KR20020044288A - Fringe field switching mode lcd - Google Patents

Abstract

PURPOSE: A fringe field switching mode liquid crystal display is provided to reduce residual DC by interposing a floating electrode between the teeth of comb of a counter electrode and between the teeth of comb of a pixel electrode. CONSTITUTION: Upper and lower substrates(40,20) face each other, having a predetermined distance between the two substrates, to define a plurality of unit pixels. A liquid crystal layer(50) is interposed between the upper and lower substrates and includes a plurality of liquid crystal molecules. A transparent counter electrode(22) is formed at each unit pixel and has a comb shape having a plurality of teeth. The first floating electrode(23) is formed on the same plane on which the counter electrode is formed, and arranged between the teeth of comb of the counter electrode. A gate insulating layer(25) covers the lower substrate including the counter electrode and the first floating electrode. A transparent pixel electrode(27) is formed on the gate insulating layer, forms a fringe field together with the counter electrode, and has a comb shape having a plurality of teeth. The second floating electrode(44) is formed on the same plane on which the pixel electrode is formed and arranged between the teeth of comb of the pixel electrode.

Description

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

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to fringe field switching mode LCDs (FFS-LCDs) liquid crystal displays, and more particularly, to FFS-LCDs that can reduce residual direct current (DC).

In general, IPS (in-plane switching) LCD has been proposed by Hitachi, Japan, to compensate for the low viewing angle characteristics of twisted nematic (TN) mode LCD. This IPS mode liquid crystal display has the following configuration. The upper and lower substrates face each other at a predetermined distance, and a liquid crystal layer including several liquid crystal molecules is interposed between the upper and lower substrates. The opaque pixel electrode and the counter electrode for driving the liquid crystal molecules are both formed on the lower substrate, for example, and the pixel electrode and the counter electrode are spaced at a larger interval than the gap between the upper and lower substrates so that a parallel electric field is formed. In addition, the pixel electrode and the counter electrode have a relatively large width in order to secure a constant electric field intensity. In addition, a horizontal alignment film is interposed between the upper and lower substrates and the liquid crystal layer, respectively.

The IPS mode liquid crystal display device has an advantage that the viewing angle is excellent because the liquid crystal molecules are arranged in a state lying on the substrate surface, but the transmittance is very low.

In order to improve the low transmittance characteristics of such an IPS mode liquid crystal display device, a conventional FFS-LCD has been proposed by the present applicants, and has been filed in Korean Patent Application No. 98-9243.

In the fringe field driving liquid crystal display, the counter electrode and the pixel electrode are formed of a transparent conductor, and the gap between the counter electrode and the pixel electrode is formed to be smaller than the gap between the upper and lower substrates so that the fringe field is formed on the counter electrode and the pixel electrode. Be sure to

This general fringe field driving liquid crystal display is shown in FIG. 1.

Referring to FIG. 1, the lower substrate 1 and the upper substrate 10 face each other with a predetermined distance d (hereinafter, referred to as a cell gap). Here, the distance between the lower substrate 1 and the upper substrate 10 is referred to as a cell gap d hereinafter. The liquid crystal layer 15 is interposed between the lower substrate 1 and the upper substrate 10. In this case, the liquid crystal layer 15 may include predetermined liquid crystal molecules, and the liquid crystal molecules may have negative or positive dielectric anisotropy.

Although not shown in the figure on the lower substrate 1, the gate bus lines and the data bus lines are arranged in an intersecting manner to define unit pixels, and a thin film transistor for active driving near the intersection point of the gate bus lines and the data bus lines (not shown). Is placed). The counter electrode 3 is formed in the unit pixel of the lower substrate 1. The counter electrode 3 is formed of a transparent indium tin oxide (ITO) layer, and is formed in the shape of a comb teeth. The gate insulating film 4 is formed on the lower substrate 1 on which the counter electrode 3 is formed. The pixel electrode 5 is formed in the shape of a comb on the gate insulating film 4. At this time, the comb teeth of the pixel electrode 5 are arranged to be sandwiched between the comb teeth of the counter electrode 3, respectively. Here, the interval l between the counter electrode 3 and the pixel electrode 5 is formed to be narrower than the cell gap d so that the fringe field can be formed. In addition, a first horizontal alignment layer 6 is formed on the resultant surface of the lower substrate 1 to control the initial arrangement of the liquid crystal molecules. At this time, the horizontal alignment film 6 has a rubbing axis in a predetermined direction and has a predetermined pretilt angle. Here, reference numeral 3a denotes a common electrode line.

