KR100529572B1 - Thin film transistor liquid crystal display - Google Patents

Abstract

In a liquid crystal display device having a liquid crystal capacitor and a plurality of pixels having a switching element, a storage capacitor having one terminal connected to a switching element of one pixel and the other terminal connected to a pixel electrode of a pixel adjacent to the pixel. To form. In this way, two holding capacitors are connected to the switching elements of the remaining pixels except for the two pixels at both edges, thereby ensuring sufficient holding capacity, and reducing parasitic capacity while preventing the reduction of the aperture ratio. When a device is defective, the defect can be easily repaired.

Description

Thin film transistor liquid crystal display

The present invention relates to a thin film transistor liquid crystal display device.

At present, an active matrix liquid crystal display (AMLCD) using a thin film transistor as a switching element has been widely spotlighted for its portability and excellent image quality. In particular, an in-plane switching (IPS) liquid crystal display device driven by an electric field essentially parallel to the substrate formed between two parallel electrodes is expected to be widely used because it can secure a wide viewing angle.

Each pixel of the liquid crystal display device receives an image signal transmitted through the switching element and maintains the signal by the liquid crystal capacitor until the next signal comes in. At this time, in order to protect the electric charge holding ability of a liquid crystal, a normal holding capacitor is connected in parallel with a liquid crystal capacitor.

The method of forming the storage capacitor can be divided into an independent wiring method and a shear gate method according to its structure.

Next, a thin film transistor liquid crystal display according to the related art will be described with reference to the accompanying drawings.

1 is an equivalent circuit diagram of a unit pixel of a conventional thin film transistor liquid crystal display device of an independent wiring method.

As shown in FIG. 1, the gate line GL transmitting the scan signal and the data line DL transmitting the image signal cross each other, the gate electrode is connected to the gate line GL, and the source electrode There is a thin film transistor TFT connected to the data line DL. The drain electrode of the thin film transistor TFT is connected to one terminal of the liquid crystal capacitor C _LC and the storage capacitor Cst. That is, the liquid crystal capacitor C _LC and the storage capacitor Cst are connected in parallel with each other. The other terminal of the liquid crystal capacitor C _LC is applied with a constant voltage Vcom expressed as a common voltage, and the other terminal of the storage capacitor Cst is connected to the storage electrode line SL formed separately from the gate line GL. . However, this method has a disadvantage in that the number of wirings is increased and the opening ratio is reduced because of forming a separate sustain electrode line.

2 is an equivalent circuit diagram of a unit pixel of a conventional thin film transistor liquid crystal display of a shear gate type.

As shown in FIG. 2, the front gate method is a method in which the front gate line GL is used as one terminal of the storage capacitor Cst. The other configuration is similar to that of the independent wiring method shown in FIG. This method has the advantage of increasing the aperture ratio because it does not form a separate storage electrode line other than the gate line, while the parasitic capacitance of the gate line is increased.

In addition, as in the prior art, when using a gate line of a front end or a separate storage electrode line to form a storage capacitor, a high voltage of about 6 to 12 volts is generally applied between both electrodes of the storage capacitor. At this time, a leakage current flows through the insulating film on both electrodes of the storage capacitor due to this voltage, so that self-discharge or defects in the insulating film may cause insulation breakdown, resulting in a decrease in yield.

An object of the present invention is to form a storage capacitor without a decrease in aperture ratio or an increase in wiring in a flat drive type liquid crystal display device.

In order to achieve the above object, in the present invention, a liquid crystal display device includes a storage capacitor having one terminal connected to a switching element of one pixel and the other terminal connected to a pixel electrode of a pixel adjacent to the pixel. do.

In the thin film transistor liquid crystal display according to the present invention, a gate line for transmitting a scan signal from the outside and a gate electrode connected thereto, a plurality of linear common electrodes and a storage capacitor electrode are formed on the substrate, and the storage capacitor electrode is disposed thereon. A gate insulating film having a first contact hole for exposing a portion of is covered. An amorphous silicon layer and a doped amorphous silicon layer are sequentially formed on the gate insulating film on the gate electrode, and a source electrode and a drain electrode are formed on the doped amorphous silicon layer, respectively. The drain electrode overlaps with the storage capacitor electrode with the gate insulating film interposed therebetween, and is connected to the storage capacitor electrode of the adjacent pixel through a first contact hole formed in the gate insulating film, and alternately parallel to the common electrode on the gate insulating film. It is also connected to a plurality of linear pixel electrodes formed. The source electrode is connected to a data line for transmitting an image signal from the outside.

