JP2002040484A - Active matrix type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease irregular luminance caused when an active matrix liquid crystal display device is used for a long time. SOLUTION: A signal electrode or common electrode of a liquid crystal display device is partly formed from a conductive oxide film. By forming a part of the signal electrode or common electrode from a conductive oxide film, the proportion of a metal film in the signal electrode or common electrode in the positive potential than a scanning electrode is decreased, and contact between the metal film and a liquid crystal caused when defects are produced in a protective film or insulating film can be decreased. As a result, production of impurity ions by the electrochemical reaction caused by the contact of the metal electrode and the liquid crystal is suppressed, and the obtained liquid crystal display device has high picture quality and a wide viewing angle and does not cause irregular luminance even when it is used for a long time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a liquid crystal display device, and more particularly to an active matrix type liquid crystal display device that drives liquid crystal using thin film transistors (TFTs).

[0002]

2. Description of the Related Art In a conventional active matrix type liquid crystal display device, an IPS in which a voltage is applied to a liquid crystal layer which is homogeneously aligned between a pair of substrates to perform display by changing the alignment direction of the liquid crystal in the in-plane direction of the substrates. As a method in which the (in-plane switching) mode dramatically expands the viewing angle of the liquid crystal display device, for example, Japanese Patent Publication No. 63-21907, US Pat. No. 4,345,249, WO91 / 10936.
JP-A-6-222397 and JP-A-6-221497
No. 60878 and the like have been proposed and put to practical use. In this case, a comb-shaped metal electrode is usually used as an electrode for applying a voltage to the liquid crystal. Further, for example, Japanese Patent Application Laid-Open No. 9-73101 proposes a method of improving transmittance by using a transparent electrode such as ITO as a pixel electrode for applying a voltage for driving a liquid crystal and a counter electrode.

In these active matrix type liquid crystal display devices, an inorganic insulating film or a protective film is usually formed of silicon nitride or the like on the substrate in order to prevent the metal electrode on the substrate from directly contacting the liquid crystal. In the manufacturing process of these insulating films, defects such as pinholes may occur due to, for example, defective film formation or poor etching of silicon nitride. When a liquid crystal display device having such a defect is used for a long time, ionic impurities are generated at a defective portion where the liquid crystal and the metal electrode are in direct contact, and thus uneven brightness occurs on the display surface. As a method for reducing luminance unevenness caused by direct contact between a liquid crystal and a metal electrode in a horizontal electric field method,
A method of forming an organic layer between an electrode on an FT substrate and an alignment film and a method of covering a pixel electrode and a signal electrode with an oxide film have been proposed in Japanese Patent Application Laid-Open No. H11-2955763.

[0004]

As disclosed in the above-mentioned prior art, luminance unevenness can be reduced by covering the pixel electrode and the signal electrode with an oxide film, but the protective film generated in the manufacturing process can be reduced. In the case where the defect of the oxide film and the defect of the oxide film occur in the same place, the metal electrode and the liquid crystal come into direct contact with each other, so that there is still a problem that uneven brightness occurs.

On the other hand, Japanese Patent Laid-Open No. 9-73101 discloses a pixel structure in which a common electrode is formed using ITO which is a transparent conductive oxide film in the same manner as the counter electrode. Even if the defect of the protective film and the ITO occurs in the same place, the direct contact between the metal electrode and the liquid crystal can be eliminated. However, since the specific resistance of the ITO is higher than that of the metal film, the resistance of the common electrode increases. The problem arises. When the resistance of the common electrode is increased, the voltage to the counter electrode is not smoothly transmitted, so that a display defect called smear tends to occur. That is, the conventional lateral electric field type TFT-LC
In the case of D, there is a problem that when trying to suppress luminance unevenness that occurs when defects of the protective film and the oxide film occur at the same place, the resistance of the common electrode increases and the image quality is likely to deteriorate.

An object of the present invention is to provide a liquid crystal display device having high image quality and a wide viewing angle.

More specifically, the suppression of the increase in the resistance of the common electrode and the signal electrode and the suppression of the contact between the metal electrode and the liquid crystal when the protective film or the oxide film on the electrode has a defect are both achieved. An object of the present invention is to provide an active matrix type liquid crystal display device having a high image quality and a wide viewing angle which does not cause luminance unevenness even when driven over time.

[0008]

According to one embodiment of the present application, a liquid crystal display device has a pair of substrates and a liquid crystal layer sandwiched between the pair of substrates, and a pixel is provided on one of the pair of substrates. electrode,
A counter electrode, a scanning electrode, a signal electrode, a common electrode, and an active element are arranged. The pixel electrode and the counter electrode are formed of a transparent conductive film, and a liquid crystal in a liquid crystal layer is formed by applying a voltage to the pixel electrode and the counter electrode. In a liquid crystal display device that performs display by controlling, at least one of a signal electrode and a common electrode is formed of a metal film and a conductive oxide film.

