JPH0980469A - Display device with surge voltage protective function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an effect of a surge voltage from affecting a display area when the surge voltage is applied to a feeding electrode pad of a signal line and an address line. SOLUTION: A liquid crystal display device is provided with plural pixels 40 arranged in matrix, and a thin film transistor 43 is arranged on each pixel 40. For optionally selecting respective pixels 40, the address lines 41 and the signal lines 42 are arranged, and the thin film transistors 43 are arranged on these intersected points. The signal line 42 is grounded through a surge voltage protective means 48 between the feeding electrode pad of the signal line 42 and the thin film transistor 43, and the surge voltage protective means 48 is provided with a diode 52 and a capacitor 54 connected in series each other. The cathode of the diode 52 is connected to the signal line 42, and the anode is connected to one end of the capacitor 54, and the other end of the capacitor 54 is grounded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device having a surge voltage protection function, and more specifically, an active display device which is prevented from being affected by a surge voltage due to static electricity applied to a power supply electrode pad. The present invention relates to a matrix type display device.

[0002]

2. Description of the Related Art A liquid crystal display device (LCD) includes two opposing substrates, which are transparent to visible light, such as glass substrates.
A liquid crystal sandwiched between the substrates. As described above, most of the layers constituting the liquid crystal display device are occupied by the insulator.
Therefore, charges are easily accumulated in the liquid crystal display device. For example, during the manufacturing process, in the transport system of the manufacturing apparatus, electric charges are accumulated in the liquid crystal display device due to friction, drying, peeling charging and the like. In a liquid crystal display device that is mostly occupied by a glass substrate, it is difficult to make the potentials of the manufacturing device and the liquid crystal display device the same during the manufacturing process. Therefore, static electricity may be accumulated and discharged in the liquid crystal display device during the manufacturing process.

In an active matrix type liquid crystal display device in which transistors are arranged in a matrix as switching elements of each pixel, static electricity significantly deteriorates image quality. In this type of liquid crystal display device, in order to control the pixel potential, address lines (gate lines) made of conductive wiring and signal lines are arranged in a grid pattern with an insulating film interposed therebetween. When the potential difference between the address line and the signal line increases due to static electricity, the insulating film interposed therebetween is destroyed. The destruction of the insulating film causes a leak or a short circuit between the address line and the signal line. As a result, the signal applied to the address line or the signal line is not normally transmitted, the pixel potential control becomes impossible, and the image quality of the liquid crystal display device is significantly deteriorated. Specifically, it is recognized as a point defect or a line defect of the liquid crystal display device.

Particularly in an active matrix type liquid crystal display device in which a thin film transistor is connected to each pixel, it must be taken into consideration that the performance of the thin film transistor is deteriorated by a surge voltage due to static electricity or the like. That is, when the surge current flows due to electrostatic discharge on the address line and the signal line,
The characteristics of the thin film transistor are deteriorated by propagating through the wiring, and a short circuit occurs in the thin film transistor region, or insufficient writing of a pixel potential occurs due to the deterioration of the characteristic.

FIG. 9 shows a conventional liquid crystal display device having a conventional electrostatic protection function. A plurality of address lines 11 and a plurality of signal lines 12 are arranged in a matrix, and a thin film transistor 13 is connected to each intersection as a switching element for controlling a pixel. Address line 11 and signal line 12
Electrode pads 14 and 15 for power supply are arranged at the end of the. A short ring 16 formed of conductive wiring is arranged between the display area and the pad. The short ring 16 and the address line 11 and the signal line 12 are connected via an electrostatic protection means 17. That is, the wirings 11 and 12 are connected via the two electrostatic protection means 17.

The electrostatic protection means 17 plays a role of reducing a potential difference generated in the display area. For example, consider a case where a potential difference occurs between the address line 11a and the address line 11b shown in FIG. As a cause of potential difference,
Examples include friction between the liquid crystal display device and the manufacturing apparatus, and peeling charging. Since such static electricity is not uniformly applied to the liquid crystal display device, a potential distribution is generated in the substrate surface. For example, the potential distribution between the address lines 11a and 11b is mitigated like the path 18 via the electrostatic protection means 17, and electrostatic breakdown can be prevented. Since all the wirings are connected by the short ring 16, the electrostatic breakdown between the signal lines and the electrostatic breakdown between the signal lines and the address lines can be mitigated in the same manner as between the address lines.

