KR20070121629A - Liquid crystal display - Google Patents

Abstract

An LCD(Liquid Crystal Display) is provided to maintain an electric field in a domain in a horizontal direction weaker than an electric field in a domain in a horizontal direction all the time to improve lateral visibility. An LCD includes a plurality of pixels(90). Each of the pixels is split into a plurality of domains(91,92,93), and each of the plurality of domains is divided into a first-direction domain and a second-direction domain according to an average direction in which liquid crystal molecules included in the domain are tilted when a driving electric field is applied to the liquid crystal molecules. The driving electric field in the first-direction domain is weaker than the driving electric field of the second-direction domain. The first direction corresponds to a horizontal direction and the second direction corresponds to a vertical direction.

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY}

The present invention relates to a liquid crystal display device.

In general, a liquid crystal display device injects a liquid crystal material between an upper substrate on which a common electrode, a color filter, and the like are formed, and a lower substrate on which a thin film transistor and a pixel electrode are formed. By applying a different potential to form an electric field to change the arrangement of the liquid crystal molecules, and through this to control the light transmittance is a device that represents the image.

However, it is an important disadvantage that the liquid crystal display device has a narrow viewing angle. In order to overcome these disadvantages, various methods for widening the viewing angle have been developed. Among them, liquid crystal molecules are oriented vertically with respect to the upper and lower substrates, and a method of forming a constant opening pattern or forming protrusions on the pixel electrode and the common electrode opposite thereto is performed. This is becoming potent.

As a method of forming the opening pattern, an opening pattern is formed in each of the pixel electrode and the common electrode, and the viewing angle is widened by adjusting the direction in which the liquid crystal molecules lie down using a fringe field formed by the opening patterns. .

The method of forming the protrusions is a method of controlling the lying direction of the liquid crystal molecules by using the electric field distorted by the protrusions by forming protrusions on the pixel electrode and the common electrode formed on the upper and lower substrates, respectively.

In another method, an opening pattern is formed on the pixel electrode formed on the lower substrate, and a protrusion is formed on the common electrode formed on the upper substrate, so that the liquid crystal lies down using the fringe field formed by the opening pattern and the protrusion. There is a way to form a domain by controlling.

In such a multi-domain liquid crystal display, the gray scale inversion reference viewing angle defined as a contrast ratio reference viewing angle based on a contrast ratio of 1:10 or a limit angle of luminance inversion between gray scales is excellent, more than 80 ° in all directions. However, the gamma curve of the front side and the gamma curve of the side do not coincide with each other, resulting in inferior visibility in the left and right sides compared to the TN (twisted nematic) mode liquid crystal display. For example, in the patterned vertically aligned (PVA) mode in which openings are formed by domain dividing means, the screen looks brighter toward the side and the color tends to shift toward white. Occasionally, the picture appears clumped and disappears. However, visibility is becoming more and more important as monitors are being used for multimedia in recent years.

The technical problem to be achieved by the present invention is to implement a multi-domain liquid crystal display device having excellent side visibility.

In order to solve this problem, the present invention maintains the electric field in the left and right domains weaker than the electric field in the upper and lower domains.

Specifically, one pixel region is divided into a plurality of small domains, and each of the small domains has a first direction domain and a second direction domain according to an average direction in which the liquid crystal molecules contained therein are inclined when a driving electric field is applied. In the liquid crystal display classified into, the driving electric field inside the first directional domain is provided with a liquid crystal display weaker by a predetermined value than the driving electric field inside the second directional domain.

In this case, the first direction is a left-right direction when the liquid crystal display is viewed from the front, the second direction is an up-down direction, and the driving electric field inside the first direction domain is applied to the driving electric field inside the second direction domain. In comparison, a weak predetermined value is preferably 0.02 / d (V / um) to 0.5 / d (V / um) when the cell gap of the liquid crystal display device is d.

More specifically, the first insulating substrate, the first signal line formed in the first direction on the first insulating substrate, the second signal formed in the second direction on the first insulating substrate and insulated from and intersecting the first signal line. A first thin film transistor connected to a second signal line, the first signal line and the second signal line, a second thin film transistor connected to the first signal line and the second signal line connected to the first thin film transistor, and A first pixel electrode connected to a first thin film transistor, a second pixel electrode connected to the second thin film transistor, a second insulating substrate facing the first insulating substrate, and a common layer formed on the second insulating substrate At least one of an electrode, a liquid crystal material layer injected between the first substrate and the second substrate, the first insulating substrate and the second insulating substrate Domain dividing means formed on the plate and dividing the first pixel electrode and the second pixel electrode into a plurality of small domains, wherein the domain dividing means respectively divides the first pixel electrode and the second pixel electrode; A liquid crystal display device may be divided into a first direction domain and a second direction domain, and the first pixel electrode and the second pixel electrode form a capacitive coupling with each other.

