KR20000040118A - Vertical alignment mode liquid crystal display device - Google Patents

Abstract

PURPOSE: A vertical alignment mode liquid crystal display device is provided to make a stable disclination line. CONSTITUTION: A vertical alignment mode liquid crystal display device includes upper and lower substrates(20,10), a liquid crystal layer, a gate bus line and a data bus line(12), a pixel electrode(14), a first vertical alignment layer(16), a common electrode(21), and a second vertical alignment layer(22). The upper and lower substrates(20,10) are facing each other with a predetermined spacing. The liquid crystal layer is applied between the substrates and includes liquid crystal molecules with negative dielectric anisotropy characteristic. The gate bus line and a data bus line(12) are arranged so as to confine a unit pixel of matrix form. The pixel electrode(14) is allocated on each unit pixel. The first vertical alignment layer(16) is implemented on the surface of the lower substrate. The common electrode(21) is arranged on the inner surface of the upper substrate, and includes an aperture in the center of the unit pixel. The second vertical alignment layer(22) is formed on the common electrode.

Description

Vertical alignment mode liquid crystal display

The present invention relates to a liquid crystal display device, and more particularly, to a vertical alignment mode liquid crystal display device which can stably implement a disclination line and can form a dual domain without a plurality of rubbing processes.

In general, in a vertical alignment mode liquid crystal display, a liquid crystal having negative dielectric anisotropy is sandwiched between upper and lower substrates, a vertical alignment layer is provided on opposite surfaces of the upper and lower substrates, and a polarizing plate is attached to each of the rear surfaces of the upper and lower substrates. Has a structure. At this time, each of the opposing surfaces of the upper and lower substrates is provided with a liquid crystal driving electrode, and the polarization axes of the upper and lower polarizing plates are attached to cross each other.

In the vertical alignment mode liquid crystal display, the liquid crystal molecules are vertically arranged on the substrate under the influence of the vertical alignment layer before the electric field is formed. At this time, the screen becomes dark because the vertical polarizers cross vertically. On the other hand, when an electric field is formed between the driving electrodes of the upper and lower substrates, the liquid crystal molecules are distorted to be perpendicular to the shape of the electric field according to the liquid crystal property of negative dielectric anisotropy. Accordingly, light leaks through the twisted liquid crystal molecules, and the screen becomes white.

At this time, since the liquid crystal molecules are rod-shaped, the refractive index and the dielectric constant of the long axis and the short axis are different from each other. Accordingly, the refractive index is different depending on the direction in which the liquid crystal molecules are viewed, resulting in a difference in viewing angle between the front and the side views of the screen. Therefore, in order to solve this problem, conventionally, the initial arrangement of the liquid crystal molecules in one unit pixel is different, thereby forming a double domain. That is, when the electric field is formed between the pixel electrode and the common electrode, the direction in which the liquid crystal molecules are distorted is changed to compensate for the anisotropy of the long axis and the short axis of the liquid crystal molecule.

Here, conventionally forming a double domain in one pixel is achieved by rubbing the alignment film.

That is, as shown in FIG. 1A, the alignment layer 3 of the lower substrate (not shown) is rubbed in the r1 direction as a whole. At this time, rubbing is a step of rubbing the surface of the alignment film with a material such as a roller in a predetermined direction as is known. In the drawing, reference numeral A1 denotes a first domain predetermined region, and A2 denotes a second domain predetermined region.

Then, as shown in FIG. 1B, the photoresist film 4 is coated on the alignment film 3, and then exposed and developed so as to expose the second domain predetermined region A2. Thereafter, the exposed second domain predetermined region A2 is rubbed in the r2 direction, which is a direction crossing with r1.

Thereafter, as shown in FIG. 1C, the photoresist film 4 is removed to form two domains A1 and A2 in the unit pixel space. Thereafter, the alignment film on the upper substrate is also rubbed in the same process as above to form a double domain.

