JPH09311324A - Active matrix type liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a wide visual field angle and to obtain a high picture quality without generating orientation disturbances of liquid crystal moleculars due to static electricity by providing a conductive film formed with material whose specific resistance is specified on the substrate of at least one side of opposed transparent substrates to impress a proper transverse electric field on liquid crystal layer. SOLUTION: A liquid crystal layer is held in between first and second transparent substrates disposed to face oppositely and the layer is impressed with a traverse directional electric field substantially parallel with the substrates to be controlled and the conductive film formed with material whose specific resistance is 10<8> Ω.cm-10<12> Ω.cm is provided on the substrate of at least one side of opposed substrates. For example, epoxy high moleculars are coatingly formed as the overcoat film 24 of color filters 23 on the substrate of a side in which the color filters 23 with a black matrix 22 are formed. At this time, the specific resistance of the film is made to become, for example, 1.5<8> >.cm by mixing particulates of indium-tin oxide in the overcoat film 24.

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, and more particularly to an active matrix type liquid crystal display device which can obtain a wide viewing angle and a high image quality by applying an electric field parallel to a substrate. The present invention relates to a matrix type liquid crystal display device.

[0002]

2. Description of the Related Art As a liquid crystal display device using a method in which a direction of an electric field applied to a liquid crystal is substantially parallel to a substrate (hereinafter referred to as a lateral electric field method), a comb-teeth shape provided on one substrate. The method using the electrode of, for example, Japanese Patent Publication No. 63-
It is proposed and known from 21907, U.S. Pat. No. 4,345,249 and the like. In this display device, it is not necessary to use a transparent electrode as an electrode, and an opaque metal electrode having high conductivity can be used. The electrodes need only be formed on one substrate, and the electrodes are not necessarily required on the other substrate.

[0003]

Insulators generally have the property of accumulating static electricity. The liquid crystal is an insulator having the property of changing the orientation of its liquid crystal molecules by an electric field. Therefore, in the liquid crystal, when static electricity is present around the liquid crystal, the static electricity is induced and accumulated.

Therefore, in the above-described conventional horizontal electric field type liquid crystal display device, when static electricity is accumulated, the alignment of liquid crystal molecules is disturbed by the static electricity and it is difficult to improve the image quality. Have a point.

That is, the horizontal electric field type liquid crystal display device is
The electrode group is arranged only on one of the substrates, and the conductor is not arranged on the other substrate at all, and the conductor that is the transparent electrode is formed on the two substrates. Compared to the twisted nematic liquid crystal display device, the number of conductors formed on the substrate is smaller, so static electricity is more likely to be accumulated, and the static electricity thus accumulated disturbs the alignment of liquid crystal molecules and impairs image quality. ing.

Further, the horizontal electric field type liquid crystal display device has a problem that the alignment of liquid crystal molecules is disturbed by static electricity generated by touching a display screen with a finger or the like, and normal display is not performed for a while. There is.

In order to solve such a problem, a transparent electrode may be attached to a counter substrate of a substrate provided with an electrode group by a usual structure used in the twisted nematic system. In this case, the substrate is provided. Therefore, there arises a problem that an appropriate lateral electric field parallel to is unable to be applied. That is, in this case, the horizontal electric field type liquid crystal display device cannot achieve both application of an appropriate horizontal electric field for displaying and elimination of alignment disorder of the liquid crystal molecules due to static electricity, and still high There is a problem that the image quality cannot be obtained.

The object of the present invention is to solve the above-mentioned problems of the prior art, to obtain a wide viewing angle by applying an appropriate lateral electric field, and to prevent the occurrence of alignment disorder of liquid crystal molecules due to static electricity and to achieve high image quality. An object of the present invention is to provide an in-plane switching type active matrix liquid crystal display device that can achieve both of the above and the above.

[0009]

According to the present invention, the above object is to provide a first transparent substrate having a large number of display pixels formed by an active element and electrodes for driving the element, and the first transparent substrate. An active matrix type liquid crystal in which a liquid crystal layer is sandwiched between a transparent substrate and a second transparent substrate which is arranged to face the transparent substrate, and a lateral electric field substantially parallel to the substrate is applied to the liquid crystal layer to control the liquid crystal layer. In the display device, at least one of the opposing transparent substrates has a specific resistance of 10 ⁸ Ω · c.
This is achieved by providing a conductive film formed of a material of m to 10 ¹² Ω · cm.

