KR20020027049A - Smectic liquid crystal display in a transverse electrode configuration - Google Patents

Abstract

PURPOSE: A smectic LCD(Liquid Crystal Display) device using a horizontal electrode alignment structure is provided to form more than two electrodes on at least one substrate, and to inject smectic liquid crystal to fabricate a horizontal configuration sample. CONSTITUTION: A first substrate(10) in which an alignment layer(20) is applied to more than two electrodes(40) formed on an internal side. A second substrate(11) to which an alignment layer(20) is applied in an internal side. Smectic liquid crystal(30) is injected between the first substrate(10) and the second substrate(11). The first substrate(10) and the second substrate(11) are glass substrates or plastic substrates. The alignment layer(20) is made of a horizontal configuration polymer layer for configuring liquid crystal. The smectic liquid crystal(30) has positive or negative dielectric anisotropy. And polymers(70,71) are respectively added on each external surface of the first substrate(10) and the second substrate(11).

Description

Smectic liquid crystal display using transverse electrode array structure {SMECTIC LIQUID CRYSTAL DISPLAY IN A TRANSVERSE ELECTRODE CONFIGURATION}

The present invention relates to a smectic liquid crystal display device, and more particularly, to a liquid crystal display device having a transverse electrode array structure having a wide and symmetrical viewing angle and a high-speed response characteristic.

LCDs with current twisted nematic (TN) modes are becoming a critical weakness of narrow viewing angles and slow response speeds as they become higher quality and larger screens. Among them, various methods have been proposed as a way to overcome the narrow viewing angle. Optical compensation is a commonly used technology. Based on the structurally asymmetrical driving of TN-LCD, the birefringence change is compensated for by the azimuth angle using a uniaxial optical compensation film. There is a disadvantage that the manufacturing cost increases.

In contrast, an in-plane switching (IPS) method is proposed, in which an electrode surface is formed and driven on one side of a liquid crystal substrate. For example, an electric field is obtained by aligning a liquid crystal horizontally and matching an optical axis of the liquid crystal with one polarization axis. When this is not applied, a dark state is obtained and a bright state is obtained as an electric field is applied. For the conventional method, this method has the advantage of ensuring a wide viewing angle because the change of the average optical axis occurs in a plane parallel to the surface of the specimen, but has the disadvantage of long response time, low aperture ratio, and high driving voltage.

In addition, there are techniques for improving viewing angle characteristics by using a multi-domain alignment method, unlike the above-described method. The axially symmetric aligned microcell (ASM) method is a technique for securing a viewing angle of circular symmetry by manufacturing liquid crystals and polymers and then using phase separation. It is possible to maintain a constant specimen spacing in a large area without rubbing, so it is highly applicable, but at present, the complexity of the process, the reproducibility problem, and the reliability of the polymer are low. Another method, a-TN (amorphous twisted nematic) method is a technique that widens the viewing angle by dividing the pixel into minute regions having an arbitrary direction and size in order to increase the number of division of the pixel. This method has the advantage that the fabrication process is very simple, but it is difficult to control the size of the micro area, which makes it difficult to apply to large area LCD. The multi-domain twisted nematic (MD-TN) method divides a pixel into a plurality of constant regions and secures a viewing angle symmetry according to an azimuth angle by changing the twist direction of nematic molecules in each region. However, since the rubbing process must be performed in different directions for each region, the manufacturing process is complicated and there is a disadvantage in that the production yield is reduced. MD-VA (multi-domain vertical alignment) is a method of dividing a pixel into several different areas and maintaining the vertical direction of the liquid crystal director in the initial state. Rain has a big advantage. However, there is a difficulty in rubbing each region in different directions. In addition, there is also a method of differently pre-tilt angle according to the region on the surface of the specimen without rubbing, but this method requires a uniform deposition of an alignment material such as SiOx, which is difficult in the process.

