JP2000284320A - Liquid crystal display device and method for correcting its defect - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for correcting the defective pixels of a liquid crystal display device with which the corrected pixels are more inconspicuous and a method for correcting the defective pixels of a perpendicular alignment type LCD having alignment control windows. SOLUTION: Branch lines 2 of data lines are previously formed in superposition on pixel electrodes 57. A TFT 53a having the defect is first irradiated with a laser and is cut. Next, the branch line 2 is irradiated with the laser so as to be shorted. At this time, a common electrode 61 is provided with apertures 3 and 6 in order to avoid the shorting of the common electrode and the pixel electrode 57. Further, the apertures 3 and 6 are used as the alignment control windows for controlling the alignment direction of liquid crystal molecules.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal display (Li)
More particularly, the present invention relates to a liquid crystal display (LCD) and a method of repairing the defect, and more particularly, to a method of repairing a point defect caused by an operation failure of a thin film transistor (TFT) as a switching element and an LC that facilitates the repair method.
D.

[0002]

2. Description of the Related Art In recent years, an active matrix type LCD in which individual pixel electrodes for driving a liquid crystal and a data line for applying a voltage thereto are connected via a TFT which is a switching element has become mainstream. . FIG. 3A is a plan view showing an example of a conventional active matrix type LCD, and FIG. 3B is a sectional view taken along the line AA ′. A plurality of gate lines 51 extending in the row direction are formed on the first substrate 50. A TFT 53 made of a polysilicon film is formed thereon via an insulating film 52. Gate line 5
Part of 1 is a gate electrode 51a of the TFT 53. The gate line 5 is formed on the TFT 53 via an insulating film 54.
A plurality of data lines 55 orthogonal to 1 are formed and connected to the drain region of the TFT 53 via contacts. ITO (in) is formed on the data line 55 via an insulating film 56.
A pixel electrode 57 made of dium tin oxide) is formed, and is connected to the source region of the TFT 53 via a contact. On the pixel electrode 57, an alignment film 58 for controlling the alignment direction of the liquid crystal is formed. A common electrode 61 covering each pixel electrode 57 is formed on a second substrate 60 provided to face the first substrate 50, and an alignment film 62 is formed on the common electrode 61. A liquid crystal 70 is sealed between the first and second substrates. The liquid crystal is a pixel electrode 5
Driven by the voltage applied to 7, the light transmittance changes. The LCD performs display using this.

[0006] A constant voltage is always applied to the common electrode 61. On the other hand, the pixel electrode 57 is connected to the gate line 51.
While the gate voltage is applied to the gate line 51, the gate of the TFT 53 of the gate electrode connected to the gate line 51 is opened, and the signal voltage of the data line 55 connected to the pixel electrode is applied. One gate line 51 has one horizontal synchronization time (1H)
During this period, a gate voltage is applied, and a voltage is sequentially applied one by one. The gate of the TFT 53 in the row where the gate voltage is applied to the gate line 51 is opened, and during that time, the signal voltage to be applied to the pixel electrode in that row is applied by the data line 55. In the next 1H, a gate voltage is applied to the adjacent gate line 51, and a signal voltage applied to the pixel electrodes in the row is applied to the data line 55. Then, a voltage is sequentially applied to all the gate lines 51 during one vertical synchronization time (1 V),
Return to the first gate line again. While no gate voltage is applied to the gate line 51, that is, while the gate of the TFT 53 is closed, the pixel electrode 57 holds the signal voltage applied immediately before. In other words, the gate line 51 is at a constant potential (ground) for most of the period other than the period during which the gate voltage for opening the gate of the TFT 53 formed in each pixel is applied. Is applied with a voltage corresponding to display contents to be applied to the pixel electrodes in any row.

[0004] LCDs are classified into a normally white type and a normally black type according to the relationship between the voltage applied to the pixel electrode 57 and the transmittance of the liquid crystal 70.

In the normally white mode, when the voltage applied to the pixel electrode is minimum, the transmittance of the liquid crystal is maximized, ie, white is displayed. By increasing the applied voltage, the transmittance of the liquid crystal is reduced and black is displayed. Become like For example, TN (twist
nematic) and STN (supertwist nematic) types. The TN type uses a liquid crystal having a positive dielectric anisotropy.
Liquid crystals having a positive dielectric anisotropy have a property of being parallel to an electric field.

On the other hand, in the normally black mode, when the voltage applied to the pixel electrode is the minimum, the transmittance of the liquid crystal is the lowest, ie, black is displayed. By increasing the applied voltage, the transmittance of the liquid crystal is increased, and the white is displayed. Will be displayed. For example, there is a vertical alignment type using liquid crystal having negative dielectric anisotropy.

