KR20050003687A - In-Plane Switching mode Liquid Crystal Display Device - Google Patents

Abstract

PURPOSE: An IPS(In-Plane Switching) type LCD(Liquid Crystal Display) is provided to enhance the efficiency of light due to selective reflection/transmission characteristics of light in the CLC(Cholesteric Liquid Crystal), thereby capable of increasing the IPS effect and luminance with a low voltage. CONSTITUTION: The first and second substrates(110,150) are faced with each other. A CCF(Cholesteric Liquid Crystal Color Filter)(112) is positioned at the inside surface of the first substrate and selectively reflects/transmits one of left or right circular polarized lights. A phase difference plate(114) is formed on an upper portion of the CCF. The first linear polarized plate(116) is formed on an upper portion of the phase difference plate. A common electrode(152) and a pixel electrode(156) are formed separately to the inside surface of the second substrate and form a horizontal electric field. A liquid crystal layer(160) is interposed between the first linear polarized plate, common electrode and pixel electrode. The CLC polarized plate(120) is positioned at the outer surface of the first substrate and selectively reflects/transmits only circular polarized light against to the CCF. The second linear polarized plate(162) is positioned at the outer surface of the second substrate and has a polarized shaft crossed with the first linear polarized plate. A back light(170), as a light source, is arranged at the rear of the first substrate.

Description

Transverse field type liquid crystal display device {In-Plane Switching mode Liquid Crystal Display Device}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to an in-plane switching type liquid crystal display device using a CLC liquid crystal.

In general, the driving principle of the liquid crystal display device uses the optical anisotropy and polarization of the liquid crystal. Since the liquid crystal is thin and long in structure, the liquid crystal has directivity in the arrangement of molecules, and the direction of the molecular arrangement can be controlled by artificially applying an electric field to the liquid crystal.

Accordingly, when the molecular arrangement direction of the liquid crystal is arbitrarily adjusted, the molecular arrangement of the liquid crystal is changed, and light is refracted in the molecular arrangement direction of the liquid crystal due to optical anisotropy to express image information.

Currently, an active matrix liquid crystal display device (AM-LCD; abbreviated as liquid crystal display device) in which a thin film transistor and pixel electrodes connected to the thin film transistor are arranged in a matrix manner has the best resolution and video performance. It is attracting attention.

In general, a liquid crystal display device has a structure in which a substrate on which a color filter and a common electrode are formed is formed as an upper substrate, a thin film transistor and a substrate in which a pixel electrode is formed as a lower substrate, and a liquid crystal layer is interposed between the two substrates. The liquid crystal layer is driven by a vertical electric field applied up and down between the pixel electrodes, so that the characteristics such as transmittance and aperture ratio are excellent.

However, since the liquid crystal driving by the vertical electric field is not excellent in viewing angle characteristics, a transverse field type liquid crystal display device having a wide viewing angle characteristic by driving a liquid crystal by a horizontal electric field has been proposed to improve this.

1A and 1B are views of a conventional transverse electric field type liquid crystal display device. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the cutting line I-I of FIG. 1A.

In FIG. 1A, the gate wiring 12 and the data wiring 22 are formed to cross each other, and the thin film transistor T is formed at the intersection of the gate wiring 12 and the data wiring 22. The pixel region P, which is defined as the intersection of the 12 and the data lines 22, is connected to the thin film transistor T, and the first lead-out wiring 28 is formed in a direction parallel to the gate line 12. In the first lead-out wiring 28, a plurality of pixel electrodes 30 are branched in a direction parallel to the data wiring 22. In addition, ends of the plurality of pixel electrodes 30 are connected to the second drawing wirings 32.

The common wiring 14 is formed in a direction parallel to the gate wiring 12, and both ends of the common wiring 14 alternate with the pixel electrode 30 in parallel with the data wiring 22. A plurality of common electrodes 16 are formed in the direction.

Hereinafter, the cross-sectional structure of FIG. 1A will be described with reference to FIG. 1B as an example of a structure including a polarizing plate and a backlight.

As illustrated, the first and second substrates 10 and 50 are disposed to face each other, and a plurality of common electrodes 16 are formed at regular intervals on the inner surface of the first substrate 10. The first insulating layer 18 is formed in an area covering the common electrode 16, and the plurality of pixel electrodes 30 are uniformly spaced apart from each other by the intervals between the common electrodes 16 on the first insulating layer 18. The second insulating layer 34 is formed at intervals and covers the plurality of pixel electrodes 30.

A color filter layer 52 is formed on an inner surface of the second substrate 50, and a liquid crystal layer 60 is interposed between the color filter layer 52 and the second insulating layer 34.

