JPH09244065A - Active matrix liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To save energy to a back light, to simplify an active matrix substrate forming process, to reduce a manufacturing cost and to obtain high economicity by making at least a source electrode a double structure such as a transparent conductive film, etc., and making the source electrode a single structure of only the transparent conductive film in a contact hole position. SOLUTION: The source electrode and an auxiliary capacity electrode are made the double structure of the transparent conductive film 37a and a metal film 37b. Further, on the other hand, in a first contact hole 42 position connected to a pixel electrode 43 each, the metal film 37b is eliminated, and the pixel electrode is made the single structure of only the transparent conductive film 37a. Then, the opening area of the pixel electrode 43 isn't reduced even when the area of the first contact hole 42 is enlarged for obtaining sufficient connection between the source electrode or the auxiliary capacity electrode and the pixel electrode 43. Thus, the energy required for the power of the back light is saved by improvement of picture luminance.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a thin film transistor (hereinafter abbreviated as TFT) arranged in a matrix.
An active matrix substrate having as a drive element,
The present invention relates to an active matrix type liquid crystal display device in which a liquid crystal composition is held between a counter substrate and the counter substrate.

[0002]

2. Description of the Related Art In recent years, a liquid crystal display device which has a high density and a large capacity but has a high function and a high definition has been put into practical use.

Of these liquid crystal display devices, there is no crosstalk between adjacent pixels, a high contrast display can be obtained, a transmissive display is possible, and a large area can be easily obtained. 2. Description of the Related Art Conventionally, an active matrix type liquid crystal display device including a TFT as a driving element is widely used.

Among these, TFTs using amorphous silicon are currently in the mainstream because of their large area and low temperature process capability.

In such an active matrix substrate having a TFT as a driving element, the conventional pixel electrode is
After the TFT was formed, it was patterned by a photolithography technique and electrically connected to the source electrode of the TFT.

Therefore, in consideration of the deviation of the pattern formed on the photoresist when patterning the pixel electrode, the pixel electrode must be formed with a predetermined distance from the TFT and each wiring. In particular, with respect to the signal line, in order to prevent the display quality from deteriorating due to an increase in the coupling capacitance with the pixel electrode or a leak of the pixel electrode potential to the signal potential, the above-mentioned predetermined The distance has to be further increased, which reduces the area of the pixel region, which causes a problem of reducing the aperture ratio of the active matrix substrate and thus the liquid crystal display device. In order to prevent the contrast ratio from decreasing due to light leakage between the wiring and the wiring, a black matrix was provided on the counter substrate to shield the light. The alignment accuracy between the pixel electrode and the black matrix depends on the assembly accuracy of the liquid crystal cell, and the deviation between the two becomes large. Therefore, the width of the black matrix must be set to a considerably large value. When a liquid crystal display device is formed by such a method, there is a problem that the light that is actually transmitted is further reduced and the aperture ratio of the liquid crystal display device is further reduced.

Therefore, for example, Japanese Unexamined Patent Publication No. 64-68726
As disclosed in Japanese Patent Laid-Open Publication No. 2003-242242, a TFT is covered with a transparent insulating film, a pixel electrode is formed thereon, and the pixel electrode is connected to a source electrode through a contact hole.
An apparatus has been developed in which the FT and the pixel electrode are formed on different surfaces to reduce the coupling capacitance and prevent a short circuit.
That is, as shown in FIGS. 6 to 8, the gate electrode 2, the gate insulating film 3, and the amorphous silicon thin film 4 are laminated on the insulating substrate 1 and the inorganic protective film 6a for protecting the channel region 6 is formed.
Is formed, an amorphous silicon TFT 11 provided with a source electrode 9 and a drain electrode 10 is provided on both sides of the ohmic contact layer 8, and a pixel electrode 13 is further formed via a transparent insulating film 12 to form a first contact. Hall 14
The pixel electrode 13 is connected to the source electrode 9 at.

Further, when the auxiliary capacitance electrode 17 is provided above the scanning line 16 via the gate insulating film 3, the pixel electrode 13 is connected to the auxiliary capacitance electrode 17 through the second contact hole 18.

On the other hand, as disclosed in Japanese Unexamined Patent Publication No. 6-130416, a pixel electrode is patterned on a transparent insulating film covering a TFT so as to extend above the wiring electrode, and an opening portion of the pixel electrode is formed. A device for improving the aperture ratio by defining the wiring electrode has been developed.