[0007] The manufacture of LCDs requires fine processing such as the TFT 53, but the TFT does not operate due to an increase in the number of pixels, a large screen, and high definition, due to a mask shift in the manufacturing process. Or a short circuit between the peripheral wiring and the pixel electrode 54 occurs.

[0008] A conventional normally white defective pixel correcting method will be described below. For example, TFT 53a
Is defective, first, the yttrium aluminum garnet (YAG) laser is irradiated with high energy to the connection region 81 of the TFT 53a with the pixel electrode 57a, and cut. Next, a region 82 where the YAG laser is overlapped with the gate electrode of the TFT 53a with low energy is used.
And short-circuit it. As a result, the voltage of the gate line 51 is always applied to the defective pixel electrode. Horizontal synchronization time (1H) is applied to the gate line 51.
Each time, a predetermined voltage is applied, and during most of the other periods, the potential is the ground potential, which is different from the potential of the common electrode 61 to which the constant voltage is continuously applied.
The liquid crystal of the defective pixel is constantly driven to continuously display black.

[0009] Pixels that continue to display black are called black spot defects and are almost inconspicuous. Therefore, an LCD having several such black spot defects can be regarded as a good product.

[0010]

However, in the conventional defective pixel repairing method, the repaired pixel becomes a black point defect, so that the black pixel is always displayed. For example, when the front surface is displayed in white, it becomes conspicuous.

In the normally black system,
When the pixel electrode and the gate line are short-circuited by applying the same correction method as in the past, the potential (ground) of the gate line during most of the period is different from the constant voltage applied to the common electrode. A potential difference always occurs between the pixel electrode and the common electrode, and the corrected pixel always becomes a white point defect that displays white. The white spot defect is very conspicuous as compared with the black spot defect, so that the LCD with this correction cannot be regarded as a non-defective product. Therefore, the conventional defective pixel correction method cannot be applied to the normally black method. In the normally black method, there is no effective defective pixel repair method.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a defective pixel correcting method in which corrected pixels are less noticeable. Another object of the present invention is to provide a method for correcting a defective pixel in a normally black liquid crystal display device.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a structure in which a liquid crystal is sealed between first and second substrates disposed opposite to each other. A plurality of pixel electrodes connected to the gate line and the data line, the data line, and the data line via switching elements are formed on the substrate, and a counter electrode facing the plurality of pixel electrodes is formed on the second substrate. A method for repairing a defective pixel in a liquid crystal display device in which a data line and a pixel electrode are formed in an overlapping manner, wherein a switching element connected to the defective pixel is cut off, and a data line connected to the defective pixel is removed. This is a defect correction method for short-circuiting a defective pixel with a pixel electrode.

In the method of short-circuiting the data line and the pixel electrode, a laser is applied to a region where the data line and the pixel electrode overlap.

An opening is formed in the common electrode at a position where the data line and the pixel electrode overlap, and the laser is irradiated to the opening.

The data line is branched at a position where the data line overlaps the pixel electrode, and a laser beam is applied to the branched portion.

The liquid crystal has a negative dielectric anisotropy, and the opening of the common electrode controls the alignment direction of the liquid crystal.

[0018]

FIG. 1A is a plan view of an LCD having an alignment control window, and FIG. 1B is a sectional view taken along the line AA 'of FIG. A gate line 51 is formed on a first substrate 50, and a gate insulating film 52 is formed to cover the gate line 51. On this, a TFT 53 made of a polysilicon film is formed. The gate electrode 51 a of the TFT 53 is connected to the gate line 51. An interlayer insulating film 54 is formed so as to cover them, and the data line 1 is formed on the interlayer insulating film 54 and is covered with the interlayer insulating film 55. Data line 1 is T
A signal voltage is applied to the pixel electrode 57 connected to the source region of the FT 53 and the gate line 51 is turned on. In order to prevent the liquid crystal from being directly tilted by the signal voltage applied to the data line 57, the data line 57 is connected to the pixel electrode 57.
Are formed so as to overlap with each other. A pixel electrode 57 made of ITO is formed on the interlayer insulating film 55, and the interlayer insulating film 5
TFTs via contact holes opened in 4, 55
53. The vertical alignment film 11 made of an organic material such as polyimide or an inorganic material such as a silane material is formed on the pixel electrode 57.

