JPH10177186A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a liquid crystal display device having nonlinear element, which does not bring increase of production stages, by connecting the gate electrode formed simultaneously with pixel electrode to drain electrode through the contact holes formed at protective film. SOLUTION: The gate electrode ITO are formed of the same material as the material of the pixel electrodes ITO and simultaneously with the formation of the pixel electrodes ITO in the regions of the front surfaces of the protective films 38 where the nonlinear elements NR on the respective sides with respect to scanning signal wirings Gi are formed. The gate electrodes ITO are connected to the drain electrodes of the respective nonlinear elements NR through the contact holes TH in these elements. The contact holes TH are formed simultaneously with the formation of the contact holes TH for connecting the pixel electrodes ITO and the source electrodes of thin-film transistors TFTs in a display section. The formation of the nonlinear elements NR without increasing the production constitution is, therefore, made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display, and more particularly to an active matrix type liquid crystal display.

[0002]

2. Description of the Related Art An active matrix type liquid crystal display device extends in the x direction and is arranged in the y direction on a liquid crystal side surface of one of a pair of transparent substrates disposed opposite to each other via a liquid crystal. Scanning signal lines to be provided, and video signal lines extending in the y-direction and insulated from each of the scanning signal lines, are formed in parallel with each other in the x-direction, and rectangular regions surrounded by these signal lines are formed. Are configured as pixel regions.

To each of these pixel regions, a thin film transistor turned on by a scanning signal (voltage) from a scanning signal line and a video signal (voltage) from a video signal line are applied via the turned on thin film transistor. Pixel electrodes.

On the other hand, in such a liquid crystal display device,
Since the characteristics of each thin film transistor are easily changed by static electricity applied for some reason through the scanning signal wiring or the video signal wiring, those having a so-called static electricity protection circuit have been known.

That is, in the peripheral portion of the display section composed of a group of pixel areas, and in a portion filled with liquid crystal, an unterminated common line is formed so as to surround the display section. The scanning signal wiring and the video signal wiring are connected to each other via non-linear elements at respective intersections to form the electrostatic protection circuit. In such an electrostatic protection circuit, even if static electricity enters from the scanning signal wiring or the video signal wiring, the static electricity is distributed to the common wiring via the nonlinear element, and the thin film transistor can be protected.

In this case, in order to prevent the number of steps from being increased by manufacturing the non-linear element, a configuration almost similar to that of the thin-film transistor is adopted, and the non-linear element is formed in parallel with the manufacturing of the thin-film transistor. And a drain electrode (or a source electrode) are connected to each other via a conductive layer.

On the other hand, in such a liquid crystal display device, in order to realize a bright screen display, a device for increasing a so-called aperture ratio by increasing a pixel electrode in a pixel region as much as possible has been devised.

For this reason, the pixel electrode is formed on the upper surface of the insulating film (protective film) formed to cover the scanning signal wiring, the video signal wiring and the thin film transistor, and the contact hole formed in the insulating film is formed. Through a thin film transistor connected to one electrode (source electrode) of the thin film transistor.

In the liquid crystal display device having such a configuration, for example, a large pixel electrode can be formed without worrying about contact with a video signal wiring or the like, so that the aperture ratio can be improved.

[0010]

However, in such a liquid crystal display device in which the pixel electrode is formed on the upper surface of the protective film, if the non-linear element of the electrostatic protection circuit is formed in the same configuration as the conventional thin film transistor,
The problem of increasing the number of manufacturing steps has been pointed out.

That is, since the gate electrode and the drain electrode (source electrode) of the non-linear element are arranged via the insulating film (gate insulating film), in order to connect with each of these electrodes, the insulating film However, there is a problem that a contact hole must be specially formed.

The present invention has been made based on such circumstances, and an object of the present invention is to provide a liquid crystal display device having a non-linear element which does not increase the number of manufacturing steps.

[0013]

In order to achieve the above object, the present invention basically comprises the following means.

