KR20020043943A - Fringe field swiching mode lcd - Google Patents

Abstract

PURPOSE: A fringe field switching mode liquid crystal display is provided to remove color shift and to eliminate black smear. CONSTITUTION: An upper substrate and a lower substrate(20) are arranged having a predetermined distance between the two substrates. Gate bus lines(21) and data bus lines(23) are formed on the lower substrate and arranged in matrix form to define pixel regions. A thin film transistor(TFT) is placed at each of the intersections of the gate bus lines and the data bus lines. A liquid crystal layer including liquid crystal molecules is interposed between the upper and lower substrates. A counter electrode(25) is formed at each pixel of the lower substrate. A pixel electrode(27) forms a fringe field together with the counter electrode. The first horizontal alignment film is formed on the inner side of the lower substrate and has the rubbing axis at 45 degrees to the gate bus lines. The second horizontal alignment film is formed on the inner side of the upper substrate and has the rubbing axis that is not parallel with the rubbing axis of the first horizontal alignment film. A polarizer having a predetermined polarizing axis is formed on the outer side of the lower substrate. A decomposer having an absorption axis perpendicular to the polarizing axis is formed on the outer side of the upper substrate.

Description

Fringe field drive mode liquid crystal display device {FRINGE FIELD SWICHING MODE LCD}

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a fringe field switching liquid crystal display (FFS-LCD), and more particularly to an FFS-LCD capable of preventing color shift and black line unevenness.

In general, FFS-LCD has been proposed to improve the low aperture ratio and transmittance of the general in-plane switching (IPS) mode LCD, which has been filed in Korean Patent Application No. 98-9243.

1 is a plan view showing a lower substrate structure of an FFS-LCD.

Referring to FIG. 1, the gate bus line 3 and the data bus line 7 are cross-arranged on the lower substrate 1 to define a unit pixel Pix. In the thin film transistor TFT, the thin film transistor TFT is disposed near an intersection point of the gate bus line 3 and the data bus line 7. The counter electrode 2 is formed of a transparent conductor and is formed for each unit pixel pix. In this case, the counter electrode 2 may be formed in the shape of a square plate or in the form of a comb. The common signal line 30 is disposed in contact with the counter electrode 2 in order to continuously supply the common signal to the counter electrode 2. In this case, the common signal line 30 is formed of a metal film having excellent signal transmission characteristics, and is generally formed of a metal film for a gate bus line. In addition, the common signal line 30 includes a first portion 30a parallel to the gate bus line 3 and in contact with a predetermined portion of the counter electrode 2, and the data bus line 7 from the first portion 30a. And a second portion 30b extending in parallel with each other and disposed between the counter electrode 2 and the data bus line 7, respectively. The pixel electrode 9 is formed in the unit pixel pix so as to overlap with the counter electrode 2. At this time, the pixel electrode 9 and the counter electrode 2 are electrically insulated. The pixel electrode 9 is formed in a comb shape, and connects a plurality of comb portions 9a formed at equal intervals in parallel with the data bus line 7 and one end of the comb portion 9a of the thin film transistor TFT. And a bar 9b in contact with the predetermined portion. On the other hand, although not shown in the figure, the upper substrate facing the lower substrate 1 is opposed and replaced with a width greater than the distance between the pixel electrode 9 and the counter electrode 5, the lower substrate 1 and the upper substrate In between, a liquid crystal layer containing several liquid crystal molecules is interposed. In addition, a horizontal alignment layer is disposed on the inner surface of the lower substrate 1 and the inner surface of the upper substrate (not shown). Among them, the horizontal alignment layer of the lower substrate has a rubbing axis that forms 12 ° with the projection line (ie, the gate bus line) of the fringe field in order to obtain the maximum transmittance when using liquid crystal molecules having a negative dielectric anisotropy, for example. The horizontal alignment film of has a rubbing axis that is in parallel with the rubbing axis of the horizontal alignment film of the lower substrate.

The FFS-LCD having such a configuration operates as follows.

When an electric field is formed between the counter electrode 5 and the pixel electrode 9, the distance between the counter electrode 5 and the pixel electrode 9, that is, the distance between the upper and lower substrates is larger than the thickness of the gate insulating film, so that the two electrodes are larger. Fringe fields are formed between and over the electrodes. This fringe field extends over the counter electrode 5 and the pixel electrode 9 so that all of the liquid crystal molecules on the electrode are operated. Thereby, a high opening rate and a high transmittance can be realized.