Here, a common electrode line connecting the plurality of common electrodes to each other and transmitting a common signal from the outside may be further formed, and a protective layer covering the source electrode, the drain electrode, the pixel electrode, and the data line may be further formed.

The passivation layer has a second contact hole formed to cover the source electrode, the drain electrode, and the pixel electrode to expose a portion of the source electrode, and the data line may be formed on the passivation layer and connected to the source electrode through the second contact hole.

In order to manufacture such a liquid crystal display, first, a gate line, a gate electrode, a common electrode, and a storage capacitor electrode are formed on a substrate, a gate insulating film is formed, and then an amorphous silicon layer and a doped amorphous silicon layer are formed on the gate insulating film on the gate electrode. An amorphous silicon layer is formed and a first contact hole for exposing a portion of the storage capacitor electrode is formed in the gate insulating film. Next, a source electrode, a drain electrode, and a pixel electrode are formed on the doped amorphous silicon layer, and a data line connected to the source electrode is formed.

In the forming of the common electrode, a common electrode line may be further formed, and a passivation layer covering the source electrode, the drain electrode, the pixel electrode, and the data line may be formed.

The passivation layer may be formed on the source electrode, the drain electrode, and the pixel electrode, form a second contact hole exposing a portion of the source electrode, and a data line may be formed on the passivation layer.

Then, 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.

FIG. 3 is an equivalent circuit diagram of a thin film transistor liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 4 illustrates a repair method when a switching element of the thin film transistor liquid crystal display shown in FIG. 3 is defective.

As shown in FIG. 3, the gate lines GL are arranged horizontally, and the data lines DL are arranged vertically. The gate terminal of the thin film transistor Q is connected to the gate line GL, the source terminal is connected to the data line DL, and the drain terminal is connected to the liquid crystal capacitor C _LC . The other terminal of the storage capacitor Cst in which one terminal is connected to the drain terminal of the thin film transistor Q is connected to the thin film transistors of neighboring pixels in the neighboring rows of the same row, that is, the gate terminal is connected to the same gate line GL. It is connected to the drain terminal of Q). Here, the other terminal of the liquid crystal capacitor is applied with a constant voltage Vcom indicated by a common voltage.

At this time, the other terminal of the storage capacitor Cst _L formed on the left side of the storage capacitors connected to the drain electrode of the thin film transistor of the pixel at the left end is isolated, and the storage capacitor is formed at the rightmost pixel. It doesn't work. As a result, each pixel has two storage capacitors, and only the rightmost pixel has one storage capacitor.

In a pixel having such a structure, when there is a defect in a switching element such as a thin film transistor or other active element used for driving purposes, the defective active element Q ₀ , as shown in part I of FIG. The drain terminal is cut using a laser or the like to separate from the other capacitors. Alternatively, the same applies when the terminal is electrically cut by a defect. Then, the data signal V to the pixel voltage of the pixel to the right is not supplied to the liquid crystal capacitor of the pixel, the voltage Vp of the liquid crystal capacitor of the pixel is referred to as the pixel voltage of the pixel positioned on the left side of the pixel V _{L, Suppose R} is given by

V _p = (V _L + V _R + V _com C _LC / C _st ) / (2 + C _LC / C _st )

At this time, C _LC / C _st is smaller than 1, and as C _st increases, C _LC / C _st decreases. In this case, the pixel voltage approaches the arithmetic mean of the voltages of the liquid crystal capacitors of the pixels positioned to the left and right of the pixel. Therefore, the brightness of this pixel approaches the middle brightness of the left and right screens and can be compensated automatically.

This structure is particularly advantageous in monochrome liquid crystal display devices. In the case of a color panel composed of three color filters, in order to achieve the purpose of the automatic compensation, it is preferable to connect holding capacitors between third adjacent pixels, that is, pixels displaying the same color. However, in the case where automatic compensation is not aimed as described above, the color panel may be connected to adjacent pixels on the left and right sides.

FIG. 5 is a plan view of a planar drive type liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 6 is a cross-sectional view taken along line VI-VI 'of FIG. 5.

As shown in FIGS. 5 and 6, a gate line 20 for transmitting a scan signal in a horizontal direction is formed on the transparent insulating substrate 100, and a common electrode line for transmitting a common signal in parallel with the gate line 20. 90 is formed. A portion of the gate line 20 becomes a gate electrode, and the common electrode line 90 is connected to a plurality of linear common electrodes 91 formed in parallel in the vertical direction. On the substrate 100, the storage capacitor electrodes 11 and 12 are formed to be separated from the gate line 20 and the common electrode line 90 in parallel with the gate line 20.

