KR100320102B1 - Vertically Aligned Helix-Deformed Liquid Crystal Display - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertically oriented spiral strain liquid crystal display device, and in particular, the device of the present invention comprises first and second glass substrates having two surfaces facing each other, and formed on the first surface of the first glass substrate. A first glass electrode having a first potential, a second transparent electrode formed on a first surface of the first glass substrate and having a second potential different from the first potential, and a first glass having first and second transparent electrodes formed thereon; A first vertical alignment layer formed on the first surface of the substrate, a second vertical alignment layer formed on the first surface of the second glass substrate, and first and second glass substrates in which the first and second vertical alignment layers face each other; A ferroelectric liquid crystal in which a spiral structure is deformed and molecules rotate in a specific direction in response to an electric field formed between the first and second transparent electrodes and has a spiral pitch shorter than a wavelength of light, and is enclosed between the first and second wavelengths. Made of substrate And a second polarizing plate provided on the second surface of the first polarizing plate and the second glass substrate, the second polarizing plate having polarization perpendicular to the first polarizing plate. Therefore, in the present invention, it is possible to uniformly vertically align a large area, have a high contrast ratio, and can be continuously deformed according to the size of the electric field, so that continuous gradation display is possible, and by multiple orientations by the arrangement of electrodes on the same substrate. It has a wide viewing angle characteristic.

Description

Vertically Aligned Helix-Deformed Liquid Crystal Display

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a vertically oriented spiral modified liquid crystal display, and in particular, a large area is obtained by vertically aligning a ferroelectric liquid crystal having a spiral pitch shorter than the wavelength of light and controlling the direction of molecular rotation through the deformation of the spiral structure by an electromagnetic field parallel to the substrate. The present invention relates to a new vertically-aligned spiral-modified liquid crystal display device having a high contrast ratio with a uniform orientation of, enabling continuous gray scale display, and securing a wide viewing angle by arranging electrodes on the same substrate.

Conventional liquid crystal display device uses the electro-optic effect of the liquid crystal, the transparent electrode is formed on each of the two substrates, the alignment layer to align the liquid crystal on the electrode surface, and the liquid crystal is injected between the two substrates It was made by enclosing.

In addition, polarizers are provided on the outer surfaces of the two substrates such that the polarities are perpendicular to each other.

The conventional liquid crystal display device displays information on a screen by acting to pass or block light by itself. Therefore, in order to pass or block light, a voltage must be applied to induce molecular rotation of the liquid crystal to change the orientation direction.

Meanwhile, liquid crystals used in liquid crystal display devices are classified into nematic liquid crystals having only an aromatic order and smacktic liquid crystals having a positional order according to the molecular alignment structure. Can be broken down into

The interaction of the dielectric with the nematic liquid crystal and the electric field is nonpolar and is explained macroscopically by the dielectric anisotropy of the liquid crystal molecules. In the twisted nematic liquid crystal display using the nematic liquid crystal, the response speed of molecules due to dielectric anisotropy is in the range of tens to hundreds of ms, which makes it difficult to apply to liquid crystal display devices requiring high-speed response.

Moreover, there are disadvantages of showing narrow viewing angles and low contrast ratio properties without the use of multiple orientations or additional optical films.

Compared to nematic liquid crystals, ferroelectric liquid crystals have high response speeds of molecules due to spontaneous polarization and polar interaction between electric fields, which is very high in the order of several tens of microseconds, which is suitable for high speed moving images.

However, the conventional surface stabilized ferroelectric liquid crystal display device operates in bistable mode, and thus it is impossible to continuously display gray scales, and it is very difficult to obtain a uniform orientation of a large area because a layer structure having a positional order is formed.

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 display of gray scales is impossible and the introduction of a complex driving system is required.

Recently introduced anti-ferroelectric liquid crystal display device has faster response speed and limited multi-gradation display function than nematic, but the problem of uniform orientation of large area and screen shaking is still a serious problem.

On the contrary, a horizontally oriented spiral-modified ferroelectric liquid crystal display has been proposed in which a spiral field is modified by applying an electric field to a horizontal alignment structure of a ferroelectric liquid crystal having a very short spiral pitch compared to a wavelength of light to achieve continuous gray scale display.