Further, the object is to form a color filter and an overcoat film for protecting the color filter on the second transparent substrate, and use the overcoat film as the conductive film or the color filter. This can be achieved by using the conductive film as the dye carrier of the constituent dyes.

Further, the above-mentioned object is to form an extremely thin transparent conductive film of several tens of liters on a substrate or a color filter,
It is achieved by forming a color filter or an overcoat film as an insulating film on it.

According to the present invention, the resistance of the overcoat film originally formed of an insulating material of the color filter or the polymer layer carrying the dye constituting the color filter is reduced within a range that does not affect the electric field. Static electricity can be prevented from being accumulated in the liquid crystal without affecting the electric field for display control applied in the direction. Then, according to the present invention, an appropriate lateral electric field can be applied to obtain an image with a wide viewing angle, and high quality can be obtained without causing alignment disorder of liquid crystal molecules due to static electricity.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an active matrix type liquid crystal display device according to the present invention will be described in detail below with reference to the drawings. First, the configuration of a horizontal electric field type active matrix liquid crystal display device to which the present invention is applied will be described with reference to FIGS.

FIG. 1 is a diagram for explaining the structure of an active matrix type liquid crystal display device to which the present invention is applied, FIG. 2 is a diagram showing the concept of an active element and a drive circuit portion, and FIG. 3 is an electrode in a unit pixel. FIG. 4 is a diagram showing an example of the structure, FIG. 4 is a diagram for explaining the definitions of the rubbing direction and the axial direction of the polarizing plate, and FIG. 5 is a diagram for explaining the operation of liquid crystal molecules in the horizontal electric field system. FIG.
In FIG. 5, 1 is a common electrode (common electrode), 2 is a gate insulating film, 3 is a video signal electrode (drain electrode), 4 is a pixel electrode (source electrode), 5'is an alignment film, and 6 is a liquid crystal. Molecules, 7 and 7 ′ are substrates, 8 is a polarizing plate, 9 is an electric field, 10 is a rubbing direction, 11 is a polarizing plate transmission axis direction, 12 is a scanning electrode, 13 is a-silicon, 14 is a thin film transistor, 1
6 is a storage capacitor, 17 is a control circuit, 18 is a scan electrode driving circuit, 19 is a signal electrode driving circuit, 20 is a common electrode driving circuit, 21 is an active matrix type liquid crystal display element, 22 is a black matrix, and 23 is The color filter 24 is an overcoat film.

The liquid crystal display device to which the present invention is applied is shown in FIG.
As shown in the exploded perspective view of (a) and the cross-sectional view of FIG. 1 (b), two glass substrates, which are transparent substrates with a thickness of 1.1 mm and whose surface is polished, are used. A liquid crystal is sandwiched between them. Then, a thin film transistor 14 is formed on one of the two substrates 7, a silicon nitride film which is an insulating film is formed on the outermost surface thereof, and an alignment film 5 is applied thereon. ing. As the alignment film 5, for example, polyimide is used, and the surface thereof is subjected to a rubbing treatment for aligning the liquid crystal. The color filter 23 having the black matrices 22a and 22b is formed on the other substrate 7 ', polyimide is applied as the alignment film 5'on the outermost surface thereof, and the same rubbing treatment as described above is performed.

The thin film transistor 1 formed on the substrate 7
As shown in FIG. 2, the active matrix type liquid crystal display element 21 constituted by 4 includes a large number of thin film transistors 14 arranged in a matrix and each of the transistors 1
4 are configured to form one pixel. And
These thin film transistors 14 are used in the control circuit 1
Under the control of 7, the drive control is performed by the scan electrode drive circuit 18 and the means electrode drive circuit 18, and the drive control is performed by the common electrode drive circuit 20.

Next, the structure of the thin film transistor and various electrodes will be described with reference to FIG. FIG. 3 is a front view seen from a direction perpendicular to the substrate surface, and AA ′ and BB ′ of the front view.
And a side cross-sectional view at is shown.

