JPH04265946A - Active matrix display device - Google Patents

Abstract

PURPOSE:To improve the yield of the active matrix display device and reduce the cost by easily confirming and correcting a picture element defect. CONSTITUTION:A gate bus line projection part 43 which projects toward a picture element electrode 41 is formed on a gate bus line 21 and a TFT 31 is formed close to its base end. The TFT 31 functions as a switching element and is connected to a picture element electrode 41. The tip of the gate bus line projection part 43 is extended up to the front of a source bus line projection part 46 which is formed projecting toward the picture element electrode 41 from the source bus line 23 and a conductor piece 44 is superposed on the tip part through a gate line insulating film 13. The halfway part of the gate bus line projection part 43 which crosses the source bus line projection part 46 is superposed upon the source bus line projection part 46 through the gate insulating film 13. If a picture element becomes defective in this structure, the source bus line 23 and picture element electrode 41 are short-circuited by laser light irradiation.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention applies a driving signal to a display picture element electrode through a switching element.
The present invention relates to a display device that performs display, and particularly relates to an active matrix drive type display device that performs high-density display by arranging picture element electrodes in a matrix.

0002

2. Description of the Related Art Conventionally, in liquid crystal display devices, EL display devices, plasma display devices, etc., a display pattern is formed on a screen by selectively driving picture element electrodes arranged in a matrix. As a display pixel selection method,
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 to drive display. As switching elements for selectively driving picture element electrodes, TFT (thin film transistor) elements, MIM (metal-insulating layer-metal) elements, MOS transistor elements, diodes, varistors, etc. are generally used. A voltage applied between opposing electrodes is switched by a switching element to optically modulate a display medium such as a liquid crystal, an EL light-emitting layer, or a plasma light-emitting material interposed between both electrodes, and the optical modulation is performed by switching the voltage applied between opposing electrodes. is visually recognized as a display pattern. Such an active matrix drive system is capable of high-contrast display and has been put to practical use in liquid crystal televisions, word processors, computer terminal display devices, and the like.

FIGS. 9 and 10 show conventional examples of active matrix liquid crystal display devices. In the conventional example shown in FIG. Wire 21, 21... horizontally,
In the vertical direction perpendicular to this, source bus lines 23, 23...
It becomes by wiring. Adjacent gate bus lines 21, 21
A picture element electrode 41 is arranged in each rectangular area surrounded by the source bus lines 23 and 23.

In addition, a branch (
A TFT 31 functioning as a switching element is formed on the protruding gate bus branch line 22. The gate bus branch line 22 has a portion that functions as a gate electrode of the TFT 31 and a portion whose width is smaller than that portion. TFT
The drain electrode 33 of 31 is electrically connected to the picture element electrode 41, and the source electrode 32 is connected to the source bus line 23.

In the conventional example shown in FIG. 10, a source bus branch line 90 branched (protruding) from the source bus line 23 overlaps the gate bus line 21, and a TFT is formed in the overlapping portion.
31 is formed. The drain electrode 33 of the TFT 31 is electrically connected to the picture element electrode 41, and the source electrode 32 is connected to the source bus line 23 via a source bus branch line 90.

[0006]

[Problems to be Solved by the Invention]) In such an active matrix display device, for example, if a switching element is formed as a defective element, the signal that should originally be given to the picture element electrode connected to the defective element is is not input, so dot-like pixel defects appear on the display screen.
That is, it is recognized as a point defect. Such point defects are
This significantly impairs the display quality of the display device and becomes a big problem from the viewpoint of product yield.

The main causes of pixel defects can be broadly classified into the following two types. One is a defect (hereinafter referred to as ON defect) that occurs because the pixel electrode cannot be sufficiently charged within the time when the switching element is selected by the scanning signal (signal from the gate bus line). is a defect (hereinafter referred to as OFF defect) in which the charge charged in the picture element electrode leaks when the switching element is not selected.

[0008] Here, ON failure is caused by a failure of the switching element, while OFF failure is caused by electrical leakage occurring through the switching element or between the picture element electrode and the bus line. There are two types. ON
In both cases of failure and OFF failure, the voltage applied between the picture element electrode and the counter electrode does not reach the required value, so the normally white mode (the voltage applied to the liquid crystal is 0)
When using a display mode in which the light transmittance is at its maximum when In this case, it will look like a sunspot.

