KR100658060B1 - Liquid crystal display device - Google Patents

Abstract

The present invention discloses a liquid crystal display device capable of reducing residual DC and preventing afterimages on a screen. The present invention discloses an upper and lower substrate spaced apart from each other by a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates, the liquid crystal layer having several liquid crystal molecules having positive or negative dielectric anisotropy; A counter electrode and a pixel electrode formed on the lower substrate and arranged to form a fringe field for driving liquid crystal molecules in the liquid crystal layer; A positive electrode and a negative electrode formed inside the upper substrate to remove charged impurities remaining in the liquid crystal layer; And upper and lower alignment layers disposed on the resultant surfaces of the upper and lower substrates, respectively, each having a rubbing axis, wherein the positive electrode and the negative electrode are formed of a transparent conductor.

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY DEVICE}

1 is a cross-sectional view of a typical FFS mode liquid crystal display device.

2 is a cross-sectional view of a liquid crystal display according to an exemplary embodiment of the present invention.

3 is a cross-sectional view of a liquid crystal display according to another exemplary embodiment of the present invention.

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

30-lower substrate 32-counter electrode

34-gate insulating film 36-pixel electrode

38-first horizontal alignment layer 40-upper electrode

42-positive electrode 44-negative electrode

46-second horizontal alignment layer 48-transparent electrode

50-liquid crystal layer

The present invention relates to a liquid crystal display device, and more particularly, to a fringe field switching (FFS) mode liquid crystal display device having an electrode for driving liquid crystal molecules on a lower substrate.

In general, an IPS mode liquid crystal display is a mode proposed to improve a narrow viewing angle characteristic of a twisted nematic (TN) mode liquid crystal display, and has a structure in which a counter electrode formed on an upper substrate is disposed on a lower substrate on which a pixel electrode is formed. .

That is, in the conventional TN mode liquid crystal display, an electric field perpendicular to the substrate surface is formed between the counter electrode formed on the upper substrate and the pixel electrode formed on the lower substrate. On the other hand, in the IPS mode liquid crystal display, since the counter electrode and the pixel electrode are disposed on the lower substrate, an electric field parallel to the surface of the substrate is formed. Due to the generation of a parallel electric field parallel to the substrate surface, the liquid crystal molecules are moved with their long axes parallel to the substrate surface, so that the IPS mode liquid crystal display device has a much better viewing angle than the TN mode liquid crystal display device.

However, the IPS mode liquid crystal display device has an advantage of having an excellent viewing angle. However, since the electrodes for driving the liquid crystal molecules are formed of an opaque metal film, the aperture ratio and the transmittance are very low.

Accordingly, in order to improve the low aperture ratio and transmittance of the IPS mode liquid crystal display, a fringe field driving liquid crystal display 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 narrower than the gap between the upper and lower substrates, and the fringe field is formed on the counter electrode and the pixel electrode. field) so that all of the liquid crystal molecules present on the electrodes are operated.

1 is a cross-sectional view of a typical fringe field driving liquid crystal display device.

Referring to FIG. 1, a counter electrode 2 and a gate bus line 4 are formed in a plate shape in each of the unit pixel areas of the transparent lower substrate 1 where the unit pixel areas are limited. The first and second insulating films 5 and 6 and the channel layer 7 which serve as the gate insulating film are sequentially stacked on the lower substrate 1 on which the counter electrode 2 and the gate bus line 4 are formed. In this case, a silicon nitride film (SiON) having excellent insulating properties is used as the first insulating film 5, and a silicon nitride film (SiN) having excellent adhesive properties with the channel layer 7 is used as the second insulating film 6. . In addition, the channel layer 7 and the second insulating film 5 are formed in an active form existing only on a predetermined portion of the gate bus line 4. Source and drain electrodes 9a and 9b are formed on both sides of the channel layer 7 around the gate bus line 4 to form a thin film transistor. Here, a doped amorphous silicon layer 8 as an ohmic layer is disposed between the source and drain electrodes 9a and 9b and the channel layer 7, respectively. The pixel electrode 9 is disposed on the second insulating layer 5 to overlap the counter electrode 2. In this case, the pixel electrode 9 is formed of an ITO layer similarly to the counter electrode, and is formed in a comb-tooth shape, and contacts the drain electrode of the thin film transistor. An alignment layer 10 is formed on the resultant surface of the lower substrate 1 on which the thin film transistor and the pixel electrode 9 are formed.

