KR20070003499A - Fringe field switching mode liquid crystal display device - Google Patents

Abstract

An FFS(Fringe Field Switching) mode LCD is provided to improve the aperture ratio, increase the brightness, and suppress the generation of disclination, by improving the structure of a pixel electrode. A plurality of data lines(9) and a plurality of gate lines(11) cross one another to define respective unit pixels(100). A common electrode(2) is disposed within each unit pixel. A pixel electrode is disposed to form a fringe field together with the common electrode within the unit pixel. The pixel electrode is composed of plural bar-shaped portions(1) and a connection portion(3) for connecting the bar-shaped portions. Openings(5) are formed in regions adjacent to both end portions of each bar-shaped portion, which dose not cross the connection portion. The connection portion has a predetermined angle with respect to the bar-shaped portions.

Description

FFS mode liquid crystal display device

1 is a plan view showing the structure of a unit pixel in the first embodiment.

2A is an enlarged view of the region 13 of FIG. 1 when no electric field is applied.

2B is an enlarged view of region 13 of FIG. 1 when applying an electric field.

3 is a view showing the direction of the electric field in the area 19 of FIG. 2B.

4 is a plan view showing the structure of a unit pixel in the second embodiment.

FIG. 5 is a cross-sectional view taken along the line II ′ of FIG. 4.

6 is a plan view showing the structure of a unit pixel in the third embodiment.

FIG. 7A is a diagram for describing a structural feature of the unit pixel of FIG. 6.

FIG. 7B is a diagram for describing a structural feature of the unit pixel of FIG. 6.

8 is a plan view illustrating a structure of unit pixels in a liquid crystal panel of a conventional liquid crystal display device.

9A is an enlarged view of region 87 of FIG. 8 when no electric field is applied.

9B is an enlarged view of the region 87 of FIG. 8 when an electric field is applied.

FIG. 10 is a view showing the direction of an electric field in the region 86 of FIG. 9N.

* Description of the symbols for the main parts of the drawings *

100, 200, 300: unit pixels 1, 3, 25, 31: pixel electrode

2 common electrode 5 opening

7: TFT 9: data line

11: gate line 12: common line

15: liquid crystal molecules

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a structure of a FFS (Fringe Field Switching) mode liquid crystal display device.

Recently, in the field of flat panel display (FPD), liquid crystal display (LCD), plasma display (PDP), field emission display (FED) and vacuum fluorescent display (VFD) have been actively studied.

Background Art Liquid crystal display devices (hereinafter referred to as LCDs) are currently in the spotlight for reasons of mass production, ease of driving means, and high image quality. LCD is a device for displaying information on the screen using the refractive anisotropy of the liquid crystal.

The LCD has been developed to operate in various modes such as TN (Twist Magnetic) Mode, Super Twist Magnetic (STN) Mode, and In Plane Switching (IPS) Mode.

Among these, the IPS mode is a mode in which the liquid crystal molecules are always horizontal with respect to the substrate of the liquid crystal panel, and the switching is performed with the horizontal electric field in the horizontal direction with respect to the substrate.

Therefore, it is known that the liquid crystal molecules are not tilted so that the change in optical characteristics due to the viewing angle is small, thereby obtaining a wider viewing angle than the TN mode or the STN mode.

In recent years, similarly to the IPS mode, the FFS mode, which is a mode for switching a substrate using a horizontal electric field in the horizontal direction, has been developed.

The FFS mode LCD includes a pixel electrode and a common electrode made of a transparent electrode, and forms a fringe field by making the gap between the pixel electrode and the common electrode smaller than the cell gap between the upper and lower substrates of the liquid crystal panel.

Since the liquid crystal molecules of the liquid crystal layer are operated by the electric field generated in the fringe field, it is known that the opening ratio and the high transmittance are higher than those of the IPS mode LCD (see Patent Document 1, for example).

In addition, in order to achieve a wider viewing angle, a dual domain mode has been developed. The dual domain mode is a method of dividing an orientation direction of liquid crystal molecules of a liquid crystal layer in two directions in one unit pixel in a liquid crystal panel to widen a viewing angle.

