JPH0437823A - Active matrix type display device - Google Patents

Abstract

PURPOSE:To produce a display device with high yield and to reduce production cost by correcting a picture element defect so as to make it quiet in a state capable of easily detecting it. CONSTITUTION:When a picture element defect is generated, an area 51 is irradiated with optical energy and a gate bus extension 22 is disconnected and electrically insulated from a gate bus wire 21. When areas 52, 53, i.e. parts shown by arrows 26, 27, are irradiated with laser beams, a source electrode 32 is electrically connected to a gate electrode 25 in the area 52 and a drain electrode 33 is electrically connected to the electrode 25 in the area 53, so that both electrodes 32, 33 are electrically connected with each other through the electrode 25. Since the signal from a source bus wire 23 is always impressed to a picture element electrode 41 to be connected to a TFT 31 corrected by said procedure, the TFT 31 is not normally functioned. However, a picture element displayed by the electrode 41 is displayed corresponding to the effective value of the signal to be impressed to a wire 23, so that the picture element is not displayed as a complete luminescent point or a black point and is displayed with the average brightness of picture elements arranged along the wire 23 as a picture element defect which can not be easily discriminated.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a display device that performs display by applying a drive signal to a display pixel electrode via a switching element, and particularly relates to a display device that performs display by applying a drive signal to a display pixel electrode via a switching element. The present invention relates to an active matrix drive type display device that is arranged in a matrix and performs high-density display.

(Prior Art) Conventionally, in liquid crystal display devices, EL display devices, plasma display devices, etc., display patterns are formed on the screen by selectively driving pixel electrodes arranged in a matrix. . A voltage is applied between a selected picture element electrode and a counter electrode facing the selected picture element electrode, and optical modulation of a display medium such as a liquid crystal interposed between these electrodes is performed. This optical modulation is visually recognized as a display pattern. As a method for driving picture element electrodes, an active matrix driving method is known in which individual independent picture element electrodes are arranged and a switching element is connected to each of the picture element electrodes and driven. As a switching element for selectively driving the picture element electrode, TP
T (thin film transistor) element, MIM (metal-insulating layer-metal) element, MOS transistor element, diode,
Barista etc. are generally known. The active matrix drive method allows for high contrast display.
It has been put to practical use in LCD televisions, word processors, computer terminal display devices, etc.

FIGS. 8 and 9 show plan views of active matrix substrates used in conventional active matrix display devices. The substrate in FIG. 8 includes gate bus lines 21 arranged parallel to each other and source bus lines 23 arranged orthogonally to the gate bus lines 21. A picture element electrode 41 is arranged in each rectangular region surrounded by two gate bus lines 21 and two source bus lines @23. A TPT 31 functioning as a switching element is formed on the gate bus line 21 near the intersection of the gate bus line 21 and the source bus line 23.

A part of the gate bus wiring 21 functions as a gate electrode of the TPT 31. A drain electrode of the TPT 31 is electrically connected to the picture element electrode 41.

A branch line branched from the source bus wiring 23 is connected to the source electrode of the TPT 31 .

The one-chip matrix substrate in FIG. 9 is similar to the substrate in FIG. 8, but the structure around the TPT 31 is different. That is,
The TFT 3i is formed on a gate bus branch line 22 branched from the gate bus wiring 21. A part of the gate bus branch line 22 functions as a gate electrode of the TPT 31.

(Problem to be solved by the invention) When performing high-density display using such a display device,
It is necessary to arrange a very large number of picture element electrodes 41 and TPTs 31. However, the TPT 31 may be formed as a malfunctioning element at the time of fabrication on the substrate.

A picture element electrode connected to such a defective element produces point defects that do not contribute to display. Point defects significantly impair the image quality of display devices and greatly reduce product yield.

There are two main causes of point defects.

One is a defect (hereinafter referred to as "ON defect") that occurs because the picture element electrode is not sufficiently charged during the time when the picture element electrode is selected by the scanning signal. The other one is a defect in which the charge of the charged picture element electrode leaks during a non-selection time (hereinafter referred to as an "off defect").

