KR20070096528A - Liquid crystal display device - Google Patents

Abstract

An LCD is provided to improve light efficiency by implementing colors using time-division driving and to achieve high transmittance and a wide viewing angle by reducing a thickness of a liquid crystal layer and a twist angle of a liquid crystal and using a nematic liquid crystal with high reflective anisotropy. A panel includes a nematic liquid crystal layer(36) formed between a plurality of alignment layers(35). A light source(71) is provided at one side surface of the panel. A time-division driving driver is electrically connected to the panel and the light source. A thickness of the liquid crystal layer ranges from 0.5 m to 2.5 m. A twist angle of a liquid crystal within the liquid crystal layer ranges from 0 to 45 degrees.

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY DEVICE}

1 is a schematic diagram showing the configuration of a conventional time division liquid crystal display device;

2 is a schematic view showing the configuration of a conventional see-through liquid crystal display device;

3A and 3B are cross-sectional views of a horizontally oriented liquid crystal panel with or without an applied voltage;

4A and 4B are cross-sectional views of a vertically oriented liquid crystal panel with or without an applied voltage;

5 is a graph showing the reaction time of the liquid crystal according to the thickness of the liquid crystal layer according to the present invention,

6 is a graph showing the transmittance according to the twist angle of the liquid crystal according to the present invention;

7 is a schematic view showing the configuration of a transmissive liquid crystal display device according to an embodiment of the present invention;

8 is a schematic diagram showing the configuration of a reflective liquid crystal display device according to another embodiment of the present invention;

9 is a schematic diagram showing a configuration of a projection type liquid crystal display device according to another embodiment of the present invention.

10 is a schematic diagram showing the configuration of a projection type liquid crystal display device according to another embodiment of the present invention.

* Description of the main parts of the drawings *

33: first substrate 34: second substrate

35: alignment film 36: liquid crystal

61: light source 82: polarizing film

91: reflective electrode 92: dichroic mirror

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device in which color is implemented using a time division driving method, and more particularly, to a liquid crystal display device suitable for a time division driving method and improving a reaction speed of a liquid crystal.

Conventional liquid crystal display device has a liquid crystal panel composed of a transparent first and second glass substrate bonded to a certain space, and the liquid crystal layer filled between the first, second, glass substrate, and on the back of the first glass substrate And a backlight for supplying light to the liquid crystal panel.

In order to realize color using the liquid crystal display device having such a structure, a color filter layer including R (Red), G (Green), and B (Blue) cells that transmit only light of a specific wavelength band and absorb the remaining light should be used.

However, light passes through a color filter with a maximum transmittance of 33% or less, and the luminance is largely lost. The disadvantage is that the power consumption of the backlight must be increased to compensate for the lost luminance.

In addition, the color filter is very expensive compared to other materials of the liquid crystal display device, thereby increasing the manufacturing cost of the liquid crystal display device.

In order to solve this problem, a time division type liquid crystal display device capable of realizing full-color without a color filter is proposed.

1 is a schematic diagram illustrating a general time division type liquid crystal display device.

A time division type liquid crystal display device has almost the same structure as a conventional liquid crystal display device except for a light source and a color filter.

The structure includes a liquid crystal panel composed of a transparent first and second glass substrates 12 and 13 bonded to each other with a predetermined space, and a liquid crystal layer 14 filled between the first and second glass substrates 12 and 13. And an R, G, and B light source 11 positioned on the rear surface of the first glass substrate 12 to supply light to the liquid crystal panel.

A general liquid crystal display device is a method of supplying white light to a liquid crystal panel while the backlight is always turned on, but a time division type liquid crystal display device uses the R, G, and B light sources 11 of the R, G, and B backlight units for one frame. It is a method of displaying color images by sequentially lighting at regular time intervals.

However, it has been difficult to develop a liquid crystal mode having a high response speed that corresponds to the technology according to the high speed operation of the light source.

In particular, the conventional nematic liquid crystal is not suitable for a light source driven at high speed because of a slow response speed, and there has been a demand for the development of a liquid crystal capable of replacing it.

Recently, with the development of liquid crystal display technology, a time division type liquid crystal display using ferroelectric liquid crystal (FLC) having fast response characteristics has been proposed.

