JPH07122720B2 - Active matrix display device - Google Patents

Description

Description: TECHNICAL FIELD 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, The present invention relates to an active matrix drive type display device which is arranged in a matrix and performs high density display.

(Prior Art) Conventionally, in a liquid crystal display device, an EL display device, a plasma display device, etc., a display pattern is formed on a screen by selectively driving pixel electrodes arranged in a matrix. . A voltage is applied between the selected pixel electrode and a counter electrode facing the pixel electrode, and a display medium such as a liquid crystal interposed between these electrodes is optically modulated. This optical modulation is visually recognized as a display pattern. As a driving method of the picture element electrodes, an active matrix driving method is known in which individual picture element electrodes are arranged and a switching element is connected to each of the picture element electrodes for driving. As a switching element that selectively drives the pixel electrodes, a TFT
(Thin film transistor) element, MIM (metal-insulating layer-metal) element, MOS transistor element, diode, varistor and the like are generally known. The active matrix drive system is capable of high-contrast display, and has been put to practical use in liquid crystal televisions, word processors, terminal display devices of computers, and the like.

8 and 9 are plan views of an active matrix substrate used in a conventional active matrix type display device. The substrate of FIG. 8 includes gate bus lines 21 arranged in parallel with each other and source bus lines 23 provided orthogonal to the gate bus lines 21. Two gate bus wiring
A pixel electrode 41 is arranged in each rectangular region surrounded by 21 and the two source bus lines 23. A TFT 31 that functions 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 the gate electrode of the TFT 31. The drain electrode of the TFT 31 is electrically connected to the pixel electrode 41. A branch line branched from the source bus line 23 is connected to the source electrode of the TFT 31.

The active matrix substrate shown in FIG. 9 is the same as the substrate shown in FIG. 8, but the structure around the TFT 31 is different. That is, TFT31
Is formed on the gate bus branch line 22 branched from the gate bus line 21. A part of the gate bus branch line 22 functions as a gate electrode of the TFT 31.

(Problems to be Solved by the Invention) When high-density display is performed using such a display device,
It is necessary to arrange a large number of pixel electrodes 41 and TFTs 31. However, the TFT 31 may be formed as a malfunctioning element when it is formed on the substrate. The pixel electrode connected to such a defective element causes a point defect that does not contribute to display. The point defect significantly impairs the image quality of the display device and greatly reduces the product yield.

There are two main causes of point defects. One is a defect (hereinafter referred to as “on defect”) that occurs because the pixel electrode is not sufficiently charged within the time when the pixel electrode is selected by the scanning signal. The other one is a defect (hereinafter referred to as "off defect") in which the charge of the charged pixel electrode leaks within the non-selection time. The ON failure is caused by the TFT failure. The off failure may be caused by electrical leakage through the TFT or may be caused by electrical leakage between the pixel electrode and the bus wiring. No matter which defect occurs, a necessary voltage is not applied between the pixel electrode and the counter electrode, which causes a point defect. When such a defect occurs, it appears as a bright spot in the normally white mode in which the light transmittance is maximum when the voltage applied between the pixel electrode and the counter electrode is 0 V, and the voltage is 0 V. Sometimes it appears as a black dot in the normally black mode where the light transmittance is the lowest.

Such defects can be corrected by performing laser trimming or the like. However, this defect correction must be performed at the stage of the active matrix substrate before assembling the display device. Although it is easy to detect pixel defects after assembling them as a display device, it is extremely difficult to detect pixel defects at the stage of the active matrix substrate. Especially on a substrate used for a large-sized display device having 100,000 to 500,000 or more picture elements, it is extremely accurate to detect the defective TFT by detecting the electrical characteristics of all picture element electrodes. Measurement equipment must be used. For this reason,
The inspection process becomes complicated and the production of quantity is hindered. Therefore,
This results in higher costs. For this reason,
In a large-sized display device having a large number of picture elements, the fact is that it is not possible to correct picture element defects in the state of the substrate using the above laser light.

The present invention solves such a problem, 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 so as not to be noticeable when the display device is assembled. It is to provide a device.