However, in the above-described FFS-LCD, most liquid crystal molecules in the unit pixel were operated to achieve high opening ratio and high transmittance. However, when a field is formed between the counter electrode and the pixel electrode, the liquid crystal molecules having refractive index anisotropy operate simultaneously in the same direction, so that the polar angle is near 0 ° and the azimuth is near 0 °, 90 °, 180 °, and 270 °. In spite of the condition, a certain color appears. This phenomenon is called color shift, and the color shift is explained in more detail by the following equation (1).

T ≒ T ₀ sin2 (2χ) · sin2 (π · Δnd / λ) .............. (Equation 1)

T: transmittance

T ₀ : Transmittance for reference light

χ: angle formed between the optical axis of the liquid crystal molecules and the polarization axis of the polarizer

Δn: refractive index anisotropy

d: distance or gap between the upper and lower substrates (thickness of the liquid crystal layer)

λ: incident light wavelength

According to Equation 1, in order to obtain the maximum transmittance T, χ should be π / 4 or Δnd / λ should be π / 2. At this time, when Δnd is changed (because the refractive index anisotropy value of the liquid crystal molecules changes depending on the viewing direction), the λ value is changed to satisfy π / 2. Accordingly, the color corresponding to the changed light wavelength [lambda] is displayed on the screen.

Therefore, in the? Direction in the figure, as? N is relatively reduced, the wavelength of incident light for reaching the maximum transmittance is relatively shortened. Accordingly, the user sees blue having a wavelength shorter than that of white.

On the other hand, in the beta direction of the figure, as Δn is relatively increased, the wavelength of the incident light becomes relatively long. Accordingly, the user sees yellow with a wavelength longer than that of white. For this reason, the image quality characteristic of a white state falls.

Also, as shown in FIG. 2, the black line unevenness of the FFS-LCD generally decreases as the angle between the projection line of the fringe field and the rubbing axis (hereinafter referred to as the rubbing angle) approaches 45 °. However, in the conventional FFS-LCD described above, when a liquid crystal having a negative dielectric anisotropy is used, the rubbing angle is 12 °, and black line unevenness is inevitably generated.

Accordingly, it is an object of the present invention to provide an FFS-LCD capable of removing black spots while at the same time removing color shift.

1 is a plan view showing a conventional fringe field drive mode liquid crystal display device.

2 is a graph showing the degree of black line staining according to the rubbing angle of the FFS-LCD.

3 is a plan view of an FFS-LCD in accordance with an embodiment of the present invention.

4 is a graph showing the transmittance according to the rubbing angle.

5 is a plan view of an FFS-LCD according to another embodiment of the present invention;

Explanation of symbols on main parts of drawing

20-lower substrate 25-counter electrode

27,270-pixel electrode

In order to achieve the above object of the present invention, the present invention, the upper and lower substrates disposed at a predetermined distance; A gate bus line and a data bus line formed on the lower substrate and disposed in a matrix to define unit pixels; A thin film transistor disposed at each intersection of the gate bus line and the data bus line; A liquid crystal layer comprising several liquid crystal molecules interposed between the upper and lower substrates; A counter electrode formed on each unit pixel of the lower substrate; A pixel electrode forming a fringe field together with the counter electrode and including several comb teeth; A first horizontal alignment layer formed on an inner surface of the lower substrate and having a rubbing axis formed at 45 ° with the gate bus line; A second horizontal alignment layer formed on an inner surface of the upper substrate and having a rubbing axis that is non-parallel to a rubbing axis of the first horizontal alignment layer; A polarizer formed on an outer surface of the lower substrate and having a predetermined polarization axis; And a decomposer formed on an outer surface of the upper substrate and having an absorption axis perpendicular to the polarization axis, wherein the comb teeth of the pixel electrode form 45 + α ° with a gate bus line in the selected unit pixel. And 45-α degrees with the gate bus line in upper, lower, left, and right unit pixels.