The application of this dual domain mode to an LCD driving in FFS mode has also been developed (see Patent Document 2, for example).

In addition, the method in which the orientation direction of liquid crystal molecules applied to a conventional general LCD is in one direction is called a mono domain mode.

Patent Document 1 Japanese Laid-Open Patent Publication 2005-107535

Patent Document 2: Japanese Patent Application Laid-Open No. 2002-182230

Referring to Fig. 8, a conventional FFS mode LCD will be described below.

8 is a front view illustrating the structure of unit pixels in a liquid crystal panel of a mono domain mode LCD driving in FFS mode.

The unit pixel 80 is a data line 81, a gate line 82, a thin film transistor (hereinafter referred to as TFT) 83 formed at an intersection of the data line 81 and the gate line 82, and common. And a common line 92 for supplying a voltage to the electrode 84, the pixel electrode 85, and the common electrode 84.

The source electrode of the TFT 83 is connected to the data line 81 and the drain electrode is connected to the pixel electrode 85.

In addition, the gate electrode of the TFT 83 is connected to the gate line 82.

Next, the operation of liquid crystal molecules when an electric field is applied to the unit pixel 80 will be described with reference to FIGS. 9A and 9B.

9A and 9B are enlarged views of a partial region 87 of the unit pixel 80 of FIG. 8, and FIG. 9A shows the alignment state of the liquid crystal molecules 88 when no electric field is applied, and FIG. 9B is The orientation state of the liquid crystal molecules 88 when a voltage is applied is shown.

As shown in FIG. 9A, when no electric field is applied, all liquid crystal molecules 88 are aligned with the rubbing direction 89.

At this time, the liquid crystal molecules 88 have a rubbing angle of an angle θ ₉ (for example, 15 degrees) with respect to the X direction.

When an electric field is applied in this state, the liquid crystal molecules 88 are rotated counterclockwise so that the major axes are parallel to the Y direction.

This is because an electric field in the Y direction occurs when an electric field is applied.

By the way, as shown in FIG. 9B, the liquid crystal molecule 88 located in the area | region 86 shown to FIG. 8 and FIG. 9B rotates in a different direction from the liquid crystal molecule 88 located in the area | region other than the area | region 86. FIG. It works.

This is because the pixel electrode 85 is made parallel to the Y direction in the region 86, an electric field in the X direction is generated as shown in FIG. 10, and the liquid crystal molecules 88 located in the region 86 have the long axis direction. This is because it rotates to be parallel to the electric field direction of ie, to be parallel to the X direction.

In this way, when a part of the liquid crystal molecules 88 performs different operations, generation of the foreground is caused. The generation of the foreground causes a problem on the display such as spots or floating on the display screen.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an LCD having a high opening ratio and high brightness while preventing the occurrence of foreground and / or preventing the display screen from being lifted.

In order to solve the above problems, the present invention provides a pair of transparent insulating substrates disposed to face each other at a predetermined interval through a liquid crystal layer composed of a plurality of liquid crystal molecules, and inside each of the pair of transparent insulating substrates. An alignment layer formed, a plurality of gate lines and data lines formed on one side of the pair of transparent insulating substrates and arranged in a matrix so as to define each unit pixel, and a transparent conductor disposed on each unit pixel. A pixel electrode comprising a common electrode and a transparent conductor disposed on each unit pixel to form a fringe field together with the common electrode, wherein the pixel electrode includes a plurality of rod-shaped portions disposed at predetermined intervals. And connecting portions arranged to intersect the rod-shaped portions and intersect with the rod-shaped portions. Minutes, both ends of the rod-like portion that does not intersect the portion has an opening, wherein the connection part is characterized in that connection has a predetermined angle with respect to the rod-shaped part.

