JP2003315812A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of being manufactured without precise registration between an array substrate and a counter substrate even in the case of adopting an MVA mode. <P>SOLUTION: The liquid crystal display device is provided with an array substrate provided with pixel electrodes 10 on one of the main surfaces, a counter substrate which is placed to be faced to the surface formed with pixel electrodes on the array substrate 10 and provided with common electrodes on the counter surface to the array substrate, and a liquid crystal layer held between the array substrate and the counter substrate, the constitution is characterized in that the pixel electrode 10 includes comb shape parts 10a-10d, the outline of the comb shape parts 10a-10d has a shape of alternately connecting a plurality of curves with a plurality of straight lines, and each of the plurality of curves has either two of the plurality of straight lines as its tangents. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art Liquid crystal display devices have various characteristics such as thinness, light weight and low power consumption, and are applied to various uses such as office automation equipment, information terminals, watches, and televisions. . In particular, a liquid crystal display device having a thin film transistor (hereinafter referred to as a TFT) is used as a monitor for displaying a large amount of information such as a portable television or a computer because of its high responsiveness.

In recent years, as the amount of information has increased, there has been an increasing demand for higher definition of images and higher display speed. Among these requirements, the high definition of the image is described in the above-mentioned T
This is realized by miniaturizing the array structure formed by the FT.

On the other hand, regarding the speeding up of the display speed, an OC using a nematic liquid crystal is used instead of the conventional display mode.
B-mode, VAN (Vertical Aligned Nematic) mode, HAN mode, and π-aligned mode, and surface-stabilized ferroelectric liquid crystal (Surface Stabilization) using smectic liquid crystal
The adoption of an ized Ferroelectric Liquid Crystal) mode and an antiferroelectric liquid crystal mode is under consideration.

Among these display modes, the VAN mode can obtain a faster response speed than the conventional TN (Twisted Nematic) mode, and further, the rubbing process which causes defects such as electrostatic breakdown due to the vertical alignment is unnecessary. Is. Among them, a multi-domain VAN mode (hereinafter referred to as MVA mode) in which each pixel region is divided into a plurality of domains in which the tilt directions of liquid crystal molecules are different from each other
Has attracted particular attention because the compensating design of the viewing angle is relatively easy.

However, in the conventional liquid crystal display device adopting the MVA mode, a structure for dividing the pixel region into a plurality of domains must be provided on both the array substrate and the counter substrate. That is, in the conventional liquid crystal display device adopting the MVA mode, not only the array substrate,
It is necessary to form a ridge-shaped projection structure also on the counter substrate or to provide a slit or the like on the common electrode on the counter substrate. Therefore, the alignment between the array substrate and the counter substrate must be performed with extremely high accuracy, resulting in an increase in cost and a decrease in reliability.

In recent years, in the manufacture of a TN mode liquid crystal display device, a technique of forming a color filter layer on an array substrate has begun to be put into practical use. According to this technique, when the array substrate and the counter substrate are bonded to each other to form a cell, it is not necessary to align each color region forming the color filter layer with the pixel electrode. Therefore, it is desired to apply such a technique to the manufacture of the MVA mode liquid crystal display device. However, in the conventional MVA mode liquid crystal display device, when an array substrate and a counter substrate are bonded together to form a cell. First, it is necessary to align the ridge structure and the slit between them. Therefore, the conventional M
In the VA mode liquid crystal display device, even if the color filter layer is formed on the array substrate, the benefit obtained in the TN mode liquid crystal display device cannot be enjoyed.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is possible to accurately align the array substrate and the counter substrate even when the MVA mode is adopted. It is an object of the present invention to provide a liquid crystal display device that can be manufactured without any need.

[0009]

According to the present invention, an array substrate having a pixel electrode on one main surface and an array substrate which is arranged so as to face a surface of the array substrate on which the pixel electrode is provided. And a liquid crystal layer sandwiched between the array substrate and the counter substrate, wherein the pixel electrode includes a comb-shaped portion, and the contour of the comb-shaped portion is A liquid crystal display device is provided, which has a shape in which a plurality of curves and a plurality of straight lines are alternately connected, and each of the plurality of curves has any two of the plurality of straight lines as a tangent line. . The “curve” here means that the radius of curvature is 2.0 μm or more at any position.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each drawing, the same or similar components are designated by the same reference numerals, and duplicated description will be omitted.