Meanwhile, the color filter 12 is formed on the opposite surface of the upper substrate 10 corresponding to the lower substrate 1. Also on the surface of the color filter 12, a second horizontal alignment film 14 for controlling the initial arrangement of the liquid crystal molecules is formed. At this time, the second horizontal alignment layer 14 of the upper substrate 10 also has a pretilt angle of a predetermined angle, and rubbing to form an angle of 180 ° with the rubbing axis of the first horizontal alignment layer 6 of the lower substrate 1. Has an axis.

Further, a polarizer 8 having a predetermined polarization axis is disposed outside the lower substrate 1, and a decomposer 18 having an absorption axis orthogonal to the polarization axis of the polarizer is disposed outside the upper substrate 10.

The FFS-LCD having such a configuration is operated as follows.

When a voltage difference is generated between the counter electrode 3 and the pixel electrode 5, the fringe field is formed because the distance between the counter electrode 3 and the pixel electrode 5 is smaller than the cell gap d. At this time, since the width and spacing of the comb teeth of the counter electrode 3 and the pixel electrode 5 are sufficiently fine, the fringe field extends over both the counter electrode 3 and the pixel electrode 5, and thus the liquid crystal molecules in the unit pixel. Most of them work. Accordingly, the transmittance and the aperture ratio are improved.

However, the following problems exist with conventional FFS-LCDs.

The driving power of a general liquid crystal display device is an alternating current component, and voltages of opposite phases are applied to the counter electrode 3 and the pixel electrode 5 for each frame. That is, as shown in FIG. 1A, in the nth frame, a negative voltage is applied to the counter electrode 3, a positive voltage is applied to the pixel electrode 5, and the field is the pixel electrode 5. Is formed as a counter electrode (3). On the other hand, in the n + 1th frame, a positive voltage is applied to the counter electrode 3, a negative voltage is applied to the pixel electrode 5, and the field is applied to the pixel electrode 5 from the counter electrode 3. Is formed.

However, due to the difference in the reaction rate of the liquid crystal molecules in the liquid crystal layer 15 and the supply speed of the AC power source, the liquid crystal molecules do not react according to the frequency of the driving voltage, but only in polarity. Therefore, a direct current by a direct current power source is generated between the counter electrode 3 and the pixel electrode 5. In order to cancel this DC current, the voltage of the counter electrode is offset. However, this offset also does not completely remove the direct current component, so that the direct current component still remains between the counter electrode and the pixel electrode. In addition, the remaining direct current component accumulates in proportion to time. Accordingly, as time passes, particles having negative charge among contaminants in the liquid crystal layer 15 collect around the residual DC component having a positive charge state. Therefore, a parasitic electric field is generated between the residual DC component and the contaminant of the liquid crystal layer 15, causing an afterimage on the screen.

Accordingly, it is an object of the present invention to provide an FFS-LCD capable of reducing residual DC.

1A and 1B are cross-sectional views of a typical fringe field drive mode liquid crystal display.

2 is a cross-sectional view of an FFS-LCD in accordance with an embodiment of the present invention.

3 is a cross-sectional view of an FFS-LCD according to another embodiment of the present invention.