In this case, when n and m are integers, the first and second thin film transistors of the n-row pixels in the m columns are connected to the m-th data line, and the first and second thin film transistors of the n + 1 row pixels in the m columns are It may be connected to the m + 1 th data line. In addition, the second pixel electrode occupies 30% to 70% of the entire pixel area. The liquid crystal molecules included in the liquid crystal material layer are vertically aligned with respect to the first and second insulating substrates without a driving electric field applied thereto.

The semiconductor device may further include a storage capacitor line formed on the thin film transistor substrate and forming a storage capacitor between the first pixel electrode and the second pixel electrode, respectively, between the second pixel electrode and the common electrode. When the liquid crystal capacitance formed is Clcb, the storage capacitance formed between the second pixel electrode and the storage capacitor line is Cstb, and the coupling capacitance formed between the first pixel electrode and the second pixel electrode is Cpp,

T is defined as having a value between 0.65 and 0.95.

In another configuration, a first insulating substrate, a first signal line formed in a first direction on the first insulating substrate, and a second signal formed in a second direction on the first insulating substrate and insulated from and intersecting the first signal line. A thin film transistor connected to a second signal line, the first signal line and the second signal line, a pixel electrode connected to the thin film transistor and having a plurality of slits, a second insulating substrate facing the first insulating substrate, and the second A common electrode formed on an insulating substrate, a liquid crystal material layer injected between the first substrate and the second substrate, and formed on at least one of the first insulating substrate and the second insulating substrate, and the pixel electrode Domain dividing means for dividing a into a plurality of small domains, wherein the domain dividing means divides the pixel electrode in a first direction, respectively. And it is divided in the main direction and the second domain, the first domain is the direction that the liquid crystal display device that is disposed in the portion where the slit position.

In this case, it is preferable that the width of the slit of the pixel electrode is between 2 and 5 μm, and the distance between two adjacent slits is between 2 and 10 μm.

In another configuration, the first insulating substrate, the first signal line formed in the first direction on the first insulating substrate, the first signal line formed in the second direction, and insulated from and cross the first signal line, A second signal line, a thin film transistor connected to the first signal line and the second signal line, a pixel electrode connected to the thin film transistor, a second insulating substrate facing the first insulating substrate, and on the second insulating substrate. A common electrode formed thereon, a dielectric layer formed on at least one of the pixel electrode and the common electrode, a liquid crystal material layer injected between the first substrate and the second substrate, the first insulating substrate and the first 2 domain dividing means formed on at least one of the two insulating substrates and dividing the pixel electrode into a plurality of small domains; And also the domain partition means is to divide the pixel electrodes each in a first direction and a second domain, the domain direction, the dielectric layer is a liquid crystal display device that is formed in a portion in which the first direction, a domain location.

In this case, the thickness of the dielectric layer is preferably between 500 μm and 1.5 μm, and the domain division means may be openings of the pixel electrode and the common electrode, respectively.

In the present invention, the visibility in the left and right sides can be improved by keeping the electric field in the left and right domains weaker than the upper and lower domains at all times.

Next, a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to the drawings.

1 is a layout view of a liquid crystal display according to a first exemplary embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line II-II 'of FIG. 1.

A gate line 20 extending in the horizontal direction is formed on a transparent insulating substrate 10 such as glass, and a storage capacitor line 30 is formed in parallel with the gate line. The gate electrode 20 is formed in the form of a protrusion 21 of the gate electrode, and the first to fourth storage electrodes 31, 32, 33, and 34 and the storage electrode connection part 35 are formed on the storage capacitor line 30. 36 are connected in the form of branches. The first storage electrode 31 is directly connected to the storage capacitor line 30 and is formed in the vertical direction, and the second storage electrode 32 and the third storage electrode 33 are respectively connected to the first storage electrode 31. Connected and stretched in the horizontal direction. The fourth storage electrode 34 is connected to the second and third storage electrodes 32 and 33 and extends in the vertical direction. The storage electrode connectors 35 and 36 connect the fourth storage electrode 34 to the first storage electrode 31 of the neighboring pixel. A gate insulating film 40 is formed on the gate wirings 20 and 21 and the storage capacitor wirings 30, 31, 32, 33, 34, 35, and 36, and on the gate insulating film 40 above the gate electrode 21. A semiconductor layer 50 made of amorphous silicon is formed. On the semiconductor layer 50, contact layers 61 and 62 made of amorphous silicon doped with N-type impurities such as phosphorus (P) at a high concentration are formed. A source electrode 71 and a drain electrode 72 are formed on both contact layers 61 and 62, respectively, and the source electrode 71 is formed on the data line 70 extending in the vertical direction on the gate insulating film 40. It is connected. A passivation film 80 having a contact hole 81 exposing the drain electrode 72 is formed on the data wires 70, 71, and 72. The passivation film 80 is formed on the passivation film 80 through the contact hole 81. The pixel electrode 90 connected to the pole 72 is formed. The pixel electrode 90 is made of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO).

