JPH05341326A - Liquid crystal display device and its production - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display device which decreases photolithographic stages as compared with three times of the conventional process and improves the symmetry of the current-voltage characteristic and the process for production of this display device. CONSTITUTION:At least one 10 of a pair of substrates facing each other by clamping a liquid crystal consists of a matrix array substrate which is disposed with plural nonlinear resistance elements 17 in an array form, is disposed with pixel electrodes 15 respectively in series on the respective nonlinear resistance elements 17 and is further connected with respective rows or column directions by wiring electrodes 16. Each of the nonlinear resistance elements 17 consists of a first conductor (pixel electrode part 15)-insulator 11-second conductor 12- insulator-11-third conductor (wiring electrode part 16). The first conductor and the third conductor consist of the same material and both exist on one surface of the insulator 11. The second conductor 12 exists on the other surface of the insulator 11.

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 in which a switching element composed of a non-linear resistance element is incorporated in each pixel, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have changed from relatively simple devices such as clocks, calculators and measuring instruments to personal computers, word processors, OA terminal devices, large-capacity TV image displays and the like. It has been used for information display, and higher image quality has been demanded.

As a driving method in this type of liquid crystal display device, a simple multiplex driving method has been generally adopted for a word processor used as a two-gradation display product. However, a liquid crystal display device is required to have a larger screen, higher resolution, and higher definition, and a driving method for improving the contrast ratio, which has been a drawback of the multiplex driving method so far, is
Various things are done. One of them directly switches and drives each pixel, and uses a thin film transistor or a non-linear resistance element as a switching element. Among them, the non-linear resistance element basically has two terminals as compared with three terminals of the thin film transistor, and therefore has a simple structure and is easy to manufacture. Therefore, improvement in manufacturing yield can be expected,
There is an advantage of cost reduction.

Such a non-linear resistance element is a diode type formed by using a material similar to that of a thin film transistor, a varistor type using zinc oxide, a metal-insulator-metal sandwiching an insulator between electrodes. A (MIM) mold, and a mold using a semiconductive layer between metal electrodes have been developed.
Of these, the MIM type is one of the simplest in structure,
Currently, it is already in practical use. Now, Fig. 7 shows the conventional MI
FIG. 3 is a cross-sectional view showing an example of one pixel portion of a matrix array substrate having an M-type nonlinear resistance element, which will be described according to the manufacturing process.

First, a Ta film 2 is formed on a glass substrate 1 by a thin film forming method such as a sputtering method or a vacuum evaporation method,
Patterning is performed by a photo-etching method. As a result, the wiring (data line) and the electrode terminal that is the end of this wiring,
An electrode made of the first metal of one of the nonlinear resistance elements integrated with these is obtained.

Next, the Ta film 2 is anodized in an aqueous solution of citric acid, for example, to form an oxide film 3 which constitutes an insulator of the nonlinear resistance element. At this time, it is necessary to protect the oxide film 3 from growing on the electrode terminals. As this method, there is sticking of silicone rubber or application of a negative resist. Subsequently, when the Cr film 4 is formed as the other second metal of the nonlinear resistance element by the thin film forming / processing method,
The nonlinear resistance element 5 is completed. Further, the transparent electrode 6 for image display may be formed so as to be connected to the Cr film 4. Such a basic manufacturing technique is disclosed in JP-B-55-161273, and an improved technique thereof is disclosed in JP-A-58-178320.

[0007]

A conventional non-linear resistance element is a non-linear resistance element 5 and a transparent electrode 6 for image display as described in Japanese Patent Publication No. 55-161273.
In order to form a pattern, it was necessary to form a thin film and photolithography three times. Therefore, compared to the conventional simple matrix, the process is complicated while the performance is excellent,
It was inferior in terms of production yield. Therefore, increase productivity,
It was desired to manufacture the device in fewer steps to increase the yield. Furthermore, although the non-linear resistance element is symmetrical in structure, it is difficult for both electrode / insulating film interfaces to be in the same state, and it is difficult to obtain bidirectional current-voltage symmetry, which is essential for switching the liquid crystal layer. It was For this reason, a flicker phenomenon called flicker on the display screen, and display information called an afterimage remains unerased, which is a problem. As a means for solving this, it has been reported that two non-linear resistance elements are connected in series or in parallel in a direction that complements the symmetry, but in both cases, the process is made more complicated and the current-voltage characteristics are symmetrical. The productivity was poor, but the productivity was poor.

The present invention has been made in view of the above circumstances, and provides a liquid crystal display device in which the photolithography process is reduced as compared with the conventional three times, and the symmetry of current-voltage characteristics is improved, and a manufacturing method thereof. The purpose is to do.

