JP2000243608A - Zinc oxide varistor and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zinc oxide varistor for low-voltage, together with its manufacturing method, which comprises an excellent surge absorption characteristic as a zinc oxide group varistor, with low electrostatic capacitance. SOLUTION: A ceramic 11 of zinc oxide group containing at least one oxide from among MnO, CoO, Fe2O3, NiO, MgO, Al2O3, and BeO is produced. On the surface of the ceramic 11, two electrode materials containing an electrode subjected to a heat treatment in the range of 400 to 700 deg.C additive oxide wherein a mixture comprising at least two oxides out of Bi2O3, Sb2O3, B2O3, Cr2O3, PbO, TiO2, SiO2, SnO2, Ta2O5, GeO2, BaO, SrO, Y2O3, Pr2O3, CoO, and MnO is thermally processed at 400-700 deg.C are formed, then thermally processed at 700-1000 deg.C to form electrodes 12 and 13 which are attached with lead wires 14 and 15, providing a zinc oxide varistor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc oxide varistor used for absorbing surges generated in an electric circuit and a method for manufacturing the same.

[0002]

2. Description of the Related Art Zinc oxide varistors are roughly classified into two types, a grain boundary barrier type and a surface barrier type. A varistor characteristic is created by forming a barrier that regulates the flow of current at the so-called grain boundary between the particles and the zinc oxide particles, and the varistor characteristic is produced. (A zinc oxide-based porcelain is sometimes referred to as a zinc oxide-based porcelain), and a metal is brought into contact with the surface to form a Schottky barrier on the surface of the zinc oxide-based porcelain.

The former grain boundary barrier type zinc oxide varistor is
Zinc oxide-based porcelain obtained by molding and firing a zinc oxide raw material powder containing ZnO and basic additives Bi ₂ O ₃ , MnO and CoO, and various oxides added for further performance improvement It is manufactured using the composition. A depletion layer is formed on the surface portion of each zinc oxide particle on both sides of the grain boundary along the ZnO grain boundary of the zinc oxide-based porcelain composition thus produced, and a Schottky-type barrier for adjusting the current at the grain boundary is formed. It is formed. In this case, it is said that a double Schottky barrier is formed because a Schottky barrier is formed on both sides of the grain boundary. Due to the presence of this barrier, no current flows at first even when an electrode is formed on the porcelain composition and a voltage is applied, and when the voltage reaches a rising voltage that is a varistor voltage, a current starts to flow rapidly, so-called varistor characteristics appear .

It is known that the rising voltage of a grain boundary barrier type zinc oxide varistor rises almost in proportion to the number of zinc oxide grain boundaries existing between the electrodes of the device. In order to manufacture a zinc oxide varistor for a high voltage of about 300 V per 1 mm in thickness, a Z particle having a small average particle diameter of about 10 μm is required.
It is necessary to produce a sintered body having nO particles. Therefore, conventionally, in order to manufacture a zinc oxide varistor for high voltage, a method of suppressing the growth of ZnO particles by adding a grain growth inhibitor of ZnO particles such as Sb ₂ O ₃ has been used. Sb ₂ O ₃ also plays an important role in stabilizing the nonlinear resistance characteristics of the zinc oxide varistor in addition to suppressing the growth of ZnO particles. In the case of a grain boundary barrier type zinc oxide varistor, in order to manufacture a zinc oxide varistor for a low voltage having a rising voltage of about 20 V per 1 mm in thickness, an average particle diameter of 150 mm is required.
It is necessary to produce a sintered body having ZnO particles having a large particle size of about μm. Therefore, conventionally, in order to manufacture a zinc oxide varistor for a low voltage, a method of promoting the growth of ZnO particles by adding a grain growth promoter of ZnO particles such as TiO ₂ has been used.

[0005] The rising voltage means that the varistor is 1
The voltage between both electrode terminals when a current of mA flows, V1mA
Is represented by In a grain boundary barrier type zinc oxide varistor, the voltage between both electrode terminals when a current of 1 mA flows through a sample having a thickness of 1 mm is regarded as one of the constants of this material, and is often V1mA.
Expressed in / mm. This means a rising voltage per 1 mm thickness of the sample. The electrical properties of zinc oxide varistors are often described by the rise voltage and the nonlinear resistance index α. The nonlinear resistance index α is defined by the following equation. I = (V / V0) α where I represents the current flowing through the device, and V represents the voltage applied between both terminals. V0 is a constant. The excellent electrical characteristics of the zinc oxide varistor means, for example, that the leakage current is small and the nonlinear resistance index α is high. In addition, excellent reliability means that electrical characteristics deteriorate even when a long-term voltage is applied, when a long-term power load is applied at a high temperature, or when a high-current pulse is applied. And the original electrical characteristics are maintained.