[0009] If such point defects are discovered during the manufacturing stage of the substrate on which the switching elements are disposed, they can be corrected by laser trimming or the like. However, it is extremely difficult to detect such point defects from among a huge number of picture elements during the production of the substrate, and considering the manufacturing time and manufacturing cost, it can be said that it is impossible at a mass production level. In particular, it can be said that this is completely impossible for large display panels with 100,000 to 500,000 picture elements.

On the other hand, there is a method in which point defects are visually detected by applying an electric signal for inspection to the bus line at the stage where a counter substrate is attached to the substrate and a liquid crystal is sealed. Defects can be easily detected. However, according to this method, in order to improve the product yield, for example, by short-circuiting the source bus line and the pixel electrode, the signal voltage from the source bus line is reduced regardless of whether the gate is selected or not. However, in the conventional example shown in FIGS. 9 and 10, the source bus line 23 and the pixel electrode 4
1, it is difficult to make such corrections, and products with point defects must be discarded, which is disadvantageous in terms of cost.

[0011] Due to the above-mentioned reasons, the current situation is that there are major restrictions on improving the yield of products.

The present invention solves these drawbacks of the prior art, and provides an active matrix display device that can easily correct pixel defects even if they occur, and can significantly improve product yield. The purpose is to

[0013]

[Means for Solving the Problems] In the active matrix display device of the present invention, gate bus lines and source bus lines are wired in a grid pattern on one of a pair of insulating substrates, and are surrounded by both bus lines. In an active matrix liquid crystal display device, in which pixel electrodes are disposed in respective regions, and switching elements are connected to the pixel electrodes, the gate bus line, and the source bus line, respectively, the pixel electrodes are disposed on the source bus line. protruding towards
A source bus line protrusion that is not in electrical contact with the picture element electrode is provided, and a source bus line protrusion that protrudes toward the picture element electrode on the gate bus line and has a tip reaching forward of the source bus line protrusion. forming a switching element in a portion near the base end of the gate bus line protrusion, and overlapping a midway portion of the gate bus line protrusion with the source bus line protrusion with an insulating film in between; Further, a conductor piece is provided at the tip of the gate bus line protrusion with an insulating film interposed therebetween, and the conductor piece is brought into electrical contact with the picture element electrode, thereby achieving the above object. .

Further, an additional capacitor bus line may be provided below the picture element electrode with an insulating film sandwiched therebetween, or a part of the picture element electrode may be overlapped with a gate bus line adjacent to the gate bus line with an insulating film sandwiched therebetween. You may decide to do so.

[0015]

[Operation] In the active matrix display device having the above configuration, the substrate on which the switching elements are disposed and the substrate on the counter electrode side are bonded together, and after filling liquid crystal between them, the gate bus line, the source bus line, and the picture element are connected. When an appropriate drive signal is applied to the electrodes, the active matrix display device displays a display pattern, so that point defects can be easily found by viewing the display screen.

When a point defect is discovered, first, energy such as a laser beam is irradiated from outside the substrate between the switching element forming part of the gate bus line protrusion and the overlapped part of the source bus line protrusion. , release the electrical connection on both sides of the irradiation section. Next, the overlapping portion of the source bus line protrusion and the gate bus line protrusion is similarly irradiated with laser light. It is assumed that the irradiation spot of the laser beam is sufficiently small compared to the area of the overlapping portion. As a result, the insulating film in the overlapping portion is destroyed, and the protruding parts of the metal wiring located on both sides of the insulating film, that is, the source bus line and the gate bus line, are melted and the two are electrically connected. That is, by providing a source bus line protrusion and a gate bus line protrusion, and providing an overlapping portion of both, it is possible to easily electrically connect the two.

Next, a laser spot having a smaller area than the overlapping portion is irradiated onto the overlapping portion of the tip of the gate bus line protruding portion and the conductor piece overlapped here, and the gate bus line protruding portion and the overlapping portion are irradiated in the same manner as described above. Electrically connect the conductor pieces. This connection work can also be easily performed due to the structure.

Here, since the conductor piece is electrically connected to the picture element electrode in advance, the source bus line and the picture element electrode will be electrically connected by the next two laser irradiations. . In other words, both are short-circuited.

