KR20010108844A - Fringe field switching mode lcd device - Google Patents

Abstract

The present invention discloses a fringe field drive liquid crystal display having optimized electro-optical characteristics and screen quality. The present invention discloses an upper and lower substrate facing each other at a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A transparent counter electrode formed inside the lower substrate; A transparent pixel electrode formed inside the lower substrate and forming a fringe field together with the counter electrode to operate most of the liquid crystal molecules; A first horizontal alignment layer disposed on an inner surface of the lower substrate; And a second horizontal alignment layer disposed on an inner surface of the upper substrate, wherein the first and second horizontal alignment layers have a pretilt angle of 0 ° to 10 °.

Description

Fringe field driving liquid crystal display device {FRINGE FIELD SWITCHING MODE LCD DEVICE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fringe field drive liquid crystal display, and more particularly, to a fringe field drive liquid crystal display having optimized electro-optical characteristics and screen quality.

In general, the fringe field driving liquid crystal display has been proposed to improve low aperture and transmittance characteristics of a general IPS mode liquid crystal display, and has been filed with 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).

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.

Although not shown in the drawing, the gate bus lines and the data bus lines are arranged on the lower substrate 1 to define unit pixels, and thin film transistors for active driving are disposed near the intersection points of the gate bus lines and the data bus lines. . 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 form of a comb teeth or a plate. 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 so as to overlap the counter electrode 3. At this time, when the gap 1 between the counter electrode 3 and the pixel electrode 5, that is, the counter electrode 3 is formed in a plate shape, the thickness of the gate insulating film 4 is narrower than the cell gap d. In addition, a horizontal alignment layer 6 is formed on the resultant surface of the lower substrate 1 to control the initial arrangement of 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.

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 horizontal alignment film 14 for controlling the initial arrangement of the liquid crystal molecules is formed. At this time, the horizontal alignment layer 14 of the upper substrate also has a pretilt angle of a predetermined angle, and has a rubbing axis that forms an angle of 180 ° with the rubbing axis of the horizontal alignment layer 6 of the lower substrate.

A fringe field drive liquid crystal display device 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, the width of the counter electrode 3 opened through the space between the pixel electrode 5 and the pixel electrode 5 is sufficiently fine, so that the fringe field extends over both the counter electrode 11 and the pixel electrode 13. Thus, the liquid crystal molecules in the unit pixel are mostly operated. Accordingly, the transmittance and the aperture ratio are improved.

As the horizontal alignment layer applied to the conventional fringe field driving liquid crystal display described above, a horizontal alignment layer applied to the conventional TN mode or a horizontal alignment layer applied to the IPS mode is selectively used.

At this time, the horizontal alignment layer of the TN mode has a high pretilt angle, preferably a high pretilt angle of 10 ° or more, for quick operation of the liquid crystal molecules. On the other hand, since the liquid crystal molecules are operated by the transverse electric field, the horizontal alignment layer in the IPS mode has a relatively low pretilt angle of about 2 ° or less.

Since the pretilt angles are different even in the horizontal alignment film as described above, the electro-optical characteristics and the screen quality of the fringe field driving liquid crystal display are changed depending on how much of the horizontal alignment film having the pretilt angle is applied.

In addition, the conditions of the dielectric anisotropy of the liquid crystal molecules also change the electro-optical properties and the screen quality.

Accordingly, an object of the present invention is to provide a fringe field drive liquid crystal display device having optimized electro-optical characteristics and screen quality.

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

2A is a graph of transmittance according to voltage when a liquid crystal having a dielectric constant anisotropy is used and the pretilt angle is changed.

2B is a graph of transmittance according to voltage when a liquid crystal having a positive dielectric anisotropy is used and the pretilt angle is changed.

3A is a graph of transmittance according to response time when a negative liquid crystal is used and the pretilt angle is changed.

3B is a graph of transmittance according to response time when a positive liquid crystal is used and the pretilt angle is changed.

4A to 4D are graphs of brightness versus viewing angle when using negative liquid crystals.

