JPH04340930A - Active matrix liquid crystal display device with two-terminal element - Google Patents

Abstract

PURPOSE:To obtain a bright liquid crystal panel which is free from after-images, seizure and problems in reliability and is bright by oxidizing the metal of one-side metallic ultra-thin films constituting MIMs to prevent the deterioration in transmittance and forming MIM elements which are free from the polarity difference of electric characteristics and shift. CONSTITUTION:The two-terminal elements of the MIMs are formed by using the metal oxide 3 to form the electrode material on the opposite side near at least the boundary with the insulating film 2 of the opposite side electrodes of the MIM elements constituted by forming the insulating film 2 on the surface of a 1st metallic thin film forming pattern 1 and forming the film pattern of the opposite side metallic ultra-thin films thereon. The electrode material to be formed on this insulating film 2 is formed of a 2nd metallic ultra-thin film consisting of Cr, etc., and further, this film is oxidized during or after the film formation. Then, the 2nd metallic ultra-thin film is formed of the metal oxide ultra-thin film 3, by which the transmittance of visible light is improved. The polarity difference of the electrical characteristics of the MIM elements is eliminated by executing some annealing treatment when the Cr is used for the 2nd metal.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in the basic structure of an MIM element, and particularly to providing a means for simplifying the photo process and a highly reliable MIM.

0002

[Prior Art] The basic process of conventional MIM is Ta film formation pattern formation - anodization - Cr film formation pattern formation - ITO film formation pattern formation as a pixel transparent electrode, and the number of photo steps for pattern formation. required at least three times. Figure 3 shows a cross-sectional view of a conventional MIM element forming substrate.
Shown below. A first insulating film 2 is formed on the surface of a first metal 1 such as Ta by a method such as anodic oxidation, and a second metal 7 such as Cr is deposited and patterned thereon. Finally, the pixel transparent electrode 4 is formed into a film pattern to complete the MIM element forming substrate. The reason why the photo process is required three times is as follows.
This is due to the fact that in order to eliminate the asymmetry of the electrical characteristics of the MIM element, that is, to eliminate the polarity difference, it is necessary to independently pattern the second metal 7, which is the electrode on the opposite side of the MIM, using a metal material such as Cr. . If the film such as ITO as the pixel transparent electrode could also be used as the electrode on the opposite side of the MIM, it would require two photo steps, but in this case there would be a large polarity difference, and therefore a DC voltage component would be applied to the liquid crystal, resulting in an afterimage as a liquid crystal display. Due to other reliability problems, it cannot be used. There is also a method of correcting the polarity difference by forming two elements in one pixel, but in this case, the process becomes complicated and production efficiency and yield are reduced.

[0003] Conventional Japanese Patent Application Laid-Open No. 1983-1989, which is currently a powerful method.
The MIM device described in the publication No. 164724 is
By setting the thickness of the second metal to 100 Å or less and forming the second metal and the transparent ITO electrode in the same shape, MIM with two photo steps is achieved. . FIG. 4 shows a cross-sectional view of the MIM element forming substrate that can be formed by two photo steps. In this case, the second metal 8 such as Cr, although thin, functions as an electrode for the MIM.
The polarity difference between the elements disappears or becomes very small. Further, since the second metal 8 is formed of an ultra-thin film of 100 Å or less, the visible light transmittance of this ultra-thin film itself is improved and it also functions as a transparent electrode of the pixel. Due to the above,
A second ultra-thin metal film 8 and a pixel transparent electrode 4 made of ITO etc.
Since the same pattern can be formed in one photo process, MIM can be achieved in two photo processes.

0004

[Problems to be Solved by the Invention] However, the only drawback of the MIM method shown in FIG. 4, which can be achieved with two photo steps, is that the visible light transmittance of the second ultra-thin metal film 8 is as low as about 70%. , although it functions as a transparent electrode of the pixel,
The LCD screen becomes dark. The contrast looks poor on dark screens, which is a big negative in terms of image quality.