That is, a scanning signal line extending in the x-direction and juxtaposed in the y-direction is provided on the surface of one of the pair of transparent substrates opposed to each other via the liquid crystal on the liquid crystal side; A video signal line insulated by the scanning signal line and extending in the y direction and arranged in the x direction is formed, and supply of the scanning signal from the scanning signal line to each pixel region surrounded by the signal lines. A thin film transistor that is turned on by a pixel electrode to which a video signal from a video signal wiring is applied via the turned on thin film transistor;
The pixel electrode is formed on a protective film formed to cover each of the signal lines and the thin film transistor. The pixel electrode includes a common line formed around a display unit including a group of the pixel regions. In a liquid crystal display device provided with an electrostatic protection circuit including a non-linear element formed between the common wiring and each of the signal wirings, the non-linear element is a semiconductor layer formed simultaneously with a semiconductor layer of a thin film transistor. And a drain electrode and a source electrode formed simultaneously with the video signal wiring on the semiconductor layer;
A gate electrode formed on the surface of the protective film and formed simultaneously with the pixel electrode, wherein the gate electrode is connected to the drain electrode through a contact hole formed in the protective film. is there.

In the liquid crystal display device configured as described above, the connection between the drain electrode and the gate electrode of the non-linear element must be performed through a contact hole formed in the protective film. In addition, the contact hole for connecting the pixel electrode in the display portion to the source electrode of the thin film transistor can be formed at the same time.

Therefore, it is possible to obtain a liquid crystal display device having a non-linear element which does not increase the number of manufacturing steps.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the liquid crystal display device according to the present invention will be described below with reference to FIGS.

The entire TFT substrate configuration First, FIG. 2, one of the transparent substrate of the pair of transparent substrates which are arranged to face each other through a liquid crystal, the liquid crystal side surface of the transparent substrate, referred to as a so-called TFT substrate TFTSUB FIG. 3 is a plan view showing a configuration. Although the other transparent substrate opposed to the TFT substrate TFTSUB is not shown, it is arranged opposite to the one-dot chain line as an outer contour in the figure, and a common electrode (common to each pixel) is provided on its liquid crystal side surface. In the case of color display, a color filter is formed for each corresponding pixel.

On the surface of such a TFT substrate FTFSUB, first, scanning signal lines G0 to Gi to Gn are formed which extend in the x direction in the drawing and are arranged in parallel in the y direction. At one end (left side in the figure) of each of the scanning signal lines G0 to Gi to Gn, a terminal portion GPAD is provided at a side portion of the TFT substrate TFTSUB. These terminals GPA
D is a terminal unit connected to, for example, an external drive circuit for supplying a scanning signal.

Each of the scanning signal lines G0 to Gi to
Video signal wirings D1 to Di to Dm are formed extending in the y direction in the drawing and juxtaposed in the x direction via Gn and an interlayer insulating film.

At one end (upper side in the figure) of each of these video signal wirings D1 to Di to Dm, a TFT substrate TFTS
A terminal portion DPAD is provided at a side portion of the UB.
Each of these terminal portions DPAD is a terminal portion connected to, for example, an external drive circuit for supplying a video signal.

Each of the regions surrounded by each of the scanning signal lines G0 to Gi to Gn and each of the video signal lines D0 to Di to Dm constitutes a pixel region.
1), (1, 2), ..., (2, 1), (2, 2), ...,
A set of (m, n) constitutes a display unit (a part surrounded by a dotted line in the figure). The detailed configuration of each pixel region in the display unit will be described later.

Further, in the peripheral portion of the display portion, a portion filled with liquid crystal between another opposing transparent substrate OPSUB (a portion constituting the outline thereof is formed with a sealant for sealing the liquid crystal). And is indicated by a dashed line in the figure).
An electrostatic protection circuit is formed.

In this electrostatic protection circuit, an unterminated common line NRGND is formed so as to surround the display section, and the common line NRGND is connected to the scanning signal lines G0 to G0 crossing the common line NRGND.
Gn and each of the video signal lines D1 to Dm are connected via a non-linear element NR.

This static electricity protection circuit includes a scanning signal line Gi
Alternatively, when static electricity enters the video signal line Dj for some reason, the common line NRG
It has a function of distributing to ND.

In such an electrostatic protection circuit, the nonlinear elements INT of the scanning signal lines G0 to Gi to Gn are provided.
Are connected to the common wiring NRGND via the scanning signal wiring side, and are called video signal wirings D0 to Dj to
The connection between the Dm nonlinear element INT and the common line NGND is referred to as an electrostatic protection circuit on the video signal line side.

The structure of each pixel region and the electrostatic protection circuit will be described below in order separately for the electrostatic protection circuit on the scanning signal wiring side and the electrostatic protection circuit on the video signal wiring side.