On the other hand, in order to solve the problem of the slow response speed of LCD, recently, techniques mainly using ferroelectric liquid crystals have been proposed. Liquid crystals used in liquid crystal display devices are classified into nematic liquid crystals having only an orientation order according to the molecular arrangement structure, and smectic liquid crystals having a positional order, and subdivided into ordinary dielectric liquid crystals and ferroelectric liquid crystals according to the presence or absence of spontaneous polarization. can do. The interaction of the nematic liquid crystal with the electric field and the electric field is nonpolar and is explained macroscopically by the dielectric anisotropy of the liquid crystal molecules. In the twisted liquid crystal display device using the nematic liquid crystal, it is difficult to apply to the liquid crystal display device requiring high-speed response with the response speed of molecules due to dielectric anisotropy of several tens ms.

Compared to nematic liquid crystals, ferroelectric liquid crystals are very fast by several tens of microseconds because the response speed of molecules is induced by spontaneous polarization and the polarity interaction between the electric field, which is suitable for high speed moving images. However, since the surface stabilized ferroelectric liquid crystal (SSFLC) is operated in a bistable mode, it is impossible to continuously display gradations and forms a layer structure having a positional order. It is very difficult to obtain a uniform orientation of a large area. Recently, a multi-gradation display function has been achieved by a time or space division driving method, but there are still many problems such as continuous gray scale display is impossible, and introduction of a complex driving system is required.

Recently introduced anti-ferroelectric liquid crystal display device has a faster response speed and limited multi-gradation display function than nematic, but the large-area uniform alignment problem and the screen shake phenomenon remain serious problems.

On the contrary, a horizontally oriented spirally deformed ferroelectric liquid crystal which achieves continuous gray scale display by deforming the helical structure by applying an electric field to the horizontally oriented structure of the ferroelectric liquid crystal having a very short spiral pitch relative to the wavelength of light. Crystal: DHF) has been proposed. However, this device also shows a fast response speed, but in order to obtain a uniform orientation of a large area, an additional alignment process such as twisting or electric field treatment is required, and a band structure or the like is formed to reduce the contrast ratio and cause problems such as screen shaking. Is present.

As described above, the biggest problem common in manufacturing ferroelectric or antiferroelectric liquid crystal display devices having a layer structure is the uniform orientation of large areas, and problems such as difficulty in display of gray scales and deterioration of image quality at each device. Have. Specifically, ferroelectric or semiferroelectric liquid crystals generally have a spiral pitch, and because of a strong polarization interaction between spontaneous polarization and an electric field, a defect structure such as a band structure appears, and thus it is very difficult to obtain a uniform single alignment structure. As a result, in the case of the conventional horizontally oriented spirally deformed ferroelectric liquid crystal display, the contrast ratio is lowered, and it is impossible to obtain high transmittance.

In the case of the most recently proposed Vertical Configuration Deformed Helix Ferroelectric Liquid Crystal (VC-DHF), the application of a strong electric field results in deformation or breaking of the layer arrangement and an electro-optical clear threshold. Since there is no voltage, it is difficult to apply to a passive driving liquid crystal display. Therefore, active driving using TFTs is indispensable.

An object of the present invention is to form a horizontal alignment specimen by forming two or more electrodes on at least one substrate and injecting smectic liquid crystal to solve the problems of the prior art, unlike smetic liquid crystal There is no interlayer interference, which enables high-speed response characteristics, not only has a threshold voltage that does not exist in the spirally deformed ferroelectric liquid crystal, but also continuous gray scale display, which is impossible in a surface stabilized ferroelectric liquid crystal display device, as in the TN mode. By using a technology similar to In-Plane Switching, it is to provide a liquid crystal display device that can obtain a wide and symmetrical viewing angle.

1A is a cross-sectional view of a horizontally oriented specimen according to the present invention.

1b is an internal perspective view of a horizontally oriented specimen according to the present invention;

2 is a partial plan view showing a transverse electrode array structure.

3A is a graph showing the intensity of transmitted light according to an applied voltage in the case of having positive dielectric anisotropy.

3B is a graph showing the intensity of transmitted light according to an applied voltage in the case of having negative dielectric anisotropy.

Figure 4a is a driving state of the specimen when the electric field is not applied in the absence of the pretilt angle.