In addition, the present invention is a pair of transparent insulating substrates disposed to face each other at a predetermined interval through a liquid crystal layer made of a plurality of liquid crystal molecules, an alignment film formed inside each of the pair of transparent insulating substrates, A plurality of gate lines and data lines formed on one side of the pair of transparent insulating substrates and arranged in a matrix so as to define each unit pixel, a common electrode disposed on each unit pixel and made of a transparent conductor; And a pixel electrode made of a transparent conductor disposed in each unit pixel so as to form a fringe field together with the common electrode, wherein the pixel electrode includes a plurality of V-shaped portions disposed at predetermined intervals and each V-shaped portion. A connecting portion disposed on a center line connecting the V-shaped portions between the shape portions at the center thereof, Forms part of the central line with the predetermined angle to the forming the center line and the V-shaped portion and the acute angle (銳角) direction in the same direction, characterized in that the line-symmetrical shape with respect to the center line.

EMBODIMENT OF THE INVENTION Hereinafter, the 1st-3rd Example which applied this invention is described, referring drawings.

1 to 3 correspond to the description of the first embodiment, FIGS. 4 to 5 describe the second embodiment, and FIGS. 6 to 7B correspond to the description of the third embodiment.

<First Embodiment>

1 is a plan view showing the structure of a unit pixel in the first embodiment.

As shown in Fig. 1, in the FFS mode LCD according to the present invention, the unit pixel 100 is the same as the conventional unit pixel 80 shown in Fig. 8, such as the data line 9, the gate line 11, and the TFT. (7), the common electrode 2, the pixel electrodes 1 and 3, and the common line 12.

The difference between the unit pixel 100 of the present embodiment and the conventional unit pixel 80 lies in the shape of the pixel electrodes 1 and 3.

In addition, although the TFT 7 shown in FIG. 1 is arrange | positioned above the unit pixel 100, in this invention, it is also possible to arrange | position below.

In the shape of the pixel electrodes 1 and 3 which are different from the conventional unit pixel 80, a plurality of pixel electrodes 1 parallel to the X direction are formed, but parallel to the Y direction to form the region 86 of FIG. 8. There is no one pixel electrode, and the pixel electrode 3 is made between the pixel electrodes 1 in order to connect the some pixel electrode 1 instead.

However, the widths of all the Y-directions of each pixel electrode 1 are set to substantially the same size as 4 μm, which is the width of a conventional general pixel electrode, and the width of the pixel electrode 3 is selectively set according to the use or purpose. do.

For example, in order to realize the improvement of the aperture ratio, the width of the pixel electrode 3 is set to a width narrower than that of a conventional general pixel electrode.

Thus, since there is no pixel electrode parallel to the Y direction which forms the area | region 86 of FIG. 8, the opening part 5 is provided in the both end area | regions between each pixel electrode 1. As shown in FIG. By having the openings 5 in the both end regions between the pixel electrodes 1, the aperture ratio and the luminance can be improved as compared with the LCD employing the structure of the conventional unit pixel 80.

Moreover, the shape characteristic of the pixel electrode 3 is demonstrated below with reference to FIG. 2A, FIG. 2B, and FIG. 3 which is the figure which expanded the area | region 13 of FIG.

2A is an enlarged view of the area 13 of FIG. 1 when no electric field is applied.

As shown in Fig. 2A, when no electric field is applied, the liquid crystal molecules 15 constituting the liquid crystal layer sandwiched between the upper and lower substrates of the liquid crystal panel of the LCD are aligned in the rubbing direction 17 by the alignment film. By this rubbing, each rubbing angle of the liquid crystal molecules 15 is θ ₁ is the (e.g., 15 degrees).

The shape of the pixel electrode (3) is that the rubbing direction (17) with respect to θ ₁ rotating in one direction in the same direction with respect to the X direction in the Y direction, performing θ _2. However, θ ₂ is an angle satisfying the condition of θ ₂ > θ ₁ . The reason for whether this condition needs to be satisfied is mentioned later.

2B is an enlarged view of the area 13 of FIG. 1 when an electric field is applied.

As shown in FIG. 2B, each of the liquid crystal molecules 15 oriented in the rubbing direction 17 in FIG. 2A is aligned in a direction parallel to the Y direction, which is the direction of the applied electric field.