As described above, the conventional electrostatic protection means prevents electrostatic breakdown by reducing the in-plane potential difference of the liquid crystal display device. That is, the electrostatic protection means holds the array substrate at the same potential, and prevents the occurrence of interlayer short circuit in the display region and the characteristic deterioration of the thin film transistor due to the potential difference on the surface of the array substrate.

[0008]

However, when a surge voltage is directly applied to the electrode pads 14 and 15 by electrostatic discharge or the like, the conventional electrostatic protection means becomes useless. The static electricity is directly applied to the pad, for example, when only the substrate periphery of the liquid crystal display device is in contact with a part of the manufacturing apparatus. That is, when a potential difference occurs between the manufacturing apparatus and the substrate, electrostatic discharge occurs on the electrode pad, which is the conductive material closest to the edge of the substrate. Further, in the inspection device, the electrode pads 14, 1
Since the inspection probe directly approaches 5, the electric discharge occurs directly from the probe if there is a potential difference between the inspection device and the substrate.

Electrode pad 1 for supplying power to address lines and signal lines
When a surge voltage is applied to Nos. 4 and 15, the influence extends to the display area. The application of such a surge voltage corresponds to application of a high voltage pulse for a short time, instead of application of a drive waveform to the address line and the signal line. Therefore, a high voltage is applied to the wiring itself, and at the same time, the thin film transistor connected to the pixel is affected. Therefore, an interlayer short circuit occurs between the address line and the signal line, and at the same time, an interlayer short circuit occurs in the thin film transistor section.

Further, when electrostatic discharge occurs in the electrode pad, a display defect of the liquid crystal display device may occur even with a weak surge voltage which does not cause the interlayer short circuit as described above. As described above, when the surge voltage is applied to the electrode pad, the thin film transistor is driven with a high voltage for a short time. It is generally known that characteristic changes are observed when electrical stress is applied to a thin film transistor. Although the surge voltage is a short pulse, the voltage reaches several hundreds of volts even with a weak electrostatic discharge in which no interlayer short circuit occurs. The characteristics of the thin film transistor to which electrical stress is applied fluctuates, and affects the pixel potential control.

For example, when a positive surge voltage is applied to the electrode pad of the address line, the threshold voltage of the thin film transistor becomes high and it becomes impossible to apply a sufficient potential to the pixel. As a result, in the normally white mode, the liquid crystal display device produces white image defects. When electrostatic discharge occurs in the electrode pad, electrical stress is applied only to the thin film transistor connected to the pad,
Therefore, the defect caused by this is recognized as a white line defect.

As described above, the conventional static electricity protection means is provided for the purpose of eliminating the potential difference between the wirings, so that the non-uniformity of the in-plane potential distribution caused by the static electricity gradually accumulated during the manufacturing process is eliminated. be able to. However, when a surge voltage due to static electricity or the like is directly applied to the electrode pad, it is impossible to eliminate the potential difference between the wirings in a sufficiently short time without affecting the thin film transistor of the display section. That is, in the conventional liquid crystal display device having such an electrostatic protection function, the influence of the surge voltage applied to the electrode pad due to static electricity or the like cannot be sufficiently prevented from reaching the display area.

The present invention has been made in view of the above problems of the prior art, and when a surge voltage such as static electricity is applied to the power supply electrode pads of the signal lines and address lines, the influence thereof does not reach the display area. It is an object of the present invention to provide a display device having such a surge voltage protection function.

The first object of the present invention is to protect an active matrix type display device against a negative surge voltage to a power supply electrode pad of a signal line, which has the largest adverse effect among surge voltages.

[0015]

A display device having a surge voltage protection function according to a first aspect of the present invention selects a plurality of pixels arranged in a matrix and each having a switching element, and the pixels. In order to achieve, in the active matrix type display device comprising a plurality of signal lines and a plurality of address lines respectively connected to the switching element, between the power supply electrode pad of the signal line and the switching element, Each of the signal lines is grounded via a first surge voltage protection means, wherein the first surge voltage protection means includes a rectifying element and a capacitive element that are connected in series with each other. The cathode is connected to the signal line, the anode is connected to one end of the capacitance element, and the other end of the capacitance element is grounded.

