JP3097282B2 - Varistor element manufacturing method - Google Patents

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 two-terminal element type nonlinear element used in an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art For example, in an image display device of a liquid crystal television,
Broadly classified, there are a simple matrix system and an active matrix system.

In the simple matrix system, a plurality of liquid crystal pixels are arranged in a matrix and connected between a pair of orthogonally provided strip-shaped electrode groups (row electrode group and column electrode group). During this time, a predetermined voltage is applied by the drive circuit to operate the liquid crystal pixels. This method has the advantage that the system can be realized at a low cost because of its simple structure, but crosstalk between the liquid crystal pixels occurs, so that the pixel contrast is low and image quality is low when displaying images on a liquid crystal television. Was inevitable.

On the other hand, in the active matrix system, a switching element is provided for each liquid crystal pixel to hold a voltage applied to the liquid crystal pixel only for a predetermined time interval. However, since the liquid crystal pixels can hold the voltage at the time of selection, the display capacity can be increased, and characteristics relating to image quality such as contrast are good, so that high-quality display of a liquid crystal television can be realized.

However, the active matrix method has a disadvantage that the structure becomes complicated and the manufacturing cost increases. For example, in a TFT type using a thin film transistor as a switching element, at least five or more thin films are usually stacked in the manufacturing process, so that it is very difficult to increase the product yield, increase the manufacturing cost, and lower the productivity. There is a problem that a long manufacturing period is required.

In view of the above, it has been desired to realize a liquid crystal display device which has a good image quality characteristic such as contrast, has a simple structure, and is manufactured at low cost.
A two-terminal element type liquid crystal display device using a varistor element has attracted attention as a method for realizing such a demand.

The two-terminal element type liquid crystal display device is obtained by improving the simple matrix system and applying a liquid crystal pixel 14 and a predetermined varistor voltage between the row electrode 11 and the column electrode 15 as shown in FIG. The varistor element 13 is electrically connected in series with the varistor element 13 that conducts, and utilizes the non-linear current-voltage characteristics of the varistor element 13 as shown in FIG. Vc indicates a threshold voltage, and usually I = 1
It is defined as the value of V at 0 ^-6 (A). In the case of a varistor element, this threshold voltage is usually referred to as a varistor voltage.

FIG. 5 shows a general two-terminal element type liquid crystal display device. As shown in the figure, a large number of pixel electrodes 12 are provided at a fixed distance d to each of the row electrodes 11, and the varistor element 13 is provided between the row electrodes 11 and the pixel electrodes 12. Varistor voltage Vc. As shown in FIGS. 6 and 7, each liquid crystal pixel is provided with a row electrode 11 and a pixel electrode 12 on a lower glass substrate 10 at a predetermined interval d. And pixel electrode 1
2 are connected by a varistor element made of zinc oxide.
Then, the liquid crystal 1 is placed above them via a predetermined structural element.
4, the column electrode 15, the color filter 16,
An upper glass substrate 17 and the like are provided.

The varistor element 13 has a surface of zinc oxide crystal particles 131 of manganese, as shown in FIG.
The varistor particles 13a are covered with an inorganic insulating film 132 such as a cobalt oxide. Further, as shown in FIG. 9, the varistor particles 13a are sintered and solidified using a glass frit 13b. It is formed in a predetermined shape.

Next, an example of a conventional method for manufacturing a varistor element will be described. A minute amount of aluminum is added as a dopant to a zinc oxide fine powder raw material, mixed, heated, sintered and polycrystallized, and then the sintered body is pulverized and classified to obtain zinc oxide crystal particle powder. Next, after the zinc oxide crystal particles are heat-treated and squared, powder varistor particles are formed by coating the surface of the zinc oxide crystal particles with an inorganic insulating film such as a manganese or cobalt oxide insulating film. . Next, glass frit and an organic binder are added to the powder of the varistor particles to form a paste. The paste is printed in a predetermined pattern on an insulating substrate provided with electrodes by a screen printing method, and then baked, melted, and singulated. A varistor element was obtained from the glass frit obtained.

In particular, in order to realize a two-terminal element type liquid crystal display device having good image quality, the varistor element at this time has a high performance, a high stability, and an enormous number of varistors. It is required to be constant between elements as an essential element.

However, in the method of manufacturing a varistor element according to the prior art, since the glass frit is baked and solidified immediately after printing, the organic binder, which is one component of the paste, is not sufficiently removed, and the baked glass frit is not completely removed. Residual components after combustion had an adverse effect on the varistor element characteristics. In other words, this contributes to a large variation in the varistor element characteristics between the elements, making it very difficult to obtain a high quality liquid crystal display device.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and there is no variation in varistor element characteristics over the entire surface of a liquid crystal display device. Another object of the present invention is to provide a method for manufacturing a varistor element having excellent electrical characteristics, and as a result, to obtain a high-quality liquid crystal display device having no display unevenness and high contrast.

