KR20120055123A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: A liquid crystal display device is provided to reduce a storage capacitance, thereby reducing the size of a TFT and reducing line widths of gate and data lines. CONSTITUTION: A gate line(20) vertically crosses a data line(22) on a substrate to define a pixel area. A thin film transistor is arranged in a crossing point of the gate line and the data line. A common line(24) is arranged in parallel with the gate line. A common voltage is supplied to the common line. A pixel electrode(26) includes a first connection unit(26a) and a plurality of first finger units(26b). The first connection unit is connected to the thin film transistor and is horizontally arranged on the pixel electrode. The first finger units are separated from the first connection unit and extended. A common electrode(28) includes a second connection unit(28a) and a plurality of second finger units(28b). The second connection unit is connected to the common line and is horizontally arranged on the common electrode. The second finger units are separated from the second connection unit and extended.

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY DEVICE}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a liquid crystal display device for reducing the size of thin film transistors and reducing the line widths of gate and data lines by reducing storage capacitance.

Recently, the liquid crystal display (Liquid Crystal Display) is the most used because of the excellent image quality, lightweight, thin, low power characteristics of the display elements.

Such a liquid crystal display includes a twisted nematic (TN) mode, an in-plane switching mode (IPS) mode, a fringe field switching (FFS) mode, and the like according to a method of driving a liquid crystal. Here, the IPS mode and the FFS mode are techniques introduced to solve the viewing angle problem of the TN mode, and form a pixel electrode and a common electrode on one substrate, and drive the liquid crystal by an electric field formed therebetween.

Hereinafter, the liquid crystal display of the FFS mode will be described in detail.

FIG. 1 is a plan view showing a portion of an array substrate of a conventional FFS mode liquid crystal display, and FIG. 2 is a cross-sectional view taken along line II ′ of FIG. 1.

A general liquid crystal display includes an array substrate 2 having a thin film transistor (hereinafter, referred to as a TFT), a color filter substrate (not shown) opposing the array substrate 2 and having a color filter layer, and an array substrate ( 2) and a liquid crystal layer between the color filter substrate.

As shown in FIGS. 1 and 2, the array substrate 2 of the conventional FFS mode liquid crystal display includes a gate wiring 4 and a data wiring 6 formed of an opaque metal and vertically crossing each other to define subpixels. )and; A common wiring 8 arranged in parallel with the gate wiring 4; A TFT disposed at the intersection of the gate and data wirings 4 and 6; A common electrode 14 and a pixel electrode 16 formed of a transparent metal, insulated by the gate insulating film 10 and the protective film 12, and overlapping each other in the pixel area are formed. At this time, the common electrode 14 and the common wiring 8 are in contact with each other.

Specifically, the common electrode 14 is formed in a plate shape in the pixel area, and the pixel electrode 16 is branched in the direction of the data line 6 and the slits 18 are formed between the branched pixel electrodes. do. At this time, a common voltage is supplied to the common electrode 14, and a data voltage switched by the TFT is supplied to the pixel electrode 16, so that an electric field is generated between the common electrode 14 and the pixel electrode 16. Then, the liquid crystal is driven by an electric field formed between the pixel electrode 16 and the common electrode 14.

On the other hand, storage capacitance is required to maintain the voltage charged in the liquid crystal capacitor in the turn-off period of the TFT in order to prevent image quality degradation due to parasitic capacitance. The storage capacitance is overlapped with the common electrode 14. It is formed between the pixel electrodes 16. That is, as shown in FIG. 2, the common wiring 8 and the pixel electrode 16 overlap each other at the edge of the pixel region to form a storage capacitance Cst1, and the common electrode 14 and the pixel electrode ( 16) overlaps to form the storage capacitance Cst2.

However, the conventional FFS mode liquid crystal display as described above has the following problems.

That is, in the pixel area, the plate-shaped common electrode 14 and the pixel electrode 16 on which the slits 18 are formed overlap each other, and the storage capacitance Cst2 is formed at the overlapped portion. This increases the storage capacitance.

Specifically, in the case of the general IPS mode liquid crystal display, only the storage capacitance is formed by overlapping the common wiring and the pixel electrode at the edge of the pixel region. However, in the case of the FFS mode liquid crystal display, the storage capacitance Cst2 is additionally generated due to the overlap of the common electrode 14 and the pixel electrode 16 inside the pixel region in addition to the edge of the pixel region, thereby increasing the storage capacitance beyond the required amount. You lose.