(Means for Solving the Problems) An active matrix display device of the present invention is provided with a pair of insulating substrates, at least one of which has a light-transmitting property, and a matrix provided on one of the pair of substrates. And a scanning line and a signal line that are wired in a state of intersecting with each other, passing through the periphery of the pixel electrode, and a switching element provided in the vicinity of the intersection of the scanning line and the signal line. The switching element is provided at the tip end of the scanning branch line branched from the scanning line, and a small width portion is provided between the scanning line and the switching element of the scanning branch line. The switching element is provided at the normal pixel portion where the pixel electrode is connected to the scanning line and the signal line and at the tip of the scanning branch line that is cut by the portion with a small width for cutting. The defective pixel portion in which the overlapping portion of the gate electrode and the source electrode of the element and the overlapping portion of the gate electrode and the drain electrode are respectively connected, and the pixel electrode is electrically directly connected to the signal line is formed. It has, and thereby achieves the above objectives.

(Operation) In the active matrix display device of the present invention, when an ON defect or an OFF defect occurs due to a defect of a switching element, a weak leak current between a signal line and a pixel electrode, or the like, The correction can be made in the state of the display device. First, in a portion other than the portion where the switching element of the scanning branch line is formed, which is smaller in width than the portion where the switching element of the scanning branch line is formed,
The scanning branch line is cut by laser light irradiation or the like. In the display device of the present invention, since such a portion having a small width is formed, the scanning branch line can be reliably cut off by irradiation with light energy such as laser light.

Forming such a portion having a small width on the scanning branch line has the following advantages. First, since the length of the portion to be cut is short, it is easy to cut by laser light irradiation. In addition, since the amount of metal melted by the laser light irradiation is small, it is difficult for electrical leakage to occur between the scan line and the signal line due to the melted metal reattaching to the scan line or the signal line. Secondly, since the distance between the portion to be cut and the signal line becomes large, the signal line is not damaged when the laser beam or the like is irradiated. Thirdly, since the distance between the portion to be cut and the pixel electrode becomes large, leakage between the scanning line and the pixel electrode due to redeposition of the molten metal does not occur.

After the scanning branch line is cut as described above, the electrode connected to the pixel 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 TFT, this electrical connection is performed by irradiating light 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 light energy, holes are formed in spots in these overlapping portions. Around the 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.

As described above, in the present invention, by using the TET itself as the pixel short-circuit portion, there is no reduction in the aperture ratio for the defect correction by using the defect correction member separately from the TFT as in the conventional case. .

The voltage applied to the pixel electrode (hereinafter referred to as "corrected pixel electrode") connected to the switching element modified as described above will be described with reference to FIG. In FIG. 7, G _n represents the relationship between the signal voltage (vertical axis) of the n-th scanning line and time (horizontal axis), and S _m is the signal voltage of the m-th signal line (vertical axis). Shows the relationship with time (horizontal axis). P _nm represents the voltage applied to the normal pixel electrode connected to the nth scanning line and the mth signal line. P '
_nm represents the voltage applied to the modified pixel electrode connected to the nth scan line and the mth signal line.

A signal (V _gh ) for sequentially selecting switching elements is output to the scan line for a selection time T _on , as indicated by G _n and G _{n + 1} .
The video signal voltage V ₀ is output to the signal line corresponding to the scanning line selection time T _on , and this signal voltage V ₀ is the non-selection time T _off for the normal pixel electrode as indicated by P _nm . Hold for a while.
Then, when the selection signal voltage V _gh is applied next, the video signal of −V ₀ is applied to the signal line.

On the other hand, in the modified pixel electrode, as shown by _P'nm ,
Since the video signal from the signal line is always applied, the modified pixel electrode cannot function normally. However, the picture element displayed by the modified picture element electrode performs a display corresponding to the effective value of the video signal applied to the signal line during this one cycle when viewed through one cycle. Therefore, this picture element does not become a complete bright spot or a black spot, and the average brightness of the picture elements arranged along the signal line is displayed. Therefore, this picture element becomes a picture element defect that is extremely difficult to distinguish.