However, in order to form the above-mentioned double domain, two rubbing steps must be performed on the alignment film of the lower substrate, and then two rubbing steps must be performed on the alignment film of the upper substrate, which is cumbersome.

In addition, damage is caused to the alignment film by several rubbing steps.

In addition, even if a worker rubs so as to be symmetrical correctly up, down, left, and right, it is difficult for the top, bottom, left and right rubbing angles to be symmetrical accurately.

In this way, when the left and right rubbing angles are not symmetrical and rubbing defects occur, the disclination line, which is a boundary line between the domains, is not stably established, and thus a perfect double domain cannot be formed.

Accordingly, an object of the present invention is to provide a vertical alignment mode liquid crystal display device capable of stably constructing a disclination line in order to solve the above-described conventional problems.

1A to 1C are diagrams for explaining a conventional double domain forming method.

2A and 2B are cross-sectional views of a vertical alignment mode liquid crystal display device according to the present invention;

3A to 3C are cross-sectional views of respective processes for explaining a method of forming a dual domain in a vertical alignment mode liquid crystal display according to the present invention.

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

10-lower board 12-data bus line

14-pixel electrode 15-insulating film

16,22-First and second alignment layers 18,28-First and second polarizers

20-upper substrate 21-common electrode

29-phase correction plate

In order to achieve the above object of the present invention, according to one aspect of the invention, the present invention, the upper and lower substrates opposed to each other at a predetermined distance, and the liquid crystal molecules interposed between the upper and lower substrates, the dielectric anisotropy is negative One pixel per unit pixel surrounded by a liquid crystal layer, a gate bus line and a data bus line arranged to define a unit pixel in a matrix form on the lower substrate, and a pair of gate bus lines and a pair of data bus lines An electrode, a first vertical alignment layer disposed on the lower substrate resultant surface, and an opening in a direction parallel to the data bus line or the gate bus line disposed at an inner side of the upper substrate, the center of each unit pixel A common electrode formed thereon, and a second vertical alignment layer formed on the common electrode; When the opening of the through electrode is parallel to the data bus line, a portion corresponding to at least one of the first or second alignment layers corresponding to the data bus line is photo-aligned so that the liquid crystal molecules are tilted toward the unit pixel, and the opening of the common electrode is When parallel to the gate bus line, a portion corresponding to at least one gate bus line of the first or second alignment layer is optically aligned such that the liquid crystal molecules are tilted toward the unit pixel.

In this case, a first polarizing plate having a polarization axis in a predetermined direction is disposed on an outer side surface of the lower substrate, and a second polarizing plate having a polarizing axis orthogonal to the polarization axis is further disposed on an outer side surface of the upper substrate, and the second polarizing plate is disposed. And a phase compensating plate having negative refractive anisotropy between the substrate and the upper substrate. In addition, the polarization axis of the first polarizing plate is characterized in that 45 degrees with the long axis of the liquid crystal molecules that are twisted when the electric field is formed between the common electrode and the pixel electrode. In addition, the width | variety of an opening part is 2-10 micrometers.

The present invention also provides a liquid crystal layer including upper and lower substrates opposed to each other at a predetermined distance, liquid crystal layers interposed between the upper and lower substrates, and having negative dielectric anisotropy, and unit pixels in a matrix form on the lower substrate. A gate electrode line and a data bus line arranged, a pixel electrode disposed one per unit pixel surrounded by the pair of gate bus lines and a pair of data bus lines, a first vertical alignment layer disposed on a surface of the lower substrate resultant; A common electrode formed on an inner surface of the upper substrate, the common electrode having an opening in a direction parallel to the data bus line and the gate bus line in the center of each unit pixel, and a second vertical alignment layer formed on the common electrode; Correspond to the gate bus lines and the data bus lines of the first and second alignment layers. Part is characterized in that the photo-alignment to the liquid crystal molecules tilt towards the unit pixel.