However, in this way, when the pixel electrode is extended above the wiring electrode, a parasitic capacitance is formed at the overlapping portion of the pixel electrode and the wiring electrode, which causes crosstalk and is likely to cause display failure. In order to solve this problem, in order to improve this, a negative type resist is used to expose from the side of the insulating substrate to expose each of the electrodes made of a light-shielding material and each wiring as a mask. A liquid crystal display device has also been developed in which a pattern for leaving an exposed portion is formed on a resist, and this is used as a mask to form a pattern of pixel electrodes.

[0011]

Conventionally, in a transmissive liquid crystal display device using an active matrix substrate having a TFT as a driving element, when a pixel electrode is formed on a transparent insulating film covering the TFT, The pixel electrode was connected to the source electrode of the TFT through a contact hole.

However, the connection through such a contact hole has a problem that a connection failure is more likely to occur than in the case where the connection is made directly on the same surface.

Therefore, in order to obtain a sufficient connection, it is necessary to enlarge the area of the contact hole. However, since the source electrode is conventionally formed of a light-shielding material, the increase of the area of the contact hole depends on the device. The aperture ratio is further reduced, which in turn lowers the light transmittance of the liquid crystal display device, lowers the displayed screen brightness, and in order to obtain the required brightness, the light quantity of the backlight must be increased. In addition, power consumption is increased, which hinders energy saving of the device.

Conventionally, when a pixel electrode is patterned by a backside exposure technique using a negative resist, the source electrode is shielded from light at the contact hole position, and the negative resist is not exposed. Since the electrode pattern does not remain, first, as shown in FIGS. 7 and 8, after the mask pattern which is not masked by each wiring or electrode (the I region) is exposed by the back surface exposure technique, the contact hole portion is further formed ( For the second region (II), the pixel electrode pattern must be left by re-exposing from the surface, which complicates the mask forming process and raises the manufacturing cost.

Therefore, the present invention eliminates the above-mentioned problems by improving the aperture ratio and thus the light transmittance of a liquid crystal display device using an active matrix substrate having a TFT as a driving element and improving the screen brightness. It is an object of the present invention to provide an economically active matrix type liquid crystal display device by saving energy conventionally required for a backlight, simplifying an active matrix substrate forming process and reducing manufacturing cost. .

[0016]

According to a first aspect of the present invention for solving the above problems, there is provided a gate electrode formed on a transparent insulating substrate and supplied with a scanning signal by a scanning line, and the gate electrode. A plurality of thin film transistors arranged in a matrix and provided with a source electrode and a drain electrode to which a video signal is supplied by a signal line across the active region, the scanning line and the signal being provided above the gate insulating film. An insulating protective film that covers the lines and the thin film transistor, and a pixel electrode that is arranged in a matrix on the insulating protective film and is connected to the source electrode through a contact hole formed in the insulating protective film An active matrix substrate, a counter substrate facing the active matrix substrate and having a counter electrode, and the active matrix substrate. And a liquid crystal composition sealed between the counter substrates, wherein at least the source electrode has a double structure in which a transparent conductive film and a metal film are laminated, and the contact hole is provided. At the position, the source electrode has a single layer structure including only the transparent conductive film.

According to a second aspect of the present invention, in the active matrix type liquid crystal display device according to the first aspect, the source electrode removes the upper metal film by using the pattern of the contact hole as a mask to remove the contact. At the hole position, the transparent conductive film only has a single structure.

According to a third aspect of the present invention, in the active matrix liquid crystal display device according to the first aspect, all the pixel electrodes are covered with an insulating protective film by a backside exposure technique from the insulating substrate side. The light-shielding material is used as a mask to perform shape processing in a self-aligning manner.

The source electrode is composed of a transparent conductive film and a metal film.
On the other hand, by adopting a single structure consisting only of a transparent conductive film at the contact hole position, even if the contact hole is enlarged to obtain a sufficient connection between the pixel electrode and the source electrode, Since the light transmission area is not reduced, it is possible to prevent defective connection between the pixel electrode and the source electrode without lowering the aperture ratio of the active matrix substrate.
By providing a good display and improving the screen brightness, the energy required for the power of the backlight is saved.

Further, according to the present invention, when the pattern of the pixel electrode is formed, the mask pattern which leaves the pixel electrode pattern including the contact hole portion on the negative resist can be formed by the one-time back exposure. On the other hand, the mask pattern forming process can be simplified and the manufacturing cost can be reduced.

