KR100312754B1 - wide viewing angle liquid crystal displays and a manufacturing method thereof - Google Patents

Abstract

A liquid crystal display device wherein the direction of the liquid crystal director on a plane parallel to the substrate includes all directions on the plane. Ultraviolet rays are irradiated to an alignment layer made of a self-assembled monolayer (SAM) that gives vertical alignment by using a mask in which transparent and opaque portions are alternately arranged in the form of concentric circles. The liquid crystal molecules positioned on the alignment layer irradiated with ultraviolet rays are arranged parallel to the substrate along the tangential direction of the circle due to the elastic anisotropy of the liquid crystal. A chiral additive is added slightly to the liquid crystal material to control the pretilt direction, and the center of the concentric circles is opaque so that the liquid crystal molecules on the corresponding alignment film portion maintain the vertical alignment state. The alignment layer of the opposite substrate forms a transparent portion and an opaque portion in a radial shape to direct liquid crystal molecules toward a radial center direction or the opposite direction, thereby achieving a twist angle of 90 °.

Description

Wide viewing angle liquid crystal displays and a manufacturing method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device and a method for manufacturing the same, and a liquid crystal display device having a wide viewing angle and a method for manufacturing the same.

BACKGROUND ART A liquid crystal display generally displays an image by sandwiching a liquid crystal layer between two substrates on which an electrode is formed, applying a voltage to the electrode, generating an electric field in the liquid crystal layer, and rearranging the liquid crystal molecules.

The most widely used twisted nematic (TN) liquid crystal display has a structure in which electrodes are formed on two substrates, and the liquid crystal director is different from one substrate in an off state in which an electric field is not applied. Twist to the substrate.

The twisted nematic liquid crystal display has a narrow viewing angle, and in order to overcome this problem, both types of electrodes are formed on a single substrate or the long axes of the liquid crystal molecules are arranged perpendicular to the substrate in an off state. Although structures have been proposed, they have disadvantages of high driving voltage and small aperture ratio. In addition, a multi-domain structure having a plurality of regions having different average alignment directions of long axes of liquid crystal molecules has been proposed, which has disadvantages of low contrast ratio and slow response speed due to the foreground. See also SID 95 DIGEST, pp. 575-578 show a mono-domain structure which can be characterized by an axially symmetric orientation, but this is done by using polymerizable resins to form polymer walls in the liquid crystal layer. There is a cumbersome problem.

The technical problem to be achieved by the present invention is to widen the viewing angle of the liquid crystal display while simplifying the process.

1A is a perspective view of a liquid crystal display according to an exemplary embodiment of the present invention.

1B is a schematic plan view of a liquid crystal display according to an exemplary embodiment of the present invention.

2 shows liquid crystal molecules on a plane parallel to the substrate,

3A and 3B illustrate an arrangement of liquid crystal molecules on two substrate surfaces according to an embodiment of the present invention.

4A and 4B illustrate an arrangement of liquid crystal molecules on two substrate surfaces according to an embodiment of the present invention.

5A and 5B illustrate patterns of masks used for ultraviolet irradiation of alignment films of two substrates manufactured according to one embodiment of the present invention.

6A, 6B, 7, 8A, 8B, and 9 illustrate patterns of masks according to embodiments of the present invention.

In order to achieve this problem, in the present invention, the alignment film is processed so that the liquid crystal director on a plane parallel to the two substrates is present in all regions on this plane in an arbitrary region.

Specifically, the liquid crystal display according to the present invention includes a plurality of pixels, the alignment layers facing each other at intervals and formed on the inner surfaces of the two substrates and the two substrates, and a liquid crystal layer interposed between the two alignment layers. It includes. Here, the two substrates have electrodes for generating an electric field and are divided into a plurality of main regions, and the alignment film is processed so that the liquid crystal director of the liquid crystal layer on a plane parallel to the two substrates exists in all directions on this plane in each main region. It is.

Here, the main region preferably includes at least one subregion in which the change of the liquid crystal director is continuous, and more preferably, the degree of change of the liquid crystal director in the sub region is constant. For example, the liquid crystal director in the subregion is preferably symmetrical, in particular rotationally symmetrical with respect to a specific point. In addition, the liquid crystal director may be continuously changed by 2π when viewed along one closed curve located on the plane in the subregion.