According to the present invention, an opening is provided in the center of the common electrode for each pixel in the vertical alignment mode liquid crystal display, thereby forming a vertical electric field having an oblique component in which both sides are symmetrical about the opening. Accordingly, double domains can be easily formed, and the alignment layer portion above the data bus line or the gate bus line is photo-aligned to allow the liquid crystal molecules to be driven at a higher speed. In addition, since the portion where the opening is formed becomes the portion of the disclination line, the disclination line is stably formed in the center of the pixel.

Thus, perfect double or multiple domains are formed stably without several rubbing processes.

(Example)

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

2A and 2B are cross-sectional views of a vertical alignment mode liquid crystal display according to the present invention, and FIGS. 3A to 3C are angles for explaining a method of forming a dual domain in the vertical alignment mode liquid crystal display according to the present invention. It is cross section by process.

First, referring to FIG. 2A, the lower substrate 10 and the upper substrate 20 are opposed to each other at a predetermined distance.

A gate bus line (not shown) and a data bus line 12 are disposed in a matrix form on the lower substrate 10 to define a unit pixel pix. In the figure, a pair of data bus lines 12 are shown to show one unit pixel. A pixel electrode 14 made of a transparent conductor is disposed on the lower substrate 10 between the data bus lines 12. An insulating film 15 is covered on the data bus line 12 and the pixel electrode 14, and a first alignment layer 16 is formed thereon. In this case, the first alignment layer 16 may be directly formed without the insulating layer 15. Here, the first alignment layer 16 is a vertical alignment layer having a pretilt angle of 85 to 95 °, and the portion of the first alignment layer 16 corresponding to the upper portion of the data bus line 12 or the upper portion of the gate bus line (not shown). Is partially photo-aligned. The first polarizing plate 18 is attached to the outer surface of the lower substrate 10, and the first polarizing plate 18 has a long axis (or a long axis) when the liquid crystal molecules are twisted in parallel with the electric field direction. Short axis) and about 45 ° polarization axis.

The common electrode 21 is disposed on an inner surface of the upper substrate 20 facing the lower substrate 10. The common electrode 21 is formed to have one or two openings ap per unit pixel, and the openings ap are formed in parallel with the data bus line or the gate bus line. In this case, when the openings ap are formed parallel to the data bus lines 12, the openings ap are preferably disposed at the center of the unit pixel, preferably between the pair of data bus lines 12, and the openings ap are formed on the gate bus lines ( When formed in parallel with the one (not shown), a pair of gate bus lines (not shown) are preferably arranged in the unit pixel center. Here, when one opening (ap) is formed in the unit pixel, it is formed to be parallel to the data bus line 12 or the gate bus line, and when two openings (ap) are formed in the unit pixel, the data bus line and It is formed in a + shape so as to be parallel to each of the gate bus lines. The width of the opening ap is preferably about 2 μm to 10 μm. Here, in the present embodiment, an example has been described in which an opening ap parallel to the data bus line 12 is formed. The second alignment layer 22 is formed on the surface of the common electrode 21. At this time, the second alignment layer 22 is a vertical alignment layer having a pretilt angle of 85 to 95 °. In this case, a predetermined portion of the second alignment layer 22 may or may not be optically aligned. When the second alignment layer 22 is optically aligned, a portion corresponding to the alignment direction of the first alignment layer 16 is optically aligned.

Here, the photo-aligned portion of the first alignment layer 16 or the second alignment layer 22 is determined by the direction of the opening ap. That is, when the opening ap is parallel to the data bus line 12, the optically oriented portion becomes the upper portion of the data bus line 12 and its corresponding portion, and the opening ap corresponds to the gate bus line (not shown). In parallel, the light oriented portion becomes the gate bus line (not shown) and its corresponding portion. In addition, when the opening ap is parallel with the gate bus line (not shown) and the data bus line 12, respectively, the upper portion of the gate bus line and the data bus line and corresponding portions thereof become the light alignment portion. Further, in this photo-oriented portion, the liquid crystal molecules are photo-aligned so as to be tilted into the unit pixel by a predetermined angle, for example, an angle of 90 degrees or less. Thus, the photo-oriented portion allows the liquid crystal molecules to be easily distorted and arranged by the electric field after the electric field is applied.