[0021]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described with reference to FIGS. Reference numeral 20 denotes an active matrix type liquid crystal display device, in which a liquid crystal composition is provided between an active matrix substrate 22 using an amorphous silicon TFT 21 as a driving element and a counter substrate 23 with alignment films 24 and 26 made of polyimide interposed therebetween. The nematic liquid crystal 27 is held, and the polarizing plates 53 and 54 are provided.

Here, the active matrix substrate 22 is
A scanning line 30 made of thallium (Ta), which is a light-shielding material, is provided on a transparent glass insulating substrate 28 to supply a scanning signal and a part of which is used as a gate electrode 31.
Are patterned. A transparent gate insulating film 3 made of silicon oxide (SiOx) is formed on these.
2, the semiconductor layer 34 made of i-type hydrogenated amorphous silicon (hereinafter referred to as i-type a-Si: H) and the silicon nitride (above the gate electrode 31 via the gate insulating film 32) and the silicon nitride ( SiNx) protective insulating film 35 and n-type amorphous silicon (hereinafter referred to as n-type a-Si) in order to obtain good ohmic contact.
The ohmic layer 40 consisting of is formed by patterning, sandwiching the channel region (A), and forming the source region (B) and the drain region (C).

Further, on the gate insulating film 32, a source electrode 37, a signal line 38, and a signal line which connect the pixel electrode 43 and the ohmic layer 40 of the source region (B) at a first contact hole 42 described later. The drain electrode 39 is branched from 38 and is connected to the ohmic layer 40 in the drain region (C), and the auxiliary capacitance electrode 44 is connected to the pixel electrode 43 through a second contact hole 52 described later. There is.

Here, the source electrode 37, the signal line 38, the drain electrode 39, and the auxiliary capacitance electrode 44 are all made of indium tin oxide (hereinafter referred to as ITO) transparent conductive film 3.
It has a double structure of 7a to 44a and metal films 37b to 44b made of a molybdenum (Mo) film and an aluminum (Al) film.

However, the first and second contact holes 4
At the positions 2, 52, the source electrode 37 and the auxiliary capacitance electrode 44 have a single-layer structure composed of only the transparent conductive films 37a, 44a.

The auxiliary capacitance electrode 44 is formed by the gate insulating film 3
It is stacked above the scanning line 30 one row before via the line 2, and the auxiliary capacitance is formed at the overlapping portion with the scanning line 30 one row before. Furthermore, silicon nitride (SiNx) having first and second contact holes 42 and 52 on their upper surfaces
Is covered with an insulating protective film 41.

The scanning line 3 is formed on the insulating protective film 41.
0, signal line 38, source electrode 37, drain electrode 39,
A pixel electrode 43 made of an ITO film which is patterned in a self-aligned manner with respect to the auxiliary capacitance electrode 44 is provided.
The pixel electrode 43 is connected to the transparent conductive film 37a of the source electrode 37 through the first contact hole 42, and the auxiliary capacitance electrode 44 through the second contact hole 52.
Connected to the transparent conductive film 44a.

On the other hand, the counter substrate 23 is made of an insulating substrate 46 made of transparent glass, made of chrome (Cr) which is a light-shielding material, and made of ITO and a black matrix 47 having red, green and blue colored layers in respective regions. Has a counter electrode 48.

Next, a method of manufacturing the active matrix substrate 22 will be described. First, a scanning line 30 and a part thereof are formed by using a photolithography technique of forming a film of thallium (Ta) on the insulating substrate 28 by a sputtering method and photoetching thallium (Ta) using a photoresist (not shown) as a mask. The gate electrode 31 is formed by patterning.

Next, the gate insulating film 32, (i-type a-Si: H) film, and silicon nitride (SiN) are formed by the plasma CVD method.
x) a film is laminated and formed by photolithography,
Silicon nitride (SiNx) film and (i-type a-Si: H)
The film is photo-etched to pattern the protective insulating film 35 and the semiconductor layer 34.

Subsequently, plasma CVD is performed on the semiconductor layer 34.
Then, an (n-type a-Si) film is formed by a method, and the ohmic layer 40 is patterned by etching.

Further, an ITO film, a molybdenum (Mo) film, and an aluminum (Al) film are sequentially stacked by a sputtering method, and then photoetching is performed to form a source electrode 37, a signal line 38, a drain electrode 39 integrated therewith, an auxiliary capacitor. The electrode 44 is patterned.