[0014]

In order to solve the above-mentioned problems, the present invention provides a method for manufacturing a varistor element used in a two-terminal element type active matrix type liquid crystal display device. varistor particles of the powder having been subjected to coating with inorganic insulating film on the surface of the crystal grains, the ink comprising a paste by adding insulating glass frit and an organic binder, predetermined on the insulating substrate in advance arranged predetermined electrode printed on the pattern shape, then facilities a heat treatment at a temperature below the softening point of the glass frit is a component of it and the ink in the combustion temperature or more organic binders is a component of the ink, it fired and solidified thereafter A method for manufacturing a varistor element, characterized in that:

[0015] Preferably, in the method for manufacturing a varistor element, the heat treatment is performed in an oxygen atmosphere.

[0016]

According to the method for manufacturing a varistor element according to the present invention, after forming a predetermined pattern by the printing method as described above, a predetermined temperature range,
That is, by performing the heat treatment at a temperature equal to or higher than the combustion temperature of the organic binder and equal to or lower than the softening point of the glass frit, the organic binder as a component in the ink can be completely burnt and removed before firing. . Therefore, thereafter, the varistor element can be obtained by baking according to the conventional technique to melt and individualize the glass frit as a component in the ink. That is, it is possible to avoid in advance that the residual foreign matter composed of the organic binder, which is one of the factors that adversely affect the electrical characteristics, does not exist between the varistor particles.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a process diagram showing a method for manufacturing a varistor element according to one embodiment of the present invention.

First, in the granulation step 101, 0.003 mol% of aluminum as a dopant was added to a commercially available zinc oxide fine powder (particle diameter: 1 μm or less) using a V-type mixer. Next, in the sintering step 102, 1200 ° C.
For 1 hour to form a polycrystal containing crystal particles having an average particle size of about 6 μm. Next, in a pulverizing step 103, the polycrystal was pulverized. Subsequently, in a classifying step 104, classification was performed using an air classifier to obtain zinc oxide crystal particles having a particle size of 5 μm to 8 μm. Next, in the cornering firing step 105, the zinc oxide crystal particles were spheroidized by firing at 1000 ° C. for 1 hour to be squared. Next, in an insulating film forming step 106, 0.25 mol% of cobalt nitrate and 0.50 mol% of manganese nitrate are dissolved in water to form an aqueous solution, and the zinc oxide crystal particle powder is dispersed in the aqueous solution.
First, water is evaporated at 120 ° C. to coat the zinc oxide crystal particles with a metal coating, and then the temperature is raised to 200 ° C. to oxidize the metal coating to form an oxide coating. 1100 ° C
After firing for a time, an inorganic insulating film was formed on the surface of the zinc oxide crystal particles, and the obtained powder was lightly loosened in a mortar or the like to obtain varistor particles.

Next, after a powder removing step 107, in an ink forming step 108, 4 parts by weight of glass frit, 1 part by weight of ethyl cellulose (viscosity 45 cps) as an organic binder, and carbine as an organic solvent are added to 16 parts by weight of the varistor particles. 8 parts by weight of tall was added and kneaded to form a paste. Next, in a printing step 109, as shown in FIG. 5, the paste is placed on a glass substrate 10 on which a row electrode 11 made of chromium and a pixel electrode 12 made of indium oxide / tin oxide (ITO) are provided in advance. Was applied in a predetermined shape using a 400 mesh screen printing plate to obtain a printed substrate. Next, in a heat treatment step 110, the printed circuit board was subjected to a heat treatment at 350 ° C. for 3 hours in a ventilation operation in the air. Finally, in a firing step 111, the varistor element 13 was obtained by firing at 420 ° C. for 1 hour to solidify.

Next, the heat treatment step 110 will be described in more detail.

The heat treatment is performed at a temperature higher than the combustion temperature of the organic binder and lower than the softening point of the glass frit.

In the present embodiment, ethyl cellulose having a combustion temperature of 350 ° C. (viscosity of 45 cp) was used as the organic binder.
s) and the use of a lead oxide-based glass frit having a softening point of 370 ° C., when the heat treatment temperature is lower than 350 ° C., combustion of ethyl cellulose is insufficient, and
If the temperature is higher than 70 ° C., the glass frit will soften at the same time as the ethyl cellulose burns,
The burned ethyl cellulose is trapped and remains.

