JPH08262497A - Liquid crystal display device and its production - Google Patents

Abstract

PURPOSE: To provide a hihg-grade liquid crystal display device with which a sufficient contrast ratio is stably assured and burning does not arise even when the device is operated over a long period of time. CONSTITUTION: A lower metal 2 consisting of tantalum and an insulating film 3 consisting of tantalum oxide are formed on a glass substrate 1 and upper metals 4a, 4b consisting of titanium are formed. Two nonlinear resistance element part 5a, 5b are formed with the lower metal 2 as a common conductor in correspondence to the upper metals 4a, 4b. Oxygen atoms migrate to the upper metal 4a, 4b side at the boundary of the upper meals 4a, 4b consisting of the tantalum oxide and numbers of oxygen atoms/numbers of tantalum atoms ratio of X<2.0 is resulted at the boundary as well in the heat process in a post stage if titanium and aluminum or aluminium smaller in the free energy for oxide formation than the free energy for oxide formation of Ta2 O5 are selected for the upper metals 4a, 4b. The influence that contaminated layers exert on the characteristics of the nonlinear resistance element parts 5a, 5b is lessened. The current-voltage characteristics are stabilized by attaining X<2.0.

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 having a non-linear resistance element having a lower metal-insulator-upper metal structure in a pixel display transparent electrode, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a display device using a liquid crystal display has been
It has been used for large-capacity display applications such as personal computers, word processors, terminal devices for office automation, and image display for televisions, and higher image quality has been demanded.

There are various types of switching arrays for such a liquid crystal display, but a two-terminal non-linear resistance element having a simple structure and easy to manufacture, among them, as a currently practically used lower part, There is a metal-insulator-top metal (MIM) type, for example, Japanese Examined Patent Publication No. 55-16127.
No. 3 and JP-A No. 62-62333.

And, these Japanese Patent Publications No. 55-161273
The configurations described in Japanese Patent Laid-Open No. 62-62333 and Japanese Patent Laid-Open No. 62-62333 are as follows.
It is as shown in FIGS. 1 and 2.

As shown in FIGS. 1 and 2, tantalum (Ta) is deposited on the glass substrate 1 by a thin film forming method such as a sputtering method or a vacuum deposition method, and is patterned by a photo-etching method to form a lower metal. 2 is formed, an insulating film 3 formed by anodic oxidation is formed on the lower metal 2, and upper metal 4a, 4b formed by forming a thin film of chromium (Cr) on the insulating film 3 is formed, These upper metal 4a,
Two non-linear resistance elements (MIM elements) corresponding to 4b 5
a and 5b are formed.

The upper metal 4a is formed on the glass substrate 1 together with the wiring 6, and the pixel display transparent electrode 7 is formed on a part of the upper metal 4b to form an array substrate 8.

On the other hand, a transparent electrode 12 is formed on the glass substrate 11 to form a counter substrate 13.

The array substrate 8 and the counter substrate 13 are opposed to each other, and the liquid crystal composition 15 is sealed between the array substrate 8 and the counter substrate 13.

[0009]

However, the non-linear resistance element portion (MIM element) 5a thus created,
Impurities easily infiltrate the insulating film 3 of 5b and the upper metal 4a, 4b and the current-voltage characteristics are affected by the impurities, and the element characteristics become unstable. For example, when image display is continued for a long time as a TFD-LCD, the contrast There is a problem that a change in the ratio over time or a problem of image sticking may occur, and high-quality display may be impaired.

The present invention has been made in view of the above problems, and even when operated for a long time, the current-voltage characteristic is stable, a practically sufficient contrast ratio is stably secured, and burn-in occurs. An object of the present invention is to provide a high-quality liquid crystal display device that does not occur and a method for manufacturing the same.

[0011]

According to another aspect of the present invention, there is provided a liquid crystal display device having a plurality of pixel display transparent electrodes formed on a transparent insulating substrate and electrically connected to each of the plurality of pixel display transparent electrodes. An array substrate having a non-linear resistance element part of a lower metal-insulator-upper metal structure, a counter substrate arranged to face the array substrate, and a liquid crystal composition sandwiched between the array substrate and the counter substrate. In the liquid crystal display device including, the insulator is made of tantalum oxide,
The upper metal is made of a metal whose free energy of formation of an oxide is smaller than that of tantalum oxide, and the oxygen atom number / tantalum atom number ratio X is X < It is 2.0.