As described above, when the storage capacitance is increased, it serves as an advantage in improving characteristics such as flicker due to ΔVp, but there is a problem in that the size of the TFT must be increased to charge the storage capacitor. That is, when the size of the storage capacitor increases, the TFT must be driven for a sufficient time to charge the storage capacitor. However, since the time is limited, the size of the TFT needs to be large. Here, since the TFT is a portion through which light is not transmitted, the larger the size of the TFT, the lower the opening ratio.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a liquid crystal display device which reduces the size of TFTs and reduces the line widths of gate and data lines by reducing storage capacitance.

In order to achieve the above object, a liquid crystal display according to an exemplary embodiment of the present invention includes a gate line and a data line defining a pixel area by vertically crossing a substrate; A thin film transistor disposed at an intersection point of the gate line and the data line; A common wiring disposed in parallel with the gate wiring and supplied with a common voltage; A pixel electrode connected to the thin film transistor and including a first connection part disposed in a lateral direction and a plurality of first finger parts spaced apart at a predetermined interval in the longitudinal direction from the first connection part; And a common electrode including a second connection part electrically connected to the common wire and disposed in a transverse direction, and a plurality of second finger parts spaced apart at a predetermined interval in the longitudinal direction from the second connection part. The plurality of first fingers and the plurality of second fingers are bent in the same direction, and the angles at which the plurality of first fingers and the plurality of second fingers are bent are different from each other.

The pixel area may be divided into two domains that are vertically symmetric with respect to a domain boundary line, and the plurality of first fingers and the plurality of second fingers are bent at the domain boundary.

Wherein the plurality of first fingers forms a first angle with a normal perpendicular to the domain boundary, the plurality of second fingers forms a second angle with the normal, and the first and second angles are less than 15 degrees. It features.

The pixel electrode and the common electrode are partially overlapped with an insulating layer therebetween to form a storage capacitor.

A fringe field electric field is formed between the pixel electrode and the common electrode.

The present invention can reduce the storage capacitance Cst by forming a plurality of openings having a bent shape in the common electrode 28. As a result, the size of the TFT charging the storage capacitance Cst can be reduced, and the width of the gate and data lines 20 and 22 that supply various signals to the TFT can be reduced, thereby increasing the aperture ratio and the brightness.

In addition, the bending angle of the common electrode 28 is formed differently from the bending angle of the pixel electrode 26, so that the overlap area of the common electrode 28 and the pixel electrode 26 can be reduced more efficiently, and the common electrode 28 ) And various liquid crystal field angles are formed between the pixel electrode 26 and the pixel electrode 26.

1 is a plan view showing a part of an array substrate of a conventional FFS mode liquid crystal display device.
FIG. 2 is a cross-sectional view taken along line II ′ of FIG. 1.
3 is a plan view illustrating a portion of an array substrate of a liquid crystal display according to an exemplary embodiment of the present invention.
4 is a cross-sectional view taken along line II-II ′ of FIG. 3.
5A and 5B are plan views comparing overlapping areas between the pixel electrode 26 and the common electrode 28 in the related art and the present invention.
FIG. 6 is an enlarged plan view of a portion of the first and second fingers 26b and 28b illustrated in FIG. 3.
Fig. 7 is a simulation comparing and measuring the transmission efficiency in the pixel region of the prior art and the present invention.

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

3 is a plan view illustrating a portion of an array substrate of a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 4 is a cross-sectional view taken along line II-II ′ of FIG. 3.

3 and 4 include a gate wiring 20 and a data wiring 22 defining a pixel region by vertically crossing the array substrate 34; A TFT disposed at the intersection of the gate wiring 20 and the data wiring 22; A common wiring 24 disposed in parallel with the gate wiring 20; A plurality of elongated spaced apart at regular intervals in the longitudinal direction (y direction) from the first connecting portion 26a and the first connecting portion 26a arranged in the lateral direction (x direction) by being connected to the TFT through the first contact hole 32. A pixel electrode 26 comprising a first finger portion 26b of the pixel electrode 26; And a plurality of second connecting parts 28a electrically connected to the common wiring 26 through the second contact hole 30 and being spaced apart at regular intervals in the longitudinal direction from the second connecting parts 28a. It includes a common electrode 28 including a second finger portion 28b of the.

Meanwhile, although the embodiment of the present invention is not shown, the color filter layer is formed to be opposite to the array substrate 34 and further includes a liquid crystal layer between the array substrate 34 and the color filter substrate.

The common voltage is supplied to the common electrode 28, and the data voltage switched by the TFT is supplied to the pixel electrode 26. Then, a fringe field is formed between the common electrode 28 and the pixel electrode 26, and the liquid crystal is driven by the fringe field.