The main region may be one pixel, a part of the pixels, or several pixels, and the liquid crystal director may be twisted from one alignment layer to another.

Polarizers are attached to the outer surfaces of the two substrates, respectively, and the transmission axes of the polarizers may be perpendicular to each other. In addition, a short-axis optical compensation film may be attached to an outer surface of at least one of the two substrates to compensate for a viewing angle in a direction perpendicular to the substrate.

According to one feature of the present invention, the alignment of the liquid crystal director can be controlled by forming the first portion of the stripe to which the ultraviolet ray is irradiated and the second portion which are not. At this time, the first portion has a portion that is bent or curved at least once.

This alignment film is preferably made of a self-assembled monolayer (SAM) giving vertical alignment.

The second part is in the form of a string, and the first part and the second part are preferably arranged alternately in the form of concentric closed curves, for example, concentric squares with rounded corners or rounded corners. At this time, the second portion preferably includes a central portion of the concentric closed curve. Alternatively, the first part and the second part may be alternately arranged in the form of concentric arcs with respect to a specific point.

The alignment layer of the other substrate may also include the third and fourth portions having a row shape, and the third and fourth portions may be angled with respect to the first and second portions, respectively.

The tilt direction may be controlled by including a chiral additive in the liquid crystal layer.

According to the present invention, similar results can be obtained by patterning the alignment layer instead of performing ultraviolet irradiation.

That is, the alignment layer pattern formed on at least one of the two substrates includes at least one or more strip-shaped portions having at least one bent or curved portion.

In this case, the alignment layer pattern may include a plurality of stripe portions spaced apart from each other, and an area between the stripe portions may also be formed in a stripe shape, and the stripe portion and the area therebetween of the first alignment layer pattern may have a specific point. It is preferred that they are arranged alternately in the form of concentric closed curves or concentric arcs.

In this case, an alignment layer pattern including a plurality of stripe portions may be formed on other substrates, and the stripe portions of the alignment layer on different substrates may be angled to each other.

Next, a liquid crystal display according to an exemplary embodiment of the present invention and a manufacturing method thereof will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

First, a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to FIGS. 1A and 1B.

The liquid crystal display device 1 according to the exemplary embodiment of the present invention includes the alignment layer 11 applied to the lower substrate 10 and the inner surface of the substrate 10 and the polarizer 12 attached to the outer surface of the substrate 10. And an alignment layer 21 and an outer surface of the substrate 20 which are positioned opposite to the lower substrate 10 and are coated on the inner side of the upper substrate 20 and the substrate 20 where the thin film transistor is formed. And a compensation film 23 inserted between the attached polarizing plate 22 and the substrate 20 and the polarizing plate 22. The liquid crystal display device 1 according to the embodiment of the present invention also includes a liquid crystal layer 30 interposed between the two alignment layers 11 and 21.

The liquid crystal display device 1 according to the exemplary embodiment of the present invention includes a plurality of pixels as shown in FIG. 1B, and electrodes (not shown) that form an electric field are formed in each pixel. The electrode may be formed on both substrates 10 and 20 and may be formed only on one substrate. When electrodes are formed on both substrates 10 and 20, a plurality of electrodes of the upper substrate 20 are formed in a matrix form as pixel electrodes, and one electrode of the lower substrate 10 is formed across the entire substrate. Can be.

As shown in FIG. 1A, a horizontal axis parallel to the substrates 10 and 20 is referred to as x, an axis parallel to the substrates 10 and 20 and perpendicular to the x axis is referred to as y, and an axis perpendicular to the xy plane is referred to as z-axis. Assume that there is a lower substrate 10 (strictly lower alignment film 11), and the upper substrate 20 (strictly upper alignment film 21) at the point where z = d. Then, the distance between the two substrates 10 and 20, or the thickness of the liquid crystal layer 30 is d.

