KR20050121381A - Liquid crystal display - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, comprising: a first liquid crystal display panel comprising a liquid crystal panel assembly, a backlight for irradiating light to the liquid crystal panel assembly, and a first and second luminance display pixels receiving the backlight light to display different luminance; It includes a luminance display. In this case, the first and second luminance display pixels include first and second thin film transistors that receive backlight light and generate different photocurrents, and first and second liquid crystal capacitors that change the transmittance of the backlight light according to different photocurrents. . According to the present invention, by providing a plurality of luminance display pixels including thin film transistors having widths and channel thicknesses of different control terminal electrodes, it is possible to easily determine whether the backlight device is defective. The uniformity of the backlight light can be determined.

Description

Liquid crystal display {LIQUID CRYSTAL DISPLAY}

The present invention relates to a liquid crystal display device.

A typical liquid crystal display (LCD) includes two display panels provided with pixel electrodes and a common electrode, and a liquid crystal layer having dielectric anisotropy interposed therebetween. The pixel electrodes are arranged in a matrix and connected to switching elements such as thin film transistors (TFTs) to receive data voltages one by one in sequence. The common electrode is formed over the entire surface of the display panel and receives a common voltage. The pixel electrode, the common electrode, and the liquid crystal layer therebetween form a liquid crystal capacitor, and the liquid crystal capacitor becomes a basic unit that forms a pixel together with a switching element connected thereto.

In such a liquid crystal display, a voltage is applied to two electrodes to generate an electric field in the liquid crystal layer, and the intensity of the electric field is adjusted to adjust the transmittance of light passing through the liquid crystal layer to obtain a desired image. In this case, in order to prevent degradation caused by an electric field applied to the liquid crystal layer for a long time, the polarity of the data voltage with respect to the common voltage is inverted frame by frame, row by pixel, or pixel by pixel. In this case, the light may be a separate artificial light source or natural light.

A light source device for a liquid crystal display, that is, a backlight device, typically uses a plurality of fluorescent lamps as a light source and includes an inverter for driving the lamp. The inverter converts an input DC voltage into an AC voltage and then applies it to a lamp to light the lamp, and adjusts the brightness of the LCD screen by controlling the light source according to the brightness control voltage input from the system.

However, due to the failure of the backlight device, the brightness of the screen of the liquid crystal display, that is, the luminance may be low or uneven, and the display quality of the liquid crystal display may be degraded.

Accordingly, an object of the present invention is to provide a liquid crystal display device capable of preventing display quality defects caused by poor luminance of a backlight device.

According to an aspect of the present invention, there is provided a liquid crystal display device comprising: a liquid crystal panel assembly, a backlight for irradiating light to the liquid crystal panel assembly, and at least first and second light sources having different luminance from the backlight light; And a first luminance display unit including two luminance display pixels, wherein the first and second luminance display pixels receive the backlight light and generate different photocurrents according to the first and second thin film transistors and the different photocurrents. And first and second liquid crystal capacitors for varying the transmittance of the backlight light.

The first and second thin film transistors may further include first and second semiconductors having different channel thicknesses, respectively.

The first and second semiconductors may include amorphous silicon.

The first and second thin film transistors may include first and second control terminal electrodes having different widths, respectively.

The first and second thin film transistors further include first and second input terminals and first and second output terminals, respectively, and the first and second control terminal electrodes turn the first and second thin film transistors. A voltage for turning off may be applied, a predetermined data voltage may be applied to the first and second input terminals, and the first and second output terminals may be connected to the first and second liquid crystal capacitors, respectively.

The first and second luminance display pixels may further include a light blocking film that blocks the first and second thin film transistors from external light.

The first luminance display unit may be disposed in an edge region of the liquid crystal panel assembly.

And a second luminance display unit including at least third and fourth luminance display pixels receiving the backlight light and displaying different luminance, wherein the first and third luminance display pixels are substantially the same. The fourth luminance display pixels may be substantially the same.

The first and second luminance displays may be disposed at different edge regions of the liquid crystal panel assembly.

DETAILED DESCRIPTION Embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like parts are designated by like reference numerals throughout the specification. When a part of a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the other part being "right over" but also another part in the middle. On the contrary, when a part is "just above" another part, there is no other part in the middle.

A liquid crystal display according to an exemplary embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

1 is a block diagram of a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram of one pixel of the liquid crystal display according to an exemplary embodiment of the present invention.