The ON failure is caused by a TPT failure. Off failure is TPT
In some cases, this is caused by electrical leakage between the picture element electrode and the bus wiring, and in other cases, it is caused by electrical leakage between the picture element electrode and the bus wiring. No matter which defect occurs, a point defect will occur because a necessary voltage is not applied between the picture element electrode and the counter electrode. If such a defect occurs, it will appear as a bright spot in the normally white mode in which the light transmittance is maximum when the voltage applied between the picture element electrode and the counter electrode is 0; In the normally black mode, where the light transmittance is at its lowest in case (2), it appears as a black dot.

Such defects can be corrected by laser trimming or the like. However, this defect correction must be performed at the active matrix substrate stage before the display device is assembled. Although it is easy to detect pixel defects after the display device is assembled, it is extremely difficult to detect pixel defects at the active matrix substrate stage.

In particular, in substrates used in large display devices with 100,000 to 500,000 or more picture elements, extremely high precision is required to detect the electrical characteristics of all picture element electrodes and discover defective TPTs. Measuring equipment, etc. must be used. Therefore, the inspection process becomes complicated and mass productivity is hindered. This results in increased costs. For these reasons, the reality is that in large display devices with a large number of picture elements, it is not possible to correct pixel defects in the substrate using the above-mentioned laser beam.

The present invention solves these problems, and an object of the present invention is to provide an active matrix display in which even if a pixel defect occurs, the defect can be corrected unnoticeably while the display device is assembled. The purpose is to provide equipment.

(!!Means for Solving Problem I) The active matrix display device of the present invention includes a pair of insulating substrates, at least one of which is translucent, and wiring on one of the pair of substrates. an active matrix display device comprising: a scanning line branched from the scanning line; a switching element formed at the tip of the scanning branch line; and a pixel electrode connected to the switching element. and the scanning branch line has a portion smaller in width than the portion of the scanning branch line where the switching element is formed in a portion other than the portion where the switching element is formed. This achieves the above objective.

(Function) In the active matrix display device of the present invention, if an on-failure or an off-failure occurs due to a defective switching element, generation of a weak leakage current between a signal line and a picture element electrode, etc. Modifications can be made to the state of the display device. First, the scanning branch line is cut by laser beam irradiation, etc. in a part other than the part where the switching element of the scanning branch line is formed, and which is smaller in width than the part where the switching element of the scanning branch line is formed. Ru. In the display device of the present invention, since such a small width portion is formed, the scanning branch line can be reliably cut by irradiation with light energy such as a laser beam.

When such a narrow width portion is formed on the scanning branch line, there are the following advantages. First, since the length of the portion to be cut is shortened, it is easier to cut by laser beam irradiation. Furthermore, since the amount of metal melted by laser beam irradiation is small, electrical leakage between the scanning line and the signal line due to melted metal reattaching to the scanning line or signal line is less likely to occur. Second, the distance between the part to be cut and the signal line is large, so the signal line will not be damaged when irradiated with laser light, etc. Third, the part to be cut and the picture Since the distance between the scanning line and the pixel electrode is increased, leakage between the scanning line and the pixel electrode due to redeposition of molten metal does not occur.

After cutting the scanning branch line as described above, the electrode connected to the picture element electrode of the switching element and the electrode connected to the signal line are electrically connected by light energy irradiation. When the switching element is a TPT, this electrical connection is made by irradiating optical energy to the overlapping portion of the source electrode and the gate electrode and the overlapping portion of the drain electrode and the gate electrode, respectively. By irradiating laser light as optical energy, holes are formed in the form of spots in these overlapping parts. Around this hole, the source electrode and the gate electrode are electrically connected, and the drain electrode and the gate electrode are electrically connected. In this way, the source electrode and the drain electrode are electrically connected via the gate electrode.

The voltage applied to the picture element electrode (hereinafter referred to as "corrected picture element electrode") connected to the switching element modified as described above will be explained with reference to FIG. In FIG. 7, Gn is the signal voltage (
S represents the relationship between the signal voltage of the m-th signal line (vertical axis) and time (horizontal axis). pHl+ represents a voltage applied to a normal picture element electrode connected to the nth scanning line and the mth signal line.

P'. represents the voltage applied to the modified picture element electrode connected to the nth scanning line and the mth signal line.

G on the scan line. The signal (Vgh) that sequentially selects the switching elements is the selection time T, as shown in S Gn and . , will be output. Corresponding to the scanning line selection time Tc1n,
A video signal voltage Vl is output to the signal line, and in a normal picture element electrode, this signal voltage ■θ is the non-selection time T, as shown by Pl'llll. It is held for rr. Then, when the selection signal voltages V and h are applied next, the video signal of -■ day is applied to the signal line.

