JP2002072246A - Liquid crystal display - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To prevent the occurrence of liquid crystal spots on a display unit. SOLUTION: A switching element driven by supply of a scanning signal from a gate signal line to a pixel region on a liquid crystal side surface of one of the substrates opposed to each other via a liquid crystal, and A pixel electrode to which a video signal is supplied from the drain signal line, and a counter electrode for generating an electric field having a substantially parallel component of the substrate are formed between the pixel electrode and the pixel electrode. A conductive layer which is hardly oxidized is formed on the surface so as to overlap with the gate signal line, and this conductive layer is maintained at a potential serving as an anode with respect to a low potential of the scanning signal.

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 a liquid crystal display called a horizontal electric field type.

[0002]

2. Description of the Related Art In an in-plane switching mode liquid crystal display device, a pixel electrode and a counter electrode are formed in each pixel region of one of the transparent substrates opposed to each other via a liquid crystal on the liquid crystal side. The light transmittance of the liquid crystal is controlled by an electric field having a component substantially parallel to the transparent substrate between the electrodes.

In the active matrix type, each pixel area is provided with a switching element, and each pixel area extends in the x direction on the one transparent substrate side and y
Switching which is constituted by a region surrounded by gate signal lines juxtaposed in the direction and drain signal lines extending in the y direction and juxtaposed in the x direction and driven by a scanning signal from one of the gate signal lines. A video signal from one drain signal line is supplied to the pixel electrode via the element.

[0004] The liquid crystal side surface of such a transparent substrate is formed of a laminate of a conductive layer, a semiconductor layer and an insulating layer selectively etched into a predetermined pattern by a photolithography technique. Etc. are formed.

[0005]

However, it has been pointed out that in the liquid crystal display device constructed as described above, a stain due to a decrease in the specific resistance of the liquid crystal is often confirmed on the display portion.

[0006] The present inventors have investigated the cause, and as a result,
If there is a pinhole due to poor coverage or foreign matter in an insulating film or the like that avoids direct contact with liquid crystal such as a signal line or an electrode, a leak current flows between the signal line or the electrode and the like, and the signal line Alternatively, it has been found that the ions of the metal constituting the electrodes flow out into the liquid crystal, causing a decrease in the specific resistance of the liquid crystal.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a liquid crystal display device in which a display section is prevented from being stained.

[0008]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, the liquid crystal display device according to the present invention comprises:
Basically, a switching element driven by supplying a scanning signal from a gate signal line to a pixel region on a liquid crystal side surface of one of the substrates opposed to each other via a liquid crystal, and the switching element A pixel electrode to which a video signal is supplied from a drain signal line via the pixel electrode, and a counter electrode for generating an electric field having a substantially parallel component of the substrate are formed between the pixel electrode and the pixel electrode. A conductive layer which is hardly oxidized so as to be superposed on the gate signal line, and which is kept at a potential serving as an anode with respect to a low potential of the scanning signal. is there.

[0010] The liquid crystal display device configured as described above can be connected to the liquid crystal through the liquid crystal when, for example, a coverage defect occurs in a part of the insulating film covering the gate signal line, or when a pinhole is caused by a foreign substance or the like. Then, a current flows between the conductive layer and another transparent substrate facing the conductive layer (in this case, electrons move from the gate signal line side to the conductive layer side), but the conductive layer is hardly oxidized. Since it is made of a material, the metal ions (which are ionized by the electrons) are not eluted, and it is possible to prevent the liquid crystal from being stained by the metal ions.

[0011] Also, at other places close to the gate signal line, if the insulation film covering the metal layer to which a higher voltage is applied has poor coverage or a pinhole, this metal layer and the gate An electric current flows between the signal lines and metal ions may be eluted from the metal layer, but when the distance between the gate signal line and the conductive layer is shorter than the distance between them, Since the current easily flows in this shorter portion, elution of metal ions from the metal layer can be prevented.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the liquid crystal display of the present invention will be described below with reference to the drawings. << Overall Configuration >> FIG. 2 is an overall configuration diagram showing one embodiment of the liquid crystal display device according to the present invention. In the figure, first, TF
There is a transparent substrate SUB1 called a T substrate. Then, an FI arranged opposite to the transparent substrate SUB1 via a liquid crystal is provided.
There is a transparent substrate SUB2 called an L substrate.