On the other hand, the latter surface barrier type zinc oxide varistor is formed by applying a metal paste such as silver containing glass frit or the like to the surface of a zinc oxide based porcelain and subjecting it to a heat treatment.
It is manufactured by forming a so-called non-ohmic electrode. In the surface barrier type varistor thus manufactured, a depletion layer is formed inside the zinc oxide-based porcelain along the portion where the non-ohmic electrode is formed on the surface of the zinc oxide-based porcelain, and a current is applied to the surface of the zinc oxide-based porcelain. A Schottky-type barrier for preventing the formation of the pit is formed. Due to the presence of this barrier, current does not flow at first even when an electrode is formed on the other side of the porcelain and a voltage is applied, and when the voltage exceeds the rising voltage, which is the varistor voltage, current starts to flow rapidly. Appears. In the surface barrier type zinc oxide varistor, depending on the number of non-ohmic electrodes formed, one non-ohmic electrode type (in this case,
The other electrode includes an ohmic electrode and a non-ohmic electrode type. When a current flows from the electrode side to the zinc oxide-based porcelain at the barrier portion (forward direction), the rising voltage is about 1 V, and when a current flows from the zinc oxide-based porcelain side to the electrode (the reverse direction). ) Has a rising voltage of 3
Take a value near V. Therefore, one non-ohmic electrode type varistor is divided into two types, a 1V type and a 3V type, depending on how current flows. On the other hand, in the two non-ohmic electrode type varistors, the current flows through both the forward and reverse barriers.
Becomes

[0007]

In recent years, with the progress of digitization of electronic circuits, high-frequency noise has been generated, and it has become urgent to remove high-frequency noise in various digitized electronic devices. . Conventional grain boundary barrier type zinc oxide varistors have excellent surge absorption characteristics. Large-sized ones have been used as arresters in power transmission and distribution circuits, and small-sized ones have been used as surge absorbers in electronic circuits. ing. However, these zinc oxide varistors cannot absorb high-frequency noise because of their large capacitance, and there has been a demand for a high-performance high-performance zinc oxide varistor having a small capacitance. In particular, in a circuit using a semiconductor, a low-voltage varistor having a rising voltage of 10 volts or less is required.

In a grain boundary barrier type zinc oxide varistor, the rising voltage of the varistor is determined by the number of crystal boundaries between the electrodes of the device. In the sintered body of the zinc oxide varistor, the rising voltage between the zinc oxide crystals, that is, one grain boundary is about 3.0 to 3.3 volts. In order to obtain a low-voltage varistor of 10 volts or less, it is necessary to attach an electrode to a sintered body having 1 to 3 crystal grain boundaries. Bi promotes liquid phase sintering at the grain boundaries of zinc oxide varistors
The presence of ₂ O ₃ and CoO and MnO, which trap electrons at the grain boundaries to form a depletion layer in the zinc oxide particles along the grain boundaries, have been required. In addition, the presence of Sb ₂ O ₃ was indispensable to obtain stability as a varistor and to improve nonlinear characteristics.

The ZnO—Bi ₂ O ₃ system, which is the basic composition of the porcelain composition of the zinc oxide varistor, has a eutectic composition having a eutectic temperature of 740 ° C. Therefore, the two of ZnO and Bi ₂ O ₃ Reacts easily even at temperatures around 800 ° C. But here Sb ₂ O ₃
Presence hinders this reaction. Sb ₂ O ₃ sublimates at several hundred degrees and covers the zinc oxide surface, and Sb ₂ O ₃ itself or a compound of ZnO and Sb ₂ O ₃ contacts between the above ZnO and Bi ₂ O ₃ Hinder. Further, there is a case where Sb ₂ O ₃ first reacts with ZnO and then reacts with Bi ₂ O ₃ to form a chemically stable solid phase pyrochlore phase. Therefore, when Sb ₂ O ₃ is added, in order to obtain excellent varistor characteristics,
It was necessary to fire at a high temperature of 1200 ° C. or more.