FIG. 1 is a sectional view schematically showing a liquid crystal display device according to an embodiment of the present invention. A liquid crystal display device 1 shown in FIG. 1 is an MVA type liquid crystal display device and has a structure in which a liquid crystal layer 4 is sandwiched between an active matrix substrate (or an array substrate) 2 and a counter substrate 3. There is.
The distance between the active matrix substrate 2 and the counter substrate 3 is kept constant by spacers (not shown). Polarizing films 5 are attached to both surfaces of the liquid crystal display device 1.

The active matrix substrate 2 has a transparent substrate 7 such as a glass substrate. Wirings and switching elements 8 are formed on one main surface of the transparent substrate 7. Further, a color filter layer 9, a pixel electrode 10 and an alignment film 11 are sequentially formed on them.

Wirings formed on the transparent substrate 7 are scanning lines and signal lines made of aluminum, molybdenum, copper or the like. The switching element 8 is, for example,
Amorphous silicon or polysilicon as the semiconductor layer,
The TFT is a TFT having a metal layer of aluminum, molybdenum, chromium, copper, tantalum, or the like, and is connected to wirings such as scanning lines and signal lines and the pixel electrode 10. With the active matrix substrate 2 having such a configuration,
It is possible to selectively apply a voltage to a desired pixel electrode 10.

The color filter layer 9 interposed between the transparent substrate 7 and the pixel electrode 10 includes blue, green and red colored layers 9a-9.
It is composed of c. A contact hole is provided in the color filter layer 9, and the pixel electrode 10 is connected to the switching element through this contact hole.

The pixel electrode 10 may be made of a transparent conductive material such as ITO. The pixel electrode 10 can be formed by forming a thin film by, for example, a sputtering method, and then patterning the thin film using a photolithography technique and an etching technique.

The alignment film 11 is composed of a thin film made of a transparent resin such as polyimide. In the present embodiment, the alignment film 11 is given a vertical alignment property without being subjected to rubbing treatment.

The counter substrate 3 has a structure in which a common electrode 16 and an alignment film 17 are sequentially formed on a transparent substrate 15 such as a glass substrate. These common electrode 16 and alignment film 1
7 can be formed of the same material as the pixel electrode 10 and the alignment film 11. In this embodiment, the common electrode 16 is formed as a flat continuous film.

FIG. 2 is a plan view schematically showing an example of a structure usable in the liquid crystal display device shown in FIG. In the structure shown in FIG. 2, one pixel electrode 10 has four portions 10a ...
It is composed of 10d. A plurality of slit portions 10-1 are provided in each of the portions 10a to 10d forming the pixel electrode 10 at substantially constant intervals and substantially in parallel with each other, and the portion 10 located between the slit portions 10-1 of the pixel electrode 10 is formed. -2 has a comb-like shape. That is, each of the portions 10 a to 10 d forming the pixel electrode 10 has a plurality of comb tooth portions 10.
It is a comb-shaped part including -2. Further, the longitudinal directions of the slit portion 10-1 and the comb tooth portion 10-2 are different among the portions 10a to 10d. In the liquid crystal display device 1 shown in FIG. 1, by adopting such a configuration, the pixel region corresponds to the comb-shaped portions 10 a to 10 d forming the pixel electrode 10, and the tilt directions of the liquid crystal molecules are different from each other. It can be divided into domains. For this, see Figure 3.
A description will be given with reference to (a) to (d).

3 (a) to 3 (d) are diagrams schematically showing alignment changes of liquid crystal molecules which occur when the structure shown in FIG. 2 is adopted in the liquid crystal display device shown in FIG. Note that FIG.
3A and 3C are plan views, and FIGS. 3B and 3D are side views of the structure shown in FIGS. 3A and 3C as viewed from the lower side in the drawing. Further, in FIGS. 3A to 3D, some components are omitted for simplification.

When no voltage is applied between the pixel electrode 10 and the common electrode 16, the alignment films 11 and 17 are formed of the liquid crystal layer 4.
The liquid crystal molecules 25 constituting the above, specifically the liquid crystal molecules having a negative dielectric anisotropy, act to vertically align them. Therefore, in the liquid crystal molecules 2, their long axes are oriented to the alignment film 1.
The film is oriented so as to be substantially perpendicular to the film surface of No. 1.

When a relatively low first voltage is applied between the pixel electrode 10 and the common electrode 16, a leak electric field is generated above the slit portion 10-1 provided in the pixel electrode 10. Therefore, there, the lines of electric force are inclined as shown in FIG.