Configuration of each pixel area These pixel areas (1, 1), (1, 1),.
Each of n) is configured as shown in FIG. FIG. 3B is a cross-sectional view taken along the line IIIb-IIIb in FIG. Hereinafter, each component will be described in the order of the manufacturing process.

In the figure, first, a TFT substrate TFTS
The scanning signal lines Gi and Gi-1 are formed on the UB so as to extend in the x direction in the drawing and to be separated from each other. The material of the scanning signal lines Gi and Gi-1 is not particularly limited, but in this embodiment, for example, an alloy layer of Cr and Mo is used.

The vicinity of the scanning signal wiring Gi (the lower scanning signal wiring in the figure) is a region where a so-called inverted staggered thin film transistor TFTT is formed.
At the time of forming the scanning signal wiring Gi, a part thereof is extended to the region so that the gate electrode 26G of the thin film transistor TFT is formed.

Then, a silicon nitride film to be a gate insulating film 26I and a semiconductor layer 26S made of amorphous Si, for example, are formed so as to cover the gate electrode 26G.
Is formed.

The thin film transistor TFT is formed by forming the drain electrode Ed and the source electrode Es apart from each other on the upper surface of the semiconductor layer 26S. The electrodes Ed and Es are connected to the video signal wiring Dj. Are formed simultaneously with the formation of

That is, the video signal wiring Dj is, for example, C
A drain electrode Ed is formed by being formed of an alloy layer of r and Mo, a part of which is formed to extend, and at the same time, a source electrode Es is formed to achieve conduction with a pixel electrode ITO described later. Have been.

In order to insulate the video signal wiring Dj from the scanning signal wiring Gi or the like, an interlayer insulating film formed simultaneously with the above-described laminated body of the silicon nitride film and the semiconductor layer at the intersection thereof is formed. It is formed on the film 36.

In this embodiment, the semiconductor layer 26
For example, N for making ohmic contact with the drain electrode Ed and the source electrode Es is formed on the entire surface of S.
Forming a contact layer doped with a p-type impurity layer, forming the electrodes Ed and Es, and then forming the electrodes Ed and Es.
The contact layer is etched using the mask as a mask, so that the contact layer is left under the electrodes Ed and Es.

A protective film 38 made of, for example, a silicon nitride film is formed on the entire upper surface of the TFT substrate TFTSUB thus processed. This is for avoiding direct contact between the thin film transistor TFT and the liquid crystal to prevent deterioration of the characteristics of the thin film transistor TFT.

Further, on the upper surface of the protective film 38, a pixel electrode ITO is formed by a transparent conductive material made of, for example, ITO (Indium-Tin-Oxide), and a part thereof is formed by a contact formed on the lower protective film 38. It is connected to the source electrode Es through a hole TH.

By forming such a pixel electrode ITO on the protective film 38, the video signal lines Dj, D
As described above, since there is no fear of electrical contact of j + 1, the area can be increased and the so-called aperture ratio can be improved.

A part of the pixel electrode ITO is extended, and another video signal wiring Gi- adjacent to a video signal wiring Gi for turning on the thin film transistor TFT in the figure is provided.
By being superimposed one by one, an additional capacitance element Cadd using the protective film 38 as a dielectric film is configured. This additional capacitance element Cadd is a thin film transistor T
This is provided for storing a video signal in the pixel electrode ITO for a long time when the FT is turned off.

The diagram 1 of the electrostatic protection circuit of the scanning signal line side, the scanning signal lines G0, ..., Gi, ..., shows the structure of an electrostatic protection circuit which is formed between the Gn and the common wiring NRGND 2 shows the configuration of a portion surrounded by, for example, a dotted circle A in FIG.

FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view taken along line bb of FIG. 1A.

In the figure, first, a scanning signal wiring Gi extending in the x direction is formed, and on both sides of the scanning signal wiring Gi, a region where a nonlinear element NR is formed is formed.

Here, first, the scanning signal wiring Gi has a structural feature in that an electrode corresponding to the gate electrode 26G of the thin film transistor TFT is not formed in the formation region of the nonlinear element NR. As described later in detail, an ITO formed simultaneously with the formation of the pixel electrode ITO is formed.
This is because a film is formed as the electrode.