In recent years, with the development of manufacturing technology, Sb ₂ O ₃ and B
When i ₂ O ₃ was reacted in advance and added to zinc oxide together with other additives, an excellent varistor could be obtained even when firing at a low temperature of 850 to 950 ° C. With these new technologies, various low-voltage varistors with a rise voltage of about 20 V have been developed, and the nonlinear resistance index α value is 2
A device that can withstand 1000 Amp / cm ² (8 × 20 μsec) at 0 to 30 has also been developed. However, these low-voltage zinc oxide varistors have a large capacitance and cannot be used for absorbing high-frequency noise and the like. The rise voltage of a grain boundary barrier type zinc oxide varistor is determined almost entirely by the number of grain boundaries existing between the electrodes of the device, but the capacitance of the device increases in proportion to the electrode area as in the case of a capacitor, and the voltage between the electrodes increases. It is inversely proportional to the thickness of the insulating layer. Also, the capacitance increases as the number of barriers between the electrodes decreases. Therefore, in an element having a low rise voltage, the number of grain boundaries is small at the same time, so that the capacitance is large. In the case of a disk-type practical zinc oxide varistor having an electrode diameter of 10 mm, the rising voltage can be reduced to about ten and several volts, but the capacitance at that time is 10 nF.
It was the value before and after. In order to further reduce the rising voltage or to reduce the electrode area, the conventional grain boundary barrier type has a problem that the variation in the rising voltage and the capacitance is rapidly increased and the production becomes difficult. As described above, the conventional method for producing a ZnO sintered body cannot stably produce a low-capacity low-voltage zinc oxide varistor having excellent electric characteristics and reliability. The grain boundaries formed by sintering are naturally generated in the sintered body. In the conventional sintering method, the grain boundaries are controlled to form a sintered body having one or two layers of barriers. Because it could not be obtained.

In order to obtain a rising voltage per one grain boundary in a conventional grain boundary barrier type zinc oxide varistor, an experiment for forming a microelectrode on one surface of a sintered body of a zinc oxide varistor and obtaining current-voltage characteristics has been carried out. Had been reported.
In other words, a metal film is formed on one surface of a sintered body of a zinc oxide varistor, and microelectrodes are appropriately formed by making use of techniques such as etching, and the number of grain boundaries between the two electrodes, current-voltage characteristics, and I was seeking a relationship. As a result, as described above, the rising voltage of one zinc oxide crystal grain boundary is about 3.
0 to 3.3 volts, and some excellent non-linear resistance characteristics were also observed. However, these have large variations in data and unstable characteristics when used as practical devices, and cannot be used as devices.

On the other hand, a thin film of bismuth oxide or the like is formed on a zinc oxide single crystal, and an electrode is directly formed thereon, or a zinc oxide thin film is formed and an electrode is formed thereon, or a bismuth oxide film is formed. Efforts have been made to obtain a varistor having one grain boundary by, for example, performing a heat treatment on the entire surface of the varistor with a zinc oxide single crystal. But,
The obtained product had unstable electric characteristics and was not excellent in non-linear resistance characteristics, and was difficult to use as an element. This is due to the fact that the grain boundaries equivalent to those of the grain boundary barrier type zinc oxide varistors that are practically used are not formed in those used in these experiments.

In the conventional surface barrier type zinc oxide varistor, the characteristics of the varistor have been improved by combining a zinc oxide-based porcelain containing various additives with a silver electrode. In comparison, the voltage varied greatly and the stability was insufficient for pulse application. The surface barrier type zinc oxide varistor is expected to provide a low-voltage varistor with a low rising voltage, and various attempts have been made but have not been put to practical use. In particular, when the baking temperature is high, the stability with respect to the application of the pulse is increased, but the voltage varies greatly.

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems, the present invention provides a zinc oxide varistor for low voltage with low capacitance and excellent electrical characteristics such as non-linear resistance characteristics having one or two barrier layers and excellent reliability. And a method for manufacturing the same. It is another object of the present invention to provide a zinc oxide varistor having a required rising voltage and capacitance and a method for manufacturing the same by multiplexing them.

[0015]

In order to achieve the above object,
Therefore, the zinc oxide varistor of the present invention comprises MnO, CoO, Fe_TwoO_Three, N
iO, MgO, Al_TwoO_Three, At least one oxide of BeO
Bi on the surface of high-density zinc oxide-based porcelain containing_TwoO_Three, S
b_TwoO_Three, B_TwoO_Three, Cr_TwoO _Three, PbO, TiO_Two, SiO_Two, SnO_Two, Ta_TwoO_Five, G
eO_Two, BaO, SrO, Y_TwoO_Three, Pr_TwoO_Three, CoO and MnO
An electrode containing an electrode-added oxide consisting of two oxides
It has a configuration in which two so-called non-ohmic electrodes are formed.
Things.