As shown in FIG. 1, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal panel assembly 300, a gate driver 400, a data driver 500, and a data driver And a gray voltage generator 800 connected to 500, a brightness detector 700, a backlight device 900 for irradiating light to the liquid crystal panel assembly 300, and a signal controller 600 for controlling the gray voltage generator 800.

The liquid crystal panel assembly 300 includes a plurality of display signal lines G ₁ -G _n , D ₁ -D _m and a plurality of pixels connected to the plurality of display signal lines G ₁ -G _n , D ₁ -D _m , and arranged in a substantially matrix form. .

The display signal lines G ₁ -G _n and D ₁ -D _m are a plurality of gate lines G ₁ -G _n for transmitting a gate signal (also called a “scan signal”) and a data line D for transmitting a data signal. ₁ -D _m ). The gate lines G ₁ -G _n extend substantially in the row direction and are substantially parallel to each other, and the data lines D ₁ -D _m extend substantially in the column direction and are substantially parallel to each other.

Each pixel includes a switching element Q connected to a display signal line G ₁ -G _n , D ₁ -D _m , and a liquid crystal capacitor C _LC and a storage capacitor C _ST connected thereto. It includes. The holding capacitor C _ST can be omitted as necessary.

The switching element Q, such as a thin film transistor, is provided in the lower panel 100, and the control terminal and the input terminal are three-terminal elements, respectively, with gate lines G ₁ -G _n and data lines D ₁ -D _m . The output terminal is connected to a liquid crystal capacitor (C _LC ) and a holding capacitor (C _ST ).

The liquid crystal capacitor C _LC has two terminals, the pixel electrode 190 of the lower panel 100 and the common electrode 270 of the upper panel 200, and the liquid crystal layer 3 between the two electrodes 190 and 270. It functions as a dielectric. The pixel electrode 190 is connected to the switching element Q, and the common electrode 270 is formed on the front surface of the upper panel 200 and receives a common voltage V _com . Unlike in FIG. 2, the common electrode 270 may be provided in the lower panel 100. In this case, at least one of the two electrodes 190 and 270 may be linear or rod-shaped.

The storage capacitor C _ST , which serves as an auxiliary part of the liquid crystal capacitor C _LC , is formed by overlapping a separate signal line (not shown) and the pixel electrode 190 provided on the lower panel 100 with an insulator interposed therebetween. A predetermined voltage such as the common voltage V _com is applied to this separate signal line. However, the storage capacitor C _ST may be formed such that the pixel electrode 190 overlaps the front end gate line directly above the insulator.

On the other hand, to implement color display, each pixel uniquely displays one of the three primary colors (spatial division) or each pixel alternately displays the three primary colors over time (time division) so that the desired color can be selected by the spatial and temporal sum of these three primary colors. To be recognized. 2 shows that each pixel includes a red, green, or blue color filter 230 in a region corresponding to the pixel electrode 190 as an example of spatial division. Unlike FIG. 2, the color filter 230 may be formed above or below the pixel electrode 190 of the lower panel 100.

A polarizer (not shown) for polarizing light is attached to an outer surface of at least one of the two display panels 100 and 200 of the liquid crystal panel assembly 300.

The backlight device 900 includes an inverter 920 that controls the brightness of the screen by blinking the lamp unit 910 and the lamp unit 910 and controlling the blinking time. The inverter 920 may be provided on an inverter PCB (not shown) mounted separately. The lamp unit 910 may include a fluorescent lamp or a light emitting device, and in the case of the light emitting device, the inverter 920 may be omitted.

The luminance display unit 700 receives light from the backlight device 900 and displays luminance according to the amount of light.

The gray voltage generator 800 generates two sets of gray voltages related to the transmittance of the pixel. One of the two sets has a positive value for the common voltage (V _com ) and the other set has a negative value.

The gate driver 400 is connected to the gate lines G ₁ -G _n of the liquid crystal panel assembly 300 to receive a gate signal formed by a combination of a gate on voltage V _on and a gate off voltage V _off from the outside. It is applied to the gate lines G ₁ -G _n and may be formed of a plurality of integrated circuits.

The data driver 500 is connected to the data lines D ₁ -Dm of the liquid crystal panel assembly 300 to select the gray voltage from the gray voltage generator 800 and apply the gray voltage to the pixel as a data signal. Can be done.

The plurality of gate driving integrated circuits or data driving integrated circuits may be mounted in a chip carrier package (TCP) (not shown) in the form of a chip to attach the TCP to the liquid crystal panel assembly 300, or may not use TCP. These integrated circuit chips may be directly attached onto a glass substrate (chip on glass, COG mounting method), and these integrated circuits may be directly formed on the liquid crystal panel assembly 300 together with the thin film transistors of the pixel.

