KR20070049405A - Thin film transistor substrate and liquid crystal display device and driving method thereof - Google Patents

Abstract

The present invention provides a substrate, an optical sensor formed of at least one thin film transistor having a top gate structure in which a gate electrode is formed to be overlapped with a gate insulating layer interposed therebetween on a non-display area of the substrate, and external light; The present invention provides a thin film transistor substrate, a liquid crystal display device, and a driving method thereof, comprising a reflective tape reflecting the light to the optical sensor.

Description

Thin Film Transistor Substrate, Liquid Crystal Display and Driving Method {THIN FILM TRANSISTOR SUBSTRATE AND LIQUID CRYSTAL DISPLAY DEVICE AND DRIVING METHOD THEREOF}

1 is a diagram illustrating a thin film transistor substrate according to an exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view of the first thin film transistor of FIG. 1.

3 is a cross-sectional view of the second thin film transistor of FIG. 1.

4 is a block diagram illustrating a liquid crystal display device having a thin film transistor substrate according to an exemplary embodiment of the present invention.

5 is a flowchart sequentially illustrating a method of driving a liquid crystal display according to an exemplary embodiment of the present invention.

<Brief Description of Drawings>

100: substrate 101: buffer film

102: first active layer 103: gate insulating film

104S: first source contact hole 104D: first drain contact hole

105: first gate electrode 106: interlayer insulating film

107: first source electrode 108: first drain electrode

109: protective film 110: pixel contact hole

111: pixel electrode 112: second active layer

114S: second source contact hole 114D: second drain contact hole

115: second gate electrode 117: second source electrode

118: second drain electrode 120: reflective tape

130: gate line 140: data line

150: light sensor 200: liquid crystal panel

210: data driver 220: gate driver

250: power supply unit 260: timing controller

270: backlight driving unit 280: backlight

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a thin film transistor substrate, a liquid crystal display device, and a driving method including an optical sensor that can form an optical sensor in a non-display area and automatically adjust brightness through the liquid crystal display device.

Recently, with the development of portable display devices such as mobile phones, PDAs, notebook phones, and the like, there is an increasing demand for thin and light display devices that can be applied thereto. Such display devices include liquid crystal displays (LCDs), field emission displays (FEDs), and vacuum fluorescent displays (VFDs). Among these, liquid crystal displays have mass production technology, ease of driving means, and high quality. It is easy to receive the spotlight.

These portable liquid crystal displays are very sensitive to power consumption because they are driven by batteries. Therefore, a method of reducing power consumption by measuring the brightness of external light and adjusting the brightness of the backlight accordingly is used. In this case, when an optical sensor for detecting external light is incorporated in the display panel, a liquid crystal display using a thin film transistor having a bottom gate structure is relatively easily manufactured.

However, when a thin film transistor having a top gate structure is used, it is difficult to detect external light because a gate electrode is formed on the active layer to prevent transmission of external light.

In order to solve the above problems, it is an object of the present invention to provide a thin film transistor substrate, a liquid crystal display device and a driving method thereof which can implement an optical sensor with a top gate type thin film transistor.

In order to achieve the above object, the present invention provides a substrate and at least one thin film transistor having a top gate structure formed on a non-display area of the substrate and having a gate electrode overlapped with a gate insulating film interposed therebetween. It provides a thin film transistor substrate having an optical sensor formed by the and a reflective tape for reflecting the external light to the optical sensor.

In order to achieve the above object, the present invention provides a liquid crystal panel, an optical sensor formed of at least one thin film transistor having a top gate structure in a non-display area of the liquid crystal panel, and a reflective tape reflecting external light by the optical sensor. And a backlight driver for controlling a backlight driving voltage through a photocurrent generated by the optical sensor and a backlight for irradiating light to the liquid crystal panel through a voltage of the backlight driver.

One of the source electrode and the drain electrode of the thin film transistor is floated, and the other is connected to the backlight driver.

The gate electrode of the thin film transistor may be floated.

The backlight driver may include a photocurrent comparison circuit comparing the photocurrent and a reference value.

In order to achieve the above object, the present invention comprises the steps of generating the photocurrent by the external light reflected from the reflective tape to the active layer of the optical sensor, supplying the photocurrent to the backlight driver, the photocurrent and the reference value Comparing the magnitudes of the two, adjusting the backlight driving voltage according to the magnitude of the photocurrent, and driving the backlight by the backlight driving voltage to supply light to the liquid crystal panel. To provide.