Figure 4b is a driving state of the specimen when the electric field is applied in the absence of the pretilt angle.

Figure 4c is a driving state of the specimen when the electric field is not applied when there is a pretilt angle.

Figure 4d is a driving state of the specimen when the electric field is applied when there is a pretilt angle.

5A is a view of the microscope when an orthogonal polarizer is disposed and no electric field is applied to the specimen.

5B is a view of microscope observation when an orthogonal polarizing plate is disposed and an electric field is applied to the specimen.

6A is a diagram illustrating a voltage waveform applied to a specimen.

6b is a diagram showing the response characteristics of a specimen in the case of positive dielectric anisotropy.

6C is a diagram illustrating a voltage waveform applied to a specimen.

6D is a diagram showing the response characteristics of a specimen in the case of negative dielectric anisotropy.

7A shows the viewing angle characteristics of a specimen in the case of positive dielectric anisotropy.

FIG. 7B shows the viewing angle characteristics of a specimen when having negative dielectric anisotropy. FIG.

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

10: first substrate 11: second substrate

20, 21: alignment film 30: smectic liquid crystal

40 electrode 50 liquid crystal director

60: smectic liquid crystal layer 70, 71: polarizing plate

80: rubbing direction 90: thickness of specimen

100: approved electric field

110: liquid crystal director moving direction by the electric field

An apparatus of the present invention for achieving the above object is a liquid crystal display device in which a liquid crystal is injected between a first substrate and a second substrate facing each other, the alignment film is applied on at least two electrodes formed on the inner surface portion And a smectic liquid crystal injected between the first substrate, the second substrate having the alignment layer coated on the inner side portion, and the first substrate and the second substrate.

In addition, at least one electrode may be formed on the second substrate of the present invention, and a horizontal alignment layer or a vertical alignment layer may be coated on the electrode.

According to the present invention, a polarizing plate may be attached to the outer side surfaces of the first and second substrates, respectively, and the polarizing plate formed on the first substrate and the polarizing plate formed on the second substrate may be perpendicular to or parallel to each other, or 0 ° to 90 °. It consists of an angle between and a back light source is used, It is characterized by the above-mentioned.

In addition, the front light source may be used by forming a reflecting plate on the inner surface or the outer surface of any one of the two substrates.

The present invention is characterized in that an additional optical compensation film may be inserted between the outer surface of the first substrate and the second substrate and the polarizing plate.

In the present invention, the smectic liquid crystal injected between the first substrate and the second substrate may be made of positive or negative dielectric anisotropic liquid crystal.

In addition, in the present invention, the light transmittance, that is, the light transmittance can be adjusted by adjusting the distance between the plurality of electrodes formed on the first substrate.

The rotation angle (azimuth angle) of the liquid crystal molecules of the smectic liquid crystal moving from the first substrate to the second substrate of the present invention is made from 0 ° to 180 °, and the molecular tilt angle of the smectic liquid crystal is Is made from 0 ° to 90 °.

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

The structure of a specimen according to one embodiment of the present invention is the same as that of FIGS. 1A and 1B.

As shown in FIGS. 1A and 1B, a smectic liquid crystal display device using the transverse electrode array structure according to the present invention includes a first method in which an alignment layer 20 is coated on at least two electrodes 40 formed on an inner side surface thereof. And a smectic liquid crystal 30 injected between the substrate 10, the second substrate 11 having the alignment layer 21 coated on the inner side surface, and the first substrate 10 and the second substrate 11. It is done. 2 is a partial plan view of an electrode formed in the transverse direction on the first substrate.

The first and second substrates 10 and 11 may be glass substrates or plastic substrates, and the alignment layer 20 may be formed of a horizontal alignment polymer layer for liquid crystal alignment. Heat treatment by spin coating.

In addition, in the present invention, the smectic liquid crystal 30 is made of a smectic liquid crystal having positive or negative dielectric anisotropy.