The response of ferroelectric liquid crystals is essentially different from conventional liquid crystals, where each molecule is directly driven by a force proportional to the product of the dipole moment and the electric field. For this reason, the response time of the ferroelectric liquid crystal is 1 to 100 ㎲, which is superior in the reaction speed to the nematic liquid crystal. In addition, the change in contrast is caused by the inversion of the spontaneous polarization and has the characteristic that the rising time and falling time of the liquid crystal are the same.

However, ferroelectric liquid crystals are sensitive to shocks, and thus the alignment is easily disturbed by external shocks, and gray scales are difficult to display.

In addition, the ferroelectric liquid crystal is a very expensive material, there is a problem that increases the unit cost of the product.

2 illustrates a projection LCD.

In recent years, as life is abundant and residential spaces have increased, the desire for large-sized TVs is increasing. However, PDP, which is a large image display device, has a disadvantage of being expensive.

Accordingly, some image display manufacturers have recognized the need for large screen displays that are low cost and simple to manufacture. The technology developed according to this is a projection image display device.

Conventional projection type liquid crystal display devices include a plurality of dichroic mirrors 23, relay lenses 25, reflective mirrors 24 and cross dichroic prisms 26, including a light source 21 and a dimming LCD 22. And a complicated optical engine including a liquid crystal light valve 27 and the like.

In addition, such a device requires a respective LCD in an optical path through which each RGB signal passes, and has a disadvantage in that a product is expensive due to a high manufacturing cost in designing a suitable position for realizing a high brightness resolution. In addition, these components are expensive and increase the volume of the manufactured projection type liquid crystal display device.

Furthermore, when the cooling fan is operated to cool the projection type liquid crystal display, there is a problem that fine dust or the like introduced through the fan is absorbed by the lens or the mirror to cause distortion of the image.

The present invention improves the response speed of the nematic liquid crystal by reducing the thickness of the liquid crystal layer and the twist angle of the liquid crystal, and by using a liquid crystal having high refractive index anisotropy, a high-color full-color liquid crystal capable of high transmittance and time division driving. It is an object to provide a display device.

Another object of the present invention is to provide a projection type liquid crystal display device which does not use a complicated optical engine by applying a time-division driving type short panel liquid crystal display device to a projection type.

In the high speed response liquid crystal display of the present invention, a first substrate and a second substrate face each other, a plurality of alignment layers are formed on the first and second substrates, and a plurality of pixels are arranged on any one of the substrates. A liquid crystal display device including at least one switching element in each pixel, comprising: a panel including a nematic liquid crystal layer formed between the plurality of alignment layers; a light source provided on one side of the panel; It includes a time-division drive driver electrically connected to the light source.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in the specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention.

Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

3A and 3B are cross-sectional views of a horizontally oriented liquid crystal panel according to the present invention.

3A is a cross-sectional view of a liquid crystal panel before applying a voltage, and FIG. 3B shows a cross section of a liquid crystal panel after applying a voltage. The panel according to the present invention includes a first substrate 33 and a second substrate having a conductive material deposited thereon as an electrode. An alignment film 35 is formed between the layers 34. The alignment layer 35 is formed by the liquid crystal layer 36 having a predetermined thickness d.

As the material of the electrode, ITO is used when the liquid crystal display is a transmissive type, and in the reflective type, any one of the electrodes formed on the first substrate or the second substrate may be used as a thin film on which Al is deposited.

The crossing angles of the two alignment layers 35 which are formed on the electrode and face each other are 45 degrees or less, and thus the twist angle of the liquid crystal is 45 degrees or less. When the angle of intersection of the alignment layers is 0 °, the rubbing direction of the alignment layers is in the opposite direction.

The driving mode of the liquid crystal can be selected according to the crossing angle of the alignment layer. For example, if the crossing angle is 0 °, ECB (electrically compensation bend) mode can be used.

The liquid crystal adjacent to the alignment layer has a pretilt angle a of 30 degrees or less.

The panel formed as described above is classified into passive-matix and active-matrix according to a driving method. In the case of active driving, a plurality of transistors may be used as a switching element for switching pixels.

As the semiconductor material used in the active region of the transistor, amorphous silicon may be used in the case of a transmission type, and polycrystalline silicon and single crystal silicon may be used in the case of a projection type.

4A and 4B are cross-sectional views of a vertically oriented liquid crystal panel according to the present invention.

FIG. 4A shows a cross section of the liquid crystal panel before applying a voltage, and FIG. 4B shows applying a voltage.

The liquid crystal adjacent to the alignment layer has a pretilt angle (a) of 60 ° or more, and the rest of the configuration is the same.

