JPH07225399A - Production of liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal display device which does not generate flicker and burn and is capable of making display with high image quality by forming nonlinear resistance elements of a three-layered structure consisting of a metallic layer-insulator layer-metallic layer electrically connected to display pixel electrodes on a glass substrate, then heat treating the elements CONSTITUTION:The nonlinear resistance elements l formed by successively laminating the lower metallic layer 3 consisting of tantalum, the insulator layer 5 consisting of a tantalum oxide and the upper metallic layer 6 consisting of titanium and the display pixel electrodes 7 are formed on the glass substrate 2. Next, the glass substrate 2 formed with the nonlinear resistance elements 1 and the display pixel electrodes 7 is heat treated in a clean oven. The fluctuation in the current-voltage characteristic of the nonlinear resistance elements is decreased and simultaneously, the poorness in the symmetry of the current values of the positive electrodes and negative electrodes of the current-voltage characteristics is ameliorated if the heat treatment is executed at least for two hours at >=200 deg.C. The generation of the flicker and burn is thus prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a liquid crystal display device, and more particularly to a method of manufacturing a liquid crystal display device having a switching element composed of a non-linear resistance element.

[0002]

2. Description of the Related Art In recent years, a display device using a liquid crystal display has been
Applications are expanding from relatively simple devices such as clocks, calculators, and measuring instruments to large-capacity information displays such as personal computers, word processors, terminal devices for office automation equipment, and image display devices for TVs. In such a liquid crystal display device for displaying a large amount of information, a multiplex drive system of matrix display is generally adopted.

However, in this matrix display driving method, the contrast ratio between the display portion (on pixel) and the non-display portion (off pixel) is 2 due to the essential characteristics of the liquid crystal itself.
There is a problem that even if the number of scanning lines is about 100, it is not sufficient, and when a large-scale matrix drive with about 500 or more scanning lines is performed, the deterioration of contrast becomes fatal.

Therefore, developments for solving the drawbacks of the liquid crystal display device have been actively made. As one of the directions, there is one that directly switches and drives each pixel.
A thin film transistor or a non-linear resistance element is used as the switching element. Of these, since the non-linear resistance element has two terminals, it is basically simpler in structure than a thin film transistor. Further, there are advantages that the manufacturing is easy, and that the manufacturing yield can be improved and the cost can be reduced.

For this non-linear resistance element, a diode type junction formed using the same material as the thin film transistor,
A varistor type formed using zinc oxide, a three-layer MIM type including a metal layer-insulator layer-metal layer in which an insulator is interposed between metal electrodes, and a semiconductive layer between the metal electrodes. An intervening mold has been developed. Of these, MI
The M type has one of the simplest structures and can be said to be the most practically applicable nonlinear resistance element at present.

FIGS. 5 and 6 show one pixel portion of a matrix array substrate having the MIM element. The MIM element 1 of this matrix array substrate has a lower metal layer 3 made of a tantalum (Ta) film formed on a glass substrate 2.
An electrode wiring portion 4 integrally formed with the lower metal layer 3, an insulator layer 5 made of an oxide film covering the surfaces of the lower metal layer 3 and the electrode wiring portion 4, and the upper portion of the lower metal layer 3. Upper metal layer 6 extending over the glass substrate 2 across the insulator layer 5
Consists of. The upper metal layer 6 is connected to the display pixel electrode 7 formed of a transparent electrode formed in the display pixel area on the glass substrate 2.

In the method of forming the MIM element 1, first, a tantalum film is formed on the glass substrate 2 by a thin film forming method such as a sputtering method or a vacuum evaporation method, and the tantalum film is patterned by a photolithography method to form a lower metal. The layer 3 and the electrode wiring portion 4 integrally connected to the lower metal layer 3 are formed. Next, the lower metal layer 3 and the electrode wiring portion 4
By anodizing using an aqueous solution of citric acid,
An insulator layer 5 made of a tantalum oxide film is formed on the surface.
After that, a chrome (Cr) film is formed by a thin film forming method, and the chrome film is patterned by a photolithography method to form an upper metal layer 6 to manufacture.

