KR100494680B1 - Thin film transistor-liquid crystal display device - Google Patents

Abstract

The present invention provides a TFT-LCD that can improve image quality by obtaining a constant Cgs value even when misalignment between mask shots occurs.

TFT-LCD according to the present invention comprises a gate line and a data line arranged in a matrix form on an insulating substrate; A thin film transistor disposed at an intersection between the gate line and the data line; And a pixel electrode arranged to contact the thin film transistor in a pixel region defined by the gate line and the data line, wherein the thin film transistor comprises: a gate electrode drawn from the gate line; An active layer disposed on the gate, first and second drain electrodes drawn from the data line and spaced apart from each other while overlapping with one side of the gate electrode, and overlapping with the other side of the gate electrode; And a source electrode disposed in the center between the drain electrode and the second drain electrode and in contact with the pixel electrode. Further, the separation distance between the first and second drain electrodes and the source electrode is the same, and the width of the source electrode is larger than the separation distance. In addition, the area of the capacitance between the source electrode and the gate electrode is the capacity per unit area of the gate insulating film x the width of the gate x (the width of the source electrode + the distance between the source electrode and the drain electrode).

Description

Thin film transistor-liquid crystal display device

The present invention relates to an active matrix liquid crystal display device, and more particularly to a thin film transistor liquid crystal display device capable of improving image quality.

In general, an active matrix-type liquid crystal display (AM-LCD) device is thin and is used in various display devices. In such an AM-LCD device, a thin film transistor (TFT) is provided as a switching element for each pixel, so that individual pixel electrodes are driven independently, so that the contrast due to the reduction in the duty ratio is reduced. It does not decrease and also the viewing angle does not decrease even when the display capacity increases and the number of lines increases.

1 is a plan view showing a conventional TFT-LCD.

Referring to FIG. 1, a gate line 11 and a data line 15 are arranged in a matrix on a transparent insulating substrate 10 (see FIG. 2) such as glass, and the gate line 11 and the data line 15 are arranged in a matrix form. The TFT 100 is arranged at the intersection of. The TFT 100 includes a gate 11A protruding from the gate line 11, an active layer 13, a drain 15B protruding from the data line 15 and overlapping one side of the gate 11A, and a drain. A source 15A is spaced apart from the predetermined distance 15B and overlapped with the other side of the gate 11A. In the space formed by the gate line 11 and the data line 15, the pixel electrode 16 in contact with the source 15A of the TFT 100 is disposed.

FIG. 2 is a cross-sectional view taken along line II-II 'of the TFT 100 shown in FIG. 1, and as shown in FIG. The insulating film 12 is formed. The semiconductor layer 13 is formed on the gate insulating layer 12 corresponding to the gate 11A, and the source and drain 15A spaced apart from each other while overlapping both sides of the gate 11A, respectively, on the semiconductor layer 13. 15B) is formed. The ohmic layer 14 is interposed between the source and drain 15A, 15B and the semiconductor layer 13.

Referring to the operation of the TFT, when the gate voltage Vg is greater than the threshold voltage Vth, as shown in FIG. 2, electrons (−) are induced in the semiconductor layer 13 to form a channel. On the other hand, when the gate voltage Vg is smaller than the threshold voltage Vth, electrons (-) which have been induced in the semiconductor layer 13 exit to the source 15A.

As described above, in order to form a channel in the TFT, the source 15A must be arranged to overlap the gate 11A. At this time, the capacitance Cgs between the gate and the source is a change in pixel voltage, which is a variable of kick-back voltage (ΔVp) that determines the image quality of the TFT-LCD.

That is, ΔVp can be expressed as follows.

ΔVp = ΔVgCgs / (Cst + C _LC + Cgs)

Here, ΔVg is the change in gate voltage, Cgs is the gate-source capacitance, Cst is the storage capacitance, and C _LC is the liquid crystal capacitance.

On the other hand, the area of Cgs which is a variable of ΔVp is the area of the semiconductor layer 13 in the portion overlapping with the gate 11A from the middle of the source 15A and the drain 15B.

However, since the exposure area of the exposure machine used in the exposure process is about 6 inches or 5 inches, in order to fabricate TFT-LCDs of 6 inches or more, the divisional exposure must be performed using a plurality of photo masks. Misalignment of the liver occurs. For example, when misalignment of the source and drain 15A, 15B occurs, as shown in Figs. 3 and 4, the areas A and B of Cgs appear differently.

Accordingly, ΔVp of each shot is different from each other, and a difference in the effective voltage applied to the liquid crystal is generated. As a result, not only the luminance difference between shots is generated, but also a flicker phenomenon occurs on the screen, resulting in deterioration of the image quality of the TFT-LCD.

Accordingly, an object of the present invention is to provide a TFT-LCD capable of improving image quality by obtaining a constant Cgs value even when misalignment between shots occurs.