In this case, the pixel electrodes 90 are separated into first to third small portions 91, 92, and 93, and the small portions are connected to each other through the connection portions 94, 95, and 96. The first small portion 91 has a rectangular shape in which four corners are cut out (hereinafter referred to as "chamfering") at the lower half of the pixel area defined by the intersection of the two gate lines 20 and the two data lines 70. It is formed and is directly connected to the drain electrode 72 through the contact hole 81. The second and third small portions 92 and 93 are formed in a rectangular shape with four corners cut out on the upper half of the pixel region. The second small portion 92 is connected via the first small portion 91 and the first and second connecting portions 94 and 96, and the third small portion 93 is connected to the second small portion 92 and the second small portion 92. 3 is connected via a connecting portion (95).

At this time, a plurality of slits 99 are formed in the first small portion 91. Due to these slits 99, an electric field formed between the first small portion 91 and the common electrode 400 is between the second small portion 92 or the third small portion 93 and the common electrode 400. It is weak compared to the electric field formed in.

On the other hand, the second storage electrode 32 is positioned between the first small portion 91 and the second small portion 92, and the third holding portion 32 is positioned between the second small portion 92 and the third small portion 93. The electrode 33 is positioned, and the first storage electrode 31 and the fourth storage electrode 34 are positioned between the pixel electrode 90 and the data line 70. The first small portion 91 is longer than the side parallel to the data line and the side parallel to the gate line, and the second small portion and the third small portion is shorter than the side parallel to the data line and the side parallel to the gate line. In this case, the second and third small portions 92 and 93 overlap the first and fourth storage electrodes 31 and 34, but the first small portion 91 is the first and fourth storage electrodes 31 and 34. Do not overlap with). The storage capacitor line 30 is positioned between the gate line 20 and the third small portion 93. At this time, a potential applied to the common electrode of the color filter substrate, which will be described later, is usually applied to the storage capacitor line 30, the storage electrodes 31, 32, 33, 34, and the storage electrode connection portions 35 and 36.

As described above, when the storage capacitor line or the storage electrode to which the common potential is applied between the data line and the pixel electrode and between the gate line and the pixel electrode is disposed, the influence of the data line potential and the gate line potential on the electric field of the pixel region is maintained. The electrodes may be blocked to form stable domains.

Next, a color filter substrate of the liquid crystal display according to the first embodiment of the present invention will be described.

A black matrix 200 formed of a chromium / chromium oxide bilayer is formed on a transparent substrate 100 made of glass or the like to define a pixel region. A color filter 300 is formed in each pixel area, and a common electrode 400 made of a transparent conductor is formed on the entire surface of the substrate 100 on the color filter 300. Opening patterns 510, 520, and 530 are formed in the common electrode 400. In this case, the opening patterns 510, 520, and 530 may include first to third openings 510, 520, and 530. The first opening portion 510 divides the lower half of the pixel region from side to side, and the second opening portion 520 and the third opening portion 530 divide the upper half portion of the pixel region up and down. Both ends of each of the openings 510, 520, 530 are gradually expanded to form an isosceles triangle, and the openings 510, 520, 530 are separated from each other.

The black matrix may be formed of an organic material, and the color filter may be formed of a thin film transistor substrate.

Next, the liquid crystal display according to the first embodiment of the present invention will be described.

Aligning and combining the thin film transistor substrate and the color filter substrate, injecting the liquid crystal material 900 between the two substrates to align the directors of the liquid crystal molecules included therein, and vertically align the two polarizing plates 11 and 101 to the two substrates. If the polarization axes are arranged to be perpendicular to each other outside the (10, 100), the liquid crystal display device according to the first embodiment is provided.