However, the liquid crystal molecules 15 positioned in the peripheral region 19 of the pixel electrode 3 are oriented in a direction different from that of the liquid crystal molecules 15 positioned in the regions other than the region 19.

This is because the direction of the electric field in the region 19 is different from the direction of the electric field in regions other than the region 19 and is not in a direction parallel to the Y direction.

3 is a diagram for describing the direction of the electric field in the region 19.

As shown in FIG. 3, the direction 21 of the electric field around the pixel electrode 3 becomes a direction perpendicular to the pixel electrode 3.

In other words, the angle at which the direction 21 of the electric field is inclined with respect to the X direction is the same as the angle θ ₂ at which the pixel electrode 3 is inclined with respect to the Y direction. At this time, the liquid crystal molecules 15 located in the region 19 are operated to rotate in the direction in which the major axis thereof is parallel to the direction 21 of the electric field (the direction indicated by the arrow 23 in the drawing).

By the way, the foreground is a phenomenon in which after the application of the electric field, the orientation of the liquid crystal molecules does not return to the state before the application of the electric field, the rubbing traces become the foreground line, and noise appears on the display screen. For this reason, in order to prevent the foreground, when the electric field is applied, the operation directions of the liquid crystal molecules are made to coincide with each other, so as not to cause a deviation (fluctuation) in the operation of each liquid crystal molecule.

In order to prevent variation in the operation of the liquid crystal molecules 15, the liquid crystal molecules 15 positioned in regions other than the region 19 are rotated in a direction in which the liquid crystal molecules 15 positioned in the region 19 rotate. What is necessary is just to make it the same direction as a rotating direction.

For example, when the angle θ ₂ of the direction 21 of the electric field is inclined with respect to the X direction, the region 19 is smaller than the angle θ _{1 of the} rubbing direction 17 with respect to the X direction. The liquid crystal molecules 15 positioned at are operated in the direction of clockwise rotation.

This is because the liquid crystal molecules 15 located in regions other than the region 19 are in the opposite direction to the direction in which the liquid crystal molecules rotate. On the contrary, when θ ₂ is larger than θ ₁ , the liquid crystal molecules 15 located in the region 19 also operate in the direction of counterclockwise rotation, so that there is no variation in the operation of each liquid crystal molecule 15.

Therefore, in order to generate the foreground, it is necessary to satisfy the condition of θ ₂ > θ ₁ .

As described above, in the present embodiment, by forming the unit pixels 100 having the structures of the pixel electrodes 1 and 3 described above, an LCD which improves the aperture ratio and the luminance and can prevent the occurrence of the foreground is provided. Can be configured.

Second Embodiment

In this embodiment, the display screen is lifted while utilizing the openings at both ends of the pixel electrode 1 parallel to the X direction, which is one of the shape features of the pixel electrodes 1 and 3 in the first embodiment. A unit pixel having a structure effective for preventing the problem will be described.

In addition, about the part which is common in the said 1st Example, the same code | symbol is attached | subjected in drawing, and description is abbreviate | omitted.

4 is a plan view showing the structure of a unit pixel in the present embodiment.

As shown in FIG. 4, the part where the unit pixel 200 differs from the unit pixel 100 of FIG. 1 is the pixel electrode 25 formed to connect the pixel electrodes 1.

The angle θ ₃ at which the pixel electrode 25 is inclined with respect to the Y direction needs to satisfy the condition θ ₃ > θ _{1 for} the same reason as θ ₂ in the first embodiment.

In addition, the characteristic of the pixel electrode 25 is that the pixel electrode 3 of the first embodiment serves as two electrodes. However, the electrode width of the pixel electrode 25 is the same as the conventional general electrode width of 4 mu m. As a result, the area of the pixel electrode 25 can be made slightly wider without affecting the aperture ratio.

5 is a cross-sectional view of the unit pixel 200 taken along the line II ′ of FIG. 4.

As shown in FIG. 5, the unit pixel 200 is formed by stacking an insulating film 29 on the common electrode 27 and forming pixel electrodes 1 and 25 on the insulating film 29.