Next, in order to achieve the above object, a method for producing a zinc oxide varistor according to the present invention comprises:
Obtaining a high-density zinc oxide-based porcelain containing at least one oxide of O, CoO, Fe ₂ O ₃ , NiO, MgO, Al ₂ O ₃ and BeO; Bi ₂ O ₃ , Sb ₂ O _{3, B 2 O 3, Cr} 2 O 3, PbO, TiO 2,
SiO ₂ , SnO ₂ , Ta ₂ O ₅ , GeO ₂ , BaO, SrO, Y ₂ O ₃ , Pr ₂ O ₃ , Co
A step of preparing a mixture composed of at least two oxides of O and MnO, performing a heat treatment in the range of 350 ° C. to 700 ° C., and pulverizing the mixture to form a synthetic electrode-added oxide; Mixing the metal powder to be mixed with the electrode additive oxide containing the synthetic electrode additive oxide to obtain an electrode material, and applying the electrode material in two places on the zinc oxide-based porcelain; Forming a non-ohmic electrode by performing a heat treatment at a temperature of from 1000C to 1000C.

In order to achieve the above object, the zinc oxide varistor of the present invention comprises MnO, CoO, Fe ₂ O ₃ , NiO, MgO, Al ₂ O ₃ , Be ₂
Bi ₂ O ₃ , Sb ₂ O ₃ , B ₂ O ₃ , Cr ₂ O ₃ , PbO, Ti on a surface of a zinc oxide based porcelain containing at least one oxide of O
O ₂ , SiO ₂ , SnO ₂ , Ta ₂ O ₅ , GeO ₂ , BaO, SrO, Y ₂ O ₃ , Pr
An electrode containing an oxide containing at least two oxides of ₂ O ₃ , CoO, and MnO is formed as a single electrode containing a so-called non-ohmic electrode, and an ohmic electrode is further formed on the surface of the zinc oxide-based porcelain. It has a configuration in which one electrode is formed.

Next, in order to achieve the above object, a method for producing a zinc oxide varistor according to the present invention comprises MnO, CoO, Fe ₂ O ₃ ,
two steps of obtaining a zinc oxide-based porcelain containing at least one oxide of iO, MgO, Al ₂ O ₃ , BeO, Bi ₂ O ₃ , Sb ₂ O
_{3, B 2 O 3, Cr} 2 O 3, PbO, TiO 2, SiO 2, SnO 2, Ta 2 O 5, Ge
A mixture comprising at least two oxides of O ₂ , BaO, SrO, Y ₂ O ₃ , Pr ₂ O ₃ , CoO, and MnO is formed at 350 ° C. to 7 ° C.
A step of preparing a synthetic electrode-added oxide by performing heat treatment in the range of 00 ° C. and pulverizing, and a metal powder containing silver or a silver alloy as a main component and an electrode-added oxide containing the synthetic electrode-added oxide. Mixing the electrode material to obtain an electrode material, and applying the electrode material in one place on the zinc oxide based porcelain, 700
The method includes a step of forming one non-ohmic electrode by performing a heat treatment at a temperature of about 1000C to about 1000C, and a step of forming one ohmic electrode on the surface of the zinc oxide-based porcelain.

Further, in order to achieve the above object, the zinc oxide varistor of the present invention comprises MnO, CoO, Fe ₂ O ₃ , NiO, MgO, Al ₂
Zinc oxide-based porcelain containing at least one oxide of O ₃ and BeO, Bi ₂ O ₃ , Sb ₂ O ₃ , B ₂ O ₃ , Cr ₂ O ₃ , PbO, Ti
O ₂ , SiO ₂ , SnO ₂ , Ta ₂ O ₅ , GeO ₂ , BaO, SrO, Y ₂ O ₃ , Pr
_It has a configuration in which a plurality of electrodes containing an electrode-added oxide composed of at least two oxides of ₂ O ₃ , CoO, and MnO are alternately formed.