At least one of the signal electrode and the common electrode is
A wiring structure in which a metal film and a conductive oxide film are alternately formed may be employed.

[0010] In addition, these electrodes can be basically formed of a metal wiring with a desired portion formed of a conductive oxide film.
Basically, a desired portion of the conductive oxide film wiring can be formed as a metal wiring.

[0011] These conductive oxide films are transparent electrodes, for example, ITO.

According to this embodiment, it is possible to suppress the generation of ionic impurities when these electrodes are in direct contact with the liquid crystal without increasing the resistance of the signal electrodes and the common electrodes. The signal electrode and common electrode are usually 1
The potential is higher than 0 V. For this reason, when these electrodes come into contact with the liquid crystal and an electrochemical reaction occurs, a metal film such as a signal electrode or a common electrode which is relatively at a positive potential is likely to be dissolved. The dissolution of the metal film is caused by an oxidation reaction in which metal atoms lose electrons and are ionized. Therefore, when the electrode is formed of a conductive oxide film which has already been oxidized, the electrode hardly dissolves. Although the conductive oxide film has a higher resistance than the metal film, an increase in resistance can be reduced by forming the electrode with the conductive oxide film and the metal film.

Further, by forming a part of the electrode such as the signal electrode and the common electrode formed of the metal film and the conductive oxide film only by the conductive oxide film, the area of the metal part of the signal electrode and the common electrode can be reduced. Can be. For this reason, even when a defect occurs in the protective film or the insulating film, the probability of direct contact between the liquid crystal and the easily soluble metal film can be reduced. Since the dissolution of the metal film generates ionic impurities that cause luminance unevenness, the means for suppressing the dissolution of the metal film can suppress the occurrence of luminance unevenness.

In addition, the dissolution of the metal film can be reduced by forming only the conductive oxide film over the signal electrode and the common electrode over the scanning electrode. Since the scanning electrode has a negative potential of 10 V or more as compared with the other electrodes, the metal film in a portion of the signal electrode or the common electrode which is close to the scanning electrode is easily melted. Therefore, by forming the portion of the signal electrode or the common electrode over the scanning electrode using only the conductive oxide film, it is possible to eliminate the portion of the metal film which is easily dissolved, thereby suppressing generation of ionic impurities.

The wiring electrodes such as the signal electrode and the common electrode can be formed as a laminated structure of a metal film and a conductive oxide film. With such a configuration, the resistance is reduced as compared with the case where the electrode is formed only of the metal film or only the conductive oxide film, and at the same time, a part of the electrode is easily made conductive only by patterning the metal film. It can be formed only with an oxide film. At this time, by making the width of the metal film constituting the electrode narrower than the width of the conductive oxide film, the area ratio of the metal film is reduced, and when a defect occurs in the insulating film or the protective film, the conductive oxide film of the electrode is not oxidized. Since the probability that the film portion comes into contact with the liquid crystal increases, the effect of suppressing the dissolution of the metal film increases. In this case, even if the width of the metal film is reduced, the electrode has a laminated structure of the metal film and the conductive oxide film, so that an increase in wiring resistance can be suppressed. Further, at this time, by making the width of the metal film at the intersection of the common electrode and the signal electrode wider than the width of the portion extending between the adjacent signal electrodes, the width at the intersection of the stacked conductive oxide films is increased. Even if the width is narrower than the width of a portion extending between adjacent signal electrodes, it is possible to suppress an increase in resistance of the entire common electrode. As a result, the area of the metal film can be reduced without increasing the area of the intersection between the signal electrode and the common electrode. When the area of the intersection between the common electrode and the signal electrode increases, the coupling capacitance generated between these electrodes increases,
Image quality is likely to deteriorate due to crosstalk. Therefore, the effect of suppressing the generation of ionic impurities by reducing the area of the metal film by the above means is increased, and also the effect of suppressing the deterioration of image quality due to crosstalk is obtained.

On the other hand, by extending the conductive oxide film laminated on the common electrode in the direction of the display area in the pixel to form the counter electrode, the counter electrode can function as a part of the common electrode. Thus, the effect of reducing the resistance of the common electrode can be obtained. In particular, by forming the counter electrode in substantially the same shape as the display area in the pixel, the effect of lowering the resistance of the common electrode can be further increased. In this case, the area extending between the signal electrodes of the common electrode is formed only of the conductive oxide film integrated with the counter electrode, so that the area of the metal film can be further reduced. The effect of suppressing generation of impurities is increased.