When the source bus line and the picture element electrode are short-circuited in this way, the source signal of the source bus line is directly input to the picture element electrode, regardless of the gate signal from the gate bus line. Therefore, in a picture element in a normal state, only the source signal supplied to the picture element electrode within the selection time of the gate bus line is charged, and this is held for one cycle (the time until the next selection time). On the other hand, in a defective pixel where a point defect occurs and the source bus line and pixel electrode are short-circuited as described above, the selection of the gate bus line,
The source signal is always charged to the picture element electrode regardless of whether it is unselected or not. Therefore, when looking at one period, the actual value of the source voltage input during this period is applied to the liquid crystal.

Therefore, a defective picture element lights up at an average brightness of all the picture elements attached to the source bus line to which the defective picture element belongs. This is neither a perfect bright spot nor a perfect sun spot. As a result, although the picture elements that have been subjected to the correction process are not operating normally, they are in a state where it is extremely difficult to visually distinguish them as defects. In other words, the picture element is in a state where it can be said to be a normal picture element in terms of display.

Note that the electrical resistance at the short-circuited portion must be set to a value smaller than the resistance (ON resistance) of the switching element in the selected state. The reason is shown below. Normally, the ON resistance is set so that enough current flows to charge the picture element electrode within the switching element selection time, and if the shorted resistance is larger than this ON resistance, the switching element selection It becomes impossible to faithfully write source signals that are input one after another within a time range, and the effective value of the voltage applied to the picture element electrode becomes small, making the brightness with other picture elements noticeable. This is because it will be recognized as a defective picture element.

[0022]

[Examples] Examples of the present invention will be described below.

FIGS. 1 to 4 show an active matrix display device of this embodiment, and this display device has a liquid crystal 18 sealed between a pair of upper and lower transparent insulating substrates 1 and 2. On the lower substrate 1, a plurality of gate bus lines 21, 21, . . . which function as scanning lines, and a plurality of source bus lines 23, . A picture element electrode 41 is arranged in a matrix in each rectangular area surrounded by 23. A gate bus line protrusion 43 is formed on the gate bus line 21 and protrudes toward the picture element electrode 41 side, and a TFT 3 is formed in a portion near the base end of the gate bus line protrusion 43.
1 is formed. The TFT 31 functions as a switching element and is connected to the picture element electrode 41. The tip of the gate bus line protrusion 43 extends to the front of the source bus line protrusion 46 formed to protrude from the source bus line 23 toward the picture element electrode 41, and the gate insulating film 13 (FIG. 2 and The conductor piece 44 is superimposed via the conductive material (see 3). On the other hand, a midway portion of the gate bus line protrusion 43 that intersects with the source bus line protrusion 46 overlaps the source bus line protrusion 46 with the gate insulating film 13 interposed therebetween.

The details of each part will be explained below according to the production procedure. As shown in FIG. 2, first, a gate bus line 21 is created on a transparent insulating substrate 1. This creation is generally done by Ta
, Ti, Al, Cr, etc., in a single layer or multiple layers are deposited on the transparent insulating substrate 1 by sputtering, and then patterned. At this time, the gate bus line protrusion 43 is created at the same time. In this example, a glass substrate 1 was used as the transparent insulating substrate 1. Note that, as shown in FIG. 4, an insulating film 11 such as Ta2O5 may be formed as a base coat film under the gate bus line 21.

Next, a gate insulating film 13 is laminated on the gate bus line 21 (including the gate bus line protrusion 43). In this example, SiN was formed by plasma CVD method.
A gate insulating film 13 was formed by depositing an x film to a thickness of 300 nm. Note that before forming the gate insulating film 13, the gate bus line 21 is anodized to form an oxide film 12 made of Ta2O5.
may be formed.

Next, the semiconductor layer 14 and the etching stopper layer 15 are deposited on the gate insulating film 1 by plasma CVD.
Continuously form on top of 3. The semiconductor layer 14 is made of an amorphous silicon (a-Si) layer, and the etching stopper layer 15 is made of a SiNx layer. The respective film thicknesses are 30 nm and 200 nm. Then, the etching stopper layer 15 is patterned, and then a phosphorus-doped n+ type a-Si layer 16 is formed to a thickness of 80 nm by plasma CVD.
Laminated to a thickness of . This n+ type a-Si layer 16 is formed in order to improve the ohmic contact between the semiconductor layer 14 and the source electrode 32 or drain electrode 33 (see FIG. 2) laminated thereafter.