In an embodiment of the present invention, the pixel area is divided into two domains D1 and D2 to prevent image distortion. In detail, the two domains D1 and D2 are vertically symmetric with respect to the domain boundary line B, and the plurality of first fingers 26b are bent in a “<” or “>” shape with respect to the domain boundary line. .

However, as described above, the large storage capacitance generated in the overlapping region of the common electrode 28 and the pixel electrode 26 causes the increase in the TFT size and the decrease in the aperture ratio. In order to prevent this, an embodiment of the present invention forms a plurality of openings bent in the common electrode 28. That is, the common electrode 28 includes a second connecting portion 28b connected to the common wire 24 and a plurality of second finger portions 28b extending and spaced apart at regular intervals in the longitudinal direction from the second connecting portion 28a. do.

In this case, like the plurality of first fingers 26b, the plurality of second fingers 28b are vertically symmetric with respect to the domain boundary and bent in a “<” or “>” shape. The direction in which the plurality of second fingers 28b are bent is the same as the direction in which the plurality of first fingers 26b are bent.

In addition, the angle at which the plurality of second fingers 28b are bent is different from the angle at which the plurality of first fingers 26b are bent, which means that the plurality of first fingers 26b and the plurality of second fingers ( This is to reduce the storage capacitance (Cst) by reducing the overlap area between 28b). For example, as shown in FIG. 3, the plurality of first and second fingers 26b, 28b are bent in a “<” shape, and these 26b, 28b are bent at different angles.

If the angles at which the plurality of first and second fingers 26b and 28b are bent are different, the storage capacitance Cst is reduced, and the following effects are obtained. That is, in the conventional structure, the liquid crystal electric field is formed only by the angle at which the pixel electrode is bent, but according to the exemplary embodiment of the present invention, not only the pixel electrode 26 but also the common electrode 28 are bent together, so that these (26, 28) are bent. Combining the angles to form a variety of liquid crystal field angles. Accordingly, the embodiment of the present invention has the effect of improving the viewing angle characteristics compared to the conventional structure.

In summary, according to the embodiment of the present invention, the plurality of second fingers 28b constituting the common electrode 28 are bent at regular intervals, and the bent angle is different from the plurality of first fingers 26b. Is formed. Then, as shown in FIG. 4, since the plurality of first and second fingers 26b and 28b partially overlap each other, the storage capacitance Cst is reduced. When the angles at which the plurality of first and second fingers 26b and 28b are bent are different, various liquid crystal electric field angles are formed between them 26b and 28b to improve viewing angle characteristics.

The reduction in the area where the plurality of first and second fingers 26b and 28b overlap is more easily understood in the plan views shown in FIGS. 5A and 5B. 5A and 5B are plan views comparing overlapping areas between the pixel electrode 26 and the common electrode 28 in the related art and the present invention.

In detail, a plan view showing the pixel electrode 26 and the common electrode 28 according to the exemplary embodiment of the present invention is shown on the left side of FIG. 5A, and the pixel electrode 26 and the pixel electrode 26 according to the present invention on the right side of FIG. 5A. The overlap area of the common electrode 28 is shown. Similarly, a plan view showing a common electrode and a pixel electrode formed in a plate shape according to the prior art is shown on the left side of FIG. 5B, and an overlapping area of the common electrode and the pixel electrode according to the prior art is shown on the right side of FIG. 5B. Accordingly, the smaller the area in the right side of Figs. 5A and 5B, the smaller the storage capacitance Cst.

Referring to FIG. 5A, in the embodiment of the present invention, as described above, the plurality of second fingers 28b constituting the common electrode 28 are bent at regular intervals, and the bent angle is a plurality of firsts. It is formed to be different from the finger portion 26b. Accordingly, it can be seen that the plurality of first and second finger portions 26b and 28b overlap in some regions and do not overlap in some regions.

Referring to FIG. 5B, in the liquid crystal display according to the related art, since the common electrode is formed in a plate shape, it can be seen that the pixel electrode overlaps the common electrode over the entire area.

As described above, according to the embodiment of the present invention, the overlapping area formed between the plurality of first and second fingers 26b and 28b is reduced, thereby reducing the storage capacitance Cst. As a result, the size of the TFT charging the storage capacitance Cst can be reduced, and the width of the gate and data lines 20 and 22 that supply various signals to the TFT can be reduced, thereby increasing the aperture ratio and the brightness.

In FIG. 4, reference numeral 36 is an insulating film, 38 is a protective film, and various manufacturing methods for having the above-described characteristics may exist.