A display device having a surge voltage protection function according to a second aspect of the present invention is the display device according to the first aspect of the present invention, wherein the power supply electrode pad of the address line and the switching element are provided. And each address line is grounded via a second surge voltage protection means, where the second
The surge voltage protection means includes a second rectifying element and a second capacitance element connected in series with each other, one end of the second capacitance element being connected to the address line and the other end being the second capacitance element. Is connected to the anode of the rectifying element and the cathode of the second rectifying element is grounded.

A display device having a surge voltage protection function according to a third aspect of the present invention is the display device according to the first or second aspect of the present invention, wherein a connection node of the first surge voltage protection means is provided. In order to repair the disconnection of the signal line,
The signal line has a redundant structure adjacent to the connection node.

In the device according to the first aspect of the present invention,
When a large negative surge voltage is applied to the power supply electrode pad of the signal line, dielectric breakdown occurs in the capacitive element of the first surge voltage protection means. Therefore, it is possible to prevent the surge current from flowing to the ground and the negative surge voltage from affecting the display area.

In the device according to the second aspect of the present invention,
When a large positive surge voltage is applied to the power supply electrode pad of the address line, dielectric breakdown occurs in the capacitive element of the second surge voltage protection means. Therefore, the surge current is prevented from flowing to the ground and the influence of the positive surge voltage on the display area is prevented.

In the device according to the third aspect of the present invention,
When the signal line is disconnected at the connection node of the first surge voltage protection means due to the surge voltage, the disconnection of the signal line is repaired by the redundant structure, whereby the signal can be sent to the display area.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an equivalent circuit of an active matrix type liquid crystal display device having a surge voltage protection function according to an embodiment of the present invention. The present liquid crystal display device has a plurality of pixels 40 arranged in a matrix, and a thin film transistor 43 is arranged in each pixel 40 as a switching element. To arbitrarily select each pixel 40, a plurality of address lines 41 and a plurality of signal lines 42 are provided. A thin film transistor 43 is arranged and connected at the intersection of the address line 41 and the signal line 42. An electrode pad 4 for power supply is provided at the end of the address line 41 and the signal line 42.
4, 45 are provided. Display area and electrode pads 44, 4
A short ring 46 formed of a conductive wiring is provided between the wiring 5 and the wiring 5 in order to reduce the in-plane distribution of static electricity in the display area. The short ring 46, the address line 41, and the signal line 42 are connected via an electrostatic protection means 47.
That is, the wirings 41 and 42 are connected via the two static electricity protection means 47.

The static electricity protection means 47 can be the same as the static electricity protection means 17 shown in FIG. FIG.
(A), (b) and (c) show circuits that can be used as the electrostatic protection means 47. FIG. 2A shows BACK-TO-B.
The ACK diode 21 is shown in FIG. 2B, the resistor 22 is shown, and FIG. 2C shows the circuit in which the resistor 23 and the capacitor 24 are combined.

Each signal line 42 has a corresponding electrode pad 45.
A surge voltage protection means 48 is connected between the thin film transistor 43 and the switching element. In the present embodiment, the protection means 48 is a circuit in which a diode 52 which is a rectifying element and a capacitor 54 which is a capacitive element are connected in series. The cathode of the diode 52 is connected to the signal line, and the anode is connected to one end of the capacitor 54. The other end of the capacitor 54 is grounded via a ground wire 56.

FIG. 3 is a diagram showing the structure of the thin film transistor 43 and the surge voltage protection means 48 formed on the transparent insulating substrate, for example, the glass substrate 61. The thin film transistor 43 has a gate electrode 62 arranged on the substrate 61, and this is covered with a gate insulating film 63. The gate electrode 62 constitutes a part of the address line 41. An active layer 64 made of an i-type semiconductor is provided on the gate insulating film 63, and the active layer 64 constitutes the source, drain and channel regions of the thin film transistor. A channel protective film 65 made of an insulator is provided on the active layer 64 corresponding to the channel region. Further, contact layers 66a and 66b made of an n + type semiconductor are separately provided on the active layer 64 and the protective film 65 corresponding to the source and drain regions. Source and drain electrodes 67a and 67b are further provided on the contact layers 66a and 66b, respectively. The source electrode 67a is connected to the corresponding pixel electrode 68. The drain electrode 67b constitutes a part of the signal line 42.

