KR20040046330A - Storage capacitor of liquid crystal display - Google Patents

Abstract

PURPOSE: A storage capacitor of an LCD(Liquid Crystal Display) is provided to prevent a short of an electrode relating to a pixel electrode and a source/drain electrode within an adjacent pixel region by constructing an electrode shape forming the storage capacitor as a step shape. CONSTITUTION: A subsidiary electrode is formed as a step shape, that is, a curve. Accordingly, distances among the subsidiary electrode, source/drain electrodes(19,20), a pixel electrode(17), and a data line(15) are maintained constantly to some extent. The distance is larger than the size of a foreign substance as about 10um, so that short due to the foreign substance can be overcome. To reduce the distance between the subsidiary electrode and the data line and to increase the distance between the source/drain electrodes and the pixel electrode, the curve of step shape is formed.

Description

Storage capacitor of liquid crystal display

The present invention relates to a liquid crystal display device, and more particularly, to a structure of a storage capacitor of a liquid crystal display device having an on-gate storage capacitor.

In general, CRT (Cathode Ray Tube) has been the most used among the screen display devices that display image information on the screen, which is inconvenient to use because it is bulky and heavy compared to the display area. .

Accordingly, a thin film type flat panel display device having a small display area that can be easily used in any place even though the display area is large has been developed, and is gradually replacing the CRT display device. In particular, liquid crystal displays (LCDs) exhibit superior display resolution than other flat panel displays, and exhibit fast response speeds as compared to CRTs when a moving image is realized.

Such a liquid crystal display device basically constitutes a so-called liquid crystal panel in which a liquid crystal layer is sandwiched between two (pair) substrates, at least one of which is made of transparent glass or the like, which is largely passive matrix depending on its structure and driving method. It is divided into a passive matrix type and an active matrix type liquid crystal display device.

Passive matrix type liquid crystal display device has advantages of being easy to manufacture and simple driving method compared to active matrix type, but the disadvantage is that driving becomes more difficult as power consumption is larger and the number of scan lines is increased. Unlike the passive matrix structure, the matrix type liquid crystal display device includes a thin film transistor (TFT) in each pixel area so that each pixel part in the plurality of pixel areas can be driven independently. The advantage of making devices is that they are efficient. Such an active matrix liquid crystal display uses a thin film transistor as a switching element to express a natural moving image. 1 is a plan view schematically showing a conventional active matrix liquid crystal display device.

Referring to FIG. 1, a conventional active matrix liquid crystal display 11 includes an upper substrate on which a transparent common electrode 18 is formed on a color filter 7 including a black matrix 6 and a sub color filter 8. (5), the pixel region P and the pixel electrode 17 formed on the pixel region, the thin film transistor as the switching element T and the lower substrate on which the data line 15 and the gate line 13 are formed. The liquid crystal 14 is filled between the upper substrate 5 and the lower substrate 22.

The lower substrate 22 is also referred to as an array substrate, and the thin film transistor T, which is the switching element, is positioned in a matrix form, and a gate line 13 and a data line 15 passing through the plurality of thin film transistors are formed. In addition, an area defined by the intersection of the gate line 13 and the data line 15 becomes the pixel area P. FIG.

The gate line 13 transfers a pulse voltage driving the gate electrode 16 of the thin film transistor T, and the data line 15 drives the source electrode 19 of the thin film transistor T. Means for transmitting a signal voltage. At this time, if a voltage capable of driving the liquid crystal is applied to an arbitrary source electrode 19 by the signal of the gate electrode 16, and a voltage smaller than the liquid crystal driving voltage is applied to the rest, the liquid crystal driving voltage is applied. Only the pixel will work.

That is, the active matrix liquid crystal display device is a capacitor formed by the presence of the liquid crystal 14 between the thin film transistor T as the switching element and the upper and lower electrodes, that is, the common electrode 18 and the pixel electrode 17, Auxiliary capacitor, gate line 13 and data line 15 are provided.

In addition, in driving the liquid crystal display, first, when a constant voltage is applied to the gate electrode 16, the thin film transistor T is turned on, and during this time, a data signal having information about an image is displayed. It is applied to the liquid crystal 14 through the thin film transistor T. At this time, the liquid crystal portion, which is a capacitor, is charged. In the ideal case, the total charge charged in the liquid crystal 14 is turned off and the next signal is It stays in until it comes in.

The liquid crystal voltage, that is, the voltage between the common electrode 18 and the pixel electrode 17 is actually due to the presence of a plurality of capacitances generated in the liquid crystal display device. As much as Is approximately expressed by the equation

here, Is the amount of change in the liquid crystal voltage, C _gd is the parasitic storage capacity that exists due to the overlap of the gate electrode 16 and the drain electrode 20, C _LC is the pixel capacity, and C _st is the storage capacity of the storage capacitor and V _g represents the difference in gate voltage. In other words, the amount of variation in the liquid crystal voltage causes distortion of the liquid crystal voltage, which is a major cause of flicker.