As shown in FIGS. 1A and 1B, polarizing plates 70 and 71 are respectively added to the outer surface portions of the first and second substrates 10 and 11 of the present invention, and the polarizing plates 70 and 71 are perpendicular to each other. This allows the polarizer and analyzer to have + 90 ° or -90 °. Alternatively, the polarizers 70 and 71 may be disposed in parallel to each other so that the polarization axes of the polarizer and the analyzer may be parallel to each other. In addition, the polarizing plates 70 and 71 may be installed at an angle between 0 ° and 90 °, so that the polarization axes of the polarizer and the analyzer may form an angle between 0 ° and 90 °.

As an embodiment of the present invention, the spacing of the specimens of the Smectic liquid crystal display using the transverse electrode array structure was maintained using a 2 μm glass spacer. The smectic liquid crystal injected into the specimen has either positive or negative dielectric anisotropy, either IS5512 (Δε> 0) or IS5511 (Δε <0) (Merck Co.).

The transmission characteristics of the specimen of the smectic liquid crystal display of the present invention produced by the above-described method are the same as in FIGS. FIG. 3A shows voltage vs. transmittance characteristics of smectic liquid crystals having positive dielectric anisotropy, and FIG. 3B shows voltage vs. transmittance characteristics of smectic liquid crystals having negative dielectric anisotropy. As shown in the same figure, the high driving threshold voltage is due to the voltage drop due to the low dielectric anisotropy value and the wide electrode spacing. The larger the dielectric anisotropy of the liquid crystal and the narrower the electrode gap, the lower the threshold voltage.

4A to 4D show the change of the liquid crystal director when the specimen of the Smectic liquid crystal display device is made by the above configuration, and FIG. 4A shows that the inclination angle of the Smectic liquid crystal is lower than 22.5 °. Fig. 4b shows the driving state of the specimen when the electric field is not applied when there is almost no, and Fig. 4b shows the driving of the specimen when the electric field is applied when the molecular tilt angle α of the smectic liquid crystal is 22.5 ° or less and there is almost no pretilt angle. State diagram. In this case, the liquid crystal director has a 180 ° azimuth angle Φ on the smectic cone.

FIG. 4C is a driving state diagram of a specimen when an electric field is not applied when the inclination angle α of the smectic liquid crystal is 22.5 ° or more, and FIG. 4D is a 22.5 degree molecular inclination angle α of the smectic liquid crystal. This is the driving state of the specimen when an electric field is applied when there is a pretilt angle above °.

4A to 4D, 50 represents a liquid crystal director, 60 represents a smectic liquid crystal layer, 80 represents a rubbing direction, 90 represents a thickness of the specimen, 100 represents an applied electric field, and 110 represents a direction in which the liquid crystal director moves by the electric field. . In addition, γ is an angle formed between the z-axis and the rubbing direction 80, which is larger than 0 °, so that the liquid crystal molecules have directivity when an electric field is applied. In this case, the magnitude of the azimuth angle at which the liquid crystal director moves on the smectic cone is 90 ° ≦ Φ <180 °. In the same figure, the pretilt angle θ _p of the liquid crystal molecules may be expressed by 0 ° ≦ θ _p ≦ 2α − 45 °. As shown in Figs. 4A and 4C, the liquid crystal in the specimen is arranged in an inclined direction with respect to the electrode when no electric field is applied. When the electric field is applied, the liquid crystal moves along the conical surface of the smectic liquid crystal as shown in FIGS. 4B and 4D.

5A and 5B are views of the specimen under orthogonal polarizer. FIG. 5A shows a dark state when no electric field is applied, and FIG. 5B shows driving characteristics of circular symmetry when an electric field is applied. 6A and 6C show applied voltage waveforms. 6B and 6D show the response characteristics of the specimen by the voltage waveforms of FIGS. 6A and 6C, respectively, and are much faster than the slow response time of the IPS method using the conventional nematic liquid crystal. 6A shows positive dielectric anisotropy, with a rise time of 3.20 ms and a fall time of 13.80 ms, for a total of 17.00 ms. 6B shows negative dielectric anisotropy, with a rise time of 3.20 ms and a fall time of 5.60 ms, for a total of 8.80 ms. This shows at least three times faster results than the TN method. 7A and 7B are viewing angle characteristics of smectic liquid crystals having positive or negative dielectric anisotropy, respectively, and it can be seen that a wide viewing angle is secured because a change in the average optical axis of the liquid crystal molecules occurs on a plane parallel to the surface of the specimen.