[0009]

According to the present invention, at least one of a pair of substrates sandwiching a liquid crystal and facing each other has a plurality of nonlinear resistance elements arranged in an array, and each nonlinear resistance element has a pixel electrode. In a liquid crystal display device including a matrix array substrate arranged in series and connected in the respective row or column directions by wiring electrodes, the nonlinear resistance element includes a first conductor-insulator-second conductor-insulator-third conductor. The liquid crystal display device is made of a conductor, the first conductor and the third conductor are made of the same material, and both are located on one surface of the insulator, and the second conductor is located on the other surface of the insulator.

Further, according to the present invention, the step of forming a conductor on a light-transmissive substrate, and the light transmittance of the conductor is not significantly reduced.
A step of forming an insulator by performing anodization while slightly leaving the upper limit of 00 angstrom to form an insulator, and a step of patterning a wiring, a both-end electrode of an element, and a liquid crystal drive electrode on the insulator by a transparent conductive film. It is a method of manufacturing a liquid crystal display device.

[0011]

According to the present invention, by connecting the non-linear resistance elements in series, the current-voltage symmetry is ensured, which is very effective in preventing afterimages, and the photolithography process is basically 1-2 steps. The number of times is less than that of the conventional one, and improvement in display characteristics and productivity can be expected.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Three embodiments of the present invention will now be described in detail with reference to the drawings. The present invention is an improvement of the matrix array substrate of a liquid crystal display device, particularly the vicinity of its non-linear resistance element. Only the vicinity of the resistance element will be described.

Before describing each embodiment, the outline of the present invention will be described. That is, in the matrix array substrate used in the liquid crystal display device of the present invention, the first conductor and the third conductor, which are a pair of electrodes, are arranged at a constant interval on the insulator that causes the current-voltage switching characteristic, and further insulation is performed. By arranging the second conductor under the body and providing a series connection type non-linear resistance element having a structure of a first conductor-insulator-second conductor-insulator-third conductor,
The symmetry of current-voltage characteristics is improved.

For this reason, a thin light-transmissive conductor layer and an insulator layer that causes current-voltage switching characteristics are laminated on the entire surface of the substrate without increasing extra steps. These layers may be formed by vapor deposition or sputtering in order, but from the viewpoint of uniformity of the formed film thickness sensitive to current-voltage switching characteristics, after forming Ta or Al, a light-transmissive conductor is formed. A method of obtaining a laminated structure by performing anodic oxidation with 100 angstrom being the upper limit at which the light transmittance does not remarkably decrease and leaving a small amount of it is preferable. Then, wiring, electrodes on both sides of the device, and electrodes for driving liquid crystal are patterned on the insulator to complete the array substrate by only one photolithography process.

In this case, as shown in FIG. 6A, the distance A between the adjacent pixel electrode portions 15 (first conductor) and the distance between the pixel electrode portion 15 and the wiring electrode portion 16 (third conductor) are set. Distance B
Is larger than the distance C between both end electrodes of the element, and is effective when the resistance of the insulator is large to the extent that an unnecessary current does not flow between the adjacent pixel electrode portions 15 or between the pixel electrode portion 15 and the wiring electrode portion 16. If this poses a problem, please refer to FIG.
As shown in (b), the insulating layer and the light transmissive conductor layer may be patterned so as to surround the wiring, the element, and the liquid crystal driving electrode. Alternatively, a similar process may be performed by previously patterning a metal into a shape in which wirings, elements, and liquid crystal driving electrodes are connected in advance before anodizing. Even with these methods, the number of photolithography steps is as small as twice compared with the conventional three times. In this way, it was possible to realize a liquid crystal display device that eliminates afterimages and flicker in a few steps. (First embodiment)

The matrix array substrate in the first embodiment is constructed as shown in FIGS. 1 (a) to 1 (c), FIG. 2 and FIG. 3, and FIG. 2 is an enlarged view of an essential part of FIG. 1 (c). FIG. 3 is a plan view of FIG. 1C, and FIG.
It is the same as (a). A manufacturing method will be described with reference to the drawings.

First, as shown in FIG. 1A, for example, S
1.1mm with a protective coating of alkali of io _{2 on} the surface
On a thick glass substrate 10, an insulating layer 11 made of tantalum pentoxide and a light transmissive conductor layer 1 made of Ta (tantalum).
2 is formed by the sputtering method of Ta and the subsequent anodic oxidation. At this time, Ta of 450 angstrom
Is formed in advance, and a voltage of 60 V is applied with Pt as a counter electrode in a 0.01% aqueous solution of citric acid, and the original Ta of 450 Å is transferred to the oxide film.
An insulator layer 11 of tantalum pentoxide of 00 Å is obtained. Original Ta obtained by sputtering method
Has a film thickness variation of 10% depending on the location, 430-4
It was in the 70 angstrom range. Further, the variation of the anodic oxide film was extremely small and was 990 to 1010 Å.