Next, in order to achieve the above object, the present invention
The manufacturing method of the zinc oxide varistor is MnO, CoO, Fe_TwoO_Three, Ni
O, MgO, Al_TwoO_Three, At least one oxide of BeO
Obtaining a zinc oxide-based porcelain containing Bi;_TwoO_Three, Sb_TwoO_Three,
B_TwoO_Three, Cr_TwoO _Three, PbO, TiO_Two, SiO_Two, SnO_Two, Ta_TwoO_Five, GeO_Two, B
aO, SrO, Y_TwoO_Three, Pr2O_Three, CoO, MnO at least 2
A mixture of two oxides at 350 ° C to 700 ° C
Heat treatment in the range described above and pulverization to produce a synthetic electrode additive oxide.
And a metal powder mainly composed of silver or silver alloy, etc.
Oxide containing the body and the synthetic electrode additive oxide
To obtain an electrode material by mixing
And the electrode material are alternately laminated to form a laminate.
Process and heat-treating the laminate at a temperature of 700 ° C. to 1000 ° C.
And forming an electrode.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention belongs to a surface barrier type zinc oxide varistor. MnO, CoO, Fe ₂ O ₃ , NiO, MgO, Al
Zinc oxide-based porcelain containing at least one oxide of ₂ O ₃ and BeO; Bi ₂ O ₃ , Sb ₂ O ₃ , B ₂ O ₃ , Cr ₂ O ₃ , PbO, Ti
O ₂ , SiO ₂ , SnO ₂ , Ta ₂ O ₅ , GeO ₂ , BaO, SrO, Y ₂ O ₃ , Pr
Excellent non-linear resistance characteristics formed on the surface of zinc oxide-based porcelain by non-ohmic contact with an electrode containing an oxide containing at least two oxides of ₂ O ₃ , CoO and MnO And a Schottky barrier composed of a single stable layer. Since the capacitance of these elements depends on the area of the barrier portion, a low-voltage varistor with low capacitance can be manufactured by reducing the area of the barrier portion. Further, by combining these, a low voltage varistor with a required low capacitance can be obtained. The surface barrier type zinc oxide varistor is manufactured by applying a metal paste such as silver containing an electrode-added oxide to the surface of a zinc oxide-based porcelain and subjecting it to a heat treatment to form a non-ohmic electrode. In the surface barrier type zinc oxide varistor thus manufactured, a depletion layer is formed along the electrode on the surface of the zinc oxide based porcelain, and a Schottky barrier is formed.
Due to the presence of this barrier, current does not flow at first even when an electrode is formed on a zinc oxide-based porcelain and a voltage is applied. appear. The nonlinear resistance index α is high due to the effects of various additives, and a stable one against a large current pulse can be obtained.

Since the surface barrier type zinc oxide varistor has a single Schottky barrier, the rising voltage is almost fixed. When a current flows from the electrode side to the zinc oxide-based porcelain at the barrier portion (forward direction), the rising voltage often takes a value of about 1V. When a current flows from the zinc oxide-based porcelain toward the electrode (in the reverse direction), the rising voltage takes a value near 3V.

There are mainly three types of surface barrier type zinc oxide varistors of the present invention. The first one is to apply a metal paste such as silver or silver alloy containing an oxide for electrode addition to two places on the surface of a zinc oxide-based porcelain and heat-treat it to form two non-ohmic electrodes. Is formed. The rising voltage is about 4 V. In the second type, a metal paste such as silver containing an oxide added to an electrode is applied to one portion of the surface of a zinc oxide-based porcelain, and a heat treatment is applied to the paste.
And an ohmic electrode is formed at another place on the surface of the zinc oxide based porcelain. Depending on the direction of the current, the rising voltage takes a value of around 1V or around 3V. Note that the ohmic electrode means an electrode that does not form a barrier on the surface of the zinc oxide-based porcelain at the electrode forming portion, and for example, a forming method of spraying metallic aluminum on the surface of the zinc oxide-based porcelain is used. . The third one alternately laminates a zinc oxide-based porcelain and a film made of a metal paste such as silver or a silver alloy containing an electrode-added oxide, etc., and heat-treats the laminate to form an ohmic electrode. Alternatively, a non-ohmic electrode is formed.

[0024]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples. In the following examples, "weight ratio"
May be displayed as “wt ratio”.

Example 1 ZnO powder, Co ₃ O ₄ , MnO ₂ , Ni
81.38 g: 0.954 g: 0.414 g: 0.383 by weight ratio of O powder
g, wet-mixed and pulverized and dried, and then 1.51 mg of aluminum nitrate was added in the form of an aqueous solution in terms of Al ₂ O ₃ . After molding this mixed powder and subjecting it to hot press firing at 1300 ° C for 1 hour in an air atmosphere, 0.7 mm × 1.7 mm, thickness 0.3
By cutting into a sample size of mm, a plate-shaped zinc oxide-based porcelain containing zinc oxide as a main component was obtained.