The electric resistance in the parts connected as described above is
It must be smaller than the resistance of the switching element in the selected state (hereinafter referred to as “on resistance”). The reason is as follows. During the ON resistance of the switching element, a current sufficient to charge the pixel electrode is set to flow during the time when the switching element is selected. Therefore, if the resistance in the portion where the above connection is made is larger than the on-resistance, the signal voltage that changes every selection time of the switching element is not surely written in the modified pixel electrode and is applied to the modified pixel electrode. The effective value of voltage becomes small. In such a state, the difference in brightness between the picture element displayed by the corrected picture element electrode and another normal picture element becomes large, and it is visually recognized as a picture element defect.

(Example) The Example of this invention is 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 is a sectional view taken along line III-III in FIG. 1 of a display device using the substrate of FIG. The active matrix display device of this embodiment will be described according to the manufacturing process. In this example, a transparent glass substrate was used as the insulating substrate. Gate bus wiring 21 that functions as a scanning line on the glass substrate 1
And a gate bus branch line 22 branching from the gate bus wiring 21
And formed. 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 formed of a single layer of Ta, Ti, Al, Cr or the like or a multilayer metal thereof, but Ta is used in this embodiment. The gate bus wiring 21 and the gate bus branch line 22 are formed by patterning a Ta metal layer formed by a sputtering method. Before forming the gate bus wiring 21 and the gate bus branch line 22, a base coat film made of Ta ₂ O ₅ 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.

A gate insulating film 11 made of SiN _x was formed on the entire surfaces of the gate bus wiring 21 and the gate bus branch line 22. Gate insulation film
11 is formed to a thickness of 3000 Å by the plasma CVD method.

Next, the TFT 31 functioning as a switching element was formed at the tip of the gate bus branch line 22. A part of the gate bus branch line 22 functions as the gate electrode 25 of the TFT 31. After forming the gate insulating film 11 as described above, an amorphous silicon (a-Si) layer to be the channel layer 12 later and SiN _x to be the etching stopper layer 13 later were deposited. The thickness of the a-Si layer is 300Å and the thickness of SiN _x is 2000Å. Next, the SiN _x layer was patterned to form the etching stopper layer 13. Further, on the entire surface of the a-Si layer and the etching stopper layer 13, an n ⁺ type a-Si layer containing P (phosphorus), which will be contact layers 14 later, is formed to a thickness of 800 Å by the plasma CVD method. Deposited. Then, the a-Si layer and the n ⁺ -type a-Si layer are simultaneously patterned to form the channel layer 12 and the contact layer.
14 and 14 were formed.

Next, a source electrode 32, a source bus line 23 functioning as a signal line later, and a Ti metal layer to be the drain electrode 33 were formed. The above-mentioned source bus wiring 23 etc. are generally made of Ti, Al, M
o, Cr, etc. are formed of a single layer or multilayer metal of these,
Ti is used in this embodiment. The Ti metal layer is formed by the sputtering method. By patterning this Ti metal layer, the source electrode 32, the source bus line 23, and the drain electrode 33 were formed. The source bus line 23 and the gate bus line 21 cross each other with the gate insulating film 11 interposed therebetween.

Next, as shown in FIG. 1, ITO (Indium ti) is formed in a rectangular area surrounded by the gate bus wiring 21 and the source bus wiring 23.
A pixel electrode 41 made of n oxide) was formed. Picture element electrode 41
Are superposed on the ends of the drain electrode 33 of the TFT 31 and are electrically connected to the drain electrode 33.

Further, a protective film 17 made of SiN _x was deposited on the entire surface of the substrate 1 on which the TFT 31 and the pixel electrode 41 were formed. The protective film 17 may have a window-like shape removed on the central portion of the pixel electrode 41. An alignment film 19 was formed on the protective film 17. Glass substrate 1
The counter electrode 3 and the alignment film 9 are formed on the glass substrate 2 facing the. A liquid crystal layer 18 is enclosed between the substrates 1 and 2 to complete the active matrix display device of this embodiment.