The surge voltage protection means 48 has a capacitor electrode 72 arranged on the substrate 61, which is covered with a capacitor insulating film 73. The capacitor electrode 72 and the capacitor insulating film 73 are formed simultaneously with the gate electrode 62 and the gate insulating film 63 of the transistor 43, respectively. The capacitor electrode 72 constitutes a part of the ground wire 56. An anode layer 74 made of an i-type semiconductor and a cathode layer 76 made of an n + type semiconductor are stacked on the capacitor insulating film 73, whereby the diode 52 is formed. The anode layer 74 and the cathode layer 76 are formed simultaneously with the active layer 64 and the contact layers 66a and 66b of the transistor 43, respectively. A cathode electrode 77 is arranged so as to cover the anode layer 74 and the cathode layer 76. The cathode electrode 77 is the source and drain electrodes 67a, 6a of the transistor 43.
It is formed simultaneously with 7b. The cathode electrode 77 is the signal line 4
It forms part of 2.

FIG. 4 shows a method of manufacturing the structure shown in FIG. 3 in the order of steps. First, a transparent insulating substrate, for example, a glass substrate 61
A conductive thin film 82 is deposited on top. The conductive thin film 82 is, for example, a metal thin film formed by depositing Mo, Ta, Al, W, or an alloy containing at least two of them by a sputtering method. Next, the conductive thin film 81 is patterned to form the address line 41 including the gate electrode 62 and the ground line 56 including the capacitor electrode 72. Further, the patterning of the conductive thin film 81 also forms the portion 46b of the short ring 46 (FIG. 4A).

Next, the insulating film 83, the i-type semiconductor layer 84, and the insulating film 85 are sequentially deposited on the substrate 61 by the plasma CVD method (FIG. 4B). Then, the insulating film 85 is patterned to form a channel protective film 65 (FIG. 4C).

The insulating film 83 is, for example, a silicon oxide film,
It is made of a silicon nitride film or a deposited film thereof. The thickness of the insulating film 83 is about 20 in the gate insulating film 63.
0 nm to about 450 nm. When the insulating film 83 has a laminated structure of, for example, a silicon oxide film and a silicon nitride film, the signal line 42 (electrode 67 a) and the address line 41.
In consideration of the insulation property with the (electrode 62), it is preferable that the thickness of the silicon oxide film is about 200 nm to about 400 nm and the thickness of the silicon nitride film is about 30 nm to about 50 nm. Further, in order to improve the state of the interface between the active layer 64 and the gate insulating film 63, the silicon nitride film is in contact with the semiconductor layer 84.

The i-type semiconductor layer 84 is made of, for example, hydrogenated amorphous silicon. The film thickness of the semiconductor layer 84 is about 20.
nm to about 100 nm is preferred. The insulating film 85 serving as the channel protection film 65 is made of, for example, a silicon oxide film, a silicon nitride film, or a deposited film thereof. The thickness of the insulating film 85 is preferably about 100 nm to about 300 nm.

Unlike the structures shown in FIGS. 3 and 4, when the channel protection film can be formed by a self-aligning method using, for example, the gate electrode as a mask, a diode structure near the address line electrode pad is realized. Therefore, a step of removing the channel protective film is required. In this case, the method of removing the channel protective film for realizing the diode structure is as follows. First, a resist pattern formed by exposure using the gate electrode as a mask is subjected to normal photomask exposure to remove the resist pattern other than the thin film transistor portion. Since there is no address line near the signal line pad, no resist pattern is formed, and consideration for such double exposure is unnecessary.