In order to achieve the above object of the present invention, a TFT-LCD according to the present invention includes a gate line and a data line disposed in a matrix form on an insulating substrate; A thin film transistor disposed at an intersection between the gate line and the data line; And a pixel electrode arranged to contact the thin film transistor in a pixel region defined by the gate line and the data line, wherein the thin film transistor comprises: a gate electrode drawn from the gate line; An active layer disposed on the gate, first and second drain electrodes drawn from the data line and spaced apart from each other while overlapping with one side of the gate electrode, and overlapping with the other side of the gate electrode; And a source electrode disposed in the center between the drain electrode and the second drain electrode and in contact with the pixel electrode.

Further, the separation distance between the first and second drain electrodes and the source electrode is the same, and the width of the source electrode is larger than the separation distance. In addition, the area of the capacitance between the source electrode and the gate electrode is the capacity per unit area of the gate insulating film x the width of the gate x (the width of the source electrode + the distance between the source electrode and the drain electrode).

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention.

5 is a plan view illustrating a TFT-LCD according to an embodiment of the present invention.

Referring to FIG. 5, a gate line 51 and a data line 55 are arranged in a matrix on a transparent insulating substrate (not shown) such as glass, and an intersection portion of the gate line 51 and the data line 55 is formed. The TFT 200 is arranged in this. The TFT 200 overlaps the gate 51A protruding from the gate line 51, the active layer 53 disposed above the gate 51A, and protruding from the data line 55 and overlapping one side of the gate 51A. The first and second drains 55B and 55C arranged in parallel with each other, and the first and second drains while overlapping the other side of the gate 51A at the center on the first and second drains 55B and 55C. Sources 55A arranged parallel to 55B, 55C).

Here, the separation distances L1 and L2 between the source 55A and the first and second drains 55B and 55C are equal, and the width W2 of the source 55A is larger than the separation distance L1 and L2. In the space formed by the gate line 51 and the data line 55, a pixel electrode 56 in contact with the source 55A of the TFT 200 is disposed.

As described above, in the present invention, the source 55A is disposed in parallel between them between the first and second drains 55B and 55C. The area C of Cgs is the area of the semiconductor layer 53 in the portion overlapping with the gate 51A from the middle between the source 55A and the first and second drains 55B and 55C, as follows. Can be represented.

Area of Cgs (C) = Ci x W1 x (W2 + L1)

Where Ci is the capacitance per unit area of the gate insulating film, W1 is the width of the gate, W2 is the width of the source, and L1 is the distance between the drain and the source.

6 and 7 illustrate a case in which misalignment between mask shots occurs, and the distances M1 and M2 between the gate 55A and the data line 55 are different from each other. However, as shown in Figs. 6 and 7, even if misalignment between mask shots occurs, the intervals L1 and L2 between the drains 55B and 55C and the source 55A are constant, so that the area of each Cgs ( It can be seen that C1 and C2) are constantly shown.

That is, since Cgs is constant, ΔVp for determining the image quality of the TFT appears the same for each shot, and no difference in the effective voltage applied to the liquid crystal is generated. Accordingly, not only does the luminance difference between shots occur, but also the flicker phenomenon is prevented.

According to the present invention described above, by disposing the drains in duplicate and disposing the source therebetween, the variation of the Cgs value due to the misalignment between the mask shots is prevented, so that the luminance difference and the flicker phenomenon between the shots can be effectively prevented, resulting in a TFT- LCD image quality is improved.

In addition, since the drain can be repaired even if disconnection of the drain on one side occurs due to the double arrangement, the effect of yield improvement can be obtained.

In addition, this invention is not limited to the said Example, It can variously deform and implement within the range which does not deviate from the technical summary of this invention.

1 is a plan view of a conventional TFT-LCD.

2 is a cross-sectional view of a conventional TFT.

3 and 4 are plan views showing differences in Cgs due to conventional mask misalignment.

5 is a plan view of a TFT-LCD according to an embodiment of the present invention;

6 and 7 are plan views showing Cgs of the present invention when mask misalignment occurs.

(Explanation of symbols for the main parts of the drawing)

51: gate line 53: active layer

55: data line 55A: source

55B, 55C: first and second drain

56 pixel electrode

W1: width of gate

W2: width of source

L1, L2: separation distance between source and drain

C, C1, C2: Area of Cgs

200: TFT

Claims (4)

Gate lines and data lines arranged in a matrix form on the insulating substrate; A thin film transistor disposed at an intersection between the gate line and the data line; And a pixel electrode disposed in contact with the thin film transistor in a pixel region defined by the gate line and the data line, the thin film transistor liquid crystal display device comprising: The thin film transistor may include a gate electrode drawn from the gate line, an active layer disposed on the gate, first and second parallel lines spaced apart from the data line and overlapped with one side of the gate electrode. And a second drain electrode and a source electrode disposed in the center between the first drain electrode and the second drain electrode while overlapping the other side of the gate electrode and contacting the pixel electrode. . The thin film transistor liquid crystal display of claim 1, wherein the separation distance between the first and second drain electrodes and the source electrode is the same. The thin film transistor liquid crystal display of claim 2, wherein a width of the source electrode is greater than the separation distance. The method of claim 1, wherein an area of capacitance between the source electrode and the gate electrode is a capacity per unit area of the gate insulating film x width of the gate x (width of the source electrode + distance between the source electrode and the drain electrode). Thin film transistor liquid crystal display device.