The signal controller 600 controls operations of the gate driver 400 and the data driver 500.

Next, the image display operation of the liquid crystal display will be described in more detail.

The signal controller 600 may control the input image signals R, G, and B and their display from an external graphic controller (not shown), for example, a vertical sync signal V _sync and a horizontal sync signal. (H _sync ), a main clock (MCLK), a data enable signal (DE) is provided. The signal controller 600 properly processes the image signals R, G, and B according to the operating conditions of the liquid crystal panel assembly 300 based on the input image signals R, G, and B and the input control signal, and controls the gate control signal. After generating the CONT1 and the data control signal CONT2, the gate control signal CONT1 is sent to the gate driver 400, and the data control signal CONT2 and the processed image signal DAT are transmitted to the data driver 500. Export to

The gate control signal (CONT1) includes a gate-on voltage vertical synchronization start signal (STV) for instructing the start of output of the (V _on), the gate-on voltage gated clock signal that controls the output timing of the (V _on) (CPV) and the gate-on An output enable signal OE or the like that defines the duration of the voltage V _on .

The data control signal CONT2 includes a horizontal synchronization start signal STH indicating the start of input of the image data DAT, a load signal LOAD for applying a corresponding data voltage to the data lines D ₁ -D _m , and a common voltage. The inversion signal RVS and the data clock signal HCLK for inverting the polarity of the data voltage with respect to (V _com ) (hereinafter referred to as the "polarity of the data voltage by reducing the polarity of the data voltage with respect to the common voltage"). Include.

The data driver 500 sequentially receives and shifts the image data DAT for one row of pixels according to the data control signal CONT2 from the signal controller 600, and the gray voltage from the gray voltage generator 800. By selecting the gray scale voltage corresponding to each of the image data DAT, the image data DAT is converted into the corresponding data voltage and then applied to the corresponding data line D ₁ -D _m .

The gate driver 400 applies the gate-on voltage V _on to the gate lines G ₁ -G _n in response to the gate control signal CONT1 from the signal controller 600, thereby applying the gate lines G ₁ -G _n. ) Turns on the switching element Q connected thereto, so that the data voltage applied to the data lines D ₁ -D _m is applied to the corresponding pixel through the turned-on switching element Q.

The difference between the data voltage applied to the pixel and the common voltage V _com is shown as the charging voltage of the liquid crystal capacitor C _LC , that is, the pixel voltage. The arrangement of the liquid crystal molecules varies according to the magnitude of the pixel voltage, thereby changing the polarization of light passing through the liquid crystal layer 3. The change in polarization is represented by a change in transmittance of light by a polarizer (not shown) attached to the display panels 100 and 200.

After one horizontal period (or “1H”) (one period of the horizontal sync signal H _sync , the data enable signal DE, and the gate clock CPV), the data driver 500 and the gate driver 400 are next. The same operation is repeated for the pixels in the row. In this manner, the gate-on voltages V _{on are} sequentially applied to all the gate lines G ₁ -G _n during one frame to apply data voltages to all the pixels. At the end of one frame, the next frame starts and the state of the inversion signal RVS applied to the data driver 500 is controlled so that the polarity of the data voltage applied to each pixel is opposite to that of the previous frame ("frame inversion). "). In this case, the polarity of the data voltage flowing through one data line may be changed (“line inversion”) within one frame or the polarity of the data voltage applied to one pixel row may be different according to the characteristics of the inversion signal RVS ( "Dot reversal").

Next, the luminance display unit 700 of the liquid crystal display will be described in more detail with reference to FIGS. 3 to 5.

3 is an equivalent circuit diagram of a luminance display unit of a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 4 is a cross-sectional view of one of the luminance display pixels of a luminance display unit of a liquid crystal display according to an exemplary embodiment of the present invention. 5 is a cross-sectional view illustrating a position in which the luminance display unit of the liquid crystal display according to the exemplary embodiment of the present invention is mounted on the liquid crystal panel assembly.

As shown in FIG. 3, the luminance display unit 700 of the liquid crystal display according to the exemplary embodiment includes three luminance display pixels Pa, Pb, and Pc. The luminance display pixels Pa, Pb, and Pc each include the thin film transistors Qa, Qb, and Qc and the liquid crystal capacitor C _LC connected thereto.

The thin film transistors Qa, Qb, and Qc are provided in the lower panel 100. As a three-terminal device, a gate-off voltage V _off is applied to a control terminal thereof, and a white data voltage Vwh is applied to an input terminal thereof. The output terminal is connected to the liquid crystal capacitor C _LC .