Returning to FIG. 4, after forming the channel protective film 65, the n + type semiconductor layer 86 is deposited by the plasma CVD method (FIG. 4D). The n + type semiconductor layer 86 is made of, for example, a P-doped amorphous silicon film (n + type silicon film). This film can be formed by, for example, a plasma CVD method by mixing a film-forming gas with PH ₃ gas. Next, the i-type semiconductor layer 84 and the n + -type semiconductor layer 8
6 is patterned, and each thin film transistor 43 and the surge voltage protection means 48 are separated (FIG. 4E). At this time, the element (not shown) corresponding to each static electricity protection means 47 is also separated.

Next, a transparent conductive thin film such as ITO (Indi
um Tin Oxide) to form the pixel electrode 68. Next, a contact hole (not shown) is formed in the insulating film 83 in order to connect to the metal layer on the same level as the address line. Next, a metal thin film is deposited and patterned to form the signal line 42 together with the source and drain electrodes 67a and 67b and the cathode electrode 77. At this time, the portion 46a of the short ring 46 is also formed. At this time, an electrode is formed in the contact hole, the address line 41 is connected to the short ring portion 46a via the static electricity protection means 47, and the signal line is also connected via the static electricity protection means 47 to the short ring portion. 46b is connected.

As described above, the thin film transistor 43, the surge voltage protection means 48 and the static electricity protection means 47 can be simultaneously formed in the liquid crystal display device. In the active matrix type liquid crystal display device shown in FIG.
When a large negative surge voltage is applied to the second electrode pad 45, the capacitor 54 of the protection means 48 causes dielectric breakdown. Therefore, it is possible to prevent the surge current from flowing through the ground line 56 and the negative surge voltage from affecting the display area.
On the other hand, when a positive surge voltage is applied to the electrode pad 45 of the signal line 42, the action of the rectifying element 52 does not cause dielectric breakdown of the capacitor 54 of the protection means 48. Therefore, when a positive surge voltage is applied to the electrode pad 45, the influence thereof will reach the display area.
As described below, its adverse effect is small compared to the negative surge voltage.

FIG. 5 shows that in the conventional device, a positive or negative surge voltage (± 400
It shows how the characteristics of the thin film transistor of the pixel closest to the pad shift when V) is applied. Here, the source-drain voltage is 0.1V. In the figure,
"○" shows the reference characteristic when no surge voltage is applied, "x" shows the characteristic after the -400V surge voltage is applied, and "△" shows the + 400V surge voltage after the surge voltage is applied. Show the characteristics. From FIG. 5, it can be seen that the characteristics of the thin film transistor do not significantly deteriorate with respect to the positive surge voltage. That is, in the electrode pad for feeding the signal line, it is only necessary to consider the negative surge voltage.

FIG. 6 shows how much the threshold value of the thin film transistor of each pixel shifts when a negative surge voltage (-400 V) is applied to the power supply electrode pad of the signal line. In the figure, the horizontal axis represents the address line number, that is, this represents the distance from the power supply electrode pad. The shift amount shown on the vertical axis is the difference in the threshold value from the normal time, that is, if it is 0 V, it means that the shift has not occurred from the normal time.
Further, in the figure, line L1 shows the case of the conventional liquid crystal display device shown in FIG. 9, and line L2 shows the case of the liquid crystal display device shown in FIG.

As shown in FIG. 6, in the case of the conventional liquid crystal display device, the closer the transistor of the pixel is to the electrode pad for feeding,
The threshold has shifted significantly. The more the distance from the electrode pad, that is, the internal transistor, the smaller the difference from the normal threshold value, but the shift amount thereof is still large enough to affect the display function.

On the other hand, in the case of the liquid crystal display device of the present invention, even in the transistor of the pixel closest to the power supply electrode pad, the threshold shift amount is 1 V or less, which is a value that does not affect the display function. is there. Also, the further the distance from the electrode pad, the smaller the shift amount of the transistor,
Therefore, in the liquid crystal display device of the present invention, it is understood that even if a negative surge voltage is applied to the power supply electrode pad, the influence thereof does not affect the display region.