In the state in which the two substrates 10 and 100 are aligned, the first through the second portions 91, 92 and 93 of the pixel electrode 90 of the thin film transistor substrate and the common electrode 400 of the color filter substrate are formed. The three openings 510, 520, and 530 overlap to divide the pixel region into a plurality of small domains. Here, the small domain divided by the first small portion 91 and the first opening portion 510 is formed in the upper and lower domains (which are formed long in the horizontal direction), and the second and third small portions 92 and 93 and the second and third portions. The small domain divided by the three openings 520 and 530 is divided into left and right domains (longer in the vertical direction). This is classified according to the direction in which the liquid crystal is tilted when an electric field is applied. In this case, each of the small portions 91, 92, and 93 of the pixel electrode 90 has two long sides and two cross sections, and the long sides of each of the small portions are parallel to the data line 70 or the gate line 20. And it forms 45 degrees with the polarization axis of a polarizing plate (refer FIG. 3). Here, when the long side of each of the small portions 91, 92, 93 of the pixel electrode 90 is located adjacent to the data line 70 or the gate line 20, between the data line 70 and the long side and the gate thereof. The storage capacitor line 30 and the storage electrodes 31, 32, 33, and 34 are disposed between the line 20 and the long side. On the other hand, the storage capacitor wirings 30, 31, 32, 33, and 34 are not arranged around the short sides of the small portions 91, 92, and 93 of the pixel electrode, or the pixel electrodes 90 are disposed when the storage capacitor wirings 30, 31, 32, 33, 34 are arranged. It is preferably completely covered or at least 3 μm away from the pixel electrode 90. The reason for arranging the storage capacitor wirings 30, 31, 32, 33, and 34 in this manner is that the data line 70 or the gate line 20 is a portion adjacent to the long side of the pixel electrode small portions 91, 92, and 93. In this case, the potential of the data line 70 or the gate line 20 acts in a direction that prevents the formation of the domain. In contrast, the potential of the data line 70 or the gate line 20 assists the domain formation in the portion adjacent to the short side. Because it acts in the direction.

On the other hand, the electric field formed in the left and right domains due to the slit 99 formed in the first small portion 91 of the pixel electrode is weaker to a certain extent than the electric field formed in the upper and lower domains. This improves the left and right side visibility of the liquid crystal display. In this case, when the cell gap of the liquid crystal display device is d (m), a predetermined degree in which an electric field formed in the left and right domains is weak compared to an electric field formed in the upper and lower domains is 0.5 to 0.02 / d (V / um). It is appropriate to be a value between / d (V / um). That is, the voltage difference between the common electrode and the pixel electrode is preferably about 0.1V to 1V weaker than that of the upper and lower domains. For this purpose, the width of the slit 99 is preferably between 2 ~ 5㎛, the distance between two adjacent slits 99 is preferably between 2 ~ 10㎛.

Then, the reason why the viewing angle is improved when the electric field formed in the left and right domains is weaker by a predetermined value than the electric field formed in the upper and lower domains will be described.

3 is a graph showing a gamma curve at 60 ° of the front and side surfaces of the test cell.

Referring to FIG. 3, it can be seen that the gamma curve when viewed from the side (60 °) is higher than the gamma curve when viewing the liquid crystal display from the front. In particular, at low gray scales, the width between the front gamma curve and the side gamma curve is very large, so that a luminance difference of 2 to 10 times or more occurs depending on whether the same gray scale is viewed from the front or the side. However, since the gray levels of the red, green, and blue pixels are changed independently of each other, the degree of distortion of the gamma curve on the side is also different from the red, green, and blue pixels. Therefore, when viewed from the side, it feels a completely different color than when viewed from the front. For example, as shown in FIG. 5, when the red, green, and blue pixels represent 56, 48, and 24 gray levels, respectively, when viewed from the front, the ratio of red, green, and blue is

R: G: B = 73:50:10 = 55%: 37%: 8%

On the other hand, looking from the side 60 °, the ratio of red, green, and blue

R: G: B = 75:66:41 = 41%: 36%: 23%

The ratio of blue is more than three times higher than that of the front face, which makes the color look completely different from the front face.

When the gamma curve is distorted in the form as shown in FIG. 5, the color of the lower ratio in the front is higher in the side, and in contrast, the ratio of the color in the front is lower in the side, so that the ratio of red, green, and blue is similar. Will be displayed. As a result, when viewed from the front, the different colors appear to be similar colors because the color difference is reduced on the side, and the overall color becomes thin and becomes white-shifted. This phenomenon results in poor color reproducibility and blurry picture. The biggest cause of white-shift is the large distortion of the gamma curve at low grayscale. Although gamma distortion occurs at high gradation, it is not a big change in proportion, but at low gradation (below 32 gradations), the luminance varies by 2 to 10 times due to gamma distortion. This large change causes the white shift phenomenon to appear remarkably.