The second polarizing plate 28 is disposed on the outer surface of the upper substrate 20, and the phase compensating plate 29 is interposed between the upper substrate 20 and the second polarizing plate 28. In this case, the phase compensating plate 29 is made of liquid crystal molecules having negative refractive anisotropy, and the second polarizing plate 28 has a polarization axis in a predetermined direction and is orthogonal to the polarization axis of the first polarizing plate 18. Has

In addition, a liquid crystal layer 30 including several liquid crystal molecules 30a and 30b is interposed between the lower substrate 10 and the upper substrate 20. At this time, it is preferable that the liquid crystal molecules 30a and 30b use a material having negative dielectric anisotropy. In the present invention, the product of the cell gap (distance between the upper and lower substrates) and the refractive index anisotropy (Δn) of the liquid crystal molecules is about 0.2 to 0.8 mu m.

The vertical alignment mode liquid crystal display device having such a configuration is operated as follows.

First, when no electric field is formed between the pixel electrode 14 and the common electrode 21, the liquid crystal molecules 30a are influenced by the first and second alignment layers 15 and 22, which are vertical alignment layers, and their major axes are mostly It is arranged to be perpendicular to the substrate 10 surface. In this case, the liquid crystal molecules 30b are arranged to be tilted toward the unit pixel in the region where the light alignment is performed, that is, the data bus line 12 and the corresponding region. Then, the light passing through the first polarizing plate 18 does not change the polarization state while passing through the liquid crystal layer 30, and thus cannot pass through the second polarizing plate 28. Thus, the screen is dark. In this case, the full compensation may be realized by the phase compensating plate 29, and light leakage may occur due to some tilted liquid crystal molecules, but the part is a part shielded by the data bus line and does not affect the contrast ratio. Do not.

On the other hand, when a voltage difference is generated between the pixel electrode 14 and the common electrode 21, as shown in FIG. 2B, a vertical electric field E having an oblique component is formed. At this time, the vertical electric field E having an oblique component is generated in a symmetrical form with respect to the opening ap. Here, the vertical electric field E has an oblique component because the electric field is distorted by the opening ap.

In addition, since the liquid crystal molecules 30c in the opening ap are not affected by the electric field, the liquid crystal molecules 30c maintain the initial arrangement and become a disclination line. Here, since the opening ap is disposed at the center of the unit pixel as described above, the disclination line is positioned at the center of the unit pixel.

Furthermore, the liquid crystal molecules on the data bus line 12 or the gate bus line are tilted by an angle toward the unit pixel, so that they are driven at a higher speed. Therefore, the driving voltage can be lowered.

When such an electric field is formed, the liquid crystal molecules 30a and 30b positioned in the electric field forming portion are rearranged such that the electric field and its short axis are parallel to each other. At this time, since the polarization axis of the first polarizing plate 18 forms 45 degrees with the long axis of the driven liquid crystal molecules, the light passing through the first polarizing plate 18 passes through the liquid crystal layer 30 and the polarization state is changed. Passes through the second polarizing plate 28. Thus, the screen is in a white state.

Hereinafter, a method of photoaligning a predetermined portion of the alignment layers 16 and 22 will be described with reference to FIGS. 3A to 3C. 3A to 3C, only the alignment layer 16 of the lower substrate 11 will be described by way of example.

First, as shown in FIG. 3A, a substrate 10 having a data bus line 12, a pixel electrode 14, and an insulating film 15 is prepared. Thereafter, the first alignment layer 16 is formed on the insulating film 15.