(Explanation of symbols for the main parts of the drawing)

20-lower substrate 22-counter electrode

22a-common electrode line 23-first floating electrode

25-gate insulating film 27-pixel electrode

28-second floating electrode 29-first horizontal alignment layer

30a-polarizer 30b-decomposer

40-Top Board 42-Color Filter

44-second horizontal alignment layer 50-liquid crystal layer

In order to achieve the above object of the present invention, according to an embodiment of the present invention, the upper and lower substrates facing each other at a predetermined distance, the number of unit pixels is limited; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A transparent counter electrode formed in each unit pixel inside the lower substrate and formed in a comb shape having a plurality of combs; A first floating electrode formed on the same plane as the counter electrode and disposed between comb teeth of the counter electrode; A gate insulating layer covering a lower substrate on which the counter electrode and the first floating electrode are formed; A transparent pixel electrode formed on the gate insulating layer, forming a fringe field together with the counter electrode, and having a comb shape having a plurality of comb teeth; And a second floating electrode formed on the same plane as the pixel electrode and disposed between comb teeth of the pixel electrode.

In addition, according to another embodiment of the present invention, the upper and lower substrates opposed to each other at a predetermined distance and limited to several unit pixels; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A transparent counter electrode formed in each unit pixel inside the lower substrate and formed in a comb shape having a plurality of combs; A first floating electrode formed on the same plane as the counter electrode and disposed between comb teeth of the counter electrode; A gate insulating layer covering a lower substrate on which the counter electrode and the first floating electrode are formed; A transparent pixel electrode formed on the gate insulating layer, forming a fringe field together with the counter electrode, and having a comb shape having a plurality of comb teeth; A second floating electrode formed on the same plane as the pixel electrode and disposed between comb teeth of the pixel electrode; A first horizontal alignment layer interposed between the lower substrate resultant surface and the liquid crystal layer and having a predetermined rubbing axis; A second horizontal alignment layer interposed between the upper substrate and the liquid crystal layer and having a rubbing axis that is non-parallel to the rubbing axis of the first horizontal alignment film; A polarizer attached to an outer surface of the lower substrate and having a polarization axis; And an decomposer attached to an outer surface of the upper substrate and having an absorption axis perpendicular to the polarization axis.

Here, the first floating electrode is formed of the same material as the counter electrode, and the second floating electrode is formed of the same material as the pixel electrode. The first floating electrode may be formed to correspond to the comb teeth of the pixel electrode, and the second floating electrode may be formed to correspond to the comb teeth of the counter electrode. In addition, the first floating electrode and the second floating electrode are electrically connected to each other, or the first floating electrode is connected to the first floating electrode of the adjacent unit pixel, and the second floating electrode of the adjacent unit pixel It may be connected to the second floating electrode.

(Example)

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

2 is a cross-sectional view of the FFS-LCD according to an embodiment of the present invention, Figure 3 is a cross-sectional view of the FFS-LCD according to another embodiment of the present invention.

Referring to FIG. 2, the lower substrate 20 and the upper substrate 40 face each other with a predetermined cell gap d. A liquid crystal layer 50 including several liquid crystal molecules is interposed between the lower substrate 20 and the upper substrate 40.

Although not shown in the figure above the lower substrate 20, the gate bus lines and the data bus lines are cross-arranged to limit unit pixels, and the thin film transistors for active driving may be formed near the intersection points of the gate bus lines and the data bus lines. Not shown).

In the unit pixel of the lower substrate 20, the counter electrode 22 is formed in the shape of a comb including a plurality of combs. At this time, the counter electrode 22 is formed of an ITO layer, which is a transparent conductive layer, and is in electrical contact with the common electrode line 22a. At this time, the comb teeth of the counter electrodes 22 are spaced at equal intervals.

In addition, the first floating electrodes 23 are disposed between the comb teeth of the counter electrodes 22, respectively. In this case, the first floating electrode 23 is preferably formed of the same material in the same plane as the counter electrode 22, and the first floating electrode 23 and the counter electrode 22 are spaced at equal intervals. Here, the width of the first floating electrode 23 can be adjusted appropriately, and preferably has a narrower width than the comb teeth of the counter electrode 22. The first floating electrode 23, as the name suggests, is not electrically connected. The gate insulating layer 25 is formed on the lower substrate 20 on which the counter electrode 22 is formed.