As described above, in the present invention, two or more electrodes are formed on one surface of the specimen, and both surfaces of the specimen are coated with a horizontal alignment agent, thereby implementing a horizontal alignment smectic liquid crystal display device having excellent viewing angle symmetry and high-speed response characteristics. Since the method implemented in the present invention uses an electrode structure similar to the existing In-Plane Switching, it is not necessary to develop additional new electrode-related technologies, and has a wide and symmetrical viewing angle characteristic similar to that of IPS, continuous gray scale display characteristics such as TN mode, and It is a technique suitable for a liquid crystal display which simultaneously has the high-speed response characteristics of the smectic liquid crystal.

Claims (18)

In a liquid crystal display device in which a liquid crystal is injected between a first substrate and a second substrate facing each other, A first substrate on which an alignment film is applied on at least two electrodes formed on an inner surface portion, A second substrate having an alignment film applied to an inner surface portion thereof, and A smectic liquid crystal display using a transverse electrode array structure, characterized in that the smectic liquid crystal is injected between the first substrate and the second substrate. 2. The smectic liquid crystal display device according to claim 1, wherein at least one electrode is formed on the second substrate. The smectic liquid crystal display device using the horizontal electrode array structure according to claim 2, wherein a horizontal alignment layer is coated on the electrodes. The smectic liquid crystal display device using the horizontal electrode array structure according to claim 2, wherein a vertical alignment layer is coated on the electrodes. 2. The smectic liquid crystal display device using the horizontal electrode array structure according to claim 1, wherein polarizing plates are respectively added to outer surface portions of the first and second substrates, and a rear light source is used. 6. The smectic liquid crystal display device according to claim 5, wherein the polarizer formed on the first substrate and the polarizer formed on the second substrate are orthogonal to each other. 6. The smectic liquid crystal display device according to claim 5, wherein the polarizing plate formed on the first substrate and the polarizing plate formed on the second substrate are parallel to each other. 6. The smectic liquid crystal display device according to claim 5, wherein the polarizing plate formed on the first substrate and the polarizing plate formed on the second substrate have an angle between 0 ° and 90 °. 6. The smectic liquid crystal display device according to claim 5, wherein an additional optical compensation film is inserted between an outer surface of the first substrate or the second substrate and the polarizing plate. The transverse electrode array of claim 1, wherein a reflecting plate is formed on an inner side or an outer side of one of the first and second substrates, and a polarizing plate is attached to the outer side of the other substrate. Smectic liquid crystal display using the structure. 11. The smectic liquid crystal display device according to claim 10, wherein an additional optical compensation film is inserted between the one substrate and the polarizing plate. 12. The smectic liquid crystal display device according to any one of claims 1 to 11, wherein the smectic liquid crystal comprises a positive dielectric anisotropic liquid crystal. 12. The smectic liquid crystal display device according to any one of claims 1 to 11, wherein the smectic liquid crystal comprises a negative dielectric anisotropic liquid crystal. 2. A smectic liquid crystal display device using a transverse electrode array structure according to claim 1, wherein light transmission characteristics are adjusted by adjusting a distance between the electrodes. The method of claim 1, wherein the rotation angle (azimuth angle) of the liquid crystal molecules of the smectic liquid crystal moving from the first substrate to the second substrate is from 0 ° to 180 °. Mechtic liquid crystal display. 2. The smectic liquid crystal display device using a transverse electrode array structure according to claim 1, wherein a molecular tilt angle of the smectic liquid crystal is made from 0 ° to 45 °. 2. The smectic liquid crystal display device using a transverse electrode array structure according to claim 1, wherein a molecular tilt angle of the smectic liquid crystal is made from 45 ° to 60 °. 2. The smectic liquid crystal display device using a transverse electrode array structure according to claim 1, wherein a molecular tilt angle of the smectic liquid crystal is made from 60 ° to 90 °.