As a result, the remaining Ta was in the range of 30 to 70 angstroms and had a practically sufficient light transmittance of 97% or more in the visible light region. It is known that ordinary metals such as Ta, Al, and Ti have a practically sufficient light transmittance as long as they are 100 angstroms or less.
The insulator layer 11 made of tantalum pentoxide was also transparent and flat.

Next, as shown in FIG. 1B, a transparent conductive film 13 made of ITO is formed on the insulator layer 11 by a sputtering method. At this time, the substrate temperature is raised to 200 ° C. in order to increase the transmittance, sufficiently lower the resistivity, and improve the etching processability. Subsequently, after a resist (photosensitive resin) is applied on the entire surface of the transparent conductive film 13, the resist pattern 14 is formed by exposure using a photomask and development. The resist pattern 14 is the transparent conductive film 13
Of these, a portion to be a pixel electrode portion and a wiring electrode portion described later is covered.

Next, as shown in FIG. 1 (c) and FIGS. 2 and 3, water, hydrochloric acid and nitric acid were mixed at a ratio of 1: 1: 0.1 (volume ratio) and heated to 30.degree. The same pattern as the resist pattern 14 is formed with an etching solution, and the resist pattern 14 is removed to obtain the pixel electrode portion 15 and the wiring electrode portion 16. Then, as is clear from FIG. 2, the first conductor (pixel electrode portion 15) -insulator (insulator layer 11) -second conductor (light-transmissive conductor layer 12) -insulator (insulator layer 1)
1) -The non-linear resistance element 17 having the structure of the third conductor (wiring electrode portion 16) is formed. The current is E →
It flows in the route of F → G or G → F → E. Further, in FIG. 3, the distance A between the adjacent pixel electrode portions 15 and the distance B between the pixel electrode portion 15 and the wiring electrode portion 16 are both set to 20 μm, and the inter-element electrode distance C is set to 7 μm. Since the light-transmissive conductor layer 12 is thin, it has a high resistance, and an extra current flow between them through the light-transmissive conductor layer 12 is extremely small and can be ignored.

In the first embodiment, the single layer of the transparent conductive film 13 is used as the electrode, but the wiring electrode portion 16 side is made of Cr, Al,
Further, a metal such as Ta may be used. In this case, the number of photolithography steps is usually increased by one. However, in the case of large-scale and high-definition display, the wiring resistance is lowered, and thus it is necessary to apply such an auxiliary electrode layer even in the conventional technique. In this respect, the technique of the present invention is not inferior. Further, in order to stabilize the device characteristics, a metal layer such as Ti, Cr, Al having a thickness of several tens to 100 angstroms may be provided at the contact portion between the pixel electrode portion 15, the wiring electrode portion 16 and the insulator layer 11. .. Depending on the structure, if the transparent conductive film 13 is continuously formed on or below the transparent conductive film 13 and etching is performed using the same photoresist mask, the photolithography process does not increase. If the pixel electrode portion 15 is a metal film having such a thin thickness, the transmission of light is not significantly impaired, and there is no problem. To form a liquid crystal display device using the matrix array substrate as described above, for example, the following may be performed.

First, an alignment film made of a polyimide resin is applied to the surface of the matrix array substrate on which the non-linear resistance element 17 is formed, baked, and rubbed to regulate the liquid crystal alignment direction. The same process is performed on the counter substrate, and rubbing is performed in a direction twisted by about 90 ° from one liquid crystal display substrate. The above-mentioned two types of substrates are prepared, and the liquid crystal is injected by holding the liquid crystal at a distance of 5 to 10 μm so that the major axis direction of the liquid crystal is twisted by about 90 ° between the two substrates, and a liquid crystal cell is formed. Then, the polarizing plate may be arranged outside the liquid crystal cell with the polarization axis twisted by about 90 °. (Second embodiment)

