KR101107705B1 - Reflective Type Liquid Crystal Display Device - Google Patents

Abstract

The present invention is a reflection type liquid crystal display for improving the viewing angle of the device by rotating the liquid crystal in the horizontal and vertical directions by a horizontal electric field and a vertical electric field to reduce the effective refractive index _{dΔn eff} so that the color is constant regardless of the angle A device, comprising: a gate wiring and a data wiring defining a pixel by vertically crossing a first substrate on a first substrate, a thin film transistor formed at an intersection point of the gate wiring and a data wiring, and a first surface formed on the front surface including the thin film transistor. An insulating layer, a reflective electrode formed on the front surface in pixel units on the first insulating layer, a second insulating layer formed on the front surface including the reflective electrode, and a plurality of stripes formed in parallel on the second insulating layer. A second substrate opposed to each other with two pixel electrodes interposed therebetween with a liquid crystal layer interposed therebetween; It characterized in that it comprises a polarizing film attached to the outer surface of the second substrate.

Viewing angle, reflective, effective refractive index

Description

Reflective Liquid Crystal Display Device

1 is a cross-sectional view of a reflective liquid crystal display device according to the prior art.

2 is a perspective view of a reflective liquid crystal display device according to the prior art.

3 is a cross-sectional view of a reflective liquid crystal display device according to the present invention.

Figure 4 is a curve graph showing the reflectance for each wavelength of R, G, B according to the effective refractive index d Δ n _eff of the reflective liquid crystal display device according to the present invention.

* Explanation of symbols on the main parts of the drawings

111: thin film array substrate 112a: gate electrode

114: semiconductor layer 115a: source electrode

115b: drain electrode 116: first insulating layer

117: reflective electrode 118: second insulating layer

121: counter substrate 125: liquid crystal layer

125a: liquid crystal molecule 127: pixel electrode

150: polarizing film 151: compensation film

190: Vcom Pad

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a reflective liquid crystal display device for driving a liquid crystal by a horizontal electric field and a vertical electric field in order to improve viewing angle characteristics.

Recently, the liquid crystal display device, one of the flat panel display devices that are attracting attention, is an element that changes the optical anisotropy by applying an electric field to a liquid crystal that combines the liquidity and the optical properties of the crystal, which is applied to a conventional cathode ray tube. Compared with its low power consumption, small volume, large size, and high definition, it is widely used.

The LCD has a structure in which a color filter substrate as an upper substrate and a thin film transistor (TFT) substrate as a lower substrate are disposed to face each other, and a liquid crystal having dielectric anisotropy is formed therebetween. The TFTs are driven by switching a TFT added to hundreds of thousands of pixels through a pixel selection address wiring to apply a voltage to the corresponding pixels.

Meanwhile, the liquid crystal display device includes a transmissive liquid crystal display device using a backlight as a light source, a reflective liquid crystal display device using external natural light without using the backlight as a light source, and a transmissive liquid crystal display device with high power consumption due to the backlight. It can be classified into a semi-transmissive liquid crystal display device for overcoming the disadvantages and disadvantages of the reflective liquid crystal display device that cannot be used when the external natural light is dark.

In this case, the pixel electrode may be classified into a transmissive electrode or a reflective electrode according to the liquid crystal display device. A transmissive electrode is formed inside a unit pixel in a transmissive liquid crystal display device, and a reflective electrode is formed in a reflective liquid crystal display device. In the device, a reflecting part and a transmitting part are simultaneously formed in a unit pixel, and a reflecting electrode is formed in the reflecting part and a transmitting electrode is formed in the transmitting part.

Here, the transmissive electrodes of the transmissive liquid crystal display device and the transflective liquid crystal display device emit light from the backlight incident through the lower substrate into the liquid crystal layer to brighten the brightness, and reflect the reflective liquid crystal display device and the transflective liquid crystal display device. The electrode reflects the external light incident through the upper substrate when the external natural light is bright to brighten the brightness.

Hereinafter, a reflective liquid crystal display device according to the related art will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view of a reflective liquid crystal display device according to the prior art, and FIG. 2 is a perspective view of a reflective liquid crystal display device according to the prior art.

In the reflective LCD according to the related art, as illustrated in FIG. 1, the gate line 12 and the data line 15 cross each other to define a sub-pixel on the lower substrate 11. Thin film transistors (TFTs) are formed at intersections of the gate lines 12 and the data lines 15, and the reflective electrodes 17 are electrically connected to the thin film transistors in each unit pixel. Is formed.

