JPH07199221A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device capable of detecting a defective TFT, restraining the lowering of numerical aperture and perfectly relieving the defective TFT in redundant structure where the TFTs are connected in parallel. CONSTITUTION:In this liquid crystal display device equipped with a picture element electrode 105 arranged in a matrix state and the TFT connecting the electrode 105 and a signal line 106; two TFTs 101 and 102 are provided in parallel per one picture element; and the picture element electrode side of the TFT 101 has structure 112 where cutoff can be feasible by the irradiation of a laser beam and also has structure 109 where connection can be performed again after the cutoff, then the picture element electrode side of the TFT 102 has structure 113 where the cutoff can be feasible by the irradiation of the laser beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a plurality of thin film transistors for one pixel.

[0002]

2. Description of the Related Art In recent years, new display devices which replace conventional CRTs have been actively developed. Among them, the liquid crystal display device is thin and can operate at low power, and therefore, there are great expectations in the market of home appliances and OA equipment. Conventionally, many liquid crystal display devices are of simple matrix type, but active matrix type display devices having excellent display characteristics are expected. Above all, thin film transistors (T
The use of FT) for switching elements is expanding the market in the field of small TVs, and promising products are being developed with the aim of increasing the size and high definition such as 10-20 inch size and projection TVs. ing.

FIG. 6 is a plan view of a conventional TFT array. The scanning line 103 is also common to the gate electrode, but the gate electrode may be drawn from the scanning line 103. The signal line 106 is connected to the drain electrode 107 of the TFT 101, and the intersection of the scanning line 103 and the signal line 106 is insulated by an insulating film. TFT1
The source electrode 108 of 01 is connected to the pixel electrode 105. The semiconductor film forming the TFT 101 is connected to the drain electrode 107 and the source electrode 108, and is insulated from the gate electrode 103 by an insulating film. Reference numeral 104 denotes an auxiliary capacitance line, which is insulated from the pixel electrode 105 by an insulating film.

When a signal voltage and a scanning voltage are applied to the TFT array configured as described above, the individual TFTs become conductive and a voltage corresponding to the signal voltage is applied to the pixel electrode 105. If no scan voltage is applied, the individual T
The FT becomes non-conductive, and the voltage applied to the pixel electrode 105 is held.

As described above, such a liquid crystal display device has been increased in size and definition, leading to an increase in the number of pixels or a pixel density, resulting in an increase in the occurrence rate of pixel defects. However, it is a big problem that the manufacturing yield is remarkably reduced. As a way to solve this problem,
Methods have been proposed for repairing pixel defects using a high energy beam such as a laser.

[0006] One is a method of cutting and correcting a short-circuit portion which mainly occurs during pattern formation. FIG. 7 shows an example of repair. A short circuit portion 701 between the signal line 106 and the pixel electrode 105, which is caused by a defective pattern formation of the signal line.
Then, the beam 702 that has passed through the aperture is irradiated to cut the short-circuited portion 701. The other is a method of electrically connecting the upper and lower electrodes by irradiating a laser on a portion where the upper and lower electrodes are opposed to each other with an insulating film interposed therebetween.

By the way, as a method for relieving a defect that has occurred in a TFT, it is possible to adopt a redundant structure of the TFT. An example of a TFT array realized by using the redundant structure of TFT is shown in FIG. This is 2 TFs per pixel
It is a redundant structure having T. In the normal state, the TFT10
1 and the TFT 102 are electrically connected in parallel, and both TFTs operate to transmit a signal to the pixel electrode 105. As a result, the capacity of each TFT may be one-half that in the case of operating a pixel with one TFT as shown in FIG.
The size of each TFT is about one half of that shown in FIG. Therefore, there is almost no decrease in the aperture ratio.

If the TFT 101 does not operate normally due to some reason, the TFT may fail to turn on when the TFT fails to turn on.
Although it is effective even if the FT is not cut off, it is not effective for the OFF defect of the TFT. Therefore, for the off defect, the laser irradiation portion 110 is irradiated with a laser to be cut, and
Disconnect T101 from the circuit. As a result, the TFT 102
Although the display state is slightly different from that of the pixel in the normal state due to the insufficient capacity of the TFT, there is almost no problem in display and the defective pixel can be relieved. TFT 102
This is also the case when the pixel is defective, and the TFT 102 may be cut from the pixel by some means.