Accordingly, the It is advantageous to increase the storage capacitor C _st of the storage capacitor to make it small, so that the storage capacitor is necessary for the liquid crystal to keep the data signal stable.

In addition, the storage capacity of the storage capacitor is The size of the storage capacity is determined by, and C is the storage capacity, Denotes the dielectric constant, A denotes the area of the electrode, and d denotes the distance between the electrodes.

The storage capacitor formed in the liquid crystal display may be divided into an on common method and an on gate method according to a method of using an electrode for charging.

Comparing these methods, the on-gate method uses a part of the n-1th gate line as the charging electrode of the (n) pixel, so that the reduction of the aperture ratio is small, and when the defect occurs in the NW method (Normally White Mode) Although the yield is good, the scan signal time is long, and there is a disadvantage in that the on-communication method uses a charging electrode separately wired, and the scan signal time is short while the decrease of the aperture ratio is large. In the NW method, when a defect occurs, it is easy to see and has a disadvantage of low yield.

At present, in order to increase the storage capacitance of the storage capacitor in an on-common method and an on-gate method, an attempt has been made to narrow the electrode spacing d or enlarge the area A of the electrode.

According to the present invention, a pixel electrode and a source / drain electrode in neighboring pixel regions are formed by forming a stepped shape of an electrode forming the storage capacitor in a liquid crystal display having an on gate type storage capacitor. It is an object of the present invention to provide a storage capacitor of the liquid crystal display device to prevent the short circuit.

1 is a plan view schematically showing a conventional active matrix liquid crystal display device.

2 is a plan view of a liquid crystal display device including a conventional on-gate storage capacitor.

3 is a sectional view of a specific portion A-A 'of FIG.

4 is a view showing that a short circuit occurs due to a narrow gap between the auxiliary electrode and the source / drain electrode as described above.

5 is a plan view of a liquid crystal display device having an on-gate storage capacitor according to the present invention.

<Explanation of symbols for the main parts of the drawings>

13: gate line 15: data line

17, 17 ': pixel electrode 19: source electrode

20: drain electrode 24, 34: auxiliary electrode

①, ① ': Spacing between auxiliary electrode and data line

②, ② ': spacing between auxiliary electrode and source electrode

③, ③ ': distance between the auxiliary electrode and the drain electrode

④, ④ ': distance between auxiliary electrode and pixel electrode

⑤, ⑤: spacing between auxiliary electrode and pixel electrode

In order to achieve the above object, a storage capacitor of a liquid crystal display according to the present invention includes a substrate, a gate line formed on the substrate, a gate insulating film covering the gate line, and a gate capacitor formed on the gate insulating film so as to overlap the gate line. It characterized in that the auxiliary electrode for the storage capacitor of the stepped form is included.

In addition, the staircase auxiliary electrode is an auxiliary electrode having a predetermined portion of curvature, and the spacing between the auxiliary electrode, the data line, the source electrode, the drain electrode, and the pixel electrode is constantly maintained by the bending. The auxiliary electrode and the data line and the source electrode, the drain electrode, the pixel electrode is maintained at a constant interval, respectively characterized in that 10um.

More preferably, the spacing between the auxiliary electrode and the data line is 10um, the spacing between the auxiliary electrode and the source electrode is 10um, and the spacing between the auxiliary electrode and the drain electrode is 11um. The distance between the auxiliary electrode and the pixel electrode is 7 ~ 8.9um.

The display device may further include a passivation layer covering an exposed front surface of the substrate including the auxiliary electrode, a contact hole formed to expose the auxiliary electrode on the passivation layer, and a pixel electrode connected to the exposed auxiliary electrode. It is done.

According to the present invention as described above by forming a stepped shape of the electrode forming the storage capacitor while maintaining the storage capacitance of the storage capacitor to prevent the short circuit with the pixel electrode and the source / drain electrode in the adjacent pixel region There is an advantage of improving the yield of the liquid crystal display device.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 illustrates a planar structure of a liquid crystal display device having an on-gate storage capacitor.

2 shows a thin film transistor T, which is a switching element, a gate line 13, a data line 15, and the gate line passing through the thin film transistor. An area defined by the intersection of 13 and the data line 15 is a view of part of the pixel area P. As shown in FIG.

Referring to FIG. 2, in order to increase the storage capacity of an on-gate storage capacitor, a portion of the n−1 th gate line 13 and a portion of the n th pixel electrode 17 ′ overlapped with the n th pixel may be formed. The auxiliary electrode 24 connected to the n th pixel electrode 17 ′ is formed on the gate insulating layer formed on the n−1 th gate line instead of the storage capacitor electrode.

