KR20040034341A - In-Plane Switching mode Liquid Crystal Display Device - Google Patents

Abstract

PURPOSE: An In-plane switching mode liquid crystal display is provided to prevent the transmissivity of a unit area from reducing by realizing uniform tilt of liquid crystal on the whole area, thereby improving the light efficiency even if a gap between a common electrode and a pixel electrode increases. CONSTITUTION: A common electrode and a pixel electrode are formed on a lower substrate on the same layer as data lines, being separated from each other at predetermined gaps. A passivation film is deposited on the data lines and the pixel electrode. A first aligning film for defining initial alignment of liquid crystal is formed on the passivation film. The first aligning film is processed in a rubbing direction of 25 deg. to 45 deg. to a length direction of the common electrode and the pixel electrode.

Description

In-Plane Switching mode Liquid Crystal Display Device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a transverse field type liquid crystal display device in which the rubbing direction of the alignment layer is changed, and the ratio of the distance between the electrodes and the electrode width is adjusted to optimize light utilization even when the distance between the electrodes is increased. It is about.

As the information society develops, the demand for display devices is increasing in various forms, and in recent years, the liquid crystal display device (LCD), plasma display panel (PDP), electro luminescent display (ELD), and vacuum fluorescent (VFD) Various flat panel display devices such as displays have been studied, and some of them are already used as display devices in various devices.

Among them, LCD is the most widely used as the substitute for CRT (Cathode Ray Tube) for mobile image display device because of its excellent image quality, light weight, thinness, and low power consumption. In addition to the use of the present invention has been developed in various ways such as a television and a computer monitor for receiving and displaying broadcast signals.

In order to use such a liquid crystal display as a general screen display device in various parts, it is a matter of how high quality images such as high definition, high brightness and large area can be realized while maintaining the characteristics of light weight, thinness and low power consumption. Can be.

A general liquid crystal display device may be largely divided into a liquid crystal panel displaying an image and a driving unit for applying a driving signal to the liquid crystal panel, wherein the liquid crystal panel includes first and second glass substrates bonded to each other with a predetermined space; It consists of a liquid crystal layer injected between the said 1st, 2nd glass substrate.

Here, the first glass substrate (TFT array substrate) has a plurality of gate lines arranged in one direction at regular intervals, a plurality of data lines arranged at regular intervals in a direction perpendicular to the gate lines, A plurality of pixel electrodes formed in a matrix form in each pixel region defined by crossing a gate line and a data line, and a plurality of thin film transistors switched by signals of the gate line to transfer the signal of the data line to each pixel electrode. Is formed.

In the second glass substrate (color filter array substrate), a light shielding layer for blocking light in portions other than the pixel region, an R, G, and B color filter layer for expressing color colors are common to implement an image. An electrode is formed.

The driving principle of the general liquid crystal display device uses the optical anisotropy and polarization property of the liquid crystal. Since the liquid crystal is thin and long in structure, the liquid crystal has directivity in the arrangement of molecules, and the direction of the arrangement of molecules can be controlled by artificially applying an electric field to the liquid crystal.

Therefore, when the molecular arrangement direction of the liquid crystal is arbitrarily adjusted, the molecular arrangement of the liquid crystal is changed, and light is refracted in the molecular arrangement direction of the liquid crystal by optical anisotropy, thereby representing image information.

Currently, an active matrix LCD, in which a thin film transistor and pixel electrodes connected to the thin film transistor are arranged in a matrix manner, is attracting the most attention due to its excellent resolution and ability to implement video.

Hereinafter, a liquid crystal display according to the related art will be described with reference to the accompanying drawings.

1 is an exploded perspective view showing a typical twisted nematic liquid crystal display device.

As shown in FIG. 1, the lower substrate 1 and the upper substrate 2 are bonded to each other with a predetermined space, and the liquid crystal 3 injected between the lower substrate 1 and the upper substrate 2.

More specifically, the lower substrate 1 has a plurality of gate lines 4 arranged in one direction at regular intervals to define the pixel region P, and in a direction perpendicular to the gate line 4. A plurality of data lines 5 are arranged at regular intervals, and a pixel electrode 6 is formed in each pixel region P where the gate line 4 and the data line 5 intersect, and each gate line The thin film transistor T is formed at the portion where (4) and the data line 5 intersect.