FIG. 2 illustrates a plane in which the center of the liquid crystal molecules is positioned among the planes parallel to the xy plane, and reference numeral 100 denotes a projection of the liquid crystal molecules onto the xy plane along the z direction or a plane parallel thereto. to be. Assume that the angle formed by the vector toward the center of the molecular event 100 with the x axis is φ, and the angle formed by the major axis direction of the liquid crystal molecule 100 with the x axis is α (z).

In this case, the liquid crystal molecules are arranged such that the liquid crystal director n on a plane parallel to the xy plane is present in substantially all directions through the physical and chemical treatment of the alignment layer. In other words, when the long axis of the liquid crystal molecules is the same, but the inclination direction is different, the long axis direction (or liquid crystal director) of the liquid crystal molecules is to cover all directions when the long axes of the liquid crystal molecules are directed in different directions. To arrange the molecules (in the description of the invention and claims, the direction of the major axis of the liquid crystal molecules is used as described above unless otherwise specified). In addition, it is preferable that the change of the direction proceeds continuously, and the degree of change is preferably constant. For example, when following a closed curve on the xy plane or a plane parallel thereto, the long axis direction of the liquid crystal molecules centered on the closed curve may be continuously changed to point in all directions, particularly the long axis of the liquid crystal molecules. The directions can be arranged to vary in rotational symmetry about a point.

Such an arrangement may exist within one pixel, a portion of a pixel or several pixels. In other words, when the substrate is divided into several regions, the arrangement of the liquid crystal molecules in each region exists as described above. This arrangement prevents the problem of the conventional multi-domain method, that is, the problem such as the foreground appearing at the boundary between regions, thereby increasing the contrast ratio, increasing the response speed, securing a wider viewing angle, and reducing the gray level inversion.

In addition, it can be arranged so that twist occurs when moving in the z-axis direction at any point on the xy plane. For example, when the torsion angle is 90 ° and the field generating electrodes generating the electric field are formed on each of the two substrates, a twisted nematic (TN) method is used.

According to one embodiment of the invention, α (0) = φ + c (c is any constant) in the plane with z = 0 and α (d) = φ + c + Φ (Φ in the plane with z = d Is the angle at which the liquid crystal molecules are twisted from the top plate to the bottom plate), and arranges the liquid crystal molecules 100 such that α (z) = φ + c + Φ × (z / d) from z = 0 to z = d. . In this embodiment, the array of liquid crystal molecules centered on this closed curve is continuously contiguous by 2π when viewed along any closed curve including the origin, for example, a circle about the origin, on a plane parallel to the xy plane. Change.

Here, in the case of a normal twisted nematic system, Φ = ± π / 2. Here, the constant c is an arbitrary constant, but the process is simple when c = 0 or c = ± π / 2.

Some arrangement examples of this embodiment are given.

3A and 3B show the surfaces of z = 0 and z = d, that is, on the lower and upper alignment layers 11 and 12, respectively, when c =-(π / 2) and Φ = (π / 2). 4A and 4B show an arrangement of liquid crystal molecules, and when c =-(π / 4) and Φ = (π / 2), respectively, z = 0 and z = d, that is, bottom and top The arrangement of liquid crystal molecules on the alignment films 11 and 12 is shown. 3A to 4B are views of one pixel as viewed in the z-axis direction, and the liquid crystal molecules are illustrated in a nail shape and correspond to a portion of the nail head raised to the observer.

As can be seen from the z-axis at any point on the xy plane, the arrangement of the liquid crystal molecules has a twisted structure. In addition, since the liquid crystal molecules are distributed in all directions at the point between the two substrates, the uniaxiality on the xy plane cancels each other so that the viewing angle is widened and gray inversion disappears. However, uniaxiality in the z-axis direction is canceled by using a uniaxial optical compensation film (reference numeral 23 in FIG. 1) having negative birefringence.

In the liquid crystal display, the lower and upper polarizers 12 and 22 may be arranged such that transmission axes are orthogonal to each other to have a normally white manner. Also, in this case, the contrast ratio is higher than that of the multi-domain method having the boundary between the micro areas.

Next, a method for producing an arrangement of such liquid crystal molecules will be described.