The gate insulating film 30 made of silicon nitride or the like is covered on the gate line 20, the common electrode line 90, the common electrode 91, and the storage capacitor electrodes 11 and 12. Contact holes 31 and 32 exposing a part of the electrodes 11 and 12 are formed.

A channel layer 40 of a thin film transistor made of amorphous silicon or the like is formed on the gate insulating layer 30 on the gate electrode that is part of the gate line 20, and the ohmic contact layer 51 made of doped amorphous silicon or the like is formed thereon. 52 is formed on both sides of the gate line 20.

The source electrode 61 and the drain electrode 62 are formed on the doped amorphous silicon layers 51 and 52, respectively. The drain electrode 62 extends in the horizontal direction and overlaps the storage capacitor electrode 11 with the gate insulating film 30 interposed therebetween, and is formed in the gate insulating film 30 with the storage capacitor electrode 12 of the adjacent pixel. It is connected via the contact hole 32. That is, the drain electrode 62 becomes one terminal of the storage capacitor, and the storage capacitor electrode 11 which overlaps with the drain electrode 62 and the gate insulating film 30 interposes as the other terminal of the storage capacitor. On the other hand, the drain electrode 62 is connected to the pixel electrode 63 which is formed in parallel to the common electrode 91 in the longitudinal direction. The source electrode 61 is formed in the vertical direction on the gate insulating film 30 and is connected to the data line 60 which transmits an image signal from the outside.

A protective film 70 made of silicon nitride or the like is formed on the source electrode 61, the drain electrode 62, and the pixel electrode 63.

In the embodiment of the present invention, the protective film 70 covers the entire surface of the substrate, but a portion may be removed depending on other needs, such as securing a sufficient electric field for driving the liquid crystal material in the pixel region.

Now, a method of manufacturing a thin film transistor liquid crystal display substrate according to an embodiment of the present invention will be described in detail.

7 to 10 are cross-sectional views illustrating a process of manufacturing a thin film transistor liquid crystal display substrate according to an exemplary embodiment of the present invention. In order to manufacture such a thin film transistor liquid crystal display substrate, all five masks are required.

First, as shown in FIG. 7, a metal such as aluminum is deposited and patterned on the substrate to form the gate line 20, the common electrode line 90, the common electrode 91, and the storage capacitor electrodes 11 and 12.

Next, as shown in FIG. 8, silicon nitride or the like is deposited to form a gate insulating layer 30, and amorphous silicon and doped amorphous silicon are sequentially deposited and patterned together to form a channel layer 40 of the thin film transistor.

As shown in FIG. 9, the gate insulating film 30 is patterned to form contact holes 31 and 32 exposing a part of the storage capacitor electrodes 11 and 12.

As shown in FIG. 10, a metal such as chromium is deposited and patterned to form the data line 60, the source electrode 61, the drain electrode 62, and the pixel electrode 63, and the source electrode 61 and the drain. The amorphous silicon layer 50 doped with the electrode 62 as a mask is etched to complete the ohmic contacts 51 and 52.

Finally, silicon nitride or the like is deposited on the entire surface of the substrate to form the protective film 70 as shown in FIGS. 5 and 6.

In the second embodiment of the present invention, in order to secure a sufficient holding capacity, a connecting portion for connecting the pixel electrodes is formed, and the connecting portion overlaps with the common electrode line.

11 is a plan view of a thin film transistor liquid crystal display according to a second exemplary embodiment of the present invention.

As shown in FIG. 11, a pixel electrode line 64 connecting the pixel electrodes 63 formed in the vertical direction to each other in the pixel region is formed to overlap the common electrode line 90 with the gate insulating layer 30 interposed therebetween. have. In this case, since the storage capacitor is formed between the pixel electrode line 64 and the common electrode line 90, a larger storage capacitor can be obtained than in the first embodiment of the present invention. The rest of the structure is similar to that of the first embodiment shown in Figs.

On the other hand, the same storage capacitor as the embodiment of the present invention can be formed in a plane to line switching (PLS) type liquid crystal display device. This will be described in detail below.

In the PLS type liquid crystal display, a linear first electrode and a planar second electrode are formed on one substrate. First, a driving principle of the PLS type liquid crystal display will be described.

