JPH0850304A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device having an anodically oxidized film enhanced in withstand voltage. CONSTITUTION:This array substrate 1 is produced by the following method. An aluminum gate electrode 3 is formed on a glass substrate. An aluminum oxide (Al2O3) gate insulating film 4 is formed on the gate electrode 3 by anodically oxidizing the gate electrode 3 in a wet process. As for the liquid for chemical conversion used in the anodic oxidation process, a soln. prepared by mixing 3wt.% aq. soln. of tartaric acid, 15wt.% acetic acid and ethylene glycol with 9:1:10 mixing ratio and adding ammonia water to the mixture to control pH to 7 is used. The carbon content of the anodically oxidized film is specified to 1 to 3atm%. By adding acetic acid to the liquid for chemical conversion, carbon is added to the aluminum oxide (Al2O3) insulating film 4 to enhance the withstand voltage. A silicon oxide gate insulating film 5 is formed on the whole surface. Then a semiconductor layer 7, etching stopper layer 8 contact layer 9, 10, pixel electrode 11, source electrode 12 and drain electrode 13 are formed.

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 device in which a gate wiring and a data wiring are provided so as to intersect with each other and a gate insulating film provided so as to cover the gate wiring has an improved insulating property.

[0002]

2. Description of the Related Art As a conventional liquid crystal display device of this type,
For example, a configuration of a thin film transistor (TFT) for a liquid crystal display device shown in FIG. 1 is known.

As shown in FIG. 1, an array substrate 1 used in a liquid crystal display device has a gate electrode 3 of aluminum (Al) formed on a glass substrate 2 and connected to a gate wiring (not shown). This gate electrode 3 on top
An aluminum oxide gate insulating film 4 of aluminum oxide (Al ₂ O ₃ ) anodized by a wet process is formed on the glass substrate 2 including the aluminum oxide gate insulating film 4.
The silicon oxide gate insulating film 5 of ₂ ) is formed on the entire surface. Then, these aluminum oxide gate insulating films 4
The silicon oxide gate insulating film 5 forms the gate insulating film 6 having a multilayer laminated structure. By using the wet process during the anodization, short-circuit defects due to foreign matter such as dust are less likely to occur. The aluminum oxide gate insulating film 4 is formed of aluminum oxide (Al
_{Since it is} formed of ₂ O ₃ ), the generation of hillocks in the gate electrode 3 is suppressed in the heat step when forming the silicon oxide film or the silicon nitride film.

Amorphous silicon (a-SiO 2) is formed on the silicon oxide gate insulating film 4 above the gate electrode 3.
₂ ) a semiconductor layer 7 is formed, and an etching stopper layer 8 of silicon nitride (SIN _x ) is formed on the semiconductor layer 7.
Is formed on one side of the etching stopper layer 8 and amorphous silicon (n ⁺ a-S) serving as a source region is formed.
The contact layer 9 of i) and the contact layer 10 of amorphous silicon (n ⁺ a-Si) which becomes the drain region are formed on the other side by etching.

Further, a pixel electrode 11 made of ITO (Indium Tin Oxide) is formed on the silicon oxide gate insulating film 5.

Then, on the contact layer 9, molybdenum, aluminum and molybdenum (Mo, A
a source electrode 12 having a multi-layered structure of Mo, Al, M and molybdenum, aluminum and molybdenum (Mo, Al, M).
The drain electrode 13 having a multi-layer structure of o) is formed, and the thin film transistor 14 serving as a switching element is formed by these.

Further, a protective film 15 is formed on the entire surface.

Here, as the anodic oxidation of the gate electrode 3 by the wet process, a solution obtained by diluting a 3.68% ammonium tartrate aqueous solution with ethylene glycol is used as a chemical conversion liquid, the chemical conversion liquid temperature is room temperature, and the chemical conversion voltage is 150V. After the anodization, heat treatment was performed at 250 ° C. for 2 hours. The withstand voltage of the aluminum oxide gate insulating film 4 thus formed is 110 V (5.5 V) at a film thickness of 200 nm.
MV / cm). The use of ethylene glycol is to eliminate irregularities on the film surface.

Further, for example, in the anodic oxidation disclosed in Japanese Patent Laid-Open No. 3-232274, aluminum (Al) or a metal containing aluminum as a main component, such as Al-Si or Al-Pd, is used. And
For the anodizing chemical solution, a 3% tartaric acid solution was diluted with ethylene glycol, and ammonium water was added to adjust the pH to 7.0.
The solution adjusted to ± 0.5 is used. Further, the formation voltage is preferably 150 V or less because aluminum disappears due to discharge, and in order to improve the insulating characteristics of aluminum oxide (Al ₂ O ₃ ), the formation voltage is set to 200 ° C. after completion of anodization.
Heat treatment is performed at / 400 ° C. And in this case A
The breakdown voltage of the l ₂ O ₃ film is 25 at a film thickness of 500 Å.
V (5 MV / cm).

