CN100412671C - Liquid crystal display device having a plurality of pixel electrodes - Google Patents

Abstract

A liquid crystal display device includes a gate line formed on an insulating substrate, an active layer formed on the gate line, a source line, and a drain line coupled to a pixel electrode and spanning the overlapping area of the active layer and the gate line, wherein the gate line includes a first width portion and a second width portion, and the first width portion is narrower than the second width portion and overlaps with the drain line.

Description

Liquid crystal display device

technical field

The present invention relates to a liquid crystal display (Liquid Crystal Display; LCD), and in particular to a thin film transistor (Thin Film Transistor; TFT) capable of reducing gate-drain parasitic capacitance and avoiding uneven gate-drain capacitance - Liquid crystal display (TFT-LCD) devices.

Background technique

FIG. 1 is a plan view showing a typical device using a thin film transistor-liquid crystal display (TFT-LCD). The TFT-LCD device 10 includes a gate line 11 disposed on an insulating substrate (not shown) along the horizontal direction, and the gate line 11 has an extended region as a gate 12 . An active layer 13 is formed on the gate 12, for example, made of semiconductor materials such as amorphous silicon. A source line 14 extends in a direction perpendicular to the gate line 11 and crosses the gate line 11 , and has an extended region serving as a source 15 . A drain line 16 is coupled to a pixel electrode 18 and has a drain 17 along the extending direction of the gate line 11 . The source 15 and the drain 17 respectively overlap two opposite sides of the gate 12 . The pixel electrode 18 is usually made of a transparent conductive material with good conductivity, such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO).

However, when the machine variation in the photolithography process causes the mask to shift during the TFT formation process, the overlapping area between the source 15/drain 17 and the gate 12 changes, and the gate-source The capacitance (hereinafter referred to as C _GS ) and the gate-drain capacitance (C _GD ) accordingly vary accordingly. FIG. 2 is an equivalent circuit diagram of a pixel unit in a TFT-LCD to illustrate the influence of C _GD on brightness. In the figure, G represents the gate, S represents the source, D represents the drain, C _LC liquid crystal capacitor, C _S storage capacitor, and these two capacitors are connected in parallel between a pixel electrode P and a shared electrode C. When the TFT-LCD is turned on, the gate voltage is equal to a relatively high voltage V _GH , and the relationship between the total charge Q ₁ in the TFT-LCD and the pixel electrode voltage V _P1 can be expressed as:

Q ₁ ＝C _GD (V _P1 -V _GH )+(C _LC +C _S )(V _P1 -V _COM ) ...(1)

where V _COM is the voltage of the common electrode.

Conversely, when the TFT-LCD is turned off, the gate voltage is equal to a relatively low voltage V _GL , and the relationship between the total charge Q ₂ in the TFT-LCD and the pixel electrode voltage V _P2 can be expressed as:

Q ₂ ＝C _GD (V _P2 -V _GL )+(C _LC +C _S )(V _P2 -V _COM ) ...(2)

Since the total charge is conserved, that is, Q1=Q2, it can be known from (1)(2):

ΔV _P ＝V _P1 -V _P2 ＝(V _GH -V _GL )(C _GD /(C _CL +C _S +C _GD )) ...(3)

It can be seen from formula (3) that ΔV _P (hereinafter referred to as feedthrough voltage) is affected by C _GD . Since the brightness of the LCD is controlled by the voltage of the pixel electrode, when the variation of the machine in the lithography process causes the C _gd of the TFT in different regions to deviate, the result is that the brightness of the liquid crystal display is uneven, and if it is serious, it will cause the so-called "Mura".

In addition to the above-mentioned problems, the surface of the display screen also suffers from flickering problems due to excessive C _GD values, which is caused by the effective value of the voltage applied to the liquid crystal varying from one frame to the next.

When the gate-drain capacitance (C _GD ) increases, the time constant of the gate line increases accordingly. As a result, when the applied gate voltage changes from high to low on the surface of the display from the driving side to the far side, there will be a delay, and the adjacent area on the far side will experience the so-called rewriting phenomenon, which means , the data (that is, the drain potential) of adjacent horizontal periods of a predetermined horizontal period will be written in the predetermined horizontal period. As a result, the potential of a given pixel is shifted.