When the conductive oxide film is formed on the metal film, the conductive oxide film functions as a protective film for the metal film. Therefore, even if a defect occurs in the protective film, the conductive oxide film has the same defect. The contact between the metal film and the liquid crystal is suppressed as long as the metal film is not generated at the location, and the effect of suppressing the generation of ionic impurities due to the dissolution of the metal film is improved.

Further, by forming the conductive oxide film constituting the signal electrode in the same layer as the pixel electrode, the signal electrode can be formed of the conductive oxide film and the metal film without increasing the number of manufacturing steps. Similarly, by forming the conductive oxide film forming the common electrode in the same layer as the counter electrode, the common electrode can be formed of the conductive oxide film and the metal film without increasing the number of manufacturing steps.

The conductive oxide film forming the pixel electrode and the counter electrode may include at least one of ITO (indium tin oxide), IZO (indium zinc oxide), indium oxide, tin oxide, zinc oxide, and titanium oxide. A highly transparent film can be used. When these transparent conductive films are used, light is no longer blocked by the pixel electrode and the counter electrode, so that the transmittance of the liquid crystal panel increases.

Further, by including a compound having a cyano group in the liquid crystal composition layer, the driving voltage can be reduced.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to examples, but these examples are exemplifications of the present invention and do not limit the scope of the present invention. (Embodiment 1) FIG. 1 is a plan view showing one pixel on a TFT substrate and its periphery in an active matrix type liquid crystal display device according to the present invention. The TFT substrate has various electrode groups on a dielectric substrate, an insulating film to prevent short-circuit, a thin film transistor,
A protective film for protecting the thin film transistor and the electrode group is formed. In FIG. 1, reference numeral 1 denotes a signal electrode formed of a metal film. Reference numeral 2 denotes a part of the signal electrode, which is formed of a conductive oxide film. 3 is a drain electrode for transmitting the voltage of the signal electrode to the TFT, 4 is a counter electrode, 5 is a common electrode, 6 is a pixel electrode, 7 is a scanning electrode, 8 is an i-type semiconductor layer, 9 is a thin film transistor, 10 is a storage capacitor, 43 Denotes a pixel opening.
As shown in FIG. 1, each pixel includes a scanning electrode 7 and a common electrode 5.
Are arranged in an intersecting area between two adjacent signal electrodes 1 and 2 (in an area surrounded by four signal lines). Each pixel includes a thin film transistor 9, a storage capacitor 10, a pixel electrode 6, and a counter electrode 4. Scanning electrode 7, common electrode 5
Extend in the left-right direction in the figure, and a plurality of them are arranged in the up-down direction. The signal electrodes 1 and 2 extend in the up-down direction and are arranged in a plurality in the left-right direction. The pixel electrode 6 is connected to the thin film transistor 9, and the counter electrode 4 is integrated with the common electrode 5. The pixel electrode 6 and the opposing electrode 4 are formed in a comb shape opposing each other, and each is an electrode that is elongated in the vertical direction in the figure.

FIG. 2 shows a part of a cross section of a pixel in an active matrix type liquid crystal display device according to the present invention.
The cross-sectional structure showing a part of the pixel of the liquid crystal display device shown in FIG. 2 corresponds to a section taken along the line AA 'in FIG. 2, reference numeral 11 denotes a first dielectric substrate, 12 denotes an insulating film, 13 denotes a protective film, 14 denotes an alignment film, 15 denotes a liquid crystal layer, 16 denotes an overcoat film, 17 denotes a color filter, 18 denotes a black matrix, and 19 denotes a black matrix. The second dielectric substrate 20 is a polarizing plate. In the active matrix type liquid crystal display device of the present invention, an image is displayed by applying a voltage between the counter electrode 4 and the pixel electrode 6 to control the orientation direction of the liquid crystal molecules in the liquid crystal layer 15.

FIG. 3 is a diagram showing a cross section of the thin film transistor 9 taken along the line BB 'in FIG. The thin film transistor 9 includes a gate electrode also serving as the scanning electrode 7, an insulating film 12,
It has a source electrode and a drain electrode 3 which are also formed integrally with the i-type semiconductor layer 8 and the pixel electrode 6.

FIG. 4 is a diagram showing a cross section of the signal electrodes 1 and 2 taken along the line CC 'of FIG. As shown in this figure, the signal electrode has a conductive oxide film 2 at the intersection with the scanning electrode.