In this way, the array substrate 1 shown in FIG.
Is formed, the array substrate 1 is opposed to a counter substrate (not shown), and liquid crystal is injected between the array substrate 1 and the counter substrate to complete the liquid crystal display device.

[0011]

However, the aluminum oxide gate insulating film 4 formed by the above conventional technique.
Has a problem that the breakdown voltage is as low as 5.5 MV / cm even in the higher one.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device having an anodized film having an increased dielectric strength.

[0013]

A liquid crystal display device according to claim 1, wherein a gate wiring formed on a substrate, a gate insulating film formed to cover the gate wiring, and the gate wiring on the substrate. In a liquid crystal display device including an array substrate having a data line arranged to intersect with the gate line and a switching element provided near the intersection of the gate line and the data line, the gate line is made of aluminum, and The gate insulating film has a multilayer laminated structure including an aluminum anodic oxide film and a silicon oxide film,
The anodic oxide film contains carbon and has a carbon content of 1 to 3 atomic%.

A liquid crystal display device according to a second aspect is the first aspect.
In the liquid crystal display device described above, the anodic oxide film is formed of a chemical conversion liquid containing a carboxylic acid.

A liquid crystal display device according to a third aspect is the second aspect.
In the liquid crystal display device described, the carboxylic acid has a low molecular weight.

[0016]

In the liquid crystal display device according to the first aspect, since the carbon content of aluminum oxide in the anodized film is 1 to 3 atomic%, the dielectric strength is improved.

A liquid crystal display device according to a second aspect is the first aspect.
In the liquid crystal display device described above, since the anodic oxide film is formed of the chemical conversion liquid containing carboxylic acid, it can be easily formed.

A liquid crystal display device according to a third aspect is the second aspect.
In the liquid crystal display device described above, since the carboxylic acid has a low molecular weight, the withstand voltage can be improved at low cost.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the liquid crystal display device of the present invention will be described below with reference to FIG.

As shown in FIG. 1, an array substrate 1 used in a liquid crystal display device has an aluminum (Al) gate electrode 3 connected to a gate wiring (not shown) formed on a glass substrate 2 and an auxiliary substrate (not shown). A capacitor wiring is formed, and an aluminum oxide gate insulating film 4 of aluminum oxide (Al ₂ O ₃ ) is formed on the gate electrode 3 as an anodized film by anodizing the gate electrode 3 by a wet process. A silicon oxide gate insulating film 5 of a silicon oxide film (SiO ₂ ) is formed on the entire surface of the glass substrate 2 including the aluminum oxide gate insulating film 4. The aluminum oxide gate insulating film 4 and the silicon oxide gate insulating film 5 form a gate insulating film 6 having a multilayer laminated structure.

Amorphous silicon (a-SiO 2) is formed on the silicon oxide gate insulating film 5 above the gate electrode 3.
₂ ) a semiconductor layer 7 is formed, and an etching stopper layer 8 of silicon nitride (SIN _x ) is formed on the semiconductor layer 7.
Is formed on one side of the etching stopper layer 8 and amorphous silicon (n ⁺ a-S) serving as a source region is formed.
The contact layer 9 of i) and the contact layer 10 of amorphous silicon (n ⁺ a-Si) which becomes the drain region are formed on the other side by etching.

Further, a pixel electrode 11 made of ITO (Indium Tin Oxide) is formed on the silicon oxide gate insulating film 5.

Then, on the contact layer 9, molybdenum, aluminum and molybdenum (Mo, A
a source electrode 12 having a multi-layered structure of Mo, Al, M and molybdenum, aluminum and molybdenum (Mo, Al, M).
The drain electrode 13 having a multi-layer structure of o) is formed, and the thin film transistor 14 serving as a switching element is formed by these.

Further, a protective film 15 is formed on the entire surface.

Next, the manufacture of the array substrate 1 of the above embodiment will be described.

First, an aluminum film having a thickness of 350 nm is deposited on the glass substrate 2 by a sputtering method, and a pattern of the gate electrode 3, a gate wiring (not shown) and an auxiliary capacitance wiring is formed by photolithography.

Then, aluminum (Al) of the gate electrode 3 is anodized. At the time of this anodic oxidation, as the chemical conversion solution, a 3 wt% tartaric acid aqueous solution, 15 wt% acetic acid and ethylene glycol are mixed at 9: 1: 10, and ammonia water is added to adjust the pH to 7. Further, by adding acetic acid to the chemical conversion liquid, carbon is added to the aluminum oxide (Al ₂ O ₃ ) of the aluminum oxide gate insulating film 4 to increase the dielectric strength voltage. It becomes 5 MV / cm.

