JPH03261645A - Ceramic composition for varistor - Google Patents

Abstract

PURPOSE:To obtain a ceramic composition for varistor having a discharge voltage ratio of <=1.4 and improved surge resistance by adding an oxide of a metal such as cobalt as a subsidiary component to a main component consisting of multiple oxides of zinc and titanium having a specific compounding ratio. CONSTITUTION:The objective ceramic composition for varistor is produced by adding a metal oxide as a subsidiary component to multiple oxides of zinc and titanium used as main component. The multiple oxide is produced by mixing zinc oxide with 10-40atom% (based on zinc oxide) of titanium oxide. The subsidiary component is oxides of praseodymium and cobalt and the amount of addition is 0.1-5atom% of praseodymium and 0.5-5atom% of cobalt in terms of atom.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a ceramic composition for varistors, particularly for use as a material for varistors that function as voltage nonlinear resistors such as surge absorbing elements and voltage stabilizing elements. be able to,
The present invention relates to a porcelain composition for baristas.

(Prior art) Conventional porcelain Mi base materials for varistors include, for example, ZnO-based materials containing zinc oxide as the main component and several metal oxides added as sub-components, and ST-based materials containing strontium titanate as the main component. There are materials etc. In particular, varistors using ZnO-based materials have characteristics such as low limiting voltage due to large voltage nonlinearity over a wide current range, and excellent surge resistance, so they are currently the mainstream varistor. .

Such varistors are widely used as surge absorbing elements, voltage stabilizing elements, and the like. The electrical characteristics of the varistor are expressed by the following equation.

1/1-(V/V, )" Here, ■ is the current flowing through the varistor element, and ■ is the applied voltage. Also, Vl is the voltage between the terminals when a current of 1 (A) flows through the varistor element. Then, take the voltage between the terminals when a current of 1 (mA) normally flows and calculate the varistor voltage VImA.
It is called. Further, α is called a voltage nonlinear coefficient and indicates how the voltage is controlled when the varistor is incorporated into an electric circuit, and the larger α is, the better the voltage control is.

In recent years, in the field of electronic equipment used in communications equipment, etc.
Miniaturization, use of ICs, and integration are progressing rapidly, and along with this, there is a strong demand for varistors to be ultra-miniaturized or to lower voltage in order to increase the packaging density. To meet such demands, for example, the
A multilayer varistor as shown in Japanese Patent No. 3921 has been proposed. In such a laminated varistor, the number of inter-electrode grain boundaries can be reduced without causing semiconductor crystal grains to grow to a large size, and therefore the operating voltage can be easily lowered.

(Problems to be Solved by the Invention) However, in varistors using such conventional varistor ceramic compositions, voltage nonlinearity decreases as the operating voltage decreases, resulting in an increase in limiting voltage or surge resistance. The decline in energy consumption has become a problem. For example, for a ZnO-based varistor with a varistor voltage VlffiA of -30 (V),
The peak value of the voltage between the terminals when the standard impulse current of (A) is applied, that is, the maximum limit voltage at I = 5 (A), is:
Current commercially available products are 45 (V) (limiting voltage ratio 1
5 times), and is still not sufficient for overvoltage protection of semiconductor devices with small overcurrent withstand capability.

Although improvements have been made to ZnO-based varistors, the limiting voltage ratio has been considered to be limited to around 1.5 times. It is believed that voltage nonlinearity and surge resistance largely depend on the intracrystalline resistance of zinc oxide, which is the main component. Therefore, although some methods have been considered to lower the intra-grain resistance by doping with aluminum ions, etc., there is a problem that the resistance cannot be lowered below a certain value. Therefore, it was not possible to reduce the limiting voltage ratio, and it was not possible to increase voltage nonlinearity or surge resistance.

Therefore, the main object of the present invention is to provide a ceramic composition for a varistor that can reduce the limiting voltage ratio and provide a varistor with high surge resistance.

(Means for solving the problem) This invention has a composite oxide of zinc and titanium as the main component,
This is a ceramic composition for a varistor, to which at least one metal oxide is added as a subcomponent.

As the composite oxide of zinc and titanium, one in which a titanium oxide is added to zinc oxide in an amount of 10 to 40 atomic % in terms of titanium is used.

In addition, as subcomponents, praseodymium and cobalt oxides are added in an amount of 0.1 to 5.0 at% and cobalt in a range of 0.1 to 5.0 at%, calculated as praseodymium and cobalt, respectively. is used.

Furthermore, as subcomponents, bismuth and cobalt oxides are converted into bismuth and cobalt, respectively.
．． It may be added in an amount of 0 atomic %.