Next, the entire surface is covered with an insulating protective film 41 made of silicon nitride (SiNx) by the plasma CVD method, and the first and second contact holes 42 are formed above the source electrode 37 and the auxiliary capacitance electrode 44. 52 is etched.

Then, using the insulating protective film 41 as a mask, the source electrode 37 and the auxiliary capacitance electrode 44 located in the first and second contact holes 42 and 52 have a single-layer structure having only the transparent conductive films 37a and 44a. Then, the metal films 37b and 44b on the upper layer are removed.

After that, the insulating protective film 4 is formed by the sputtering method.
An ITO film is formed on 1 and a negative resist is further applied. Next, the scanning lines 30 and the signal lines 3 made of a light shielding material
8, the source electrode 37, the drain electrode 39, and the auxiliary capacitance electrode 44 are used as a light-shielding mask to expose from the back surface of the insulating substrate 28, and a negative resist is patterned to leave an exposed portion. Then, by etching the ITO film using this negative resist as a mask, the ITO film is processed in a self-aligning manner with respect to the light-shielding material to form the pixel electrode 43 in a pattern.

However, during exposure from the back surface of the insulating substrate 28,
Source electrode 37 located in contact holes 42 and 52
The auxiliary capacitance electrode 44 is formed of the metal film 37 which is a light-shielding material.
Since b and 44b are removed and light is transmitted, the negative resist also leaves the patterns at the contact holes 42 and 52 positions. Therefore, the entire surface of the pixel electrode 43 is patterned without exposing the contact holes 42 and 52 again. Formed mask.

Therefore, using the negative resist having the mask pattern thus formed, the pixel electrode 43 is patterned so as to leave the contact holes 42 and 52, and the active matrix substrate 22 is formed.

Next, in the counter substrate 23, the insulating substrate 4
A film of chromium (Cr) is formed on 6 by a sputtering method and etched into a predetermined shape by a photolithography technique.
The black matrix 47 is patterned in a grid pattern.
After applying a layer in which a pigment is dispersed on the black matrix 47, pattern exposure and development are repeated to form red (R), green (G), and blue (B) stripe regions on the black matrix 47. Then, the counter electrode 48 made of ITO is formed on the entire surface by the sputtering method to form the counter substrate 23.

Subsequently, alignment films 24 and 26 are applied to the entire surfaces of the active matrix substrate 22 and the counter substrate 23 on the pixel electrode 43 side and the counter electrode 48 side, respectively.
After the rubbing treatment so that the orientation axis becomes 90 ° when 3 is faced, both substrates 22 and 23 are assembled to face each other,
Make a cell.

Next, the nematic liquid crystal 27 is injected into the gap between the two substrates 22 and 23 and then sealed, and the polarizing plates 53 and 54 are attached to the insulating substrates 28 and 46 of the both substrates 22 and 23 to attach the liquid crystal display device. Form 20.

According to this structure, the source electrode 37 and the auxiliary capacitance electrode 44 have the double structure of the transparent conductive films 37a and 44a and the metal films 37b and 44b, and the first electrode connected to the pixel electrode 43, respectively. And the second contact hole 4
At positions 2, 52, the metal films 37b, 44b are removed and the transparent conductive films 37a, 44a are formed in a single layer structure. Therefore, the source electrode 37 or the auxiliary capacitance electrode 44 and the pixel electrode 43 are sufficiently formed. Even if the areas of the first and second contact holes 42 and 52 are enlarged to obtain the connection, the opening area of the pixel electrode 43 is not reduced.

Therefore, by improving the screen brightness, it is possible to save the energy required for the power of the backlight, prevent the defective connection between the pixel electrode 43 and the source electrode 37 or the auxiliary capacitance electrode 44, and obtain a good display.

Further, in order to improve the aperture ratio of the active matrix substrate 22, the pixel electrodes 43 are connected to the scanning lines 30 and the signal lines 3 by a backside exposure technique of exposing from the insulating substrate 28 side.
8, when patterning the source electrode 37, the drain electrode 39, and the auxiliary capacitance electrode 44 in a self-aligned manner, the first and second contact holes 42 and 52 are also negative type due to exposure from the insulating substrate 28 side. The resist is exposed.

In this way, since the mask pattern of the negative type resist can be formed by one back exposure step, the mask pattern forming step can be simplified and the manufacturing cost can be reduced as compared with the conventional case.