Then, the aluminum oxide gate insulating film 4
The relationship between the withstand voltage and carbon content of aluminum oxide is
According to the experiment, as shown in FIG. 2, when the carbon content is 1 atomic% or less and 3 atomic% or more, the breakdown voltage is about 5 MV / c.
In case of m and 1 to 3 atomic%, it becomes about 8 MV / cm,
The carbon content is preferably 1 to 3 atomic%.

The carbon content of aluminum oxide in the aluminum oxide gate insulating film 4 can be increased by increasing the concentrations of tartaric acid and acetic acid. It should be noted that what is added to the chemical conversion liquid is not limited to acetic acid, and low molecular weight carboxylic acids such as formic acid and carboxylic acid can also be used.

Then, the chemical conversion liquid is cooled and the chemical conversion voltage is adjusted to 14
By setting the voltage to 0 V, the surface of the gate electrode 3 is anodized to about 100 nm, and the aluminum oxide gate insulating film 4 of aluminum oxide (Al ₂ O ₃ ) is formed to a thickness of 200 nm.

By using a wet process during the anodic oxidation, a short circuit failure due to the adhesion of foreign matter such as dust is unlikely to occur. Also, the aluminum oxide gate insulating film 4
Is formed of aluminum oxide (Al ₂ O ₃ ), so that the generation of hillocks in the gate electrode 3 is suppressed in the thermal step of forming the silicon oxide film or the silicon nitride film. Next, a silicon oxide (SiO _x ) film is formed on the glass substrate 2 including the aluminum oxide gate insulating film 4 by a CVD method,
An amorphous silicon (a-Si) film and a silicon nitride (SiN _x ) film are laminated and deposited.

Then, the silicon nitride film is patterned to form the etching stopper layer 8, and after forming the pattern of the etching stopper layer 8, an amorphous silicon (n ⁺ a-Si) film is deposited by the CVD method to form the semiconductor layers 7 and The contact layers 9 and 10 are patterned.

Next, an ITO film is deposited as a transparent electrode by a sputtering method to form a pattern on the pixel electrode 11, and aluminum oxide (Al
₂ O ₃ ) and silicon oxide (SiO _x ) are removed.

Furthermore, molybdenum (Mo), aluminum (Al) and molybdenum (M
Three layers of o) are sequentially deposited and patterned to form a data wiring, a source electrode 12 and a drain electrode 13 which are not shown.

Then, after removing the amorphous silicon (n ⁺ a-Si) film on the back channel (not shown),
A silicon oxide (SiN _x ) film is deposited by the CVD method and a protective film 15 is formed to complete the array substrate 1 for liquid crystal display.

Then, the array substrate 1 is opposed to a counter substrate (not shown), and liquid crystal is injected between the array substrate 1 and the counter substrate to complete the liquid crystal display device.

[0037]

According to the liquid crystal display device of the first aspect,
The anodic oxide film has a carbon content of 1 to 1 in aluminum oxide.
Since it is 3 atomic%, the withstand voltage can be improved and the reliability can be improved.

According to the liquid crystal display device of the second aspect, in addition to the liquid crystal display device of the first aspect, since the anodic oxide film is formed of the chemical conversion liquid containing the carboxylic acid, it can be easily formed.

According to the liquid crystal display device of the third aspect, in addition to the liquid crystal display device of the second aspect, since the carboxylic acid has a low molecular weight, the withstand voltage can be improved at low cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an array substrate of an embodiment of a liquid crystal display device of the present invention.

FIG. 2 is a graph showing the relationship between carbon content in aluminum oxide (Al ₂ O ₃ ) and withstand voltage.

[Explanation of symbols]

1 Array Substrate 2 Glass Substrate 4 Aluminum Oxide Gate Insulating Film as Anodized Film 6 Gate Insulating Film 14 Thin Film Transistor as Switching Element

Claims (3)

[Claims] 1. A gate wiring formed on a substrate, a gate insulating film formed so as to cover the gate wiring, a data wiring arranged on the substrate crossing the gate wiring, and the gate wiring. In the liquid crystal display device including an array substrate having a switching element provided near the intersection of the data lines, the gate line is made of aluminum, and the gate insulating film is an anodic oxide film and a silicon oxide film of aluminum. The liquid crystal display device according to claim 1, wherein the anodic oxide film contains carbon and the carbon content is 1 to 3 atomic%. 2. The liquid crystal display device according to claim 1, wherein the anodized film is formed of a chemical conversion liquid containing carboxylic acid. 3. The liquid crystal display device according to claim 2, wherein the carboxylic acid has a low molecular weight.