In addition, as shown in FIG. 2 , during the transition of the gate voltage from high to low, the parasitic capacitance of the TFT will cause the pixel electrode to have a voltage drop ΔV _P as represented by formula (3). As this fed voltage increases, the voltage gap between the source and drain within the thin film crystal increases. As a result, when the gate voltage changes from high to low from the driving side to the far side of the display surface, the rewriting phenomenon caused by delay is more likely to occur. It can be clearly seen from formula (3) that there is a close relationship between ΔV _P and C _GD values. When C _GD decreases, _ΔVP also decreases. Therefore, by reducing C _GD , the rewrite phenomenon can be suppressed.

In view of this, a TFT-LCD device that can reduce gate-drain parasitic capacitance and avoid uneven gate-drain capacitance is desired by those skilled in the art.

Contents of the invention

The present invention discloses a liquid crystal display (LCD) device using a thin film transistor and its forming method, which can avoid the deviation of the gate-drain capacitance when the alignment of the machine is not accurate, and thus prevent the phenomenon of uneven brightness in different areas of the LCD . Moreover, the liquid crystal display device also has reduced C _GD , so problems such as flickering of the display can be prevented.

The invention provides a liquid crystal display device. The liquid crystal display device includes an insulating substrate, a gate line is formed on the insulating substrate, an active layer is formed on the gate line, a source line, and a drain line are coupled to a pixel electrode and span the The overlapping region of the active layer and the gate line, wherein the gate line has a gate including a first width portion and a second width portion, and the first width portion is narrower than the second width portion and is in line with the second width portion The drain lines overlap.

The invention provides a liquid crystal display device, which comprises an insulating substrate, a gate line is formed on the insulating substrate, an active layer is formed on the gate line, and a source line crosses the gate line and has an extension area, and a drain line coupled to a pixel electrode and across the overlapping area of the active layer and the gate line, and has at least one extension area formed in one of the extension areas of the source line side and the overlapping area of the active layer and the gate line, wherein the gate line includes a first width portion and a second width portion, and the first width portion is narrower than the second width portion and is in line with the The drain lines overlap.

Description of drawings

Fig. 1 is a plan view of a conventional TFT-LCD device;

Fig. 2 is an equivalent circuit diagram of a TFT-LCD;

3 is a plan view showing an embodiment of a liquid crystal display device of the present invention;

FIG. 4 is a plan view showing another embodiment of a liquid crystal display device of the present invention.

Symbol Description:

10～Traditional thin film transistor-liquid crystal display device

30, 40~The liquid crystal display device of the present invention

11~Gate line 12~Gate

13～active layer

14~source line 15~source

16～drain line 17～drain

18～Pixel electrode

31～gate line 32～gate

33～active layer

34～source line 35～source

36～drain line 37～drain

38～Pixel electrode

39, 391, 392, 394, 395 ~ channel area

Detailed ways

The structure and method of forming the present invention, together with additional objects and advantages thereof, may be best understood from the following description of specific embodiments and when read with reference to the accompanying figures.

The icons referenced herein are not scaled down to scale. The relative sizes of the various components depicted in the drawings are not intended to represent the proportional characteristics of the actual sizes of these components, but are only used to assist ordinary skill in the art so that they can clearly understand how to make and use the present invention, as well as understand the implications of the present invention. Inventive concepts within inventions.

Referring to FIG. 3, it is a plan view showing an embodiment of a liquid crystal display device of the present invention. The liquid crystal display device 30 includes a gate line 31 disposed on an insulating substrate along a horizontal direction. As shown in the figure, the gate line 31 includes a first width portion and a second width portion, wherein the first width portion is narrower than the second width portion. An active layer 33 is formed on the first width portion and the second width portion of the gate line 31, wherein the gate line 31 has a gate 32 located at the first width portion and the second width portion and the active layer. The area where layers 33 overlap. A source line 34 crosses the gate line 31 substantially perpendicular to the extending direction of the gate line 31 , and has an extension region on the active layer 33 as a source 35 . A drain line 36 is substantially perpendicular to the extending direction of the gate line 31 and across the overlapping area of the active layer 33 and the first width portion of the gate line 31, the drain line 36 has a drain 37 is on the active layer 33 and coupled to a pixel electrode 38 , wherein there is a channel region 39 in the active layer 33 between the source electrode 35 and the drain electrode 37 .

