JPH04295827A - Production of varistor element - Google Patents

Abstract

PURPOSE:To provide the process for producing the varistor element exhibiting good characteristics. CONSTITUTION:Glass frit consisting of 85 to 35 pts.wt. lead oxide, 6 to 25 pts.wt. boron oxide, 3 to 20 pts.wt. zinc oxide, 3 to 10 pts.wt. manganese oxide, and 3 to 10 pts.wt. cobalt oxide and org. binder are added to the powder of varistor particles formed by coating the surfaces of at least zinc oxide crystal particles with an inorg. insulating film and the mixture is made into paste. This paste is printed to prescribed shapes by screen printing on an insulating substrate disposed with electrodes and is then solidified at 440 deg.C to 520 deg.C calcination temp., by which the varistor element is obtd.

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 varistor element suitable for use as a nonlinear element in, for example, a two-terminal element type liquid crystal display device.

0002

2. Description of the Related Art Currently, image display devices for, for example, liquid crystal televisions are broadly classified into simple matrix type and active matrix type. In the simple matrix method, a plurality of liquid crystal pixels are arranged in a matrix and connected between a pair of band-shaped electrode groups (row electrode group and column electrode group) arranged at right angles. A driving circuit applies a predetermined voltage to operate the liquid crystal pixels. This method has the advantage of being able to realize a system at a low cost due to its simple structure, but crosstalk occurs between each LCD pixel, resulting in low pixel contrast, which makes it difficult to display images on an LCD TV.
Deterioration in image quality was inevitable. In contrast,
In the active matrix method, a switching element is provided for each liquid crystal pixel to maintain the voltage, and even if the liquid crystal display device is time-divisionally driven, the liquid crystal pixel can maintain the voltage at the time of selection, so the display capacity is reduced. It can be expanded, has good image quality characteristics such as contrast, and can realize high-quality display on liquid crystal televisions. However, the active matrix method has the disadvantage that the structure is complicated and the manufacturing cost is high. for example,
TF that uses thin film transistors as switching elements
In the T-type, five or more thin films are stacked in the manufacturing process, making it difficult to increase the product yield.

[0003] In view of the above, there is a desire to realize a liquid crystal display device that has good image quality characteristics such as contrast, has a simple structure, and is low in cost. Varistor elements have been developed as a method to meet these requirements. A two-terminal element type liquid crystal display device using a 2-terminal device is attracting attention.

The two-terminal element type liquid crystal display device is an improvement on the simple matrix method, and as shown in FIG.
A liquid crystal 14 and a varistor element 13 that conducts at a predetermined threshold voltage are electrically connected in series between the varistor element 1 and the column electrode 15 as shown in FIG.
This utilizes the nonlinear current-voltage characteristics of No. 3. In other words, in time-division driving in a simple matrix method, as shown in FIG. 5, a voltage V90 turns the liquid crystal pixel on (light transmittance is 90%) and a voltage V1 turns it off (light transmittance 10%).
0 ratio γ (=V90/V10=(V10+ΔV)/V
10), the maximum allowable number of scanning lines Nmax without causing crosstalk between each liquid crystal pixel is Nmax
= ((γ2 +1)/(γ2 -1))2,
The smaller the value of γ, the greater the number of scanning lines, which is advantageous for liquid crystal television display. On the other hand, in the two-terminal element type, the voltage exceeding the threshold voltage Vv is applied to the liquid crystal pixel by the varistor element 13, so that the operating voltage of the liquid crystal pixel without the varistor element ( By providing a varistor element, the threshold voltage V
v (see Figure 7). As a result, the γ
The value of is from V90/V10 to (Vv +V90)/(Vv
+V10), and by decreasing the γ value, the maximum number of scanning lines Nmax can be increased, making it possible to realize a high-quality liquid crystal display.

As is well known, the current-voltage characteristics of the varistor element used as a nonlinear element in a two-terminal liquid crystal display device as described above are expressed by the following equation.

[0006]

[Math 1]

Here, I is the current flowing through the varistor element,
V is the voltage between the electrodes of the varistor element, K is a constant corresponding to the resistance value of the specific resistance, and α is the exponent of voltage nonlinear characteristics, and this voltage nonlinearity exponent α (usually called the α value) is large. The more excellent the varistor element characteristics are. When a varistor element is applied to a liquid crystal display device, the larger the α value, the steeper the on/off characteristics of the liquid crystal, and therefore a high quality liquid crystal display device with a high contrast ratio can be obtained.