This is because in the conventional storage capacitor, since the n−1 th gate line 13 and the n th pixel electrode 17 ′ are used as electrodes of the storage capacitor, the gate insulating layer and the protective layer become dielectric layers. In the case of forming the auxiliary electrode 24 connected to the n-th pixel electrode 17 ', the auxiliary electrode 24 and the n-th gate line 13 are formed at the portion where the auxiliary electrode 24 is formed. This is because the thickness of the dielectric film is reduced by using only the gate insulating film as the dielectric film because the electrodes are formed in the electrodes, thereby increasing the storage capacitor storage capacity.

3 is a cross-sectional view of a specific portion A-A 'of FIG. 2, that is, a cross-sectional view of the auxiliary electrode and the gate line.

Referring to FIG. 3, a gate line 13 including a gate electrode is formed on a substrate 30, and a gate insulating layer 25 is formed on an exposed surface of the substrate 30 including the gate line 13. It is. An auxiliary electrode 24 formed of a metal layer for source / drain formation is formed on the gate insulating layer 25. In addition, the passivation layer 26 covers the auxiliary electrode 24, and a contact hole (not shown) for exposing a part of the auxiliary electrode is formed in the passivation layer 26, and the pixel electrode 17 is formed through the contact hole. It is formed on the passivation layer 26 while being connected to the auxiliary electrode 24.

In the above structure, the storage electrode accumulates in the auxiliary electrode 24, the gate line 13 overlapping with the auxiliary electrode 24, the pixel electrode 17 ′ not overlapping with the auxiliary electrode 24, and the gate line 13 overlapping with the auxiliary electrode 24. Make capacity.

As described above, at present, a separate auxiliary electrode is formed to reduce the spacing of each electrode, thereby increasing the storage capacity, and also increasing the storage capacity by increasing the area A of the auxiliary electrode as much as possible.

However, in the case of forming a separate auxiliary electrode and increasing the area of the auxiliary electrode as shown in FIG. 2, the source / drain electrodes 19 and 20 and the pixel electrode formed in the auxiliary electrode 24 and the n-th pixel region are shown in FIG. 2. 17) the short distance between the auxiliary electrode 24, the source / drain electrodes 19 and 20, the pixel electrode 17, etc. may occur due to the foreign environment generated during the environment or the process. .

FIG. 4 is a diagram illustrating that a short circuit occurs because the gap between the auxiliary electrode and the source / drain electrode is narrow as described above.

Referring to FIGS. 2 and 4, although the distance ① between the auxiliary electrode 24 and the data line 15 is relatively far, other distances (②) from the source electrode 19 and the drain electrode ( Since the distance ③ to 20 and the distances ④ and ⑤ to the pixel electrodes 17 are close to each other, a short circuit occurs due to a foreign substance as described above. In the area, the image cannot be displayed.

4 shows various states in which the auxiliary electrode, the drain electrode, and / or the pixel electrode are shorted by foreign matter.

5 illustrates a planar structure of a liquid crystal display device having an on-gate storage capacitor according to the present invention.

FIG. 5 is a view of the same region as in FIG. 2, but a thin film transistor T, which is a switching element, is formed on a predetermined portion of the array substrate, a gate line 13 and a data line 15 passing through the thin film transistor, and the A region defined by the intersection of the gate line 13 and the data line 15 is a view of a part of the pixel region P. Therefore, the same reference numerals are used for the same components as in FIG.

Referring to FIG. 5, a liquid crystal display including an on-gate storage capacitor according to the present invention will be described.

In the on-gate storage capacitor according to the present invention, as shown in FIG. 2, a portion of the n−1 th gate line 13 and the n th pixel electrode 17 ′ overlapping the same may be used to increase the storage capacitance. Instead of using a portion of the n-th pixel as a storage capacitor electrode, an auxiliary electrode 34 connected to the n-th pixel electrode 17 'is formed on the gate insulating layer formed on the n-th gate line 13. .

As described above, since the auxiliary electrode 34 and the n−1 th gate line 13 serve as electrodes of the storage capacitor in the portion where the auxiliary electrode 34 is formed, only the gate insulating film is used as the dielectric film, thereby reducing the thickness of the dielectric film. This is because by reducing the spacing of the electrodes can increase the storage capacity of the storage capacitor.

However, according to the present invention, the auxiliary electrode 34 has a stepped shape as shown in FIG. 5, which is distinguished from the shape of the auxiliary electrode 34 of the LCD shown in FIG. 2. will be.

In more detail, the auxiliary electrode 34 according to the present invention is formed in a step shape, that is, in a shape having a predetermined portion, and through this, unlike the auxiliary electrode 24 shown in FIG. The distance between the 34 and the source / drain electrodes 19 and 20 and the pixel electrode 17 can be kept constant.