Next, as illustrated in FIG. 3B, the first mask 50 is disposed to open the one side data bus line 12a on the substrate, and then the polarized laser light is irradiated to adjust the first light orientation. Conduct.

Thereafter, as shown in FIG. 3C, after the first mask 50 is removed, the second mask 51 is disposed to open the other data bus line 12b. Thereafter, the exposed portion is irradiated with polarized laser light to effect the second light alignment.

As described in detail above, according to the present invention, an opening is provided in the center of the common electrode for each pixel in the vertical alignment mode liquid crystal display, thereby forming a vertical electric field having an oblique component in which both sides are symmetric about the opening. . Accordingly, double domains can be easily formed, and the alignment layer portion above the data bus line or the gate bus line is photo-aligned to allow the liquid crystal molecules to be driven at a higher speed. In addition, since the portion where the opening is formed becomes the portion of the disclination line, the disclination line is stably formed in the center of the pixel.

Thus, perfect double or multiple domains are formed stably without several rubbing processes.

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

Claims (8)

Upper and lower substrates opposed to each other by a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates and including liquid crystal molecules having negative dielectric anisotropy; A gate bus line and a data bus line arranged to define unit pixels in a matrix form on the lower substrate; One pixel electrode disposed per unit pixel surrounded by the pair of gate bus lines and the pair of data bus lines; A first vertical alignment layer disposed on a surface of the lower substrate resultant; A common electrode disposed on an inner side of the upper substrate and having an opening in a direction parallel to the data bus line or the gate bus line at the center of each unit pixel; And A second vertical alignment layer formed on the common electrode; When the opening of the common electrode is parallel to the data bus line, a portion corresponding to one or more data bus lines of the first or second alignment layer is photo-aligned so that the liquid crystal molecules are tilted toward the unit pixel. When the opening of the common electrode is parallel to the gate bus line, a portion corresponding to at least one gate bus line of the first or second alignment layer is optically aligned such that liquid crystal molecules are tilted toward the unit pixel. Mode liquid crystal display. The method of claim 1, wherein a first polarizing plate having a polarization axis in a predetermined direction is disposed on an outer surface of the lower substrate, and a second polarizing plate having a polarizing axis orthogonal to the polarization axis is further disposed on an outer surface of the upper substrate. A vertical alignment mode liquid crystal display device. The vertical alignment mode liquid crystal display of claim 2, further comprising a phase compensating plate having negative refractive anisotropy between the second polarizing plate and the upper substrate. 3. The vertical alignment mode liquid crystal display of claim 2, wherein the polarization axis of the first polarizing plate forms an angle of 45 ° with a long axis of the liquid crystal molecules that is distorted when an electric field is formed between the common electrode and the pixel electrode. The vertical alignment mode liquid crystal display device of claim 1, wherein the opening has a width of 2 μm to 10 μm. The vertical alignment mode liquid crystal display of claim 1, wherein a product of the upper and lower substrate distances and the refractive index anisotropy of the liquid crystal molecules is 0.2 to 0.8 μm. The vertical alignment mode liquid crystal display of claim 1, wherein the angle tilted by the optical alignment is 90 degrees or less. Upper and lower substrates opposed to each other by a predetermined distance; A liquid crystal layer interposed between the upper and lower substrates and including liquid crystal molecules having negative dielectric anisotropy; A gate bus line and a data bus line arranged to define unit pixels in a matrix form on the lower substrate; One pixel electrode disposed per unit pixel surrounded by the pair of gate bus lines and the pair of data bus lines; A first vertical alignment layer disposed on a surface of the lower substrate resultant; A common electrode disposed on an inner side of the upper substrate and having an opening in a direction parallel to the data bus line and the gate bus line at the center of each unit pixel; And A second vertical alignment layer formed on the common electrode; And a portion of the first and second alignment layers corresponding to the gate bus line and the data bus line is optically aligned such that the liquid crystal molecules are tilted toward the unit pixel.