The transparent substrate SUB2 is formed to be slightly smaller in area than the transparent substrate SUB1, and the lower side and the right side in the figure are flush with each other to form the upper side of the transparent substrate SUB1 in the figure. The left side portion is exposed from the transparent substrate SUB2.

A drain signal terminal group DTM is formed on the upper side of the transparent substrate SUB1, and each of these drain signal terminals is connected to a drain signal line DL described later.

A gate signal terminal group GTM is formed on the left side of the transparent substrate SUB1, and each of these gate signal terminals is connected to a gate signal line GL described later.

Transparent substrate SUB to transparent substrate SUB1
2 is a sealing material S having a function of sealing liquid crystal.
L, and a region surrounded by the sealing material SL is a liquid crystal display region AR. The sealing material SL contains a spacer for holding each of the transparent substrates SUB1 and SUB2 at a predetermined gap.

The liquid crystal display area AR is formed by arranging a large number of pixel areas in a matrix, and each of these pixel areas incorporates a circuit corresponding to an equivalent circuit shown in FIG.

That is, each pixel region is surrounded by a gate signal line GL extending in the x direction and juxtaposed in the y direction and a drain signal line DL extending in the y direction and juxtaposed in the x direction. In the pixel region, for example, a counter voltage signal line CL extending in the x direction is arranged.

In the pixel area, a thin film transistor TFT driven by the supply of a scanning signal from one gate signal line GL and a pixel to which a video signal from a drain signal line DL is supplied via the thin film transistor TFT. A transparent substrate SUB is provided between the electrode PX and the pixel electrode PX.
Counter electrode C for generating an electric field having a component parallel to 1
T is formed.

The counter electrode CT is supplied with a reference voltage signal (for a video signal) from the counter voltage signal line CT.

<< Structure of Pixel >> FIG. 3 is a view showing the structure of a pixel region of a liquid crystal display device (panel) according to the present invention. The liquid crystal of one of the transparent substrates disposed opposite to each other with the liquid crystal interposed therebetween. It is the top view seen from the side.

FIG. 3 is a sectional view taken along the line III-III in FIG. 3, and FIG. 4 is a sectional view taken along the line VI-VI in FIG.

First, in FIG. 3, a gate signal line GL extending in the x direction and juxtaposed in the y direction is formed of, for example, chromium (Cr). The gate signal line GL forms a rectangular area with a drain signal line DL described later, and the area forms a pixel area.

In this pixel region, a counter electrode CT for generating an electric field with a pixel electrode PX, which will be described later, is formed. This counter electrode CT is formed in the entire area except the periphery of the pixel region, and is formed of a transparent conductive material. Body, for example, ITO1 (In
dium-Tin-Oxide).

The counter electrode CT is formed with a counter voltage signal line CL connected to the counter electrode CT so as to border the entire area around the counter electrode CT. It is formed integrally with the counter voltage signal line CL similarly formed on the counter electrode CT in each pixel region arranged along the gate signal line GL).

In this case, the connection between the counter voltage signal lines CL in the pixel region is made at each of the upper portion and the lower portion of the pixel region. This is intended to minimize the overlap between the counter voltage signal line CL and a drain signal line DL described later, and to reduce the capacitance generated between them.

The counter voltage signal line CL is formed of an opaque material made of, for example, chromium (Cr). In this case, an electric field acting as noise is generated between a drain signal line DL described later and a side portion of the counter electrode CT adjacent to the drain signal line DL, whereby the light transmittance of the liquid crystal cannot be obtained as desired. However, that part is the opposite voltage signal line C
Since the light is shielded by L, it is possible to eliminate the inconvenience in terms of display quality.

This means that the inconvenience due to the electric field (noise) generated between the gate signal line GL and the peripheral portion of the counter electrode CT adjacent thereto can be solved.