4 is a graph showing VT curves when the single domain vertically oriented liquid crystal cell is viewed from the side in eight directions.

4, the phenomenon that the VT curve shifts to the left at a low gray level is remarkable on the upper side or the lower side, and at the left and the right side, it rises with the same curve as the front side at the low gray level, and initially at the lower left and lower right sides. It can be seen that the gray scale reversal occurs and the VT moves to the right again and draws a rising curve. As a result, the gamma curve is distorted upward at low gray levels, which is severe when the direction in which the liquid crystal molecules lie in the same direction as the direction in which the liquid crystal cells are observed and when the electric field is applied (viewed from the head or tail side of the liquid crystal molecules). When the direction of observing and the direction in which the liquid crystal molecules lie perpendicular to the application of the electric field are perpendicular to each other, the number appears less. Therefore, the gamma curve distortion of the left and right domains is important as a factor that adversely affects the viewing angle of the visibility criteria on the left and right sides, and the gamma curve distortion of the upper and lower domains is important as a factor that adversely affects the viewing angles of the visibility criteria on the upper and lower sides. Do. However, from the viewpoint of using a liquid crystal display device, the viewing angles on the left and right sides are more important than the viewing angles on the upper and lower sides. Therefore, in the present invention, the electric field strength in the left and right domains is weaker than in the upper and lower domains in a way to compensate for the gamma curve distortion of the left and right domains which adversely affects the left and right side visibility. Let's take a closer look at this.

Fig. 5 shows a single domain for making rubbing anti-parallel in the vertical direction (the liquid crystal molecules are tilted in the vertical direction in the same way as the vertical domain). VT curve at the front in the VA cell, VT at 60 degrees in the left and right directions The average curve of the curve, the average curve of the VT curve at 60 degrees up and down, and the curve of 0.3V shifted in the vertical direction on the same graph.

As shown in Fig. 5, the left and right VT curves almost coincide with the front VT curve at low gradation, but the up and down VT curves start to rise at a lower voltage than the front VT curve. That is, Vth (threshold voltage) appears lower in the up and down direction than in the front. However, if the vertical VT curve is shifted by about 0.3V, it is almost coincident with the front VT curve at low gradation. When the up-and-down VT curve coincides with the front VT curve, it means that the visibility on the upper and lower sides becomes the same as the visibility on the front. As a result, the left and right side VT curves of the left and right domains may be moved by a predetermined voltage in order to improve the visibility on the left and right sides to the same level as the front visibility. The same effect as shifting the left and right side VT curves is to make the electric field in the left and right domains lower than the electric field in the upper and lower domains.

FIG. 6 is a layout view of a thin film transistor substrate for a liquid crystal display according to a second and third embodiment of the present invention, and FIG. 7 is a cross-sectional view taken along line VII-VII 'of FIG. 6, according to a second embodiment of the present invention. It is a cross section.

The liquid crystal display according to the second exemplary embodiment differs from the fact that the dielectric layer 600 is formed on the first small portion 91 instead of forming a slit in the first small portion 91 of the pixel electrode. It is the same as the liquid crystal display device according to the embodiment.

The effect of forming the dielectric layer 600 in the second embodiment is the same as forming the slit in the first small portion 91 in the first embodiment. That is, the electric field in the left and right domains is made weaker than the electric fields in the upper and lower domains. Herein, the thickness of the dielectric layer 600 is preferably formed between 500 mV and 1.5 m.

FIG. 8 is a cross-sectional view taken along line VIII-VIII ′ of FIG. 7 and according to a third exemplary embodiment of the present invention.

In the liquid crystal display according to the third exemplary embodiment, the dielectric layer 600 is disposed at a portion corresponding to the first small portion 91 on the common electrode 400 instead of the slit formed on the first small portion 91 of the pixel electrode. The difference is that it is formed, the rest is the same as the liquid crystal display device according to the first embodiment.

The effect of forming the dielectric layer 600 in the third embodiment is the same as forming the slit in the first small portion 91 in the first embodiment, as in the second embodiment. That is, the electric field in the left and right domains is made weaker than the electric fields in the upper and lower domains.

9 is a layout view of a thin film transistor substrate for a liquid crystal display according to a fourth exemplary embodiment of the present invention. FIGS. 10 and 11 are cross-sectional views taken along lines XI-XI ′ and XII-XII ′ of FIG. 9, respectively. 9 is an equivalent circuit diagram of a liquid crystal display device to which the thin film transistor substrate of FIG. 9 is applied.