5a to 5d are graphs of brightness versus viewing angle when using positive liquid crystals;

6A and 6B are graphs showing up, down, left and right viewing angles when using a negative liquid crystal.

7A and 7B are graphs showing up, down, left and right viewing angles when using a positive liquid crystal.

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

1: lower substrate 3: counter electrode

4: gate insulating film 5: pixel electrode

6,14 horizontal alignment layer 10 upper substrate

12: color filter

In order to achieve the above object of the present invention, the present invention comprises a top and bottom substrate facing each other at a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A transparent counter electrode formed inside the lower substrate; A transparent pixel electrode formed inside the lower substrate and forming a fringe field together with the counter electrode to operate most of the liquid crystal molecules; A first horizontal alignment layer disposed on an inner surface of the lower substrate; And a second horizontal alignment layer disposed on an inner surface of the upper substrate, wherein the first and second horizontal alignment layers have a pretilt angle of 0 ° to 10 °.

In addition, the present invention is the upper and lower substrate facing each other at a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A transparent counter electrode formed inside the lower substrate; A transparent pixel electrode formed inside the lower substrate and forming a fringe field together with the counter electrode to operate most of the liquid crystal molecules; A first horizontal alignment layer disposed on an inner surface of the lower substrate; And a second horizontal alignment layer disposed on an inner surface of the upper substrate, wherein the liquid crystal layer has negative dielectric anisotropy, and the first and second horizontal alignment layers have a pretilt angle within 0 ° to 10 °. It features.

(Example)

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

2A is a graph of transmittance according to voltage when a liquid crystal having a negative dielectric anisotropy is used and the pretilt angle is changed, and FIG. 2B is a liquid crystal having a positive dielectric anisotropy, when the pretilt angle is changed. It is a graph of transmittance according to voltage. 3A is a graph of transmittance according to response time when a negative liquid crystal is used and the pretilt angle is changed, and FIG. 3B is a response to response time when the pretilt angle is changed using a positive liquid crystal. Permeability graph. 4A to 4D show brightness graphs according to viewing angles when using negative liquid crystals, and FIGS. 5A to 5D show brightness graphs according to viewing angles when using positive liquid crystals. 6A and 6B are graphs showing up, down, left and right viewing angles when using negative liquid crystals, and FIGS. 7A and 7B are graphs showing up, down, left and right viewing angles when using positive liquid crystals.

As described below, in order to obtain a fringe field driving liquid crystal display having optimized electro-optical characteristics and screen quality, various experiments were conducted as follows.

(Relationship between Transmittance to Voltage in Dielectric Constant Anisotropy of Liquid Crystal and Pretilt Angle of Alignment Film)

First, FIG. 2A illustrates a liquid crystal having a negative dielectric anisotropy (hereinafter, referred to as a negative liquid crystal), and a graph of transmittance according to voltage when the pretilt angle is changed. FIG. It is a graph of the transmittance according to voltage when the pretilt angle is used. At this time, the pretilt angle θp of the alignment layer was changed to 0 °, 2 °, 4 °, 6 °, 10 °, and 20 °, and the x-axis of the graph represents the voltage applied to the pixel electrode. , the y-axis represents the transmittance of the liquid crystal display.

According to FIG. 2A, when a negative liquid crystal is used as the liquid crystal layer and the pretilt angle θp is changed to 0 °, 2 °, 4 °, 6 °, and 10 °, almost similar transmittance is shown. For example, when about 4V is applied, transmittance of about 0.3% is shown. On the other hand, when the pretilt angle θp was set to 20 °, relatively low transmittance of 0.27% was observed at the same voltage band.

Also, as in FIG. 2B, when the positive liquid crystal is used and the pretilt angle θp is changed to 0 °, 2 °, 4 °, 6 °, and 10 °, the same as when the negative liquid crystal is used. The transmittances are similar to each other, and when about 4V is applied, the transmittance is about 0.27%. On the other hand, when the pretilt angle θp was set to 20 °, the transmittance was very low (about 0.12%).