Further, as described above, the counter voltage signal line C
By using the same material for the gate signal line GL as the material for L, it is possible to form them in the same process, thereby avoiding an increase in the number of manufacturing steps.

Here, the counter voltage signal line CL is
It is needless to say that the present invention is not limited to this and may be made of, for example, Al or a material containing Al.

On the upper surface of the transparent substrate on which the counter electrode CT, the counter voltage signal line CL and the gate signal line GL are formed, an insulating film GI made of, for example, SiN is formed so as to cover them. I have.

This insulating film GI is used to form a drain signal D described later.
L, the counter voltage signal line CL and the gate signal line G
L functions as an interlayer insulating film, has a function as a gate insulating film in a region where a thin film transistor TFT described later is formed, and has a function as a dielectric film in a region where a capacitive element Cstg described later is formed. ing.

Then, a thin film transistor TFT is formed so as to be superimposed on a part of the gate signal line GL (lower left in the figure),
On this portion of the insulating film GI, a semiconductor layer AS made of, for example, a-Si is formed.

The source electrode SD is formed on the upper surface of the semiconductor layer AS.
1 and the drain electrode SD2, an MIS transistor having an inverted staggered structure using a part of the gate signal line GL as a gate electrode is formed. The source electrode SD1 and the drain electrode SD2 are formed simultaneously with the drain signal line DL.

That is, a drain signal line DL extending in the y direction in the figure and arranged in parallel in the x direction is formed, and a part of the drain signal line DL extends to the surface of the semiconductor layer AS. Thereby constitutes a drain electrode SD2 of the thin film transistor TFT.

Further, a source electrode SD1 is formed when the drain signal line DL is formed. The source electrode SD1 also has a contact portion extending to the inside of the pixel region to establish connection with a pixel electrode PX described later. It is designed to be integrally formed.

As shown in FIG. 5, a contact layer d0 doped with, for example, an n-type impurity is formed at the interface of the semiconductor layer AS with the source electrode SD1 and the drain electrode SD2.

In the contact layer d0, an n-type impurity doping layer is formed over the entire surface of the semiconductor layer AS, and after the formation of the source electrode SD1 and the drain electrode SD2, the contact electrode d0 is exposed from these electrodes using the electrodes as a mask. It is formed by etching the n-type impurity doping layer on the surface of the formed semiconductor layer AS.

The thin film transistor TF
On the surface of the transparent substrate SUB1 on which the T is formed, a protective film PSV made of, for example, SiN is formed so as to cover the thin film transistor TFT. This is to avoid direct contact of the thin film transistor TFT with the liquid crystal LC.

Further, on the upper surface of the protective film PSV, the pixel electrode PX is formed by a transparent conductive film made of, for example, ITO2 (Indium-Tin-Oxide).

In this embodiment, five pixel electrodes PX are formed so as to overlap with the formation region of the counter electrode CT, and are formed at equal intervals so as to extend in the y direction in the figure. Are connected to each other by the same material layer extending in the x direction.

In this case, the same material layer at the lower end of each pixel electrode PX is connected to the source electrode SD1 of the thin film transistor TFT through a contact hole CH formed in the protective film PSV.
It is designed to be connected to the contact part of
The same material layer at the upper end is formed so as to overlap with the counter voltage signal line CL.

In the case of such a structure, the insulating film GI and the protective film PS are provided at the overlapping portion of the counter electrode CT and each pixel electrode PX.
A capacitive element Cstg having a laminated film with V as a dielectric film is formed.

After the video signal from the drain signal line DL is applied to the pixel electrode PX via the thin film transistor TFT, the capacitance element Cstg is
This is provided so that the video signal is stored in the pixel electrode PX for a relatively long time even when the FT is turned off.

Here, the capacitance of the capacitive element Cstg is:
Proportional to the overlapping area of the counter electrode CT and each pixel electrode PX,
There is a concern that the area becomes relatively large and is set to an unnecessarily large value. However, since the dielectric film has a laminated structure of the insulating film GI and the protective film PSV, as a result, It is a structure without such anxiety.