5 is a graph showing the reaction time versus the thickness of the liquid crystal layer according to the present invention.

The liquid crystal layer according to the present invention has a thickness of 0.5 μm to 2.5 μm, and a 180 Hz drive can be achieved by implementing a reaction time at 60 ° C., which is the temperature of a liquid crystal panel of a general projection type projector, to 5 ms or less. However, when the thickness d of the liquid crystal layer 36 is reduced in order to reduce the reaction time of the liquid crystal, there is a problem that the transmittance is lowered.

This problem can be solved by using a liquid crystal having high refractive index anisotropy.

6 is a graph showing a change in transmittance versus torsion angle of the liquid crystal panel according to the present invention.

There is a method for reducing the twist angle of the liquid crystal as a method for reducing the reaction time of the liquid crystal. As shown in the figure, when the torsion angle of the liquid crystal is 45 ° or less, the transmittance is 95% or more and the change is small, so it is preferable to set the range of the torsion angle to 0 ° to 45 °.

The reason is that the reaction time of the liquid crystal can be shortened and the transmittance due to the error of the angle is small, so that the yield of the product can be improved in the production process. However, the torsion angle is proportional to the transmittance of the liquid crystal.

Therefore, in order to maintain or increase the transmittance instead of reducing the torsion angle, a liquid crystal having a large refractive index anisotropy Δn should be used.

As a result, in order to shorten the reaction time of the liquid crystal, while reducing the thickness and the twist angle of the liquid crystal layer, in order to maintain the minimum transmittance that can be used as a product, a liquid crystal having a refractive index anisotropy in the range of 0.13 to 0.22 is used. The maximum refractive index anisotropy value of the nematic liquid crystal is 0.22.

7 illustrates a transmissive liquid crystal display according to an exemplary embodiment of the present invention.

The panel according to the present invention comprises an alignment layer 35 formed between a first substrate 33 and a second substrate 34 having a transparent electrode such as ITO, a liquid crystal layer 36, and a polarizing plate 72 attached to both sides of the substrate. Include.

As the light source 71, a diode emitting R (Red), G (Green), and B (Blue) light is used as one pixel, or R (Red), G (Green), B (Blue), and W (White). ) Can be used as one pixel.

A scan pulse is applied to the gate circuit of the panel, and a time division driving driver (not shown) capable of applying a divided scan pulse is connected to the data circuit of the panel.

When the R, G, and B light sources are sequentially turned on at regular time intervals to display a color image, color breaking may occur. Therefore, in the time division driving according to the present invention, by dividing the time allotted for the lighting of each of R, G, and B by two or more divisions (two divisions, three divisions, or four divisions), the light source is driven. Can be controlled.

According to another embodiment of the present invention, as shown in FIG. 3A, when the alignment direction of the liquid crystal is horizontal, a compensation film (not shown) is provided between the substrate 33 and the polarizing plate 72 to improve contrast ratio. Is preferably used. The compensation film may use any one of uniaxial, biaxial, hybrid, warp and twisted structures.

8 is a schematic diagram of a reflective liquid crystal display device according to another exemplary embodiment of the present invention.

According to the present invention, a reflective liquid crystal display device includes a panel including an alignment layer 35 and a liquid crystal layer 36 formed between a first substrate 33 and a second substrate 34, a light source 71, and a dichroic mirror ( 82).

A transparent electrode (not shown) such as ITO is formed between the second substrate 34 and the alignment layer 35, and reflects light incident from the light source 71 between the first substrate 33 and the alignment layer 35. In order to do this, a reflective electrode 81 such as Al may be used.

A time division drive driver (not shown) is connected to the panel together with the light source 71.

The light emitted from the light source 61 is incident through the dichroic mirror 92 to the reflecting plate 91 provided in the liquid crystal panel, and then reflected back to the outside.

9 is a schematic diagram of a projection liquid crystal display according to another embodiment of the present invention.

The projection type liquid crystal display according to the present invention includes a panel 120 and a light source 71 including an alignment layer and a liquid crystal layer formed on a first substrate and a second substrate on which a transparent electrode (not shown) such as ITO is deposited, and an optical It consists of an engine.

The optical engine may include a lens system 91 for condensing light to the panel 92 and a mirror 93 for guiding the path of light to form an image on the screen 94.

10 is a schematic diagram of a projection type liquid crystal display device according to another embodiment of the present invention.