There may be a variety of methods for physically and / or chemically treating the alignment layer to make the arrangement as described above. For example, an ultraviolet patterned self-assembled monolayer (SAM) may be used as the alignment layer. It can be mentioned. In other words, when UV rays are irradiated through a mask in which a string-shaped opaque pattern and a transparent pattern are engraved on a SAM alignment layer that induces vertical alignment, liquid crystal molecules disposed on the UV-exposed alignment layer are disposed in the longitudinal direction of the string due to elastic anisotropy. Parallel to the horizontal orientation. In addition to this method, a similar result can be obtained by irradiating an electron beam or by forming an alignment layer using a method such as photo etching or printing. This is possible because the liquid crystal molecules show a horizontal orientation when the liquid crystal molecules are positioned on an insulating film or glass plate without an alignment layer, and the elastic anisotropy of the liquid crystal molecules causes the molecules to align in parallel with the longitudinal direction of the string. See doctoral dissertation (Baek-Woon Lee, Ph. D thesis, Department of Physics, University of Colorado, Bouler, CO, USA)

Next, the mask pattern for making the liquid crystal array shown in FIGS. 3A and 3B will be described in detail with reference to FIGS. 5A and 5B, respectively.

5A shows a mask pattern in which opaque portions (black bands) 41 and transparent portions (white bands) 42 are alternately arranged concentrically in a circular band shape. Here, the alignment film portion corresponding to the transparent portion 42 is a portion to which ultraviolet rays are irradiated, and the alignment layer portion corresponding to the opaque portion 41 is a portion to which the ultraviolet rays are not irradiated. When the UV irradiation is performed using such a mask, the liquid crystal molecules on the UV-irradiated portion are arranged in the tangential direction of the circle, and the liquid crystal molecules on the non-UV-radiated portion are arranged in parallel with each other due to the nature of the nematic liquid crystal. Ultraviolet rays are also tilted in the tangential direction of the circle along the liquid crystal molecules on the irradiated portion (confirmation !!!).

FIG. 5B shows a mask pattern in which opaque portions (black bands) 41 and transparent portions (white bands) 42 are alternately arranged in a radial band shape, wherein the liquid crystal on the ultraviolet-irradiated part is shown. The molecules align in the radial center direction.

The opaque portion 41 and the transparent portion 42 of the mask shown in FIG. 5B are arranged so as to be perpendicular to the portions 41 and 42 shown in FIG. 5A, whereby the liquid crystal molecules shown in FIG. 5B are arranged. The direction is perpendicular to the direction of the liquid crystal molecules shown in FIG. 5A and a twist angle of 90 ° can be obtained.

Here, it is preferable to make the central portions of the concentric circles and the radial shapes opaque, since the curvature of the central circles is large when the pattern is repeated to the central portion, so that the arrangement of the liquid crystal molecules may not follow the shape of the pattern. Liquid crystal molecules above this central portion maintain a vertical orientation.

In addition, by forming a variety of patterns of the mask it is possible to obtain an array of liquid crystal molecules rotationally symmetric about a certain point.

In the case of printing the alignment film, the portions corresponding to the opaque portions 41 in FIGS. 5A and 5B leave the alignment films inducing vertical alignment, and the portions corresponding to the transparent portions 42 are formed without the alignment films. Form.

On the other hand, the average bulk θ _bulk in the patterned SAM alignment layer is determined by the following relationship.

θ _bulk = 90 ° × a / (a + b) = 90 ° × 1 / (1 + b / a)

Where a is the line width of the portion of the alignment layer exposed to ultraviolet light (or the portion that induces horizontal alignment) and b is the line width of the portion of the alignment layer that is not exposed (or the portion inducing vertical alignment). Therefore, the desired inclination angle can be made by adjusting the ratio of b / a. Since the birefringence of the liquid crystal depends on the inclination angle of the liquid crystal, dispersion can be compensated for by adjusting the ratio of (b / a) to pixels of different colors.