Therefore, the heat treatment temperature here is 350
A range of from 370C to 370C is suitable. The heat treatment time is, for example, when the heat treatment temperature is 350 ° C. (FIG. 2).
As shown in (1), it is preferable that (A) 3 hours or more under the condition of circulating operation in the atmosphere and (B) 1 hour or more under the condition of ventilation operation in the atmosphere. Furthermore, when the heat treatment atmosphere is in oxygen, a sufficiently good result can be obtained by heat treatment in a short time as compared with the case in the air.

Next, the electrical characteristics of the varistor element obtained by the manufacturing method of the present invention will be described. As is well known, the current-voltage characteristic of the varistor element is expressed by the following equation.

[0026]

(Equation 1)

Where I is the current flowing through the varistor element,
V is a voltage applied between both electrodes of the varistor element, K is a constant corresponding to the resistance value of the specific resistance, and α is an index of the voltage nonlinear characteristic of the varistor element. Incidentally, the fact that the varistor element has excellent electrical characteristics means that the varistor element has a smaller varistor voltage Vc and a larger voltage non-linear index characteristic α (usually called an α value). Normally, the evaluation of the variation in the characteristics of the varistor elements is performed using the ratio of the variation of the varistor voltage Vc to the average value of the varistor voltage Vc.

[0028]

[Table 1]

Table 1 shows the varistor voltage Vc, α value, and varistor value between the varistor element obtained by performing the heat treatment according to the manufacturing method of the present invention and the varistor element according to the prior art not subjected to the heat treatment. It shows the result of comparing the variation of the voltage Vc. According to this, it is apparent that the varistor voltage Vc of the present invention is greatly reduced as compared with the conventional method, and that both the varistor voltage and the α value have the same characteristics. That is, according to the present invention, it is possible to obtain a varistor element having high performance and small variation in characteristics between elements.

The present invention can be applied not only to a varistor element for a liquid crystal display device but also to a generally used thick-film varistor element.

[0031]

As described above in detail, according to the method for manufacturing a varistor element according to the present invention, variation in characteristics among elements is small, and the varistor voltage is low for each varistor element. It is possible to provide a method for manufacturing a varistor element which has a large voltage non-linear characteristic, that is, has no variation in electric characteristics over the entire surface and has excellent electric characteristics. This makes it possible to obtain a two-terminal element type active matrix liquid crystal display device with high image quality and high contrast without display unevenness.

[0032]

[Brief description of the drawings]

FIG. 1 is an explanatory view showing steps in one embodiment of a method for manufacturing a varistor element according to the present invention.

FIG. 2 is a graph showing heat treatment time characteristics at a heat treatment temperature of 350 ° C. in one example of a method for manufacturing a varistor element according to the present invention.

FIG. 3 is an equivalent circuit showing a schematic configuration of a two-terminal element type liquid crystal display device.

FIG. 4 is an explanatory diagram showing voltage-current characteristics of a varistor element.

FIG. 5 is an explanatory diagram showing a plan view of a general liquid crystal display device.

FIG. 6 is an explanatory diagram showing, in a plan view, a section near a pixel electrode of a general liquid crystal display device.

FIG. 7 is an explanatory diagram showing a cross section taken along (A)-(A) in (FIG. 6).

FIG. 8 is an explanatory diagram showing a cross-sectional view of varistor particles.

FIG. 9 is an explanatory diagram showing an enlarged main part of an example of the varistor element (FIG. 7).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Insulating substrate 11 ... Row electrode 12 ... Pixel electrode 13 ... Varistor element 13a ... Varistor particle 13b ... Glass frit 14 ... Liquid crystal 15 ... Column electrode 16 ... -Alignment film 17 ... insulating substrate (opposite side) 18 ... polarizing plate 131 ... zinc oxide crystal particles 132 ... inorganic insulating film A ... when circulating in the air B ... air When ventilation operation is performed inside

Claims (2)

(57) [Claims] 1. A method of manufacturing a varistor element for use in a two-terminal element type active matrix type liquid crystal display device, comprising: a powdery varistor particle obtained by coating at least a surface of zinc oxide crystal particles with an inorganic insulating film; the ink with addition of glass frit and an organic binder formed by paste was printed in a predetermined pattern on an insulating substrate in which pre-arranged predetermined electrode, in a component of then the ink
An ink having a temperature equal to or higher than the combustion temperature of an organic binder and
One to facilities heat treatment at a temperature below the softening point of the glass frit is a component, the manufacturing method of the varistor element characterized that you fired and solidified thereafter the. 2. The method according to claim 1, wherein the heat treatment is performed in an oxygen atmosphere.