In addition, according to another embodiment of the present invention, the upper and lower substrates disposed at a predetermined distance; A gate bus line and a data bus line formed on the lower substrate and disposed in a matrix to define unit pixels; A thin film transistor disposed at each intersection of the gate bus line and the data bus line; A liquid crystal layer comprising several liquid crystal molecules interposed between the upper and lower substrates; A counter electrode formed on each unit pixel of the lower substrate; A pixel electrode forming a fringe field together with the counter electrode and including several comb teeth; A first horizontal alignment layer formed on an inner surface of the lower substrate and having a rubbing axis forming −45 ° with the gate bus line; A second horizontal alignment layer formed on an inner surface of the upper substrate and having a rubbing axis that is non-parallel to a rubbing axis of the first horizontal alignment layer; A polarizer formed on an outer surface of the lower substrate and having a predetermined polarization axis; And a decomposer formed on an outer surface of the upper substrate and having an absorption axis perpendicular to the polarization axis, wherein the comb teeth of the pixel electrode form a-(45 + α °) with the gate bus line in the selected unit pixel. The unit bus may be connected to the gate bus line at − (45−α °) within the selected unit pixel.

In addition, the upper and lower substrates disposed at a predetermined distance; A gate bus line and a data bus line formed on the lower substrate and disposed in a matrix to define unit pixels; A thin film transistor disposed at each intersection of the gate bus line and the data bus line; A liquid crystal layer comprising several liquid crystal molecules interposed between the upper and lower substrates; A counter electrode formed on each unit pixel of the lower substrate; A pixel electrode forming a fringe field together with the counter electrode and including several comb teeth; A first horizontal alignment layer formed on an inner surface of the lower substrate and having a rubbing axis formed at 45 ° with the gate bus line; A second horizontal alignment layer formed on an inner surface of the upper substrate and having a rubbing axis that is non-parallel to a rubbing axis of the first horizontal alignment layer; A polarizer formed on an outer surface of the lower substrate and having a predetermined polarization axis; And a decomposer formed on an outer surface of the upper substrate, the decomposer having an absorption axis perpendicular to the polarization axis, wherein a part of the comb teeth of the pixel electrode disposed in the unit pixel form 45 + α ° with a gate bus line. The remaining portion of the comb teeth of the pixel electrode arranged in the pixel is characterized by forming a 45-? Degree with the gate bus line.

(Example)

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Figure 3 is a plan view of the FFS-LCD according to an embodiment of the present invention, Figure 4 is a graph showing the transmittance according to the rubbing angle, Figure 5 is a plan view of the FFS-LCD according to another embodiment of the present invention to be.

Referring to FIG. 3, a plurality of gate bus lines 21 and data bus lines 23 are intersected on the lower substrate 20 to define a unit pixel in a matrix form. The thin film transistor TFT as a switching element is disposed near the intersection of the gate bus line 21 and the data bus line 23.

The counter electrode 25 is arranged in a plate form in each unit pixel. In this case, the counter electrode 25 is formed of a transparent conductive material, for example, an indium tin oxide (ITO) material, and is spaced apart from the gate bus line 21 and the data bus line 23 defining a unit pixel by a predetermined distance. .

The common signal line 25a is in contact with the counter electrode 25 to transmit a common signal to the counter electrode 25. At this time, the common signal line 25a extends in parallel with the gate bus line 21.

The pixel electrode 27 is formed to overlap the counter electrode 25 in each unit pixel. Like the counter electrode 25, the pixel electrode 27 is formed of a transparent conductive material, and a predetermined portion is in contact with the thin film transistor TFT. In this case, the pixel electrode 27 is formed in a comb shape having a plurality of comb teeth, and these comb teeth extend in a diagonal shape to form a predetermined angle with respect to the gate bus line 21 or the common electrode line. In addition, the comb teeth 27-1 (hereinafter referred to as the first comb teeth) formed in any one selected unit pixel are formed to form 45 + α degrees with the gate bus line 21 and in other unit pixels adjacent to the selected unit pixel. The formed comb 27-2 (hereinafter referred to as the second comb) is formed to form a 45-? Degree with the gate bus line 21, and this rule is equally applied to several unit pixels. Here, FIG. 4 is a graph showing the transmittance according to the change of the rubbing angle (the angle formed between the projection line of the fringe field and the rubbing axis) in the FFS-LCD, and the drawing shows the rubbing angle Rd of 12 °, 25 °, and 30 ° The transmittance was measured when each changed to. According to the present experiment, the maximum transmittance was shown at a voltage of 2.5 to 5.5V when the rubbing angle Rd was 12 ° in the FFS-LCD. Based on this, the first comb 27-1 forms 57 ° (45 + 12 °) with the gate bus line 21 so that the maximum transmittance can be obtained, and the second comb 27-2 forms the gate bus. 33 ° (45-12 °) with line 21. In addition, the plurality of comb teeth 27-1 and 27-2 formed in each unit pixel are arranged to be spaced at equal intervals, and the data at the time of switching the thin film transistor TFT to each comb 27-1 or 27-2. The ends are partially connected so that all the signals of the bus line 23 can be transmitted. Here, the connection of the ends can be changed in various forms.