The thin film transistor TFT is formed of a laminated film of a gate electrode 12a, a gate insulating layer 13, a semiconductor layer 14, and source / drain electrodes 15a and 15b.

In addition, the upper substrate 21 includes a black matrix layer 24 that blocks light at an outer portion of the unit pixel, and R, G, and B (Red, Green) for implementing color in each unit pixel. And a color filter layer 22 of blue and a common electrode 23 forming an electric field together with the reflective electrode 17 are formed.

The upper and lower substrates 11 and 21 are bonded to each other with a predetermined gap, and a liquid crystal layer 25 is formed therebetween.

When the liquid crystal display device as described above is a reflective liquid crystal display device, the reflective electrode 17 is formed of aluminum, copper, or the like, for example, a metal having a high reflectance.

The compensation film 54 and the polarizing film 55 are further disposed on the upper surface of the upper substrate 21 of the liquid crystal display device as described above.

Next, a compensation film 54 having a function of changing a polarization state of light is disposed on an upper surface of the upper substrate 21. The compensation film 54 uses a quarter wave plate (QWP) having a phase difference corresponding to λ / 4 to change the incident linearly flattened light into circularly polarized light or circularly polarized light into linearly polarized light.

Then, a polarizing film 55 is disposed outside the compensation film 54 to convert natural light into linearly polarized light by passing only light in a direction parallel to the light transmission axis.

When external natural light is incident on the liquid crystal display device, the incident natural light is converted into linearly polarized light through the polarizing film 55, and the converted linearly polarized light is converted into circularly polarized light while passing through the compensation film 54.

Next, the circularly polarized light passes through the upper substrate 21, the color filter layer 23 and the common electrode 24, which have no effect on the phase of the circularly polarized light.

Subsequently, circularly polarized light passes through the liquid crystal layer 25. When the liquid crystal layer 25 is formed to have a phase difference value of λ / 4, the circularly polarized light is converted into linearly polarized light. The linearly polarized light is reflected by the reflective electrode 17 to be circularly polarized again through the liquid crystal layer 25, and then linearly polarized while passing through the compensation film 54, and then passes through the polarizing film 55. In this case, when the polarized direction of the linearly polarized light coincides with the light transmission axis of the polarizing film 55, all the light is transmitted, and when the light polarization direction is perpendicular to the light transmission axis, no light is output.

However, when light is output, all colors other than the desired color in the color filter layer are absorbed by the color filter layer, so only specific colors of R, G, and B are emitted.

The reflective liquid crystal display device thus formed is displayed by external light incident through the upper substrate, thereby reducing power consumption by using a backlight.

On the other hand, according to the kind of liquid crystal and the selection of a compensation film, the method which can express a color without providing a color filter layer using the wavelength characteristic of the light by birefringence of a liquid crystal is proposed. That is, the transmittances of red, green, and blue vary depending on the phase difference of the liquid crystal panel. When the effective refractive index _{dΔn eff} changes according to the voltage change, white, black ( Colors are continuously changed in the order of black, blue, green, and red.

Such a reflective liquid crystal display device has an advantage of high reflectance because it can display color without a color filter layer.

However, the conventional reflective liquid crystal display device has a problem in that the refractive anisotropy (birefringence) is different depending on the viewing angle, so that it appears in a different color in the oblique direction.

The present invention has been made to solve the above problems, by rotating the liquid crystal in the horizontal and vertical directions by a horizontal electric field and a vertical electric field to reduce the effective refractive index d △ n _eff so that the color is constant regardless of the angle An object of the present invention is to provide a reflective liquid crystal display device for improving the viewing angle of the device.

In order to achieve the above object, a reflective liquid crystal display device includes a gate wiring and a data wiring defining a pixel by vertically crossing a first substrate, a thin film transistor formed at an intersection point of the gate wiring and the data wiring; A first insulating layer formed on the front surface including the thin film transistor, a reflective electrode formed on the front surface in pixel units on the first insulating layer, a second insulating layer formed on the front surface including the reflective electrode, and the second insulating layer formed on the first insulating layer. 2 a plurality of pixel electrodes formed in parallel in a stripe shape on the insulating layer, a second substrate opposed to each other with a liquid crystal layer interposed between the first substrate, and a polarizing film attached to an outer surface of the second substrate. Characterized in that comprises a.