The electric field generated by applying a voltage between the pixel electrode 10 and the common electrode 16 acts to align the liquid crystal molecules 25 in a direction perpendicular to the lines of electric force.
Therefore, the liquid crystal molecules 25 tend to be aligned as shown in FIG. 3A by the action of the alignment films 11 and 17 and the electric field.

However, in the state shown in FIG. 3A, the alignment state of the liquid crystal molecules 25 on the right side and the liquid crystal molecules 2 on the left side are aligned.
5 and the alignment state of 5 interfere with each other. Therefore, the liquid crystal molecules 25
In the figure, the tilt direction is changed upward or downward in order to attain a more stable alignment state.

Here, as shown in FIG. 3A, the comb-teeth portion 10-2 of the pixel electrode 10 and its vicinity have a symmetrical (or isotropic) shape in the vertical direction in the figure. Suppose you have it. In this case, the probability that the liquid crystal molecule 25 changes the tilt direction upward as shown by the arrow 31, and the arrow 3
As indicated by 2, the probability of changing the tilt direction downward is equal.

On the other hand, as shown in FIG. 3C, the comb-teeth portion 10-2 of the pixel electrode 10 and its vicinity have an asymmetric (or anisotropic) shape in the vertical direction in the figure. When it has, the electric force lines are asymmetric between both ends of the pixel electrode 10, and similarly, the electric force lines are also asymmetric between both ends of the slit portion 10-1. Therefore, the alignment state in which the liquid crystal molecules 25 are aligned in the direction indicated by the arrow 32 is more stable than the alignment state in which the liquid crystal molecules 25 are aligned in the direction indicated by the arrow 31. As a result, the average tilt direction (director) of the liquid crystal molecules 25 is downward as shown by the arrow 32 in FIG.

When the voltage applied between the pixel electrode 10 and the common electrode 16 is increased to the second voltage higher than the first voltage, the alignment films 11 and 17 have the effect of vertically aligning the liquid crystal molecules 25. On the contrary, the action of the electric field for orienting the liquid crystal molecules 25 in the direction perpendicular to the lines of electric force becomes greater. Therefore, the liquid crystal molecules 25 change the tilt angle in a direction approaching horizontal alignment.

Here, even when the voltage applied between the electrodes 10 and 16 is the second voltage, the liquid crystal molecules 25 have arrows 32 as in the case where the voltage applied between the electrodes 10 and 16 is the first voltage. The liquid crystal molecules 2 are aligned in the direction shown by
5 is more stable as compared with the orientation state in which the orientation is indicated by the arrow 31. Therefore, when the voltage applied between the electrodes 10 and 16 is changed between the first voltage and the second voltage, the director of the liquid crystal molecules 25 is a plane perpendicular to the arrangement direction of the slit portion 10-1 and the comb tooth portion 10-2. It will change within. That is, when the voltage applied between the electrodes 10 and 16 is changed between the first voltage and the second voltage, the liquid crystal molecules 25 have an average tilt direction of the slit portion 10-1 and the comb tooth portion 10-2. The tilt angle is changed while being maintained in the plane perpendicular to the arrangement direction.

Therefore, the slit portion 10-1 and the comb tooth portion 1 are provided between the four portions 10a to 10d constituting the pixel electrode 10.
By changing the longitudinal direction of 0-2, liquid crystal molecules 2
The tilt angle can be changed while maintaining the tilt direction of No. 5 as shown in FIG. That is, with only the structure provided on the active matrix substrate 2, four domains in which the tilt directions of the liquid crystal molecules 25 are different from each other can be formed in one pixel region. Further, in the present embodiment, the tilt angle can be changed while maintaining the average tilt direction of the liquid crystal molecules 25 in the plane perpendicular to the arrangement direction of the slit portions 10-1 and the comb tooth portions 10-2. In addition to achieving a high response speed, poor orientation is unlikely to occur, and good orientation division is possible.

In the present embodiment, the comb-shaped portions 10a ...
Each contour of 10d has a shape in which a plurality of curves and a plurality of straight lines are alternately connected, and each of these curves has any two of the above straight lines as a tangent line. When such a structure is adopted, the comb-shaped portions 10a to
Apparently, a faster response speed can be realized as compared with the case where each contour of 10d is composed of only a plurality of straight lines.