According to a second aspect of the present invention, there is provided a method of manufacturing a liquid crystal display device, wherein a plurality of pixel display transparent electrodes formed on a transparent insulating substrate, and a lower metal electrically connected to each of the plurality of pixel display transparent electrodes. Insulator-An array substrate provided with a non-linear resistance element part having an upper metal structure, a counter substrate arranged to face the array substrate, and a liquid crystal composition sandwiched between the array substrate and the counter substrate. In the method for manufacturing a liquid crystal display device, a step of forming a tantalum film on the transparent insulating substrate, a step of oxidizing the formed tantalum film to form tantalum oxide, and a step of forming an oxide film on the tantalum oxide film. Forming a metal film having a free energy of formation smaller than that of tantalum oxide;
A heat treatment step performed after these steps is provided.

[0013]

According to the present invention, the insulator is made of tantalum oxide, the upper metal is made of a metal having a free energy of formation of an oxide smaller than that of tantalum oxide, and the ratio of the number of oxygen atoms / the number of tantalum atoms is X. Since X <2.0 in the film and near the upper metal interface, the intermediate oxidation state of tantalum increases in the insulating film as X decreases, and the influence of impurities on the current-voltage characteristics of the nonlinear resistance element section. Is relatively small, the stability of current-voltage characteristics is increased, and if X <2.0, the image sticking can be made invisible, and the free energy of oxide formation is the free energy of oxide formation of tantalum oxide. If a smaller one is selected, oxygen atoms move to the upper metal side at the upper metal interface of tantalum oxide in the subsequent thermal process, and X <2.0 at the interface.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A matrix type liquid crystal display device according to an embodiment of the present invention will be described below with reference to the drawings. The parts corresponding to the conventional example will be described with the same reference numerals.

As shown in FIGS. 1 and 2, tantalum (Ta) is formed on a glass substrate 1 as a transparent insulating substrate.
Lower metal 2 is formed, an insulating film 3 as an insulator is formed on the lower metal 2, and upper metal 4a, 4b of titanium (Ti) is formed on the lower metal 2 via the insulating film 3. , Two non-linear resistance element portions (MIM (Metal In
sulator metal) elements) 5a and 5b are formed, and an alignment film (not shown) is formed on the upper surfaces of these elements.

The upper metal 4a is formed on the glass substrate 1 together with the wiring 6, and ITO is formed on a part of the upper metal 4b.
The pixel display transparent electrode 7 made of (Indium Tin Oxide) is formed, and the array substrate 8 is formed.

On the other hand, on the glass substrate 11, ITO (Indium
A thin film transparent electrode 12 made of Tin Oxide) is formed to form a counter substrate 13.

The array substrate 8 and the counter substrate 13 are opposed to each other, and the liquid crystal composition 15 is sealed between the array substrate 8 and the counter substrate 13.

Therefore, the driving voltage is supplied from the wiring 6 to the pixel display transparent electrode 7 through the two non-linear resistance element portions 5a and 5b connected in series with opposite polarities.

Next, a method of manufacturing this liquid crystal display device will be described with reference to FIGS.

First, as shown in FIG. 3, the plate thickness is 0.7 mm.
An alkali protection film (not shown) that protects SiO ₂ is formed on the opposite surface of one of the glass substrates 1, and a Ta thin film 21 having a thickness of 3000 Å is formed and patterned on the alkali protection film by a sputtering method. For patterning this Ta thin film 21, CF ₄ and O _{2 are used.}
The chemical dry etching method using the mixed gas of is used.

Next, as shown in FIG. 4, the entire surface of the Ta thin film 21 patterned into a predetermined shape is oxidized to form a uniform Ta oxide film 22 having a film thickness of 350 to 800 Å on the surface. This Ta oxide film 22 is formed by Ta thin film.
21 is used as an anode, a Pt-plated Ti mesh is used as a cathode, and a 1-8 wt% ammonium borate aqueous solution is used as an electrolytic solution to form an anodizing method. Specifically, by applying a voltage of 21 to 48 V between the positive and negative electrodes, a uniform T having a film thickness of 350 Å to 800 Å can be obtained.
The a oxide film 22 is formed.

Further, as shown in FIG. 5, a Ta oxide film 22 is formed.
The Ta thin film 21 having a predetermined shape is patterned again, and the lower metal 2 made of the Ta thin film 21 and the Ta on the surface thereof are formed.
The element portion 24 having a predetermined shape is formed of the non-linear resistance film 23 having the insulating film 3 of the oxide film 22. This patterning is performed by the same method as the etching for patterning the Ta thin film 21 into a predetermined shape.

Next, in a vacuum of 10 ^-4 Torr or less, 43
Heat treatment at 0 ° C. is performed. In addition, this heat treatment is a temperature rising process from room temperature to 430 ° C. for 1 hour.
It consists of a constant temperature process at 10 ° C. for 1 hour and a radiation cooling process from 430 ° C. to room temperature for 5 hours. Moreover, the heating apparatus used the normal electric furnace.

Further, a Ti thin film 25 having a thickness of 1200 Å is formed by the sputtering method.