Hereinafter, the pixel electrode 26 and the common electrode 28 having the above characteristics will be described in more detail.

FIG. 6 is an enlarged plan view of a portion of the first and second fingers 26b and 28b illustrated in FIG. 3.

Referring to FIG. 6, the first finger portion 26b of the pixel electrode 26 is vertically symmetric with respect to the domain boundary line B, and is perpendicular to the domain boundary line B and the first angle θ1. Are formed. The second finger 28b of the common electrode 28 is vertically symmetrical with respect to the domain boundary line B, and is formed to form a second angle θ2 with a normal line N perpendicular to the domain boundary line B. .

In this case, the first and second angles θ1 and θ2 are different from each other in order to reduce the overlapping area between the first and second finger parts 26b and 28b. Here, the magnitudes of the first and second angles θ1 and θ2 only need to be different from each other, and either of them may be large.

However, as the size of the first and second angles θ1 and θ2 is smaller, the angle at which the liquid crystal moves relative to the applied voltage increases, so that the driving voltage can be reduced. It can get close to 45 degrees, which can raise the brightness. Therefore, the sizes of the first and second angles θ1 and θ2 are preferably smaller than 15 degrees.

On the other hand, in the embodiment of the present invention, the structure of the common electrode 28 is changed compared with the conventional, but the transmission efficiency is not reduced thereby.

Fig. 7 is a simulation comparing and measuring the transmission efficiency in the pixel region of the prior art and the present invention. Specifically, a simulation of measuring the transmission efficiency in the pixel area according to the conventional structure is shown on the left side of FIG. 7, and a simulation of the transmission efficiency in the pixel area according to the present invention is shown on the right side of FIG. 7. .

First, the method of measuring the transmission efficiency is as follows. That is, a window for measuring transmission efficiency is set in an arbitrary pixel region, and a non-transmissive region BM through which light is not transmitted is set in the peripheral edge of the set window. The light is transmitted through the window, and the transmission efficiency is measured.

As a result of measuring the transmission efficiency according to the structure of the present invention according to the method described above, if the transmission efficiency of the conventional structure is 100%, the present invention was measured to 98.7%. That is, the transmission efficiency of the conventional structure and the present invention shows a 1.3% difference, and this difference is substantially negligible.

As described above, the present invention has the same level of transmission efficiency as compared with the conventional structure, and thus there is no difference in sharpness, and the luminance is increased according to the above-described feature, thereby improving display quality.

As described above, the embodiment of the present invention can reduce the storage capacitance Cst by forming a plurality of openings having a bent shape in the common electrode 28. As a result, the size of the TFT charging the storage capacitance Cst can be reduced, and the width of the gate and data lines 20 and 22 that supply various signals to the TFT can be reduced, thereby increasing the aperture ratio and the brightness.

In addition, the bending angle of the common electrode 28 is formed differently from the bending angle of the pixel electrode 26, so that the overlap area of the common electrode 28 and the pixel electrode 26 can be reduced more efficiently, and the common electrode 28 ) And various liquid crystal field angles are formed between the pixel electrode 26 and the pixel electrode 26.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and it is common in the art that various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

20: gate wiring 22: data wiring
26: pixel electrode 28: common electrode

Claims (5)

Gate wiring and data wiring defining vertically crossing pixel regions on the substrate;
A thin film transistor disposed at an intersection point of the gate line and the data line;
A common wiring disposed in parallel with the gate wiring and supplied with a common voltage;
A pixel electrode connected to the thin film transistor and including a first connection part disposed in a lateral direction and a plurality of first finger parts spaced apart at a predetermined interval in the longitudinal direction from the first connection part; And
A common electrode including a second connecting portion electrically connected to the common wiring and arranged in a transverse direction, and a plurality of second fingers extending longitudinally spaced apart from the second connecting portion in a longitudinal direction; And
And wherein the plurality of first fingers and the plurality of second fingers are bent in the same direction, and the angles at which the plurality of first fingers and the plurality of second fingers are bent are different from each other. The method of claim 1,
The pixel region is divided into two domains that are vertically symmetric with respect to a domain boundary line.
And the plurality of first fingers and the plurality of second fingers are bent at the domain boundary. The method of claim 2,
The plurality of first fingers forms a first angle with a normal perpendicular to the domain boundary line,
The plurality of second fingers forms a second angle with the normal,
And wherein the first and second angles are less than 15 degrees. The method of claim 1,
And the pixel electrode and the common electrode partially overlap each other with an insulating layer therebetween to form a storage capacitor. The method of claim 1,
A fringe field electric field is formed between the pixel electrode and the common electrode.

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