Comparing these two graphs, a degree of pretilt angle of 0 ° to 10 ° shows good transmittance in both the positive liquid crystal and the negative liquid crystal layer, and is particularly advantageous in terms of transmittance when using a negative liquid crystal.

(Relationship between Transmittance to Voltage when the Liquid Crystal Dielectric Anisotropy and the Pretilt Angle of the Alignment Film Change)

First, FIG. 3A is a graph of transmittance according to response time when a negative liquid crystal is used and the pretilt angle is changed, and FIG. 3B is a response of response time when the pretilt angle is changed using a positive liquid crystal. Permeability graph. In this case, the pretilt angle θp of the alignment layer was also changed to 0 °, 2 °, 4 °, 6 °, 10 °, and 20 °, and the x-axis of the graph represents the response time, and y The axis represents the transmittance of the liquid crystal display.

According to FIG. 3A, when a negative liquid crystal is used as the liquid crystal layer and the pretilt angle θp is 0 °, 2 °, 4 °, 6 °, 10 °, and 20 °, the respective 90% rise time times) are 23.6 ms, 23.6 ms, 23.7 ms, 23.8 ms, 24.1 ms, and 25.4 ms. Meanwhile, the 90% decay time is 60.3 ms, 60.3 ms, 60.4 ms, 59.5 ms, 58.1 ms, and 51.4 ms at the respective pretilt angle conditions. In addition, when the pretilt angle θp is 0 °, 2 °, 4 °, 6 °, and 10 °, the transmittance is about 44% in the settling time region, whereas the pretilt angle θp is At this 20 °, the settling time zone has only 42% transmission. Therefore, in the case of a negative liquid crystal, when the pretilt angle θp is 0 °, 2 °, 4 °, 6 °, and 10 °, the pretilt angle θp is better than the case where the pretilt angle θp is 20 °, The rising time is faster the smaller the pretilt angle, and the decay time is faster the larger the pretilt angle.

On the other hand, when a positive liquid crystal is used as the liquid crystal layer and the pretilt angles θp are 0 °, 2 °, 4 °, 6 °, 10 °, and 20 °, each of the 90 is shown in FIG. 3B. The% rising time is 43.9ms, 44.3ms, 46.2ms, 45.7ms, 45,1ms, 42.9ms. Meanwhile, the 90% decay time is 56.1 ms, 55.5 ms, 55.6 ms, 54.4 ms, 52.4 ms, and 45.7 ms at the respective pretilt angle conditions. In addition, when the pretilt angle θp is 0 °, 2 °, 4 °, 6 °, and 10 °, the transmittance is about 35% in the settling time region, whereas the pretilt angle θp is At 20 °, the transmission in the settling time zone is only 30%. Therefore, in the case of a positive liquid crystal, when the pretilt angle θp is 0 °, 2 °, 4 °, 6 °, and 10 °, the pretilt angle θp is superior in the transmission plane than when the angle is 20 °, Rising time and decay time are advantageous as the pretilt angle is smaller.

In addition, when comparing negative liquid crystal and positive liquid crystal, negative liquid crystal is advantageous in terms of transmittance and rising time, but positive liquid crystal is advantageous in decay time.

(Comparison of Brightness Uniformity for Viewing Angle with Varying Dielectric Constant Anisotropy of Liquid Crystal)

4A to 4D show graphs of brightness according to a viewing angle when using a negative liquid crystal, FIG. 4A shows a pretilt angle of 0 °, FIG. 4B shows a pretilt angle of 6 °, and FIG. 4C shows a pretilt angle of 10 °, 4D is a case where the pretilt angle is 20 °. Meanwhile, FIGS. 5A to 5D show graphs of brightness according to viewing angles when using positive liquid crystals. FIG. 5A shows a pretilt angle of 0 °, FIG. 5B shows a pretilt angle of 6 °, and FIG. 5C shows a pretilt angle of 10. FIG. 5D illustrates a case where the pretilt angle is 20 degrees.

As shown in FIGS. 4A to 4D, when the negative liquid crystal is used, the pretilt angle shows even characteristics at most viewing angles up to 10 °, while the pretilt angle is one quadrant, that is, 45 ° direction at 20 °. The uniformity at is not good.