Thereafter, as shown in FIG. 6, two upper metal layers 4a, 4a,
At the same time as forming 4b, the wiring 6 is formed. Then, the patterning of the upper metal 4a, 4b made of the Ti thin film 25 is performed by using 9 g of EDTA, 400 cc of water, and 3 ml of ammonia water.
The temperature is kept at room temperature with the etching solution mixed in the ratio of.

Then, the substrate temperature is changed from 180 ° C to 220 ° C.
The film thickness of 1000
The thin film pixel display transparent conductive film made of angstrom ITO is formed and patterned into a predetermined shape to form the pixel display transparent electrode 7.

Here, tantalum oxide (Ta ₂ O ₅ ) is used.
It is known that the ratio of the number of oxygen atoms / the number of tantalum atoms of X is 2.5 stoichiometrically, but when formed by the anodic oxidation method, -OH or -C = O or O. Oxygen atoms as impurities such as ₂ are mixed in the oxide film, or suboxides are formed.
At the interface between a and 4b, it is about 2.3 to 2.7.
The ratio of oxygen atoms to tantalum atoms is, for example, RBS.
(Rutherford backscattering) method, ESCA, SIMS, A
It can be measured by a method such as ES. And as a result of the research, X
The smaller is the intermediate oxidation state (suboxide) of tantalum in the insulating film 3, the more impurities are in the nonlinear resistance element portion.
The influence on the current-voltage characteristics of 5a and 5b is relatively small, the stability of the current-voltage characteristics of the non-linear resistance element portions 5a and 5b is increased, and if approximately X <2.0, a gradation of about 16 gradations is obtained. It was found that the image sticking can be made invisible even when the key display is performed.

Even if X <2.0 in the insulating film 3,
The surface is easily contaminated by being exposed to the atmosphere between the anodic oxidation process and the formation process of the upper metal 4a, 4b, and after forming the nonlinear resistance element parts 5a, 5b, X is formed at the interface of the upper metal 4a, 4b. It may be <2.0. If the contaminated part functions as an insulating layer of the nonlinear resistance element parts 5a and 5b, the reliability is adversely affected. Further, as the upper metals 4a and 4b, those having a free energy of oxide formation smaller than that of Ta ₂ O ₅ , such as titanium (Ti).
If aluminum or aluminum (Al) is selected, oxygen atoms move to the upper metal 4a, 4b side at the interface of the upper metal 4a, 4b of tantalum oxide in the thermal process in the subsequent process, and X <
Since it is 2.0, the influence of the contaminated layer on the characteristics of the nonlinear resistance element portions 5a and 5b can be reduced. However, when the free energy of oxide formation is larger than the free energy of oxide formation of Ta ₂ O ₅ , for example, when Cr or ITO is the upper metal, oxygen is more likely to bond with Ta rather than the upper metal, and the contaminant layer at the interface has a nonlinear resistance. This causes the element portions 5a and 5b to function as an insulating film, resulting in a significant loss of stability of current-voltage characteristics.

Therefore, the insulating film 3 of the non-linear resistance element portions 5a and 5b on the array substrate 8 obtained as described above has the number of oxygen atoms / tantalum atoms in the film and near the interface with the upper metals 4a and 4b. Number ratio X is SIMS, AES, ESC
The results of A and RBS satisfy the condition of X <2.0.

In the AES, the primary electron beam conditions were an acceleration voltage of 5 kV, a sample current of 0.05 μmA, and an incident angle of 60 °. The ion beam conditions are raster range: 2 mm × 2 mm, ion species Ar, accelerating voltage 3 kV.
And Under these conditions, the atomic number ratio X was determined by assuming that the 503 eV and 179 eV Auger electrons were caused by oxygen atoms and tantalum atoms, respectively. In addition, X-ray diffraction
According to the analysis of ESCA, the oxide film is β-T in the film.
It was found that the fine crystal grains of a, the intermediate oxidation state of Ta (suboxide) and tantalum pentoxide (Ta ₂ O ₅ ) were mixed. Further, compared with a tantalum oxide film formed by thermal oxidation and a tantalum oxide film formed by a normal anodic oxidation method, X is apparently small and β-Ta fine crystal grains are large. At the interface, β-Ta fine crystal grains, an intermediate oxidation state of Ta (suboxide) and a mixed state of Ti are formed.
_The proportion of ₂ O ₅ is extremely small as compared with that in the film.

Thus, in manufacturing the liquid crystal display device, a polyimide resin is applied to the surface of the array substrate 8 on which the non-linear resistance element portions 5a and 5b and the pixel display transparent electrode 7 are formed and the surface opposite to the counter substrate 13. And baked to form an alignment film (not shown). Then, rubbing for controlling the alignment of the liquid crystal composition 15 is performed.