Next, the n+ type a-Si layer 16 is patterned, and then a source metal is deposited by sputtering. Source metals generally include Ti, Al,
Although Mo, Cr, etc. are used, Ti was used in this example. Then, the Ti metal layer is patterned to obtain a source electrode 32 and a drain electrode 33. As a result, a TFT 31 whose structure is shown in FIG. 2 is created. At this time,
As shown in FIG. 4, the source bus line protrusion 46 and the conductor piece 44 are formed at the same time.

Next, a transparent conductive material that will become the picture element electrode 41 is laminated. In this example, I
TO (indium tin oxide) is laminated by a sputtering method, and this is patterned to obtain a picture element electrode 41. The picture element electrode 41 is laminated in a rectangular area surrounded by the gate bus line 21 and the source bus line 23 as described above, and as shown in FIG.
Laminated on the end of the drain electrode 33 of the FT 31, and
As shown particularly clearly in FIG.
layered on top. As a result, the picture element electrode 41, the drain electrode 33 of the TFT 31, and the conductor piece 44 are brought into conduction.

A protective film 17 made of SiNx is deposited over the entire surface of the glass substrate 1 on which the picture element electrodes 41 are formed. The protective film 17 may be removed in the center of the picture element electrode 41 to form a window. An alignment film 19 is formed on the protective film 17 . The protective film 17 may also have a window-perforated shape with its central portion removed. As shown in FIG. 2, a counter electrode 3 and an alignment film 9 are formed on a glass substrate 2 facing the glass substrate 1. Then, a liquid crystal 18 is sealed between these glass substrates 1 and 2, and the active matrix display device of this embodiment is fabricated.

Next, a method of repairing a pixel defect when it occurs in the active matrix display device of this embodiment will be explained. Usually, the picture element electrode 41 is TFT31TFT3
1 and as long as the TFT 31 is operating normally, the picture element in the area surrounded by the gate bus line 21 and the source bus line 23 will operate normally and no display problem will occur. However, when TFT31 malfunctioned,
When a weak current leak occurs between the source bus line 23 and the picture element electrode 41, a picture element defect appears and is recognized as a display problem. In this embodiment, this problem is repaired as follows.

That is, when the active matrix display device is driven and pixel defects are confirmed, as shown in FIG. The metal in the region 51 is scattered, thereby breaking the electrical connection between the gate bus line 21 and the gate bus line protrusion 43. Next, the region 52 similarly surrounded by the broken line is irradiated with laser light to destroy the gate insulating film 13 between the source bus line protrusion 46 and the gate bus line protrusion 43, and to destroy both protrusions 46, 43. Melts the metal to create electrical continuity between the two.

Note that the laser beam irradiation may be performed from the side of the substrate 1 where the TFT 31 is disposed, or from the side of the substrate 2 on the counter electrode side. In the display device, since the front side of the substrate 2 is covered with a light-shielding metal and cannot be directly irradiated with laser light, the irradiation is performed from the substrate 1 side. In FIG. 4, the irradiation direction of the laser beam is shown by a white arrow.

Next, a region 53 indicated by a similar broken line,
That is, the gate bus line protrusion 43 and the conductor piece 44
A laser beam is irradiated on the overlapped area with the By irradiating this region 53 with laser light, the gate insulating film 13 is destroyed, and the gate bus line protrusion 43 and the conductive piece 44 are melted, thereby making them electrically conductive. When the upper and lower metal wirings are brought into conduction at two locations in the regions 52 and 53 by the above laser irradiation, the source bus line 23 and the conductive piece 44, that is, the picture element electrode 41 are eventually short-circuited.

Due to this short circuit, for the reasons mentioned above,
The defective picture element is illuminated with the average brightness of all the picture elements, and the display defect is eliminated. On the other hand, gate bus branch line 2
2 and TFT 31 are protected by a protective film 17,
Metal atoms melted by laser light irradiation do not mix into the liquid crystal 18, which is a display medium. Therefore, the characteristics of the liquid crystal 18 will not deteriorate.

Note that the order in which the regions 51, 52, and 53 are irradiated with laser light is not limited to the above order. Further, the irradiation spot is not limited to the illustrated area, and for example, the areas 52 and 53 may be any area where conductive layers are overlapped above and below.

Next, according to FIG. 5, when the picture element electrode 41 and the source bus line 23 are short-circuited as described above, the TF
The operation of T31 will be explained. In FIG. 5, Gn is the signal (voltage signal) of the n-th gate bus line 21, and S
m is the signal of the m-th source bus line 23, Pn, m is the signal given to the picture element electrode 41 existing at the intersection of the n-th gate bus line 21 and the m-th source bus line 23. It shows.