In addition, as shown in FIGS. 5A to 5D, even when a positive liquid crystal is used, uniformity is exhibited at most viewing angles up to 10 °, whereas uniformity is obtained when the pretilt angle is 20 °. Is not excellent.

Accordingly, it can be seen that the positive or negative liquid crystals are almost the same in terms of uniformity, and the pretilt angle is superior to 10 degrees or less.

(Relationship between vertical and horizontal viewing angles when the dielectric anisotropy of the liquid crystal and the pretilt angle of the alignment film are changed)

6A and 6B are graphs showing up, down, left and right viewing angles when using negative liquid crystals, and FIGS. 7A and 7B are graphs showing up, down, left and right viewing angles when using positive liquid crystals. Here, the x-axis of the figure represents the polar angle (y-axis), the y-axis represents the transmittance (transmittance).

6A and 6B, when the negative liquid crystal is used, in the range of the pretilt angle of 10 degrees or less, the upper and lower, left and right viewing angles are relatively symmetrical, while when the pretilt angle is 20 °, both the upper, lower, and left and right viewing angles are Asymmetrical and very low transmittance.

Meanwhile, according to FIGS. 7A and 7B, when the positive liquid crystal is used, the upper and lower, left and right viewing angles are relatively symmetrical in the range of pretilt angles of 10 degrees or less, whereas the upper and lower viewing angles are shown when the pretilt angle is 20 °. All are asymmetrical and very low in transmittance.

As described above, the pretilt angle is excellent at the viewing angle in terms of 10 degrees or less, while the viewing angle difference is slightly generated at higher values.

According to the above experimental results, the fringe field liquid crystal display device was excellent in terms of transmittance, response speed, uniformity, and up, down, left and right viewing angles when the pretilt angle of the alignment layer was in the range of 0 ° to 10 °. In addition, the use of a negative liquid crystal was superior to the case of using a positive liquid crystal in terms of transmittance and rising time.

Therefore, in order to obtain optimized transmittance, response speed, uniformity, and up, down, left and right viewing angles, the pretilt angle is in the range of 0 ° to 10 °, more preferably in the range of 0 ° to 6 ° while using negative liquid crystals.

As described in detail above, according to the present invention, in the liquid crystal display device driven by the fringe field, a liquid crystal having a negative dielectric anisotropy is used as the liquid crystal layer, and the pretilt angle of the vertical alignment film is 0 ° to 10 °. Within Accordingly, an optimized transmittance, response speed, uniformity, and up, down, left and right viewing angles can be obtained.

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

Claims (5)

Upper and lower substrates facing each other at a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A transparent counter electrode formed inside the lower substrate; A transparent pixel electrode formed inside the lower substrate and forming a fringe field together with the counter electrode to operate most of the liquid crystal molecules; A first horizontal alignment layer disposed on an inner surface of the lower substrate; And A second horizontal alignment layer disposed on an inner surface of the upper substrate; The first and second horizontal alignment layers have a pretilt angle of 0 ° to 10 °. The fringe field driving liquid crystal display device according to claim 1, wherein the liquid crystal layer has negative dielectric anisotropy. The fringe field driving liquid crystal display of claim 1, wherein the first and second horizontal alignment layers have a pretilt angle of 0 ° to 6 °. Upper and lower substrates facing each other at a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates and including several liquid crystal molecules; A transparent counter electrode formed inside the lower substrate; A transparent pixel electrode formed inside the lower substrate and forming a fringe field together with the counter electrode to operate most of the liquid crystal molecules; A first horizontal alignment layer disposed on an inner surface of the lower substrate; And A second horizontal alignment layer disposed on an inner surface of the upper substrate; The liquid crystal layer is negative dielectric anisotropy, The first and second horizontal alignment layers have a pretilt angle of 0 ° to 10 °. The fringe field driving liquid crystal display device of claim 4, wherein the first and second horizontal alignment layers have a pretilt angle of 0 ° to 6 °.