First, a thin film transistor substrate is described.

Gate wirings 20 and 21 and storage capacitor lines 30 are formed on a transparent insulating substrate 10 such as glass.

The gate lines 20 and 21 include gate lines 20 extending in the horizontal direction, and a portion of the gate lines 20 protrude upward and downward to form the gate electrode 21.

The storage capacitor line 30 is formed to be parallel to the gate line 20, and may have branch lines although not illustrated.

The gate wirings 20 and 21 and the storage capacitor line 30 are covered with the gate insulating film 40, and the semiconductor layer 50 made of amorphous silicon is formed on the gate insulating film 40. The semiconductor layer 50 overlaps the gate electrode 21 to form a channel portion of the thin film transistor. On the semiconductor layer 50, ohmic contacts 61, 62, and 63 made of amorphous silicon doped with N-type impurities such as phosphorus at a high concentration are formed.

The data wirings 70, 71, 72, and 73 and the coupling electrode 74 are formed on the contact layers 61, 62, 63, and the gate insulating layer 40. The data lines 70, 71, 72, and 73 may include a data line 70 extending along the semiconductor layer 50, a source electrode 71 connected thereto, and first and second drain electrodes 72 and 73 separated from the data line 70. It includes. The source electrode 71 protrudes from the data line 70 on the gate electrode 21, and the first and second drain electrodes 72 and 73 are disposed on both sides of the source electrode 71, respectively. One end extends inwardly of the first and second pixel regions positioned at both sides with respect to the gate line 20. The coupling electrode 74 partially overlaps the storage capacitor line 30, and as will be described later, the first pixel electrode 91 and the second pixel are separated from each other around the storage capacitor line 30. Electrode 92 is electromagnetically coupled. Here, the ohmic contacts 61, 62, and 63 are formed only at the portion where the semiconductor layer 50 and the data lines 70, 71, 72, and 73 overlap.

The passivation film 80 is formed on the data wirings 70, 71, 72, and 73. In this case, the passivation layer 80 exposes one end of the first and second contact holes 81 and 82 and one end of the coupling electrode 74 that respectively expose one end of the first and second drain electrodes 72 and 73. It has a 3rd contact port 83 to make.

First and second upper surfaces of the passivation layer 80 connected to the first drain electrode 72 and the second drain electrodes 72 and 73 through the first contact hole 81 and the second contact hole 82, respectively. Pixel electrodes 91 and 92 are formed. The second pixel electrode 92 is connected to the coupling electrode 74 through the third contact hole 83, and the first pixel electrode 91 overlaps the coupling electrode 74 to be electromagnetically coupled ( Capacitively coupled). As a result, the first pixel electrode 91 and the second pixel electrode 92 form capacitive coupling through the coupling electrode 74. The pixel electrodes 91 and 92 are made of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO). On the other hand, the first pixel electrode 91 has a horizontal opening 95 extending in the horizontal direction. Unlike in FIG. 9, a plurality of horizontal openings 95 may be formed, and vertical openings may be formed in the second pixel electrode 92. It is preferable that the ratio of the first pixel electrode 91 in one pixel area is 30% to 70%.

It is common to apply the potential of the common electrode opposite to the pixel electrode 90 to the storage capacitor wiring 30.

Next, the color filter substrate will be described.

A black matrix, a color filter, and a common electrode are formed in the color filter substrate as in the liquid crystal display according to the first embodiment, and the first to third openings 510, 520, and 530 are formed in the common electrode. In this case, the first opening 510 extending in the vertical direction is divided into two left and right domains by dividing the second pixel electrode 92 from side to side, and the second and third openings extending in the horizontal direction ( The 520 and 530 are formed at positions dividing the first pixel electrode 91 up and down. The first pixel electrode 91 is divided into four vertical domains by the second and third openings 520 and 530 and the horizontal opening 95.

In the fourth embodiment, the coupling electrode 74 is formed on the same layer as the data wires 70, 71, 72, and 73. However, the coupling electrode 74 is formed on the same layer as the gate wires 20 and 21. It may be formed. In this case, the storage capacitor wiring 30 should be formed so as not to overlap the coupling electrode 74.

The liquid crystal display using the thin film transistor substrate has the following structure.

The common electrode substrate is disposed at a predetermined interval to face the thin film transistor substrate, and a liquid crystal material is injected between the thin film transistor substrate and the common electrode substrate. At this time, the liquid crystal material is oriented perpendicular to the substrate. In addition, a compensation film such as a biaxial film is attached on the color filter substrate, and two polarizing plates are disposed outside the thin film transistor substrate and the common electrode substrate.