FIG. 8 shows a general two-terminal element type liquid crystal display device. As shown here, a large number of pixel electrodes 12 are provided for each row electrode 11 at a constant interval d, and the row electrode 11 and pixel electrode 12 are connected to each varistor element 13.
are connected with a constant threshold voltage Vv. As shown in FIGS. 9 and 10, each liquid crystal pixel includes a row electrode 11 and a pixel electrode 12 provided on a lower glass substrate 10 with a predetermined distance d between them. They are connected by a varistor element made of zinc oxide. The upper portions of these are filled with liquid crystal 14, and further provided with column electrodes 15, color filters 16, and an upper glass substrate 17. As shown in detail in FIG. 11, the varistor element 13 is composed of varistor particles 13a in which the surface of zinc oxide crystal particles 131 is coated with an inorganic insulating film 132 made of manganese, cobalt oxide, etc., as shown in detail in FIG. , these varistor particles 13a are sintered and solidified with a glass frit 13b.

Next, an example of a conventional method for manufacturing a varistor element will be described. A small amount of aluminum is added and mixed as a dopant to a fine powder raw material of zinc oxide, and after further heating and sintering to polycrystallize, the sintered body is crushed and classified to obtain a zinc oxide crystal particle powder. Next, after the zinc oxide crystal particles are heat-treated and cornered, the surface of the zinc oxide crystal particles is coated with an inorganic insulating film such as a manganese or cobalt oxide insulating film to form varistor particle powder. Next, a glass frit and an organic binder are added to the varistor particle powder to form a paste, and the paste is applied in a predetermined shape by screen printing onto an insulating substrate on which electrodes are arranged, and then fired to obtain a varistor element.

0010

[Problems to be Solved by the Invention] In particular, in order to realize a high-quality two-terminal element type liquid crystal display device with good image quality,
Varistor elements are required to have high performance, high stability, and constant performance between elements. Conventionally, lead-zinc borate glass, which is a low-melting glass, has been used for the glass frit interposed between varistor particles forming a varistor element. However, in the past, there was a problem in that the performance of the varistor element could not be improved and it was difficult to improve the quality of the liquid crystal display device.

The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide a method for manufacturing a high-performance varistor element.

0012

[Means for Solving the Problems] A method for manufacturing a varistor element according to the present invention includes powder of varistor particles in which the surface of at least zinc oxide crystal particles is coated with an inorganic insulating film, 85 to 35 parts by weight of lead oxide, and boron oxide. A glass frit consisting of 6 to 25 parts by weight, 3 to 20 parts by weight of zinc oxide, 3 to 10 parts by weight of manganese oxide, and 3 to 10 parts by weight of cobalt oxide and an organic binder were added to form a paste, and the paste was arranged with electrodes. The above problem was solved by printing a predetermined shape on an insulating substrate by screen printing and then solidifying it at a firing temperature of 440°C to 520°C.

[0013]

[Operation] The present invention provides a high-performance varistor element by using manganese and cobalt-doped lead-borate zinc glass as the binder glass frit and solidifying it at a firing temperature of 440°C to 520°C. It becomes possible to obtain a liquid crystal display device of.

[0014]

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

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

First, in a granulation step 101, 0.003 mol % of aluminum as a dopant was added and mixed to a commercially available zinc oxide fine powder (particle size of 1 μm or less) using a V-type mixer. Next, in a sintering step 102, the material was sintered at 1200° C. for 1 hour to form a polycrystalline body containing crystal grains with an average grain size of about 6 μm. Next, in a pulverizing step 103, the polycrystalline material was pulverized, and then in a classifying step 104, it was classified using an air classifier to obtain zinc oxide crystal particles having a particle size of 5 μm to 8 μm. Next, in the corner cutting firing step 105,
The zinc oxide crystal particles were spheroidized by firing at 1000° C. for 1 hour to round off the corners. Next, insulating film forming step 106
In this step, 0.25 mol% of cobalt nitrate and 0.05 mol% of manganese nitrate are dissolved in water to form an aqueous solution,
Disperse the zinc oxide crystal particles in this aqueous solution, first evaporate water at 120°C, coat the zinc oxide crystal particles with a metal film, and then raise the temperature to 200°C to oxidize the metal film to form an oxide film. . Further, it was fired at 1100° C. for 1 hour to form an inorganic insulating film 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, in the ink forming step 107, 4 parts by weight of glass frit is added to 16 parts by weight of the varistor particles. Here, the glass frit is lead-zinc borate glass doped with manganese and cobalt, and lead oxide is 85 to 3
5 parts by weight, 6 to 25 parts by weight of boron oxide, 3 to 2 parts by weight of zinc oxide
The composition used was 0 parts by weight, 3 to 10 parts by weight of manganese oxide, and 3 to 10 parts by weight of cobalt oxide. To the above varistor particles and glass frit, 1 part by weight of ethyl cellulose (viscosity: 45 cps) as an organic binder and 8 parts by weight of carbitol as an organic solvent were added and kneaded to form a paste.