The inventors of the present invention, when the respective contours of the comb-shaped portions 10a to 10d are constituted by only a plurality of straight lines, the alignment change of the liquid crystal molecules 25 according to the change of the applied voltage causes a change in the comb-teeth portion 10-2. It has been confirmed that the corners, in particular, the acute corners, propagate so as to sequentially spread from the region located above. That is, the alignment change of the liquid crystal molecules 25 does not occur simultaneously in the region near the corner of the comb tooth portion 10-2 and the region far from the corner of the comb tooth portion 10-2. Since the time required from the start to the end of the orientation change has a great influence on the apparent response speed, the liquid crystal molecule 2
When the orientation change of 5 does not proceed rapidly, it is difficult to obtain a high apparent response speed.

On the other hand, in the present embodiment, the comb-shaped portion 1
Each contour of 0a to 10d has the above-mentioned shape. That is, in the present embodiment, the comb-shaped portions 10a to 10 are formed.
Each contour of d is composed of smooth lines with no corners. Therefore, the change in the orientation of the liquid crystal molecules 25 does not proceed so as to sequentially spread from one location, but it may proceed so as to spread from a large number of locations or at almost all locations at the same time. Therefore, the time required from the start of the alignment change of the liquid crystal molecules 25 to the end thereof is shortened, and therefore the apparent response speed can be increased.

If the radius of curvature of the curve forming the contours of the comb-shaped portions 10a to 10d is excessively small, the above effect may not be obtained. Therefore, in this embodiment, the curve has a radius of curvature of 2.0 μm at any position.
m or more, preferably 2.5 μm or more.

In this embodiment, as described above, the display is performed by forming the distribution of the intensity of the plane wave electric field in the pixel region and changing the intensity to control the optical characteristics of the liquid crystal layer 4. . By the way, in the case of performing the control as described above, a stronger electric field is formed in the portion on the pixel electrode 10 in the liquid crystal layer 4 than in the portion on the slit portion 10-1. Therefore, in the portion on the pixel electrode 10, the liquid crystal molecules 25 fall more largely than in the portion on the slit portion 10-1. That is, the average tilt angle of the liquid crystal molecules 25 is different between the portion on the pixel electrode 10 of the liquid crystal layer 4 and the portion on the slit portion 10-1. Such a difference in tilt angle can be observed as an optical difference.

FIG. 4 is a diagram showing an example of the transmittance distribution observed when the structure shown in FIG. 2 is adopted in the liquid crystal display device shown in FIG. It should be noted that FIG. 4 shows a range of the first voltage to the second voltage between the electrodes 10 and 16 in a state where polarizing plates (or polarizing films) are arranged on the light source side and the viewer side of the liquid crystal layer 4. 3 shows a plane-wave-like transmittance distribution observed when a third voltage inside is applied. As described above, according to this embodiment, the features described with reference to FIGS. 1 to 3 can also be observed as optical features.

In the structure described with reference to FIGS. 2 to 4, the widths of the slit portion 10-1 and the comb tooth portion 10-2 are constant, but the slit portion 10-1 and the comb tooth portion 10-2 have the same width. The width may vary along their length.

FIG. 5 is a plan view schematically showing another example of the structure which can be used in the liquid crystal display device shown in FIG. Also,
FIG. 6 is a diagram schematically showing an alignment change of liquid crystal molecules which occurs when the structure shown in FIG. 5 is adopted in the liquid crystal display device shown in FIG. It should be noted that in FIG.
Of the two parts 10a to 10d, only the part 10a is drawn, and in FIG. 6, only part of the part 10a shown in FIG. 5 is drawn.

In the structure shown in FIGS. 5 and 6, the width of the slit portion 10-1 continuously increases from the central portion of the pixel electrode 10 toward the peripheral portion thereof, and the width of the comb tooth portion 10-2 increases. It decreases continuously from the central part of 10 toward the peripheral part. According to such a structure, as shown in FIG.
In addition to the liquid crystal orientation at the lower end of -1 and the liquid crystal orientation at the upper end of the comb tooth portion 10-2, the liquid crystal orientation at both side ends of the slit portion 10-1 also acts so that the direction of the director becomes the direction indicated by the arrow 32. . Therefore, according to the structures shown in FIGS. 5 and 6, the transmittance and the response speed can be further improved.