The first and second polarizers 70 and 72 are disposed on the outer surfaces of the first and second substrates 10 and 50, and the backlight, which is a light source device that supplies light to the rear surface of the first polarizer 70, 74 is located.

Since a horizontal electric field 36 is formed between the common electrode 16 and the pixel electrode 30, and the liquid crystal molecules in the liquid crystal layer 60 are driven by the horizontal electric field 36, the viewing angle is widened.

For example, when viewed from the front, the transverse electric field type liquid crystal display device may be visible in an up / down / left / right direction at about 80 to 85 °.

However, since the conventional transverse electric field type liquid crystal display uses an opaque metal material, the low aperture ratio causes a significant decrease in luminance, and it is difficult to drive at least 5 V or less for effective transverse electric field generation. book) There was a disadvantage that the LCD is not suitable for the liquid crystal display device.

In order to solve this problem, it is an object of the present invention to provide a transverse electric field type liquid crystal display device capable of improving luminance and driving at low voltage.

To this end, in the present invention, by using a CLC (Cholesteric Liquid Crystal) having a characteristic of selectively reflecting / transmitting light as a color filter, the brightness is improved by using the reflected light again, and thus the light efficiency is not deteriorated. It is possible to narrow the electrode gap, and to achieve the lateral field effect by low voltage driving.

The characteristics of the aforementioned CLC will be described in more detail as follows.

The rotation of the liquid crystal molecules of the CLC may be regarded as a kind of spiral structure. Two characteristics of this spiral structure are the direction of rotation of the spiral and the pitch, the repetition period of the spiral. The pitch can be understood as the distance until the liquid crystal layer returns to the same arrangement again, and this pitch is a variable that determines the color of the CLC.

Hereinafter, for convenience of description, the CLC color filter is abbreviated as CCF (Cholesteric Liquid Crystal Color Filter).

1A and 1B are views of a conventional transverse electric field type liquid crystal display device. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along the cutting line I-I of FIG. 1A.

2 is a cross-sectional view of a transverse electric field type liquid crystal display device using a CLC according to a first embodiment of the present invention.

3A and 3B are views of a CLC transverse field type liquid crystal display device according to a second embodiment of the present invention.

<Description of Symbols for Major Parts of Drawings>

110: first substrate 112: CCF

112a, 112b: first and second CCF material layers

114: phase difference plate 116: first linear polarizing plate

120: CLC polarizer 150: second substrate

152: common electrode 154: first insulating layer

156: pixel electrode 158: second insulating layer

160: liquid crystal layer 162: second linear polarizing plate

164: horizontal electric field 170: backlight

First and second substrates disposed to face each other to achieve the above object; A CCF positioned on an inner surface of the first substrate and selectively reflecting / transmitting only one of left circularly polarized light and right circularly polarized light; A retardation plate formed on the CCF; A first linear polarizer plate formed on the retardation plate; A common electrode and a pixel electrode formed on the inner surface of the second substrate to be spaced apart from each other, and forming a horizontal electric field; A liquid crystal layer interposed between the first linear polarizer and the common electrode and the pixel electrode; A CLC polarizer positioned on an outer surface of the first substrate and selectively reflecting / transmitting only circularly polarized light in a direction opposite to the CCF; A second linear polarizer disposed on an outer surface of the second substrate and having a polarization axis orthogonal to the first linear polarizer; Provided is a transverse electric field type liquid crystal display device including a backlight which is a light source for supplying light disposed on the back surface of the first substrate.

The CCF is composed of a double layer CCF material layer in which two color CCF material layers other than the color to be implemented among red, green, and blue colors are sequentially stacked, and an insulating layer is interposed between the common electrode and the pixel electrode. The retardation plate is a quarter wave plate (QWP) having a phase difference of λ / 4, and the liquid crystal layer has a phase difference value of zero in a voltage-off state and a λ / 2 in a voltage-on state. It is done.

In the transverse electric field type liquid crystal display according to the present invention, in the voltage-off state, the light supplied through the backlight is selectively reflected through the CLC polarizing plate to reflect the first circularly polarized light, and the second circularly polarized light is the reverse circularly polarized light. The polarized light is transmitted into the substrate, the second circularly polarized light passes through the CCF as it is, the second circularly polarized light becomes the first linearly polarized light through the QWP, and the first linearly polarized light coincides with the polarization axis of the first linearly polarized plate as it is. The first linearly polarized light passes through a liquid crystal layer having a phase difference value of 0 as it is, and is blocked by a second linearly polarized plate having a transmission axis that is incompatible with the first linearly polarized light to form a black screen.