Counter electrode 4, common electrode 5 and scanning electrode 7
Are simultaneously formed in the same layer by patterning chromium (Cr). Also, the portion of the common electrode 5 and the scanning electrode 7 that intersects with the signal electrode is thinned to reduce the probability of short-circuiting between the signal electrode and the scanning electrode 7, and even if it is short-circuited, it is forked so that it can be separated by laser trimming. It is. On the common electrode and the scanning electrode 7, an insulating film is formed of silicon nitride, and the film thickness in this embodiment is about 0.24 μm.

The i-type semiconductor layer 18 is made of 0.2 μm amorphous silicon. In order to reduce a short circuit at the intersection between the scanning electrode 7 and the signal electrode 2 and at the intersection between the common electrode 5 and the signal electrode 1, an i-type semiconductor layer 18 is also formed at these intersections. I have. Between the source and drain electrodes 3 and the i-type semiconductor layer 8, N-type doped with phosphorus (P) on the surface of the i-type semiconductor layer 8 for ohmic contact.
A (+) type amorphous silicon semiconductor layer 21 is formed.

The signal electrode 1, the pixel electrode 6 and the drain electrode 3 are simultaneously formed in the same layer by patterning chromium (Cr). On the thin film transistor 9, the signal electrode 1 and the pixel electrode 6, a protective film 13 of 0.3 μm is formed of silicon nitride.

The signal electrode over the scanning electrode is formed by patterning an ITO film which is a conductive oxide film, and is laminated and connected to a Cr film at a position slightly away from the scanning electrode. .

Here, in the manufacturing process of the insulating film 12 and the protective film 13, a defect such as a pinhole may be caused due to a defective film formation or etching of silicon nitride. Such defects are caused by the insulating film 12 and the protective film 13.
When this occurs, metal electrodes such as the scanning electrode 7 and the signal electrode 1 come into contact with the liquid crystal, which promotes the generation of impurity ions due to an electrochemical reaction, thereby causing uneven brightness.

In this embodiment, a part of the signal electrode is formed of a conductive oxide film, for example, an ITO film. Therefore, even when a defect occurs in the insulating film 12 or the protective film 13 in this portion, the metal film does not come into contact with the liquid crystal. Unlike the case where the metal film is covered with the ITO film, the metal film does not come into contact with the liquid crystal even when a defect occurs in the ITO film, so that the metal film does not dissolve. Further, since the scanning electrode 7 has a potential lower than that of the signal electrode 1 or the common electrode 5 by 10 V or more, when the signal electrode 1 of the metal film comes into contact with the liquid crystal due to a defect, the electrode dissolution is particularly remarkable. Easy to occur. Therefore, if the signal electrode near the scanning electrode is formed of the conductive oxide film 2 such as an ITO film as in this embodiment, a particularly large electrode dissolution suppressing effect can be obtained. As a result, the generation of ionic impurities due to the electrochemical reaction is suppressed, and the effect of suppressing the occurrence of uneven brightness is obtained. In this embodiment, the metal film is C
Although r is used, it is not particularly limited to Cr, and a metal film of Al, Ta, Nb, Mo, Ti, Cu, or the like can be used. Although an ITO film is used as the conductive oxide film, it is not particularly limited to ITO, and may be IZO (indium zinc oxide),
A conductive oxide film containing indium oxide, tin oxide, zinc oxide, titanium oxide, or the like can be used. Further, in the present embodiment, the common electrode is arranged in parallel with the scanning electrode. However, it is also possible to arrange the common electrode so as to be orthogonal to the scanning electrode. In this case, the common electrode intersects with the scanning electrode. May be formed with a conductive oxide film.

FIG. 5 shows a color filter substrate formed by sequentially forming a black matrix 18, a color filter 17, and an overcoat film 16 on a second dielectric substrate 19. For the black matrix 18, for example, a material in which carbon or an organic pigment is mixed in a resist material is used.
The color filter 17 is formed in a stripe shape by repeating red, blue, and green. For the color filter 17, for example, a material in which a pigment is dispersed in an acrylic resin is used.
The overcoat film 16 is formed of, for example, a transparent resin material such as an acrylic resin or an epoxy resin.

An alignment film 14 is formed on the protective film 13 of the TFT substrate and on the overcoat film 16 of the color filter substrate.
About 80 nm thick polyimide is formed as
The surface is rubbed to align the liquid crystal. The rubbing directions are parallel to each other on the upper and lower substrates, and the angle between the rubbing direction and the direction of the applied electric field is 75 °.

The liquid crystal layer 15 is formed between the TFT substrate and the color filter substrate, and the surfaces of both substrates on which the alignment film 14 is formed are in contact with the liquid crystal layer 15. Further, polymer beads are dispersed between the TFT substrate and the color filter substrate as spacers for keeping the thickness (gap) of the liquid crystal layer constant, and the liquid crystal layer 15 between the two substrates is sealed with a sealing material so as to surround the display area. Sealed. As the sealing material, for example, an epoxy resin is used.