[0038] In the embodiment described above, the sum W ₁₂ of the width W ₂ of width W ₁ and the comb portion 10-2 of the slit portion 10-1 2
It is preferably 0 μm or less. Normally, the sum W ₁₂ is 20
When it is not more than μm, the orientation of the liquid crystal molecules can be controlled as described above, and a sufficient transmittance can be realized. Further, the sum W ₁₂ is preferably 6 μm or more.
In general, when the sum W ₁₂ is 6 μm or more, it is possible to form a structure for generating a region where the electric field strength is stronger and a region where the electric field strength is weaker in the liquid crystal layer 4 with sufficiently high accuracy. The liquid crystal alignment described above can be stably generated.

In this embodiment, the width W ₁ and the width W ₂ are
It is preferable that each is 8 μm or less. The width W ₁ and the width W ₂ are preferably 4 μm or more. In this range, practically sufficient performance can be expected in terms of response speed and transmittance.

In the present embodiment, the length of the slit portion 10-1 and the length of the comb tooth portion 10-2 may be longer than the width W ₁ and the width W ₂ , respectively. W ₁₂
2 times or more is preferable. In this case, more liquid crystal molecules can be aligned in the length direction of those regions.

In this embodiment, the VAN mode in which the nematic liquid crystal having a negative dielectric anisotropy is vertically aligned is adopted, but it is also possible to use the nematic liquid crystal having a positive dielectric anisotropy. In particular, when high contrast is desired, by adopting the VAN mode and providing normally black, a high contrast of 400: 1 or more and a bright screen design by a high transmittance design are possible.

In the present embodiment, in order to accelerate the apparent optical response, the angle formed by the light transmission easy axis or the light absorption axis of the polarizing film 5 and the arrangement direction of the region where the electric field is strong and the region where the electric field is weak is from 45 °. It may be shifted by a predetermined angle θ. This angle θ can be set according to the viewing angle and the like, but it is most effective to set it to 22.5 ° in order to shorten the response time.

In the present embodiment, the shape of the comb-shaped portions 10a to 10d forming the pixel electrode 10 is not particularly limited,
For example, it can be rectangular or fan-shaped. Further, in the present embodiment, since the liquid crystal display device 1 is of the MVA type, the pixel electrode is composed of a plurality of comb-shaped portions 10a to 10d.
When one pixel region is not divided into a plurality of domains having different tilt directions, the pixel electrode can be configured by only one comb-shaped portion.

In this embodiment, only the active matrix substrate 2 is provided with the structure for producing a region having a stronger electric field and a region having a weaker electric field in the liquid crystal layer when the third voltage is applied. It may be provided on both the counter substrate 3 and the counter substrate 3. However, in the former case, it is not necessary to perform highly accurate positioning using an alignment mark or the like when the active matrix substrate 2 and the counter substrate 3 are bonded to each other to form a cell.

In this embodiment, the color filter layer 9 is provided on the active matrix substrate 2, but the color filter layer 9 may be provided on the counter substrate 3. However, in the former case, it is not necessary to perform highly accurate positioning using an alignment mark or the like when the active matrix substrate 2 and the counter substrate 3 are bonded to each other to form a cell.

[0046]

EXAMPLES Examples of the present invention will be described below.

(Example) FIG. 7A is a plan view schematically showing the shape of the pixel electrode 10 adopted in the example of the present invention. Further, FIG. 7B is an enlarged plan view showing a part of the pixel electrode 10 shown in FIG. In this example, the liquid crystal display device 1 shown in FIG. 1 was manufactured by adopting the planar shape shown in FIGS. 7A and 7B for the pixel electrode 10 by the following method.

First, film formation and patterning were repeated in the same manner as a normal TFT forming process to form wirings such as scanning lines and signal lines and the TFT 8 on the glass substrate 7. Next, the color filter layer 9 was formed on the surface of the glass substrate 7 on which the TFTs 8 and the like were formed by a conventional method.

Next, with respect to the surface of the glass substrate 7 on which the transparent insulating film 9 is formed, IT is applied through a mask having a predetermined pattern.
O was sputtered. Then, a resist pattern was formed on this ITO film, and the exposed portion of the ITO film was etched using this resist pattern as a mask. As described above, the pixel electrode 10 as shown in FIGS. 7A and 7B was formed. In addition, here, the slit portion 10
The width W ₂ of width W ₁ and comb teeth 10-2 of -1 are all set to 5 [mu] m.

Then, a thermosetting resin is applied to the entire surface of the glass substrate 7 on which the pixel electrodes 10 are formed, and the coating film is baked to form an alignment film 11 having a thickness of 70 nm and exhibiting vertical alignment. did. The active matrix substrate 2 was produced as described above.