Similar to the first embodiment, the first conductor (pixel electrode portion 15) -insulator (on the glass substrate 10 having a thickness of 1.1 mm provided with an alkali protective coating of, for example, SiO _{2 on} the surface portion. A non-linear resistance element 17 having a structure of insulator layer 11) -second conductor (light-transmitting lower conductor layer 12) -insulator (insulator layer 11) -third conductor (wiring electrode portion 16) is formed. .. In the first embodiment, as shown in FIG. 3, the distance A between the adjacent pixel electrode portions 15 and the distance B between the pixel electrode portions 15 and the wiring electrode portions 16 are both set to 20 μm,
Although the distance C between the element electrodes was set to 7 μm, it becomes a finer pattern in high-definition display. In the second embodiment, as shown in FIGS. The distance A between the portions 15 and the distance B between the pixel electrode portion 15 and the wiring electrode portion 16 are both set to 5 μm, and the distance C between the element electrodes is set to 2 μm. Incidentally, FIG. 4B is a sectional view taken along line XX ′ in FIG. 4A and seen in the direction of the arrow. Although the light-transmissive conductor layer 12 is thin and has high resistance, an extra current flows between them through the light-transmissive conductor layer 12 due to the short distance between the electrodes. Therefore, in order to cut off the current path at the distance A and the distance B,
As shown in FIG.
Then, the light-transmissive conductor layer 12 is patterned so as to surround wirings, elements, and liquid crystal driving electrodes. For this purpose, a resist is formed by photolithography in the shape of the pattern to be left, and the insulator layer 11 and the light-transmissive conductor layer 12 are subjected to chemical dry etching in a well-known gas plasma containing CF ₄ and O _2. Good. After removing the resist,
In this state, a leak current does not flow in an unnecessary portion, and good switching characteristics can be obtained. 1
Resistance value of metal below 00 angstrom is 10μ
This processing is effective because the influence of the above-mentioned leak occurs at a distance of about m or less. A liquid crystal display device can be formed using this matrix array substrate in the same manner as in the first embodiment. (Third embodiment)

In the second embodiment, the insulating layer 11 and the light-transmissive conductor layer 12 are finally patterned.
As shown in (a), Ta 18 is formed on the glass substrate 10 in advance, and the Ta 18 is patterned into a shape in which wirings, elements, and liquid crystal driving electrodes are roughly connected, and then anodized to form Ta 18. By applying the steps described above, the arrangement shown in FIG. 5B or 5C or 5D may be formed. The liquid crystal display device can be formed using this matrix array substrate in the same manner as in the first embodiment.

[0025]

According to the present invention, in a liquid crystal display device, a first conductor and a third conductor, which are a pair of electrodes, are arranged at regular intervals on an insulator that causes a current-voltage switching characteristic.
Furthermore, a third conductor is arranged under the insulator, and the first conductor-
Since the non-linear resistance element of the series connection type including the insulator-the second conductor-the insulator-the third conductor is included, the symmetry of the current-voltage characteristics can be improved.

As a result, it is possible to perform display with extremely small afterimage and flicker. Furthermore, for this reason, without increasing extra steps, rather than taking a normal array substrate fabrication,
Rather, it can be manufactured by a small number of photolithography processes, which is very effective for practical use of matrix type liquid crystal display devices.

[Brief description of drawings]

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

FIG. 2 is an enlarged cross-sectional view showing a main part of FIG.

FIG. 3 is a plan view of a part of FIG.

FIG. 4 is a plan view and a sectional view showing a manufacturing process of a matrix array substrate in a liquid crystal display device according to a second embodiment of the present invention.

FIG. 5 is a plan view showing a manufacturing process of a matrix array substrate in a liquid crystal display device according to a third embodiment of the present invention.

FIG. 6 is a plan view showing a main part of a matrix array substrate in a liquid crystal display device used for explaining the outline of the present invention.

FIG. 7 is a cross-sectional view showing an example of one pixel portion of a matrix array substrate in a conventional liquid crystal display device.

[Explanation of symbols]

10 ... Glass substrate, 11 ... Insulator layer (insulator), 12 ...
Light-transmissive conductor layer (second conductor), 15 ... Pixel electrode portion (first conductor), 16 ... Wiring electrode portion (third conductor), 17 ...
Non-linear resistance element.

Claims (2)

[Claims] 1. A plurality of non-linear resistance elements are arranged in an array on at least one of a pair of substrates sandwiching a liquid crystal and facing each other, and pixel electrodes are arranged in series in each non-linear resistance element, and wiring electrodes are further arranged. In the liquid crystal display device including a matrix array substrate in which each row or each column direction is connected by, the non-linear resistance element includes a first conductor-insulator-second conductor-insulator-third conductor, and A liquid crystal display device, wherein the first conductor and the third conductor are made of the same material and are both located on one surface of the insulator, and the second conductor is located on the other surface of the insulator. 2. A step of forming a conductor on a light-transmissive substrate, and a step of forming an insulator by performing anodization while slightly leaving the conductor to 100 angstrom as an upper limit at which the light transmittance does not significantly decrease and leaving a slight amount. And a step of patterning wiring, a both-ends electrode of an element, and a liquid crystal driving electrode on the insulator with a transparent conductive film, and a step of patterning the liquid crystal driving electrode.