Other objects and advantages of the present invention in addition to the above object will be apparent from the description of the preferred embodiment of the present invention with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIGS. 1 to 5.

1 is a plan view illustrating a thin film transistor substrate according to an exemplary embodiment of the present invention, FIG. 2 is a cross-sectional view illustrating a first thin film transistor of FIG. 1, and FIG. 3 is a cross-sectional view illustrating a second thin film transistor of FIG. 1.

Referring to FIG. 1, a thin film transistor substrate according to the present invention is formed at an intersection of a gate line 130 and a data line 140 formed on a substrate 100, and a gate line 130 and a data line 140. The first thin film transistor TFT1, the pixel electrode 111 formed in the pixel region defined by the intersection of the gate line 130 and the data line 140, and the second sensor formed in the non-display region and the optical sensor 150. A reflective tape 120 is attached to the thin film transistor TFT2 and the rear surface of the substrate to reflect external light.

The gate line 130 formed on the substrate 100 supplies a gate driving signal to the gate electrode 105 of the first thin film transistor TFT1.

The data line 140 supplies a data driving signal to the first source electrode 107 of the first thin film transistor TFT1.

The data line 140 is formed to intersect the gate line 130 with the gate insulating layer 103 and the interlayer insulating layer 106 therebetween to define a pixel area.

Referring to FIG. 2, the first thin film transistor TFT1 includes a first gate electrode 105, a first active layer 102, a first source electrode 107, and a first drain electrode 108. 1 The active layer 102 is formed of a polysilicon thin film. The first active layer 102 includes a first source region 102S and a first drain region 102D which are non-overlapping with the first gate electrode 105 and implanted with N-type impurities. The first source region 102S and the first drain region 102D of the first active layer 102 face each other with the first channel region 102C overlapping the first gate electrode 105.

The pixel electrode 111 is formed of a transparent conductive film in the pixel region and is connected to the first drain electrode 108. Accordingly, an electric field is formed between the pixel electrode 111 supplied with the pixel signal through the first thin film transistor TFT1 and the common electrode supplied with the common voltage. The electric field rotates the liquid crystal molecules between the color filter substrate and the thin film transistor substrate by the dielectric anisotropy, and thus the light transmittance through the pixel region is changed, thereby achieving gray scale.

In addition, the second thin film transistor TFT2 serving as an optical sensor is formed in the non-display area of the substrate 100, and the reflective tape 120 is attached to the rear surface of the substrate on which the second thin film transistor TFT2 is formed. The second thin film transistor TFT2 is formed in the same manner as the first thin film transistor TFT1.

Referring to FIG. 3, the second thin film transistor TFT2 includes a second gate electrode 115, a second active layer 112, a second source electrode 117, and a second drain electrode 118. The active layer 112 is formed of a polysilicon thin film. The second active layer 112 includes a second source region 112S and a second drain region 112D that are not overlapped with the second gate electrode 115 and have an N-type impurity implanted therein. The second source region 112S and the second drain region 112D of the second active layer 112 face each other with the second channel region 112C overlapping the second gate electrode 115.

As described above, the second thin film transistor TFT2, which is the optical sensor 150, has a top gate shape in which the second gate electrode 115 is formed with the gate insulating layer 103 interposed between the second active layer 112. Accordingly, since the second active layer 112 of the second thin film transistor TFT2 is covered by the second gate electrode 115, the reflective tape 120 capable of supplying external light to the second active layer 112 is provided. It is provided further.

When the external light is introduced into the non-display area, the external light is reflected through the reflective tape 120 attached to the rear surface of the substrate 100 to be incident and incident on the second active layer 112 of the second thin film transistor TFT2. The external light causes current to flow between the second source region 112S and the second drain region 112D.

In other words, when external light having an energy bandgap or more is incident on the polysiliconized second active layer 112, current flows between the second source electrode 117 and the second drain electrode 118 by electron excitation.

In the case of a semiconductor, for example, a band gap exists between a conduction band and a balance band. At this time, when there is no external energy, a large number of electrons are distributed in the balance band, but when energy outside the band gap is supplied from the outside, electrons are excited from the balance band to the conduction band, and the electrons in the conduction band move to flow current. do.

In the case of the second thin film transistor TFT2 using the semiconductor characteristic, when the intensity of external light incident on the second active layer 112 is greater than or equal to an energy band gap, photocurrent generated by electron excitation is generated.