The upper substrate 2 includes a light shielding layer 7 for blocking light in portions other than the pixel region P, R, G, and B color filter layers 8 for expressing color colors, and an image. A common electrode 9 is formed for implementation.

The thin film transistor T may include a gate electrode protruding from the gate line 4, a gate insulating film (not shown) formed on a front surface, an active layer formed on the gate insulating film above the gate electrode, and the data. And a source electrode protruding from the line 5 and a drain electrode to face the source electrode.

The pixel electrode 6 uses a transparent conductive metal having a relatively high light transmittance, such as indium-tin-oxide (ITO).

In the liquid crystal display device configured as described above, the liquid crystal 3 positioned on the pixel electrode 6 is aligned by a signal applied from the thin film transistor T, and the liquid crystal 3 is aligned according to the degree of alignment of the liquid crystal 3. (3) The image can be expressed by adjusting the amount of light passing through.

As described above, the liquid crystal panel drives the liquid crystal by an electric field applied up and down, and has excellent characteristics such as transmittance and aperture ratio, and the common electrode 9 of the upper substrate 2 serves as a ground to prevent static electricity. It is possible to prevent the destruction of the liquid crystal cell.

However, the liquid crystal drive by the electric field applied up-down has a disadvantage that the viewing angle characteristics are not excellent.

Accordingly, in order to overcome the above disadvantages, a new technology, that is, a liquid crystal display device having an in-plane switching mode, has been proposed.

Hereinafter, a conventional transverse electric field type liquid crystal display device will be described with reference to the accompanying drawings.

2 is a schematic cross-sectional view showing a general transverse electric field type liquid crystal display device.

As shown in FIG. 2, the pixel electrode 12 and the common electrode 15 are formed on the lower substrate 10 on the same plane.

The liquid crystal 3 formed between the lower substrate 10 and the upper substrate 20 bonded to the lower substrate 10 may have a transverse electric field between the pixel electrode 12 and the common electrode 15 on the lower substrate 10. Works by

3A to 3B are views illustrating a change in orientation direction of liquid crystals occurring when voltage off / on in a transverse electric field type liquid crystal display.

That is, FIG. 3A shows an off state in which the transverse electric field is not applied to the pixel electrode 12 or the common electrode 15, so that the change in the alignment direction of the liquid crystal 3 does not occur.

FIG. 3B is an on state in which a transverse electric field is applied to the pixel electrode 12 and the common electrode 15, and the alignment change of the liquid crystal 3 occurs, and is twisted about 45 ° compared to the off state of FIG. 3A. With an angle, it can be seen that the horizontal direction of the pixel electrode 12 and the common electrode 15 coincide with the twist direction of the liquid crystal.

4A and 4B are plan views illustrating alignment directions of liquid crystals according to FIGS. 3A and 3B, respectively.

As shown in FIG. 4A, when no voltage is applied to the pixel electrode 12 or the common electrode 15, the liquid crystal array direction is arranged in the same direction as the rubbing direction of the initial alignment layer (not shown).

As shown in FIG. 4B, when a voltage is applied to the pixel electrode 12 and the common electrode 15, the alignment direction of the liquid crystal is a direction in which an electric field is applied.

The advantage of this transverse electric field method is that a wide viewing angle is possible. That is, when the liquid crystal display device is viewed from the front, since the liquid crystal is aligned along the transverse electric field, the pole value of each of the aligned liquid crystals is small, so that a wide viewing angle is possible. In addition, the manufacturing process is simpler than the liquid crystal display device generally used, and there is an advantage that the color shift according to the viewing angle is small.

However, the conventional transverse electric field type liquid crystal display device has the following problems.

That is, in order to secure a high opening rate, the distance between the common electrode and the pixel electrode formed on the same substrate becomes larger. In this case, as the distance between the two electrodes increases, a voltage difference occurs for each region between the two electrodes.

Therefore, a large electric field is formed when a voltage is applied in a region adjacent to the common electrode or the pixel electrode, and the closer the center region between the common electrode and the pixel electrode is, the lower the electric field value is.