The configuration near the TFT 31 will be described. An enlarged view around TFT31 is shown in Fig. 2. As described above, the TFT 31 is formed on the gate bus branch line 22 branched from the gate bus line 21. The drain electrode 33 of the TFT 31 is electrically connected to the pixel electrode 41, and the source electrode 32 is electrically connected to the source bus line 23. Gate bus branch line 22 is gate bus branch line 22
In a portion other than the portion where the TFT 31 is formed, the gate bus branch line 22 has a portion having a smaller width than the portion where the TFT 31 is formed. By providing such a portion having a small width, the distance X from the pixel electrode 41 to the gate bus branch line 22 can be made larger than that of the conventional example shown in FIG. Since the distance X is large, it is possible to easily and surely cut the gate bus branch line 22 by using light energy such as laser light. Distance X is 10μ
It was confirmed that if the length was at least m, it could be reliably cut. When the distance X is small, it is not only difficult to cut the gate bus branch line 22 without damaging the TFT 31, but also the irradiated laser light is emitted by the gate bus line 21 and the source bus line 23.
It adversely affects the intersection with the bus wiring 21 and
In some cases, insulation failure between the two may occur.

In the active matrix type display device having the above configuration, when the TFT 31 becomes defective or a weak leak current occurs between the source bus line 23 and the pixel electrode 41, a pixel defect occurs. In such a case, the correction is performed as follows. First, the area shown by the broken line in FIG.
The gate bus branch line 22 is cut by irradiating 51 with light energy. In this embodiment, the light energy is YA
G laser light was used. As a result, 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 a portion other than the portion where the TFT 31 is formed. Therefore, the gate bus branch line 22 is easily and surely cut. The laser light may be emitted from either the substrate 1 or the substrate 2, but in many cases, a light-shielding film is formed on the substrate 2, and in that case, the laser light is emitted from the substrate 1 side.
Also in this example, irradiation was performed from the substrate 1 side.

Next, the regions 52 and 53 indicated by broken lines in FIG. 2, that is, 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.

Since the signal of the source bus line 23 is always applied to the picture element electrode 41 (correction picture element electrode) connected to the TFT 31 modified as described above, the correction picture element electrode normally functions. I can't. However, since the picture element displayed by the modified picture element electrode performs display corresponding to the effective value of the signal applied to the source bus line 23, this picture element does not become a complete bright spot or a 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 distinguish.

Even if laser light irradiation is performed as described above, the gate bus branch line
Since the protective film 17 is formed on the TFT 22 and the TFT 31, the molten metal or the like does not mix into the liquid crystal layer 18 which is a display medium and does not affect the display. It has also been confirmed that it is possible to perform fusion connection between metal layers and cutting of metal layers by using the same laser light by changing the irradiation conditions of laser light.

In the above modification, the gate electrode 25 of the TFT 31 may be connected to the source electrode 32 and the drain electrode 33 first, and the gate bus branch line 22 may be cut later.

The gate bus branch line 22 may have a planar configuration shown in FIG. 4 (a) or (b). In the gate bus branch line 22 shown in FIG. 4 (a), only the portion of the gate bus branch line 22 of FIG. Has been formed. Similarly, the gate bus branch line 22 shown in FIG. 4B has the width of the gate bus branch line 22 removed by removing only the portion of the gate bus branch line 22 of FIG. A small part is formed.

The present invention can also be applied to an active matrix type display device having an additional capacitor 42 as shown in FIG. The display device shown in FIG. 5 is obtained by adding the additional capacitor 42 to the embodiment shown in FIGS. The additional capacitance 42 is formed in the overlapping portion (hatched portion) of the pixel electrode 41 and the additional capacitance electrode 24 provided in parallel with the gate bus line 21 on the substrate 1. Also in the display device of FIG. 5, the above-described FIGS.
The pixel defects can be repaired as in the illustrated embodiment.