The photocurrent generated in this way is applied to the backlight driver through either the second source electrode 117 or the second drain electrode 118. At this time, the remaining electrodes of the second source electrode 117 or the second drain electrode 118 that are not connected to the backlight driver 280 are floated.

The second gate electrode 115 may be floated or connected to the gate driver 220. When a driving signal is applied to the second gate electrode 115 connected to the gate driver 220, that is, when the liquid crystal display is driven, the second thin film transistor TFT2 is driven and external light is sensed to generate a photocurrent. ..

On the other hand, when the magnitude of the photocurrent is not easy to measure and compare, the area of the active layer may be increased to increase the magnitude of the photocurrent even when the same light is incident.

The optical sensor may be configured by connecting a plurality of thin film transistors in parallel or in series.

The thin film transistor substrate on which the first and second thin film transistors TFT2 are formed is manufactured by a process described later.

2 and 3, a buffer film 101 is formed on a substrate 100, and first and second active layers 102 and 112 are formed thereon.

The buffer film 101 is formed by depositing an inorganic insulating material such as SiO ₂ on the substrate 100.

The first and second active layers 102 and 112 deposit amorphous silicon on the buffer film 101 and crystallize the amorphous silicon with a laser to make polysilicon, and then the polysilicon is subjected to a photolithography process. It is formed by patterning in an etching process.

Next, a gate insulating film 103 is formed on the buffer film 101 on which the first and second active layers 102 and 112 are formed, and the first and second gate electrodes 105 and 115 and the gate line are formed thereon. A first conductive pattern group including 130 is formed.

The gate insulating layer 103 is formed by depositing an inorganic insulating material such as SiO ₂ on the buffer layer 101 on which the first and second active layers 102 and 112 are formed.

In the first conductive pattern group, a gate conductive layer having Al, Ta, Mo, MoW, Cu, an alloy thereof, or a multilayer structure thereof is formed on a substrate on which the gate insulating film 103 is formed, and then the gate conductive layer is photolithography. It is formed by patterning in a process and an etching process.

Next, N-type impurities are injected into each of the first and second active layers 102 and 112 using the first and second gate electrodes 105 and 115 as masks, thereby non-overlapping with the first gate electrode 105. The first source region 102S and the first drain region 102D of the first active layer 102, and the second active layer 112 non-overlapping with the second gate electrode 115 is formed as the second source. The region 112S and the second drain region 112D are formed. The first source region 102S and the first drain region 102D of the first active layer 102 face each other with the first channel region 102C overlapping the first gate electrode 105 interposed therebetween. The second source region 112S and the second drain region 112D of the second active layer 112 face each other with the second channel region 112C overlapping the second gate electrode 115.

An interlayer insulating film 106 is formed on the gate insulating film 103 on which the first conductive pattern group is formed, and the first and second source contact holes 104S and 114S penetrating the interlayer insulating film 106 and the gate insulating film 103. And first and second drain contact holes 104D and 114D.

The interlayer insulating layer 106 may be formed of an inorganic insulating material such as SiO ₂ or SiN ₂ on the gate insulating layer 103 on which the first conductive pattern group including the gate line 130 and the first and second gate electrodes 105 and 115 are formed. It is formed by depositing an insulating material such as

Subsequently, the first source region 102S and the first source of the first active layer 102 formed in the first thin film transistor TFT1 through the interlayer insulating layer 106 and the gate insulating layer 103 by a photolithography process and an etching process. The first source contact hole 104S and the second drain contact hole 104D are formed to expose the drain region 102D, respectively, and the second source of the second active layer 112 formed in the second thin film transistor TFT2. A second source contact hole 114S and a second drain contact hole 114D are formed to expose the region 112S and the second drain region 112D, respectively.

A second conductive pattern group including a data line 140, first and second source electrodes 107 and 117, and first and second drain electrodes 108 and 118 is formed on the interlayer insulating layer 106.

The second conductive pattern group including the data line 140, the first and second source electrodes 107 and 117, and the first and second drain electrodes 108 and 118 may be formed on the interlayer insulating layer 106. After the rain conductive layer is formed, the source and drain conductive layers are formed by patterning the photolithography process and the etching process.

The first source electrode 107 and the first drain electrode 108 may each have a first source region 102S of the first active layer 102 through a first source contact hole 104S and a first drain contact hole 104D. ) And the first drain region 102D, and the second source electrode 117 and the second drain electrode 118 are respectively connected to the second source contact hole 114S and the second drain contact hole 114D. The second source region 112S and the second drain region 112D of the second active layer 112 are respectively connected.