At this time, the liquid crystal layer is driven by a horizontal electric field and a vertical electric field formed between the reflective electrode and the pixel electrode, and the color is displayed by the effective refractive index of the liquid crystal layer.

Hereinafter, a reflective liquid crystal display device according to the present invention will be described with reference to the accompanying drawings.

3 is a cross-sectional view of a reflective liquid crystal display device according to the present invention, and FIG. 4 is a curve graph showing reflectance for each wavelength of R, G and B according to the effective refractive index _{dΔn eff} of the reflective liquid crystal display device according to the present invention. to be.

As shown in FIG. 3, the reflective LCD according to the present invention opposes the thin film array substrate 111 on which a plurality of wirings, a thin film transistor, a reflective electrode, and a pixel electrode are formed, and the thin film array substrate 111. A counter substrate 121, a liquid crystal layer 125 enclosed between the thin film array substrate 111 and the counter substrate 121, and a compensation film 151 bonded to an outer circumferential surface of the counter substrate 121. Comprising a polarizing film 150, the liquid crystal molecules 125a are driven by a horizontal electric field and a vertical electric field formed on the thin film array substrate.

In this case, the thin film array substrate 111 may be arranged in a direction perpendicular to each other to form a gate line (not shown) and a data line (not shown) that define a unit pixel, and an intersection portion of the gate line and the data line. A formed thin film transistor (TFT), a first insulating layer 116 formed on the front surface including the thin film transistor, a reflective electrode 117 connected to the thin film transistor on the first insulating layer, and the reflective electrode 117 A plurality of second insulating layers 118 formed on the front surface of the reflective electrode layer 118 and a plurality of pixel electrodes 127 formed in a stripe shape on the second insulating layer on the reflective electrode and parallel to each other and connected to the Vcom pad 190 are formed.

In this case, a pixel voltage is applied to the reflective electrode 117 and a Vcom voltage is applied to the pixel electrode 127 to form a vertical electric field and a horizontal electric field. The liquid crystal molecules initially aligned in the horizontal direction by the vertical and horizontal electric fields. Rotate vertically and horizontally.

However, by connecting the pixel electrode to the drain electrode of the thin film transistor and the reflective electrode to the Vcom pad, a horizontal electric field and a vertical electric field may be formed by applying a pixel voltage to the pixel electrode and applying a Vcom voltage to the reflective electrode. .

The thin film transistor TFT may include a gate electrode 112a branched from the gate wiring, a semiconductor layer 114 insulated from the gate electrode 112a, and formed in an island shape on the gate electrode 112a. And source / drain electrodes 116a and 116b branched from the data line and formed on the semiconductor layer 114.

In such a reflective liquid crystal display device, the effective optical index is decreased by the liquid crystal rotated in the horizontal and vertical directions, and the average optical axis is changed. Since the effective refractive index is small depending on the viewing direction, the color becomes constant regardless of the angle. Viewing angle characteristics are improved.

Here, the polarizing film 150 that transmits only light in any one direction among the light scattered in various directions, and the QWP (Quater Wave Plate) for converting the linear polarization to circular polarization or the circular polarization to linear polarization to change the phase of the light Compensation film 151, etc. are disposed, and the liquid crystal layer cell gap is 2 to 10 µm, or _{dΔn eff} has a range of 0.2 to 1 µm.

When the electric field is applied to the liquid crystal display device, the effective refractive index ( _{dΔn eff} ) decreases and the transmittance for each wavelength is changed. As shown in FIG. 4, magenta, red, yellow, and green are shown. The color changes in the order of green and blue. Here, the effective refractive index is a refractive index value that varies depending on the voltage change. When the effective refractive index is 0.535, the magenta color (M) is displayed. When the effective refractive indexes are 0.45 and 0.34, yellow (Y) and blue (B), respectively. Is displayed.

In addition, since the color can be changed in accordance with the change of the electric field, the color filter layer becomes unnecessary, and the degradation of the reflectance characteristic by the color filter layer can be prevented.

However, in FIG. 4, at least two curve graphs of each of the R, G, and B curves have a minimum reflectance, so that the color reproducibility of R, G, and B is increased, thereby improving color purity. It is easy to secure the condition that the color has the minimum reflectance, but it is difficult to secure the condition that the two colors are minimized.

Therefore, in order to improve color purity, the primary and complementary colors are composed of sub-pixels to increase the color reproducibility of R, G, and B.