The first horizontal alignment layer (not shown) is covered on the result of the lower substrate 20. This first horizontal alignment film has a pretilt angle of 10 ° or less and has a predetermined rubbing axis R. As shown in FIG. Here, the rubbing axis R of the first horizontal alignment layer is 45 ° with respect to the gate bus line 21 regardless of the unit pixel.

On the other hand, the upper substrate (not shown) is opposed to the above-described lower substrate 20 at a predetermined distance. Here, a color filter (not shown) for realizing colorization is disposed on the inner surface of the upper substrate, and a second horizontal alignment film (not shown) is formed on the surface of the color filter. Here, the second horizontal alignment layer has a rubbing axis that is not parallel to the rubbing axis R of the first horizontal alignment layer.

A liquid crystal layer (not shown) is interposed between the upper substrate and the lower substrate 20. Here, the liquid crystal layer is composed of several liquid crystal molecules 100a and 100b. In addition, the phase retardation dΔn of the liquid crystal layer is set to satisfy 0.2 to 0.4 μm in consideration of transmittance.

The polarizer (not shown) is disposed on the outer surface of the lower substrate 20 and has a polarization axis coincident with the rubbing axis R to be driven in the normally black mode. On the other hand, an optically related decomposer (not shown) is disposed on the outer surface of the upper substrate and has an absorption axis orthogonal to the polarization axis.

This FFS-LCD of the present invention operates as follows.

First, if no voltage difference is generated between the counter electrode 25 and the pixel electrode 27, the liquid crystal molecules 100a and 100b are arranged such that their long axes coincide with the rubbing axis R. As shown in FIG.

Thereafter, when a voltage difference is generated between the counter electrode 25 and the second pixel electrode 27, a fringe field is formed in each unit pixel. At this time, in the selected unit pixel, a fringe field E1 having a normal shape is formed on the first comb 27-1 by the first comb 27-1 and the counter electrode 25. On the other hand, in another unit pixel adjacent to the selected unit pixel, a fringe field E2 having a normal form is formed on the second comb 27-2 by the second comb 27-2 and the counter electrode 25. . That is, the fringe fields E1 and E2 symmetrical with respect to the rubbing axis are generated in the selected unit pixel and other adjacent unit pixels. Accordingly, the liquid crystal molecules 100a in the selected unit pixel are twisted in the clockwise direction, and the liquid crystal molecules 100b in another unit pixel adjacent thereto are twisted in the counterclockwise direction.

Accordingly, when the field is applied, the liquid crystal molecules 100a and 100b are symmetrically twisted for each unit pixel to compensate for the refractive anisotropy of the liquid crystal molecules, thereby reducing the color shift problem.

Furthermore, the rubbing axis R is rubbed to form 45 ° with the gate bus line 21, so that the problem of black line staining is improved.

This invention is not limited only to the above-mentioned embodiment.

In this embodiment, fringe fields symmetrical with respect to the rubbing axis are formed for each unit pixel. However, as shown in FIG. 4, the same effect can be obtained when the fringe field symmetrical to the rubbing axis is formed in the unit pixel. That is, the arrangement of the gate bus line 21, the data bus line 23, the thin film transistor TFT, and the counter electrode 25 are the same, and the pixel electrode 270 is formed on a portion of the unit pixel and the gate bus First comb teeth 270-1 forming 45 + α degrees with the line 21, and second combs 270-2 formed in the remaining portion of the unit pixel and forming 45-α degrees with the gate bus line 21; It is formed to include). In this way, the fringe fields in two directions symmetrical with respect to the rubbing axis are formed in the unit pixel, thereby improving color shift and black line unevenness.

Further, in the present embodiments, the comb teeth of the pixel electrodes are configured to form 45 + α degrees and 45-α degrees with respect to the gate bus lines 21, but the rubbing axis forms -45 degrees with the gate bus lines, and the comb teeth of the pixel electrodes are formed. The same effect can be obtained when the gate bus line is configured to form-(45 + α °) and-(45-α °).

