KR20000026837A - Multi domain lcd - Google Patents

Abstract

PURPOSE: A multi domain LCD is provided to secure an excellent view angle characteristic by composing a compensation film in which one domain is divided into a multi domain field control double refraction. CONSTITUTION: A liquid crystal film(first compensation film)(301) having a characteristics which is cured by a ultra violet ray is coated on a transparent substrate(300)(S1). The liquid crystal film(first compensation film)(301) is restrained by an optical mask(303) and then the ultra violet ray is emitted(S2). A region exposed by the photo mask(303) and a region restrained by the photo mask(303) are divided into a domain(D1) and a domain(D2)(S3). A second compensation film(305) is attached in a vertical direction to a photo axis of the domain(D1) and the other domain(D2)(S4).

Description

Multi-domain liquid crystal display device

The present invention relates to a liquid crystal display device, and more particularly, to a multi-domain liquid crystal display device having a domain divided compensation film.

Liquid crystal display devices can be roughly classified into twisted nematic (TN) type, guest host (GH) type, electronically controlled Birefringence (ECB) type, and optically compensated birefringence (OCB) type depending on the operation mode. Recently, the above-described TN mode LCD has been widely applied to portable computers, measuring devices, and the like. However, these TN-LCDs have a problem that the viewing angle is narrow and the response speed is slow.

On the other hand, when a voltage is applied to the liquid crystal cell, the arrangement of the liquid crystal molecules is changed by the dielectric anisotropy of the liquid crystal, thereby changing the birefringence in the liquid crystal cell. The method of inducing a change in the light transmittance by changing the birefringence of the liquid crystal cell is called an electric field control birefringence (ECB mode).

Homogeneous LCDs are typical of ECB-LCDs. In such LCDs, homogeneous alignment liquid crystal cells in which the major axes of liquid crystal molecules are arranged in parallel with the substrate and the dielectric anisotropy of the liquid crystals have a positive nematic liquid crystal ( Np).

Figure 1 (a) is a cross-sectional view of a general homogeneous LCD, (b) is a view showing the relationship between the alignment direction of the liquid crystal of Figure 1 (a) and the optical axis direction of the compensation film, as shown in the figure, In the transparent first substrate 100, a switching element (not shown), a pixel electrode (not shown), and a first alignment layer 103 that control the arrangement of the liquid crystal molecules 120 are sequentially formed, and the substrate 100 is formed. The polarizer 105 is attached to the other side of the (). An opposite electrode (not shown), a color filter layer (not shown), and a second alignment layer 109 are formed on the second substrate 107 that faces the first substrate 100, and is opposite to the substrate 107. The compensation film 111 and the analyzer 113 are formed in order, and the liquid crystal cell made of the liquid crystal molecules 120 is disposed between the two substrates 100 and 107.

When no voltage is applied to the liquid crystal display device having the above-described structure (Voff), the liquid crystal 120 is aligned in the alignment direction of the first alignment layer 103 and the second alignment layer 109, and the pixel electrode and the counter electrode are aligned. When a voltage is applied (Von) between the liquid crystals 120, the arrangement is changed along the direction of the electric field.

In the homogeneous liquid crystal display device of the normally white mode having such a structure, the compensation film 111 is used to compensate for the phase difference generated between the normal light and the abnormal light when the incident light passes through the liquid crystal cell in the black state. ) Is an essential component.

As shown in FIG. 1B, both the alignment direction 103a of the liquid crystal 120 by the first alignment layer 103 and the alignment direction 109a of the liquid crystal 120 by the second alignment layer 109 are compensated for. It crosses perpendicularly to the optical axis direction 111a of the film 111, and each is arrange | positioned so that it may be parallel to each other. As a result, θ with respect to the reference axis 115 when viewed on a plane_One= 135 °, θ₂= θ₃ = 45 °.

The liquid crystal display device uses a Np-type liquid crystal, which is generally used in the TN type, and thus has a wide selection range of liquid crystal materials and provides a stable initial orientation, and has a poor viewing angle and gray inversion. The disadvantage is that the area is narrow. The disadvantage of the homogeneous liquid crystal display device can be solved by manufacturing a multi-domain liquid crystal cell, and a multi-domain compensation film is required to make a black state in the multi-domain.