As shown in FIG. 5(a), when the potential of the signal on the gate bus line 21 is Vgh (high level), the TF
When T31 is selected and the potential is Vgl (low level), TFT31 becomes unselected. As shown in FIG. 5C, when the TFT 31 is selected, the picture element electrode 41 is charged with a pulsed signal V0. When the picture element electrode 41 is operating normally, this signal is held during the non-selection time Toff shown in FIG.
A signal of 0 is written to the source bus line 23.

Gn+1 shown in FIG. 5(b) indicates a signal applied to the (n+1)th gate bus line 21, and the signal Gn+1 is applied when the selection time Ton of the nth gate bus line 21 ends. selection state is started,
At this time, a signal of -V1 is written to the source bus line 21 (see FIG. 5(c)). As can be seen from FIGS. 5(a) and 5(b), the signal input to the gate bus line 21 is sequentially delayed along with the line number, and then n
The non-selected state continues for the above-mentioned time Toff until the selected state circulates to the gate bus line 21. Even in this non-selected state, signals to be written to each picture element electrode 41 are constantly input to the source bus line 21.

As shown in FIG. 5(d), when the gate signal Gn is in the selected state, the normal picture element electrode 41 is connected to the picture element electrode 41 in response to the signal Sm input from the source bus line 23. The counter electrode 3 on the substrate 2 side is charged with electric charge.
The molecular arrangement of the liquid crystal 18 changes due to the potential difference between the two and performs the display function. At this time, the signal Sm input to the source bus line 23 during the non-selection time Toff of the gate bus line 21 does not contribute to the display at all.

On the other hand, in the state where the picture element electrode 41 and the source bus line 23 are short-circuited by laser beam irradiation as described above, the picture element electrode 41 is connected regardless of whether the gate bus line 21 is selected or not. It reacts to all the signals Sm input from the source bus line 23 and charges and discharges the electric charges. The signals at this time are shown as P'n and m in FIG. 5(e). Picture element electrode 4 modified by laser light irradiation
1, source bus line 2 during non-selection time Toff.
Since the signal Sm of 3 is input as is, the liquid crystal 18
The voltage acting on is the effective value of the applied signal Sm. Therefore, the signal Sm given to the source bus line 23
It is impossible for the effective value of the signal P'n, m to become V0 except when all of the signal voltages P'n, m
The effective value of the voltage is the average value of all the picture element electrodes 41 connected to the m-th source bus line 23. This means that for the display device, the m-th source bus line 23
This means that each picture element electrode 41 is lit with the average brightness of each picture element electrode 41 arranged along the line, and in a normal display state, the brightness of each picture element electrode 41 hardly impairs display quality.

FIG. 6 shows a modification of the above embodiment,
In this modification, between the gate insulating film 13 and the conductor piece 44 and between the gate insulating film 13 and the source bus line protrusion 46
A semiconductor layer 14, an etching stopper layer 15,
It has a structure in which a contact layer 16 is inserted. These layers 14 to 16 are provided to enhance the insulation between the upper and lower conductors. Although not shown, the semiconductor layer 14, the etching stopper layer 15, or the contact layer 1
A structure in which only 6 is inserted may be used.

FIG. 7 shows another embodiment of the present invention,
In this embodiment, each picture element electrode 41 has an additional capacitance 42. The additional capacitor 42 is connected to the gate bus line 21
The gate insulating film 13 is interposed between the additional capacitor bus line 24 and the picture element electrode 41. To explain a little more, the gate bus line 21 is overlapped with the picture element electrode 41, and an additional capacitor 42 shown by diagonal lines in the figure is formed at the overlapped portion of the gate bus line 21 and the picture element electrode 41. The additional capacitor bus line 24 is formed by laminating the same metal as the gate bus line 21, and is formed at the same time as the gate bus line 21 is patterned.

In this embodiment, the same signal as the counter electrode 3 is input to the additional capacitance bus line 24. Therefore, the additional capacitance 42 is connected to the picture element electrode 4 in terms of an electric circuit.
1 and the glass substrate 2 in parallel to the liquid crystal capacitor of the liquid crystal 18 sealed between the liquid crystal 18 and the glass substrate 2. The presence of such an additional capacitor 42 improves the charge retention ability of the picture element electrode 41, and ultimately improves the performance of the display device. In this embodiment as well, pixel defects can be corrected in the same manner as in the above embodiments.