12 is a schematic diagram illustrating a principle of a PLS type liquid crystal display device according to an exemplary embodiment of the present invention.

As shown in FIG. 12, a pair of transparent substrates 10 and 11 on which alignment layers 30 and 31 are formed, respectively, face each other, and indium tin oxide (ITO) is formed on the inner surface of the lower substrate 10. It is made of a transparent conductive material of the planar electrode 2 having a predetermined width is formed long in the horizontal direction. The insulating film 3 covers the planar electrode 2, and many linear electrodes 1 which are narrow in width are formed in parallel with each other in the vertical direction. The linear electrode 1 can be used as a transparent or opaque material, the width of which is smaller than the distance between the linear electrodes 1, that is, the distance between adjacent border lines of two adjacent linear electrodes 1. Polarizers 20 and 21 are attached to the outer surfaces of the two substrates 10 and 11, and a liquid crystal material layer having optical anisotropy is inserted between the alignment layers 30 and 31 of the two substrates 10 and 11. The liquid crystal material inserted between the two substrates 10, 11 may have positive or negative dielectric anisotropy and is oriented vertically or horizontally with respect to the two substrates 10, 11.

When a voltage is applied to the two electrodes 1 and 2 to give a potential difference between the two electrodes 1 and 2, the longitudinal center line C of the region between the linear electrode 1 and the region between the linear electrodes 1 and the linear electrode 1 ( An electric field is formed which is symmetrical with respect to B) and has a parabolic or semi-elliptic electric field line centered on the boundary lines A and D between the two electrodes 1 and 2. These electric field lines have vertical and horizontal components on the two electrodes 1 and 2 and on the boundary line between the two electrodes 1 and 2, and the liquid crystal molecules are rearranged by a twist angle and an inclination angle by the electric field. Due to the rearrangement of the liquid crystal molecules, the polarization of the incident light changes, thereby enabling the display operation.

13 is a plan view of a PLS type liquid crystal display according to a third exemplary embodiment of the present invention.

A common electrode line 90 for transmitting a common signal is formed in the horizontal direction, and a transparent planar common electrode 92 connected to the common electrode line 90 is formed between the linear pixel electrodes 63. The transparent planar common electrode 92 may be formed so as to overlap the linear pixel electrode 63, but in such a case, the transparent planar common electrode 92 and the linear pixel electrode 63 are further maintained with an insulating layer therebetween. Since a capacitor is formed, this embodiment shows a case where the common electrode 92 of the portion overlapping with the pixel electrode 63 is removed. The other structure is similar to that of the embodiment of the present invention shown in FIG.

In the PLS type liquid crystal display, as in the fourth exemplary embodiment of the present invention shown in FIG. 14, the common electrode 93 of the lower portion of the pixel is not removed without removing all of the common electrode 93 overlapping the pixel electrode 63. ) May be formed in a connected form. In this case, even when the connection from the common electrode line 90 is disconnected to a part of the common electrode 93, a redundancy structure in which the lower common electrode 93 is electrically connected by the connected portion can be made. have.

As in the embodiment of the present invention, one electrode of the storage capacitor of one pixel is connected to the switching element of the pixel and the other electrode is connected to the switching element of the adjacent pixel to form the storage capacitor, thereby reducing the parasitic capacitance. When a device is defective, the defect can be easily repaired.

1 is an equivalent circuit diagram of a unit pixel of a conventional thin film transistor liquid crystal display device of an independent wiring method.

FIG. 2 is an equivalent circuit diagram of a unit pixel of a conventional thin film transistor liquid crystal display of a shear gate type.

3 is an equivalent circuit diagram of a thin film transistor liquid crystal display according to an exemplary embodiment of the present invention;

FIG. 4 is a circuit diagram illustrating a repair method of a bad pixel in the liquid crystal display shown in FIG. 3.

5 is a plan view of a thin film transistor liquid crystal display according to a first embodiment of the present invention;

6 is a cross-sectional view taken along the line VI-VI 'of FIG. 5,

7 to 10 are cross-sectional views illustrating a manufacturing process of a thin film transistor liquid crystal display device according to a first embodiment of the present invention;

11 is a plan view of a thin film transistor liquid crystal display according to a second exemplary embodiment of the present invention;

12 is a cross-sectional view for describing a driving principle of the liquid crystal display according to the third and fourth embodiments of the present invention.

13 and 14 are plan views of a thin film transistor liquid crystal display device according to third and fourth embodiments of the present invention, respectively.