That is, while the thin film transistor TFT has an inverted stagger structure, the nonlinear element NR in this embodiment is of a coplanar type.

The nonlinear elements NR on both sides of the scanning signal line Gi
Is formed in the region where the insulating film 26I and the semiconductor layer 26S are sequentially laminated. This laminate P
L is formed in the same step as that in the formation region of the thin film transistor TFT.

Here, each of the stacked bodies PL in each of the nonlinear elements NR may be formed independently. However, in this embodiment, the stacked bodies PL are formed as an integrated body connected in a formation region of a common wiring NGND described later. I have.

The common wiring N extending in the y direction in the drawing
RGND is formed. This common wiring NGND
Are the video signal wirings D1,..., Dj,.
Dm and the same material as the video signal wiring D
, Dj,..., Dm.

The common line NRGND is connected to the stacked body PL of the upper non-linear element NR with respect to the scanning signal line Gi.
The drain electrode is formed integrally with a drain electrode (an electrode to be connected to a gate electrode described later is referred to as a drain electrode for convenience, and the other electrode is referred to as a source electrode) formed on the surface of the drain electrode. Electrode and common wiring N
The connection portion with RGND has a relatively large area for connection with a gate electrode described later.

Further, the common wiring NRGND is provided with a stacked body P of non-linear elements NR below the scanning signal wiring Gi.
It is formed integrally with a source electrode formed on the surface of L.

On the other hand, another conductive layer CL (a conductive layer physically separated from the common wiring NRGD) made of the same material as the common wiring NRGND and formed in the same process as the common wiring NRGND is used. The conductive layer CL has
A source electrode formed on the surface of the stacked body PL of the upper non-linear element NR with respect to the scanning signal wiring Gi is integrally formed, and the stacked body PL of the lower non-linear element NR with respect to the scanning signal wiring Gi is formed. A drain electrode formed on the surface is integrally formed.

The connection between the drain electrode formed on the surface of the stacked body PL of the non-linear element NR below the scanning signal wiring Gi and the conductive layer CL is for connection with the gate electrode described later. The area is relatively large.

A contact layer doped with an N-type impurity is formed over the entire surface of the upper semiconductor layer 26S constituting the stacked body PL. After forming each electrode, the contact layer is used as a mask. The contact layer is etched so that the contact layer is left under each electrode as in the case of the thin film transistor TFT.

On the surface thus processed, a protective film 38 formed in the same process as the protective film 38 in the display section is formed.
Are formed on the protective film 38, a part of the connection between the drain electrode formed on the surface of the stacked body PL of the nonlinear element NR above the scanning signal wiring Gi and the common wiring NGND, and the scanning signal wiring A contact hole TH for exposing a part of a connection portion between the drain electrode formed on the surface of the stacked body PL of the nonlinear element NR below Gi and the conductive layer CL is formed.

The contact hole TH is formed simultaneously with the formation of the contact hole TH for connecting the source electrode Es of the thin film transistor TFT and the pixel electrode ITO in the display section.

Then, on the upper surface of the protection film 38, the formation region of the nonlinear element NR on each side with respect to the scanning signal wiring Gi is formed.
The gate electrode ITO is formed of the same material as the pixel electrode ITO and simultaneously with the formation of the pixel electrode ITO.

The gate electrode ITO is connected to the drain electrode of each nonlinear element NR via the contact hole TH.

As will be apparent from the above description, the connection between the drain electrode and the gate electrode of the nonlinear element NR must be made through the contact hole TH formed in the protective film 38. The hole TH can be formed simultaneously with the formation of the contact hole TH for connecting the pixel electrode ITO and the source electrode Es of the thin film transistor TFT in the display unit.

Therefore, the non-linear element NR can be formed without increasing the manufacturing structure.

[0059] Configuration 4 of the electrostatic protection circuit of the video signal wiring side, each video signal lines D1, ..., Dj, ..., shows the structure of an electrostatic protection circuit which is formed between the Dm and the common wiring NRGND 2 shows a configuration of a portion surrounded by, for example, a dotted line circle B in FIG.

FIG. 4A is a plan view, and FIG. 4B is a cross-sectional view taken along the line bb of FIG. 4A.

First, as shown in FIG. 4A, both sides of a later-described common line NGND (extending in the x direction in the figure) are formed with the nonlinear element NR.
The nonlinear element NR in this case also has a coplanar structure similarly to the nonlinear element NR on the scanning signal wiring side.

