KR20040055394A - Liquid crystal display - Google Patents

Abstract

PURPOSE: An LCD device is provided to apply the first common voltage to the first common electrode area, and to apply the second common voltage lower than the first voltage to the second common electrode area, thereby improving display properties of the LCD device. CONSTITUTION: An LCD panel(400) comprises as follows. A color filter substrate(200) is faced with a TFT substrate(100). A liquid crystal layer(300) is interposed between the TFT substrate(100) and the color filter substrate(200). Plural unit pixels are formed on the first insulating substrate(110) of the TFT substrate(100) in matrix type. Each unit pixel includes data lines extended in the first direction and gate lines extended in the second direction. Within pixel areas divided by the data lines and the gate lines, the first TFTs(120) connected with the data lines and the gate lines and the second TFTs(130) connected with the gate lines are further comprised. A transparent electrode(150) is connected to the first TFTs(120). A reflective electrode(160) is connected to the second TFTs(130).

Description

Liquid Crystal Display {LIQUID CRYSTAL DISPLAY}

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of improving display characteristics while increasing light efficiency.

The liquid crystal display device is classified into a reflective liquid crystal display device that receives an external first light and displays an image and a transmissive liquid crystal display device that receives an internally generated second light and displays an image. Recently, semi-transmissive liquid crystal display devices utilizing both the advantages of a reflective liquid crystal display device and a transmissive liquid crystal display device have been developed to realize high quality images while reducing power consumption.

The transflective liquid crystal display displays an image in a reflection mode using first light when the amount of external light is abundant, and a transmissive mode using second light generated by consuming electric energy charged therein when the amount of external light is insufficient. Display the image on the screen.

The transflective liquid crystal display device includes a liquid crystal display panel comprising a TFT substrate, a color filter substrate facing the TFT substrate, and a liquid crystal layer interposed between the TFT substrate and the color filter substrate.

The TFT substrate includes a transparent electrode and a reflective electrode in a pixel region partitioned by a data line and a gate line. Here, the region where the reflective electrode is formed is a reflective region, and the region where the reflective electrode is not formed is a transmission region.

In general, the transflective liquid crystal display is driven with a difference between the cell gap in the reflection region and the cell gap in the transmission region in order to improve light efficiency in the reflection mode and the transmission mode. In other words, the cell gap of the reflective region is half that of the cell gap of the transmissive region.

As described above, a method of providing a difference in cell gap between the reflective region and the transmissive region includes a method of controlling the thickness of the insulating film disposed under the reflective electrode and the transparent electrode. However, due to process characteristics, it is difficult to secure the uniformity of the cell gap because the amount of the insulating film cannot be precisely controlled.

Accordingly, it is an object of the present invention to provide a liquid crystal display device capable of improving display characteristics while increasing light efficiency.

1 is a cross-sectional view of a liquid crystal display according to an exemplary embodiment of the present invention.

FIG. 2 is a plan view of the TFT substrate shown in FIG. 1.

3 is a plan view of the color filter substrate shown in FIG. 1.

FIG. 4 is a plan view specifically illustrating a unit pixel of the LCD shown in FIG. 1.

5 is an equivalent circuit diagram of a unit pixel illustrated in FIG. 4.

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

100 TFT substrate 120 First TFT

130: second TFT 150: transparent electrode

160: reflective electrode 200: color filter substrate

231: first common electrode 232: second common electrode

300: liquid crystal layer 400: liquid crystal display device

The liquid crystal display according to the present invention for achieving the above object of the present invention comprises a pixel region consisting of a switching element, a pixel electrode coupled to the switching element, the pixel electrode is a plurality of regions in the pixel region A first substrate consisting of; A second substrate having a common electrode facing the pixel electrode, the common electrode comprising a plurality of electrode regions respectively corresponding to the plurality of regions; And a liquid crystal layer interposed between the first substrate and the second substrate.

According to the liquid crystal display device, the TFT substrate includes a pixel region including a transparent electrode region and a reflective electrode region, and the color filter substrate includes a first common electrode region corresponding to the transparent electrode region and a second common region corresponding to the reflective electrode region. A common electrode consisting of an electrode region is provided. Therefore, the display characteristic of a liquid crystal display device can be improved.

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

1 is a cross-sectional view illustrating a liquid crystal display device according to an exemplary embodiment of the present invention, FIG. 2 is a plan view of the TFT substrate shown in FIG. 1, and FIG. 3 is a plan view of the color filter substrate shown in FIG. 1.

1 to 3, a liquid crystal display according to an exemplary embodiment of the present invention includes a TFT substrate 100, a color filter substrate 200 facing the TFT substrate 100, and the TFT substrate 100. The liquid crystal display panel 400 includes a liquid crystal layer 300 interposed between the color filter substrate 200 and the color filter substrate 200.