2 illustrates a TN type liquid crystal display device employing a multi-domain compensation film proposed in US Patent No. 5,589,963. As shown in the drawing, a first alignment layer 203 is formed on the first substrate 201, and a first compensation film (C-plate) 205 and a polarizer 207 are formed on the opposite side of the substrate 201. have. A second compensation film (O-plate) 211, a third compensation film (A-plate) 213, and a second alignment layer 215 are formed on the second substrate 209, and are opposite to the substrate 209. An analyzer 217 is formed in the chamber. The initial alignment state of the liquid crystal 220 is determined by the first and second alignment layers 203 and 215 described above.

However, the above patent is limited to the TN type liquid crystal display device, and has a disadvantage in that the response speed is slow and the reliability of the liquid crystal is low.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems in the prior art, and an object of the present invention is to provide a wide viewing angle multi-domain field control birefringence type liquid crystal display device by employing at least one domain-divided compensation film.

Another object of the present invention is to reduce the response speed of a liquid crystal by using a liquid crystal cell having a smaller retardation (dΔn, where d is a thickness of the liquid crystal cell and Δn is a change rate of the refractive index of the liquid crystal cell) compared to a conventional twist nematic liquid crystal cell. To improve.

Still another object of the present invention is to protect the substrate from dust and / or static electricity generated during the process by photoaligning the liquid crystal display, and to improve the reliability of the liquid crystal.

In order to achieve the above object, a multi-domain liquid crystal display device according to an embodiment of the present invention includes a pair of first and second substrates facing each other by placing a homogeneous liquid crystal cell and an array of liquid crystals formed on the first substrate. A switching element for controlling a voltage, a pixel electrode for applying an electric field to the liquid crystal cell by on / off control of the switching element, a first alignment film formed on the pixel electrode and determining an initial alignment state of the liquid crystal, A polarizer attached to the opposite side of the first substrate, a counter electrode formed on the second substrate and applying an electric field to the liquid crystal cell together with the pixel electrode, a color filter layer formed on the counter electrode, a first alignment film formed on the counter electrode, And a second alignment layer for determining an initial alignment state of the liquid crystal and at least one compensation film formed on the first substrate or the second substrate to compensate for the phase difference of transmitted light. , It comprises a character analyzer deposited on the compensation film.

The compensation film is a domain-compensated compensation film, and each domain has different optical properties by different refractive indices.

The compensation film forms a liquid crystal cell that reacts to light, particularly ultraviolet light, on a substrate, and then divides the domain by blocking light with a mask to irradiate light.

Another embodiment of the present invention relates to a reflective multi-domain homogeneous liquid crystal display device, and in the case of a two-domain reflective type, it exhibits the same effect as that of a four domain of a transmissive liquid crystal display device.

In addition, the hybrid-aligned nematic liquid crystal display device driven by the electric field control birefringence method similarly to the homogeneous liquid crystal display device, the homogeneous liquid crystal display device, and the homogeneous liquid crystal display device by adopting the domain-divided compensation film The same effect as in According to such a multi-domain liquid crystal display device, it is very advantageous to secure a wide viewing angle, and the color inversion region can be widened.

FIG. 1A is a cross-sectional view of a general homogeneous liquid crystal display device, and FIG. 1B is a view showing a relationship between an alignment direction of a liquid crystal of FIG. 1A and an optical axis direction of a compensation film.

FIG. 2 is a view showing a twisted nematic liquid crystal display device having a conventional pixelated compensation film. FIG.

3 is a view showing a method of manufacturing a domain-divided compensation film of the present invention.

4 is a diagram illustrating a compensation film divided into two domains by a refractive index difference on the compensation film of FIG. 3.

5 is a view showing a relationship between an optical axis and a retardation of a compensation film.

6 (a) and 6 (b) show the relationship between the alignment direction of the liquid crystal and the optical axis direction of the compensation film of the liquid crystal display device divided into four domains according to the present invention.

7 (a) to (e) are views showing the orientation of liquid crystals according to the present invention.

8 (a), (b) and (c) are views according to another embodiment of the present invention.

9 (a), (b) and (c) are views according to another embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

300: transparent substrate 301: liquid crystal film

303: photomask 601, 603: alignment direction of liquid crystal

605: optical axis direction of the compensation film 805, 811: alignment film

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

3 is a view illustrating an example of a method for manufacturing a domain-divided compensation film according to the present invention. As shown in the drawing, the domain-divided compensation film is first cured by ultraviolet rays on the transparent substrate 300. The liquid crystal film (first compensation film) 301 having is coated (S1). Thereafter, the liquid crystal film 301 is blocked by the photomask 303 and then irradiated with ultraviolet rays (S2). After the region exposed and blocked by the photomask 303 are separated into domains D1 and D2 having different refractive indices (S3). Subsequently, the second compensation film 305 is attached in a direction perpendicular to the optical axis of the domains D1 and D2 described above (S4). When the refractive index of the domain D1 of the first compensation film 301 not exposed to ultraviolet rays is A1, the refractive index of the domain D2 exposed to ultraviolet rays is A ', and the refractive index of the second compensation film 305 is A2, the magnitude of the refractive index. Is a relationship of A '< A2 < A1, and in this case, domains D1 and D2 having different refractive indices are formed.