The manufacturing method of the glass frit used here is as follows:
A well-known method was used. That is, a predetermined glass composition is blended, melted at high temperature, quenched in water, and then pulverized to a desired particle size. Since the particle size of the glass frit also affects the electrical properties, it is desirable that the average particle size is 5 μm or less.

Next, in a printing step 108, as shown in FIG. 10, the above-mentioned film is printed on a glass substrate 10 on which row electrodes 11 made of chromium and pixel electrodes 12 made of indium oxide/tin oxide (ITO) are provided in advance. 25 paste
A printing board was obtained by coating in a predetermined shape using a 0 mesh screen printing plate. Finally, in the firing step 109, 3
It was baked at 80° C. to 520° C. for 1 hour to solidify and obtain a varistor element.

FIG. 2 shows a comparison between the characteristics of the varistor element obtained in this example and the characteristics of a conventional varistor element. The solid line 1 in the figure is the firing step 1 of the above manufacturing method.
The α value of the varistor element obtained by varying the firing temperature in 09 in the range of 380°C to 520°C is shown. Moreover, the wavy line 2 indicates the α value of the conventional varistor element. As is clear from FIG. 2, by setting the firing temperature in the range of 440° C. to 520° C., it is possible to obtain a varistor element having a larger α value than the conventional one. Furthermore, the firing temperature is 480
It can be seen that the α value has a maximum value at ℃, and α=40, which means that a varistor element with much higher performance than the conventional one can be obtained.

The present invention can of course be applied not only to varistor elements for liquid crystal display devices, but also to generally used thick film varistors.

[0022]

As described above in detail, according to the present invention, it is possible to manufacture a high-performance varistor element, and therefore it is possible to obtain a high-quality liquid crystal display device.

[0023]

[Brief explanation of the drawing]

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

FIG. 2 is a graph showing the firing temperature characteristics of the α value of a varistor element obtained according to an example of the present invention.

FIG. 3 is a schematic configuration diagram of a two-terminal element type liquid crystal display device.

FIG. 4 is a graph diagram showing voltage-current characteristics of a general varistor element.

FIG. 5 is a graph diagram showing operating characteristics of a liquid crystal pixel.

FIG. 6 is a graph diagram showing operating characteristics of a liquid crystal pixel and explaining the action of a varistor element.

FIG. 7 is a graph diagram showing operating characteristics of a liquid crystal pixel and explaining the action of a varistor element.

FIG. 8 is a configuration diagram of a general liquid crystal display device.

FIG. 9 is a plan view of a general liquid crystal display device.

10 is a sectional view taken along the line IV-IV in FIG. 9. FIG.

FIG. 11 is a cross-sectional view of a varistor particle.

FIG. 12 is an enlarged view of the main part in FIG. 10 of a varistor element according to a conventional method.

[Explanation of symbols]

1 Firing temperature characteristics of α value of varistor element of the present invention 2 α value of conventional varistor element 11 Row electrode 12 Pixel electrode 13 Varistor element 13a Varistor particles 13b Glass frit 14 Liquid crystal 15 Column electrode 131 Zinc oxide crystal particles 132 Inorganic insulating film

Claims (1)

[Claims] Claim 1: Powder of varistor particles in which at least the surface of zinc oxide crystal particles is coated with an inorganic insulating film, and lead oxide 85
~35 parts by weight, 6 to 25 parts by weight of boron oxide, 3 parts by weight of zinc oxide
A glass frit consisting of ~20 parts by weight, 3 to 10 parts by weight of manganese oxide, and 3 to 10 parts by weight of cobalt oxide and an organic binder are added to form a paste, and the paste is screen printed onto an insulating substrate on which electrodes are arranged in a predetermined shape. A method for manufacturing a varistor element, which comprises printing a shape and then solidifying it at a firing temperature of 440°C to 520°C.