Since the liquid crystal capacitor C _LC is substantially the same as the liquid crystal capacitor C _LC shown in FIG. 2, detailed description thereof will be omitted.

Next, the structure of the luminance display pixels Pa, Pb, and Pc will be described in more detail.

As shown in FIG. 4, which illustrates one of the luminance display pixels Pa, Pb, and Pc, a gate-off voltage is formed on the insulating substrate 110 in the lower display panel 100 where the thin film transistors Qa, Qb, and Qc are formed. A control electrode 124 to which V _off ) is applied is formed. The control terminal electrode 124 is inclined with respect to the surface of the substrate 110 and its inclination angle is 20-80 °.

An insulating layer 140 made of silicon nitride (SiNx) is formed on the control terminal electrode 124.

A semiconductor 154 made of hydrogenated amorphous silicon (amorphous silicon is abbreviated a-Si), polycrystalline silicon, or the like is formed on the insulating layer 140.

On top of the semiconductor 154, ohmic contacts 163 and 165 made of a material such as n + hydrogenated amorphous silicon doped with a high concentration of silicide or n-type impurities are formed.

Side surfaces of the semiconductor 154 and the ohmic contacts 163 and 165 are inclined with an inclination angle of 30-80 degrees.

An input electrode 173 and an output electrode 175 to which the white data voltage Vwh is applied are formed on the ohmic contacts 163 and 165 and the insulating layer 140.

The output terminal electrode 175 and the input terminal electrode 173 are separated from each other and positioned opposite to the control terminal electrode 124. The control terminal electrode 124, the output terminal electrode 175, and the input terminal electrode 173 together with the semiconductor 154 form the thin film transistors Qa, Qb, and Qc, and the channel thereof is the output terminal electrode 175. ) And the input terminal electrode 173 are formed in the semiconductor 154.

The thin film transistors Qa, Qb, and Qc are formed to have widths L and channel thicknesses t of different control terminal electrodes 124.

Like the semiconductor 154 and the like, the output terminal electrode 175 and the input terminal electrode 173 are inclined at an angle of about 30 to 80 degrees, respectively.

On the output terminal electrode 175 and the input terminal electrode 173 and the portion of the exposed semiconductor 154, a-Si: C: O formed of organic substance, plasma enhanced chemical vapor deposition (PECVD), A passivation layer 180 made of a low dielectric constant insulating material such as a-Si: O: F or silicon nitride (SiNx) or the like is formed. The material forming the passivation layer 180 may have planarization characteristics or photosensitivity.

The pixel electrode 190 made of a transparent conductive material such as ITO or IZO is formed on the passivation layer 180. The pixel electrode 190 is connected to the output terminal electrode 175 through the contact hole 181.

On the other hand, a light blocking film 220 for blocking light is formed on the upper panel 200 facing the lower panel 100 under the upper substrate 210 made of an insulating material such as transparent glass. The light blocking film 220 blocks the semiconductor 154 of the thin film transistors Qa, Qb, and Qc from external light irradiated on the upper substrate 210.

A common electrode 270 made of a transparent conductive material such as ITO or IZO is formed under the light blocking film 220 and the upper substrate 210.

The liquid crystal layer 3 is formed between the pixel electrode 190 and the common electrode 270.

The thin film transistors Qa, Qb, and Qc receive backlight light emitted from the lower portion of the insulating substrate 110. The backlight light is irradiated to the semiconductor 154 through portions other than the portion covered by the control terminal electrode 124. In addition, the backlight light is guided by a layer constituting the thin film transistors Qa, Qb, and Qc or by a material layer around the film and a film existing together inside and outside the thin film transistors Qa, Qb, and Qc to form a semiconductor 154. Can be investigated). When the thin film transistors Qa, Qb, and Qc are exposed to backlight light, the thin film transistors Qa, Qb, and Qc generate currents Ia, Ib, and Ic according to the amount of incident light.

For convenience of description, the thin film transistors Qa, Qb, and Qc each have a width La, Lb, Lc and a channel thickness ta, tb, tc of the control terminal electrode 124, and La <Lb. <Lc, ta> tb> tc.

The thin film transistor Qa receives more backlight light than the thin film transistor Qb since the width La of the control terminal electrode 124 is smaller than that of the thin film transistor Qb, and the thin film transistor Qb is similarly received. Receives more backlight light than the thin film transistor Qc. Further, the thin film transistor Qa generates a larger current than the thin film transistor Qb for a constant amount of light since its channel thickness ta is thicker than that of the thin film transistor Qb, and similarly, the thin film transistor Qb Generates a larger current than the thin film transistor Qc. As a result, when the same backlight light is irradiated to the thin film transistors Qa, Qb, and Qc, Ia> Ib> Ic is established.