As described in detail above, according to the present invention, in the FFS-LCD, the rubbing axis forms 45 ° with the gate bus line, and when the field is applied, fringe fields in two directions symmetrical with respect to the rubbing axis are formed, thereby providing color shift. And black line staining is prevented.

Thus, the image quality characteristic of the FFS-LCD is improved.

In addition, this invention can be implemented in various changes within the range which does not deviate from the summary.

Claims (7)

Upper and lower substrates disposed at a predetermined distance; A gate bus line and a data bus line formed on the lower substrate and disposed in a matrix to define unit pixels; A thin film transistor disposed at each intersection of the gate bus line and the data bus line; A liquid crystal layer comprising several liquid crystal molecules interposed between the upper and lower substrates; A counter electrode formed on each unit pixel of the lower substrate; A pixel electrode forming a fringe field together with the counter electrode and including several comb teeth; A first horizontal alignment layer formed on an inner surface of the lower substrate and having a rubbing axis formed at 45 ° with the gate bus line; A second horizontal alignment layer formed on an inner surface of the upper substrate and having a rubbing axis that is non-parallel to a rubbing axis of the first horizontal alignment layer; A polarizer formed on an outer surface of the lower substrate and having a predetermined polarization axis; And A decomposer formed on an outer surface of the upper substrate and having an absorption axis perpendicular to the polarization axis, The comb teeth of the pixel electrode form 45 + α ° with the gate bus line in the selected unit pixel. And a gate bus line having a 45-? Degree angle in upper, lower, left, and right adjacent unit pixels with the selected unit pixel. The FFS-LCD of claim 1, wherein the α ° is 12 °. The FFS-LCD of claim 1, wherein the phase retardation of the liquid crystal layer is 0.2 to 0.4 mu m. Upper and lower substrates disposed at a predetermined distance; A gate bus line and a data bus line formed on the lower substrate and disposed in a matrix to define unit pixels; A thin film transistor disposed at each intersection of the gate bus line and the data bus line; A liquid crystal layer comprising several liquid crystal molecules interposed between the upper and lower substrates; A counter electrode formed on each unit pixel of the lower substrate; A pixel electrode forming a fringe field together with the counter electrode and including several comb teeth; A first horizontal alignment layer formed on an inner surface of the lower substrate and having a rubbing axis forming −45 ° with the gate bus line; A second horizontal alignment layer formed on an inner surface of the upper substrate and having a rubbing axis that is non-parallel to a rubbing axis of the first horizontal alignment layer; A polarizer formed on an outer surface of the lower substrate and having a predetermined polarization axis; And A decomposer formed on an outer surface of the upper substrate and having an absorption axis perpendicular to the polarization axis, The comb teeth of the pixel electrode form-(45 + α) with the gate bus line in the selected unit pixel. And-(45-α) of the gate bus line in the unit pixels vertically and horizontally adjacent to the selected unit pixel. 5. The FFS-LCD of claim 4, wherein the α is 12 degrees. Upper and lower substrates disposed at a predetermined distance; A gate bus line and a data bus line formed on the lower substrate and disposed in a matrix to define unit pixels; A thin film transistor disposed at each intersection of the gate bus line and the data bus line; A liquid crystal layer comprising several liquid crystal molecules interposed between the upper and lower substrates; A counter electrode formed on each unit pixel of the lower substrate; A pixel electrode forming a fringe field together with the counter electrode and including several comb teeth; A first horizontal alignment layer formed on an inner surface of the lower substrate and having a rubbing axis formed at 45 ° with the gate bus line; A second horizontal alignment layer formed on an inner surface of the upper substrate and having a rubbing axis that is non-parallel to a rubbing axis of the first horizontal alignment layer; A polarizer formed on an outer surface of the lower substrate and having a predetermined polarization axis; And A decomposer formed on an outer surface of the upper substrate and having an absorption axis perpendicular to the polarization axis, A part of the comb teeth of the pixel electrode disposed in the unit pixel make 45 + α ° with the gate bus line, And the remaining portion of the comb teeth of the pixel electrode arranged in the unit pixel forms a 45-? Degree with the gate bus line. 7. The FFS-LCD of claim 6, wherein the α is 12 degrees.