That is, since the insulating film GI functions as a gate insulating film of the thin film transistor TFT, its thickness cannot be increased. However, the protective film PSV has no such restriction, and therefore, the protective film PSV is formed as described above. The capacitance of the capacitor Cstg can be reduced to a predetermined value by setting the thickness to a predetermined value (for example, the thickness of only the protection film PSV is 100 nm to 4 μm) together with the insulating film GI.

The protective film PSV is made of SiN
It is needless to say that the present invention is not limited to this, and may be formed of, for example, a synthetic resin. In this case, since the film is formed by coating, there is an effect that manufacture is easy even when the film thickness is formed large.

Then, an alignment film ORI1 is formed on the surface of the transparent substrate on which the pixel electrode PX and the counter electrode CT are formed so as to cover the pixel electrode PX and the counter electrode CT. The alignment film ORI1 is a film that directly contacts the liquid crystal LC and determines the initial alignment direction of the liquid crystal LC.

In the above description, the pixel electrode PX is configured as a transparent electrode. However, the pixel electrode PX is not necessarily transparent, and may be an opaque metal material such as Cr. This slightly reduces the aperture ratio, but does not hinder the driving of the liquid crystal LC at all.

In the above embodiment, the gate signal lines GL,
The counter voltage signal line CL and the drain signal line DL have been described using chromium (Cr).
Of course, o, W, Ti, Ta, an alloy of two or more of these, or a laminated film of two or more of these may be used.

Furthermore, although the transparent conductive film has been described using ITO, it goes without saying that the same effect can be obtained with IZO (Indium-Zinc-Oxide).

In the TFT substrate thus configured, an FIL substrate is disposed opposite to the liquid crystal LC, and a black matrix BM is formed on a surface on the liquid crystal side. The black matrix has a function of blocking light irradiation to the thin film transistor TFT and a function of improving display contrast, and is formed so as to define and border each pixel region.

The color filter FI of any one of red, green and blue is provided in the opening of the black matrix BM.
L is formed such that its peripheral portion is superimposed on the black matrix BM.

Then, the black matrix B
M and a transparent substrate S on which a color filter FIL is formed
A flattening film OC is formed on the surface of the UB2 so as to cover the black matrix BM and the color filter FIL.

The flattening film OC is formed of, for example, a resin film by coating, so that a step due to the formation of the black matrix BM and the color filter FIL is not made visible on the surface.

Further, in this embodiment, the flattening film OC is used.
A conductive film COD made of, for example, ITO (Indium-Tin-Oxide) is formed on the surface of the black matrix BM. The conductive film COD has the same pattern as the black matrix BM and is formed so as to overlap with the black matrix BM. I have.

In this case, when the conductive film is formed by selective etching using the photolithography technique, there is an effect that the photomask used for forming the black matrix can be used as it is.

FIG. 1 is a plan view of the conductive film COD as viewed from the liquid crystal side, and its opening is a region through which light in each pixel region is transmitted.

This conductive film COD is connected to the transparent substrate SUB2 4
Transparent substrates SUB1 and SUB2 at any part of the corner
And the same signal as the signal supplied to the counter voltage signal line CL, for example, is supplied to the transparent substrate SUB1 side via a conductor disposed between them.

In this case, for example, VI- in FIG.
As shown in FIG. 6 which is a cross-sectional view taken along the line VI, when a coverage defect occurs in a part of the insulating film covering the gate signal line,
Or, if a pinhole is caused by foreign matter,
A current flows between the conductive layer and another transparent substrate facing the liquid crystal via the liquid crystal (in this case, the electrons e move from the gate signal line GL side to the conductive layer COD side).
However, since the conductive layer COD is made of a material that is not easily oxidized, its metal ions (which are ionized by the electrons) are not eluted, and the generation of the liquid crystal stain by the metal ions can be avoided. Become like

In other places near the gate signal line GL, poor coverage or pinholes may occur in the insulating film covering the metal layer to which a higher voltage is applied (for example, the counter voltage signal line CL). In such a case, a current may flow between the metal layer and the gate signal line GL and metal ions may be eluted from the metal layer, but the distance between the gate signal line GL and the gate signal line GL may be longer than the distance between them. Conductive layer CO
When the distance from D is short, current easily flows in the shorter portion, so that elution of metal ions from the metal layer can be prevented.