In the voltage-on state, light supplied through the backlight is selectively reflected through the CLC polarizer, and second circularly polarized light that is reverse to the first circularly polarized light is transmitted into the substrate. The second circularly polarized light is transmitted through the CCF as it is, the second circularly polarized light is the first linearly polarized light through the QWP, the first linearly polarized light is passed in accordance with the polarization axis of the first linearly polarized plate as it is, the first linearly polarized light is The second linearly polarized light is changed through the liquid crystal layer having a retardation value of λ / 2, and then transmitted to the screen in agreement with the transmission axis of the second linearly polarized plate to form a white screen.

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

First Embodiment

2 is a cross-sectional view of a transverse electric field type liquid crystal display using CLC according to a first embodiment of the present invention.

As illustrated, the first and second substrates 110 and 150 are disposed to face each other, the CCF 112 is formed on the inner surface of the first substrate 110, and the phase difference is formed in the region covering the CCF 112. The plate 114 is disposed, and the first linear polarizing plate 116 is disposed above the phase difference plate 114. For example, the retardation plate 114 may be formed of a quarter wave plate (QWP).

The CCF 112 has a structure in which the first and second CCF material layers 112a and 112b are sequentially stacked. The first and second CCF material layers 112a and 112b are implemented in red, green, and blue colors. Two color CCF material layers other than the desired color are sequentially stacked.

For example, if the minimum unit for implementing the screen is defined as a sub-pixel, the green sub-pixel layer of green-blue CCF material is sequentially stacked on the red sub-pixel. Red color is reflected, and only the red and blue color is transmitted, and then the blue color is selectively reflected through the blue CCF material layer, and the red color is transmitted. The red color is implemented. The same can be applied.

The first linearly polarizing plate 116 may be formed by coating a material on the substrate that can transmit only light corresponding to the polarization axis, and the retardation plate 114 may include a cured liquid crystal material adjusted to a desired phase difference value. It is available.

The CCF 112 has a characteristic of selectively reflecting / transmitting only left circularly polarized light or right-circular polarization. In the present embodiment, a CCF 112 selectively reflecting / transmitting only left circularly polarized light will be described as an example.

In addition, a plurality of common electrodes 152 are disposed on the inner surface of the second substrate 150 at predetermined intervals, and a first insulating layer 154 is formed in an area covering the common electrodes 152. A plurality of pixel electrodes 156 are formed to be spaced apart from each other in the interval between the common electrodes 152 under the first insulating layer 154, and the second insulating layer 158 is formed in the region covering the pixel electrodes 156. Is formed.

The liquid crystal layer 160 is interposed between the second insulating layer 158 and the first linear polarizer 116.

In addition, a CLC linear polarizing plate 120 reflecting / transmitting only circularly polarized light in the opposite direction to the CCF 112 is disposed on the rear surface of the first substrate 110. In this embodiment, only the right circularly polarized light is selectively reflected / transmitted. The case will be described as an example.

In addition, a second linear polarizing plate 162 is disposed on the rear surface of the second substrate 150, and a backlight 170, which is a light source for supplying light, is disposed on the rear surface of the CLC linear polarization 120.

In the present embodiment, since the CLC having selective reflection / transmission characteristics of light is formed as a color filter, the light efficiency can be improved as compared with the absorption type color filter using a conventional color pigment, and thus the common electrode 152 and the pixel electrode The interval d between the portions 156 can be narrowed, so that the effect of the transverse electric field 164 can be enhanced even at a low voltage.

In addition, since the decrease in transmittance due to the low opening ratio due to the selection of the common electrode 152 and the pixel electrode 156 from an opaque metal material is possible to transmit 100% theoretically due to the selective reflection / transmission characteristic of the CCF light, A high transmittance transverse electric field type liquid crystal display device can be provided.

Second Embodiment

3A and 3B illustrate a CLC transverse electric field type liquid crystal display device according to a second exemplary embodiment of the present invention. A mechanism of light propagation during voltage on / off will be described. The following prerequisites are presented.

1) The first linearly polarized light coincides with the first transmission axis of the first linearly polarized plate, the second linearly polarized light coincides with the second transmission axis of the second linearly polarized plate, and the first and second transmission axes are orthogonal to each other.

2) The liquid crystal layer has a phase difference value of zero in the voltage off state and lambda / 2 in the voltage on state.

3) As an example, a red CCF region having a structure in which a green CCF material layer and a blue CCF material layer are sequentially stacked.

4) The retarder corresponds to a QWP having a retardation value of λ / 4.

5) Light passing through the first linearly polarizing plate in the QWP corresponds to the first linearly polarized light.

6) CCF selectively reflects only the left circularly polarized light, and the CLC polarizer selectively reflects only the right circularly polarized light.