As a result, when the auxiliary electrode 34 according to the present invention is used, the problem shown in FIG. 4, that is, the distance between the auxiliary electrode and the source electrode, the distance between the drain electrode, and the distance between the pixel electrode are formed to be close to each other. The phenomenon that the short circuit between the electrodes is caused by the foreign matter that can be caused to overcome the phenomenon that the image is not displayed in the pixel region where the short circuit occurs.

The auxiliary electrode 34 according to the present invention is to form a step-shaped bend constantly, the bend is the auxiliary electrode 34 and the source / drain electrodes 19 and 20, the pixel electrode 17 and the data line It is formed to keep the interval between the 15 constant.

Referring to FIG. 2, in the case of the conventional auxiliary electrode 24, the distance ① between the auxiliary electrode 24 and the data line 15 is relatively far, but the distance between the source electrode 19 and ② ), The gap (③) from the drain electrode 20 and the distance (④, ⑤) from the pixel electrode 17 are formed close to each other. In general, the distance (①) from the data line is about 26.6 μm. The distance (②) from the source electrode is about 9.1 um, the distance ③ from the drain electrode is about 7.4 um, and the distance (④, ⑤) from the pixel electrode is about 5.3 um.

Accordingly, since the size of foreign matters generated by the surrounding environment or during the process is usually less than 10 μm, a short circuit occurs easily when foreign matters larger than a distance between the auxiliary electrode, the source / drain electrode, and the pixel electrode are generated.

In order to overcome this problem, the auxiliary electrode according to the present invention is formed in a stepped shape to reduce the distance between the auxiliary electrode and the data line and to increase the distance between the source / drain electrode and the pixel electrode.

That is, the step-shaped bending is to make the distance between the auxiliary electrode 34, the data line 15, the source / drain electrodes 19 and 20, and the pixel electrode 17 to be larger than the size of the foreign material. For sake.

Referring to FIG. 5, in the case of the auxiliary electrode 34 according to the present invention, an interval ① ′ between the auxiliary electrode 34 and the data line 15 and other intervals ② ′ between the source electrode 19 and others. The gap (3 ′ ') with the drain electrode 20 and the distance (4 ′, ⑤ ′) with the pixel electrode 17 are formed to a certain degree, and the gap is formed to be larger than the size of a general foreign material. It is possible to overcome the short-circuit phenomenon caused by the foreign matter by maintaining about 10um.

As an example of the spacing, the spacing (① ') of the auxiliary electrode and the data line is about 10 um, the spacing (②') of the source electrode is about 10 um, and the spacing of the drain electrode ( ③ ') may be formed to about 11um, and the distances ④' and ⑤ 'with the pixel electrode may be about 7 to 8.9um. However, the numerical value is not limited thereto.

As described above, according to the storage capacitor structure of the liquid crystal display according to the present invention, the electrodes in the pixel region adjacent to each other are formed by forming a stepped shape of the electrode forming the storage capacitor while maintaining the storage capacitor. There is an advantage of improving the yield of the liquid crystal display by preventing the short circuit with the electrode and the source / drain electrode.

Claims (8)

In the storage capacitor of the liquid crystal display device, Substrate, A gate line formed on the substrate, A gate insulating film covering the gate line; And a second electrode for a storage capacitor having a step shape formed on the gate insulating layer so as to overlap the gate line. The method of claim 1, The staircase auxiliary electrode is an auxiliary electrode having a predetermined portion of curvature, and the gap between the auxiliary electrode, the data line, the source electrode, the drain electrode, and the pixel electrode is constantly maintained by the bending. Storage capacitors. The method of claim 2, The storage capacitor of the liquid crystal display device, characterized in that the constant interval is maintained between the auxiliary electrode, the data line, the source electrode, the drain electrode, the pixel electrode, respectively 10um. The method of claim 2, The storage capacitor of the liquid crystal display device, characterized in that the distance between the auxiliary electrode and the data line is 10um. The method of claim 2, The storage capacitor of the liquid crystal display device, characterized in that the interval between the auxiliary electrode and the source electrode is 10um. The method of claim 2, The storage capacitor of the liquid crystal display device, characterized in that the interval between the auxiliary electrode and the drain electrode is 11um. The method of claim 2, The storage capacitor of the liquid crystal display device, characterized in that the interval between the auxiliary electrode and the pixel electrode is 7 ~ 8.9um. The method of claim 1, And a protective film covering an exposed entire surface of the substrate including the auxiliary electrode, a contact hole formed to expose the auxiliary electrode in the protective film, and a pixel electrode connected to the exposed auxiliary electrode. Storage capacitors in liquid crystal displays.