Here, the film thickness d of the pixel electrodes 1 and 25 is about 0.04 mu m. This is a structure in which the film thickness of the pixel electrode of the unit pixel in the conventional LCD has one-half thickness compared with 0.08 mu m.

By thinning the film thicknesses of the pixel electrodes 1 and 25 in this manner, an alignment film made of polyimide (PI) or the like applied thereon can be applied horizontally without irregularities.

Therefore, the effect of preventing the floating of the display screen resulting from the orientation defect by the unevenness | corrugation of an oriented film is acquired.

However, when the pixel thickness of the pixel electrode is made thin, there is a problem that voltage distribution and disconnection tend to occur because the resistance in the unit pixel becomes high.

Therefore, in the present embodiment, the unit pixel 200 has the same structure as the pixel electrode 25 in which the number of electrodes is increased as described above. In this way, if the number of pixel electrodes is increased, the resistance can be suppressed to be low. Therefore, even when the film thickness is thinned, the resistance is not higher than usual.

In the case of the fringe field, since the common electrode 2 and the pixel electrode 25 transmit light through a transparent electrode made of ITO (Indium-Tin oxide) or the like, the pixel electrode having an increased number of electrodes compared to the normal ( Even if the structure is the same as 25), the case where the luminance is lowered is small.

In addition, in this embodiment, the pixel electrode 25 can be configured to increase to three parts of a conventional general pixel electrode.

In this case, even if the film thickness of the electrode used at this time is made thin at about 0.026 micrometer which is one third of the film thickness of the conventional general pixel electrode, resistance can be prevented from becoming high.

As described above, in the present embodiment, by forming the unit pixels 200 having the structures of the pixel electrodes 1 and 25 described above, the generation of the foreground can be prevented and the LCD which is unlikely to be lifted can be formed. Can be.

Third Embodiment

In the present embodiment, the unit in the dual domain mode LCD utilizing the openings at both ends of the pixel electrode 1 parallel to the X direction, which is one of the shape features of the pixel electrodes 1 and 3 in the first embodiment. The pixel will be described.

In addition, about the part which is common in the said 1st Example, the same code | symbol is attached | subjected in drawing and description is abbreviate | omitted.

6 is a plan view showing the structure of a unit pixel in the present embodiment.

As shown in Fig. 6, the shape of the pixel electrode 31 is significantly different from the shape of the pixel electrodes 1 and 3 (see Fig. 1) in the first embodiment.

Since the LCD is in the dual domain mode in the present embodiment, the shape characteristic first of the pixel electrode 31 is linearly symmetric with respect to the center line L parallel to the Y direction for dividing the unit pixels 300 uniformly. will be.

By the shape having this characteristic, the liquid crystal molecules are equally divided into two units in the unit pixels, and are aligned so that the directions of 180 degrees are different. By the orientation of this characteristic liquid crystal, wide viewing angle is possible.

The pixel electrode 31 has openings 33 at both ends in the X direction in the same manner as the pixel electrodes 1 and 3 in the unit pixel 100 of the first embodiment. The structure having the openings 33 enables the realization of a high domain ratio and high brightness dual domain mode LCD.

In addition, the pixel electrode 31 has another characteristic shape 35.

This characteristic shape 35 means the shape which has predetermined inclination with respect to the center line L. FIG.

This characteristic shape 35 is demonstrated with reference to FIG. 7A and 7B.

FIG. 7A is a diagram for explaining the operation of liquid crystal molecules when an electric field is applied when the characteristic shape 35 is a shape parallel to the Y direction without a predetermined slope.

As shown in FIG. 7A, in the region 37 corresponding to the characteristic shape 35 of the present embodiment, the liquid crystal molecules 15 located in the region 37 are located in regions other than the region 37. Rotation in a direction different from that of the molecules 15 causes deviation (fluidity) in the operation of each of the liquid crystal molecules 15 to cause the generation of the foreground.

In this case, rubbing is performed in a direction parallel to the X direction. In the conventional general rubbing process, the variation in the rubbing angle occurs in a range of ± 1 degree.