The TFT substrate 100 is a substrate in which a plurality of unit pixels are formed in a matrix form on the first insulating substrate 110. In detail, each of the unit pixels includes a data line DL extending in a first direction and a gate line GL extending in a second direction perpendicular to the first direction. The first TFT 120, the first TFT 120, and the first TFT 120 connected to the data line DL and the gate line GL in a pixel area partitioned by the data line DL and the gate line GL. The semiconductor device further includes a second TFT 130 connected to the gate line GL. A transparent electrode 150 made of a transparent conductive film is connected to the first TFT 120, and a reflective electrode 160 having excellent reflectance is connected to the second TFT 130.

Specifically, a first source electrode 123 of the first TFT 120 is connected to the data line DL, a first gate electrode 121 is connected to the gate line GL, and a first drain The electrode 125 is connected to the transparent electrode 150. In addition, a second source electrode 133 of the second TFT 130 is connected to the first drain electrode 125, a second gate electrode 131 is connected to the gate line GL, and a second The drain electrode 135 is connected to the reflective electrode 160.

In this case, in order to connect the transparent electrode 150 only with the first drain electrode 125 and the reflective electrode 160 only with the second drain electrode 135, the first TFT 120 is connected. And an insulating film 140 are interposed between the transparent electrode 150 and the second TFT 130 and the reflective electrode 160. The first contact hole 141 exposing the first drain electrode 125 is formed in the insulating layer 140, and the second contact hole 143 exposing the second drain electrode 135 is formed.

Therefore, the transparent electrode 150 is electrically connected to the first drain electrode 125 through the first contact hole 141, and the reflective electrode 160 is connected through the second contact hole 143. It is electrically connected to the second drain electrode 135.

The transparent electrode 150 and the reflective electrode 160 are electrically insulated from each other through the second TFT 130. Here, the region in which the reflective electrode 160 is formed is a reflective region using first light provided from the outside in the place where the external light amount is abundant, and the region in which the transparent electrode 150 is formed is charged in the place where the external light amount is insufficient. It is a transmission region using the second light generated by consuming the generated electrical energy.

Meanwhile, the color filter substrate 200 is formed on the second insulating substrate 210 and includes a color filter layer 220 formed of R (Red), G (Green), and B (Blue) color pixels corresponding to each of the unit pixels. And a common electrode 230 coated on the color filter layer 220 with a uniform thickness and made of a transparent conductive film.

As illustrated in FIG. 3, the common electrode 230 corresponds to the first common electrode region Ea1 and the reflective electrode 160 on which the first common electrode 231 corresponding to the transparent electrode 150 is formed. A second common electrode region Ea1 having the second common electrode 232 formed thereon. The first common electrode area Ea1 and the second common electrode area Ea2 are electrically insulated from each other. That is, an insulating region Is without an electrode layer is formed between the first common electrode region Ea1 and the second common electrode region Ea2.

A first common voltage is applied to the first common electrode region Ea1, and a second common voltage lower than the first common voltage is applied to the second common electrode region Ea2.

As shown in FIGS. 1 and 3, the TFT substrate 100 includes the first and second TFTs 120 and 130 in a pixel area, so that the transparent electrode 150 and the reflective electrode 160 are disposed on each other. Different voltages are applied respectively. That is, a first voltage is applied to the transparent electrode, and a second voltage lower than the first voltage is applied to the reflective electrode, respectively. In this case, due to a difference in parasitic capacitance or charge rate generated in the first and second TFTs 120 and 130, respectively, the level of the proper common voltage in the reflection region and the level of the appropriate common voltage in the transmission region are different from each other. You lose.

Nevertheless, when the level of the common voltage is set for the transmission region, residual DC is generated in the reflection region, and when it is set for the reflection region, residual DC is generated in the transmission region. That is, the voltage across the liquid crystal layer in the reflective region is different between the positive frame and the negative frame, and the second voltage across the liquid crystal layer in the transmissive region is positive. It differs between the frame and the negative frame.

This voltage difference causes not only the brightness difference between the reflection area and the transmission area but also the brightness difference between the positive frame and the negative frame. Therefore, a flicker phenomenon occurs in the liquid crystal display device 400, and accordingly, display characteristics of the liquid crystal display device 400 are deteriorated.

In order to solve this problem, the first common voltage is applied to the first common electrode 231 corresponding to the transmission region, and the first common voltage is applied to the second common electrode 232 corresponding to the reflection region. A second common voltage lower than the voltage is applied. Therefore, it is possible to prevent the phenomenon in which the first voltage applied to the liquid crystal layer in the reflective region is changed between a positive frame and a negative frame. In addition, it is possible to prevent a phenomenon in which the second voltage applied to the liquid crystal layer in the transmission region is changed between a positive frame and a negative frame.

Meanwhile, the liquid crystal layer 300 is interposed between the TFT substrate 100 and the color filter substrate 200. As a result, the liquid crystal display panel 400 is completed.

1 to 3 illustrate a structure in which a plurality of electrode regions are formed by the transparent electrode 150 and the reflective electrode 160 in the pixel region of the TFT substrate 100. However, even if the structure is not provided, if a plurality of electrode regions are provided in the pixel region, a plurality of common electrode regions to which different common voltages are applied may be provided on the color filter substrate 200 side corresponding to the electrode regions. Can be.