Furthermore, the present invention can be applied to the active matrix type display device having the configuration of FIG. This display device suppresses the reduction of the area of the opening due to the portion occupied by the additional capacitance 42 in the display device of FIG. That is, in this display device, the width of the gate bus wiring 21 is increased,
It overlaps with a part of the pixel electrode 41. In this configuration, the adjacent non-selected gate bus line 21 can be used as the additional capacitance electrode. Moreover, since there is no gap between the gate bus line 21 and the additional capacitance electrode 24 as shown in FIG. 5, a reduction in the area of the opening can be suppressed. Also in this display device, the picture element defect is corrected as in the embodiment shown in FIGS.

In each of the above embodiments, the example in which the gate electrode of the TFT 31 is formed below and the source electrode and the drain electrode are formed above is shown, but the gate electrode is formed above and the source electrode and the drain electrode are formed below. It is also possible to use formed TFTs.

Further, although the TFT is used as the switching element in the above-mentioned embodiment, if the switching element can electrically connect the electrode on the signal line side and the electrode on the pixel electrode side by irradiation of light energy such as laser light. It can be used in the present invention.

(Effect of the Invention) In the active matrix type display device of the present invention, it is possible to correct the picture element defects in a state of the display device in which the picture element defects can be easily detected. Further, since the TFT itself is used as the pixel short-circuit portion, it is possible to eliminate the reduction of the aperture ratio due to the provision of a defect correction member separately from the TFT as in the conventional case. Moreover, by configuring the width of the scanning branch line to be smaller than the portion where the switching element is formed, the pixel electrodes are not damaged when the scanning branch line is melted and cut by light energy irradiation,
The distance can be set so that it can be easily cut, and the pixel opening can be made as large as possible. Therefore, according to the present invention, a display device can be produced with a high yield, which can contribute to a reduction in the cost of the display device.

[Brief description of drawings]

FIG. 1 is a plan view of an active matrix substrate used in an embodiment of the active matrix display device of the present invention, FIG. 2 is an enlarged plan view of the vicinity of the TFT of FIG. 1, and FIG. 3 is the substrate of FIG. III-II in FIG. 1 of the display device using the
Sectional views taken along line I, FIGS. 4 (a) and 4 (b) are plan views showing a gate bus branch line of another embodiment, and FIGS. 5 and 6 are planes of another embodiment of the present invention. FIG. 7 and FIG. 7 are diagrams showing the relationship between the signals applied to the scanning lines and the signal lines and the voltage of the pixel electrodes, and FIG. 8 and FIG. 9 are the active matrix used in the conventional active matrix type display device. It is a top view of a substrate. 1,2 ... Glass substrate, 3 ... Counter electrode, 9,19 ... Alignment film, 11 ... Gate insulating film, 12 ... Channel layer, 13 ... Etching stopper layer, 14 ... Contact layer, 18 ... … Liquid crystal layer, 21 …… Gate bus wiring, 22 …… Gate bus branch line, 23
...... Source bus wiring, 24 …… Additional capacitance electrode, 25 …… Gate electrode, 31 …… TFT, 32 …… Source electrode, 33 …… Drain electrode, 41 …… Pixel electrode, 42 …… Additional capacitance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hidenori Otokoton 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Kozo Yano 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Incorporated (72) Inventor Manabu Takahama 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture Incorporated in Sharp (56) Reference JP 63-225229 (JP, A) JP 63-136076 ( JP, A)

Claims (1)

[Claims] 1. A pair of insulating substrates, at least one of which has a light-transmitting property, a pixel electrode provided in a matrix on one of the pair of substrates, and a periphery of the pixel electrode. A scanning line and a signal line wired in a state of intersecting each other, and a switching element provided in the vicinity of the intersection of the scanning line and the signal line, and the tip of a scanning branch line branched from the scanning line. The switching element is provided in a portion, and a portion having a small width is provided between the scanning line of the scanning branch line and the switching element, and the pixel electrode is connected to the scanning line and the signal line through the switching element. The switching element is provided at the tip of the scanning branch line cut by the normal pixel portion that is present and the portion for cutting the width, and the overlapping portion of the gate electrode and the source electrode of the switching element and the gate electrode. And it is connected to each of the overlapping portion between the drain electrode, an active matrix display device having a defective pixel portion where picture elements electrodes are electrically directly connected to the signal line.