However, the above redundant structure has a plurality of TFTs.
When a certain pixel is defective, it is practically impossible to distinguish which one of the TFTs 101 and 102 is defective. Defective TFT
The probability of correctly cutting a defective TFT is 2
Since it is only one-half, the effect of the redundant structure is not exhibited.

In addition to the above redundant structure for the TFT, as shown in FIG. 9, a spare TFT which is not used in a normal state is used.
A method of placing the 901 in a standby state in advance may be considered. In this method, when the TFT 101 used in the normal operation is defective, the TFT 101 is electrically separated by irradiation of the laser 112, and the spare TFT 901 is connected to the pixel electrode using an electrical connection method. Unless the spare TFT 901 is defective, the spare TFT 90 that normally operates the defective TFT 101
It can be switched to 1, and the pixel can be saved. However, this method has a big problem that the aperture ratio is lowered because a spare TFT is arranged in each pixel.

[0011]

As described above, the TF is conventionally used.
The redundant structure in which Ts are connected in parallel is excellent in that the reduction in the aperture ratio can be suppressed, but it is extremely difficult to detect a defective TFT among a plurality of TFTs.
It was difficult to surely rescue T defects. The present invention has been made in consideration of the above circumstances, and an object thereof is to detect a defective TFT by detecting a defective TFT while suppressing a decrease in aperture ratio in a redundant structure in which TFTs are connected in parallel. An object of the present invention is to provide a liquid crystal display device that can be reliably relieved.

[0012]

In order to solve the above problems, the present invention employs the following configurations. That is, the present invention provides a liquid crystal display device comprising pixel electrodes arranged in a matrix and TFTs connecting these pixel electrodes and signal lines, and a plurality of TFTs are provided in parallel for one pixel. All of the TFTs have a structure capable of disconnecting the pixel electrode side or the signal line side, and at least one of the plurality of TFTs has a structure capable of being reconnected after disconnecting the pixel electrode side or the signal line side. And

The preferred embodiments of the present invention are as follows. (1) There are two TFTs per pixel, one TFT
Has a structure that can be cut and a structure that can be reconnected after cutting, and the other TFT has only a structure that can be cut. (2) There are n TFTs per pixel, and n-1 T
A structure that can be cut and a structure that can be reconnected after cutting are added to the FT, and only a structure that can be cut is added to one TFT. (3) There are n TFTs per pixel, and one TFT
Has a structure that can be cut and a structure that can be reconnected after cutting, and only n-1 TFTs have a structure that can be cut. (4) The disconnecting and reconnecting parts of the TFT should be on the pixel electrode side. (5) The cuttable structure of the TFT is that the wiring pattern is partly thin and can be cut by laser irradiation. (6) The reconnectable structure of the TFT is such that the upper and lower wirings are arranged so as to overlap each other with the insulating film interposed therebetween, and the upper and lower wirings are connected by laser irradiation. (7) If any of the plurality of TFTs is cut using a structure capable of cutting, and the cut TFT is normal, the TF
Reconnecting T using a reconnectable structure. (8) Detection, disconnection, and reconnection of defects of multiple TFTs should be performed while the liquid crystal display device is on.

[0014]

According to the present invention, when it is considered that the TFT is turned off, the TFT having the reconnectable structure is first cut. Specifically, the wiring on the pixel electrode side or the signal line side of the TFT is cut off. Cut TFT
If the TF is defective, the defect can be remedied by this, but another TF
If T is defective, it cannot be relieved. If another TFT is defective, the disconnected TFT is reconnected and then the other TFT is disconnected. As a result, only the defective TFT can be cut and the defective TFT can be relieved.

That is, by providing a disconnectable structure for all of a plurality of TFTs provided in parallel for one pixel and providing a reconnectable structure for a part thereof, an off-defective T is previously set.
Even if the FT cannot be specified, the defect relief can be surely performed. In this case, unlike the method of placing the spare TFT in a standby state in advance, the aperture ratio is not lowered. Therefore, TFs connected in parallel can identify defective TFTs.
It is possible to realize a liquid crystal display device having a T-redundant structure, capable of suppressing a decrease in aperture ratio, and having excellent display characteristics and high yield.