Then, 356.8 g of Bi ₂ O ₃ and SnO ₂ were added to 30.14 g.
And subjected to a heat treatment at 550 ° C. for 2 hours, followed by pulverization to obtain a synthetic powder of Bi ₂ O ₃ and SnO ₂ . Also, Bi ₂ O ₃ and B ₂
O ₃ was mixed at a ratio of 111.5 g: 8.7 g, heat-treated at 400 ° C. for 2 hours, and then pulverized to obtain a synthetic powder of Bi ₂ O ₃ and B ₂ O ₃ . 5.0 g of the synthesized powder of Bi ₂ O ₃ and SnO ₂ thus obtained, Bi ₂ O ₃
And a synthetic powder of B ₂ O _{3 in} a ratio of 1.0 g and silver powder 50 g,
A butyral resin, a plasticizer, and a solvent were added to paste to obtain a silver paste.

Next, a method of forming a zinc oxide varistor will be described with reference to FIG. FIG. 1 is a schematic perspective view of a plate-type zinc oxide varistor 10 of the present invention. 0.5 mm × 0 in two places on one side of the zinc oxide based porcelain 11 obtained as described above.
5 mm of the above-mentioned silver paste is applied, and the temperature is increased in the air at a heating rate of 50 mm.
After the temperature was raised at a rate of 50 ° C./hour, the temperature was lowered at a rate of 50 ° C./hour to form non-ohmic electrodes 12 and 13. Next, lead wires 14 and 15 were attached to the non-ohmic electrodes 12 and 13, and a structure other than the lead wires was coated with epoxy resin to obtain a zinc oxide varistor.

The electrical characteristics of the zinc oxide varistor thus obtained were evaluated. The initial electrical characteristics include a rise voltage V1mA (voltage between both terminals when a current of 1 mA flows) and a non-linear resistance index of 0.1 mA α1 mA (V1mA and V0.1 mA
), Capacitance (1 kHz), and tan δ (in the following description, the nonlinear resistance index of 0.1 mAα1 mA is sometimes simply referred to as α value). The larger the nonlinear resistance index, the greater the surge absorption capacity. In addition, the reliability for a DC load was evaluated. A DC load of 1.0 milliwatt is applied for 500 hours in a high-temperature atmosphere of 80 ° C., and the varistor rising voltage V1mA change rate 変 化 V1mA
/ V1mA (DC load change rate) was measured. The smaller the rate of change ΔV1mA / V1mA of the varistor rise voltage V1mA, the more stable the electrical characteristics of the zinc oxide varistor, indicating higher reliability. Further, the reliability of the surge was evaluated. Variation rate of varistor rise voltage V1mA by applying 10 times 8 × 20 μsec, 3 Amp current pulse △ V1mA
/ V1mA (surge change rate) was measured. Table 1 shows the composition of the sample, and Table 2 shows the evaluation results of the electrical characteristics. The smaller the value of the surge rate, the more stable the electrical characteristics of the zinc oxide varistor and the higher the reliability. In each case, the rate of change is 5% or less, indicating high reliability. In addition,
Numerical values indicating the evaluation results of the electrical characteristics indicate the minimum value and the maximum value in the lot.

[0029]

[Table 1]

[0030]

[Table 2]

According to Tables 1 and 2, the zinc oxide varistor using the zinc oxide-based porcelain and the electrode of the present embodiment has a small capacitance, a good non-linear resistance characteristic, and can be applied to a long-term DC load. In addition, the absolute value of the rate of change of the rising voltage V1mA (mAV1mA / V1mA) was 5% or less with respect to surge, and the reliability was excellent. Further, as shown in Table 2, the variation of the electrical characteristics in the lot was small. Although not shown in Table 2, when the zinc oxide varistor was prepared using the zinc oxide-based porcelain of the present example, the variation in the electrical characteristics between lots was as small as the variation in the electrical characteristics in the lot.