On the other hand, the corrected picture element electrode has P'. As shown in , since the video signal from the signal line is always applied, the modified picture element electrode cannot function normally. However, the picture element displayed by this modified picture element electrode performs a display corresponding to the effective value of the video signal applied to the signal line during one cycle when viewed over one cycle. Therefore, this picture element does not become a perfect bright spot or a black spot, but displays the average brightness of the picture elements arranged along the signal line. Therefore, this picture element becomes a picture element defect that is extremely difficult to identify.

The electrical resistance at the part connected as above is
It is necessary that the resistance be smaller than the resistance in the selected state of the switching element (hereinafter referred to as "on resistance"). The reason is as follows.

The value of the on-resistance of the switching element is set so that a current sufficient to charge the picture element electrode flows within the time period during which the switching element is selected. Therefore, if the resistance at the part where the above connection is made is greater than the on-resistance, the signal voltage that changes at each switching element selection time will not be reliably written to the modified picture element electrode, and will not be applied to the modified picture element electrode. The effective value of the voltage becomes small. In such a state, the difference in brightness between the picture element displayed by the corrected picture element electrode and other normal picture elements becomes large, and the picture element is visually recognized as a defective picture element.

(Example) Examples of the present invention will be described below.

FIG. 1 shows a plan view of an active matrix substrate used in an embodiment of the display device of the present invention.

FIG. 3 shows a sectional view taken along the line m--■ in FIG. 1 of a display device using the substrate shown in FIG. 1. The active matrix display device of this example will be explained according to the manufacturing process.

In this example, a transparent glass substrate was used as the insulating substrate. A gate bus wiring 21 functioning as a scanning line and a gate bus branch line 22 branching from the gate bus wiring 21 were formed on a glass substrate 1. The gate bus branch line 22 functions as a scanning branch line. The gate bus wiring 21 and the gate bus branch line 22 are generally made of Ta, TI, or AI.

Although it is formed of a single layer metal such as Cr or a multilayer metal thereof, Ta was used in this example. The gate bus wiring 21 and the gate bus branch line 22 are formed by patterning a Ta metal layer formed by sputtering. Before forming the gate bus wiring 21 and the gate bus branch line 22, a base coat film made of Ta20B or the like may be formed on the glass substrate 1. The planar shape of the gate bus branch line 22 will be described later.

On the gate bus wiring 21 and gate bus branch line 22, S
A gate insulating film 11 made of IN was formed over the entire surface. The gate insulating film 11 is formed to a thickness of 3,000 wafers by plasma CVD.

Next, a TFT 31 functioning as a switching element was formed at the tip of the gate bus support #s22.

A part of the gate bus branch line 22 is the gate electrode 2 of the TFT 31
Functions as 5. After forming the gate insulating film 11 as described above, an amorphous silicon (a-Sl) layer that will later become the channel layer 12 and an etching stopper layer 13 that will later become the channel layer 12 are formed.
A layer of SIN was deposited. The thickness of the a-Si layer is 300 mm, and the thickness of the SIN layer is 2000 mm. Next, the SiN layer was patterned to form an etching stopper layer 13. Furthermore, the entire surface of the a-Si layer and etching stopper layer 13 will be contacted later! ? A14
．． An n0 type a-81 layer doped with P (phosphorus), No. 14, was deposited to a thickness of 800 nm by plasma CVD. Next, the a-S1 layer and the n9 type a-81 layer are patterned simultaneously, and the channel layer 12 and the free layer 14, 14 are formed, and later the source electrode 32,
A source bus wiring 23 functioning as a signal line and a Ti metal layer serving as a drain electrode 33 were formed. The source bus wiring 4923 and the like are generally formed of a single layer or a multilayer metal such as T1, A1, Mo, (knee r), but in this example, TI was used.T) The metal layer is formed by sputtering method. formed by. By patterning this Ti metal layer, the source electrode 32, source bus wiring 23,
And a drain electrode 33 was formed. Source bus wiring 23
and the gate bus wiring 21 intersect with each other with the aforementioned gate insulating film 11 interposed therebetween.