[0016]

The details of the present invention will be described below with reference to the illustrated embodiments. (Embodiment 1) FIG. 1 is a plan view showing one pixel portion of a liquid crystal display device (particularly a TFT array portion) according to a first embodiment of the present invention.

A Mo-Ta alloy having a thickness of 250 nm was formed on the cleaned glass substrate, and the gate electrode, the gate line 103, the auxiliary capacitance line 104, and the lower electrode of the laser connection portion 109 were patterned. Next, the gate insulating film SiO
nm, SiN of 50 nm, a-Si film of 50 nm, and etching stopper SiN of 200 nm were continuously formed, and then the etching stopper was patterned. Further, an n ⁺ -type a-Si film, which is an ohmic contact layer in the source / drain region, doped with impurities such as phosphorus was formed to a thickness of 50 nm, and then the a-Si layer was patterned into an island shape. Further, a 100 nm thick ITO film was formed to form the pixel electrode 105.

Next, the first electrode on the terminal portion of the gate electrode
The SiO 2 insulating film was removed by etching. afterwards,
Mo film of 100 nm and Al film of 400 nm are formed, and signal line 1
06, drain electrode 107, source electrodes 108, 11
1 was formed. Further, using the metal of the drain electrode 107 and the source electrodes 108 and 111 as a mask, an n ⁺ -type aS
By removing i by etching, the drain electrode 107 and the source electrodes 108 and 111 are electrically separated to form an active matrix substrate. Finally, SiN is deposited to a thickness of 150 nm as a passivation film and patterned.

As shown in FIG. 1, the active matrix substrate thus obtained has two Ts per pixel.
FT is provided. The TFTs 101 and 102 are electrically connected in parallel, and the capacity of each TFT may be half the capacity when one TFT is provided in one pixel. Therefore, the size of the TFTs 101 and 102 is one T per pixel.
It is only half that in the case where the FT is provided, and as a result, there is almost no decrease in the aperture ratio due to the redundancy of the TFT.

If the pixel is found to be defective due to the TFT, it is not clear which of the TFTs 101 and 102 is defective. However, the probability that both TFTs are defective is very low and need not be considered. Therefore, first, the source electrode 111 is cut by irradiating the cut portion 112 with a laser through a diaphragm, and the TFT 101 is connected to the pixel electrode 105.
Electrically disconnect from. Since the electrode film is scattered from the cutting points 112, it is preferable to make the cutting points 112 thin so that the rate of occurrence of wire breakage does not increase so that the cutting can be performed with as few irradiation times as possible. In this example, as a result of setting the width of the cut portion to about 5 μm, good cutting was possible.

If the TFT 101 is defective,
Since the defective TFT is cut off, the repair is completed. TF
Since the ability of T is halved, the brightness of the pixel is up to 2 to 3% lower than that of a normal pixel, but it has been found that the defect is not visible to the human eye in this range. Here, if the brightness difference becomes large, the load of the TFT may be reduced by removing a part of the auxiliary capacitance 104 or the pixel electrode 105 according to the capability of the TFT.

If the TFT 101 is normal, the TFT
If 102 is defective, the wrong TFT has been cut, and it is necessary to reconnect the TFT 101 to the pixel electrode 105. Therefore, first, the source electrode 108 is cut by irradiating the cut portion 113 with a laser beam through a diaphragm to electrically disconnect the defective TFT 102 from the pixel electrode 105. Since the electrode film scatters from the cut portion 113, it is preferable that the cut portion 113 be thin so that the rate of occurrence of wire breakage does not increase so that the cut portion 113 can be cut with as few irradiation times as possible. In this embodiment, the width of the cut portion is 5 μm.
As a result of setting the length to about m, good cutting became possible.

Next, the laser 11 is connected to the laser connecting portion 109.
The TFT 101 is reconnected to the pixel electrode 105 by irradiating 0 and electrically connecting. As a result, the switching operation is performed by the TFT 101. TFT101 and TFT1
Since the probability that both of the two are defective is extremely low, this method can repair almost 100% of defective pixels related to the TFT.

