JPH05183214A - Active-matrix liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide an active-matrix liquid crystal display device with a two- terminal element which has current-voltage characteristics of a good symmetric property, electrodes having small resistivity, and a large ratio between the turning on and off currents of the current-voltage characteristics. CONSTITUTION:The title display device is provided with a two-terminal element which has Al thin film electrodes 2 and 4, with Si being added to the Al thin film of at least one of the electrodes 2 and 4, and an aluminum oxide thin film 3 formed between the electrodes 2 and 4 by oxidizing the surface of the Si-added thin film 2 opposed to the other thin film 4.

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, and more particularly to an active matrix liquid crystal display device using a two-terminal element, and more specifically, a two-terminal element M.
The present invention relates to an element structure of an IM element.

[0002]

2. Description of the Related Art Conventionally, active matrix type liquid crystal display devices are classified into those using three-terminal elements such as TFT elements and those using two-terminal elements such as MIM elements. In particular, since the two-terminal element has a simpler element structure than the three-terminal element, there are advantages that the number of manufacturing steps can be reduced and the manufacturing yield can be improved.

A conventional M is shown in FIGS. 3 (a) and 3 (b).
The top view and sectional drawing of an IM element are shown. The method of manufacturing the MIM element is such that the signal electrode and the MI are formed on the glass substrate 21.
After forming a Ta thin film 22 as a lower electrode of the M element, a predetermined pattern is formed by etching.
a The surface of the thin film is oxidized by an anodic oxidation method to form a Ta ₂ O ₅ thin film 23 having a predetermined film thickness, and further, MIM is formed thereon.
A Cr / Ta ₂ O ₅ / Ta structure is formed by forming and patterning a Cr thin film 24 as an upper electrode of the device. Further, the ITO thin film 25 is patterned so that the ITO thin film 25 and the Cr thin film 24 are partially overlapped, and the MIM element is completed.

[0004]

The following two characteristics are generally required for MIM elements. One is that the ratio of the on-current to the off-current of the current-voltage characteristic is sufficiently large, and the other is that the positive electrode side and the negative electrode side of the current-voltage characteristic are symmetrical. 2 (a) and 2
(B) shows the current-voltage characteristics of the MIM element having the Cr / Ta ₂ O ₅ / Ta structure and the current value ratio between the positive electrode side and the negative electrode side.

However, when the upper and lower electrode materials of the MIM element are different, the symmetry of the current-voltage characteristic is deteriorated. The Cr / Ta ₂ O ₅ / Ta structure shown in the conventional example has a relatively good symmetry, but this symmetry is not sufficient.

Further, in the Ta thin film used for the signal electrode,
Since the Ta thin film has a large resistivity of 200 μΩ · cm, there has been a problem that it is not possible to meet the demand for a liquid crystal display device having a large size and a large capacity.

In order to solve this, as a metal thin film having a low resistivity (2 μΩ · cm) and capable of anodizing,
Although it is possible to use an Al thin film, the pure Al thin film anodic oxide film has better insulation than the Ta thin film anodic oxide film as shown in FIG. However, there is a problem that it cannot be used as an MIM element because of its small size.

In consideration of such problems of the prior art, the present invention has a good current-voltage characteristic symmetry, a low electrode resistivity, and a sufficiently large on-current / off-current ratio of the current-voltage characteristic. It is an object of the present invention to provide an active matrix liquid crystal display device including a two-terminal element.

[0009]

According to the present invention, an Al thin film electrode in which Si is added to at least one Al thin film of two Al thin films and another Al thin film side of the Al thin film in which Si is added are provided. Is an active matrix liquid crystal display device including a two-terminal element having an aluminum oxide thin film formed between electrodes by oxidizing a surface facing each other.

[0010]

According to the present invention, the Al thin film electrode improves the symmetry of the current-voltage characteristics of the MIM element and reduces the resistivity of the electrode, and the oxidation is formed by oxidizing the Al thin film to which Si is added. The aluminum thin film sufficiently increases the ratio of on-current and off-current of the current-voltage characteristic.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing its embodiments.

FIGS. 1A and 1B are a plan view of an active matrix liquid crystal display device according to an embodiment of the present invention and a sectional view showing the structure of the same embodiment. That is, on the transparent insulating substrate 1, a signal electrode of a Si-added Al thin film (hereinafter referred to as an Al-Si thin film) and M
A lower electrode 2 of the IM element is formed, and an insulating thin film 3 of an anodic oxide film (hereinafter referred to as Al—Si—O _x thin film) whose surface is oxidized is formed on the lower electrode 2, and further thereon. The upper electrode 4 of the MIM element is formed. A liquid crystal driving electrode 5 is formed so as to partially overlap the upper electrode 4. Therefore, Al-Si /
An MIM element having an Al-Si- _Ox / Al-Si structure is formed.

Next, a specific manufacturing method of the above embodiment will be described.