Next, as shown in FIG.
A picture element electrode 41 made of indium tin oxide (indium tin oxide) was formed. The picture element electrode 41 overlaps the end of the drain electrode 33 of the TFT 31 and is electrically connected to the drain electrode 33.

Furthermore, a protective film 17 made of SIN was deposited over the entire surface of the substrate 1 on which the TFT 31 and the picture element electrode 41 were formed. The protection [17] may be in the form of a window removed above the central portion of the picture element electrode 41. An orientation a19 was formed on the protective film 17. On the glass substrate 2 facing the glass substrate 1,
A counter electrode 3 and a distribution film 9 are formed. A liquid crystal layer 18 is sealed between these substrates 1 and 2, and the active matrix display device of this embodiment is completed.

The configuration near the TFT 31 will be explained. TFT31
Figure 2 shows an enlarged view of the vicinity. As mentioned above, TFT31
is the gate bus branch line 22 branched from the gate bus wiring 21
formed on top. The drain electrode 33 of the TFT 31 is electrically connected to the picture element electrode 41, and the source electrode 32 is electrically connected to the source bus wiring 23. The gate bus branch line 22 has a part other than the part where the TFT 31 of the gate bus branch line 22 is formed.
It has a portion smaller in width than the portion where the No. 2 TFT 31 is formed. By providing such a narrow portion, the distance MX from the picture element electrode 41 to the gate bus branch line 22 can be made larger than that in the conventional example shown in FIG. 9 described above.

By making the distance X large, the gate bus branch line 22 can be easily and reliably cut using optical energy such as a laser beam. It was confirmed that cutting could be performed reliably if the distance X was 10 μm or more. If the distance X is small, T
Not only is it difficult to cut the gate bus branch line 22 without damaging the FT 31, but the irradiated laser light has a negative effect on the intersection of the gate bus wiring 21 and the source bus wiring 23, causing damage to these bus wirings. 21 and 23
This may cause insulation failure between the two.

In the active matrix display device having the above configuration, if the TFT 31 becomes defective or a weak leakage current occurs between the source bus wiring 23 and the picture element electrode 41, a picture element defect occurs. In such a case, corrections are made as follows. First, the gate bus branch line 22 is cut by irradiating light energy onto the region 51 indicated by the broken line in FIG. In this example, YAG laser light was used as optical energy. Thereby, the gate bus branch line 22 is electrically insulated from the gate bus wiring 21. As described above, the gate bus branch line 22 has a portion smaller in width than the portion of the gate bus branch line 22 where the TFT 31 is formed in the portion other than the portion where the TFT 31 of the gate bus branch line 22 is formed. Therefore, the gate bus branch line 22 can be easily and reliably cut. The laser beam may be irradiated from either substrate 1 or 2, but in many cases a light shielding film is formed on the substrate 2, and in that case, the laser beam is irradiated from the substrate l side. In this example, the substrate l
Irradiated from the side.

Next, regions 52 and 53 indicated by broken lines in FIG. 2, ie, the portions indicated by arrows 26 and 27 in FIG. 3, are irradiated with laser light. As a result, the source electrode 32 and the gate electrode 25 are electrically connected in the region 52, and the drain electrode 33 and the gate electrode 25 are electrically connected in the region 53. Therefore, the source electrode 32 and the drain electrode 33 are electrically connected via the gate electrode 25.

The source bus wiring 2 is connected to the picture element electrode 41 (corrected picture element electrode) connected to the TFT 31 modified as described above.
Since the signal No. 3 is always applied, the modified picture element electrode cannot function normally.

However, since the picture element displayed by the modified picture element electrode performs a display corresponding to the effective value of the signal applied to the source bus wiring 23, this picture element does not become a complete bright spot or black spot. The average brightness of the picture elements arranged along the source bus wiring 23 is displayed. Therefore, this picture element becomes a picture element defect that is extremely difficult to identify.

Even if the laser beam irradiation is performed as described above, since the protective film 17 is formed on the gate bus branch line 22 and the TFT 31, molten metal etc. will not mix into the liquid crystal layer 18 which is the display medium. Does not affect display. Furthermore, it has been confirmed that by changing the laser beam irradiation conditions, it is possible to perform fusion bonding between metal layers and cutting the metal layer using the same laser beam.

In addition, in the above modification, the gate electrode 2 of the TFT 31
5 and the source electrode 32 and drain electrode 33 may be made first, and the gate bus branch line 22 may be cut later.