On the other hand, a color filter (not shown) is formed on the inner surface of the upper substrate 15 to be bonded to the lower substrate 1, and the alignment film 17 is also formed on the color filter surface.

The liquid crystal layer 19 is interposed in the space portion between the lower substrate 1 and the upper substrate 15.

In the fringe field driving liquid crystal display device configured as described above, since the gap and width between the pixel electrode 9 and the counter electrode 2 are sufficiently narrow, a fringe field is formed to form a gap between the electrodes 2, 9 and the electrodes 2,. 9) All the liquid crystal molecules on top are operated.

However, in the conventional IPS mode liquid crystal display device and the FFS mode liquid crystal display device, since no electrode is formed on the upper substrate, afterimages due to the residual DC component are likely to occur.

That is, in more detail, the IPS mode and the FFS mode liquid crystal display device, like the general liquid crystal display device, drive power is an AC component and the drive speed has a response speed of several tens of kHz. However, when driving an fringe field driving liquid crystal display by supplying AC power, the liquid crystal molecules in the liquid crystal layer 19 do not react according to the frequency of the driving voltage but only change in polarity. Accordingly, a direct current generated by the direct current power source is generated between the counter electrode 2 and the pixel electrode 9. To offset this DC current, the voltage of the counter electrode is usually offset. However, even if the offset is made in this manner, since the DC current component cannot be completely removed, a residual DC current (hereinafter, referred to as residual DC) remains between the pixel electrode and the counter electrode, and the residual DC is accumulated over time.

That is, the residual DC is, for example, when one of the counter electrode 2 and the pixel electrode 9 shows a positive charge state, and as time passes, the negative charge of the contaminants in the liquid crystal layer 19 or the like. Particles with ions gather around the electrode, which exhibits a positive charge state, and a parasitic electric field is generated between the electrode and the contaminated particle. At this time, the parasitic electric field is canceled by the external power source. When the external power source is applied in this way, the voltage retention of the liquid crystal layer 19 is lowered, and afterimages occur on the screen.

Accordingly, an object of the present invention is to provide a liquid crystal display device which can prevent an afterimage on a screen by reducing residual DC between the counter electrode and the pixel electrode to easily remove the charged impurities in the liquid crystal layer .

In order to achieve the above object of the present invention, the present invention, the upper and lower substrate spaced at a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates, the liquid crystal layer having several liquid crystal molecules having positive or negative dielectric anisotropy; A counter electrode and a pixel electrode formed on the lower substrate and arranged to form a fringe field for driving liquid crystal molecules in the liquid crystal layer; A positive electrode and a negative electrode formed to be alternately disposed in a stripe shape with a transparent conductor to remove charged impurities remaining in the liquid crystal layer inside the upper substrate; And vertically aligned films disposed on the resultant surfaces of the upper and lower substrates, respectively, each having a rubbing axis.

Here, the extending directions of the positive electrode and the negative electrode are arranged to be perpendicular to the long axis direction of the liquid crystal molecules before the electric field application when the dielectric anisotropy of the liquid crystal molecules is positive, and the short axis direction of the liquid crystal molecules before the electric field application when the dielectric anisotropy is negative. Characterized in that arranged to be parallel.

 According to the present invention, in an FFS mode liquid crystal display device in which no electrode is provided on the upper substrate, an electrode is provided on the inner side or the outer side of the upper substrate to easily remove impurities in the charged liquid crystal layer.

(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 a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 3 is a cross-sectional view of a liquid crystal display according to another exemplary embodiment of the present invention.

First, referring to FIG. 2, the lower substrate 30 and the upper substrate 40 face each other at a predetermined distance. A liquid crystal layer 50 including several liquid crystal molecules (not shown) is interposed between the lower substrate 30 and the upper substrate 40. In this case, the liquid crystal molecules of the liquid crystal layer 50 may have positive or negative dielectric anisotropy.