The present invention is not limited to the above-mentioned embodiments, and changes can be made without departing from the spirit of the present invention. For example, the material of each electrode or wiring, the gate insulating film or the insulating protective film can be changed. The material may be arbitrary, and the metal film of the source electrode or the auxiliary capacitance electrode may be formed of a single layer of a single metal.

Further, in the above embodiment, the auxiliary capacitance is formed at the overlapping portion of the scanning line one row before and the auxiliary capacitance electrode via the gate insulating film, but it is a transparent auxiliary capacitance independent of the scanning line. Alternatively, a line may be provided, and the auxiliary capacitance line and the pixel electrode may be overlapped with each other through an insulating protective film.

[0047]

As described above, according to the present invention, the source electrode has the double structure of the transparent conductive film and the metal film, while the contact hole for connecting to the pixel electrode has the metal structure. Since the film is removed to form a single-layer structure composed of only the transparent conductive film, the opening area of the pixel electrode is not reduced even if the contact hole area is expanded to obtain sufficient connection. Good connection between the source electrode and the pixel electrode can be obtained without damaging the aperture ratio of the active matrix substrate.

Therefore, in the active matrix type liquid crystal display device, it is not necessary to increase the power of the backlight in order to improve the screen brightness, energy can be saved, and good display without connection failure can be obtained.

Further, in order to improve the aperture ratio of the active matrix substrate, when the pixel electrodes are formed in a self-aligned pattern by the backside exposure technique using the electrodes and wirings made of a light shielding material as a mask, Since the electrodes are transparent, the negative resist is subjected to the back surface exposure process only once to form the mask pattern, so that the mask pattern forming process can be simplified as compared with the conventional one. The manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a partial schematic plan view showing an active matrix substrate according to an embodiment of the present invention.

FIG. 2 is a partial schematic cross-sectional view showing a liquid crystal display device according to an embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view taken along the line AA ′ of FIG. 1 showing the active matrix substrate according to the embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view taken along line BB ′ of FIG. 1 showing the active matrix substrate according to the embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view taken along line CC ′ of FIG. 1, showing an active matrix substrate according to an embodiment of the present invention.

FIG. 6 is a partial schematic plan view showing a conventional active matrix substrate.

FIG. 7 is a schematic cross-sectional view taken along the line AA ′ of FIG. 6 showing a conventional active matrix substrate.

FIG. 8 is a schematic cross-sectional view taken along line BB ′ of FIG. 6 showing a conventional active matrix substrate.

[Explanation of symbols]

 20 ... Liquid crystal display device 21 ... Amorphous silicon TFT 22 ... Active matrix substrate 23 ... Counter substrate 27 ... Nematic liquid crystal 30 ... Scan line 31 ... Gate electrode 32 ... Gate insulating film 37 ... Source electrode 38 ... Signal line 39 ... Drain Electrode 41 ... Insulating protective film 42 ... First contact hole 43 ... Pixel electrode 44 ... Auxiliary capacitance electrode 47 ... Black matrix 48 ... Counter electrode 52 ... Second contact hole

Front page continuation (72) Inventor Rinko Kitazawa 8 Shinshinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock company Toshiba Yokohama office

Claims (3)

[Claims] 1. A gate electrode formed on a transparent insulating substrate, to which a scan signal is supplied by a scan line, and a gate electrode provided above the gate electrode with a gate insulating film interposed between the source electrode and the signal. A plurality of thin film transistors arranged in a matrix, each having a drain electrode to which a video signal is supplied by a line, and an insulating protective film covering the scanning line, the signal line, and the thin film transistor,
An active matrix substrate having a pixel electrode arranged in a matrix on the insulating protective film and connected to the source electrode through a contact hole formed in the insulating protective film, and facing and facing the active matrix substrate. An active matrix liquid crystal display device comprising a counter substrate having electrodes, and a liquid crystal composition enclosed between the active matrix substrate and the counter substrate, wherein at least the source electrode has a transparent conductive film and a metal film laminated thereon. On the other hand, the source electrode has only the transparent conductive film at the contact hole position.
An active matrix liquid crystal display device having a double structure. 2. The source electrode is formed of only the transparent conductive film at the position of the contact hole by removing the upper metal film by using the pattern of the contact hole as a mask.
The active matrix liquid crystal display device according to claim 1, wherein the active matrix liquid crystal display device has a double structure. 3. A pixel electrode is self-aligned by a backside exposure technique from the side of an insulating substrate using all light-shielding materials covered with an insulating protective film as a mask. Item 1. An active matrix liquid crystal display device according to item 1.