3A shows that in the voltage-off state, light supplied through the backlight is selectively reflected through the CLC polarizer, and right circularly polarized light is passed through the substrate. Next, the left circularly polarized light having both red, green, and blue pitches passes through a CCF structure in which a green CCF material layer and a blue CCF material layer are sequentially stacked, and the left and right polarized light of green and blue pitches is selectively reflected, and only the red left circularly polarized light is Is transmitted, the red left circularly polarized light becomes the first red linearly polarized light through QWP, and the first red linearly polarized light passes through the first red linearly polarized light coinciding with the polarization axis of the first linearly polarized plate, and the first red linearly polarized light is 0, which is a phase difference value. After passing through the liquid crystal layer with the first red linearly polarized light as it is, it is blocked through a mismatch with the transmission axis of the second linearly polarized plate, thereby displaying a black screen.

3B shows that in the voltage-off state, light supplied through the backlight is selectively reflected by the CLC polarizer and right circularly polarized light is passed through the substrate. Next, the left circularly polarized light having both red, green, and blue pitches passes through a CCF structure in which a green CCF material layer and a blue CCF material layer are sequentially stacked, and the left and right polarized light of green and blue pitches is selectively reflected, and only the red left circularly polarized light is Is transmitted, the red left circularly polarized light becomes the first red linearly polarized light through QWP, the first red linearly polarized light is passed through the first red linearly polarized light coinciding with the polarization axis of the first linearly polarized plate, and the first red linearly polarized light is The second red linearly polarized light is passed through the liquid crystal layer having a phase difference, and the second red linearly polarized light is transmitted to the screen by coinciding with the transmission axis of the second linearly polarizing plate to realize a red color. Appears as a white screen.

However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

As described above, according to the CLC transverse electric field type liquid crystal display device according to the present invention, since the optical efficiency can be enhanced by the selective reflection / transmission characteristics of the light of the CLC, the transverse electric field effect can be enhanced even at low voltage and the luminance can be improved. Has the effect.

Claims (7)

First and second substrates disposed to face each other; A CCF positioned on an inner surface of the first substrate and selectively reflecting / transmitting only one of left circularly polarized light and right circularly polarized light; A retardation plate formed on the CCF; A first linear polarizer plate formed on the retardation plate; A common electrode and a pixel electrode formed on the inner surface of the second substrate to be spaced apart from each other, and forming a horizontal electric field; A liquid crystal layer interposed between the first linear polarizer and the common electrode and the pixel electrode; A CLC polarizer positioned on an outer surface of the first substrate and selectively reflecting / transmitting only circularly polarized light in a direction opposite to the CCF; A second linear polarizer disposed on an outer surface of the second substrate and having a polarization axis orthogonal to the first linear polarizer; A backlight that is a light source for supplying light disposed on the first substrate back surface Transverse electric field type liquid crystal display device comprising a. The method of claim 1, The CCF is a transverse electric field liquid crystal display device comprising a double layer CCF material layer having a structure in which two color CCF material layers other than a color to be implemented among red, green, and blue colors are sequentially stacked. The method of claim 1, A transverse electric field liquid crystal display device having an insulating layer interposed between the common electrode and the pixel electrode. The method of claim 1, And the retardation plate is a quarter wave plate (QWP) having a phase difference of? / 4. The method of claim 1, The liquid crystal layer has a phase difference value of zero in a voltage-off state and a λ / 2 in a voltage-on state. The method of claim 1, In the voltage-off state, the light supplied through the backlight is selectively reflected through the CLC polarizer, and the first circularly polarized light and the second circularly polarized light, which is the reverse circularly polarized light, are transmitted into the substrate. 2 circularly polarized light is transmitted through the CCF as it is, the second circularly polarized light becomes a first linearly polarized light through the QWP, the first linearly polarized light is passed in accordance with the polarization axis of the first linearly polarizing plate as it is, the first linearly polarized light is a phase difference value A transverse electric field liquid crystal display device having a black screen by passing through a liquid crystal layer having a phosphorus level of 0, and being blocked by a second linear polarizing plate having a transmission axis that is incompatible with the first linear polarization. The method of claim 1, In the voltage-on state, the light supplied through the backlight is selectively reflected through the CLC polarizer, and the first circularly polarized light and the second circularly polarized light which are reverse circularly polarized light are transmitted into the substrate. 2 circularly polarized light is transmitted through the CCF as it is, the second circularly polarized light becomes a first linearly polarized light through the QWP, the first linearly polarized light is passed in accordance with the polarization axis of the first linearly polarizing plate as it is, the first linearly polarized light is a phase difference value The transverse electric field type liquid crystal display device which changes into 2nd linearly polarized light through the liquid crystal layer of (lambda) / 2, and is transmitted to a screen according to the transmission axis of the said 2nd linear polarizing plate, and has a white screen.