In addition, since the SAM alignment layer itself exposed to ultraviolet rays does not induce a pretilt angle in a specific direction, there may be two kinds of directions in which the liquid crystal molecules stand or lie down, which may result in a disclination. For example, in a twisted nematic liquid crystal display, it can be predicted that both α (d) = φ and α (d) = φ + π will occur at the same probability on the upper substrate. In practice, however, since the size of the electrode under the alignment layer is finite, fringe field disclination due to the edge of the electrode is generated, breaking the symmetry and arranging in only one direction. On the other hand, since the size of the electrode in the lower substrate is relatively large and symmetry is maintained, two states are likely to appear at the same time. In order to prevent this, a chiral dopant is mixed with the liquid crystal material to give direction. The arrangement as in FIG. 5A is a mixture of chiral additives with right-handedness.

However, since one pixel basically has a rectangular shape having a short side and a long side of about 1: 3 in length, it is necessary to change the structure slightly accordingly. This will be described with reference to FIGS. 6A to 9.

FIG. 6A illustrates a pattern in which three identical concentric patterns are formed in a line in the long side direction of the rectangle, and FIG. 6B illustrates a pattern in which the concentric circle pattern is stretched in the long side direction of the rectangle.

7 shows three square regions arranged in a line along a long side direction of a pixel, and four quarter concentric arc patterns are symmetrically formed in one square region.

8A and 8B are basically a four-domain structure, the basic shape of which is in the form of a concentric square and three concentric square patterns are arranged in a line in the long side direction of the pixel, or one concentric square pattern is arranged in the pixel. It is stretched in the direction of the long side of. In addition, the corners are rounded to increase the response speed and eliminate the foreground. In the case of the rectangular structure, four microregions are basically formed, that is, only four microregions are formed in a direction parallel to each side (of course, since the corners are rounded, the direction of the major axis of the liquid crystal molecules between the four main microregions There is a very small area that changes continuously.) In terms of viewing angle, the pattern is simple compared to the previous embodiments but has a simple advantage. However, care should be taken so that the ratio of the line width of the portion to which the ultraviolet ray is irradiated and the portion not to be irradiated, that is, the ratio of a / b, remains particularly constant at the corner portion.

9 shows a pattern in which the rectangular pattern of FIG. 8A is rotated 45 degrees.

In the case of FIGS. 8A, 8B and 9, the transmission axis directions of the polarizing plates 12 and 22 are preferably perpendicular or parallel to the rectangular side direction, in order to reduce dependency on the cell gap.

On the other hand, when the alignment film is patterned by an ultraviolet irradiation method, a printing method, or the like, the liquid crystal director may be directed in all directions on the plane as described above, but the liquid crystal director may be formed to face at least two directions at angles other than π. For example, even if at least two fine regions are formed, the effect of improving the viewing angle can be reduced compared to the case in which only at least two fine regions are arranged in one direction. For example, if the UV-irradiated portion or the portion where the alignment layer is removed is formed in a string shape, the bending angle or bending is performed at least one time to improve the viewing angle.

As described above, in the present invention, by arranging the liquid crystal molecules such that the alignment layer may be physically or chemically treated so that the major axis direction of the liquid crystal molecules may cover substantially all directions, the viewing angle is widened and the grayscale inversion is disappeared in a simple process. In addition, since the liquid crystal director is inclined at a large angle in advance because of the vertically aligned portion, the threshold voltage is lowered, so that low voltage driving is possible even with a conventional liquid crystal material, thereby reducing power consumption. By changing the long axis direction of the liquid crystal molecules continuously, it is possible to prevent problems such as the foreground appearing at the boundary between the conventional micro-regions to increase the contrast ratio and to speed up the response speed.