In FIG. 3, the thin film transistor 14 is
Pixel electrode (source electrode) 4, signal electrode (drain electrode)
3, scan electrodes (gate electrodes) 12, and amorphous silicon 13. The common electrode 1 and the scan electrode 12, and the signal electrode 3 and the pixel electrode 4 are formed by patterning metal layers formed in different layers. The capacitive element 16 is formed to have a structure in which the insulating protective film 2 is sandwiched between the pixel electrode 4 and the common electrode 1 in a region where the two common electrodes 1 are coupled to each other.

The pixel electrode 4 is arranged between the three common electrodes 1. The pixel pitch is 100 μm in the horizontal direction (that is, between the signal electrode wirings 3) and in the vertical direction (that is,
The distance between the scanning electrode wirings 12) is 300 μm. The width of each of the above-mentioned electrodes is the same as the scanning electrode 12, the signal electrode 3, and the common electrode 1.
Of the wiring part extending over a plurality of pixels of the
The part extending in the horizontal direction) is set wider to avoid line defects. The width is 10 μm and 8 respectively
μm and 8 μm.

On the other hand, in the wiring of the pixel electrode and the signal electrode of the common electrode which are independently formed in one pixel unit, the width of the portion extending in the longitudinal direction is formed to be slightly narrower, and the width is 5
μm and 6 μm. By narrowing the width of these electrodes, the possibility of wire breakage due to the inclusion of foreign matter or the like increases, but in this case, a partial defect of one pixel does not lead to a line defect. A gap of 2 μm is provided between the signal electrode 3 and the common electrode 12 via an insulating film. The number of pixels is 6
The number of signal wiring electrodes of 40 × 3 (R, G, B) and the wiring electrodes of 480 were set to 640 × 3 × 480.

On the alignment films 5 and 5'that form an interface between the liquid crystal of the substrate 7 on which the active matrix type liquid crystal display element 21 as described above is formed and the substrate 7'on which the color filter 23 with the black matrix is formed. Rubbing directions are substantially parallel to each other, and as shown in FIG. 4, the angle formed with the applied electric field direction is 75 degrees (φ _LC1 = φ _LC2 = 75 °).
And The dielectric anisotropy Δε is positive and has a value of 7.3 between the substrates 7 and 7 ′, and the refractive index anisotropy Δn is 0.0.
A liquid crystal panel is constituted by sandwiching a 74 (589 nm, 20 ° C.) nematic liquid crystal composition. In this case, the gap d was 4.0 μm in a state where spherical polymer beads were dispersed and held between the substrates and liquid crystal was sealed. Therefore,
Δn · d is 0.296 μm.

The liquid crystal panel having the above structure is sandwiched by two polarizing plates [eg, G1220DU manufactured by Nitto Denko Corporation] 8 to form a liquid crystal display device. The polarization transmission axis of one polarizing plate is set to φ _P1 = 75 °, and the polarization transmission axis of the other polarizing plate is set to φ _P2 = −15 ° orthogonal to that of the above-mentioned polarizing plate. .

The liquid crystal display device constructed as described above is
When the liquid crystal molecules 6 are controlled by adopting the normally-closed characteristic that a dark state is obtained at a low voltage (V _OFF ) and a bright state is obtained at a high voltage (V _ON ), the liquid crystal molecules 6 are aligned as shown in FIG. ,
Creates a dark state. That is, in the dark state, as shown in FIG.
As shown in FIGS. 5A and 5C, the liquid crystal molecules 6 are aligned in the rubbing direction. The display device is controlled in the dark state by the action of the alignment direction of the liquid crystal molecules and the action of the two polarizing plates. Moreover, in the case of the bright state, FIG.
As shown in (d), the liquid crystal molecules 6 are aligned in a direction rotated by a certain angle from the rubbing axis by the applied electric field. As a result, the display device is controlled to the bright state.