However, this device also shows high response speed, but in order to obtain a uniform orientation of the large area, additional alignment processes such as twisting and electric field treatment are required, and a band structure is formed to reduce the contrast ratio and to cause problems such as screen shaking. exist.

As described above, the biggest problem that is common in manufacturing ferroelectric or antiferroelectric liquid crystal display devices having a layer structure is the uniform orientation of a large area, and each device has disadvantages such as difficulty in display of gray scales and degradation of image quality. Have.

Specifically, ferroelectric or antiferroelectric 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 order to realize a high quality large screen liquid crystal display, excellent viewing angle characteristics are required in addition to a large area of uniform alignment, high response speed, and high contrast ratio. Liquid crystal is a material having very high optical anisotropy, and the effective refractive index varies greatly depending on the angle of light incident on the liquid crystal molecules. In the widely used twisted nematic mode, the contrast ratio is very asymmetrical due to the change in the azimuth angle in the inclined direction about an axis perpendicular to the substrate surface.

As an improvement method for this, an optical compensation method using a short-axis or biaxial retardation optical film under conditions for compensating the effective refractive index of the liquid crystal layer is widely used.

As another method, a method of using multiple alignments in two or four subpixels in which the alignment directions of liquid crystals are different in each pixel is used. Recently, in-substrate switching liquid crystal modes using molecular switching on the same substrate surface have been introduced.

Among the above methods, in the case of the multi-orientation method, since multiple rubbing or photo-alignment techniques are used in manufacturing, at least two or more mask processes are used, there are problems such as the complexity of the process and securing the orientation reliability.

On the other hand, in the switching mode in the substrate, nematic liquid crystals are currently employed, and the response speed is still low, resulting in a decrease in transmittance due to a low aperture ratio, a decrease in image quality due to an afterimage, and a misalignment. In addition, there are known optical compensation bending modes for compensating some viewing angle characteristics optically in the liquid crystal itself, and inverse twist nematic modes that exhibit high contrast ratio and excellent viewing angle characteristics. Does not have

An object of the present invention is to solve the problems of the prior art by vertically aligning a ferroelectric liquid crystal having a spiral pitch shorter than the wavelength of light between the two substrates and by using an electromagnetic field parallel to the substrate by the electrode arrangement in the same substrate The present invention relates to a new vertically-aligned spiral-modified liquid crystal display device having a high contrast ratio, a continuous gray scale display, and a wide viewing angle with a uniform orientation of a large area by controlling the rotation direction.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing the configuration of a transmissive vertically oriented spiral modified liquid crystal display device according to the present invention;

2 is a view for explaining the principle of operation of FIG.

3 is a graph showing the light transmission characteristics according to the electric field strength of the vertically oriented spiral modified liquid crystal display according to the present invention.

4 is a view showing light transmission response characteristics of a square wave voltage waveform of a vertically oriented spiral-modified liquid crystal display device according to the present invention;

5 is a view showing the configuration of one embodiment of the arrangement of the drive electrodes of the vertically oriented spiral modified liquid crystal display according to the present invention;

6 is a view showing the configuration of another embodiment of the drive electrode array of the vertically aligned spiral modified liquid crystal display according to the present invention.

Fig. 7 is a diagram showing the configuration of a reflective vertically aligning spiral modified liquid crystal display device according to the present invention.

<Description of the symbols for the main parts of the drawings>

10: first glass substrate 20: first transparent electrode

30: second transparent electrode 40; First vertical alignment layer

50: second glass substrate 60: second vertical alignment layer

70: ferroelectric liquid crystal 80: first polarizing plate

82: reflection plate 84: phase difference plate

90: second polarizing plate 100: pixel (ON)

110: pixel (OFF) 101-104: subpixel

120: reflector

In order to achieve the above object of the present invention, the apparatus of the present invention comprises first and second glass substrates each having two surfaces facing each other, and a first electrode formed on the first surface of the first glass substrate and having a first potential. A first transparent electrode, a second transparent electrode formed on the first surface of the first glass substrate and having a second potential different from the first potential, and on the first surface of the first glass substrate on which the first and second transparent electrodes are formed; A first vertical alignment layer formed on the second substrate, a second vertical alignment layer formed on the first surface of the second glass substrate, and first and second glass substrates facing each other; And a ferroelectric liquid crystal having a spiral pitch shorter than a wavelength of light and having a deformed spiral structure in response to an electric field formed between the first and second transparent electrodes to rotate molecules in a specific direction.