First, as the translucent insulating substrate 1, a 7059 glass substrate manufactured by Corning Incorporated was used. Si is used as a target on a glass substrate by the DC sputtering method.
Target containing 2 at% of A
r, gas pressure 0.3 Pa, and sputtering power 10 W / cm
^An Al-Si thin film was formed to a film thickness of 300 nm under the condition ² and a predetermined pattern was formed by a wet etching method to form a signal electrode and a lower electrode 2 of the MIM element. A
The surface of the 1-Si thin film was anodized by an electrolytic solution of 5% ammonium borate aqueous solution, liquid temperature 30 ° C., current density 5 mA.
Al-Si-O _x in terms of / cm ² and oxidation voltage 35V
The thin film was formed as the insulating thin film 3 with a film thickness of 50 nm.
An Al—Si thin film having a film thickness of 10 nm was formed and patterned under the same film forming conditions as the lower electrode 2 of the MIM element, and the upper electrode 4 of the MIM element was formed. And finally I
A TO thin film was formed into a film having a thickness of 100 nm by a sputtering method and patterned to obtain a liquid crystal driving electrode 5.

The current of the MIM element produced in the above process-
The voltage characteristics and the ratio of the current values on the positive electrode side and the negative electrode side are shown in FIGS. 2 (a) and 2 (b). Conventional example Cr / Ta
Compared with the ₂ O ₅ / Ta structure, the ratio of on-current and off-current of the current-voltage characteristic is almost equal, and the symmetry of the positive electrode side and the negative electrode side of the current-voltage characteristic is excellent.

Further, Al-Si, which is the upper and lower electrode materials of the MIM element, has a low resistivity of about 5 μΩ · cm,
Good display quality can be realized even for large-sized and large-capacity liquid crystal display elements.

Next, a liquid crystal display element using this MIM element was prepared. The specifications of the liquid crystal display device are as follows.
The number of lines is 1024 x 768, and the pixel pitch is 0.2
mm and the size of the screen were about 11 inches, and black and white binary display was performed. As a result, good display was possible without causing shadows and uneven brightness.

Although the amount of Si added to the Al-Si thin film is set to 2 at% in the above embodiment, it is not limited to this and may be 1 at% or more.

In the above embodiment, the electrolytic solution used for anodic oxidation was a 5% ammonium borate aqueous solution, but the electrolytic solution is not limited to this and may be a neutral electrolytic solution.

Further, in the above embodiment, the thickness of the anodic oxide film is set to 50 nm, but the thickness is not limited to this, and it may be determined from the requirement of characteristics.

Further, in the above embodiment, the same Al-Si thin film is used for the upper electrode 4 and the lower electrode 2 of the MIM element, but the present invention is not limited to this, and only the electrode on the anodized side is made of Al.
A Si thin film may be used (the lower electrode 2 in the above embodiment), and the other electrode is an Al thin film to which Si is not added,
Alternatively, an Al-Si thin film having a Si addition amount different from the Si addition amount of the Al-Si thin film to be anodized may be used.

[0022]

As is apparent from the above description, the present invention provides an Al thin film electrode in which Si is added to at least one Al thin film of two Al thin films and an Al thin film in which Si is added. Since the two-terminal element having the aluminum oxide thin film formed between the electrodes by oxidizing the surface facing the other Al thin film side is provided, the symmetry of the current-voltage characteristics is good, and the resistance of the electrode is high. The rate is small,
It has an advantage that the ratio of the on-current to the off-current of the current-voltage characteristic becomes sufficiently large.

[Brief description of drawings]

FIG. 1 (a) is a plan view of an active matrix liquid crystal display device according to an embodiment of the present invention, and FIG. 1 (b).
[FIG. 3] is a sectional view showing a structure of the embodiment.

FIG. 2A is a diagram showing current-voltage characteristics of the MIM element of the same example and a conventional MIM device, and FIG. 2B is a diagram showing a ratio of current values on the positive electrode side and the negative electrode side. Is.

3A is a plan view of a conventional MIM element, and FIG. 3B is a sectional view showing the structure thereof.

FIG. 4 is a diagram showing a comparison of current-voltage characteristics of a pure Al thin film anodized film and a Ta thin film anodized film.

[Explanation of symbols]

1 translucent insulating substrate 2 signal electrode and lower electrode of MIM element 3 insulating thin film 4 upper electrode of MIM element 5 liquid crystal driving electrode 21 glass substrate 22 Ta thin film 23 Ta ₂ O ₅ thin film 24 Cr thin film 25 ITO thin film

Claims (4)

[Claims] 1. An Al thin film electrode in which Si is added to at least one Al thin film of two Al thin films, and the Si
An active matrix liquid crystal comprising a two-terminal element having an aluminum oxide thin film formed between the electrodes by oxidizing the surface of the Al thin film to which Al is added facing the other Al thin film side. Display device. 2. The method of oxidizing the surface of an Al thin film to which Si is added is an anodic oxidation method.
The active matrix liquid crystal display device described. 3. The active matrix liquid crystal display device according to claim 1, wherein the amount of Si added to the Si-added Al thin film is 1 at% or more. 4. Si is added to any of the Al thin films,
The active matrix liquid crystal display device according to claim 1, wherein the addition amounts thereof are equal.