The so-called lateral electric field type liquid crystal display device controls the light transmittance of the liquid crystal by an electric field having a component substantially parallel to the substrate as described above, and the electric field is applied from outside the liquid crystal display device. However, the conductive layer functions as a shield against an external electric field.

For this reason, when another shield means is provided for an external electric field, it is not necessary to provide such means.

Further, the above-mentioned conductive layer COD is formed of a thin film transistor TFT and another transparent substrate (TFT substrate) different from the transparent substrate (TFT substrate) on which the gate signal line GL and the drain signal line DL connected to the TFT are also formed. (FIL substrate) side.

That is, the TFT substrate can have the same configuration as that of the related art, and has an effect that an increase in the capacitance of the wiring can be avoided.

In the embodiment described above, the conductive layer COD is formed exactly the same as the pattern of the black matrix BM. However, it is needless to say that the present invention is not limited to this. For example, the width between the openings of the conductive layer COD may be formed to be smaller or larger than the width between the openings of the black smart risk BM.

In the above-described embodiment, in particular, ITO
A conductive layer is formed by a film. This is because the ITO film is made of a material that is hardly oxidized. For this purpose,
The conductive layer need not be an ITO film, but may be another transparent conductive material such as IZO.

The black matrix BM may be made of, for example, a resin material containing carbon (C) particles, and may be formed as a conductive layer having the above-described functions. This is because such a black matrix BM is not easily oxidized.

[Embodiment 2] In the embodiment described above, the conductive layer COD is formed so as to overlap the gate signal line GL and the drain signal line DL. However, the present invention is not limited to this. For example, each gate signal line GL
May be formed so as to overlap only above.

In this case, the pattern of the conductive layer COD is as shown in FIG. This figure shows a conductive layer pattern assuming that there are nine gate signal lines GL in the display area. Needless to say, there are actually several hundred gate signal lines GL.

In this case, a voltage is supplied to the conductive layer COD so as to be maintained at a potential serving as an anode with respect to the low potential of the scanning signal supplied to the gate signal line GL. .

By supplying the same voltage as the voltage supplied to the counter voltage signal line CL, there is an effect that a special level voltage need not be formed.

In the gate signal line GL and its vicinity (including the thin film transistor TFT), when a coverage defect occurs in a part of the insulating film or when a pinhole is caused by a foreign substance or the like, the metal ion from there is removed. Elution can be avoided, and generation of the liquid crystal spot due to the metal ions can be prevented.

In this case, it is needless to say that the black matrix BM may be made of a conductive material which is hardly oxidized in the pattern shown in FIG. 7 without specially providing the conductive layer COD.

For the same purpose, the conductive layer COD may be formed so as to overlap only above each drain signal line DL. In this case, the pattern of the conductive layer is as shown in FIG. This figure shows a pattern of a conductive layer assuming that there are more than a dozen drain signal lines DL in the display area. Needless to say, there are actually several hundred drain signal lines DL.

In the case where the drain signal line DL has a poor coverage in a part of the insulating film or a pinhole due to a foreign substance or the like, elution of metal ions therefrom can be avoided. The occurrence of liquid crystal spots can be prevented.

Also in this case, a voltage is supplied to the conductive layer COD so as to be maintained at a potential serving as an anode with respect to the low potential of the video signal supplied to the drain signal line DL. I have.

By supplying the same voltage as the voltage supplied to the counter voltage signal line CL, there is an effect that a special level voltage need not be formed.

In this case, it is needless to say that the black matrix BM may be formed of a conductive material which is hardly oxidized in the pattern shown in FIG. 8 without specially providing the conductive layer COD.

In each of the embodiments described above, the pixel electrode PX (or the counter electrode CT) made of a transparent electrode is formed in the pixel region of the liquid crystal display device. However, it is needless to say that any of these electrodes can be applied to an opaque metal electrode.

In this case, there is almost no difference except that the electrodes are arranged apart from each other, and the same problem remains.