Here, the above-mentioned structure for reconnection is formed as shown in FIG. That is, the lower electrode 202 is formed on a part of the substrate 205, the insulating film 203 is formed so as to cover the lower electrode 202, and the upper electrode 2 is formed on the insulating film 203.
04 are formed. That is, the upper electrode 204 and the lower electrode 202 have a structure in which they overlap with each other with the insulating film 203 interposed therebetween. Then, a passivation film 206 is formed on these.

In the structure as shown in FIG. 2, the substrate 20
When the laser 201 is irradiated from the back surface of 5, the lower electrode 202 first absorbs the energy of the laser and is rapidly heated,
Liquefaction or vaporization causes the volume to expand. As a result, the insulating film 2
03 or the upper electrode 204 is pierced. then,
The liquid phase of the lower electrode 202 adheres to the periphery of the hole generated by laser irradiation and serves to make electrical contact with the upper electrode 204. As a result, the upper electrode 204 and the lower electrode 202 are electrically connected.

The repair described above is performed by irradiating the laser from the back surface of the array substrate, but the repair can also be performed by irradiating the laser from the front surface of the substrate. That is, after detecting the pixel in a state where the liquid crystal is sandwiched between the counter substrate and the lighted state, the repair can be performed by laser irradiation from the surface of the array substrate while confirming the lighting state of the pixel.

The source electrodes 108 and 111 are substantially symmetrical with respect to the two TFTs. Therefore, the TFT 10
Even if either one of 1, 1 is electrically disconnected,
The parasitic capacitance between the gate line 103 and the source electrodes 111 and 108 is almost the same. This parasitic capacitance is an amount that affects the level shift of the pixel potential when the transistor is off, and also affects the display characteristics. By making the source electrodes symmetrical as shown in FIG. 1, there is no change in the parasitic capacitance between the gate and the source electrode regardless of which of the TFTs 101 and 102 is cut off, and it is possible to almost eliminate the difference in display characteristics between the cut TFTs.

(Embodiment 2) FIG. 3 is a plan view showing a one-pixel configuration of a liquid crystal display device according to a second embodiment of the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. Although the basic structure is the same as that of FIG. 1, the positional relationship between the reconnection portion and the disconnection portion is different from that of FIG.

Since the manufacturing process is the same as that of the first embodiment, it is omitted here. The active matrix substrate of this embodiment also has two TFTs per pixel as shown in FIG.
Is provided, and the capacity of each TFT may be half of the capacity when one TFT is provided in one pixel, and there is almost no decrease in the aperture ratio due to the redundancy of the TFT.

If the pixel is found to be defective due to the TFT, it is not clear which of the TFTs 101 and 102 is defective. However, the probability that both TFTs are defective is very low and need not be considered. Therefore, similarly to the first embodiment, first, a laser is applied to the cut portion 112 through a diaphragm to cut the source electrode 111, and T
The FT 101 is electrically separated from the pixel electrode 105. If the TFT 101 is defective, the defective TFT has been cut, and the repair is completed.

If the TFT 101 is normal and the TFT
If 102 is defective, the wrong TFT has been cut, and it is necessary to reconnect the TFT 101 to the pixel electrode 105. Therefore, first, the source electrode 108 is cut by irradiating the cut portion 113 with a laser beam through a diaphragm to electrically disconnect the defective TFT 102 from the pixel electrode 105. Then, the laser 11 is connected to the laser connecting portion 109.
The TFT 101 is reconnected to the pixel electrode 105 by irradiating 0 and electrically connecting. As a result, the switching operation is performed by the TFT 101, and the repair is completed.

Further, in this embodiment, the contact hole 301 is formed in the end portion of the electrode 109 of the connection portion on the source electrode side, and the source electrode 111 and the connection electrode 109 are connected in advance. Therefore, the number of times of laser irradiation when reconnecting the TFT 101 is only one, and the repair success probability is improved. The structure in which a contact hole is formed in one of the laser irradiation parts at both ends of the connection part is shown in FIG.
It can also be applied to the embodiment shown in FIG. Furthermore, the connecting portion electrode 1
Even when 09 is short-circuited with the gate line 103 due to a defective pattern formation, the signal of the gate line 103 is transmitted to the electrode through the source electrode 111. Therefore, in this defective mode, the cutting point 112 can be cut with a laser. Can be repaired. There is no problem because the probability that the short circuit between the gate line and the connection electrode and the defect of the TFT 102 occur in the same pixel is extremely low.