Next, an ITO film was formed as the common electrode 16 on the one main surface of the glass substrate 15 prepared separately by the sputtering method. Then, this common electrode 16
An alignment film 17 was formed on the entire surface of the substrate by the same method as described for the active matrix substrate 2. The counter substrate 3 was produced as described above.

Next, the active matrix substrate 2 and the peripheral edge portion of the counter surface of the counter substrate 3 are aligned with their alignment films 11 and 1.
A liquid crystal cell was formed by bonding with an adhesive so that the surfaces on which 7 were formed faced each other and the injection port for injecting the liquid crystal material was left. The cell gap of this liquid crystal cell is equal to that of the active matrix substrate 2
A spacer having a height of 4 μm is interposed between the counter substrate 3 and the counter substrate 3 to keep the spacer constant. Also, those substrates 2, 3
At the time of bonding, the substrates 2 and 3 were aligned by aligning their end face positions, and highly accurate alignment using an alignment mark or the like was not performed.

Next, a liquid crystal material having a negative dielectric anisotropy was injected into this liquid crystal cell by a usual method to form a liquid crystal layer 4. Next, the liquid crystal injection port was sealed with an ultraviolet curable resin, and the polarizing film 5 was attached to both surfaces of the liquid crystal cell to obtain the liquid crystal display device 1 shown in FIG. The liquid crystal display device 1 may include, for example, the pixel electrode 10 and the common electrode 16
It can be driven by varying the voltage applied between and between about 1V and about 4V.

Next, in the liquid crystal display device 1 manufactured as described above, between the pixel electrode 10 and the common electrode 16 is 3.5.
It was observed with a voltage of V applied. As a result, a transmittance distribution corresponding to the shape of the pixel electrode 10 was found.

The apparent response speed of this liquid crystal display device 1 was examined. That is, a voltage of 3.5 V was applied between the pixel electrode 10 and the common electrode 16, and the response waveform, which is the change with time of the transmittance, was examined.

FIG. 8 is a graph showing a response waveform obtained by the liquid crystal display device 1 according to the embodiment of the present invention. In the figure, the horizontal axis represents the elapsed time from the start of voltage application between the electrodes 10 and 16, and the vertical axis represents the transmittance of the liquid crystal display device 1. As shown in FIG. 8, in the liquid crystal display device 1 according to this example, the time from the start of voltage application to the stabilization of the transmittance is 1
It was as short as 0 ms. That is, a very high apparent response speed could be realized.

Comparative Example FIG. 9A is a plan view schematically showing the shape of the pixel electrode 10 used in the comparative example. Further, FIG. 9B is an enlarged plan view showing a part of the pixel electrode 10 shown in FIG. 9A. In this example, the pixel electrode 1
1 by the same method as described in the above embodiment except that the plane shape shown in FIGS.
A liquid crystal display device 1 shown in was produced. This liquid crystal display device 1
The apparent response speed was examined by the same method as described in the above-mentioned examples.

FIG. 10 is a graph showing a response waveform obtained in the liquid crystal display device 1 according to the comparative example. In the figure, the horizontal axis is
The elapsed time from the start of voltage application between the electrodes 10 and 16 is shown, and the vertical axis shows the transmittance of the liquid crystal display device 1. Figure 1
As shown in 0, in the liquid crystal display device 1 according to this example, the time from the start of voltage application to the stabilization of the transmittance was 50 ms.

[0059]

As described above, in the present invention, since the pixel electrode includes the comb-shaped portion, it is not necessary to provide the counter substrate with a structure for dividing the pixel region into a plurality of domains. Therefore, in this case, high precision is not required for the alignment between the array substrate and the counter substrate. Further, in the present invention, the contour of the comb-shaped portion has a shape in which a plurality of curves and a plurality of straight lines are alternately connected, and each of these curves has any two of the above straight lines as a tangent line. Therefore, the apparent response speed can be increased.

That is, according to the present invention, even when the MVA mode is adopted, it is possible to manufacture the array substrate and the counter substrate without aligning them with high precision and to increase the apparent response speed. A liquid crystal display device is provided.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a plan view schematically showing an example of a structure that can be used in the liquid crystal display device shown in FIG.

3A to 3D are diagrams schematically showing alignment changes of liquid crystal molecules which occur when the structure shown in FIG. 2 is adopted in the liquid crystal display device shown in FIG.