According to one embodiment of the present invention, in the active matrix type liquid crystal display device having the above-mentioned structure, the color filter 23 with the black matrix is formed on the substrate 7'without electrode groups. A coat film is formed, on which an alignment film and a liquid crystal layer are formed. Then, the resistance of the overcoat film of the color filter 23 or the polymer layer, which is a dye-supporting member that constitutes the color filter 23, is reduced within a range that does not affect the electric field applied in the lateral direction, thereby accumulating static electricity. To prevent.

In order to eliminate the accumulation of static electricity, it is advantageous that the above-mentioned overcoat film and the polymer layer constituting the color filter have a small specific resistance, but they do not affect the electric field supplied to the liquid crystal. Has a certain lower limit.
As a result of diligent examination of this lower limit value, the present inventors have found that the specific resistance is 10 ⁸ Ω · cm. That is, it has been experimentally found that an insulator having a specific resistance of 10 ⁸ Ω · cm or less absorbs an electric field even though it is an insulator.

FIG. 6 is a diagram for explaining the influence of the specific resistance of the film material formed on the counter substrate on the electric field applied to the liquid crystal. 6A, a conductive film is formed on a counter substrate of a substrate with comb-teeth electrodes using a material having a known specific resistance, and FIG.
As shown in FIG. 2, the spot b on the comb-teeth electrode portion affected by the conductive film and the spot a on the comb-teeth electrode portion not affected by the conductive film
7 shows the experimental results of investigating the difference in drive voltage between and.

As a result, as shown in FIG. 6A, when the specific resistance of the material of the conductive film formed on the counter substrate with the comb-teeth electrode is smaller than 10 ⁸ Ω · cm, the driving voltage at the spot b is increased. Was found to be higher than the drive voltage at the spot a. That is, when the specific resistance of the conductive film is smaller than 10 ⁸ Ω · cm, the conductive film may absorb an electric field even if it is an insulator and disturb the electric field applied for display control. understood.

However, the specific resistance of the conductive film is 10 ⁸
If it is larger than Ωcm, it will not disturb the electric field,
Moreover, it has been found that it is possible to prevent static electricity from being retained in the liquid crystal. And, the specific resistance of the above-mentioned conductive film for keeping static electricity in the liquid crystal without disturbing the electric field applied for display control is larger than 10 ⁸ Ω · cm and smaller than 10 ¹² Ω · cm. Was found to be optimal.

In order to change the resistance of the overcoat film of the color filter and the polymer layer supporting the dye of the color filter, conductive fine particles may be dispersed in these polymers. , Indium-tin-oxide, indium oxide, tin oxide,
Fine particles such as zinc oxide and cadmium-tin-oxide can be used. However, it is not necessary to be limited to these compounds.

The present invention was made on the basis of the findings of the present inventors as described above, and the embodiments of the present invention will be described below.

FIG. 7 is a diagram for explaining the first embodiment of the present invention, and is a diagram showing a substrate structure on the side where a color filter with a black matrix is formed. FIG. 7 shows a front view seen from a direction perpendicular to the substrate surface and a front view of AA ′,
A side cross-sectional view at BB 'is shown.

The black matrix 22 is formed by using a material in which carbon and an organic pigment are mixed, and the arrangement of the black matrix 22 with respect to the electrode substrate is shown as a broken line window in FIG. The color filter 23 disperses a pigment in a photosensitive resin that becomes a polymer carrying a dye,
The R, G, and B colors are formed in a matrix by coating, patterning exposure, and development, respectively. Then, an epoxy polymer is applied and formed as the overcoat film 24 of the color filter 23. that time,
Fine particles of indium tin oxide were mixed in the overcoat film 24. Its specific resistance is 1.5
× 10 ⁸ Ω · cm.

An active matrix type liquid crystal display device obtained by using a substrate on which a color filter with a black matrix having the above-mentioned structure is formed has a gradation of 60 or more in the vertical and horizontal directions while maintaining a contrast of 10 or more. With a wide viewing angle that does not cause reversal, even if the display screen was rubbed with a finger, a high quality display could be performed without causing a large alignment disorder of liquid crystal molecules due to static electricity.