When the liquid crystal positioned at the center of the common electrode and the pixel electrode is tilted by 45 ° compared with the initial stage so that the transmittance is maximized by the characteristic of the liquid crystal oriented according to the electric field, the region adjacent to the common electrode or the pixel electrode is relatively As a result, the liquid crystal is tilted more than 45 ° due to a higher electric field than the central portion, so that the alignment occurs to have a tilt of different liquid crystals in a single pixel. As such, light leakage occurs at a portion where the liquid crystal alignment of another tilt occurs, and thus, a problem in that light utilization per unit area is reduced is caused by this portion.

The present invention has been made to solve the above problems, by changing the rubbing direction and adjusting the ratio of the distance between the electrodes and the width of the electrode, to provide a transverse electric field type liquid crystal display device that optimizes the light utilization even when the distance between the electrodes increases The purpose is to provide.

1 is an exploded perspective view showing a typical twisted nematic liquid crystal display device

2 is a schematic cross-sectional view illustrating electric field formation and liquid crystal alignment by a general transverse electric field type liquid crystal display device;

3A to 3B are views illustrating a change in alignment direction of liquid crystals when voltage off / on in a transverse electric field type liquid crystal display device;

4A and 4B are plan views showing alignment directions of liquid crystals according to FIGS. 3A and 3B, respectively.

5 is a graph showing the relationship between the aperture ratio and the luminance according to the distance between the electrodes.

FIG. 6 is a graph illustrating a relationship between light efficiency according to an interval between electrodes defined as characteristics of luminance with respect to the aperture ratio of FIG. 5.

7 is a graph simulating the average transmittance according to the distance between the electrodes

FIG. 8 is a graph illustrating a relationship between light efficiency relative to the transmittance of FIG. 7.

FIG. 9 is a diagram illustrating an orientation of liquid crystals when voltage is applied when a common electrode and a pixel electrode of a transverse electric field type liquid crystal display have a spacing of less than 15 μm. FIG.

10A and 10B are diagrams showing the rotation of the liquid crystal relative to the rubbing direction before and after voltage application in regions A and B of FIG. 9, respectively.

FIG. 11 is a diagram illustrating an orientation of liquid crystals when voltage is applied when a common electrode and a pixel electrode of a transverse field type liquid crystal display have a spacing of 15 μm or more. FIG.

12A and 12B are diagrams showing the orientation of the liquid crystal relative to the rubbing direction before and after voltage application in regions A and B of FIG. 11, respectively.

13A and 13B are simulation diagrams showing transmittance when the electrode gap between the common electrode and the pixel electrode of the transverse electric field type liquid crystal display device is 6 μm and is 26 μm.

14 is a plan view showing a transverse electric field type liquid crystal display device of the present invention.

15 is a cross-sectional view illustrating a transverse electric field type liquid crystal display device taken along the line II ′ of FIG. 14.

FIG. 16 is a view illustrating a rubbing direction of the first alignment layer illustrated in FIG. 15, and a liquid crystal oriented between the pixel electrode and the common electrode.

17A and 17B are views showing the alignment of liquid crystals with respect to the rubbing direction before and after voltage application in regions A and B of FIG. 14, respectively.

18A to 18C show an electric field at a predetermined position when two planar electrodes are arranged in parallel in the case of a linear electrode of an infinite length, and in the case of a planar electrode having a predetermined width, respectively.

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

100: lower substrate 110: gate line

120: common electrode 130: gate insulating film

140: data line 140a / 140b: source / drain electrodes

150: pixel electrode 160: protective film

170: first alignment layer 200: upper substrate

220: light shielding film 230: color filter layer

240: overcoat layer 250: second alignment film

A region: region between the common electrode and the pixel electrode

Region B: the periphery of the common electrode and the periphery of the pixel electrode

C region: common electrode and pixel electrode formation region

L: distance between the common electrode and the pixel electrode center

s: gap between the common electrode and the pixel electrode

d: 1/2 of width of common electrode and pixel electrode

According to an aspect of the present invention, there is provided a transverse electric field type liquid crystal display device including a lower substrate and an upper substrate, a gate line and a data line intersecting longitudinally and horizontally with each other on the lower substrate to define a pixel region, the gate line and A thin film transistor formed at an intersection region of the data line, a pixel electrode and a common electrode formed to be spaced apart from the pixel region by a predetermined interval, and an alignment layer processed to have a 25 ° to 45 ° alignment direction with respect to a length direction of the pixel electrode and the common electrode And a liquid crystal layer formed between the upper and lower substrates.