FIG. 4 is a diagram illustrating a compensation film divided into two domains by a difference in refractive index on the compensation film of FIG. 3. The retardation size of the domain-divided compensation film varies depending on the type of liquid crystal, and is an example of homogeneous alignment. In this case, the size of the retardation can be obtained from Equation 1 below.

(A1-A2) = (A2-A1 ') ≒ 40 nm

Where A1 '= 0nm plane A1 = 2A2

The liquid crystal display device manufactured by employing the compensation film as described above retains both the excellent optical characteristics of the vertical alignment and the stability of the horizontal alignment. In the same liquid crystal, the required cell thickness is thinner than that of the TN type. It can be increased (dΔn = 476 nm for TN and dΔn = 275 nm for homogeneous).

5 is a view showing the optical axis of the compensation film shown in Figure 4, if only the conditions between the n _x axis (slow axis) and the n _y (slow axis) of the compensation film, other compensation film than the compensation film of the present invention Also available. In addition, it is necessary to attach another compensation film, for example, a biaxial compensation film (C-plate), in order to increase the viewing angle. Compensation film with a change of is also available. In the figures, R represents retardation.

6A is a plan view of a liquid crystal cell of a four-domain divided liquid crystal display device according to the present invention, and (B) is a plan view of a compensation film. In the present invention, the liquid crystal cell is composed of four homogeneous domains. Reference numeral 601 in the drawing denotes the alignment direction of the liquid crystal by the alignment film of the lower plate, reference numeral 603 denotes the alignment direction of the liquid crystal by the alignment film of the top plate, and reference numeral 605 denotes the optical axis direction of the compensation film. At this time, the alignment direction of the liquid crystal forms an angle of 45 ° with the polarizer (not shown) and the analyzer (not shown). In order to make the black state, the optical axis direction of the compensation film (A-plate) should be perpendicular to the alignment direction of the liquid crystal, so the optical axis direction of each domain requires a two-domain divided compensation film having the same structure as in (b).

FIG. 7 illustrates an example in which the alignment direction of the liquid crystal shown in FIG. 6 is configured in various forms. As shown in the drawing, in the case of (A) and (B), the two-domain divided compensation film has a domain line in a horizontal row form. In the case of (C), the domain boundary is arranged in the form of a vertical stripe of the two-domain divided compensation film. In case of (D) and (E), 4 domain divided compensation film is required.

The orientation direction of the first alignment layer or the second alignment layer of the present invention is a polyamide or polyimide-based compound, PVA (polyvinylalcohol), polyamic acid (polyamic acid) or SiO ₂ to apply a material, such as rubbing It can be determined by performing, or may be determined by applying a photo-alignment material such as polysiloxanecinnamate, polyvinylcinnamate or cellulosecinnamate and irradiating light. However, photoalignment is advantageous in order to prevent loss of the substrate during the process and to increase the reliability of the liquid crystal. Light irradiation is performed by irradiating the polarized or unpolarized light once or more, wherein the above-mentioned light is preferably ultraviolet.

8A is a diagram illustrating a reflective two-domain homogeneous liquid crystal display device. A pixel electrode 809 and a first alignment layer 811 serving as a reflecting plate are formed on a first substrate 801. A counter electrode (not shown) and a second alignment layer 805 are formed on the second substrate 803 to form an electric field together with the pixel electrode 809, and a domain-compensated compensation film is formed on the opposite side of the substrate 803. It is.

8B and 8C show the orientation directions of the liquid crystals and the optical axis directions of the compensation film, which are possible in the liquid crystal display device of (A), wherein the two-domain compensation film has a vertical stripe shape in (B), ( In (c), domain boundaries are located in the form of horizontal lines. In the figure, reference numeral 801a denotes the alignment direction of the liquid crystal by the first alignment layer 811, reference numeral 803a denotes the alignment direction of the liquid crystal by the second alignment layer 805, and reference numeral 807a denotes the optical axis direction of the compensation film.