4 is a plan view specifically illustrating a unit pixel illustrated in FIG. 1, and FIG. 5 is an equivalent circuit diagram of a unit pixel illustrated in FIG. 4.

4 and 5, the unit pixel includes an m th data line DLm extending in a first direction and an n th gate line GLn extending in a second direction perpendicular to the first direction.

The first TFT 120 is formed in a region partitioned by the m-1 th and m th data lines DLm-1 and DLm and the n-1 th and n th gate lines GLn-1 and GLn. The first source electrode 123 of the first TFT 120 is connected to the m-th data line DLm, the first gate electrode 121 is connected to the n-th gate line GLn, and a first The drain electrode 125 is connected to the transparent electrode 150.

The transparent electrode 150 forms a first liquid crystal capacitor Clc1 by facing a first common electrode (not shown) formed in the first common electrode region with a liquid crystal layer interposed therebetween. In addition, the transparent electrode 150 overlaps the n−1 th gate line GLn-1 with an insulating layer interposed therebetween and is connected to the first liquid crystal capacitor Clc1 in parallel with the first storage capacitor Cst1. ).

In addition, a second TFT 130 is formed in a region partitioned by the m-1 th and m th data lines DLm-1 and DLm and the n-1 th and n th gate lines GLn-1 and GLn. do. The second source electrode 133 of the second TFT 130 is connected to the first drain electrode 125, the second gate electrode 131 is connected to the n-th gate line GLn, and the second The drain electrode 135 is connected to the reflective electrode 160.

The reflective electrode 160 forms a second liquid crystal capacitor Clc2 by facing the second common electrode (not shown) formed in the second common electrode region with the liquid crystal layer interposed therebetween. In addition, the reflective electrode 160 overlaps the n−1 th gate line GLn−1 with the insulating layer therebetween to form a second storage capacitor Cst2 connected in parallel with the second liquid crystal capacitor Clc2. do.

The first TFT 120 outputs a data voltage applied to the m th data line DLm to the first drain electrode 125 in response to a driving signal applied to the n th gate line GLn. . In this case, the data voltage is lowered by the internal resistance of the first TFT 120 and then output to the first drain electrode 125. The voltage drop data voltage is divided and applied to the transparent electrode 150 and the second source electrode 133 of the second TFT 130 respectively connected to the first drain electrode 125. That is, a first data voltage is applied to the transparent electrode 150, and a second data voltage is applied to the second source electrode 133.

Meanwhile, the second TFT 130 outputs the second data voltage to the second drain electrode 135 in response to the driving signal. In this case, the second data voltage is outputted to the second drain electrode 135 after the voltage drops by the internal resistance of the second TFT 130. The voltage lowered second data voltage is applied to the reflective electrode 160.

Therefore, even when a data voltage is provided to the m-th data line DLm, different voltages may be applied to the transparent electrode 150 and the reflective electrode 160, respectively. In addition, an optimum voltage applied to the reflective electrode 160 may be adjusted by adjusting an internal resistance of the second TFT 130. As a result, the reflectance of the reflective electrode 160 can be improved, and further, the light efficiency of the liquid crystal display can be improved.

According to the liquid crystal display, the TFT substrate includes a pixel region including a transparent electrode region and a reflective electrode region, and the color filter substrate includes a first common electrode region corresponding to the transparent electrode region and a second electrode corresponding to the reflective electrode region. The common electrode area is provided.

Therefore, the light efficiency in the transparent electrode region and the reflective electrode region can be improved by different voltages applied to the reflective electrode and the transparent electrode.

In addition, the voltage difference for each frame may be reduced by changing the level of the common voltage applied to the first and second common electrodes for each of the reflective and transmissive electrode regions. As a result, the brightness difference for each frame can be reduced, and the display characteristics of the liquid crystal display can be improved.

Although described with reference to the embodiments above, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

Claims (5)

A pixel region comprising a switching element and a pixel electrode coupled to the switching element, the pixel electrode comprising a first substrate comprising a plurality of electrode regions in the pixel region; A second substrate having a common electrode facing the pixel electrode, wherein the common electrode includes a plurality of common electrode regions respectively corresponding to the plurality of electrode regions; And And a liquid crystal layer interposed between the first substrate and the second substrate. The liquid crystal display of claim 1, wherein the first substrate comprises a plurality of the pixel areas. The method of claim 1, wherein the pixel area, A transparent electrode region for transmitting first light provided from a rear surface of the first substrate; And And a reflective electrode region for reflecting the second light provided from the front surface of the second substrate. The method of claim 3, wherein the plurality of common electrode regions, A first common electrode region corresponding to the transparent electrode region; And And a second common electrode region electrically insulated from the first common electrode region and corresponding to the reflective electrode region. The liquid crystal display of claim 4, wherein a first voltage is applied to the first common electrode region, and a second voltage lower than the first voltage is applied to the second common electrode region.