In this case, the passivation layer 109 is formed on the interlayer insulating layer 106 on which the second conductive pattern group of the first thin film transistor TFT1 is formed, and the pixel contact hole 110 penetrating the passivation layer 109 is formed.

The passivation layer 109 is formed by depositing an entire surface of an organic insulating material such as an inorganic insulating material or photoacryl on the interlayer insulating film 106 on which the second conductive pattern group is formed.

Subsequently, a pixel contact hole 110 penetrating the passivation layer 109 is formed in the first thin film transistor TFT1 by a photolithography process and an etching process. The pixel contact hole 110 penetrates the passivation layer 109 to expose the drain electrode 108 of the first thin film transistor TFT1.

A third conductive pattern group including the pixel electrode 111 is formed on the passivation layer 109.

The third conductive pattern group including the pixel electrode 111 may include indium tin oxide (ITO), indium zinc oxide (IZO), and indium tin zinc oxide on the passivation layer 109. After depositing a transparent conductive film, such as Oxide: ITZO), the transparent conductive film is formed by patterning by a photolithography process and an etching process.

The reflective tape 120 reflecting external light is further attached to the rear surface of the region where the second thin film transistor TFT2 is formed.

4 is a block diagram illustrating a liquid crystal display device having a thin film transistor substrate according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the liquid crystal panel 200 displaying an image, the gate driver 220 driving the gate line 130 of the liquid crystal panel 200, and the data line 140 of the liquid crystal panel 200 may be disposed. A data driver 210 to drive, a timing controller 260 to control the gate driver 220 and the data driver 210, a backlight 280 to supply light to the liquid crystal panel 200, and a backlight 280. A backlight driver 270 for supplying power to the gate driver, a power driver 250 for supplying power required for the gate driver 220, the data driver 210, the backlight driver 270, and the timing controller 260, and brightness of external light; It includes a light sensor 150 for measuring the, and a reflective tape 120 for reflecting the external light to supply to the light sensor 150.

The liquid crystal panel 200 displays an image by adjusting the light transmittance of the liquid crystal cells according to the image signal.

To this end, the liquid crystal panel 200 is formed by bonding the thin film transistor substrate 100 and the color filter substrate with the liquid crystal interposed therebetween. The liquid crystal panel 200 is provided with liquid crystal cells Clc independently driven by the first thin film transistor TFT1 in each region defined by the intersection of the gate line 130 and the data line 140. The first thin film transistor TFT1 supplies the pixel signal from the data line 140 to the pixel electrode 111 of the liquid crystal cell Clc in response to the scan signal from the gate line 130. The liquid crystal cell Clc drives the liquid crystal by an electric field caused by the difference between the common voltage Vcom applied to the common electrode formed on the color filter substrate and the data voltage charged in the pixel electrode 111.

The data driver 210 converts the digital data signal input from the timing controller 260 into an analog data signal using the gamma voltage from the gamma voltage unit and supplies the analog data signal to the data line 140.

The gate driver 220 sequentially supplies the scan signal of the gate-on voltage Von to the gate line 130. In addition, the gate driver 220 supplies the gate-off voltage Voff to the gate line 130 in the remaining period except for the period in which the gate-on voltage Von is supplied.

A backlight 280, such as a CCFL or an LED, is provided to supply light to the liquid crystal panel 200 where the thin film transistor substrate and the color filter substrate are bonded.

The backlight driver 270 generates a driving voltage of direct current or alternating current and supplies it to the backlight 280.

In the non-display area of the thin film transistor substrate 100, an optical sensor 150 for detecting the brightness of an ambient environment is formed, and a reflective tape 120 is attached to the rear surface of the substrate 100 to reflect external light to the optical sensor 150. do. As described above, the photosensor 150 is formed of the second thin film transistor TFT2 having a top gate shape.

At this time, any one of the second source electrode 117 or the second drain electrode 118 of the second thin film transistor TFT2 is connected to the backlight driver 270 and the rest of the second thin film transistor TFT2 is floated.

When the backlight driver 270 and the optical sensor 150 are connected, the photocurrent generated by the optical sensor 150 is supplied to the backlight driver 270. In this case, the backlight driver 270 includes a photocurrent comparison circuit and a backlight driving voltage generation circuit. The photocurrent comparison circuit compares the magnitude of the photocurrent input from the optical sensor 150 with a reference value. The backlight driving voltage generating circuit adjusts the brightness of the backlight 280 by adjusting the backlight driving voltage according to the comparison result of the photocurrent comparison circuit.