The present invention solves these conventional drawbacks and achieves a two-step photo process for MIM element substrates without impairing the visible light transmittance of a liquid crystal display, thereby improving production efficiency and yield. The goal is to achieve the following. Another object of the present invention is to eliminate afterimages and burn-in phenomena in liquid crystal displays caused by characteristic shifts of MIM elements in the conventional MIM element forming substrate shown in FIG.

[0006]

[Means for Solving the Problems] A two-terminal element active matrix liquid crystal display device of the present invention is provided by forming an insulating film on the surface of a first metal thin film forming pattern, and forming an opposite electrode pattern thereon. In the opposite electrode of the MIM element, the opposite electrode material at least near the interface with the insulating film is made of a metal oxide to form a two-terminal MIM element. In addition, the second metal of the MIM element is formed by anodizing the surface of the first metal to form an insulating film, and forming a second metal on top of the insulating film. Furthermore, in a MIM active matrix element forming substrate that simplifies the photo process by forming the second metal and the ITO pixel electrode in the same shape, the second metal is formed of a metal oxide with no film thickness restrictions. It is characterized by making it.

The method for oxidizing the second metal is characterized in that it is a reactive sputtering method in which Ar gas mixed with O2 gas is used as a plasma gas during sputtering film formation.

[0008] Another method of oxidizing the second metal is as follows:
It is characterized by thermal oxidation after film formation.

[0009] Another method of oxidizing the second metal is as follows:
It is characterized by lamp annealing after film formation.

[0010] Further, the mass film thickness of the second metal is 500
The oxidation method in the case of less than Å
At least one of the conditions for sputtering film formation using an O target etc. is that the sputtering temperature is 200°C or higher, or the 02 flow rate ratio in the plasma gas is 1% or higher.
method.

[0011]

[Operation] Visible light transmittance is improved by making the second ultra-thin metal film an ultra-thin metal oxide film. When compared with the same mass and film thickness, the visible light transmittance of the metal oxide ultra-thin film is approximately 95%, which is a significant improvement, compared to the approximately 70% visible light transmittance of the metal ultra-thin film. Moreover, experimental evaluation results when the second metal is Cr show that even if the second metal is oxidized, the polarity difference in the electrical characteristics of the MIM element disappears or becomes very large after a slight annealing treatment. It was found that there were fewer

The principle mechanism by which visible light transmittance is improved by oxidation will be described below.

[0013] Generally, metals have a conduction band and a valence band that overlap each other, so the band gap is small and light is easily absorbed and electrons are easily excited. Therefore, light is easily absorbed and light transmittance is poor. On the other hand, in metal oxides, the conduction band rises and the band gap becomes large, making it difficult for electrons to be excited, and therefore light absorption also decreases. In other words, the principle is that the light transmittance is improved.

[0014]

[Embodiment] Hereinafter, a first embodiment of the present invention will be explained using the MI shown in FIG.
This will be explained with reference to a sectional view of an M element forming substrate and a plan view of an MIM element forming substrate in FIG.

The first insulating film 2 is generally formed by oxidizing the surface of the first metal 1 by anodic oxidation. There is also a method of applying a film. The most important feature of the present invention is that the electrode material formed on the insulating film is a secondary material such as Cr.
The purpose of this method is to further oxidize the film during or after film formation. There are various specific methods for oxidation, but typical methods are listed below.

(1) A reactive sputtering method is used in which O2 is mixed into plasma gas such as Ar during sputtering film formation.

(2) After sputtering or vapor deposition, oxidation is performed by thermal oxidation or lamp annealing. As a result, the metal is oxidized after being formed as a metal thin film once.

(3) When the first metal is an ultra-thin film of 100 Å or less, no particular oxidation process is performed during or after the first metal film formation, and the pixel transparency is maintained in the next film formation process. When forming the electrode, the conditions for sputtering film formation using an ITO target or the like are such that the sputtering temperature is 200° C. or higher or the O2 flow rate ratio in the plasma gas is 1% or higher. As a result, it was found that the first metal could be oxidized simultaneously while forming the pixel transparent electrode.