(Example 2) Next, a zinc oxide-based porcelain sample was prepared in the same manner as in Example 1. ZnO powder and Co ₃
81.38 g: 0.954 g: 0.414 by weight ratio of O ₄ , MnO ₂ , and MgO powder
g: 0.806 g was mixed and pulverized, and 1.02 mg of aluminum nitrate was added in the form of an aqueous solution in terms of Al ₂ O ₃ .
After molding this mixed powder and performing hot press baking at 1300 ° C for 1 hour under air atmosphere, 0.5 mm × 0.5 mm, thickness 0.3 mm
The sample was cut to the sample size, and a zinc oxide-based porcelain containing zinc oxide as a main component was obtained.

Next, Bi_TwoO_ThreeAnd Sb_TwoO_ThreeAnd 139.8 g: 58.3 g
And heat-treated at 550 ° C for 2 hours, then pulverized.
Bi_TwoO_ThreeAnd Sb_TwoO_ThreeWas obtained. Also, Bi _TwoO_ThreeAnd B_TwoO_Three
Are mixed at a ratio of 111.5 g: 8.7 g and heat treated at 400 ° C. for 2 hours.
And then crushed to Bi_TwoO_ThreeAnd B_TwoO_ThreeWas obtained.
Furthermore, Bi_TwoO_ThreeAnd Cr_TwoO_ThreeAnd the ratio of 111.5 g: 38.0 g
Mix, heat-treat at 550 ° C for 2 hours, then pulverize_TwoO_Three
And Cr_TwoO_ThreeWas obtained. Bi thus obtained_TwoO_ThreeAnd Sb_TwoO_Three
5.0 g of synthetic powder with Bi_TwoO_ThreeAnd B_TwoO_ThreeWith synthetic powder 1.0
g, Bi_TwoO_ThreeAnd Cr_TwoO_Three1.0 g of synthetic powder and 50 g of silver powder
And then paste to form a paste by adding resin, plasticizer and solvent.
A paste was obtained.

Next, a method of forming a zinc oxide varistor will be described with reference to FIG. FIG. 2 is a schematic sectional view of a plate-type zinc oxide varistor 20 of the present invention. The silver paste is applied to the upper surface of the zinc oxide-based porcelain 21 obtained as described above, and the temperature is increased in air at a rate of 50 ° C./hour.
C. for 1 hour, and then the temperature was decreased at a rate of 50.degree. C./hour to form a non-ohmic electrode 22.
After polishing the lower surface of 1, an ohmic electrode 23 composed mainly of metallic zinc is attached to the lower surface, and lead wires 24 and 25 are attached to the two electrodes 22 and 23, and structures other than the lead wire are formed. Was coated with an epoxy resin to obtain a zinc oxide varistor.

The electrical characteristics of the zinc oxide varistor thus obtained were evaluated in the same manner as in Example 1. In addition, as the initial electric characteristics, a current is applied in the reverse direction, a rise voltage V1mA (a voltage between both terminals when a current of 1 mA is applied), a capacitance, a tanδ, a nonlinear resistance index of 0.1 mAα1m.
A (the value obtained using V1mA and V0.1mA) was measured. 8
A DC load of 1 milliwatt in a high temperature atmosphere
Time applied, varistor rise voltage V1mA change rate △ V1
mA / V1mA (DC load change rate) was measured. In addition,
The reliability of the device was evaluated. 8 × 20μsec, 3Amp
Of the varistor rise voltage V1mA by applying the current pulse 10 times, ΔV1mA / V1mA (surge change rate) was measured. Table 3 shows the composition of the sample, and Table 4 shows the evaluation results of the electrical characteristics.

[0036]

[Table 3]

[0037]

[Table 4]

According to Tables 3 and 4, the zinc oxide varistor using the zinc oxide-based porcelain and the electrode of the present embodiment has a small capacitance, a good non-linear resistance characteristic, and can be applied to a long-term DC load. In addition, the absolute value of the rate of change of the rising voltage V1mA (mAV1mA / V1mA) was 5% or less with respect to surge, and the reliability was excellent. In addition, as shown in Table 4, variations in the electrical characteristics within the lot were also small. Although not shown in Table 4, when a zinc oxide varistor was prepared using the zinc oxide-based porcelain of the present example, the variation in the electrical characteristics between lots was similar to the variation in the electrical characteristics in the lot.

(Example 3) ZnO powder, Co ₃ O ₄ , MnO ₂ , B
81.38 g: 0.954 g: 0.414 g: 0.500 by weight ratio of eO powder
g of aluminum nitrate in the form of an aqueous solution.
0.76 mg in terms of Al ₂ O ₃ was added. CIP this mixed powder
After molding and baking at 1400 ° C for 3 hours under air atmosphere, cut into a sample size of 0.5 mm x 0.5 mm, 0.3 mm thick,
A plate-like zinc oxide-based porcelain containing zinc oxide as a main component was obtained.