The pixel electrode and the common electrode are formed at intervals of 15 μm or more.

At this time, the distance between the pixel electrode and the common electrode is made three times larger than the width of each electrode.

The pixel electrode and the common electrode are formed to have the same width.

The alignment film is formed on either one of the upper and lower substrates or on the upper and lower substrates.

The distance between the pixel electrode and the common electrode is three times larger than the width of each electrode.

Hereinafter, a transverse field type liquid crystal display of the present invention will be described with reference to the accompanying drawings.

Currently, the development trend of the transverse electric field type liquid crystal display device is progressing in the direction of expanding the aperture ratio by increasing the distance between the pixel electrode and the common electrode.

First, before examining the transverse field type liquid crystal display device of the present invention, the distance between the two electrodes is increased, and thus the change in aperture ratio, transmittance, and light utilization rate will be described.

At this time, while maintaining the same width of each electrode, the aperture ratio, transmittance and light utilization are measured while gradually increasing the distance between the electrodes.

5 is a graph showing the relationship between the aperture ratio and the luminance according to the interval between the electrodes, and FIG. 6 is a graph showing the relationship of the light efficiency with the interval between the electrodes defined as the characteristics of the luminance with respect to the aperture ratio of FIG.

5 shows that as the electrode spacing is wider, the luminance is relatively less than the increase rate of the aperture ratio. Analyzing this phenomenon, the light efficiency can be newly defined as luminance with respect to the aperture ratio. In the test cell of the metal electrode, the aperture ratio is defined as the value measured as "gap between electrodes / (electrode width + gap between electrodes)".

As the electrode spacing becomes wider, the aperture ratio increases, but the increase rate does not continue and gradually decreases. When the electrode spacing is about 15 mu m or more, the decrease in the increase rate can be observed.

As shown in Fig. 6, the light efficiency is almost close to a constant value when the distance between the electrodes is almost 15 mu m or more.

In the currently manufactured transverse electric field type liquid crystal display devices, the spacing between electrodes is almost 15 μm or less. In this case, the light efficiency does not act as an important variable. However, in a pixel structure of a wider gap between electrodes for a brighter liquid crystal display device, an optimum condition of electrode gap and light efficiency should be considered.

5 and 6 show the transmission dependence along the rubbing direction as the electrode spacing increases. The luminance difference between the rubbing direction of 10 ° and the rubbing direction of 20 ° is 3.5% for the electrode gap of 6 mu m, but when the electrode gap is 28 mu m, the luminance difference reaches 7%.

Hereinafter, the influence of the rubbing direction on the transmittance when the electrode spacing is wide will be examined.

FIG. 7 is a graph illustrating an average transmittance according to the distance between electrodes, and FIG. 8 is a graph illustrating a relation of light efficiency relative to the transmittance of FIG. 7.

Here, a two-dimensional simulation of the liquid crystal alignment was performed, and the conditions of the electrode position and the liquid crystal material parameter were the same. In addition, this simulation was made on the assumption that each electrode is a transparent electrode.

Subsequently, the transmittance transmitted through the electrode was removed from the simulation result value in comparison with the above-described test cell of the metal electrode. Here, an ideal polarizing plate having a transmittance of 50% was used, and the maximum value of the light efficiency was 50%.

7 and 8 show that as the electrode interval is wider, the light efficiency decreases, and the dependence of the rubbing direction increases.

In a test cell having the same electrode width and measuring with increasing intervals between electrodes, the increase rate of light utilization decreases as the interval between electrodes increases. This means that the utilization rate of light irradiated through a device such as a backlight decreases when the electrode interval exceeds a predetermined level. The light efficiency is defined as the actual transmittance / opening ratio. As can be seen in FIGS. 7 and 8, when the distance L between the electrodes is greater than or equal to a predetermined distance (15 μm), the increase in the actual transmittance is relatively low compared to the aperture ratio. As a result, a graph showing the light efficiency draws a falling curve at a predetermined distance (15 μm) or more.