As a result of the above, the visible light transmittance of the second ultra-thin metal oxide film 3 is improved to about 99%, which is the same as the transparency of only a transparent electrode such as ITO. Incidentally, since the visible light transmittance of the conventional second metal thin film was about 70%, this means that the transmittance has been improved by about 40%. Therefore, as shown in 5 in FIG. 2, it is possible to form a two-layer film pattern with the same pattern shape as a pixel transparent electrode such as ITO, spanning from the MIM element to the pixel area, and in the photo process 2.
A simplified process is possible.

Note that the second metal oxide ultra-thin film 3 is made of Cr.
By using materials such as oxides, MI
It functions well as the electrode on the opposite side of the M element. In other words, the polarity difference in the electrical characteristics of the MIM element can be kept small. Conventionally, it has been widely accepted that the symmetry of the electrical characteristics of the device cannot be maintained unless the material for one side electrode of an MIM device is a thin metal film such as Cr. It was discovered that the symmetry of the electrical characteristics of the device can be sufficiently maintained even when the electrode material on one side is a metal oxide. This will be explained in a little more detail according to the electrical characteristic graph. The electrical characteristics of the MIM element with a large polarity difference shown in FIG.
This appears when the metal is Ta, the first insulating film is Ta2O5, and the opposite electrode is an ITO transparent electrode. When the opposite electrode=Cr, the electrical characteristics of the MIM element with small polarity difference as shown in FIG. 5 are obtained, and this structure has been commonly used in the past. The important thing here is that the opposite electrode =
CrOx also has the electrical characteristics of an MIM element with a small polarity difference as shown in Fig. 5, and Ta-TaOx-CrOx-IT
A new film formation combination of O, and Cr
It is possible to form two layers of Ox-ITO in the same pattern. In other words, since CrOx is transparent, it can be used as a pixel transparent electrode in the same way as ITO. Here, the specific state of CrOx is Cr2O3 or CrO
2, CrO3, etc. can be considered. Next, a second embodiment of the present invention will be described. This will be explained with reference to FIG. 3, which is a sectional view of a conventional MIM element forming substrate. This figure shows the basic structure of the first generation MIM, and includes at least three steps: patterning of the first metal 1, patterning of the second metal 7, and patterning of the pixel transparent electrode 4, such as ITO. Two patterning photo steps are required. The film thickness of the second metal 7 in this case can be made sufficiently thick. In the MIM element having the above basic configuration, the second metal 7 film is formed as a metal oxide film by, for example, reactive sputtering. This causes further oxidation of the first insulating film formed by metal anodic oxidation, thereby making the inside of the first insulating film oxygen-rich. The mechanism described in the second embodiment above is
The same applies to the structure described in the first embodiment. Here, if the second metal 7 is oxidized and becomes a metal oxide, the sheet resistance will increase and there is a possibility that it will not be able to perform the electrical conduction function necessary as one side electrode of the MIM element. In this case, a two-layer electrode structure in which a metal oxide is used only in the vicinity of the interface with the first insulating film and a metal thin film is formed on the upper layer, or an electrode structure in which the oxidation state is continuously changed. By doing so, it is possible to achieve both the function of electrical conduction and the oxygen-rich state of the first insulating film.

[0021]

[Effect of the invention] Cross-sectional view 4 is one of the specific measures to improve production efficiency and yield, and to thoroughly reduce costs.
There is an MIM that can be formed with only two photo steps as shown in FIG. The present invention can suppress the deterioration of the transmittance of the second ultra-thin metal film 8 and ensure sufficient brightness as a liquid crystal display.