As described above, the rectifying element 52 and the capacitive element 54
And surge voltage protection means 4 according to the present invention, which are connected in series.
By connecting 8 to the signal line 42, the display area can be protected from the negative surge voltage applied to the power supply electrode pad 45 of the signal line. Further, the surge voltage protection means 48 according to the present invention can be formed at the same time by utilizing the constituent layers of the switching element (thin film transistor 43) essential for the active matrix type liquid crystal display device. Therefore, the surge voltage protection means 48 according to the present invention
Can be formed without adding another step to the conventional manufacturing process.

FIG. 7 shows a redundant structure of the surge voltage protection means 48 according to the present invention. When a negative surge voltage is applied to the power supply electrode pad 45 of the signal line 42 and a surge current flows through the surge voltage protection means 48 according to the present invention, the protection means 4
There is a possibility that the signal line 42 will be burnt out in correspondence with the eight connection nodes (cathode electrode 77). In this case, the signal line 42
Is disconnected and it becomes impossible to send a signal to the display area.

Assuming such a case, the conductive thin film 82 for forming the gate electrode 62 and the capacitor electrode 72 is formed.
When patterning (see FIG. 4), a repair electrode 92 is provided adjacent to the capacitor electrode 72 on one side or both sides. In addition, the source and drain electrodes 67a and 67b
When patterning the metal thin film to form the cathode electrode 77 and the cathode electrode 77, branch portions 97 of the signal line 42 are provided at positions before and after the cathode electrode 77, respectively. The branch portion 97 of the signal line 42 partially opposes the repair electrode 92 via the insulating film 73. When the signal line 42 is disconnected at the connection node (cathode electrode 77) of the protection means 48 due to the surge voltage, the opposing portion 99 between the branch 97 and the repair electrode 92 is short-circuited by the laser. As a result, the disconnection of the signal line 42 is repaired, and the signal can be sent to the display area.

FIG. 8 shows an equivalent circuit of an active matrix type liquid crystal display device having a surge voltage protection function according to another embodiment of the present invention. 8, those parts that are the same as those in the embodiment shown in FIG. 1 are designated by the same reference numerals, and a description thereof will be omitted.

In this embodiment, not only when a negative surge voltage is applied to the power supply electrode pad 45 of the signal line 42, but also when the power supply electrode pad 44 of the address line 41 is used.
The display area is protected even when a positive surge voltage is applied to the display area. Therefore, the second surge voltage protection means 49 is connected to each address line 41 between the corresponding electrode pad 44 and the thin film transistor 43 which is a switching element. In the present embodiment, the protection means 49 is similar to the first surge voltage protection means 48 in that the diode 53 which is a rectifying element and the capacitor 55 which is a capacitive element.
It consists of a circuit in which and are connected in series. One end of the capacitor 55 is connected to the address line 41, and the other end is the diode 53.
Connected to the anode. The cathode of the diode 53 is grounded via a ground wire 57.

The second surge voltage protection means 49 has the same structure as the first surge voltage protection means 48 shown in FIG.
It is formed at the same time as the thin film transistor 43 by the same method as the formation method of the first surge voltage protection means 48 described above. However, the lower capacitor electrode 72 is designed to form a part of the address line 41, while the cathode electrode 77 is designed to form a part of the ground line 57.

In the active matrix type liquid crystal display device shown in FIG. 8, the electrode pad 44 of the address line 41 is used.
If a large positive surge voltage is applied to the
The capacitor 53 of 9 causes dielectric breakdown. Therefore, it is possible to prevent the surge current from flowing through the ground line 57 and the influence of the positive surge voltage from reaching the display area. On the other hand, address line 4
When a negative surge voltage is applied to the first electrode pad 44, the action of the rectifying element 53 does not cause dielectric breakdown of the capacitor 55 of the protection means 49. Therefore, when a negative surge voltage is applied to the electrode pad 44, its influence extends to the display area, but its adverse effect is smaller than that of the positive surge voltage.

As described above, the rectifying element 53 and the capacitive element 55.
By connecting the second surge voltage protection means 49 according to the present invention, which is connected in series, to the address line 41, the display area is protected from the positive surge voltage applied to the power supply electrode pad 44 of the address line. be able to. Further, the second surge voltage protection means 49 according to the present invention can be formed at the same time by utilizing the constituent layers of the switching element (thin film transistor 43) essential for the active matrix type liquid crystal display device. Therefore, the second surge voltage protection means 49 according to the present invention can be formed without adding another step to the conventional manufacturing process.