It can be clearly seen from this figure that since the drain line 36 extends beyond the boundary of the overlapping area of the active layer 33 and the gate line 31, when the alignment is not correct, the gate lines/gates 31/32, there are The overlapping area of the source layer 33 and the drain line/drain 36/37 remains unchanged, which means that the C _GD value does not deviate, so that the brightness of the display will not be uneven. On the other hand, since the gate line includes a narrow first width portion, and the drain line overlaps the first width portion, the gate line/gate 31/32, the active layer 33, The overlapping area of the drain lines/drain electrodes 36/37 is reduced, thereby reducing the C _GD value, and consequently reducing the flickering of the screen.

It should be noted that the first width portion of the gate line is not limited to the area overlapping the drain line 36 , but can extend toward the source line 34 (not shown).

In addition, since the first width portion of the gate line 31 is relatively narrow, there are idle regions on both sides of the first width portion. Therefore, in another embodiment of the present invention, the drain line 36 can increase at least one extended area on the border of the overlapping area of the active layer 33 and the gate line 31 on one side of the first width portion, so The width of the channel region between the drain line 36 and the source line 34 can be increased, thereby increasing the conduction current.

Referring to FIG. 4, it is a plan view showing another embodiment of the liquid crystal display device of the present invention. This liquid crystal display device 40 is exactly the same as the liquid crystal display device 30, and the only difference is that two extension regions are added to the drain line, which are respectively formed on both sides of the extension region 35 of the source line 34 and between the active layer 33 and the gate line 31. on the overlapping area. Therefore, the channel region defined in the active layer 33 between the source electrode 35 and the drain electrode 37 includes three regions 39 , 39 ₁ , and 39 ₂ .

It can be clearly seen from this figure that, compared with the channel area 39 in FIG. 3 , there are two more areas 39 ₁ and 39 ₂ in the channel area. In addition, the active layer 33 can extend toward the source line 34 and expand in two directions up and down, so that the channel region 39 can be further increased by two regions 39 ₄ and 39 ₅ .

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any skilled person can make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, this The scope of protection of an invention shall be determined by the scope of the patent application.

Claims (9)

1. A liquid crystal display device, comprising: an insulating substrate; A gate line is formed on the insulating substrate; an active layer is formed on the gate line; A source line is formed on the insulating substrate, perpendicular to the gate line; a pixel electrode; and a drain line coupled to the pixel electrode and across the overlapping area of the active layer and the gate line, Wherein the gate line includes a first width portion and a second width portion, and the first width portion is narrower than the second width portion and overlaps with the drain line. 2. The liquid crystal display device as claimed in claim 1 , wherein the drain line has at least one extended region, and the extended region is formed on a boundary of an overlapping region of the active layer and the gate line. 3. The liquid crystal display device as claimed in claim 1 , wherein the source line crosses the gate line, and has an extension area located on an overlapping area of the active layer and the gate line. 4. The liquid crystal display device as claimed in claim 3 , wherein the drain line has at least one extension region, the extension region is formed on one side of the extension region of the source line and between the active layer and the gate line on the overlapping area. 5. The liquid crystal display device as claimed in claim 4 , wherein the drain line has two extension regions, and the two extension regions are respectively formed on the overlap of the active layer and the gate line on both sides of the extension region of the source line on the border of the region. 6. The liquid crystal display device as claimed in claim 1 , wherein the gate line further comprises a gate, located on the first width portion and part of the second width portion. 7. The liquid crystal display device as claimed in claim 3 , wherein the extended region of the source line serves as a source. 8. The liquid crystal display device as claimed in claim 1 , wherein the drain line overlaps the active layer and the first width portion of the gate line as a drain. 9. The liquid crystal display device as claimed in claim 1, wherein the drain line extends beyond a boundary of an overlapping area of the active layer and the first width portion.

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