(Effects of the Invention) According to the present invention, the limiting voltage ratio can be made within 1.4 times, and a varistor with greater surge resistance than a varistor using a conventional composition can be obtained.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

(Example) The factory team first prepared zinc oxide and titanium oxide as the main component materials. Then, titanium oxide was converted into titanium with respect to zinc oxide and weighed so as to have the composition ratio shown in Table 1, and mixed for 24 hours using ion-exchanged water to obtain a mixture. After filtering and drying this mixture, it was heat-treated at 700° C. for 2 hours, and then pulverized and classified by a jet mill to obtain a composite oxide of zinc and titanium.

With respect to 100 atom% of the obtained composite oxide, praseodymium oxide and cobalt oxide are 05 atom% and 2.0 atom%, respectively, in terms of praseodymium and cobalt.
A weighed product was obtained by weighing to obtain a ratio of atomic %. This weighed material was mixed for 10 hours using ion-exchanged water, filtered,
After drying, it was calcined at 800° C. for 2 hours to obtain a calcined product. This calcined product was thoroughly ground with a ball mill, mixed with an organic binder, and formed into a uniform green sheet with a thickness of about 20 μm using a doctor blade method.

This green sheet was cut to form a rectangular green sheet 12 as shown in FIG.

Next, an electrode paste containing platinum and vehicle was prepared. This electrode paste was screen printed on a green sheet 12 to form an internal electrode material 14, as shown in FIG. Then, the green sheet 12 on which the internal electrode material 14 was printed was laminated together with the green sheet 15 on which the internal electrode material 14 was not printed, pressed together with a pressure of 2 ton/cm 2 and cut into a predetermined size to obtain a laminate. This laminate was fired in air at 1200° C. for 2 hours to obtain porcelain 18 having internal electrodes 16 as shown in FIG. Silver paste is applied to the end of this porcelain 18 so as to be connected to the internal electrode 16, and baked at 700°C for 10 minutes.
An external electrode 20 was formed. In this way, a multilayer varistor 10 was formed as a sample, and its electrical characteristics were measured.

Here, the varistor voltage V+I, la, I =
The maximum limiting voltage V 5 A r limiting voltage ratio VsA/VIMA and surge withstand capacity at 5 (A) were measured and shown in Table 1.
It was shown to.

The varistor voltage indicates the voltage between the terminals when a direct current of 1 (mA) is passed through the sample, and the maximum limit voltage is 8
It shows the voltage peak value between the terminals when a standard impulse current of 8x20 (μA) is applied to the sample.
When a standard impulse current of (μA) is passed twice at an interval of 5 minutes, the rate of change in varistor voltage shows a maximum current value within 10%. Further, as a comparative example, similar measurements were conducted on a multilayer varistor using zinc oxide as the main component material, and the result is shown in sample number 1. Note that *marks are outside the scope of this invention, and the others are within the scope of this invention.

As can be seen from Table 1, when the amount of titanium added to zinc oxide is within the range of the invention, the limiting voltage ratio is as small as 1.4 times or less, and the surge resistance is 500 (A), showing excellent characteristics. On the other hand, those outside the scope of the invention have a large limiting voltage ratio and a small surge resistance.

Back application group 1 First, as the main component material, titanium oxide was weighed and added to zinc oxide in an amount of 40 atomic % in terms of titanium, and mixed for 24 hours using ion-exchanged water to obtain a mixture. Ta. After filtering and drying this mixture, it was heat-treated at 700° C. for 2 hours, and then pulverized and classified into two parts using a jet mill to obtain a composite oxide of zinc and titanium.

With respect to 100 atom % of the obtained composite oxide, praseodymium oxide and cobalt oxide were converted into praseodymium and cobalt and were weighed to have the ratios shown in Table 2, respectively, to obtain weighed products.

This weighed product was mixed with ion-exchanged water for 10 hours, filtered and dried, and then calcined at 800° C. for 2 hours to obtain a calcined product. This calcined material was thoroughly ground in a ball mill, mixed with an organic binder, and then processed to a powder of about 20μ by the doctor blade method.
A uniform green sheet with a thickness of m was formed. This green sheet was cut to form a rectangular green sheet 12 as shown in FIG.

Next, an electrode paste containing platinum and vehicle was prepared. This electrode paste was screen printed on a green sheet 12 to form an internal electrode material 14, as shown in FIG. Then, the green sheet 12 on which the internal electrode material 14 was printed was laminated together with the green sheet 15 on which the internal electrode material 14 was not printed, pressed together with a pressure of 2 ton/cm 2 and cut into a predetermined size to obtain a laminate. This laminate was fired in air at 1200° C. for 2 hours to obtain porcelain 18 having internal electrodes 16 as shown in FIG. Silver paste is applied to the end of this porcelain 18 so as to be connected to the internal electrode 16, and baked at 700°C for 10 minutes.
The external electrode 20 was formed. In this way, the multilayer varistor 10 as a sample was shaped and its electrical characteristics were measured.

Here, maximum limiting voltage V S A + limiting voltage ratio Vsa/V at varistor voltage v, , r=5 (A)
ImA and surge resistance were measured and shown in Table 2.