The gate bus branch line 22 can also have a planar configuration shown in FIG. 4 (8) or (b). The gate bus branch line 22 shown in FIG. 4(a) is the same as the gate bus branch line 22 shown in FIG.
By removing only the portion on the picture element electrode 41 side, a narrow portion of the gate bus branch line 22 is formed. Similarly, the gate bus branch line 22 shown in FIG. 4(b)
In this case, a narrower width portion of the gate bus branch line 22 is formed by removing only the portion of the gate bus branch line 22 shown in FIG. 9 on the source bus wiring 23 side.

The present invention can also be applied to an active matrix type display device having an additional capacitance 42, as shown in FIG. Fifth
The display device shown in the figure is the same as the embodiment shown in FIGS. 1 to 3 described above with an additional capacitor 42 added thereto. The additional capacitor 42 is formed at an overlapped portion (hatched portion) between the additional capacitor electrode 24 provided on the substrate 1 in parallel with the gate bus wiring vA21 and the picture element electrode 41. In the display device shown in FIG. 5 as well, pixel defects can be corrected in the same manner as in the embodiments shown in FIGS. 1 to 3 described above.

Furthermore, the present invention can also be applied to an active matrix display device having the configuration shown in FIG. This display device is similar to the display device shown in FIG. 5, but the reduction in the area of the opening due to the portion occupied by the additional capacitance 42 is suppressed.

That is, in this display device, the width of the gate bus wiring 21 is increased so that it overlaps with a part of the picture element electrode 41. In this configuration, the adjacent non-selected gate bus wiring 21 can be used as an electrode for additional capacitance. Moreover, since there is no gap between the gate bus wiring 21 and the additional capacitance electrode 24 as shown in FIG. 5, it is possible to suppress a reduction in the area of the opening. In this display device as well, Figs.
Pixel defects are corrected in the same manner as in the illustrated embodiment.

In each of the above embodiments, an example was shown in which the gate electrode of the TFT 31 was formed on the bottom and the source and drain electrodes were formed on the top, but the gate electrode was formed on the top and the source and drain electrodes were formed on the bottom. A formed type of TPT can also be used.

In addition, in the above embodiment, TP is used as the switching element.
Although T is used, any switching element that can electrically connect the electrode on the signal line side and the electrode on the picture element electrode side by irradiation with light energy such as a laser beam can be used in the present invention.

(Effects of the Invention) In the active matrix display device of the present invention, pixel defects can be corrected in a way that makes them inconspicuous while the display device is in a state where pixel defects can be easily detected. Therefore, according to the present invention, it is possible to produce display devices with high yield, and it is possible to contribute to reducing the cost of display devices.

4. Don't worry! B Fig. 1 is a plan view of an active matrix substrate used in an embodiment of the active matrix type display device of the present invention, Fig. 2 is an enlarged plan view of the vicinity of the TPT shown in Fig. m-m in FIG. 1 of a display device using a substrate
4(a) and 4(b) are plan views showing gate bus branch lines of other embodiments, and FIGS. 5 and 6 are plan views of other embodiments of the present invention, respectively. , FIG. 7 is a diagram showing the relationship between signals applied to scanning lines and signal lines and voltages of picture element electrodes, and FIGS. 8 and 9 are active matrix substrates used in conventional active matrix type display devices, respectively. FIG.

1, 2...Glass substrate, 3...Counter electrode, 9,1
9... Orientation film, 11... Gate insulating film, 12...
Channel 1.13... Etching stopper 1.14.
...Contact a, 18...Liquid crystal layer, 21...Gate bus wiring, 22...Kate bus support II, 23...
Source bus wiring, 24... electrode for additional capacitance, 25...
・Gate electrode, 31... TFT, 32... Source electrode, 33... Drain electrode, 41... Picture element electrode, 4
2...Additional capacity.

that's all

Claims (1)

[Claims] 1. A pair of insulating substrates, at least one of which is translucent, a scanning line wired on one of the pair of substrates, and a scanning branch line branched from the scanning line. , a switching element formed at the tip of the scanning branch line, and a picture element electrode connected to the switching element, wherein the scanning branch line is connected to the tip of the scanning branch line. An active matrix display device having a portion of the scanning branch line other than the portion where the switching element is formed that is smaller in width than the portion where the switching element is formed.