signal wiring in a pixel, and the substrate is irradiated with light to align liquid crystal molecules. By doing so, light leakage due to non-alignment near the step such as rubbing does not occur, so that the contrast is high, and the alignment can be performed in a non-contact manner.
It is possible to provide a liquid crystal display element which can suppress contamination by impurities, secure a high voltage holding ratio, and has excellent reliability and wide viewing angle characteristics.

Further, since the common electrode and the pixel electrode are bent in the pixel, a region in which the orientation is reversed when an electric field is applied is formed, and as a result, a color change with respect to the viewing angle can be compensated. .

Further, since the irradiation light is polarized ultraviolet light, the orientation of the liquid crystal molecules can be more easily defined in a certain direction, the orientation of the liquid crystal molecules can be improved, and a higher contrast can be obtained. Become.

Further, by using a material which breaks the molecular chains of the polymer by irradiating the alignment film with light to generate uniaxial alignment with respect to the liquid crystal molecules, the molecular design of the alignment film material is facilitated and the sensitivity to light is improved. Is also easier to adjust,
The margin of irradiation conditions at the time of manufacturing can be widened.

In addition, by using a material in which molecular chains of a polymer are bonded to each other by irradiating the alignment film with light to generate uniaxial alignment with respect to liquid crystal molecules, the molecular weight of the alignment film is increased and external factors such as heat are increased. , And higher reliability can be obtained.

Further, by cleaning after irradiating the alignment film with light, a decomposition product or the like generated by the light irradiation is removed, so that a higher voltage holding ratio can be secured and reliability is further improved.

By performing the heat treatment after the light irradiation, the transistor characteristics changed by the light irradiation can be returned to a steady state.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a configuration common to each embodiment in a liquid crystal display element of the present invention.

FIG. 2 is a plan view showing a schematic configuration of a TFT pixel portion of a thin film transistor (TFT) array substrate in a liquid crystal display device for describing a first embodiment of the present invention.

FIG. 3 is a plan view showing a schematic configuration of a TFT pixel portion of a thin film transistor (TFT) array substrate in a liquid crystal display device for describing a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Array substrate 2 Counter substrate 3a, 3b Alignment film 4 Liquid crystal layer 4a, 4b Liquid crystal molecule 5a, 5b Polarizer 6 Signal wiring 7 Scanning wiring 8 Switching element 9 Pixel electrode 10 Common electrode 11 Storage capacitor part 20, 21 Array of liquid crystal molecules Area where the direction of change varies

Claims (8)

[Claims] 1. A 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 linear pixel electrodes and a plurality of linear pixel electrodes are formed in the pixels on the substrate having the active element. A common electrode is formed, and when a voltage is applied between the two electrodes, the liquid crystal display element has a configuration in which the arrangement of liquid crystal molecules changes in a horizontal direction with respect to the substrate surface, and includes at least the active element. A liquid crystal display device comprising a substrate provided with an alignment film for causing uniaxial alignment with liquid crystal molecules by light irradiation. 2. The linear pixel electrode and the common electrode are bent in a substantially rectangular shape.
The liquid crystal display element as described in the above. 3. The liquid crystal display device according to claim 1, wherein the light to be irradiated is linearly polarized ultraviolet light. 4. The liquid crystal display device according to claim 1, wherein the alignment film has a uniaxial alignment property caused by a molecular chain of a polymer constituting the film being cut by light irradiation. . 5. The liquid crystal display device according to claim 1, wherein the alignment film has a uniaxial alignment property due to a molecular chain of a polymer constituting the film being bonded by light irradiation. 6. The method for manufacturing a liquid crystal display device according to claim 1, wherein an alignment film having a uniaxial alignment by light is formed on at least a substrate having an active element. A method for manufacturing a liquid crystal display element, which comprises irradiating light and thereafter bonding this substrate to an opposing substrate. 7. The method for manufacturing a liquid crystal display device according to claim 6, wherein after irradiating the alignment film on the substrate with light, the substrate is washed and the substrate is bonded to an opposing substrate. 8. The method for manufacturing a liquid crystal display device according to claim 6, wherein after irradiating the alignment film on the substrate with light, the substrate is heat-treated and the substrate is bonded to an opposite substrate.