The counter electrode 22 and the pixel electrode 27 causing the fringe field are formed in the shape of a comb including several comb teeth on the gate insulating film 24. At this time, the predetermined portion of the pixel electrode 27 overlaps with the predetermined portion of the counter electrode 22 to form a storage capacitor (not shown), while the comb teeth of the pixel electrode 27 are interposed between the comb teeth of the counter electrode 22. The first floating electrode 23 is disposed to correspond to the first floating electrode 23. In addition, the pixel electrode 27 is appropriately disposed with a transparent conductor as is known so as to cause a fringe field between the counter electrode 22.

The second floating electrode 28 is disposed between the comb teeth of the pixel electrode 27, respectively. In this case, the second floating electrode 28 is also formed of the same transparent material on the same plane as the pixel electrode 27 and is floating. In addition, the second floating electrode 28 may be formed to correspond to the counter electrode 22, and the line width of the second floating electrode 28 may be arbitrarily adjusted, and preferably, the pixel electrode 27 and the counter electrode ( 22) to narrower than the width of the comb teeth.

In addition, as shown in FIG. 3, the second floating electrode 28 is not connected to another conductive line, but may be in contact with the first floating electrode 23 at the lower portion.

Although not shown in the drawings, each of the first floating electrode 23 and the second floating electrode 28 may be connected to the first floating electrode 23 and the second floating electrode 28 of the adjacent unit pixel.

The first horizontal alignment layer 29 is formed on the resultant surface of the lower substrate 20 to control the initial arrangement of the liquid crystal molecules. In this case, the first horizontal alignment layer 29 has a rubbing axis that forms 20 to 60 ° with the substrate projection line of the fringe field to be formed between the counter electrode 22 and the pixel electrode 27 so as to obtain a maximum transmittance.

Meanwhile, the color filter 42 is formed on an opposite surface of the upper substrate 40 corresponding to the lower substrate 20. The second horizontal alignment layer 44 is formed on the surface of the color filter 42. The second horizontal alignment film 44 has a rubbing axis of the first horizontal alignment film 29 at a predetermined angle, for example, 180 °, that is, a non-parallel rubbing axis.

In addition, a polarizer 30a for linearly polarizing light incident from a backlight (not shown) is attached to an outer portion of the lower substrate 20, and an outer portion of the upper substrate 40 passes through the liquid crystal layer 50. Attached is a decomposer 30b that selectively absorbs and passes light. Here, the polarizer 30a has a polarization axis (not shown) that coincides with the rubbing axis of the first horizontal alignment layer 29, and the decomposer 30b has an absorption axis (not shown) orthogonal to the polarization axis.

A fringe field drive liquid crystal display device having such a configuration is operated as follows.

When voltage is applied to the counter electrode 22 and the pixel electrode 27, the floating first and second floating electrodes 23 and 28 are also weakly charged through the gate insulating film 25. Accordingly, a fringe field is formed between the counter electrode 22 and the pixel electrode 27, and at the same time, between the counter electrode 22 and the first floating electrode 23 and the pixel electrode 27 and the second floating electrode 29. Fringe fields are formed between them.

That is, for example, when a positive voltage is applied to the counter electrode 22 and a negative voltage is applied to the pixel electrode, the first floating electrode 23 is affected by the corresponding pixel electrode 27 ( Is charged to the-) state, and the second floating electrode 28 is charged to the (+) state under the influence of the corresponding counter electrode 22.

Accordingly, when the field is applied, (+) and (-) polarities are simultaneously present in the plane where the counter electrode 22 is formed and the plane where the pixel electrode 27 is formed, so that residual DC does not occur when the polarity is changed.

Furthermore, the fringe field is not only between the counter electrode 22 and the pixel electrode 27, but also between the counter electrode 22 and the first floating electrode 23 and between the pixel electrode 27 and the second floating electrode 29. As it is formed, the strength of the field is further enhanced.