The counter electrode 32 is arranged in the form of a comb on the lower substrate 30 surface. The gate insulating layer 34 is formed on the lower substrate 30 on which the counter electrode 32 is formed, and the pixel electrode 36 is formed on the gate insulating layer 34 to form the fringe field with the counter electrode 32. The pixel electrode 36 is formed in a comb shape so as to be disposed, for example, between the counter electrodes 32. The first horizontal alignment layer 38 is formed on the surface of the gate insulating layer 34 on which the pixel electrode 36 is formed. The first horizontal alignment layer 38 has a rubbing axis (not shown) that forms a predetermined angle with the fringe field generated between the counter electrode 32 and the pixel electrode 36.

On the other hand, a color filter (not shown) is formed on the inner surface of the upper substrate 40 opposite the lower substrate 30 in a known manner. On the surface of the color filter, the positive electrode 42 and the negative electrode 44 for preventing residual DC are arranged at regular intervals in a stripe form. The positive electrode 42 and the negative electrode 44 extend in parallel with each other and are formed of a transparent conductive material. A second horizontal alignment layer 46 is formed on the surface of the upper substrate 40 on which the positive electrode 42 and the negative electrode 44 are formed. In this case, the second horizontal alignment layer 46 has a rubbing axis that is not parallel to the first horizontal alignment layer 38. Here, the positive electrode 42 and the negative electrode 44 are arranged to be perpendicular to the rubbing axis, that is, the direction of the long axis of the liquid crystal molecules before the electric field application when the dielectric anisotropy of the liquid crystal molecules is positive, and parallel to the rubbing axis when the dielectric anisotropy is negative. It is arranged to achieve, to minimize the electric field distortion.

In the liquid crystal display of the present invention, when the fringe field F is formed between the counter electrode 32 and the pixel electrode 36, the liquid crystal molecules are rearranged in the form of a fringe field. At this time, a positive signal is applied to the positive electrode 42 and a negative signal is applied to the negative electrode 44. Then, impurities that generate residual images remaining in the liquid crystal layer 50 are fixed to the positive electrode 42 and the negative electrode 44 of the upper substrate 40. That is, (+) impurity (A ⁺ ) is fixed to the negative electrode 44, (-) impurity is fixed to the positive electrode 42, the liquid crystal layer 50 and the pixel electrode 36 No impurities remain in the Therefore, the afterimage of the screen can be greatly reduced without supplying an external power supply directly to the liquid crystal layer 50.

In addition, instead of forming the positive electrode 42 and the negative electrode 44 on the inner side of the upper substrate 40, as shown in FIG. 3, the transparent electrode 48 is disposed on the outer side of the upper substrate 40. Since all of the charged impurities in the liquid crystal layer 50 are fixed to the upper substrate side, the same effect can be obtained.

As described in detail above, according to the present invention, in the FFS mode liquid crystal display device in which no electrode is provided on the upper substrate, an electrode is provided on the inner side or the outer side of the upper substrate to facilitate impurities in the charged liquid crystal layer. Remove it.

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

Claims (3)

Upper and lower substrates spaced apart from each other by a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates, the liquid crystal layer having several liquid crystal molecules having positive or negative dielectric anisotropy; A counter electrode and a pixel electrode formed on the lower substrate and arranged to form a fringe field for driving liquid crystal molecules in the liquid crystal layer; A positive electrode and a negative electrode formed to be alternately disposed in a stripe shape with a transparent conductor to remove charged impurities remaining in the liquid crystal layer inside the upper substrate; And And a vertical alignment layer disposed on a resultant surface of the upper and lower substrates, respectively, and having a rubbing axis. delete The method of claim 1, wherein the extending directions of the positive electrode and the negative electrode are arranged so as to be perpendicular to the long axis direction of the liquid crystal molecules before the electric field application when the dielectric anisotropy of the liquid crystal molecules is positive, and when the dielectric anisotropy is negative. And a liquid crystal display arranged in parallel with the short axis direction.

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