As described above, when two thin film transistors and two pixel electrodes are formed per pixel area, and two pixel electrodes of neighboring pixel areas are capacitively coupled using a coupling electrode, the liquid crystal display is viewed from the left and right sides. It can prevent that visibility falls. This is because the voltage of the second pixel electrode 92 constituting the left and right domains is kept lower than the voltage of the first pixel electrode 91 constituting the upper and lower domains so that the electric field in the left and right domains is weaker than the electric field in the upper and lower domains.

Next, the reason why the voltage of the second pixel electrode 92 constituting the left and right domains is kept lower than the voltage of the first pixel electrode 91 constituting the upper and lower domains will be described.

First, referring to FIG. 12, two pixel electrodes P (n) -a and P (n) -b] potentials {V [P (n) -a] and V [P disposed in one pixel region are described. (n) -b)]}.

In FIG. 12, Clca is a liquid crystal capacitor formed between a pixel electrode and a common electrode, Csta is a storage capacitor formed between a storage capacitor line and a pixel electrode, Clcb is a liquid crystal capacitor formed between a b pixel electrode and a common electrode, and Cstb is The storage capacitor formed between the storage capacitor line and the b pixel electrode, Cpp, represents the coupling capacitance formed between the a pixel electrode and the b pixel electrode.

12, the first and second thin film transistors are connected to the same gate line and the data line, and the first and second pixel electrodes are connected to the first and second thin film transistors, respectively. The first pixel electrode and the second pixel electrode having the storage capacitor line 30 therebetween form a capacitive coupling Cpp.

Based on one data line 70, when the n-th gate line 20 is turned on, two thin film transistor (TFT) channels are turned on, and thus the first and second pixel electrodes P (n) are turned on. ) -a, P (n) -b] is applied. However, P (n) -b is capacitively coupled to P (n + 1) -a so that P (n) -b is affected when P (n + 1) -a is on. Therefore, the voltages of P (n) -a and P (n) -b are given by

V [P (n) -a] = Vd (n)

In Equations 1 and 2, Vd (n) denotes a voltage applied to a data line to drive a P (n) pixel, and Vd (n + 1) denotes a data applied to drive P (n + 1). Means line voltage. In addition, V'd (n + 1) means a voltage applied to the P (n + 1) pixel of the previous frame.

As shown in Equations 1 and 2, the voltage applied to the P (n) -b pixel and the voltage applied to the P (n) -a are different from each other. In particular, when dot inversion driving or line inversion driving is performed, and the next pixel row displays the same gray scale as the previous pixel row (actually, most of the pixels have a lot of time in this case), Vd (n) =-Vd Since (n + 1) and Vd (n) =-V'd (n) (assuming that the common electrode voltage is a ground voltage), Equation 2 can be summarized as follows.

According to Equation 3, it can be seen that a voltage lower than P (n) -a is applied to P (n) -b. At this time, T is suitably about 0.65-0.95.

A liquid crystal display according to a fifth embodiment of the present invention will be described.

FIG. 13 is a layout view of a thin film transistor substrate for a liquid crystal display according to a fifth exemplary embodiment of the present invention, and FIG. 14 is an equivalent circuit diagram of the liquid crystal display device to which the thin film transistor substrate of FIG. 13 is applied.

In the fifth embodiment of the present invention, the thin film transistor and the pixel electrode included in one pixel column are alternately connected to two data lines. That is, the thin film transistor of the P (n) pixel and the two pixel electrodes a, b are connected to the mth data line, and the thin film transistor of the P (n + 1) pixel and the two pixel electrodes a, b are m It is connected to the + 1th data line. The specific structure of each of the thin film transistor and the pixel electrode is the same as in the fourth embodiment except that the positions of the openings 95, 510, 520, and 530 are changed. That is, in the fourth embodiment, the horizontal opening 95 is formed in the second pixel electrode 92, and the first opening 510 is formed at a position that bisects the first pixel electrode 91 from side to side. The second and third openings 520 and 530 are formed at positions that divide the second pixel electrode 92 up and down by three. Accordingly, the first pixel electrode 91 forms a left and right domain, and the second pixel electrode 92 forms an upper and lower domain.

When point inversion driving is performed in this structure, the electric field in the left and right domains is kept weak compared to the electric fields in the upper and lower domains. That is, the potential of the first pixel electrode 91 is always kept lower than the potential of the second pixel electrode 92 so that the visibility on the left and right sides is improved. Next, the reason why the potential of the first pixel electrode 91 is always kept lower than the potential of the second pixel electrode 92 will be described.