(Embodiment 3) FIG. 4 is a plan view showing a one-pixel configuration of a liquid crystal display device according to a third embodiment of the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. The basic structure is the same as that of FIG. 2, but is different from that of FIG.
The position of 01 and the laser irradiation part 110 are made opposite.

In the usual process, the contact hole 401 cannot be formed between the connection electrode 109 and the pixel electrode 105. However, as shown in FIG. 5, a pattern with holes is formed in the pixel electrode 105, a contact hole 401 is formed in the insulating film 203 to be smaller than that, and finally a signal line is formed so as to cover the contact hole 401. The electrode 402 is formed by the same process as the above. By using this structure, the pixel electrode 105 and the connection electrode 109
It has become possible to obtain a stable electrical connection between the two.

In the structure shown in FIGS. 3 and 4, the connection electrode 109 is located parallel to the gate line. Also,
Both ends of the pixel electrode 105 are projected to the gate electrode side. As a result, the source electrode 111 of the TFT 101
Can be disposed near the gate electrode 103, and there is almost no reduction in aperture ratio due to the connection portion 109 or the like.

The present invention is not limited to the above embodiments. In the embodiment, a TFT is provided for each pixel.
Although two TFTs are provided, the present invention is not limited to this, and three or more TFTs may be provided for each pixel. TF per pixel
When T is n, a structure that can be cut and a structure that can be reconnected after cutting are added to n-1 TFTs, and
Only a severable structure may be added to T. In this case, a relatively large driving capacity of (n-1) / n can be obtained even if one of the TFTs is defective. Also, 1
It is also possible to add a structure that can be cut and a structure that can be reconnected after cutting to each TFT, and add only a structure that can be cut to n-1 TFTs. In this case, if one of the TFTs is defective, the driving capability is as small as 1 / n, but the number of reconnectable structures can be reduced.

Although the pixel electrode side of the TFT is cut or reconnected in the embodiment, the signal line side of the TFT may be cut or reconnected. Further, an energy beam can be used in place of the laser used for disconnection and reconnection. In addition, various modifications can be made without departing from the scope of the present invention.

[0038]

As described above, according to the present invention, 1
In a redundant structure in which a plurality of thin film transistors are electrically arranged in parallel per pixel, a plurality of TFs provided in parallel are provided.
By providing a disconnectable structure for all of T and a reconnectable structure for a part of T, a liquid crystal display device capable of detecting defective TFTs and reliably relieving defective TFTs while suppressing a decrease in aperture ratio. It can be realized.

[Brief description of drawings]

FIG. 1 is a plan view showing the configuration of one pixel portion of a liquid crystal display device according to a first embodiment.

FIG. 2 is a sectional view showing an example of a laser connecting portion.

FIG. 3 is a plan view showing the configuration of one pixel portion of the liquid crystal display device according to the second embodiment.

FIG. 4 is a plan view showing the configuration of one pixel portion of a liquid crystal display device according to a third embodiment.

FIG. 5 is a sectional view showing a structure of a contact hole portion in the third embodiment.

FIG. 6 is a plan view showing an example of a conventional TFT array.

FIG. 7 is a plan view showing an example of a conventional TFT array repair method.

FIG. 8 is a plan view showing an example of a conventional redundant structure of a TFT array.

FIG. 9 is a plan view showing an example of a conventional redundant structure of a TFT array.

[Explanation of symbols]

 101 ... First TFT 102 ... Second TFT 103 ... Gate line 104 ... Auxiliary capacitance line 105 ... Pixel electrode 106 ... Signal line 107 ... Drain electrode 108 ... Source electrode for second TFT 109 ... Laser connection section 110 ... Laser Irradiation location 111 ... Source electrode 112 for first TFT 112, 113 ... Laser cutting location

Claims (1)

[Claims] 1. A liquid crystal display device comprising a matrix of pixel electrodes and thin film transistors for connecting the pixel electrodes and signal lines, wherein a plurality of the thin film transistors are provided in parallel for one pixel. All of the plurality of thin film transistors have a structure capable of cutting the pixel electrode side or the signal line side, and at least one of the plurality of thin film transistors has a structure capable of being reconnected after cutting the pixel electrode side or the signal line side. Characteristic liquid crystal display device.