In the case of the reflective type, the thickness of the liquid crystal cell is half that of the transmissive type, and light passes through the liquid crystal cell twice so that a two-domain effect of the transmissive type can be obtained in one domain. In this respect, the reflective two-domain homogeneous liquid crystal display device has the same effect as the transmissive four-domain homogeneous liquid crystal display device.

FIG. 9A is a diagram illustrating a reflective two-domain hybrid alignment nematic liquid crystal display device driven by an electric field control birefringence method as in the homogeneous liquid crystal display device of FIG. 8, and serves as a reflector on the first substrate 901. A pixel electrode 909 and a first alignment layer 911 are formed, and an opposite electrode (not shown) and a second alignment layer 905 forming an electric field together with the pixel electrode 909 on the second substrate 903. And a domain-compensated compensation film is formed on the opposite side of the substrate 903.

9 (b) and 9 (d) show the alignment directions of the liquid crystals and the optical axis directions of the compensation film, which are possible in the liquid crystal display device of (a), wherein the two-domain compensation film has a vertical stripe shape in (b), ( In (c), domain boundaries are located in the form of horizontal lines. In the drawing, reference numeral 901a denotes the alignment direction of the liquid crystal by the first alignment layer 911, reference numeral 903a denotes the alignment direction of the liquid crystal by the second alignment layer 905, and reference numeral 907a denotes the optical axis direction of the compensation film.

As described above, even when the hybrid alignment nematic liquid crystal display device is configured as a multidomain of two domains or more using a domain-compensated compensation film according to the present invention, the same effect as in the homogeneous liquid crystal display device can be expected.

According to the present invention, by adopting at least one domain-divided compensation film in a multi-domain field control birefringent liquid crystal display device driven in a white background mode, it is possible to obtain better viewing angle characteristics and to use a liquid crystal cell having a small retardation. Therefore, the response speed of the liquid crystal is relatively faster than that of the conventional twisted nematic liquid crystal display device. Further, by photoalignment of the liquid crystal alignment film, it is possible to protect the substrate from dust or static electricity generated during the process, thereby increasing the reliability of the liquid crystal.

Claims (8)

A pair of first and second substrates facing each other, An electric field controlled birefringence type liquid crystal cell formed between the first and second substrates and having a plurality of pixel regions; A switching element formed on the first substrate to control an arrangement of liquid crystals; A pixel electrode for applying an electric field to the liquid crystal cell by on / off control of the switching element; A first alignment layer formed on the pixel electrode to determine an initial alignment state of the liquid crystal; A polarizer formed on the first substrate, An opposite electrode formed on the second substrate and applying an electric field to the liquid crystal cell together with the pixel electrode; A second alignment layer formed on the counter electrode and determining an initial alignment state of the liquid crystal together with a first alignment layer; At least one domain-divided compensation film formed on the first substrate or the second substrate to compensate for the phase difference of the transmitted light passing through the liquid crystal cell; A multi-domain liquid crystal display device comprising an analyzer formed on the second substrate. The multi-domain liquid crystal display device according to claim 1, wherein the liquid crystal cell is homogeneous aligned. The multi-domain liquid crystal display device of claim 1, wherein the liquid crystal cell is hybridly aligned. The multi-domain liquid crystal display device according to claim 1, wherein the retardation of the liquid crystal cell is 476 nm or less. The multi-domain liquid crystal display device according to claim 1, wherein the retardation of the liquid crystal cell is 200 to 350 nm. The multi-domain liquid crystal display of claim 1, wherein the compensation film is divided into four domains. The method of claim 1, wherein the material constituting the first and second alignment layers is selected from the first group consisting of polysiloxanecinnamate, polyvinylcinnamate, and cellulosecinnamate. A multi-domain liquid crystal display device. A pair of first and second substrates facing each other, An electric field controlled birefringence type liquid crystal cell formed between the first and second substrates and having a plurality of pixel regions; A switching element formed on the first substrate to control an arrangement of liquid crystals; A reflective electrode for applying an electric field to the liquid crystal cell by on / off control of the switching element; A first alignment layer formed on the reflective electrode to determine an initial alignment state of the liquid crystal; An opposite electrode formed on the second substrate and applying an electric field to the liquid crystal cell together with the pixel electrode; A second alignment layer formed on the counter electrode and determining an initial alignment state of the liquid crystal together with a first alignment layer; And at least one domain-divided compensation film formed on the second substrate to compensate for the phase difference of transmitted light passing through the liquid crystal cell.