For example, when the magnitude of the photocurrent is greater than the reference value, the backlight driving voltage generation circuit generates a low backlight driving voltage to lower the brightness of the backlight 280, and when the magnitude of the photocurrent is smaller than the reference value, generates a backlight backlight to generate a high backlight driving voltage. Increase the brightness at 280. On the contrary, when the magnitude of the photocurrent is larger than the reference value, the backlight driving voltage may be increased to increase the brightness of the backlight 280. If the magnitude of the photocurrent is smaller than the reference value, the backlight driving voltage may be lowered to reduce the brightness of the backlight 280.

5 is a flowchart sequentially illustrating a method of driving a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 5, when external light reflected through the reflective tape is incident on the optical sensor, the optical sensor generates a photocurrent (S10). This photocurrent is supplied to the backlight driver (S20). The supplied photocurrent is compared with a reference value in the photocurrent comparison circuit (S30). Next, the backlight driving voltage is adjusted (S40). Then, the backlight is driven through the generated backlight driving voltage and light is supplied to the liquid crystal panel (S50).

In detail, external light is reflected by the reflective tape 120 attached to the non-display area of the liquid crystal panel 200 and is incident on the second active layer 112 of the second thin film transistor TFT2. According to the intensity of the external light, a photocurrent generated by electron excitation is generated in the second active layer TFT2. The generated photocurrent is supplied to the backlight driver 270 through an unfloated electrode among the second source electrode 117 or the second drain electrode 118 of the second thin film transistor TFT2. In the photocurrent comparison circuit provided in the backlight driver 270, the reference value is compared with the photocurrent to determine the level of the backlight driving voltage.

Next, the backlight driver 270 generates the backlight driving voltage using the power supplied from the power supply unit 250 and the signal generated by the photocurrent comparison circuit.

At this time, as described above, when the magnitude of the photocurrent is greater than the reference value, the backlight driving voltage generation circuit generates a low backlight driving voltage to lower the brightness of the backlight 280, and when the magnitude of the photocurrent is smaller than the reference value, the backlight driving voltage is high. To increase the luminance of the backlight 280.

On the contrary, when the magnitude of the photocurrent is greater than the reference value, the backlight driving voltage may be increased to increase the brightness of the backlight 280, and when the magnitude of the photocurrent is smaller than the reference value, the backlight driving voltage may be lowered to reduce the brightness of the backlight 280.

Through this, it is possible to reduce unnecessary power consumption of the backlight by automatically adjusting the brightness of the backlight according to the external brightness.

As described above, the thin film transistor substrate according to the present invention, the liquid crystal display device having the same, and a driving method thereof include a light sensor formed of a top gate thin film transistor and a reflective tape reflecting external light to the active layer of the thin film transistor. By controlling the brightness of the power consumption can be reduced.

The present invention described above will be capable of various substitutions, modifications and changes by those skilled in the art to which the present invention pertains. Therefore, the present invention should not be limited to the above-described embodiments and the accompanying drawings, and the rights thereof should be determined by the claims.

Claims (6)

A substrate; An optical sensor formed on the non-display area of the substrate and formed of at least one thin film transistor having a top gate structure in which a gate electrode is formed to overlap a gate insulating layer on an active layer; And a reflective tape for reflecting external light to the optical sensor. A liquid crystal panel; An optical sensor formed of at least one thin film transistor having a top gate structure in a non-display area of the liquid crystal panel; A reflective tape reflecting external light by the optical sensor; A backlight driver adjusting the backlight driving voltage through the photocurrent generated by the optical sensor; And And a backlight for irradiating light to the liquid crystal panel through the voltage of the backlight driver. The method of claim 2, And one of a source electrode and a drain electrode of the thin film transistor is floated and the other is connected to a backlight driver. The method of claim 2, And a gate electrode of the thin film transistor is floated. The method of claim 2, And the backlight driver includes an optical current comparison circuit comparing the photocurrent and a reference value. External light reflected from the reflective tape is incident on the active layer of the optical sensor to generate a photocurrent; Supplying the photocurrent to a backlight driver; Comparing the magnitude of the photocurrent with a reference value; Adjusting a backlight driving voltage according to the magnitude of the photocurrent; And driving a backlight by the backlight driving voltage to supply light to the liquid crystal panel.

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