JPH04367827A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To eliminate difficulty in handling during production and to provide a liq. crystal display device having high display grade and high yield. CONSTITUTION:This liq. crystal display device has display image elements with an incorporated nonlinear resistance element 27 having a three-layered structure consisting of a metal layer 22, an insulator layer 23 and a metal layer 26. The shape of the nonlinear resistance element 27 seen from a normal direction of the insulator layer 23 is nearly circular.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to a liquid crystal display device.
In particular, the present invention relates to a liquid crystal display device in which each pixel incorporates a switching element made of a nonlinear resistance element.

0002

[Prior Art] In recent years, liquid crystal display devices have been widely used in devices ranging from relatively simple devices such as watches, calculators, and measuring instruments to personal computers, word processors, and even terminal equipment for office automation.
It has been used for displaying large amounts of information such as TV image display.

[0003] In this type of large-capacity liquid crystal display device, a multiplex drive system for matrix display has generally been adopted. However, due to the essential characteristics of the liquid crystal itself, this method is insufficient in terms of contrast ratio between the display area (on pixels) and the non-display area (off pixels) even when it has about 200 scanning lines. Furthermore, when performing large-scale matrix driving with approximately 500 or more scanning lines, deterioration of contrast is fatal.

[0004] Developments to solve the drawbacks of this liquid crystal display device are actively being carried out in various places. One approach is to directly drive each pixel with a switch, using thin film transistors or nonlinear resistance elements as switching elements. Among these, the nonlinear resistance element basically has two terminals, so it has a simpler structure and is easier to manufacture than a thin film transistor. Therefore, an improvement in manufacturing yield can be expected and there is an advantage in cost reduction.

[0005] Such nonlinear resistance elements include a diode type in which a junction is formed using the same material as a thin film transistor, a varistor type in which zinc oxide is used, and a metal layer-insulating type in which an insulator is sandwiched between electrodes. A body layer-metal layer (MIM) type and a type using a semiconductive layer between metal electrodes have been developed. Among these, the MIM type has one of the simplest structures.
It is already in practical use.

Now, a liquid crystal display device using a conventional MIM type nonlinear resistance element will be explained according to the manufacturing process. FIG. 7 is a cross-sectional view showing a liquid crystal display device, and FIG. 8 is a plan view showing one pixel portion of an array substrate having a conventional MIM type nonlinear resistance element. First, T is placed on the glass substrate 1.
A (tantalum) film 2 is formed by a thin film forming method such as a sputtering method or a vacuum evaporation method, and is formed into a desired pattern by a photoetching method. As a result, the wiring and one electrode of the nonlinear resistance element are formed. Next, the Ta film 2 is chemically converted by anodic oxidation in a liquid such as a citric acid aqueous solution to form an oxide film 3.

Next, a Cr (chromium) film 4 is formed and patterned by photoetching to form the other electrode of the nonlinear resistance element, thereby completing the MIM type nonlinear resistance element. Furthermore, after this, a transparent electrode 5 for image display may be formed. These basic manufacturing techniques are
It is disclosed in Japanese Patent Application Laid-open No. 161273, and its improved technology is shown in Japanese Patent Application Laid-Open No. 178320/1983.

Separately, a counter substrate 8 is obtained by forming a striped counter electrode 7 made of, for example, ITO on a substrate 6 made of, for example, glass. Then, a polymide resin is applied to each of the counter substrate 8 and the matrix array substrate 9, and a rubbing process (rubbing with a cloth) is performed to form liquid crystal alignment layers 10 and 11. After that, both boards 8
, 9 are maintained at a gap of 5 to 20 μm, and liquid crystal 12 is injected into this gap. Here, one pixel is constituted by a combination of the connected nonlinear resistance element 13, transparent electrode 5, counter electrode 7, and liquid crystal 12.

[0009]

[Problems to be Solved by the Invention] In the conventional liquid crystal display device as described above, the nonlinear resistance element 13 is damaged due to static electricity generated during the rubbing process when forming the alignment layer 11.
There was a problem in that dielectric breakdown occurred, which appeared as point defects on the display, significantly impairing the display quality. In addition, the fact that it is easily destroyed by static electricity makes it difficult to handle during the manufacturing process, leading to a decrease in yield. The present invention was made in view of the above circumstances, and an object of the present invention is to provide a liquid crystal display device with high display quality and high yield.

0010

[Means for Solving the Problems] The present invention provides a liquid crystal display device having a display pixel incorporating a nonlinear resistance element having a three-layer structure of metal layer-insulator layer-metal layer, wherein the nonlinear resistance element is The liquid crystal display device has a substantially circular shape when viewed from the normal direction of the insulating layer.

[0011]

[Operation] The dielectric breakdown of the nonlinear resistance element 13, which has been a problem in the past, can be investigated by removing one electrode and then electroplating in a copper sulfate aqueous solution. According to this method, it was found that the dielectric breakdown occurred concentrated at the end of the nonlinear resistance element in which two electrodes crossed. In particular, they were often found in corners where the nonlinear resistance element was viewed from the normal direction of the insulator layer (square corners). This is thought to be because the electric field applied to the corner portions is larger than the other portions.