The formation region of each of these nonlinear elements NR includes
A stacked body PL in which the insulating film 26I and the semiconductor layer 26S are sequentially stacked is formed. This laminate PL is formed in the same step as that in the formation region of the thin film transistor TFT.

Here, each of the stacked bodies PL in each of the nonlinear elements NR may be formed independently, but in the present embodiment, they are formed as an integrated body connected in a formation region of a video signal wiring Dj described later. ing.

Then, a video signal wiring Dj extending in the y direction in the figure is formed. This video signal wiring Dj is connected to a non-linear element NR on the upper side with respect to a later-described common wiring NGND.
Are formed integrally with a drain electrode (an electrode to be connected to a gate electrode described later is referred to as a drain electrode for convenience, and the other electrode is referred to as a source electrode) formed on the surface of the stacked body PL. In addition, the connection portion between the drain electrode and the video signal wiring Dj has a relatively large area for connection with a gate electrode described later.

Further, the video signal wiring Dj is formed integrally with a source electrode formed on the surface of the stacked body PL of the non-linear element NR below the common wiring NGND, which will be described later.

On the other hand, another conductive layer CL1 made of the same material as the video signal wiring Dj and formed in the same step as the video signal wiring Dj (a conductive layer physically separated from the video signal wiring Dj) Layer), and the conductive layer CL1
The non-linear element N on the upper side with respect to a common wiring NGND
The source electrode formed on the surface of the stacked body PL of R is integrally formed, and the drain electrode formed on the surface of the stacked body PL of the non-linear element NR on the lower side with respect to a common wiring NGND which will be described later. Have been.

Then, a connection portion between the drain electrode formed on the surface of the stacked body PL of the non-linear element NR below the common wiring NGND to be described later and the conductive layer CL1 (in this embodiment, the connection between the common wiring NRGGND and the The “overlap” is formed to have a relatively large area for connection with a gate electrode described later.

Note that a contact layer doped with an N-type impurity is formed on the entire surface of the upper semiconductor layer 26S constituting the stacked body PL. After forming each electrode, the contact layer is formed by using each electrode as a mask. The contact layer is etched so that the contact layer is left under each electrode as in the case of the thin film transistor TFT.

On the surface thus processed, a protective film 38 formed in the same step as the protective film 38 in the display section is formed.
This protective film 38 has a common wiring N to be described later.
Part of the connection between the drain electrode formed on the surface of the stacked body PL of the nonlinear element NR on the upper side with respect to RGND and the video signal wiring Dj, and the stacking of the nonlinear element NR on the lower side with respect to the common wiring NRGND described later A contact hole TH (in this embodiment, overlaps with a later-described common wiring NGND) for exposing a part of a connection portion between the drain electrode formed on the surface of the body PL and the conductive layer CL1 is formed.

The contact hole TH is formed simultaneously with the formation of the contact hole TH for connecting the source electrode Es of the thin film transistor TFT and the pixel electrode ITO in the display section.

On the upper surface of the protective film 38, a common wiring NGND extending in the x direction in the figure is formed of the same material as the pixel electrode ITO and simultaneously with the formation of the pixel electrode ITO.

In this case, the common wiring NRGND is formed integrally with the gate electrode of the non-linear element NR below it, and is connected to the conductive layer CL1, ie, the drain electrode of the non-linear element NR, through the above-described contact hole TH. It is to be connected.

On the other hand, there is a conductive layer CL2 which is formed of the same material as that of the common wiring NRGND, and is formed physically at the same time as being separated from the common wiring NRGND. The gate electrode of the upper nonlinear element NR is formed, and is connected to the drain electrode of the nonlinear element NR through the contact hole TH.

As is apparent from the above description, the connection between the drain electrode and the gate electrode of the nonlinear element NR must be made through the contact hole TH formed in the protective film 38. The hole TH can be formed simultaneously with the formation of the contact hole TH for connecting the pixel electrode ITO and the source electrode Es of the thin film transistor TFT in the display unit.

For this reason, the nonlinear element NR can be formed without increasing the manufacturing structure.

[0076] Another embodiment Figure 5 of the present invention is a constitutional view showing another embodiment according to the present invention, FIG. 1
FIG. 3B shows a cross-sectional view of the nonlinear element NR corresponding to FIG.