Claims (12)

Board, A gate line formed on the substrate and connected to the gate line to transmit a scan signal; A plurality of linear common electrodes formed on the substrate and separated from the gate lines; A storage capacitor electrode formed separately from the gate line and the common electrode on the substrate; A gate insulating film covering the gate line, the gate electrode, the common electrode, and the storage capacitor electrode and having a first contact hole exposing a portion of the storage capacitor electrode; An amorphous silicon layer formed on the gate insulating film on the gate electrode, A doped amorphous silicon layer formed on the amorphous silicon layer and divided into both sides with respect to the gate electrode; A source electrode formed on one of the doped amorphous silicon layers, The storage capacitor of the pixel which is formed on the other side of the doped amorphous silicon layer, overlaps the storage capacitor electrode with the gate insulating film interposed therebetween, and is adjacent to the pixel through the first contact hole formed in the gate insulating film. A drain electrode connected to the electrode, A plurality of linear pixel electrodes formed on the gate insulating layer in parallel with the common electrode and connected to the drain electrode; And a data line connected to the source electrode and transmitting an image signal from the outside. In claim 1, And a common electrode line formed on the substrate and connected to the common electrode and transmitting a common signal. In claim 2, And a pixel electrode line formed on the gate insulating layer so as to be connected to the pixel electrode, and overlapping the common electrode line with the gate insulating layer interposed therebetween. Forming a gate line, a gate electrode, a common electrode, and a storage capacitor electrode on the substrate; Forming a gate insulating film on the gate line, gate electrode, common electrode, and storage capacitor electrode; Forming an amorphous silicon layer on the gate insulating film over the gate electrode, Forming a doped amorphous silicon layer on the amorphous silicon layer, Forming a first contact hole in the gate insulating layer to expose a portion of the storage capacitor electrode; Forming a drain electrode on the doped amorphous silicon layer to contact the storage capacitor electrode of an adjacent pixel through a source electrode, a pixel electrode, a data line, and the first contact hole; Method of manufacturing a thin film transistor liquid crystal display device comprising a. In claim 4, And forming a common electrode line in the forming of the gate line, the gate electrode, the common electrode, and the storage capacitor electrode. In claim 5, And forming a pixel electrode line in the forming of the source electrode, the drain electrode, the pixel electrode, and the data line. Board, A gate line formed on the substrate and connected to the gate line to transmit a scan signal; A common electrode formed on the substrate and separated from the gate line and made of a transparent conductive material, A storage capacitor electrode formed separately from the gate line and the common electrode on the substrate; A gate insulating film covering the gate line, the gate electrode, the common electrode, and the storage capacitor electrode and having a first contact hole exposing a portion of the storage capacitor electrode; An amorphous silicon layer formed on the gate insulating film on the gate electrode, A doped amorphous silicon layer formed on the amorphous silicon layer and divided into both sides with respect to the gate electrode; A source electrode formed on one of the doped amorphous silicon layers, The storage capacitor of the pixel which is formed on the other side of the doped amorphous silicon layer, overlaps the storage capacitor electrode with the gate insulating film interposed therebetween, and is adjacent to the first contact hole formed in the gate insulating film. A drain electrode connected to the electrode, A plurality of linear pixel electrodes formed on the gate insulating film inside the pixel region defined by the intersection of the gate lines and the data lines, and connected to the drain electrodes; A data line connected to the source electrode and transmitting an image signal; The common electrode has a surface continuous between the pixel electrodes, and the area on the common electrode is part of an image display area. Thin film transistor liquid crystal display. In claim 7, And a common electrode line formed on the substrate and connected to the common electrode and transmitting a common signal. In claim 8, And a passivation layer covering the source electrode, the drain electrode, the pixel electrode, and the data line. Forming a gate line, a gate electrode, and a storage capacitor electrode on the substrate; Forming a planar common electrode on the substrate using a transparent conductive material; Forming a gate insulating film on the gate line, the gate electrode, the storage capacitor electrode, and the planar common electrode; Forming an amorphous silicon layer on the gate insulating film over the gate electrode, Forming a doped amorphous silicon layer on the amorphous silicon layer, Forming a first contact hole in the gate insulating layer to expose a portion of the storage capacitor electrode; Forming a source electrode, a data line connected to the source electrode, a drain electrode, and a pixel electrode on the doped amorphous silicon layer; Method of manufacturing a thin film transistor liquid crystal display device comprising a. In claim 10, And forming a common electrode line in the forming of the common electrode. In claim 11, And forming a passivation layer on the data line after the forming of the data line.