In the second surge voltage protection means also, a redundant structure as shown in FIG. 7 can be provided in preparation for disconnection of the address line 41 at the connection node of the protection means 49 due to a surge current. In this case, a branch portion is formed in the address line 41 before and after the capacitor electrode 72, and a repair electrode is formed correspondingly by using a metal thin film for forming the cathode electrode 77.

[0047]

According to the present invention, by connecting the first surge voltage protection means in which the rectifying element and the capacitive element are connected in series to the signal line, the negative voltage applied to the power supply electrode pad of the signal line is reduced. The display area can be protected from the surge voltage.

Further, according to the present invention, by connecting the second surge voltage protection means, in which the rectifying element and the capacitive element are connected in series, to the address line, a positive voltage applied to the power supply electrode pad of the address line. The display area can be protected from the surge voltage.

Further, according to the present invention, by providing the signal line with the redundant structure corresponding to the connection node of the first surge voltage protection means, when the signal line is disconnected at the portion due to the surge voltage, the signal line is disconnected. Can be repaired and a signal can be sent to the display area.

The first and second surge voltage protection means can be formed at the same time by utilizing the constituent layers of the switching element (thin film transistor). Therefore,
The first and second surge voltage protection means according to the present invention can be formed without adding another step to the conventional manufacturing process.

[Brief description of drawings]

FIG. 1 is a diagram showing an equivalent circuit of an active matrix type liquid crystal display device having a surge voltage protection function according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of electrostatic protection means of the apparatus shown in FIG.

FIG. 3 is a cross-sectional view showing a thin film transistor and surge voltage protection means of the device shown in FIG.

4A to 4D are views showing a method of manufacturing the structure shown in FIG.

FIG. 5 is a graph showing how, when a positive or negative surge voltage is applied to a power supply electrode pad of a signal line in a conventional device, characteristics of a thin film transistor of a pixel closest to the pad shift.

FIG. 6 is a graph showing how the threshold value of the thin film transistor of each pixel shifts when a negative surge voltage is applied to a power supply electrode pad of a signal line in the device of the present invention and the conventional device.

FIG. 7 is a diagram showing a redundant structure of surge voltage protection means according to the present invention.

FIG. 8 is a diagram showing an equivalent circuit of an active matrix type liquid crystal display device having a surge voltage protection function according to another embodiment of the present invention.

FIG. 9 is a diagram showing an equivalent circuit of a conventional active matrix type liquid crystal display device.

[Explanation of symbols]

40 ... Pixel, 41 ... Address line, 42 ... Signal line, 43 ...
Thin film transistors, 44, 45 ... Electrode pads, 46 ... Short ring, 47 ... Antistatic means, 48, 49 ... Surge voltage protection means, 52, 53 ... Diodes, 54, 5
5 ... Capacitor, 56, 57 ... Ground wire.

Claims (3)

[Claims] 1. A plurality of pixels arranged in a matrix and each having a switching element, and a plurality of signal lines and a plurality of address lines respectively connected to the switching element for selecting the pixel. In the active matrix type display device, the signal lines are grounded via a first surge voltage protection means between the power supply electrode pad of the signal line and the switching element, wherein 1 surge voltage protection means comprises a rectifying element and a capacitive element connected in series with each other, the cathode of the rectifying element is connected to the signal line and the anode is connected to one end of the capacitive element, and Display device having surge voltage protection function characterized in that the other end of the capacitive element is grounded 2. The address line is grounded via a second surge voltage protection means between the power supply electrode pad of the address line and the switching element, wherein the second surge voltage protection is provided. Second means connected in series with each other
Rectifying element and a second capacitance element, one end of the second capacitance element is connected to the address line and the other end is connected to the anode of the second rectification element, and The display device having a surge voltage protection function according to claim 1, wherein the cathode of the rectifying element is grounded. 3. The signal line has a redundant structure adjacent to the connection node in order to repair the disconnection of the signal line at the connection node of the first surge voltage protection means. A display device having the surge voltage protection function described in 1 or 2.