The second substrate disposed opposite to the first substrate 50
A common electrode 61 made of ITO or the like is formed on the substrate 60 so as to cover the plurality of pixel electrodes 57. Common electrode 61
On the upper side, the same vertical alignment film 12 as that on the first substrate 50 side is provided. The common electrode 61 is provided with an alignment control window 6 which is an opening without an electrode at a position corresponding to the pixel electrode 57. The alignment control window 6 is an electrode-free area where the common electrode is opened, and has a shape in which the letter “Y” is connected upside down, for example, as illustrated.

The first substrate 50 and the second substrate 6
Between 0, the liquid crystal 71 is sealed, and the orientation of the liquid crystal molecules, that is, the orientation, is controlled in accordance with the electric field intensity formed by the voltage applied between the pixel electrode 57 and the common electrode 61.
Outside the first substrate 50 and the second substrate 60, a polarizing plate (not shown) is arranged with the polarization axes orthogonal to each other.
The linearly polarized light passing between the polarizing plates is modulated when passing through the liquid crystal 71 controlled to have a different orientation for each display pixel, and is controlled to have a desired transmittance.

The liquid crystal 71 has a negative dielectric anisotropy, that is, has a property of being oriented so as to be inclined with respect to the direction of the electric field. The vertical alignment films 11 and 12 control the initial alignment of the liquid crystal 71 in the vertical direction. In this case, when no voltage is applied, the liquid crystal molecules are perpendicular to the vertical alignment films 11 and 12, and the linearly polarized light that has passed through one polarizing plate passes through the liquid crystal 71 and is blocked by the other polarizing plate for display. Is recognized as black. In this configuration, when a voltage is applied between the pixel electrode 57 and the common electrode 61, electric fields 64 and 65 are formed, and the liquid crystal molecules are inclined. At the end of the pixel electrode 57, the electric field 64
Has a shape obliquely inclined from the pixel electrode 57 toward the common electrode 61. Similarly, since no electrode is present at the end of the alignment control window 6, the electric field 67 has a shape inclined toward the pixel electrode 57. Since the orientation direction of the liquid crystal is controlled so as to be perpendicular to the inclined electric field, the liquid crystal molecules are inclined toward the inside of the pixel electrode 57 and toward the orientation control window 6. As a result, the linearly polarized light that has passed through one polarizing plate undergoes birefringence in the liquid crystal 71, changes to elliptically polarized light, passes through the other polarizing plate, and the display approaches white. That is, the LC of the present embodiment
D is normally black.

Directly below the alignment control window 6 is a so-called disclination line in which the alignment direction of the liquid crystal 71 is discontinuous, so that light is not transmitted even when a voltage is applied. Therefore, the data line 1 is formed so that the orientation control window 6 is superimposed on the data line 1 to prevent a decrease in transmittance.

When both the gate line 51 and the data line 57 are turned on, a voltage is applied to the pixel electrode 57 via the TFT.
The liquid crystal just above is driven. Each pixel electrode 57
Then, the display on the LCD is performed by applying the respective voltages. That is, a region where the pixel electrode 57 is formed becomes a pixel.

The data line 1 has a branch line 2 in a region where the pixel electrode 57 is formed. The branch line 2 terminates at about the length of the alignment control window 6, and does not extend to the adjacent pixel electrode 57.

Next, for example, TFT
A correction method in the case where there is a defective pixel that does not completely function will be described. It is assumed that a defect has occurred in the TFT 53a. First, the YAG laser is irradiated with high energy to the region 4 on the contact where the TFT 53a and the pixel electrode 57a are connected, and the YAG laser is cut. Next, as shown in FIG. 2, the region 5 on the branch line 2 is irradiated with a YAG laser at low energy, and the data line 1 and the pixel electrode 57a are irradiated.
And are connected by welding. FIG. 2 shows B in FIG.
FIG. 14 is a sectional view taken along the line B-B '. This completes the correction.

With such correction, the pixel electrode 57 of the defective pixel is connected to the data line 1. As mentioned above,
To the data line 1, a voltage according to the display content for applying a voltage to the pixel electrode 57 in any row is always applied. That is, the voltages to be applied to the pixels in the column are sequentially applied to the data line 1 during one vertical synchronization period. The voltage applied to the pixels in the column is sequentially applied to the pixel electrode 57 directly connected to the data line 1. Therefore, for example, when the screen is displayed in full white, the corrected pixels also display white, and when displayed in full black, the corrected pixels also display black. The same applies to halftones. Therefore, the corrected pixel is not always white or black, and is less noticeable than a conventional corrected pixel.

In this embodiment, the data line 1 is connected to the pixel electrode 57.
, The connection between the data line 1 and the pixel electrode 57 can be easily performed.