As the liquid crystal material LC, dielectric anisotropy △ ε
Is positive, the value is 7.3, and the refractive index anisotropy Δn is 0.074.
(589 nm, 20 ° C.) nematic liquid crystal was used. The thickness (gap) of the liquid crystal layer was controlled by polymer beads dispersed between the upper and lower substrates, and was 4.0 μm.

The polarizing plate 20 is a polarizing plate 20 on a TFT substrate.
Are aligned with the rubbing direction, and the polarization transmission axis of the deflecting plate 20 on the color filter substrate is perpendicular to the rubbing direction. Thus, a normally-closed liquid crystal panel in which the transmittance increases as the voltage applied to the pixel of the present invention (the voltage between the pixel electrode 6 and the counter electrode 4) is increased.

FIG. 6 shows a connection diagram of an equivalent circuit of the display matrix section and its peripheral circuits. Although the figure is a circuit diagram, it is drawn corresponding to an actual geometric arrangement. Reference numeral 22 denotes a matrix array in which a plurality of pixels are two-dimensionally arranged. In the figure, X means the signal electrode 1, and subscripts G, B and R are added corresponding to green, blue and red pixels, respectively. Y means the scanning electrode 7, and the suffixes 1, 2, 3,.
The end is added according to the order of the scanning timing.
The scanning electrode Y (subscript omitted) is connected to the vertical scanning circuit 23, and the signal electrode X (subscript omitted) is connected to the video signal driving circuit 2.
4 is connected. Reference numeral 25 denotes a power supply circuit for obtaining a plurality of divided and stabilized voltage sources from one voltage source. The power supply circuit 25 receives information for a CRT (cathode ray tube) from a host (upper processing unit) for a TFT liquid crystal display device. And a circuit for driving the common electrode 5 may be included.

FIG. 7 is an exploded perspective view showing each component of the liquid crystal display module 26. 27 is a frame-shaped shield case (metal frame) made of a metal plate, 28 is its display window, 29 is a liquid crystal display panel, 30 is a video signal drive circuit board, 31 is a scan signal drive circuit board, 32 is a power supply circuit board, 33 is a flat cable for electrically connecting the drive circuit boards, 34 is a light diffusion plate, 35 is a light guide, 36 is a reflector, 37 is a backlight fluorescent tube, 38 is a backlight case, and 39 is an inverter circuit. In this case, the modules MDL are assembled by stacking the respective members in a vertical arrangement relationship as shown in the figure.

The module 26 is entirely fixed by claws and hooks provided on the shield case 27. The backlight case 38 is configured to house the backlight fluorescent tube 37, the light diffusion plate 34, the light guide 35, and the reflection plate 36, and the light of the backlight fluorescent tube 37 disposed on the side surface of the light guide 35. Is made uniform backlight on the display surface by the light guide 35, the reflection plate 36, and the light diffusion plate 34, and is emitted toward the liquid crystal display panel 29 side. An inverter circuit board 39 is connected to the backlight fluorescent tube 37 and serves as a power supply for the backlight fluorescent tube 37.

The active matrix type liquid crystal display device of this embodiment maintains a wide viewing angle at which gradation inversion does not occur while maintaining a contrast ratio of 10 or more at 160 ° or more in the vertical and horizontal directions, and can be used for 100 consecutive days. No display failure due to luminance unevenness occurred. (Embodiment 2) FIG. 8 is a plan view of a pixel of a liquid crystal display device according to the present embodiment and its peripheral portion. In this embodiment, an ITO film constituting a signal electrode is formed by being laminated on a Cr film, and a scan electrode crossing portion includes a portion connected to the drain electrode 3 including a portion connected to the drain electrode 3.
The configuration is the same as that of the first embodiment except that it is formed only of the TO film. In addition to the reduction in the area ratio of the metal film constituting the signal electrode as compared with the first embodiment, the ITO film is formed on the Cr film as shown in FIG. Even when a defect occurs in the upper protective film of the formed portion, contact between the Cr film and the liquid crystal is suppressed, and the effect of suppressing generation of ionic impurities is further enhanced.