The display pixel electrode 7 formed of a transparent electrode
Is formed by forming the MIM element 1 as described above, forming a transparent conductive film made of, for example, ITO (Indium Tin Oxide) by a thin film forming method, and patterning the transparent conductive film by a photolithography method. .

A basic manufacturing technique of this MIM element is disclosed in Japanese Patent Publication No. 55-161273, and an improved technique thereof is disclosed in Japanese Patent Publication No. 58-178320.

In the liquid crystal display device, another glass substrate is provided with a stripe-shaped counter electrode made of, for example, ITO to manufacture a counter substrate, and the counter substrate and the above MIM are manufactured.
A polyimide resin is applied to each opposing surface of the matrix array substrate on which the element 1 and the display pixel electrode 7 are formed, and a rubbing treatment is performed to form an alignment layer 11. The both substrates are opposed to each other at an interval of 5 to 20 μm. The peripheral portions are joined and liquid crystal is injected between both substrates. After that, a polarizing plate is attached to the outer surfaces of both substrates to manufacture.

By the way, the MIM formed as described above.
For a liquid crystal display device having an element, the current-voltage characteristic (I
There is a problem that the −V characteristic) fluctuates. In other words, when the pixels that have been on-displayed (black display in normally white mode) for a long time and the pixels that have been off-displayed (white display in normally-white mode) are switched to half-tone display at the same time, on-display is performed. There is a problem that the current value of the current-voltage characteristic of the MIM element of the pixel is reduced as compared with the pixel which is turned off, the transmittance of the pixel which is turned on is lowered, and it appears as a burn-in phenomenon.

As a method of reducing the fluctuation of the current-voltage characteristic of the MIM element, it is known that the MIM element should be heat-treated. That is, by heat-treating the MIM element at a temperature of 200 ° C. or higher for 30 minutes or more, the change in the current-voltage characteristic of the MIM element can be reduced to ⅓ or less.

[0013]

SUMMARY OF THE INVENTION As described above, the MIM
In a liquid crystal display device having an element, current-voltage characteristics of the MIM element fluctuate due to voltage stress on the MIM element, and pixels that have been on-displayed (black display in normally white mode) and off-displayed (normally). When the pixels that display white in white mode) are switched to half-tone display at the same time, the current value of the current-voltage characteristic of the MIM element of the pixel that was on display decreases compared to the pixel that displayed off. However, there is a problem in that the transmittance of the pixels that have been turned on is reduced, which causes a burn-in phenomenon.

As a method of reducing the fluctuation of the current-voltage characteristic of the MIM element, it has been conventionally known to heat the MIM element at a temperature of 200 ° C. or more for 30 minutes or more. However, if the MIM element is heat treated under the above conditions, M
Although the variation of the current-voltage characteristic of the IM element can be reduced, the symmetry of the positive and negative current values of the current-voltage characteristic of the MIM element is deteriorated. As a result, when the liquid crystal display device in which the symmetry of the current-voltage characteristics is deteriorated is driven to perform display, the magnitude of the effective value voltage to the liquid crystal layer is different between the positive electrode and the negative electrode, and the direct current component is the liquid crystal layer. However, it causes flicker and image sticking.

The present invention has been made to solve the above-mentioned problems, and in a liquid crystal display device having a non-linear resistance element having a three-layer structure composed of a metal layer-insulator layer-metal layer, flicker, image sticking, etc. It is an object of the present invention to obtain a method for manufacturing a liquid crystal display device capable of high-quality display that does not cause a problem.

[0016]

A non-linear resistance element having a three-layer structure including a display pixel electrode and a metal layer-insulator layer-metal layer electrically connected to the display pixel electrode is formed on a glass substrate. In the method of manufacturing a liquid crystal display device in which the nonlinear resistance element is heat-treated, the nonlinear resistance element is heat-treated at a temperature of 200 ° C. or higher for at least 2 hours.

[0017]

The cause of the change in the current-voltage characteristic due to the voltage stress on the MIM element in the conventional liquid crystal display device having the MIM element is not always clear, but the insulation interposed between the lower metal layer and the upper metal layer is not always clear. It is considered that this is due to the non-uniformity of the film quality of the oxide film formed on the surface of the body layer, that is, the lower metal layer formed by the anodic oxidation method, and the change over time.