The transmission type further includes a first polarizing plate provided on a second surface of the first glass substrate, and a second polarizing plate provided on the second surface of the second glass substrate and having polarization perpendicular to the first polarizing plate.

In this device, the reflective type reflector is provided on the first or second surface of the second glass substrate, the second surface of the second glass substrate has no polarizing plate, and has the optical delay characteristic of 1/4 of the wavelength of light. A retardation plate is further provided on the second surface of the first glass substrate, and further includes a polarizing plate having an optical axis forming an angle of 45 ° with the optical axis of the retardation plate thereon.

That is, the present invention basically uses the spiral deformation phenomenon by applying the electric field of the ferroelectric liquid crystal as a driving principle. Unlike the conventional spiral deformation ferroelectric liquid crystal display, the axial direction of the liquid crystal is oriented perpendicular to the substrate, and transparent electrodes exist on only one surface of the substrate to facilitate continuous gray scale display by applying an electric field in the same substrate. Can be achieved. In the present invention, a high contrast ratio is obtained by uniform vertical alignment of a large area without further alignment process such as rubbing or electric field treatment.

In addition, by using two or four subpixels for each pixel by using the molecular rotation direction depending on the polarity of the electric field it is possible to implement a wide viewing angle characteristics by the original multi-orientation structure.

Hereinafter, with reference to the accompanying drawings, it will be described in detail the present invention through a preferred embodiment of the present invention.

1 shows a configuration of a transmissive vertically oriented spiral modified liquid crystal display device according to the present invention.

In the liquid crystal display of the present invention, the first and second transparent electrodes 20 and 30, such as ITO, are disposed on the first surface 12 of the first glass substrate 10 as shown in FIG. 5 or 6. Form alternately. The interval between the first and second transparent electrodes 20 and 30 is maintained in the range of several tens to several hundreds of micrometers and is set to 20 micrometers in this embodiment. Subsequently, a vertical alignment agent such as JALS-204 (Japan Synthetic Rubber Co.) is applied to the surface of the first surface 12 of the first glass substrate 10 on which the transparent electrodes 20 and 30 are formed, thereby forming the first vertical. The alignment film 40 is formed.

In addition, a second vertical alignment layer 60 is formed by coating a polyimide-based vertical alignment agent such as JALS-204 (Japan Synthetic Rubber Co.) on the surface of the first surface 52 of the second glass substrate 50. do.

Subsequently, the two glass substrates 10 and 50 face each other such that the first and second vertical alignment layers 12 and 52 face each other, and the gap thereof is maintained at about several μm. do. At this time, it is preferable that the product of the refractive index anisotropy of the liquid crystal and the substrate interval be smaller than 720 nm. When the surface inclination angle of the vertical alignment film with respect to the substrate surface is θ _S , it is 75 ° ≦ θs ≦ 90 °, and it is set to 90 ° in this embodiment. Then, a ferroelectric liquid crystal 70 such as FLC-108l7 (Rolic Ltd.) is injected and encapsulated between the two substrates 10 and 50. Here, in the ferroelectric liquid crystal, the larger the spontaneous polarization, the lower the applied voltage. In the present embodiment, 115 nC / cm 2 is used. In addition, the molecular tilt angle satisfies within the range of 22.5 ° ≦ θ ≦ 45 °, but has 34 ° in this embodiment. The spiral pitch should be shorter than 0.35 µm, and in this embodiment, 0.2 µm.

In the phase transition order of the ferroelectric liquid crystal 70 to be used, it is easy to obtain a uniform orientation when the Smectic A phase is present, but most of the materials do not have the Smetic A phase when the condition of the molecular tilt angle is satisfied. Therefore, in the embodiment of the present invention, the phase transition is made to an isotropic phase- (64.5 ° to 62.4 °) -chiral nematic phase- (62.4 ° to 61.5 °) -chiral smectic C phase (ferroelectric phase).