As can be seen from Table 2, when the amounts of praseodymium and cobalt added are within the range of the invention, the limiting voltage ratio is 1.
It exhibits excellent characteristics with a surge resistance of 500 (A) and a surge resistance of 500 (A). On the other hand, those outside the scope of the invention have a large limiting voltage ratio and a small surge resistance.

Practical Group 1 First, titanium oxide was weighed and added to zinc oxide as the main component material so that it was 40 atomic % in terms of titanium, and mixed for 24 hours using ion-exchanged water to obtain a mixture. Ta. After filtering and drying this mixture, it was heat-treated at 700° C. for 2 hours and pulverized into 9 classifications using a jet mill to obtain a composite oxide of zinc and titanium.

Based on 100 atomic % of the obtained composite oxide, bismuth oxide and cobalt oxide were converted into bismuth and cobalt and weighed so as to have the ratios shown in Table 3, respectively.
A weighed object was obtained. This weighed material was washed with ion-exchanged water for 10 minutes.
Mix for an hour and filter.

After drying, it was calcined at 800° C. for 2 hours to obtain a calcined product. This calcined product was sufficiently ground in a ball mill, mixed with an organic binder, and formed into a uniform green sheet with a thickness of about 20 μm using a doctor blade method. This green sheet was cut to form a rectangular green sheet 12 as shown in FIG.

Next, an electrode paste was prepared by mixing a vehicle with an alloy of silver and palladium. This electrode paste was screen printed on a green sheet 12 to form an internal electrode material 14, as shown in FIG. Then, the green sheet 12 on which the internal electrode material 14 is printed is laminated together with the green sheet 15 on which the internal electrode material 14 is not printed.
m'' pressure and cut into a predetermined size to obtain a laminate. This laminate was fired in air at 1000°C for 2 hours, and as shown in FIG. A porcelain 18 was obtained.A silver paste was applied to the end of the porcelain 18 so as to connect it to the internal electrode 16, and the porcelain 18 was heated at 700°C for 10 minutes.
The external electrode 20 was shaped by baking for a minute. In this way, the multilayer varistor 10 as a sample was shaped and its electrical characteristics were measured.

Here, the varistor voltage V,, A, I = 5 (
Maximum limit voltage VSA + limit voltage ratio Vsa/ in A)
VIMA and surge resistance were measured and shown in Table 3.

As can be seen from Table 3, when the amounts of bismuth and cobalt added are within the range of the invention, the limiting voltage ratio is as small as 1.4 times or less, and the surge withstand capacity is 500 (A), showing excellent characteristics. On the other hand, those outside the scope of the invention have a large limiting voltage ratio and a small surge resistance.

Next, the reason for limiting the amount of titanium added to zinc oxide will be explained. In other words, if the amount of titanium added to zinc oxide is less than 10 atomic %, the intracrystalline resistance will not decrease sufficiently, the maximum limiting voltage will increase compared to the case of zinc oxide alone, and the surge resistance will deteriorate. be. On the other hand, if the amount of titanium added to zinc oxide exceeds 40 atomic %, sinterability deteriorates, voltage nonlinearity deteriorates, and the maximum limit voltage increases.

Note that in Examples 1 to 3 above, the heat treatment temperature was set at 700°C when obtaining a composite oxide of zinc and titanium, but any heat treatment temperature of 600°C or higher may be used. That is, if the heat treatment temperature is set to 600°C or higher, no unreacted Zn○ or TiOz crystal phase remains, and a single phase of
A composite oxide of zinc and titanium can be obtained.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view showing the process of manufacturing a laminated varistor using the porcelain assembly for varistor of the present invention. FIG. 2 is an illustrative view showing a multilayer varistor manufactured through the process shown in FIG. 1. In the figure, 10 is a laminated varistor, 12 and 15 are green sheets, 14 is an internal electrode material, 16 is an internal electrode, and 18 is porcelain.

Claims (1)

[Scope of Claims] 1. A porcelain composition for a varistor, the main component being a composite oxide of zinc and titanium, with at least one metal oxide added as a subcomponent. 2 The composite oxide of zinc and titanium contains 10 to 40 atomic % of titanium oxide relative to zinc oxide in terms of titanium.
The porcelain composition for a barista according to claim 1, wherein the porcelain composition is added in a range of . 3. The subcomponent is an oxide of praseodymium and cobalt, and when converted to praseodymium and cobalt, the praseodymium is 0.1 to 5.0 at%, and the cobalt is 0.5 to 5.0 at%. The porcelain composition for a barista according to claim 1 or 2, wherein the porcelain composition is added in a range of . 4 The subcomponent is an oxide of bismuth and cobalt, and each is converted into bismuth and cobalt,
3. The ceramic composition for a varistor according to claim 1, wherein the bismuth is added in an amount of 0.1 to 5.0 at%, and the cobalt is added in an amount of 0.1 to 5.0 at%.