In the above, as the overcoat film 24,
Although it has been stated that the epoxy-based polymer in which the indium-tin-oxide fine particles are mixed is formed by coating, the overcoat film 24 is formed, for example, by an acrylic-based polymer in which the zinc oxide fine particles are mixed. May be. In this case, the specific resistance was 2.2 × 10 ⁸ Ω · cm. Also in this case, the same effect as the above case could be obtained.

FIG. 8 is a diagram for explaining the second embodiment of the present invention, and is a diagram showing the substrate structure on the side on which the color filter with a black matrix is formed. FIG. 8 shows a front view seen from a direction perpendicular to the substrate surface and a front view taken along line AA ′,
A side cross-sectional view at BB 'is shown.

In the second embodiment shown in FIG. 8, an extremely thin transparent conductive film 25 of tin oxide having a thickness of about 10 Å is formed on a glass substrate 7 ', and then a color filter 23 similar to that described with reference to FIG. 7 is formed. The overcoat film 24 is formed. In this case, the overcoat film 24 does not need to have conductivity and is an insulating film. Further, if the transparent conductive film 25 is too thick, it adversely affects the driving electric field of the liquid crystal display device. Therefore, it is optimal to set it to about 10 Å. Also in the active matrix type liquid crystal display device obtained by using the substrate having such a structure, the same effect as the above case can be obtained.

The embodiment of the present invention described above is
The overcoat film 24 formed on the color filter 23 has conductivity, or the extremely thin transparent conductive film 25 is provided between the color filter 23 and the substrate 7 ′. In the invention, the polymer material carrying the dye of the color filter 23 may be made conductive.

That is, in this case, a color filter 23 with a black matrix is prepared by using a mixture of photosensitive resin and fine particles of indium tin oxide.
Then, an epoxy polymer is applied as an overcoat film 25 thereon to form a substrate on the color filter side, and this substrate is used to prepare an active matrix type liquid crystal display device. In this case, the specific resistance of the photosensitive resin was 1.7 × 10 ⁸ Ω · cm. Also in this case, the same effect as the above case could be obtained.

FIG. 9 is a diagram for explaining the third embodiment of the present invention, and is a diagram showing the substrate structure on the side where the color filter with a black matrix is formed. FIG. 9 shows a front view and a front view taken along the line AA ′ as seen from a direction perpendicular to the substrate surface.
A side cross-sectional view at BB 'is shown.

In the third embodiment shown in FIG. 9, the ultra-thin transparent conductive film 25 in the embodiment described with reference to FIG. 8 is provided between the color filter 23 and the substrate 7 ', not the color filter 23 and the overcoat film. It is arranged to be provided between 24 and 24. Also in this case, the ultrathin transparent conductive film 25 was formed of a tin oxide thin film of about 10 liters.
Also in this case, the same effect as the above case could be obtained.

Although each of the above-described embodiments of the present invention has been described as having a liquid crystal display device composed of a substrate having a driving electrode and a substrate having a color filter, the present invention forms a color filter as an active element. It may be formed on the same substrate as the substrate. However, in this case, it is necessary to have a structure in which a conductive film having a specific resistance of about 10 ⁸ Ω · cm or an extremely thin transparent conductive film and an insulating film of about several tens of liters are formed on the opposing substrates.

The liquid crystal composition and liquid crystal compound described in each of the above embodiments are some specific examples, and the present invention is not limited to those described. Further, the pixel structure and configuration of the display device are not limited to those described in the embodiments.

[0043]

As described above, according to the present invention, in a horizontal electric field type active matrix type liquid crystal display device, a wide viewing angle that does not cause grayscale inversion while maintaining a contrast of 10 or more at 60 degrees or more in the vertical and horizontal directions. Thus, high-quality display can be performed without causing significant alignment disorder of liquid crystal molecules due to static electricity generated by rubbing the display screen with a finger.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a structure of an active matrix type liquid crystal display device to which the present invention is applied.

FIG. 2 is a diagram showing a concept of an active element and a drive circuit section.

FIG. 3 is a diagram showing an example of an electrode structure in a unit pixel.

FIG. 4 is a diagram illustrating definitions of a rubbing direction and an axial direction of a polarizing plate.

FIG. 5 is a diagram illustrating an operation of liquid crystal molecules in a horizontal electric field system.