At this time, since the direction of the electric field in the area 37 is parallel to the X direction, the influence of the variation of the rubbing angle is directly reflected.

FIG. 7B is a diagram for explaining the operation of liquid crystal molecules when an electric field is applied when the characteristic shape 35 is a shape having a predetermined inclination with respect to the center line L. FIG.

As shown in FIG. 7B, the characteristic shape 35 has an inclination of the angle θ ₄ with respect to the center line L, and at this time, the liquid crystal molecules 15 located in the region 37 have a region. It rotates in the same direction as liquid crystal molecules 15 located in regions other than (37).

Since the influence of the deviation of the rubbing angle of ± 1 degree is not directly reflected, the inclination angle θ ₄ of the characteristic shape 35 is set to ± 1 degree or more.

Thereby, the direction of an electric field in the area | region 37 becomes a direction which rotated the rubbing direction in the direction which the liquid crystal molecule 15 located in areas other than the area | region 37 rotates.

Therefore, since all liquid crystal molecules 15 rotate in the same direction in the unit pixel 300, there is no variation in the operation of each liquid crystal molecule 15.

In addition, the pixel electrode 31 shown in FIG. 6 may be a shape which rotated the shape 180 degrees.

As described above, in the present embodiment, the unit pixel 300 is formed in the structure in which the pixel electrode 31 has the opening 33 and the characteristic shape 35 as described above. It is possible to configure a dual domain mode LCD with suppressed occurrence.

According to the present invention, by forming a unit pixel having a pixel electrode having a characteristic structure as described above, it is possible to prevent occurrence of foreground and / or lifting of a display screen with high opening ratio and high brightness with respect to a conventional LCD. LCD can be realized.

Claims (6)

A pair of transparent insulating substrates disposed to face each other at a predetermined interval through a liquid crystal layer composed of a plurality of liquid crystal molecules; An alignment film formed inside each of the pair of transparent insulating substrates, A plurality of gate lines and data lines formed on one side of the pair of transparent insulating substrates and arranged in a matrix to define each unit pixel; A common electrode disposed on each unit pixel and made of a transparent conductor; And a pixel electrode made of a transparent conductor disposed in each unit pixel so as to form a fringe field together with the common electrode. The pixel electrode is composed of a plurality of rod-shaped portions arranged at predetermined intervals, and a connecting portion arranged to connect between the rod-shaped portions and intersect the rod-shaped portions, wherein the connecting portion is the rod-shaped portion. And both ends of the portion not intersecting with each other are opening portions, and the connection portion is connected at a predetermined angle with respect to the rod-shaped portion. The method of claim 1, And the predetermined angle is equal to or greater than 90 degrees of the rubbing angle of the liquid crystal molecules oriented by the alignment layer of the substrate. The method according to claim 1 or 2, A thin film thickness of the pixel electrode is formed to be thin in a predetermined thickness, and a plurality of the connecting portions are arranged between the rod-shaped portions. The method of claim 3, wherein And the film thickness is 0.04 mu m or less. A pair of transparent insulating substrates disposed to face each other at a predetermined interval through a liquid crystal layer composed of a plurality of liquid crystal molecules; An alignment film formed inside each of the pair of transparent insulating substrates, A plurality of gate lines and data lines formed on one side of the pair of transparent insulating substrates and arranged in a matrix to define each unit pixel; A common electrode disposed in each of the unit pixels and made of a transparent conductor; And a pixel electrode made of a transparent conductor disposed in each unit pixel so as to form a fringe field together with the common electrode. The pixel electrode is composed of a plurality of V-shaped portions arranged at predetermined intervals and a connection portion disposed on a center line connecting the V-shaped portions at the center by connecting the respective V-shaped portions at the center. And the connecting portion has a predetermined angle with the center line in the same direction as the direction forming an acute angle with the center line and the V-shaped portion, and has a line symmetry with respect to the center line. Mode liquid crystal display device. The FFS mode liquid crystal display device according to claim 5, wherein the predetermined angle is approximately equal to an absolute value of an error range of the rubbing angle of the alignment film of the substrate.

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