In the case of the transmission type, the first polarizing plate 80 is provided on the second surface 14 of the first glass substrate 10, and the second polarizing plate 90 is provided on the second surface 54 of the second glass substrate 50. Install it. The optical axis of the first polarizing plate 80 is 45 ° ± 3 ° with respect to the direction of the electric field parallel to the substrate. The optical side of the second polarizing plate 90 forms 90 ° with respect to the optical axis of the first polarizing plate 70.

The driving principle of the transmissive vertically oriented spiral strain ferroelectric liquid crystal display configured as described above is as follows.

When the electric field is not applied in the vertical alignment structure, that is, in the case of the central pixel of FIGS. 1 to 2, the spiral structure of the smectic layers of the liquid crystal is maintained so that the liquid crystal molecules are arranged in all the conical directions. 71) is perpendicular to the substrate. The projected structure of the molecular arrangement of the central pixel in Figure 2 can be seen that the molecules are arranged in all directions.

Thus, light is completely blocked between the two orthogonal polarizers 80 and 90.

However, when the electric field is applied, the polarization interaction between the polarization moment of the ferroelectric liquid crystal molecules and the electric field causes the average optical axis to be inclined with respect to the substrate according to the polarity of the applied electric field. As a result, the incident light is 45 ° with the electric field direction. It passes through the orthogonal polarizing plates 80 and 90. That is, in the left pixel, the liquid crystal molecules are all inclined in the −90 ° direction, that is, forward, so that the average optical axis direction 72 is inclined forward from the vertical direction. In FIG. 2, it can be seen that the projected structure of the molecular arrangement of the left pixel is arranged only downward.

However, in the right pixel, the liquid crystal molecules are all inclined rearwardly in the 90 ° direction, so that the average optical axis direction 73 is an n-shaped branch having the inclination backward in the vertical direction, and the second transparent electrode 30 ) Is composed of an m shape having three branches and arranged so that the branches of these two electrodes are alternately arranged with each other. Therefore, four subpixels have a 1 × 4 shape between these branches.

Therefore, in the pixel 100 in the on state, the directions of the electric fields applied from the four subpixels 101, 102, 103, and 104 are alternately arranged, and thus the odd subpixels 101 and 103 and the even subnumber are disposed. The average optical axis directions of the pixels 102 and 103 have symmetry in opposite directions. That is, a wide viewing angle can be ensured by the symmetric average optical axis direction of the plurality of subpixels in one pixel. Therefore, in the present invention, since a wide viewing angle can be easily secured by the configuration of the transparent electrode as compared to the conventional liquid crystal display devices, an additional optical film or the like is unnecessary.

6 shows the configuration of another embodiment of the drive electrode array of the vertically oriented spiral modified liquid crystal display device according to the present invention. According to another exemplary embodiment, an electrode structure includes a second transparent electrode 30 disposed between two first transparent electrodes 20, and a plurality of branches and a second transparent layer that are repeated in a vertical direction from the first transparent electrode 20. The plurality of branches extending in the vertical direction from the electrode are configured to be alternately arranged with each other. Thus, each subpixel divided by these branches has an average optical axis direction opposite to each other alternately along the horizontal direction. In such an electrode array structure, four subpixels have a 2 × 2 shape.

7 shows a configuration of a reflection type vertically oriented spiral modified liquid crystal display device according to the present invention. FIG. 7 shows that the reflective plate 120 is installed on the first surface 52 or the second surface 54 of the second glass substrate 50, and the second surface of the second glass substrate 50 (FIG. The polarizing plate 54 does not have a polarizing plate, and the retardation plate 84 is provided between the first glass substrate 10 and the polarizing plate 80. Therefore, the same structure is processed with the same code | symbol.

The optical axis direction of the phase difference plate 84 is comprised so that it may become 45 degrees with the optical axis direction of the polarizing plate 80. FIG. The retardation plate 84 has a phase delay of 1/4 of the incident light wavelength. It is preferable that the phase difference of the retardation plate 84 has a value between 160 x N nm and 200 x N nm (where N is 1,2,3, ...).

In the reflection type, when no electric field is applied, the average optical axis is in a direction perpendicular to the substrate, so the optical characteristic is determined by the phase delay of the retardation plate. The effective phase difference of light is realized in a dark state that is twice the phase delay of the retardation plate 84.