As a method for reducing the variation of the current-voltage characteristic of the MIM element, the heat treatment as conventionally known can reduce the variation of the current-voltage characteristic, but on the other hand, the current-voltage characteristic of the MIM element is reduced. The symmetry of the current values of the positive electrode and the negative electrode deteriorates, and the display flickers or burns.

The inventor investigated the relationship between the heat treatment of the MIM element and the symmetry of the current values of the current-voltage characteristics of the positive and negative electrodes. Compared to the display device, it was found that the flicker was larger and the degree of image sticking was not significantly changed, so that it was not constant.
Furthermore, as a result of examining the heat treatment temperature and the treatment time, by performing the heat treatment at a temperature of 200 ° C. or higher for at least 2 hours, the fluctuation of the current-voltage characteristic of the MIM element is reduced, and the positive electrode and the negative electrode of the current-voltage characteristic are surely changed. It is possible to prevent deterioration of the symmetry of the current value,
It has been found that the liquid crystal display device has no flicker or image sticking.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described based on embodiments with reference to the drawings.

As shown in FIG. 1A, a tantalum film 10 having a thickness of 0.30 μm is formed on a glass substrate 2 made of, for example, borosilicate glass by a sputtering method.
This tantalum film 10 is patterned by a dry etching method using a mixed gas of CF ₄ and O _2, and the lower metal layer 3 and the lower metal layer 3 are integrated with each other as shown in (b) and (c). And the electrode wiring portion 4 connected to.

Next, the glass substrate 2 on which the lower metal layer 3 and the electrode wiring portion 4 are formed is anodized using an aqueous solution of citric acid having a concentration of 0.01% by weight, and as shown in FIG. A thickness of 0.0 on the surface of the lower metal layer 3 and the electrode wiring portion.
An insulator layer 5 made of a tantalum oxide film of 6 μm is formed.

Next, as shown in (e), a titanium (Ti) film 11 having a thickness of 0.20 μm is formed on the glass substrate 2 having the insulator layer 5 formed thereon by a sputtering method. Titanium film 11 is made up of hydrogen peroxide water 2000 ml, ammonia water 500 ml, ethylenediaminetetraacetic acid (EDT).
A) Patterning was performed by a photolithography method using an etching solution composed of a mixed solution of 60 g and 2200 ml of water, and as shown in (f) and (g) of FIG.
To form.

Then, the glass substrate 2 on which the upper metal layer 6 is formed is sputtered to a thickness of 0.15.
A transparent conductive film made of ITO having a thickness of μm is formed, and the transparent conductive film is patterned by a photolithography method using an etching solution made of a mixed solution of 1000 ml of hydrochloric acid and 1000 ml of water, as shown in (h) and (i). Then, the display pixel electrode 7 connected to the upper metal layer 6 is formed.

Thereafter, the lower metal layer 3, the insulator layer 5,
Non-linear resistance element (MI having a three-layer structure including the upper metal layer 6)
The glass substrate 2 on which the M element) and the display pixel electrode 7 are formed is heat-treated in a clean oven at a temperature of 230 ° C. for 3 hours.

In the liquid crystal display device, as shown in FIG. 2, a transparent conductive film made of ITO is formed by a sputtering method on a glass substrate 14 made of, for example, borosilicate glass different from the glass substrate 2. The transparent conductive film is patterned by photolithography using an etching solution composed of a mixed solution of 1000 ml of hydrochloric acid and 1000 ml of water to form the counter electrode 15.

Further, as shown in FIG. 3, polyimide is formed on each of the facing surfaces (electrode forming surfaces) of the glass substrate 2 on which the MIM element 1 and the display pixel electrodes 7 are formed and the glass substrate 14 on which the counter electrode 15 is formed. A resin is applied and a rubbing process is performed to form alignment layers 16a and 16b. After that, the two substrates 2 and 14 are opposed to each other at a distance of 5 μm and their peripheral portions are bonded to each other, and the liquid crystal 17 is injected between the two substrates. afterwards,
It is manufactured by sticking the polarizing plate 18 on the outer surface of the substrate 14.

When a liquid crystal display device is manufactured by the above method, the MIM element formed together with the display pixel electrode 7 on the glass substrate 2 is heat-treated at a temperature of 230 ° C. for 3 hours to obtain the current-voltage characteristics of the MIM element. And a liquid crystal display device capable of obtaining a high-quality display that does not cause flicker or burn-in by preventing the symmetry between the positive and negative current values of the current-voltage characteristics from deteriorating. You can

That is, after the MIM element 1 and the display pixel electrode 7 are formed on the glass substrate 2 by the above method,
The liquid crystal display device is assembled without heat-treating the glass substrate 2 and heat-treated at a temperature of 230 ° C. for 30 minutes, 1 hour, 1 hour 30 minutes, 2 hours, 3 hours to assemble the liquid crystal display device. As to the current-voltage characteristics of the MIM element, the symmetry of the current values of the positive electrode and the negative electrode was investigated.
As a result, the result shown by the broken line 20 in FIG. 3 was obtained. This FIG. 3 shows the symmetry of the current-voltage characteristics as a ratio of current values at ± 20 V (I + 20 V / I-20 V),
The closer the value of I + 20V / I-20V is to 1, the better the symmetry.

From this examination, when the MIM element is not heat-treated, the symmetry of the current-voltage characteristic is about 0.9, whereas when the heat treatment time is 1 hour and 30 minutes or less, the symmetry deteriorates. , It may cause flickering or burning. However, it was found that when the heat treatment time is 2 hours or more, the symmetry is improved, and the heat treatment for about 3 hours recovers to almost the same level as that in the case without heat treatment.

Therefore, by heat-treating the glass substrate 2 on which the MIM element 1 and the display pixel electrode 7 are formed at a temperature of 230 ° C. for 2 hours or more, fluctuations in the current-voltage characteristics of the MIM element can be reduced, and at the same time, the current-voltage characteristic can be reduced. It is possible to provide a liquid crystal display device that can prevent deterioration of the symmetry of the current values of the positive electrode and the negative electrode, which are characteristics, and obtain a high-quality display without flicker or burn-in.

In the above embodiment, the MIM element is 23
The MIM element was heat-treated at a temperature of 0 ° C.
Similar effects can be obtained by heat treatment at a temperature of ℃ or more.

[0033]

The display pixel electrode on the glass substrate and the metal layer electrically connected to the display pixel electrode-the insulator layer-
In a method of manufacturing a liquid crystal display device in which a non-linear resistance element having a three-layer structure made of a metal layer is formed and then the non-linear resistance element is heat-treated, when the heat treatment of the non-linear resistance element is performed at a temperature of 200 ° C. or higher for at least 2 hours, A liquid crystal display device capable of reducing fluctuations in the current-voltage characteristics of a resistance element and, at the same time, causing no deterioration in symmetry of the current values of the positive and negative electrodes of the current-voltage characteristics, and providing high-quality display without flickering or burning. can do.

[Brief description of drawings]

1A to 1I are views for explaining a method of forming an MIM element and a display pixel electrode on a glass substrate according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a method of forming a counter electrode on a glass substrate according to an embodiment of the present invention.

FIG. 3 is a diagram for explaining a method of manufacturing a liquid crystal display device by combining the glass substrate on which the MIM element and the display pixel electrode are formed with the glass substrate on which the counter electrode is formed.

FIG. 4 is a heat treatment temperature of the MIM element and a current of the MIM element-
It is a figure which shows the relationship of the positive electrode of a voltage characteristic, and the symmetry of the electric current value of a negative electrode.

FIG. 5 is a cross-sectional view showing a main configuration of a liquid crystal display device.

FIG. 6 is a plan view showing a main configuration of a liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... MIM element 2 ... Glass substrate 3 ... Lower metal layer 5 ... Insulator layer 6 ... Upper metal layer 7 ... Display pixel electrode 14 ... Glass substrate 15 ... Counter electrode

Claims (1)

[Claims] 1. A display pixel electrode on a glass substrate and a metal layer electrically connected to the display pixel electrode-an insulator layer-
In a method for manufacturing a liquid crystal display device, in which a non-linear resistance element having a three-layer structure made of a metal layer is formed and then the non-linear resistance element is heat-treated, the heat treatment of the non-linear resistance element is performed at a temperature of 200 ° C. or higher for at least 2 hours. A method for manufacturing a characteristic liquid crystal display device.