By using an ultra-thin metal oxide film as the second ultra-thin metal film, the visible light transmittance is improved, but when compared with the same mass and film thickness, the visible light transmittance of the ultra-thin metal film is about 70%. On the other hand, the visible light transmittance of ultra-thin metal oxide film is about 9
This is a significant improvement to 9%. Therefore, even if the ultra-thin metal oxide film is formed to be thick, the transmittance does not easily decrease, and therefore the film thickness limitation of 500 Å or less is eliminated, making it easy to form a thin film. Moreover, the second metal is C
The experimental evaluation results for the case where r is oxidized show that even if the second metal is oxidized, the polarity difference in the electrical characteristics of the MIM element is eliminated or becomes very small by performing a slight annealing treatment. . In this way, the present invention can simplify and simplify the process by reducing the number of photo steps to two while maintaining sufficient brightness for a liquid crystal display.

[0023] Furthermore, the present invention further oxidizes the first insulating film formed by oxidizing the surface of the first metal by oxidizing the second metal, thereby making the inside of the first insulating film rich in oxygen. can be in the state of This reduces the concentration of unoxidized mobile metal ions in the first metal, eliminates the shift in the electrical characteristics of the device caused by the movement of mobile ions, and eliminates the afterimage of the liquid crystal display that was caused by the shift. It is possible to eliminate reduction and burn-in reduction. Even in the conventional MIM shown in cross-sectional view 3, by oxidizing the second metal, it is possible to eliminate the shift in the electrical characteristics of the element caused by the movement of mobile ions as described above, so it is possible to prevent afterimages and burn-in. Similar effects can be expected.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a MIM element forming substrate of the present invention.

FIG. 2 is a plan view of the MIM element forming substrate of the present invention.

FIG. 3 is a cross-sectional view of a conventional MIM element forming substrate.

[Figure 4] MIM that can be formed using two conventional photo processes
A sectional view of an element forming substrate.

FIG. 5 is a graph showing the electrical characteristics of an MIM element with small polarity difference.

FIG. 6 is a graph showing the electrical characteristics of an MIM element with a large polarity difference.

[Explanation of symbols]

1 First metal 2 First insulating film 3 Second metal oxide ultra-thin film 4 Pixel transparent electrode 5 Second metal oxide ultra-thin film and pixel transparent electrode 2
Layer pattern 6 Two-layer pattern 7 of first metal and first insulating film
Second metal 8 Second metal ultra-thin film

Claims (6)

[Claims] Claim 1: In an opposite electrode of an MIM element in which an insulating film is formed on the surface of a first metal thin film formation pattern and an opposite electrode is formed on the surface of the insulating film, at least a portion near the interface with the insulating film is formed. A two-terminal element active matrix liquid crystal display device characterized in that a two-terminal MIM element is formed by using a metal oxide as the material for the opposite electrode. 2. An M formed by anodizing the surface of a first metal to form an insulating film, and forming a film of a second metal on top of the insulating film.
Formation of an MIM active matrix element in which the photo process is simplified by forming the second metal of the IM element as an ultra-thin film with a mass film thickness of 500 Å or less, and by forming the second metal and the ITO pixel electrode in the same shape. On the board,
A two-terminal element active matrix liquid crystal display device, characterized in that the second metal is a metal oxide with no film thickness restrictions. 3. The method of oxidizing the second metal is a reactive sputtering method in which Ar gas mixed with O2 gas is used as a plasma gas during sputtering film formation. Active matrix liquid crystal display device. 4. The two-terminal element active matrix liquid crystal display device according to claim 1, wherein the method of oxidizing the second metal is thermal oxidation after film formation. 5. The two-terminal active matrix liquid crystal display device according to claim 1, wherein the method for oxidizing the second metal is lamp annealing after film formation. 6. The mass film thickness of the second metal is 500 Å.
The oxidation method in the following case is used when forming the pixel transparent electrode, which is the next step after the second metal film formation and pattern formation.
Claim 1 characterized in that the conditions for sputtering film formation using a target or the like are at least one of setting the sputtering temperature to 200° C. or higher or setting the 02 flow rate ratio in the plasma gas to 1% or higher. The two-terminal active matrix liquid crystal display device described above.