As shown in FIG. 7, when the electrode interval is widened, the transmittance becomes relatively better. At this time, the transmittance and the electrode spacing are not in a linear relationship with the electrode spacing similarly to the opening ratio, and when the thickness is about 15 µm or more, the increase rate of the transmittance gradually decreases.

As shown in FIG. 8, the light efficiency gradually decreases when the distance between the electrodes becomes about 15 μm or more. In other words, as the distance between the electrodes increases, the light efficiency does not increase by the increase of the aperture ratio.

Next, the change in orientation of the liquid crystal when the gap between the common electrode and the pixel electrode in the actual transverse type liquid crystal display device is changed based on the experiments of the aperture ratio, transmittance, and light utilization according to the above-described gaps between the electrodes.

It is assumed that the electrode width of each electrode described below is constant regardless of changes in other conditions.

On the other hand, the orientation of the liquid crystal in the transverse electric field can be divided into the following three areas.

That is, region A is the portion between the electrode and the electrode, that is, the portion away from the electrode, region B is the portion adjacent to the electrode, and region C is the portion directly above the electrode.

FIG. 9 is a view illustrating alignment of liquid crystals when a common electrode and a pixel electrode of a transverse electric field type liquid crystal display have a spacing of less than 15 μm when voltage is applied, and FIGS. 10A and 10B are shown in regions A and B of FIG. 9, respectively. Is a diagram showing the rotation of the liquid crystal relative to the rubbing direction before and after applying the voltage.

In general, the alignment layer formed on the lower substrate on which the pixel electrode and the common electrode are disposed is processed in a rubbing direction of 10 ° to 20 ° with respect to the longitudinal direction of the pixel electrode and the common electrode.

As shown in Figs. 10A and 10B, the orientation of the liquid crystal in the initial state without a voltage is controlled by the rubbing direction of the alignment layer.

Here, when a voltage is applied so that the liquid crystal has a tilt of 45 ° with respect to the rubbing direction (polarization axis) in the region between the pixel electrode and the common electrode (hereinafter referred to as A region) so as to maximize the transmittance, Liquid crystals having an orientation in the rubbing direction of the alignment layer are rearranged by an electric field formed between the pixel electrode and the common electrode.

As shown in FIG. 9, when the distance between the pixel electrode and the common electrode is less than 15 μm, there is almost no difference in electric field strength between the region A and the pixel electrode and the region around the common electrode (hereinafter referred to as region B) during voltage application. The tilt of the liquid crystal is similar in both A and B regions by about 45 ° with respect to the rubbing direction.

FIG. 11 is a diagram illustrating an orientation of liquid crystals when voltage is applied when the common electrode and the pixel electrode have a gap of 15 μm or more in the transverse field type liquid crystal display, and FIGS. 12A and 12B respectively illustrate regions A and B of FIG. 9. It is a figure which shows the orientation of the liquid crystal with respect to the rubbing direction before and after voltage application.

12A and 12B, the alignment of the liquid crystal in the initial state without a voltage is controlled by the rubbing direction of the alignment layer.

When a voltage is applied such that the liquid crystal has a tilt of 45 ° with respect to the polarization axis in the region A so that the transmittance is maximized, as shown in FIGS. 11, 12A, and 12B, the common electrode and the pixel electrode forming region C are respectively. Regions) and B and liquid crystals are aligned at different angles due to different electric fields in the A region. This is due to the electric field difference between the A and B regions.

That is, as shown in FIG. 11, when the distance between the pixel electrode and the common electrode is 15 μm or more, the electric field applied to the B region around the electrode is much larger than that of the A region, whereby the liquid crystal positioned in the B region is located in the A region. Tilt degree becomes large compared with liquid crystal located.

In this case, the liquid crystal positioned in the region B in FIG. 11 is inclined at an angle of 45 ° + α relative to the rubbing direction, and as the distance between the electrodes increases, the degree of tilt of the liquid crystal is in a direction of 90 ° maximum with respect to the electrode length direction. Can tilt up. Where α is the deviation angle.