FIG. 4 is a diagram showing an example of a transmittance distribution observed when the structure shown in FIG. 2 is adopted in the liquid crystal display device shown in FIG.

5 is a plan view schematically showing another example of a structure that can be used in the liquid crystal display device shown in FIG.

6 is a diagram schematically showing an alignment change of liquid crystal molecules which occurs when the structure shown in FIG. 5 is adopted in the liquid crystal display device shown in FIG.

7A is a plan view schematically showing the shape of a pixel electrode adopted in an embodiment of the present invention, and FIG. 7B is a plan view showing a part of the pixel electrode shown in FIG.

FIG. 8 is a graph showing a response waveform obtained by the liquid crystal display device according to the example of the present invention.

9A is a plan view schematically showing the shape of a pixel electrode used in a comparative example, and FIG. 9B is a plan view showing a part of the pixel electrode shown in FIG.

FIG. 10 is a graph showing a response waveform obtained by the liquid crystal display device according to the comparative example.

[Explanation of symbols]

1 ... Liquid crystal display device 2 ... Active matrix substrate 3 ... Counter substrate 4 ... Liquid crystal layer 5 ... Polarizing film 7 ... Transparent substrate 8 ... Switching element 9 ... Color filter layer 9a to 9c ... Colored layer 10 ... Pixel electrode 10a to 10d ... comb-shaped portion 10-1 ... Slit part 10-2 ... comb teeth 11 ... Alignment film 15 ... Transparent substrate 16 ... Common electrode 17 ... Alignment film 25 ... Liquid crystal molecule 31, 32 ... Arrows

Continued front page    (72) Inventor Kazuyuki Sunohara             2 shares, 1-9-1 Harara-cho, Fukaya City, Saitama Prefecture             Company Toshiba Fukaya Factory (72) Inventor Yuzo Kubu             2 shares, 1-9-1 Harara-cho, Fukaya City, Saitama Prefecture             Company Toshiba Fukaya Factory (72) Inventor Takeshi Yamaguchi             2 shares, 1-9-1 Harara-cho, Fukaya City, Saitama Prefecture             Company Toshiba Fukaya Factory (72) Inventor Kisako Ninomiya             2 shares, 1-9-1 Harara-cho, Fukaya City, Saitama Prefecture             Company Toshiba Fukaya Factory (72) Inventor Natsuko Fujiyama             2 shares, 1-9-1 Harara-cho, Fukaya City, Saitama Prefecture             Company Toshiba Fukaya Factory F-term (reference) 2H090 LA01 LA15 MA01 MA15                 2H092 GA13 GA14 HA04 JA24 NA01                       PA02

Claims (8)

[Claims] 1. An array substrate having a pixel electrode on one main surface, and a common electrode disposed on the surface of the array substrate facing the pixel electrode and facing the array substrate. A counter substrate, and a liquid crystal layer sandwiched between the array substrate and the counter substrate, the pixel electrode includes a comb-shaped portion, and the contour of the comb-shaped portion has a plurality of curved lines and a plurality of straight lines. It has a shape that is alternately connected,
Each of the plurality of curves is one of the plurality of straight lines 2
A liquid crystal display device characterized in that two are tangent lines. 2. The liquid crystal display device according to claim 1, wherein the comb-shaped portions include a plurality of comb-tooth portions that are parallel to each other and each have a tapered shape. 3. The pixel electrode includes a plurality of the comb-shaped portions, each of the comb-shaped portions includes a plurality of comb-tooth portions parallel to each other, and the longitudinal direction of the comb-tooth portions is different between the comb-shaped portions. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is provided. 4. The liquid crystal display device according to claim 1, wherein the liquid crystal layer contains a liquid crystal material having a negative dielectric anisotropy. 5. The liquid crystal display device according to claim 4, further comprising an alignment film having vertical alignment property on each of the pixel electrode and the common electrode. 6. When a voltage is applied between the pixel electrode and the common electrode, the liquid crystal layer is formed in a pixel region which is a region between the pixel electrode and the common electrode of the liquid crystal layer. The liquid crystal display device according to claim 1, wherein a plurality of domains having different tilt directions of the liquid crystal molecules included in are formed. 7. The liquid crystal display device according to claim 1, wherein the common electrode is a flat continuous film. 8. The liquid crystal display device according to claim 1, wherein the array substrate includes a color filter layer.