FIG. 6 is a diagram for explaining the influence of the specific resistance of the film material formed on the counter substrate on the electric field applied to the liquid crystal.

FIG. 7 is a diagram illustrating a substrate structure on a side on which a color filter with a black matrix is formed, for explaining the first embodiment of the present invention.

FIG. 8 is a diagram illustrating a substrate structure on a side on which a color filter with a black matrix is formed, for explaining a second embodiment of the present invention.

FIG. 9 is a diagram illustrating a substrate structure on a side where a color filter with a black matrix is formed, for explaining a third embodiment of the present invention.

[Explanation of symbols]

 1 Common Electrode (Common Electrode) 2 Gate Insulating Film 3 Video Signal Electrode (Drain Electrode) 4 Pixel Electrode (Source Electrode) 5 Alignment Film 6 Liquid Crystal Molecule 7 Substrate 8 Polarizing Plate 12 Scanning Electrode 13 a-Silicon 14 Thin Film Transistor 17 Control Circuit 18 Scan electrode driving circuit 19 Signal electrode driving circuit 20 Common electrode driving circuit 21 Active matrix type liquid crystal display element 22 Black matrix 23 Color filter 24 Overcoat film 25 Ultra-thin transparent conductive film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsumi Kondo 7-1-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Keikazu Araya 7-chome, Omika-cho, Hitachi-shi, Ibaraki No. 1 in Hitachi, Ltd. Hitachi Research Laboratory

Claims (7)

[Claims] 1. A first transparent substrate having a large number of display pixels formed by an active element and electrodes for driving the element, and a second transparent substrate arranged so as to face the first transparent substrate. In an active matrix type liquid crystal display device in which a liquid crystal layer is sandwiched between a substrate and controlled by applying a lateral electric field substantially parallel to the substrate to the liquid crystal layer,
At least one of the opposing transparent substrates has a specific resistance of 1
An active matrix type liquid crystal display device comprising a conductive film formed of a material of 0 ⁸ Ω · cm to 10 ¹² Ω · cm. 2. The color filter and an overcoat film for protecting the color filter are formed on the second transparent substrate, and the overcoat film is used as the conductive film. Active matrix liquid crystal display device. 3. The active matrix liquid crystal display device according to claim 2, wherein conductive fine particles are contained in the overcoat film protecting the color filter. 4. A first transparent substrate having a large number of display pixels formed by an active element and electrodes for driving the element, and a second transparent substrate arranged so as to face the first transparent substrate. In an active matrix type liquid crystal display device in which a liquid crystal layer is sandwiched between a substrate and controlled by applying a lateral electric field substantially parallel to the substrate to the liquid crystal layer,
A color filter and an overcoat film that protects the color filter are formed on the second transparent substrate, and the specific resistance of the dye carrier that constitutes the color filter is 10 ⁸ Ω · cm to 10 ¹² Ω ·. An active matrix liquid crystal display device characterized by having a size of cm. 5. The active matrix type liquid crystal display device according to claim 4, wherein conductive fine particles are contained in a dye carrier that constitutes the color filter. 6. A color filter and an overcoat film for protecting the color filter are formed, and a large number of display pixels formed by active elements and electrodes for driving the elements are formed on the overcoat film. A liquid crystal layer is sandwiched between a first transparent substrate and a second transparent substrate which is arranged so as to face the first transparent substrate, and a horizontal direction substantially parallel to the liquid crystal layer and the substrate. In the active matrix type liquid crystal display device controlled by applying an electric field, the second transparent substrate has a specific resistance of 10 ⁸ Ω · cm.
An active matrix type liquid crystal display device comprising a conductive film formed of a material of -10 ¹² Ω · cm. 7. A first transparent substrate having a large number of display pixels formed by an active element and electrodes for driving the element, and a second transparent substrate arranged to face the first transparent substrate. In an active matrix type liquid crystal display device in which a liquid crystal layer is sandwiched between a substrate and controlled by applying a lateral electric field substantially parallel to the substrate to the liquid crystal layer,
An active matrix type liquid crystal display device comprising an extremely thin transparent conductive film and an insulating film on at least one of the opposing transparent substrates.