Hereinafter, the transmittance between the electrode and the electrode is simulated by realizing the electrode spacing with a smaller value and a larger value than the 15 μm.

13A and 13B are simulation diagrams showing transmittance when the electrode gap between the common electrode and the pixel electrode of the transverse type liquid crystal display device is 6 μm and 26 μm.

Assuming that the polarization axes of the polarizing plates located on the upper and lower substrates cross each other by 90 °, and that each polarizing plate is an ideal polarizing plate, the transmittance is 50%, and the maximum value of the light efficiency is 50%.

As shown in Figs. 13A and 13B, three different graphs in the respective simulation diagrams show the transmittances according to the states of low (L), medium (M), and high (H) of the driving voltage, respectively, in order from the bottom. The numbers in the center of each graph represent the average transmittances when the respective driving voltages are applied.

13A and 13B, the uniformity of the transmittance is lowered when the electrode interval is larger than when the electrode interval is small.

This non-uniformity is because as the electrode spacing increases, it is difficult to find a driving voltage capable of simultaneously having a maximum transmittance in all of the regions A, B, and C.

The nonuniformity can be explained as follows.

In the area A, the electric field is almost a transverse electric field. Therefore, the liquid crystal rotates substantially along the plane, and there is almost no factor in which the tilt of the liquid crystal is affected. However, only the transmittance is affected by the intensity of the driving voltage. In area C, the vertical element of the electric field is larger than the horizontal element. Accordingly, the tilt and rotation directions of the liquid crystal are changed together, and are not affected by the electrode gap, and the transmittance is also relatively low depending on the intensity of the driving voltage.

In contrast, the liquid crystal in the region B shows a different tendency according to the electrode spacing. The alignment of the liquid crystal in the region B is influenced not only by the horizontal electric field but also by the alignment of adjacent liquid crystals.

As shown in Figs. 9 and 13A, the rotation of the liquid crystal in the region B is restricted by the liquid crystal between the region A and the region C at the small electrode interval. As the driving voltage increases, the transmittances of the A region and the B region increase together.

As shown in Figs. 11 and 13B, at large electrode intervals, the electric field ratio between regions B and A increases, and the restraining force of adjacent regions decreases. As a result, the rotation of the liquid crystal in the B region becomes larger than the A region. Therefore, the transmittances in the A and B regions are maximized at different driving voltages, respectively. When the driving voltage increases, the area B approaches the maximum transmittance (about 50%) of the A, B, and C areas. As the driving voltage further increases, the region A approaches the maximum value, and the transmittance in the region B decreases.

The dependence of the transmittance | permeability of a rubbing direction can be demonstrated by the orientation of a liquid crystal. When sufficient voltage is applied, the liquid crystal in the region B reaches a saturation angle in a direction perpendicular to the electrode length at large electrode intervals. For example, the alpha value when the rubbing angle is 10 ° becomes smaller by about 10 ° compared to the alpha when the rubbing angle is 20 °. And this means that as the rubbing angle becomes large, the decrease in transmittance in the region B becomes smaller.

Hereinafter, the transverse electric field type liquid crystal display of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 14 is a plan view illustrating a transverse electric field liquid crystal display device of the present invention, and FIG. 15 is a cross-sectional view illustrating a transverse electric field liquid crystal display device taken along line II ′ of FIG. 14.

As can be seen in FIGS. 14 and 15, the transverse electric field type liquid crystal display device of the present invention is largely a liquid crystal filled between the lower substrate 100, the upper substrate 200 opposite thereto, and the two substrates 100 and 200. (Not shown).

As illustrated in FIG. 14, a gate line 110, a data line 140, and a common line 141 are formed on the lower substrate 100 to cross each other in a vertical direction, and define a pixel region. 150 and the common electrode 120 are formed.

Looking at the manufacturing process of the transverse electric field type liquid crystal display device of the present invention with reference to FIG.

A gate line 110 having a gate electrode 110a of FIG. 12 is formed on the lower substrate 100, and a common electrode 120 is formed on the same layer as the gate line 110.

Subsequently, a gate insulating layer 130 is formed on the entire lower substrate 100 including the gate line 110 and the common electrode 120.