The active matrix type liquid crystal display device of this embodiment maintains a wide viewing angle at which gradation inversion does not occur while maintaining a contrast ratio of 10 or more at 160 ° or more in the vertical and horizontal directions, and can be used for 100 consecutive days. No display failure due to luminance unevenness occurred. (Embodiment 3) FIG. 10 is a plan view of a pixel of a liquid crystal display device according to the present embodiment and its peripheral portion. This embodiment has the same configuration as the first embodiment except for the following. The signal electrode 1 was formed of a Cr film including the intersection with the scanning electrode. The common electrode 5 is I
It was formed as a laminated structure of a TO film and a Cr film. The width of the metal film forming the common electrode was smaller than the width of the ITO film. Further, the width of the metal film forming the common electrode between the signal electrodes was made smaller than the width at the intersection with the signal electrode.
Further, the counter electrode 4 was formed in the same layer by patterning the ITO film constituting the common electrode 5 at a time. Figure 1
FIG. 1 shows a cross-sectional view of the common electrode 5 corresponding to the section line AA 'in FIG. In this embodiment, the ratio of the metal film of the common electrode 5 is greatly reduced, and even when a defect occurs in the insulating film or the protective film, the contact between the liquid crystal and the Cr film constituting the common electrode is significantly suppressed. In this embodiment, since the ITO film having a width wider than the Cr film is laminated on the Cr film, an increase in the wiring resistance can be suppressed even if the width of the Cr film is reduced.

The active matrix type liquid crystal display device of this embodiment maintains a wide viewing angle at which no grayscale inversion occurs while maintaining a contrast ratio of 10 or more at 160 ° or more in the vertical and horizontal directions, and can be used for 100 consecutive days. No display failure due to luminance unevenness occurred. (Embodiment 4) FIG. 12 is a plan view of a pixel of a liquid crystal display device according to the present embodiment and its peripheral portion. The third embodiment is different from the third embodiment except that the metal film of the common electrode is formed only at the intersection with the signal electrode, and the portion extending between adjacent signal electrodes of the common electrode is formed only of the ITO film. It has the same configuration as. In the present embodiment, the ratio of the metal film of the common electrode is smaller than that of the third embodiment, and the effect of suppressing the contact between the Cr film and the liquid crystal is further enhanced even when a defect occurs in the insulating film or the protective film.

The active matrix type liquid crystal display device of this embodiment maintains a wide viewing angle at which gradation inversion does not occur while maintaining a contrast ratio of 10 or more at 160 ° or more in the vertical and horizontal directions, and can be used for 100 consecutive days. No display failure due to luminance unevenness occurred. (Embodiment 5) This embodiment is the same as Embodiment 4 except for the following. FIG. 13 is a plan view of a pixel of the liquid crystal display device according to the present embodiment and its peripheral portion. FIG. 14 shows FIG.
3 is a cross-sectional view of a part of a pixel taken along the line AA ′ of FIG. The counter electrode is formed not on a comb-like shape but on a flat plate. The pixel electrode 6 is formed in a comb-like shape with an ITO film, and is connected to a source electrode 42 formed with a Cr film. In the present embodiment, since the counter electrode 4 also functions as a common electrode, the resistance of the common electrode is reduced as compared with the fourth embodiment. Further, since both the opposing electrode 4 and the pixel electrode 6 are formed of an ITO film that is a transparent conductive oxide film, light from the backlight passes through the pixel without being shielded from light at the electrode portion. Further, since the portion where the pixel electrode 6 and the counter electrode 4 face each other via the insulating film 12 functions as a capacitor, there is no need to provide the storage capacitor 10 as provided in the fourth embodiment, so that the pixel opening 43 is widened. Can do things. As a result, in this embodiment, the effect of increasing the amount of light transmitted through the pixel and brightening the display can also be obtained.

The active matrix type liquid crystal display device of this embodiment maintains a wide viewing angle at which gradation inversion does not occur while maintaining a contrast ratio of 10 or more at 160 ° or more in the vertical and horizontal directions, and can be used for 100 consecutive days. No display failure due to luminance unevenness occurred. (Embodiment 6) This embodiment is the same as Embodiment 5 except for the following. FIG. 15 is a plan view of a pixel of the liquid crystal display device according to the present embodiment and its peripheral portion. Common electrode on Cr film
The ITO film is formed by lamination. The signal electrode is formed by laminating an ITO film on a Cr film, and the source electrode 42 and the drain electrode 3 are formed in the same layer as the metal film of the signal electrode 1. The pixel electrode 6 is formed in the same layer as a conductive oxide film constituting a signal electrode, for example, an ITO film. In the present embodiment, since the metal films of the signal electrode and the common electrode in the display area are all covered with the conductive oxide film, a defect occurs in the upper insulating film or the protective film in the portion where the metal film is formed. However, the effect of suppressing the direct contact of the metal film with the liquid crystal is further enhanced.

The active matrix type liquid crystal display device of this embodiment maintains a wide viewing angle at which no grayscale inversion occurs while maintaining a contrast ratio of 10 or more at 160 ° or more in the vertical and horizontal directions, and can be used for 100 consecutive days. No display failure due to luminance unevenness occurred. (Embodiment 7) This embodiment is the same as Embodiment 6 except for the following.