Therefore, according to the liquid crystal display device of the present invention, since the shape of the nonlinear resistance element is approximately circular when viewed from the normal direction of the insulator layer, the nonlinear resistance element is concentrated in a part of the insulator layer. No electric field is applied. Therefore, the problems of dielectric breakdown of the nonlinear resistance element due to static electricity during the rubbing process, as well as difficulty in handling during the manufacturing process and reduction in yield due to easy breakdown due to static electricity, are solved. As a result, a liquid crystal display device with high display quality and high yield can be obtained.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. 1 to 5 show the manufacturing process of a matrix array substrate in a liquid crystal display device of the present invention, and the following will be described in accordance with this manufacturing process.

First, as shown in FIG. 1, a Ta film is formed to a thickness of 0.30 μm by sputtering on a substrate 21 made of, for example, borosilicate glass, and then CF4 and O2
Dry etching is performed using a mixed gas of
The lower metal layer 22 is formed by coating the lower metal layer 22. Next, as shown in FIG. 2, the above-mentioned substrate 21 is anodized in a 0.01% by weight citric acid aqueous solution to form a 0.06 μm anodic oxide film on the surface of the lower metal layer 22. An insulator layer 23 of a resistance element is obtained.

Next, as shown in FIG. 3, the film thickness is 0.20μ.
CVD (Chemical Va.
After forming the contact hole 25 on the entire surface of the substrate 21 by por deposition, a circular contact hole 25 with a diameter of 5 μm is formed. In this dry etching, the insulator layer 23
In order to increase the selection ratio between CF4 and O2, the mixed gas ratio of CF4 and O2 is adjusted to avoid etching the insulator layer 23 as much as possible.

Next, as shown in FIG. 4, a Ti film is placed on the substrate 2.
1 to a thickness of 0.20 μm and patterned to form the upper metal layer 26. In this case, the Ti film was etched using 2000 ml of hydrogen peroxide and 50 ml of ammonia water.
The etching solution is prepared by mixing 0 ml of ethylenediaminetetraacetic acid (EDTA), 60 g of ethylenediaminetetraacetic acid (EDTA), and 2200 ml of water. A nonlinear resistance element 27 is formed by the lower metal layer 22, insulator layer 23, and upper metal layer 26 described above.

Next, as shown in FIG. 5, a transparent conductive film made of, for example, ITO is formed to a thickness of 0.15 μm by sputtering, and then patterned so as to be electrically connected to the upper metal layer 26. to form the pixel electrode 28. This patterning was done using 1000ml of hydrochloric acid and 1000ml of water.
The test was carried out using a mixed solution in the proportion of In this way, the matrix array substrate 29 is completed, and the plan view of this FIG. 5 is shown in FIG.
It is.

Next, as in the prior art, polyimide resin is coated on both the matrix array substrate 29 and the counter substrate 8 shown in FIG.
, 10 are formed. After that, both substrates 29 and 8 are coated with a thickness of 5 μm.
The liquid crystal 10 is injected into this gap. Furthermore, a driving circuit is added to form a liquid crystal display device. When the liquid crystal display device manufactured as described above was driven and the display was observed, no display defects such as point defects or unevenness were observed, and the display was of high quality.

On the other hand, in the above embodiment, the contact hole
A liquid crystal display device was fabricated in which the shape of the loop 25 was square when viewed from the normal direction of the insulating layer 23, and all other aspects were the same as in the above embodiment. However, in this case, when driving and observing the display in the same manner as in the above embodiment, it was found that approximately 9
0 point defects were observed.

Note that the order of the manufacturing steps shown in FIGS. 1 to 5 may be changed. That is, after patterning the lower metal layer 22, the insulator layer 23 and the contact hole 25 may be successively formed, and then the lower metal layer 22 may be anodized. This is because a nonlinear resistance element having the same structure as in the above embodiment can be formed.

[0021]

[Effects of the Invention] According to the present invention, since the shape of the nonlinear resistance element is approximately circular when viewed from the normal direction of the insulating layer, the electric field is concentrated on a part of the insulating layer. never be done. Therefore, the problems of dielectric breakdown of the nonlinear resistance element due to static electricity during the rubbing process, as well as difficulty in handling during the manufacturing process and reduction in yield due to easy breakdown due to static electricity, are solved. As a result, a liquid crystal display device with high display quality and high yield can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a manufacturing process of a pixel portion of a matrix array substrate in a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a perspective view as well.

FIG. 3 is a perspective view as well.

FIG. 4 is a perspective view as well.

FIG. 5 is a perspective view as well.

FIG. 6 is a plan view corresponding to FIG. 5;

FIG. 7 is a cross-sectional view showing a conventional liquid crystal display device.

FIG. 8 is a plan view showing one pixel portion of a matrix array substrate in a conventional liquid crystal display device.

[Explanation of symbols]

21... Substrate, 22... Lower metal layer, 23... Insulator layer, 25
...Contact hole, 26... Upper metal layer, 27... Nonlinear resistance element, 28... Pixel electrode.

Claims (1)

[Claims] 1. In a liquid crystal display device having a display pixel incorporating a nonlinear resistance element having a three-layer structure of a metal layer, an insulator layer, and a metal layer, the nonlinear resistance element is arranged in a direction normal to the insulator layer. A liquid crystal display device characterized by having a substantially circular shape when viewed.