In other words, green and magenta, blue and yellow, and red and cyan have primary and complementary colors, respectively, and constitute pixels as sub-pixels reflecting green and magenta (a mixture of blue and red). Or configure the pixel as a sub-pixel that reflects blue and yellow (mix of green and red) or configure the pixel as a sub-pixel that reflects red and cyan (mix of blue and green).

For example, when green and magenta are composed of pixels, blue and red are absorbed in sub-pixels reflecting green, and green is absorbed in sub-pixels reflecting magenta (mixing of blue and red), so that R, G Can increase the color gamut of B.

As shown in FIG. 3, since the reflective electrode 117 reflecting external natural light can be formed inside the TFT array substrate, the reflectance can be increased as compared with forming the reflective electrode outside the TFT array substrate. This is because when the reflective electrode is formed on the inner side of the TFT array substrate, the ratio of the area reflecting light can be sufficiently secured by forming the reflective electrode so as to cover the thin film transistor and various patterns. In the past, when the Vcom electrode and the pixel electrode were formed on the inner side of the TFT array substrate to form a horizontal electric field, the reflective electrode could not be formed on the inner side of the TFT array substrate even to prevent distortion of the transverse electric field. This problem can be solved by forming the reflective electrode on the inner side of the TFT array substrate.

The reflective electrode 117 is formed by depositing and patterning aluminum, aluminum alloy, titanium, and the like as a high reflectance metal to reflect external natural light well, and the pixel electrode 127 is formed of indium tin oxide (ITO), high It is formed by depositing and patterning a conductive material, such as a reflectance metal.

On the other hand, the present invention described above is not limited to the above-described embodiment and the accompanying drawings, it is possible that various substitutions, modifications and changes within the scope without departing from the technical spirit of the present invention. It will be apparent to those of ordinary skill in Esau.

The reflective liquid crystal display device according to the present invention as described above has the following effects.

First, the viewing angle of the device is improved by rotating the liquid crystal in the horizontal and vertical directions by the horizontal electric field and the vertical electric field to reduce the effective refractive index _{dΔn eff} so that the color is constant regardless of the angle.

Second, the reflective liquid crystal display device according to the present invention displays the color using the wavelength characteristics of the light due to the birefringence of the liquid crystal without the color filter layer, it is possible to prevent the decrease in reflectance characteristics by the color filter layer.

Third, since the reflective electrode reflecting external natural light can be formed inside the TFT array substrate, the reflectance can be increased as compared with forming the reflective electrode outside the TFT array substrate.

Fourth, in order to improve color purity, primary colors and complementary colors are composed of sub-pixels to increase the color reproducibility of R, G, and B.

Claims (11)

A gate wiring and a data wiring defining a pixel by vertically crossing the first substrate; A thin film transistor formed at an intersection point of the gate line and the data line; A first insulating layer formed on the entire surface including the thin film transistor, A reflective electrode formed on the entire surface of the first insulating layer in pixel units; A second insulating layer formed on the entire surface including the reflective electrode; A plurality of pixel electrodes formed to be parallel to each other on the second insulating layer in a stripe form; A second substrate opposed to and bonded to the first substrate with the liquid crystal layer interposed therebetween; It comprises a polarizing film attached to the outer surface of the second substrate, The pixel consists of two sub-pixels and consists of sub-pixels reflecting green and magenta respectively, or sub-pixels reflecting blue and yellow respectively, or reflects red and cyan respectively. A reflective liquid crystal display device comprising sub-pixels. The method of claim 1, The reflective electrode is connected to the thin film transistor to apply a pixel voltage, The pixel electrode is a reflective liquid crystal display device, characterized in that the Vcom voltage is applied. The method of claim 1, The reflective electrode is applied with a Vcom voltage, And the pixel electrode is connected to the thin film transistor to apply a pixel voltage. delete The method of claim 1, Reflective liquid crystal display device characterized in that the color is displayed by the effective refractive index of the liquid crystal layer. The method of claim 1, The liquid crystal layer is a reflective liquid crystal display device, characterized in that having a cell gap of 2 ~ 10㎛. The method of claim 1, And the liquid crystal layer is initially oriented parallel to the first substrate. The method of claim 1, Reflective liquid crystal display device characterized in that the compensation film is further attached between the second substrate and the polarizing film. The method of claim 8, The compensation film is a reflection type liquid crystal display device, characterized in that the QWP (Quater Wave Plate). delete delete

Images