A nematic liquid crystal composition sandwiched between a TFT substrate and a counter substrate has a cyano group-containing liquid crystal compound of 4%.
5% by weight of-(4-cyano-3,5-difluorophenyl) pentylcyclohexane was added.

Although a liquid crystal compound having a cyano group is effective for reducing the driving voltage, there is a problem that the impedance of the liquid crystal layer tends to decrease. Therefore, when the electrode and the liquid crystal come into contact with each other, generation of ionic impurities due to an electrochemical reaction is promoted. However, the active matrix type liquid crystal display device of the present embodiment maintains a wide viewing angle at which no grayscale inversion occurs while maintaining a contrast ratio of 10 or more at 160 ° or more in the vertical and horizontal directions, and maintains luminance even after continuous use for 100 days. No display failure due to unevenness occurred.
As described above, even when a liquid crystal compound that lowers the impedance of a liquid crystal layer, such as a liquid crystal compound having a cyano group, is used, dissolution of a metal electrode at a defective portion of an insulating film or a protective film is suppressed, and thus uneven brightness is obtained. It is possible to obtain a high quality image in which no image is generated.

According to these embodiments, even when a defect occurs in the protective film or the insulating film, the contact between the liquid crystal and the metal film of the signal electrode or the common electrode which is at a higher potential than the scanning electrode is reduced.
As a result, the generation of impurity ions due to the electrochemical reaction that occurs when the metal electrode comes into contact with the liquid crystal is suppressed, and it is possible to obtain a high-quality, wide-viewing-angle liquid crystal display device that does not cause luminance unevenness even when used for a long time. it can.

[0048]

According to the present invention, a liquid crystal display device having a high image quality and a wide viewing angle can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a typical example of a pixel and its peripheral electrode structure in a liquid crystal display device of the present invention.

FIG. 2 is a diagram showing a part of a cross section in a unit pixel in the liquid crystal display device of the present invention.

FIG. 3 is a cross-sectional view of a thin film transistor element in the liquid crystal display device of the present invention.

FIG. 4 is a cross-sectional view of an intersection between a signal electrode and a scanning electrode in the liquid crystal display device of the present invention.

FIG. 5 is a diagram showing a typical example of a color filter substrate in the liquid crystal display device of the present invention.

FIG. 6 is a circuit diagram including a matrix portion and its periphery of the liquid crystal display device of the present invention.

FIG. 7 is an exploded perspective view of a liquid crystal module in the liquid crystal display device of the present invention.

FIG. 8 is a diagram showing one pixel and an electrode structure around the pixel in a second embodiment of the liquid crystal display device of the present invention.

FIG. 9 is a diagram showing a part of a cross section in a unit pixel in a second embodiment of the liquid crystal display device of the present invention.

FIG. 10 is a diagram showing a pixel and its peripheral electrode structure in a third embodiment of the liquid crystal display device of the present invention.

FIG. 11 is a view showing a part of a cross section in a unit pixel in a third embodiment of the liquid crystal display device of the present invention.

FIG. 12 is a diagram showing a pixel and its peripheral electrode structure in a fourth embodiment of the liquid crystal display device of the present invention.

FIG. 13 is a view showing one pixel and a peripheral electrode structure in a fifth embodiment of the liquid crystal display device of the present invention.

FIG. 14 is a diagram showing a part of a cross section in a unit pixel in a fifth embodiment of the liquid crystal display device of the present invention.

FIG. 15 is a diagram showing a pixel and its peripheral electrode structure in a sixth embodiment of the liquid crystal display device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Signal electrode (formed of a metal film), 2 ... Conductive oxide film forming a part of signal electrode, 3 ... Drain electrode, 4 ... Counter electrode, 5 ... Common electrode, 6 ... Pixel electrode, 7 ... Scan electrode , 8 ...
i-type semiconductor layer, 9 thin film transistor, 10 storage capacitor, 11 first dielectric substrate, 12 insulating film, 13 protective film, 14 alignment film, 15 liquid crystal layer, 16 overcoat film, 17 Color filter, 18 black matrix, 19 second dielectric substrate, 20 polarizing plate, 21 N
(+) Type amorphous silicon semiconductor layer, 22: a matrix array in which a plurality of pixels are two-dimensionally arranged, 23: a vertical scanning circuit, 24: a video signal driving circuit, 25: a power supply circuit, 2
6 liquid crystal display module, 27 shield case, 28
... display window, 29 ... liquid crystal display panel, 30 ... video signal drive circuit board, 31 ... scanning signal drive circuit board, 32 ... power supply circuit board, 33 ... flat cable, 34 ... light diffusion plate, 3
5 light guide, 36 reflector, 37 backlight fluorescent tube, 38 backlight case, 39 inverter circuit board, 40 metal film forming common electrode, 41 conductive oxide forming common electrode Film, 42 ... source electrode, 43 ...
Pixel opening.