As described in detail above, according to the present invention, in a FFS-LCD comprising a comb-shaped counter electrode and a pixel electrode including a plurality of comb teeth, the floating electrode between the comb teeth of the counter electrode and the comb teeth of the pixel electrode. This intervenes. Accordingly, when a field is applied, a predetermined voltage is charged to each floating electrode, so that positive and negative voltage states exist simultaneously in the plane where the counter electrode is formed and the plane where the pixel electrode is formed. Accordingly, the residual DC generated when the polarity is changed is canceled out.

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

Claims (11)

Upper and lower substrates which face each other at a predetermined distance and have several unit pixels defined therein; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A transparent counter electrode formed in each unit pixel inside the lower substrate and formed in a comb shape having a plurality of combs; A first floating electrode formed on the same plane as the counter electrode and disposed between comb teeth of the counter electrode; A gate insulating layer covering a lower substrate on which the counter electrode and the first floating electrode are formed; A transparent pixel electrode formed on the gate insulating layer, forming a fringe field together with the counter electrode, and having a comb shape having a plurality of comb teeth; And And a second floating electrode formed on the same plane as the pixel electrode and disposed between comb teeth of the pixel electrode. The FFS-LCD of claim 1, wherein the first floating electrode is formed of the same material as the counter electrode, and the second floating electrode is formed of the same material as the pixel electrode. The FFS-LCD of claim 1, wherein the first floating electrode is formed to correspond to the comb teeth of the pixel electrode, and the second floating electrode is formed to correspond to the comb teeth of the counter electrode. 4. The FFS-LCD of claim 3, wherein the first floating electrode and the second floating electrode are electrically connected to each other. The FFS-LCD of claim 3, wherein the first floating electrode is connected to a first floating electrode of an adjacent unit pixel, and the second floating electrode is connected to a second floating electrode of an adjacent unit pixel. . Upper and lower substrates which face each other at a predetermined distance and have several unit pixels defined therein; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A transparent counter electrode formed in each unit pixel inside the lower substrate and formed in a comb shape having a plurality of combs; A first floating electrode formed on the same plane as the counter electrode and disposed between comb teeth of the counter electrode; A gate insulating layer covering a lower substrate on which the counter electrode and the first floating electrode are formed; A transparent pixel electrode formed on the gate insulating layer, forming a fringe field together with the counter electrode, and having a comb shape having a plurality of comb teeth; A second floating electrode formed on the same plane as the pixel electrode and disposed between comb teeth of the pixel electrode; A first horizontal alignment layer interposed between the lower substrate resultant surface and the liquid crystal layer and having a predetermined rubbing axis; A second horizontal alignment layer interposed between the upper substrate and the liquid crystal layer and having a rubbing axis that is non-parallel to the rubbing axis of the first horizontal alignment film; A polarizer attached to an outer surface of the lower substrate and having a polarization axis; And And a decomposer attached to an outer surface of the upper substrate and having an absorption axis perpendicular to the polarization axis. 7. The FFS-LCD according to claim 6, wherein the rubbing axis of the first horizontal alignment layer is in a range of 20 to 60 degrees with the substrate projection line of the fringe field formed between the counter electrode and the pixel electrode. The FFS-LCD of claim 6, wherein the first floating electrode is formed of the same material as the counter electrode, and the second floating electrode is formed of the same material as the pixel electrode. The FFS-LCD of claim 6, wherein the first floating electrode is formed to correspond to the comb teeth of the pixel electrode, and the second floating electrode is formed to correspond to the comb teeth of the counter electrode. 10. The FFS-LCD of claim 9, wherein the first floating electrode and the second floating electrode are electrically connected to each other. 10. The FFS-LCD of claim 9, wherein the first floating electrode is connected to a first floating electrode of an adjacent unit pixel, and the second floating electrode is connected to a second floating electrode of an adjacent unit pixel. .