In the projection type liquid crystal display according to the present invention, the panel according to the present invention includes an alignment layer 35 and a liquid crystal layer formed between the first substrate 33 and the second substrate 34 on which a transparent electrode (not shown) such as ITO is formed. 36) and a polarizing plate 32 attached to both sides of the substrate.

As a light source 71, a white light source such as a halogen lamp is used, and a time division driving unit connecting the color wheel 111 and the first and second substrates 33 and 34 of the liquid crystal panel for color realization using time division driving ( 112).

Although the present invention has been shown and described with reference to the preferred embodiments as described above, it is not limited to the above embodiments and those skilled in the art without departing from the spirit of the present invention. Various changes and modifications will be possible.

The high-speed response liquid crystal display device of the present invention has an advantage that the light efficiency can be significantly improved by implementing color using time division driving.

Further, by reducing the thickness of the liquid crystal layer and the torsion angle of the liquid crystal, and using a nematic liquid crystal having a large refractive index anisotropy, time-division driving of the liquid crystal can be realized and a liquid crystal panel having a high transmittance and a wide viewing angle can be manufactured.

Furthermore, when applying the liquid crystal panel manufactured to the see-through liquid crystal display device, there is no need to use an expensive and complicated optical engine, thereby reducing the volume and unit cost of the manufactured product, and watching a fast video without afterimages through a large screen. There is a noticeable and advantageous effect.

Claims (21)

A first substrate and a second substrate face each other, a plurality of alignment layers are formed on the first and second substrates, and a plurality of pixels are arranged on any one of the substrates, and at least one on each of the pixels. A liquid crystal display device comprising a switching element, A panel including a nematic liquid crystal layer formed between the plurality of alignment layers; A light source provided on one side of the panel; And A time division drive driver electrically connected to the panel and the light source Liquid crystal display comprising a. The method of claim 1, The liquid crystal display device has a thickness of 0.5 μm to 2.5 μm. The method of claim 2, And a twist angle of the liquid crystal in the liquid crystal layer is 0 ° to 45 °. The method of claim 3, When the twist angle of the liquid crystal is 0 °, the rubbing directions of the plurality of alignment layers are opposite to each other. The method according to any one of claims 1 to 4, The liquid crystal of the liquid crystal layer has a refractive index anisotropy of 0.13 to 0.22. The method of claim 5, And a liquid crystal alignment direction of the liquid crystal layer is perpendicular or horizontal to the first and second substrates. The method of claim 6, A liquid crystal display including a compensation film having any one of uniaxial, biaxial, hybrid, inclined, and twisted structures between the second substrate and the polarizer to compensate for the contrast ratio when the alignment direction of the liquid crystal is horizontal Device. The method of claim 6, The liquid crystal of the liquid crystal layer has a negative dielectric anisotropy when the alignment direction of the liquid crystal is vertical. The method of claim 5, The panel is a liquid crystal display device wherein a transistor using polycrystalline silicon as an active region is a switching element. The method of claim 5, The panel is a liquid crystal display in which a transistor using a single crystal silicon as an active region is a switching element. The method of claim 5, A transparent electrode between the first and second substrates and the alignment layer, respectively; And And a polarizing plate on the outer side of the first and second substrates, respectively. The method of claim 11, The transparent electrode is an indium tin oxide liquid crystal display device. The method of claim 2, A reflective electrode formed between the first substrate and the alignment layer of the panel; A transparent electrode formed between the second substrate and the alignment layer; And Dichroic mirror for changing the path of light to inject the light emitted from the light source to the panel Liquid crystal display further comprising. The method of claim 13, The transparent electrode is an indium tin oxide liquid crystal display device. The method of claim 14, The reflective electrode is Al liquid crystal display device. The method of claim 5, A lens system for condensing light emitted from the light source to a panel; A screen for displaying an image exited through the panel; And Mirror for guiding the image from the panel to the screen Liquid crystal display further comprising. The method of claim 5, The light source uses a pixel that emits R (Red), G (Green), and B (Blue) light as one pixel. The method of claim 5, The light source is a liquid crystal display using diodes emitting R (Red), G (Green), B (Blue), and W (White) light as one pixel. The method of claim 5, The time division driving driver, A gate driving circuit unit supplying a scan pulse to the panel; And A data driving circuit unit for dividing the pulse to supply data to the panel Liquid crystal display comprising a. The method of claim 19, And the data driving circuit unit divides the pulse into two, three or four divisions. The method of claim 5, And a color wheel between the panel and the light source.

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