The gate insulating layer 130 may be an inorganic insulating layer such as SiNx or SiOx or an organic insulating layer having a low dielectric constant such as photoacryl, BCB (BenzoCycloButene), or polyamide compound.

Subsequently, a data line 140 is formed on the gate insulating layer 130 so as to vertically intersect the gate line 110, and in the same process, the source electrode 140a may be formed to protrude from the data line 140. The drain electrode 140b is formed spaced apart from the predetermined interval. The pixel electrode 150 is formed on the same layer as the data line 140 and spaced apart from the common electrode 120 in a parallel direction.

Subsequently, after the passivation layer 160 is deposited on the entire surface including the data line 140 and the pixel electrode 150, the first alignment layer 170 defining the initial alignment of the liquid crystal is formed. At this time, the protective film 160 is formed of an inorganic insulating film or an organic insulating film with the same components as the gate insulating film 130.

On the upper substrate 200, a light shielding layer 220 for blocking light leakage to areas other than the pixel area, a color filter layer 230 for implementing color colors R, G, and B, and planarization A second alignment layer 250 for defining an initial alignment of the liquid crystal is formed on the overcoat layer 240 and the entire surface of the overcoat layer 240.

Therefore, the liquid crystals adjacent to the first and second alignment layers 170 and 250 are arranged in accordance with the alignment direction of the alignment layer.

FIG. 16 is a view illustrating a rubbing direction of the first alignment layer illustrated in FIG. 15 and liquid crystals oriented between the pixel electrode and the common electrode, and FIGS. 17A and 17B are voltages applied to regions A and B of FIG. 16, respectively. It is a figure which shows the orientation of the liquid crystal with respect to the rubbing direction before and after.

As illustrated in FIG. 16, the first alignment layer 170 on the lower substrate 100 on which the common electrode 120 and the pixel electrode 150 are formed has a length direction (polarization axis) of the common electrode 150 and the pixel electrode 120. Direction) in the rubbing direction of 25 ° to 45 °.

As described above, the alignment film processed in the high rubbing direction may be formed on both the upper and lower substrates 100 and 200, and may be formed only on one side of the upper and lower substrates 100 and 200. However, since the transverse electric field is formed on the lower substrate 100 when the voltage is applied due to the pixel electrode 150 and the common electrode 120 to drive the liquid crystal, an alignment layer processed in the high rubbing direction is formed on the lower substrate 100. It is more effective to form the alignment film treated in the high rubbing direction on the upper substrate 200.

As shown in Figs. 17A and 17B, the alignment of the liquid crystal in the initial state is made according to the rubbing direction due to the alignment film processed in the high rubbing direction (25 ° to 45 °) before voltage application.

The gap between the common electrode and the pixel electrode is increased to 15 µm or more so that the liquid crystal alignment of the A region is 45 degrees in the rubbing direction to maximize the transmittance, even though the electric field strength of the B region is larger than that of the A region. Since the rotation angle at which the liquid crystal is inclined from the initial state is limited to 90 ° with respect to the length direction of the electrode, the degree of rotation of the liquid crystal in the region between the electrode and the electrode when voltage is applied is not different.

In the above, assuming that the width of each electrode is constant, the transmission characteristics according to the change of the distance between the electrodes have been described.

Hereinafter, the relationship between the electrode width and the distance between the electrodes will be described.

Whether the electrode width affects the transmittance can be explained by analysis of the electric field.

In a typical liquid crystal display, the ratio of electrode length and width is about 300 µm / 5 µm >> 1, and the ratio of electrode thickness and width is 0.3 µm / 5 µm << 1. Thus, it is assumed that the electrode is infinitely long and the thickness is negligibly thin.

18A to 18C are diagrams showing electric fields at predetermined positions when two planar electrodes are arranged in parallel in the case of linear electrodes of infinite length, and in the case of planar electrodes of a predetermined width, respectively.

As shown in Fig. 18A, the electric field at a predetermined position (x, y) for an infinite length linear electrode is Is defined as

Is the charge density per length, and p is the distance from the linear electrode to a predetermined position. The z axis is selected in the longitudinal direction of the electrode.