In the reflection type, when an electric field is applied, the average optical axis of the liquid crystal is inclined in the horizontal direction from the direction perpendicular to the substrate to have an effective birefringence. The bright state is realized by the phase delay depending on the magnitude of the product of the effective birefringence and the substrate spacing.

As described above, in the present invention, the uniform orientation of the large area and the continuous gray scale display function can be easily solved, and a high contrast ratio due to the vertical alignment is obtained. In addition, the original multi-domain structure is possible by designing the electrode array structure to obtain a wide viewing angle characteristic. In addition, since an alignment film surface treatment process such as rubbing is not required, the manufacturing process is simple, which is advantageous in reducing the manufacturing cost.

Although described above with reference to a preferred embodiment of the present invention, those skilled in the art various modifications and variations of the present invention without departing from the spirit and scope of the invention described in the claims below I can understand that you can.

Claims (10)

First and second glass substrates each having two surfaces facing each other; A first transparent electrode formed on a first surface of the first glass substrate and having a first potential; A second transparent electrode formed on a first surface of the first glass substrate and having a second potential different from the first potential; A first vertical alignment layer formed on a first surface of the first glass substrate on which the first and second transparent electrodes are formed; A second vertical alignment layer formed on the first surface of the second glass substrate; The first and second vertical alignment layers are enclosed between the first and second glass substrates facing each other, have a spiral pitch shorter than a wavelength of light, and are formed between the first and second transparent electrodes. And a ferroelectric liquid crystal in which the spiral is deformed in response and the molecules are rotated in a specific direction. 2. The vertically oriented spiral strain ferroelectric liquid crystal display device according to claim 1, wherein the inclination angle of the ferroelectric liquid crystal with respect to the helix axis is θ, wherein the inclination angle of the molecules is 22.5 ° ≤ θ ≤ 45 °. 2. The vertically oriented spirally modified ferroelectric liquid crystal display according to claim 1, wherein the spiral pitch of the ferroelectric liquid crystal is shorter than 0.35 mu m. The vertically oriented spiral strain ferroelectric liquid crystal display according to claim 1, wherein when the surface inclination angle of the vertical alignment layer with respect to the substrate surface is θ _S , 75 ° ≦ θs ≦ 90 °. 2. The vertically oriented spiral strain ferroelectric liquid crystal display according to claim 1, wherein a product of refractive index anisotropy of the ferroelectric liquid crystal and a distance between the substrates is smaller than 720 nm. The device of claim 1, wherein the device is A first polarizing plate provided on a second surface of the first glass substrate; And And a second polarizing plate disposed on a second surface of the second glass substrate and having a polarization perpendicular to the first polarizing plate. 7. The vertically oriented spiral strain ferroelectric liquid crystal display according to claim 6, wherein the first polarizing plate has an optical axis direction of approximately 45 degrees with respect to a direction of an electric field formed between the first and second transparent electrodes. The vertically oriented spiral strain ferroelectric liquid crystal display of claim 1, wherein the first transparent electrode and the second transparent electrode are alternately disposed so that an average optical axis is symmetric in opposite directions in two adjacent left and right pixels. Device. First and second glass substrates each having two surfaces facing each other; A first transparent electrode formed on a first surface of the first glass substrate and having a first potential; A second transparent electrode formed on a first surface of the first glass substrate and having a second potential different from the first potential; A first vertical alignment layer formed on a first surface of the first glass substrate on which the first and second transparent electrodes are formed; A reflection plate installed on one side of the second glass substrate; A second vertical alignment layer formed on the first surface of the second glass substrate, A retardation plate having a photo-delay characteristic of 1/4 of a wavelength of light on a second surface of the first glass substrate; A polarizing plate disposed on a second surface of the first glass substrate and having an optical axis that forms an angle of 45 ° with the optical axis of the retardation plate; And The first and second vertical alignment layers are enclosed between first and second glass substrates facing each other, have a spiral pitch shorter than a wavelength of light, and are formed between the first and second transparent electrodes. And a ferroelectric liquid crystal in which helix is responsive to rotate molecules in a specific direction. 10. The vertically oriented spiral deformation according to claim 9, wherein the phase difference of the retardation plate has a value between 160 × N nm and 200 × N nm, where N is 1,2,3, ... Ferroelectric liquid crystal display device.