The structure different from FIG. 1B is that the gate electrode is formed without overlapping the source electrode. Since a protective film having a relatively low withstand voltage has a function as a gate insulating film, it is intended to secure a withstand voltage by such a configuration.

FIG. 6 is a block diagram showing another embodiment of the present invention, and is a sectional view of the nonlinear element NR corresponding to FIG. 1B.

The structure different from that of FIG. 1B is that a so-called channel protect layer CH is formed on the surface of the semiconductor layer 26S.
P is provided. Usually, the semiconductor layer 26S is made of an extremely thin layer, and when etching is performed using the drain electrode and the source electrode as a mask, the semiconductor layer 26S
Is prevented from being excessively etched.

Further, in each of the embodiments described above, the scanning signal lines G0,..., Gi,.
It is explained that it is composed of a material consisting of an alloy of o, but is not limited to this, other metals or alloys,
Alternatively, it is needless to say that Al whose surface is anodized may be used.

In the case where Al whose surface is anodized is used as the scanning signal lines G0,..., Gi,. , Gn, and requires a step of removing the anodic oxide film at the connection portion in order to make a connection between the gate electrode and the drain electrode. This has the effect that such work is not required.

[0082]

As is apparent from the above description,
ADVANTAGE OF THE INVENTION According to the liquid crystal display device by this invention, the nonlinear element of an electrostatic protection circuit can be formed, without increasing a manufacturing process.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an electrostatic protection circuit on a scanning signal wiring side of a liquid crystal display device according to the present invention, wherein (a) is a plan view and (b) is a cross section taken along line bb of (a). FIG.

FIG. 2 is an overall schematic plan view showing one embodiment of a TFT substrate of the liquid crystal display device according to the present invention.

FIG. 3 is a configuration diagram showing one embodiment of a configuration of a pixel region formed on a TFT substrate surface of the liquid crystal display device according to the present invention;
3A is a plan view, and FIG. 3B is a cross-sectional view taken along line IIIb-IIIb of FIG.

4A and 4B are configuration diagrams showing an embodiment of an electrostatic protection circuit on a video signal wiring side of a liquid crystal display device according to the present invention, wherein FIG. 4A is a plan view and FIG. 4B is a cross section taken along line bb of FIG. FIG.

FIG. 5 is a sectional view showing another embodiment of the present invention.

FIG. 6 is a sectional view showing another embodiment of the present invention.

[Explanation of symbols]

G0 to Gn: scanning signal wiring, D1 to Dm: video signal wiring, NRGND: common wiring, NR: nonlinear element, ITO
... ITO film.

Continuation of the front page (72) Inventor Minoru Hiroshima 3300 Hayano Mobara-shi, Chiba Pref. Electronic Device Division, Hitachi, Ltd.

Claims (3)

[Claims] 1. A liquid crystal side surface of one of a pair of transparent substrates disposed opposite to each other via a liquid crystal,
A scanning signal line extending in the x direction and juxtaposed in the y direction and a video signal line insulated by the scanning signal line and extending in the y direction and juxtaposed in the x direction are formed. Each pixel region surrounded by a thin film transistor that is turned on by the supply of a scanning signal from the scanning signal wiring, and a pixel electrode to which a video signal from the video signal wiring is applied through the turned on thin film transistor, The pixel electrode is formed on a protective film formed to cover each of the signal lines and the thin film transistor, and includes a common line formed to surround a display unit including a group of the pixel regions. A liquid crystal display device provided with an electrostatic protection circuit including a non-linear element formed between the common wiring and each of the signal wirings, wherein the non-linear element is a thin film transistor. A semiconductor layer formed simultaneously with the semiconductor layer of the transistor, a drain electrode and a source electrode formed simultaneously with the video signal wiring on the semiconductor layer, and a gate electrode formed on the surface of the protective film and formed simultaneously with the pixel electrode Wherein the gate electrode is connected to the drain electrode through a contact hole formed in the protective film. 2. The device according to claim 1, wherein the non-linear element is connected between a scanning signal line and a common line, and the common line is formed simultaneously with the video signal line. Liquid crystal display device. 3. The device according to claim 1, wherein the non-linear element is connected between a video signal line and a common line, and the common line is formed simultaneously with a pixel electrode.
3. The liquid crystal display device according to 1.