As shown in Fig. 18B, the electric field at a predetermined position with respect to the planar electrode having a predetermined width can be obtained by the sum of the electric fields of the linear electrodes of infinite length in Fig. 18A. When the center of the electrode is located at the coordinates (0, 0, z), the electrode width of 2d is located in the x-axis direction.

Therefore, the electric field of the electrode having a predetermined width

Where σ is the charge density per area.

Therefore, the electric field of the planar electrode divided by the value of 2πε ₀ / σ is

to be.

As shown in Fig. 18C, the electric field at a predetermined position when two planar electrodes are arranged in parallel is as follows.

Where L is the distance between the centers of the two electrodes, and electrode spacing s is L-2d.

And, x, y of x _d is an x / d, y _d when replaced by y / d, divided by the electric field between two plane electrodes in 2πε ₀ / σ value is defined as follows:

As such, the electric field at a given position for two parallel planar electrodes depends on the L / d value except for the continuously changing positions (x, y).

In this case, L / d is a value in which both the width 2d of the electrode and the electrode spacing (s = L-2d) are taken into consideration. Even though the value of the electrode width 2d increases, the distance s between the electrodes is increased. It can be seen that increasing the same ratio shows the same electric field effect according to the same position.

As described above, in the characteristic of the transverse electric field structure in which the transmittance between electrodes varies according to electric field strength, the L / d value may serve as a variable for evaluating another degree of light utilization as much as the interval s between the electrodes.

For example, when the distance s between the common electrode 120 and the pixel electrode 150 is 15 μm, the width 2d of the common electrode 120 and the pixel electrode 150 is generally 5 μm. In view of this, the distance L between the centers of the two electrodes 120 and 150 is L = s + 2d = 15 μm + 5 μm = 20 μm, thus L / d = 20 / 2.5 and 8.

As shown in FIG. 16, when the electrode width 2d of the common electrode 120 and the pixel electrode 150 is maintained, and the distance s between the two electrodes is 15 μm or more, the L / d value is The value is 8 or more.

Explaining this as the ratio of the distance s between the electrodes and the electrode width 2d, s / 2d = (L-2d) / 2d is a value of 3 or more.

Thus, in the present invention, the spacing between the electrodes is 15 µm or more, the ratio s / 2d of the distance s between the electrodes and the electrode width 2d is 3 or more, and the initial rubbing direction is in the high rubbing direction. In addition, even though the intensity of the electric field varies depending on a predetermined position between the electrode and the electrode, the tilt degree of the liquid crystal is uniformized to about 45 ° with respect to the polarization axis or the rubbing direction in each section to increase the overall transmittance of the liquid crystal display.

The pixel electrode 150 and the common electrode 120 receive voltages from the drain electrode 140b and the common line 141 of the thin film transistor TFT, respectively, and the pixel electrode 150 and the common electrode 120 respectively. ) Patterns may be spaced apart from each other by the same width in the pixel area to form a single or a plurality of patterns.

The above-described transverse electric field type liquid crystal display of the present invention has the following effects.

Even if the gap between the common electrode and the pixel electrode is increased, the alignment direction with respect to the electrode direction is processed to about 25 ° to 45 ° so that even after voltage is applied, the liquid crystals are uniform in all regions regardless of the electric field difference between the electrode and the electrode formation region. By having a tilt, it is possible to prevent a decrease in transmittance per unit area, thereby improving light efficiency.

Claims (5)

A lower substrate and an upper substrate; A gate line and a data line intersecting each other vertically and horizontally on the lower substrate to define a pixel area; A thin film transistor formed at an intersection of the gate line and the data line; A pixel electrode and a common electrode formed to be spaced apart from the pixel area by a predetermined interval; An alignment layer processed to have a 25 ° to 45 ° alignment direction with respect to the length direction of the pixel electrode and the common electrode; And a liquid crystal layer formed between the upper and lower substrates. The method of claim 1, And a gap between the pixel electrode and the common electrode is 15 μm or more. The method of claim 2, And a distance between the pixel electrode and the common electrode is three times greater than the width of each electrode. The method of claim 1, And the pixel electrode and the common electrode have the same width. The method of claim 1, And the alignment layer is formed on at least one of the upper and lower substrates.