Charges due to currents Ia, Ib, and Ic are accumulated in liquid crystal capacitors C _LC of the luminance display pixels Pa, Pb, and Pc, respectively, to form a charge voltage. The liquid crystal molecules change their arrangement depending on the charged voltage and change the transmittance of the backlight light. As a result, the luminance display pixels Pa, Pb, and Pc display luminance by varying the luminance according to the magnitudes of the currents Ia, Ib, and Ic. Since the luminance display pixels Pa, Pb, and Pc do not have a color filter unlike the pixels shown in FIG. 2, only the white light of the backlight is displayed. Therefore, when the liquid crystal display is in the normally black mode, the luminance display pixels Pa, Pb, and Pc display white when the currents Ia, Ib, and Ic are large, and black when the liquid crystal display is small.

By properly setting the widths La, Lb, Lc and the channel thicknesses ta, tb, tc of the control terminal electrode 124, white may be selectively displayed on the luminance display pixels Pa, Pb, Pc according to the backlight light. Can be. For example, white may be displayed on the luminance display pixels Pa and Pb, and black may be displayed on the luminance display pixels Pc. In this case, when the luminance of the backlight light decreases, the luminance display pixel Pb displays black instead of white, thereby easily determining whether the backlight device 900 is defective.

As shown in FIG. 5, the luminance display unit 700 may be formed in any one of the edge regions P1-P4 positioned outside the display region of the liquid crystal panel assembly 300.

Meanwhile, the luminance of the backlight may also be determined by arranging the plurality of luminance display units 700 in any two or more of the edge regions P1 to P4 to display the luminance of the backlight.

Although the luminance display unit 700 has been described as including three luminance display pixels, the luminance display unit 700 may include one, two, or four or more luminance display pixels. Although the liquid crystal display device including the backlight has been described, the present invention is not limited thereto, and the same may be applied to the light receiving display device including the backlight.

According to the present invention, by providing a plurality of luminance display pixels including thin film transistors having widths and channel thicknesses of different control terminal electrodes, it is possible to easily determine whether the backlight device is defective. The uniformity of backlight light can also be determined.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

1 is a block diagram of a liquid crystal display according to an exemplary embodiment of the present invention.

2 is an equivalent circuit diagram of one pixel of a liquid crystal display according to an exemplary embodiment of the present invention.

3 is an equivalent circuit diagram of a luminance display unit of a liquid crystal display according to an exemplary embodiment of the present invention.

4 is a cross-sectional view illustrating a cross section of one of luminance display pixels of the luminance display unit of the liquid crystal display according to the exemplary embodiment.

5 is a diagram illustrating a position where a luminance display unit of a liquid crystal display according to an exemplary embodiment of the present invention is mounted on a liquid crystal panel assembly.

Claims (9)

Liquid crystal panel assembly, A backlight for irradiating light onto the liquid crystal panel assembly, and A first luminance display unit including at least first and second luminance display pixels that receive the backlight light and display different luminance; Including; The first and second luminance display pixels may include first and second thin film transistors that receive the backlight light and generate different photocurrents, and first and second liquid crystal capacitors that change transmittance of the backlight light according to the different photocurrents. Each containing Liquid crystal display. In claim 1, The first and second thin film transistors further include first and second semiconductors having different channel thicknesses, respectively. In claim 2, The first and second semiconductors include amorphous silicon. The method of claim 1 or 2, The first and second thin film transistors include first and second control terminal electrodes having different widths, respectively. In claim 4, The first and second thin film transistors further include first and second input terminals and first and second output terminals, respectively, and the first and second control terminal electrodes turn the first and second thin film transistors. A voltage for turning off is applied, a predetermined data voltage is applied to the first and second input terminals, and the first and second output terminals are connected to the first and second liquid crystal capacitors, respectively. In claim 4, The first and second luminance display pixels may further include a light blocking layer that blocks the first and second thin film transistors from external light. In claim 4, And the first luminance display unit is disposed in an edge region of the liquid crystal panel assembly. In claim 1, And a second luminance display including at least third and fourth luminance display pixels receiving the backlight light and displaying different luminance. The first and third luminance display pixels are substantially the same, and the second and fourth luminance display pixels are substantially the same. Liquid crystal display. In claim 8, And the first and second luminance displays are disposed at different edge regions of the liquid crystal panel assembly.