FIG. 8 shows still another embodiment of the present invention. In this embodiment, although display characteristics can be improved by providing an additional capacitor 42 as in the other embodiments, the additional capacitor bus line Since the light blocking area increases by the portion 24 and the entire screen becomes dark as a result, an additional capacitor 42 is provided on the adjacent gate bus line 21 to solve this problem.

That is, the additional capacitance bus line 24 is provided to overlap the gate bus line 21, and the pixel electrode 41 and the gate bus line 2 are connected to each other with the gate insulating film 13 interposed therebetween.
The configuration is such that an additional capacitor 42 shown by diagonal lines in the figure is formed in the overlapped portion with 1. In this embodiment, when the adjacent gate bus line 21 is in a non-selected state, the same signal as the counter electrode 3 on the glass substrate 2 is input to the gate bus line 21, and the gate bus line 21 is used as the additional capacitance bus line 24. use. This reduces the light blocking area and prevents the display screen from becoming dark. According to this implemented laser light source, the display characteristics can be further improved.

Although the illustrated embodiment is as described above, the present invention can be modified in various ways as shown below. That is, the switching elements that drive the picture element electrodes are not limited to TFTs, but may also be MIM elements, MOS transistor elements, diodes, or varistors. Also, T
The structure of the FT is not limited to that of the above embodiment,
A structure may be used in which the source bus line is placed on the bottom surface and the gate bus line is placed on the top surface.

[0047]

Effects of the Invention Due to its structure, the active matrix display device of the present invention allows pixel defects to be easily detected in a state where all the pixel electrodes of the display device are driven. Moreover, pixel defects can be easily corrected by irradiating energy such as laser light from the outside of the substrate. Therefore, according to the present invention, display devices can be produced with high yield, contributing to cost reduction of display devices.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an active matrix display device of the present invention.

FIG. 2 is a sectional view taken along line AA in FIG. 1.

FIG. 3 is an enlarged view of part B in FIG. 1.

FIG. 4 is a sectional view taken along line CC in FIG. 3;

FIG. 5 is a timing chart showing signals input to gate bus lines, source bus lines, and picture element electrodes.

FIG. 6 is a sectional view similar to FIG. 4 showing a modification of the present invention.

FIG. 7 is a plan view showing another embodiment of the present invention.

FIG. 8 is a plan view showing another embodiment of the present invention.

FIG. 9 is a plan view showing a conventional active matrix display device.

FIG. 10 is a plan view showing a conventional active matrix display device.

[Explanation of symbols]

1 Glass substrate 2 on the side where the picture element electrode is arranged Glass substrate 3 on the side where the counter electrode is arranged Counter electrode 13 Gate insulating film 18 Liquid crystal 21 Gate bus line 23 Source bus line 24...additional capacitance bus line 31... TFT 32...Source electrode 33...Drain electrode 41...Picture element electrode 42...Additional capacitance 43...Gate bus line protrusion 44...Conductor piece 46...Source bus line protrusion

Claims (3)

[Claims] Claim 1: A gate bus line and a source bus line are wired in a grid pattern on one of a pair of insulating substrates, and pixel electrodes are respectively arranged in areas surrounded by both bus lines. In an active matrix liquid crystal display device in which switching elements are connected to the picture element electrode, the gate bus line, and the source bus line, respectively, the source bus line protrudes toward the picture element electrode and is electrically connected to the picture element electrode. A non-contact source bus line protrusion is provided, and a source bus line protrusion is provided on the gate bus line that protrudes toward the picture element electrode, the tip of which reaches in front of the source bus line protrusion, and the gate bus line The switching element is formed in a portion near the base end of the protrusion, and a midway portion of the gate bus line protrusion is overlapped with the source bus line protrusion with an insulating film in between, and the gate bus line protrusion is An active matrix display device in which a conductor piece is provided at the tip with an insulating film in between, and the conductor piece is brought into electrical contact with the picture element electrode. 2. The active matrix display device according to claim 1, further comprising an additional capacitance bus line provided below the picture element electrode with an insulating film interposed therebetween. 3. The active matrix display device according to claim 1, wherein a part of the picture element electrode overlaps a gate bus line adjacent to the gate bus line with an insulating film interposed therebetween.