Continued on the front page (72) Inventor Katsumi Kondo 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture F-term in Hitachi Research Laboratory, Hitachi Ltd. 2H092 GA14 GA17 JA24 JB33 JB52 JB56 JB73 KA10 KA18 MA47 NA01 NA16 NA17 NA28 PA08 PA09 PA11 PA13 5C094 AA12 AA24 AA31 AA48 AA55 BA03 BA43 CA19 CA24 DA13 DB01 DB04 EA04 EA05 EA07 EB02 ED03 FA01 FA02 FB01 FB02 FB12 FB14 FB15 GA10 5F033 HH08 HH11 HH HH HH HH HH HH HH HH HH GG02 GG15 GG35 HK02 HK03 HK04 HK07 HK09 HK16 HK21 HM19 NN02 NN24 NN72

Claims (18)

[Claims] A liquid crystal layer sandwiched between the pair of substrates; a pixel electrode, a counter electrode, a scanning electrode, a signal electrode, and a common electrode on one of the pair of substrates; , An active element is arranged, and a voltage is applied to the pixel electrode and the counter electrode to control the liquid crystal of the liquid crystal layer to perform display. At least one of the signal electrode and the common electrode The liquid crystal display device, wherein at least a part of the electrode is formed of a metal film and a conductive oxide film. 2. The liquid crystal display device according to claim 1, wherein the electrode formed of the metal film and the conductive oxide film is formed by connecting a plurality of regions formed of the metal film by a conductive oxide film. 3. A conductive oxide film connecting a plurality of regions formed of a metal film constituting an electrode formed of the metal film and the conductive oxide film, the conductive oxide film being connected to a portion where the electrode crosses the scan electrode. 3. The liquid crystal display device according to claim 2, wherein the liquid crystal display device is formed. 4. An electrode formed of the metal film and the conductive oxide film is a common electrode, and the common electrode has a metal film at a portion crossing the signal electrode, and the metal film is formed of the common film. 3. The liquid crystal display device according to claim 2, wherein the electrodes are connected by a conductive oxide film to a metal film formed at a portion crossing an adjacent signal electrode. 5. The liquid crystal display device according to claim 1, wherein the electrode formed of the metal film and the conductive oxide film has a laminated structure of the metal film and the conductive oxide film. . 6. An electrode formed of the metal film and the conductive oxide film has a width of the conductive oxide film larger than a width of the metal film.
Liquid crystal display device. 7. The liquid crystal display device according to claim 6, wherein a width of the metal film constituting the common electrode at an intersection with the signal electrode is wider than a width of a portion extending between the signal electrodes. 8. The liquid crystal display device according to claim 6, wherein said counter electrode is formed by extending a conductive oxide film constituting said common electrode in a pixel region direction. 9. The liquid crystal display device according to claim 1, wherein the electrode formed of the metal film and the conductive oxide film has a conductive oxide film formed above the metal film. 10. The liquid crystal display device according to claim 1, wherein the conductive oxide film forming the signal electrode is formed in the same layer as the pixel electrode. 11. The liquid crystal display device according to claim 1, wherein the conductive oxide film forming the common electrode is formed in the same layer as the counter electrode. 12. The liquid crystal display device according to claim 1, wherein said pixel electrode and said counter electrode are formed of a transparent conductive film. 13. The conductive oxide film according to claim 1, wherein said conductive oxide film contains at least one of ITO (indium tin oxide), IZO (indium zinc oxide), indium oxide, tin oxide, zinc oxide and titanium oxide. 13. The liquid crystal display device according to any one of 1 to 12. 14. The liquid crystal display device according to claim 1, wherein the liquid crystal composition layer contains at least one compound having a cyano group. 15. The liquid crystal display device according to claim 1, wherein at least one of the signal electrode and the common electrode has a wiring structure in which metal films and conductive oxide films are alternately arranged. 16. The liquid crystal display device according to claim 1, wherein at least one of the signal electrode and the common electrode is formed of a metal film, and a desired portion is formed of a conductive oxide film. 17. At least one of the signal electrode and the common electrode is formed of a conductive oxide film.
2. The liquid crystal display device according to claim 1, wherein a desired portion is formed as a metal film. 18. The liquid crystal display device according to claim 15, wherein said conductive oxide film is made of ITO.