On the other hand, the transparent electrode 12 is also formed on the opposite surface of the glass substrate 11, and a polyimide resin is applied and baked to form an alignment film (not shown).

About 90 ° with respect to the array substrate 8.
Rub in the twisted direction.

Next, the long axis direction of the molecules of the liquid crystal composition 15 is 2
A liquid crystal composition 15 is injected between the array substrate 8 and the counter substrate 13 so as to be twisted by about 90 ° between the array substrate 8 and the counter substrate 13 with a gap of 5 μm therebetween, and a liquid crystal cell is formed. After that, a polarizing plate (not shown) is arranged on the outer surface of the liquid crystal cell with the polarization axis twisted by about 90 ° to form a liquid crystal display device.

The liquid crystal display device thus obtained had high image quality, high reliability, and high stability in which deterioration of the contrast ratio and the occurrence of image sticking were not visually recognized even when operated for a long time.

Although the heat treatment after forming the non-linear resistance element portions 5a and 5b was 430 ° C., if the number of gradations displayed is about 16 in the liquid crystal display device, a heat treatment of 300 ° or more is sufficient. On the other hand, above 500 ° C, the glass substrate 1
Depending on the type, since the softening point is approached, the array substrate 8 is warped or shrunk, which causes peeling of tantalum and lowers the yield, which is not preferable.

Further, after the ITO patterning, heat treatment may be performed at 200 ° C. to 300 ° C. for 1 hour to 3 hours to prevent characteristic unevenness and improve the yield. On the other hand, if the temperature is 200 ° C. or lower, there is no effect, and if the temperature is 300 ° C. or higher, the device characteristics become remarkably leaky and the contrast ratio cannot be secured. The same applies to the time, and if it is less than 1 hour, there is no effect, and if it is 3 hours or more, the element characteristics become leaky and the contrast ratio cannot be secured, which is not preferable.

[0039]

According to the present invention, the insulator is made of tantalum oxide, and the upper metal is made of a metal whose free energy of formation of oxide is smaller than that of tantalum oxide. Since X is less than 2.0 in the insulating film and in the vicinity of the upper metal interface, the intermediate oxidation state of tantalum increases in the insulating film as X becomes smaller, and impurities become a current-voltage of the nonlinear resistance element section. The influence on the characteristics becomes relatively small, the stability of the current-voltage characteristic increases, and if X <2.0, the image sticking can be made invisible, and the contrast ratio changes with time even after a long time operation. Without the image sticking, the image quality is high and the reliability is high.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a matrix type liquid crystal display device of one embodiment of the present invention.

FIG. 2 is a plan view showing the structure of the above liquid crystal display device.

FIG. 3 is a cross-sectional view showing one manufacturing process of the above liquid crystal display device.

FIG. 4 is a cross-sectional view showing the next manufacturing step of FIG. 3 of the liquid crystal display device.

5 is a cross-sectional view showing the next manufacturing step of FIG. 4 of the liquid crystal display device.

FIG. 6 is a cross-sectional view showing the next manufacturing step of FIG. 5 for the liquid crystal display device.

[Explanation of symbols]

 1 Glass substrate as transparent insulating substrate 2 Lower metal 3 Insulating film as insulator 4a, 4b Upper metal 5a, 5b Non-linear resistance element part 7 Pixel display transparent electrode 8 Array substrate 13 Counter substrate 15 Liquid crystal composition

Claims (2)

[Claims] 1. A plurality of pixel display transparent electrodes formed on a transparent insulating substrate, and a non-linear resistance element portion having a lower metal-insulator-upper metal structure electrically connected to each of the plurality of pixel display transparent electrodes. In a liquid crystal display device comprising an array substrate provided with, a counter substrate arranged to face the array substrate, and a liquid crystal composition sandwiched between the array substrate and the counter substrate, wherein the insulator is The upper metal is made of tantalum oxide, the free energy of formation of oxide is smaller than that of tantalum oxide, and the oxygen atom number / tantalum atom number ratio X is in the insulating film and at the upper metal interface. A liquid crystal display device, wherein X <2.0 over the vicinity. 2. A plurality of pixel display transparent electrodes formed on a transparent insulating substrate, and a non-linear resistance element portion having a lower metal-insulator-upper metal structure electrically connected to each of the plurality of pixel display transparent electrodes. A method for manufacturing a liquid crystal display device, comprising: an array substrate having a substrate; a counter substrate arranged to face the array substrate; and a liquid crystal composition sandwiched between the array substrate and the counter substrate, wherein The step of forming a tantalum film on an insulating substrate, the step of oxidizing the formed tantalum film to form tantalum oxide, and the free energy of oxide formation on the tantalum oxide is the free energy of formation of the tantalum oxide. A method of manufacturing a liquid crystal display device, comprising: a step of forming a film of a smaller metal; and a heat treatment step performed after these steps.