[0082]

As is apparent from the above description,
ADVANTAGE OF THE INVENTION According to the liquid crystal display device by this invention, it becomes possible to prevent the occurrence of liquid crystal spots on the display portion.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a liquid crystal display device according to the present invention, and is a plan view seen from a liquid crystal side of an FIL substrate.

FIG. 2 is an overall configuration diagram showing one embodiment of a liquid crystal display device according to the present invention.

FIG. 3 is a plan view showing one embodiment of a pixel region of the liquid crystal display device according to the present invention.

FIG. 4 is a sectional view taken along line IV-IV in FIG.

FIG. 5 is a sectional view taken along line VV of FIG. 3;

FIG. 6 is a sectional view taken along line VI-VI in FIG.

FIG. 7 is a block diagram showing another embodiment of the liquid crystal display device according to the present invention, corresponding to FIG.

FIG. 8 is a configuration diagram showing another embodiment of the liquid crystal display device according to the present invention, and is a diagram corresponding to FIG.

[Explanation of symbols]

GL: gate signal line, DL: drain signal line, TFT:
Thin film transistor, PX: pixel electrode, CT: counter electrode,
BM: black matrix, FIL: color filter,
OC: flattening film, COD: conductive layer.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission Date] March 28, 2001 (2001.3.2)
8)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0022

[Correction method] Change

[Correction contents]

FIG. 3 is a sectional view taken along line IV-IV in FIG.
4 shows a cross-sectional view taken along line V-V in FIG.

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

[Correction contents]

FIG. 3

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takanori Nakayama 3300 Hayano, Mobara-shi, Chiba F-term (reference) 2H092 GA14 JA26 JA29 JA38 JA42 JA44 JA47 JB13 JB23 JB32 JB33 JB51 JB57 JB63 JB69 KA07 KB14 MA05 MA08 MA14 MA15 MA16 MA18 MA19 MA20 MA27 MA35 MA37 NA04 NA27 NA29 PA02

Claims (5)

[Claims] 1. A switching element driven by supply of a scanning signal from a gate signal line to a pixel region on a liquid crystal side surface of one of substrates opposed to each other with a liquid crystal interposed therebetween. A pixel electrode to which a video signal is supplied from a drain signal line via the pixel electrode, and a counter electrode for generating an electric field having a substantially parallel component of the substrate are formed between the pixel electrode and the pixel electrode, and a liquid crystal side of the other substrate is formed. A conductive layer which is hardly oxidized so as to be superposed on the gate signal line, and which is maintained at a potential serving as an anode with respect to a low potential of a scanning signal. apparatus. 2. A switching element driven by the supply of a scanning signal from a gate signal line to a pixel region on a liquid crystal side of one of the substrates opposed to each other via a liquid crystal, and A pixel electrode to which a video signal is supplied from a drain signal line via the pixel electrode, and a counter electrode for generating an electric field having a substantially parallel component of the substrate are formed between the pixel electrode and the pixel electrode, and a liquid crystal side of the other substrate is formed. A liquid crystal display device, wherein a conductive layer which is hardly oxidized is formed on the surface of the substrate so as to overlap the gate signal line, and a voltage applied to the counter electrode is applied to the conductive layer. 3. The liquid crystal display device according to claim 1, wherein the conductive layer hardly oxidized is made of an ITO film. 4. A switching element driven by supply of a scanning signal from a gate signal line to a pixel region on a liquid crystal side surface of one of the substrates opposed to each other via a liquid crystal, and A pixel electrode to which a video signal is supplied from a drain signal line via the pixel electrode, and a counter electrode for generating an electric field having a substantially parallel component of the substrate are formed between the pixel electrode and the pixel electrode, and a liquid crystal side of the other substrate is formed. A conductive layer which is hardly oxidized so as to be superposed on the gate signal line and the drain signal line, and a voltage supplied to the counter electrode is applied to the conductive layer. apparatus. 5. A black matrix defining each pixel region is formed on a liquid crystal side surface of one of substrates opposed to each other with a liquid crystal interposed therebetween, and the conductive layer is formed of a pattern of the same and same shape as the black matrix. The liquid crystal display device according to claim 4, comprising: