JPH07209674A - Production of liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device which has a high contrast ratio, and good visibility and is easily formable by decreasing the reflection of external light on the surface of wiring electrodes without addition of stages. CONSTITUTION:A thin film of tantalum is formed by using a sputtering method on a glass substrate 11. Lower patterns 15 of wiring electrodes in a square shape sized 2mum square for lower electrodes 13 and wiring electrodes 14 of nonlinear resistance elements 12 are formed. An oxidized film is formed on the surface of a first metallic layer by using an anodic oxidation method and is patterned with the nonlinear resistance elements 12 in an island shape which are made electrically independent to form the insulating films of the nonlinear resistance elements 12. A thin film of chromium is formed by using a sputtering method and the wiring electrode patterns of the upper electrodes and wiring electrodes 14 of the nonlinear resistance elements 12 are formed. The wiring electrode patterns are formed on the lower patterns 15 of the wiring electrodes and the surfaces of the wiring electrodes 14 becomes rugged. A thin film of ITO is formed by using a sputtering method and the display pixel electrodes are formed, by which an active matrix array substrate is completed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a liquid crystal display device in which a non-linear resistance element composed of a metal layer-insulating layer-metal layer (MIM) is provided as a switching element on a glass substrate.

[0002]

2. Description of the Related Art In recent years, a display device using a liquid crystal display has been
From relatively simple things such as clocks, calculators or measuring instruments to personal computers, word processors,
Furthermore, terminal equipment for office automation,
It has been used for displaying large-capacity information such as television image display. In such a large-capacity liquid crystal display device, a multiplex drive system of matrix display is generally adopted.

However, in this multiplex drive system, due to the essential characteristics of the liquid crystal itself, in terms of the contrast ratio between the ON pixel which is the display portion and the OFF pixel which is the non-display portion, there are about 200 scanning lines. Is insufficient, and when a large-scale matrix drive with about 500 or more scanning lines is performed, the reduction of the contrast ratio becomes extremely insufficient.

Therefore, development has been carried out to prevent a reduction in the contrast ratio of the liquid crystal display device.
As one of the directions, there is one in which individual pixels are directly switch-driven, and a thin film transistor or a non-linear resistance element is used as a switching element. Of these, the non-linear resistance element basically has two terminals, and therefore has a simpler structure and is easier to manufacture than a thin film transistor. Therefore, improvement in manufacturing yield can be expected, and there is an advantage of cost reduction.

Further, the non-linear resistance element is a diode type formed by junction using the same material as the thin film transistor,
A varistor type using zinc oxide, a metal-insulating layer-metal (MIM) type in which an insulator is sandwiched between electrodes, and a type using a semiconductive layer between metal electrodes have been developed. Of these, the MIM type has one of the simplest structures and is already in practical use at present.

The active matrix array substrate using the MIM type non-linear resistance element is usually formed by three photolithography steps of the first metal layer, the second metal layer and the display pixel electrode.

However, in the active matrix array substrate thus obtained, the current-voltage characteristics are not completely symmetrical between the positive polarity and the negative polarity due to the asymmetric structure of the MIM element, and the current -Asymmetry of voltage characteristics causes deterioration of display quality such as flicker and burn-in.

In order to solve such an asymmetry of the current-voltage characteristic, for example, a structure disclosed in Japanese Patent Laid-Open No. 157484/1982 is known.

The device described in Japanese Patent Laid-Open No. 144544/1982 will be described according to the manufacturing process with reference to FIGS.

First, a thin film of a first metal layer made of tantalum (Ta) having a thickness of 3000 angstroms is formed on a flat glass substrate 1 by a sputtering method, and a first photolithography process is used. As shown in FIG. 6, a lower metal 3 to be the non-linear resistance element 2 is formed.

Next, an oxide film of about 300 to 500 angstroms is formed on the surface of the first metal layer by anodization, and an insulating film 4 is formed on the lower electrode 3 of the non-linear resistance element 2. As shown in FIG. 7, by using the second photolithography process, the individual nonlinear resistance elements 2 are patterned into island shapes to be electrically independent.

A second layer made of chromium (Cr), etc.
Thin film of the metal layer of 1500 angstrom is formed by using the sputtering method, and the third photolithography process is used, as shown in FIGS. 8 and 10.
The upper electrode 5 and the wiring electrode 6 of the nonlinear resistance element 2 are formed.

Further, a transparent conductive film made of ITO (Indium Tin Oxide) is formed into a thin film with a thickness of 1000 angstrom by the sputtering method, and the fourth photolithography process is used, as shown in FIG. By patterning the display pixel electrode 7, the nonlinear resistance element 2 having a symmetrical structure, that is, the MIM structure of the lower electrode 3-insulating film 4-upper electrode 5-upper electrode 5-insulating film 4-lower electrode 3 is formed. The process of forming the active matrix array substrate is completed.

The active matrix array substrate thus obtained is combined with a counter substrate (not shown) in which a transparent conductive film made of ITO is patterned in a stripe pattern so as to face it, and after alignment treatment, a bonded liquid crystal is injected and sandwiched. By doing so, a desired liquid crystal display device is obtained.

However, in the liquid crystal display device having such a structure, since the wiring electrode is formed of a metal having a smooth surface, external light is reflected on the surface of the wiring electrode 6, and a black portion, that is, an off portion of the display pixel is displayed. The brightness of the electrode 7 is increased, the contrast ratio is consequently lowered, and the visibility is deteriorated.

As a structure for improving the contrast ratio, for example, a structure described in Japanese Patent Laid-Open No. 60-156051 is known. This JP-A-60-156051
In the publication, aluminum for light shielding is used for the wiring electrodes,
This aluminum shields the light from the light source.

However, even in this case, although the light from the light source is blocked, when viewed from the side opposite to the light source, the light on the viewed side is also reflected, and therefore the contrast ratio cannot be sufficiently improved.

Further, as a means for similarly improving the contrast ratio, for example, a structure described in US Pat. No. 4,804,953 is known.

According to the specification of US Pat. No. 4,804,953, the entire insulator is covered with a lower metal and an upper metal, and the upper surface of the upper metal is curved in an arc shape.

However, a complicated process is required to bend the upper surface of the upper metal, and if the upper surface has an arc shape, linear reflected light may be generated.

[0021]

As described above, the conventional liquid crystal display device has a problem that the contrast ratio cannot be sufficiently improved and a complicated process is required.

The present invention has been made in view of the above problems and has a high contrast ratio in which the reflection of external light on the surface of the wiring electrode is reduced without adding a step, has a high visibility, and can be easily formed. An object is to provide a liquid crystal display device.

[0023]

According to the present invention, a first metal layer, an insulating layer and a second metal layer are laminated on a glass substrate, and an upper electrode composed of the second metal layer-the insulating layer. A non-linear resistance element having a series MIM structure of an insulator consisting of-a lower electrode consisting of the first metal layer-an insulator consisting of the insulating layer-an upper metal consisting of the second metal layer, and the non-linear resistance element. In a method of manufacturing a liquid crystal display device connected by a wiring electrode formed by a second metal layer which is an upper metal of the nonlinear resistance element, a wiring electrode lower pattern is formed on the glass substrate by the first metal layer. Forming a wiring electrode pattern of the second metal layer on the upper surface of the wiring electrode lower pattern, and forming irregularities on the surface of the wiring electrode formed by the wiring electrode lower pattern and the wiring electrode pattern. It is intended to be formed.

[0024]

According to the present invention, the wiring electrode lower pattern is formed by the first metal layer on the glass substrate, and the wiring electrode pattern of the second metal layer is formed on the upper surface of the wiring electrode lower pattern. Since the unevenness is formed on the wiring electrode, the surface of the wiring electrode can be easily made uneven, and the unevenness of the surface of the wiring electrode scatters the reflection direction of external light to prevent an increase in the brightness of the display pixel which becomes black. The contrast ratio can be improved.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for manufacturing a liquid crystal display device of the present invention will be described below according to manufacturing steps with reference to the drawings.

First, a thin film of a first metal layer made of tantalum (Ta) having a thickness of 3000 angstrom is formed on a flat glass substrate 11 by a sputtering method.
As shown in FIG. 1, the lower electrode 13 and the wiring electrode 14 of the non-linear resistance element 12 are formed by using the photolithography process of the first time.
The wiring electrode lower pattern 15 is formed. The wiring electrode lower pattern 15 is a square dot pattern of 2 μm square.

Next, an oxide film having a thickness of 500 angstroms or less is formed on the surface of the first metal layer by anodization, and a second photolithography process is performed to form individual oxide films as shown in FIG. By patterning the non-linear resistance element 12 in an island shape, the non-linear resistance element 12 is electrically isolated to form the insulating film 16 as an insulator of the non-linear resistance element 12.

Further, a second layer made of chromium (Cr) or the like
Thin film of the metal layer of 1500 angstrom is formed by the sputtering method, and the nonlinear resistance element 12 is formed by the third photolithography process as shown in FIG.
The upper electrode 17 and the wiring electrode pattern 18 of the wiring electrode 14 are formed. Further, by forming the wiring electrode pattern 18 on the wiring electrode lower pattern 15, the surface of the wiring electrode 14 becomes uneven.

A transparent conductive film made of ITO (Indium Tin Oxide) having a thickness of 100 is formed by a sputtering method.
A thin film is formed with a thickness of 0 Å, and a display pixel electrode 19 is formed as shown in FIG. 4 by the fourth photolithography process to complete the active matrix array substrate.

Further, a counter substrate (not shown) in which a counter electrode made of ITO is patterned in a stripe pattern so as to be orthogonal to the wiring electrode 14 is opposed to the active matrix array substrate in parallel. Then, the active matrix array substrate is combined with the counter substrate, and after performing alignment treatment with each other, they are bonded together with a predetermined gap therebetween, and liquid crystal is injected and sandwiched in the gap between the active matrix array substrate and the counter substrate.

Then, the reflecting plate-polarizing plate-array substrate-
A reflective liquid crystal display device is completed by laminating a reflective plate and a polarizing plate in the order of the polarizing plate.

In the reflection type liquid crystal display device formed as described above, the surface of the wiring electrode 14 becomes uneven as shown in FIG. The brightness of the black display pixel electrode 19 is lower than that of the liquid crystal display device described above, and the contrast ratio is improved.

Although the reflective liquid crystal display device has been described, when applied to a transmissive liquid crystal display device, the wiring electrode reflects the external light under the external light and raises the brightness of black.
It has an effect of preventing the contrast ratio from being lowered.

The shape of the wiring electrode lower pattern 15 is not limited to the square dot pattern, but may be any shape such as a triangular dot, a circular dot, a random dot pattern, a continuous pattern, or a periodic pattern. it can.

Further, since the wiring electrode lower pattern 15 is formed of the first metal layer, it is not necessary to add a step such as a photolithography step and the manufacturing process is not complicated.

[0036]

According to the method of manufacturing a liquid crystal display device of the present invention, the wiring electrode lower pattern is formed on the glass substrate by the first metal layer, and the second metal layer is formed on the upper surface of the wiring electrode lower pattern. Since the wiring electrode pattern is formed and unevenness is formed on the surface of the wiring electrode, the surface of the wiring electrode can be easily made uneven, and the unevenness of the surface of the wiring electrode scatters the reflection direction of external light. It is possible to prevent an increase in the brightness of the display pixel electrode that becomes black and improve the contrast ratio with a simple manufacturing method.

[Brief description of drawings]

FIG. 1 is a front view showing a manufacturing process of an embodiment of a method of manufacturing a liquid crystal display device of the present invention.

FIG. 2 is a front view showing the next manufacturing step shown in FIG. 1 above.

FIG. 3 is a front view showing the next manufacturing step shown in FIG. 2 above.

FIG. 4 is a front view showing the next manufacturing step shown in FIG. 3 above.

5 is a sectional view taken along line VV of FIG.

FIG. 6 is a front view showing one manufacturing step of a conventional method of manufacturing a liquid crystal display device.

FIG. 7 is a front view showing the next manufacturing step shown in FIG. 6 above.

8 is a front view showing the next manufacturing step shown in FIG. 7 above.

FIG. 9 is a front view showing the next manufacturing step shown in FIG. 8 above.

10 is a sectional view taken along line XX of FIG.

[Explanation of symbols]

 11 Glass substrate 12 Non-linear resistance element 13 Lower electrode 14 Wiring electrode 15 Wiring electrode lower pattern 16 Insulating film as insulator 17 Upper electrode 18 Wiring electrode pattern

Claims (1)

[Claims] 1. A first metal layer, an insulating layer and a second metal layer are laminated on a glass substrate, and an upper electrode made of the second metal layer, an insulator made of the insulating layer, and the first electrode. Forming a non-linear resistance element having a series MIM structure of a lower electrode made of a metal layer of the above-insulator made of the insulating layer-an upper metal made of the second metal layer, and the non-linear resistance element is an upper metal of the non-linear resistance element Forming a wiring electrode lower pattern on the glass substrate by the first metal layer, and forming a wiring electrode lower pattern on the glass substrate. A wiring electrode pattern of the second metal layer is formed on the upper surface of the wiring electrode, and irregularities are formed on the surface of the wiring electrode formed by the wiring electrode lower pattern and the wiring electrode pattern. Liquid crystal display device manufacturing method.