Claims (32)

A liquid crystal display device comprising a plurality of pixels, Two substrates facing each other at intervals and having electrodes generating an electric field, divided into a number of main regions, Two alignment layers formed on inner surfaces of the two substrates, A liquid crystal layer interposed between the two alignment layers Including; The alignment layer is treated so that the liquid crystal director of the liquid crystal layer on a plane parallel to the two substrates exists in all directions on the plane in the respective main regions. Liquid crystal display. In claim 1, And the main region includes at least one sub region in which the change of the liquid crystal director is continuous. In claim 2, And a degree of change of the liquid crystal director in the subregion is constant and symmetrical with respect to a specific point. In claim 3, And the liquid crystal director in the subregion is rotationally symmetric about a specific point. In claim 2, And a liquid crystal director continuously changing by 2π when viewed along one closed curve positioned on the plane in the subregion. In claim 2, The main area is one pixel. In claim 2, The liquid crystal director is twisted from one alignment film to another alignment film. In claim 1, And a polarizing plate attached to outer surfaces of the two substrates, respectively. In claim 8, The transmission axes of the polarizing plates are perpendicular to each other. In claim 8, And a shortened optical compensation film attached to an outer surface of at least one of the two substrates. A liquid crystal display device comprising a plurality of pixels, First substrate, A second substrate facing each other at intervals from the first substrate, First and second alignment layer patterns respectively formed on inner surfaces of the first and second substrates and divided into a plurality of main regions; A liquid crystal layer interposed between the first and second alignment layer patterns Including; Electrodes for generating an electric field are formed on the first or second substrate, and the first alignment layer pattern in each of the main regions includes a stripe-shaped first portion irradiated with ultraviolet rays and a second portion not irradiated with ultraviolet rays. And the first portion has a bent or curved portion at least once. In claim 11, The first alignment layer pattern is a liquid crystal display device made of SAM. In claim 11, The first alignment layer pattern includes a vertical alignment layer. In claim 11, And the second portion has a stripe shape, and the first portion and the second portion are alternately arranged in a concentric closed curve with respect to a specific point. The method of claim 14, And the second portion includes a central portion of the concentric closed curve. The method of claim 14, The concentric closed curve is a concentric circle. The method of claim 14, The concentric closed curve is a concentric square. The method of claim 17, The corner of the concentric square is a round liquid crystal display device. In claim 11, And the second portion has a stripe shape, and the first portion and the second portion are alternately arranged in the form of concentric arcs with respect to a specific point. In claim 11, The liquid crystal layer includes a chiral additive. In claim 11, And the main region is part of the pixel. In claim 11, The pixel includes only one main area. In claim 11, The second alignment layer pattern in each of the main regions includes a third portion having a stripe pattern irradiated with ultraviolet rays and a fourth portion not irradiated with ultraviolet rays, and the third and fourth portions are respectively the first portion and the second portion. A liquid crystal display device at an angle to the portion. A liquid crystal display device comprising a plurality of pixels, First substrate, A second substrate facing each other at intervals from the first substrate, First and second alignment layer patterns respectively formed on inner surfaces of the first and second substrates and divided into a plurality of main regions; A liquid crystal layer interposed between the first and second alignment layer patterns Including; Electrodes for generating an electric field are formed on the first or second substrate, and the first alignment layer pattern in each main region includes at least one or more strip-shaped portions having at least one bent or curved portion. Liquid crystal display. The method of claim 24, The first alignment layer pattern includes a vertical alignment layer. The method of claim 24, The first alignment layer pattern includes a plurality of stripe portions spaced apart from each other, wherein the area between the stripe portions is a stripe shape, and the stripe portion and the area therebetween of the first alignment layer pattern are concentric with respect to a specific point. Liquid crystal display devices alternately arranged in the form of closed curves or concentric arcs. The method of claim 26, The second alignment layer pattern includes a plurality of stripe portions spaced apart from each other, wherein the area between the stripe portions is a stripe shape, and the stripe portion of the second alignment layer pattern is a stripe portion of the first alignment layer pattern. Liquid crystal display angled with. The method of claim 24, The liquid crystal layer includes a chiral additive. In claim 11, The liquid crystal director of the liquid crystal layer is twisted from the first alignment film to the second alignment film. Forming an alignment layer on the insulating substrate, Irradiating ultraviolet rays using a mask having an opaque stripe pattern and a transparent stripe pattern on the alignment layer. Including; The transparent stripe pattern is at least one portion bent or curved The manufacturing method of the board | substrate for liquid crystal display devices. The method of claim 30, The alignment layer is a liquid crystal display device made of SAM. The method of claim 31, The alignment layer is a liquid crystal display device.