In the structure shown in FIG. 13, since the voltage of the same polarity is applied to the pixel electrodes belonging to the same pixel column, the inversion driving is the same as that of the column inversion driving. Therefore, considering the case where the next pixel row displays the same gray scale as the previous pixel row (actually, most of the pixels have a lot of time in this case), Vd (n) = Vd (n + 1), Vd (n ) =-V'd (n) so that Equation 2 can be summarized as follows.

According to equation (4), in the fifth embodiment, the voltage of the b pixel is higher than the a pixel. Therefore, the electric field in the left and right domains can always be kept lower than the electric field in the upper and lower domains.

Although described above with reference to the most practical and preferred embodiment of the present invention, the present invention is not limited to the embodiment disclosed above. The scope of the invention also encompasses various modifications and equivalents falling within the scope of the following claims.

1 is a layout view of a liquid crystal display according to a first exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along line II-II 'of FIG. 1,

3 is a graph showing gamma (gamma: gamma) curves at 60 ° of the front and side surfaces of the test cell.

4 is a graph showing VT curves when a single domain vertically oriented liquid crystal cell is viewed from the side in eight directions,

FIG. 5 shows the average of the VT curves in the front and the VT curves in the left and right directions at 60 degrees and the VT curves at the 60 degrees in the vertical direction in a single domain VA cell which makes rubbing anti-parallel in the vertical direction. The figure which shows the curve which moved the curve and the vertical curve by 0.3V on the same graph,

6 is a layout view of a liquid crystal display device according to a second and third embodiment of the present invention;

FIG. 7 is a cross-sectional view taken along line VII-VII ′ of FIG. 6, and is a cross-sectional view according to a second exemplary embodiment of the present invention.

8 is a cross-sectional view taken along the line VII-VII 'of FIG. 6, and is a cross-sectional view according to a third embodiment of the present invention.

9 is a layout view of a liquid crystal display according to a fourth exemplary embodiment of the present invention.

10 and 11 are cross-sectional views taken along line XI-XI ′ and XII-XII ′ of FIG. 9, respectively.

FIG. 12 is an equivalent circuit diagram of a liquid crystal display device to which the thin film transistor substrate of FIG. 9 is applied.

13 is a layout view of a liquid crystal display according to a fifth exemplary embodiment of the present invention.

FIG. 14 is an equivalent circuit diagram of a liquid crystal display device to which the thin film transistor substrate of FIG. 13 is applied.

Claims (5)

First insulating substrate, A first signal line formed on the first insulating substrate in a first direction, A second signal line formed on the first insulating substrate in a second direction and insulated from and intersecting the first signal line; A first thin film transistor connected to the first signal line and the second signal line, A second thin film transistor connected to the first signal line and the second signal line to which the first thin film transistor is connected; A first pixel electrode connected to the first thin film transistor, A second pixel electrode connected to the second thin film transistor, A second insulating substrate facing the first insulating substrate, A common electrode formed on the second insulating substrate, A liquid crystal material layer injected between the first substrate and the second substrate, Domain dividing means formed on at least one of the first insulating substrate and the second insulating substrate and dividing the first pixel electrode and the second pixel electrode into a plurality of small domains; Wherein the domain dividing means divides the first pixel electrode and the second pixel electrode into a first direction domain and a second direction domain, respectively, wherein the first pixel electrode and the second pixel electrode are capacitive to each other. Liquid crystal display. In claim 1, When n and m are integers, the first and second thin film transistors of the n-row pixels in the m columns are connected to the m-th data line, and the first and second thin film transistors of the n + 1 row pixels in the m columns are m + 1. The liquid crystal display device connected to the first data line. In claim 1, The second pixel electrode occupies 30% to 70% of the entire pixel area. In claim 1, The liquid crystal molecules included in the liquid crystal material layer are vertically aligned with respect to the first and second insulating substrates without a driving electric field applied thereto. In claim 1, A storage capacitor line formed on the thin film transistor substrate and forming a storage capacitor between the first pixel electrode and the second pixel electrode, respectively; The liquid crystal capacitor formed between the second pixel electrode and the common electrode is Clcb, and the storage capacitor formed between the second pixel electrode and the storage capacitor line is formed between Cstb and the first pixel electrode and the second pixel electrode. When the binding capacity is called Cpp,

A liquid crystal display device in which T is defined as having a value between 0.65 and 0.95.

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