The irradiation position of the laser is not the branch line 2 but
Defective pixels can be corrected no matter where the data line 1 and the pixel electrode 57 are superimposed.
However, the laser irradiation time and energy for welding are
If accurate control is required and the irradiation time is too long or the energy is too high, the data line 1 may be cut off. When the data line 1 is disconnected, no voltage is applied to all the pixel electrodes 57 connected to the data line 1, and all the pixels in one column become defective, that is, a so-called line defect occurs. On the other hand, if the light is irradiated to the branch line 2, even if it is cut, the other pixels are not affected at all. Further, if the length of the branch line 2 is set to be at least twice the diameter of the laser, it can be corrected once even if it is cut once. Further, since two branch lines 2 are formed for one pixel electrode 57, even if the first branch line 2 fails, it can be corrected again.

Further, the laser irradiation may cause a short circuit with the common electrode 61, for example, by turning up a part of the pixel electrode. Pixel electrode 57 and common electrode 6
When 1 is short-circuited, the liquid crystal 70 during that time cannot be driven. Further, the data line 1 and the common electrode 61
Is short-circuited, a constant voltage applied to the common electrode is applied to the data line 1, which again causes a line defect.
On the other hand, in the present embodiment, the data line 1 is connected to the orientation control window 6.
Therefore, even if a part of the pixel electrode 57 is turned up, there is no possibility that the pixel electrode 57 is short-circuited with the common electrode 61.

In this embodiment, the vertical alignment type liquid crystal display device having the alignment control window 6 has been described by way of example. However, the defective pixel repairing method of the present invention is applied to a normally white, normally black, TN type, It can be applied to any type of LCD such as a vertical alignment type. The point is that the operation can be performed in exactly the same manner as long as the data line is superimposed on the pixel electrode and an opening is formed in the region where the data line is superimposed. In particular, normally black LCDs can be said to be more effective since there has been no effective defective pixel repair method conventionally.

[0031]

As described above, according to the present invention, since the defect correction method for short-circuiting the data line connected to the defective pixel and the pixel electrode of the defective pixel, the corrected pixel is displayed in white or black. And the corrected pixel is inconspicuous.

According to the third aspect of the present invention, an opening is formed in the common electrode at a position where the data line and the pixel electrode overlap, and the laser is irradiated to the opening. Correction can be reliably performed without short-circuiting between the pixel electrode and the common electrode.

According to the fourth aspect of the present invention, the data line is branched at a position corresponding to the pixel electrode, the branched portion is superimposed on the pixel electrode, and the laser is applied to the branched portion. Since the irradiation is performed, the data line is not cut by the irradiation of the laser, and the correction can be reliably performed.

The inventions described in claims 5 to 7 are easy to perform the above-described correction.

[Brief description of the drawings]

FIG. 1 is a plan view and a cross-sectional view showing a first embodiment of the present invention.

FIG. 2 is a plan view and a sectional view showing a second embodiment of the present invention.

FIG. 3 is a plan view and a cross-sectional view of a conventional liquid crystal display device.

[Explanation of symbols]

1 data line, 2 branches, 3, 6 opening, 4, 5,
7, 8, 81, 82 Laser irradiation area

Claims (5)

[Claims] 1. A first and a second arrangement arranged opposite to each other.
Liquid crystal is sealed between the substrates, and the first substrate is formed with a gate line and a data line, which are insulated from each other, and a plurality of pixel electrodes connected to the data line via a switching element. A method of correcting a defective pixel in a liquid crystal display device in which a counter electrode facing the plurality of pixel electrodes is formed on the second substrate, and the data line and the pixel electrode are formed to overlap with each other. Disconnecting the switching element connected to the defective pixel from the data line, and short-circuiting the data line connected to the defective pixel and the pixel electrode of the defective pixel. Defect correction method. 2. The defect of the liquid crystal display device according to claim 1, wherein the method of short-circuiting the data line and the pixel electrode includes irradiating a laser to a region where the data line and the pixel electrode overlap. How to fix. 3. The liquid crystal according to claim 2, wherein an opening is formed in the common electrode at a position where the data line and the pixel electrode overlap each other, and the laser is irradiated to the opening. A method for correcting a defect of a display device. 4. The defect of the liquid crystal display device according to claim 2, wherein the data line is branched at a position overlapping with the pixel electrode, and the laser is irradiated on the branched line. How to fix. 5. The liquid crystal has a negative dielectric anisotropy,
5. The method according to claim 1, wherein the opening is an alignment control window for controlling an alignment direction of the liquid crystal.