Next, Bi_TwoO_ThreeAnd Sb_TwoO_ThreeAnd TiO_Two178.4 g: 21.
Mix at a ratio of 9 g: 20.0 g and heat treat at 550 ° C for 2 hours
Then crushed and Bi_TwoO_ThreeAnd Sb_TwoO_ThreeAnd TiO_TwoWas obtained. Ma
Bi_TwoO_ThreeAnd B_TwoO_ThreeAnd mixed in a ratio of 111.5 g: 8.7 g and 400
After 2 hours heat treatment at ℃_TwoO_ThreeAnd B_TwoO_ThreeWhen
Was obtained. In addition, Bi_TwoO_ThreeAnd Cr _TwoO_ThreeAnd 111.5 g:
After mixing at a ratio of 38.0 g and performing heat treatment at 550 ° C for 2 hours
Crush and Bi_TwoO_ThreeAnd Cr_TwoO_ThreeWas obtained. Thus obtained
Bi_TwoO_ThreeAnd Sb_TwoO_ThreeAnd TiO_TwoSynthetic powder 5.0g, Bi_TwoO_ThreeAnd B_TwoO_ThreeWith
1.0 g of flour, Bi_TwoO_ThreeAnd Cr_TwoO_Three1.0 g of synthetic powder with silver powder 70
g and mixed with resin and solvent to form a paste.
-I got a strike.

Next, a method of forming a zinc oxide varistor will be described with reference to FIG. FIG. 3 is a schematic sectional view of a laminated zinc oxide varistor 30 of the present invention. The three zinc oxide-based porcelains 31, 32, and 33 thus obtained and the two silver pastes are alternately laminated, and the temperature is increased in the air at a rate of 5 ° C.
After the temperature was raised at 0 ° C./hour and maintained at 900 ° C. for 1 hour, the temperature was lowered at a temperature lowering rate of 50 ° C./hour to obtain two non-ohmic electrodes 3.
4 and 35 were formed, and two ohmic electrodes 36 and 37 were formed on the outside to obtain a laminated zinc oxide varistor. Next, after lead wires 38 and 39 are attached to the electrodes 36 and 37 formed on both outer surfaces of the zinc oxide based porcelain, a structure other than the lead wires is coated with an epoxy resin to form a zinc oxide varistor. I got

The electrical characteristics of the zinc oxide varistor thus obtained were evaluated in the same manner as in Example 1. 80
A DC load of 2 milliwatts is applied for 500 hours in a high-temperature atmosphere at ℃, and the change rate of the varistor rise voltage V1mA is ΔV1mA.
/ V1mA (DC load change rate) was measured. Further, the reliability of the surge was evaluated. Varistor rise voltage V1mA by applying 8 × 20μsec, 3 Amp pulse 10 times
変 化 V1mA / V1mA (surge change rate) was measured. Table 5 shows the composition of the sample, and Table 6 shows the evaluation results of the electrical characteristics.

[0043]

[Table 5]

[0044]

[Table 6]

As can be seen from Tables 5 and 6, the zinc oxide varistor using the zinc oxide-based porcelain and the electrode of the present embodiment has a good non-linear resistance characteristic, and is suitable for a long-time DC load and a surge. However, the change rate of the rising voltage V1mA (△ V1mA / V1mA
The absolute value of mA) was 5% or less, and the reliability was excellent. Further, as shown in Table 6, the variation in the electrical characteristics within the lot was small. Although not shown in Table 6, when a zinc oxide varistor is prepared using the zinc oxide-based porcelain and the electrode of the present embodiment, the variation in the electrical characteristics between lots is the same as the variation in the electrical characteristics in the lot. Was.

[0046]

As described above with reference to the three embodiments, the present invention provides a low-voltage zinc oxide varistor having excellent electrical characteristics such as non-linear resistance characteristics with low capacitance and high reliability and a high yield. To provide. As the digitization of electronic circuits progresses, high-frequency noise is generated, and there is an urgent need to remove high-frequency noise in various digitized electronic devices. In particular, in a circuit using a semiconductor, a low-voltage varistor having a rising voltage of 10 volts or less is required. Although the conventional grain boundary barrier type has excellent surge absorption capability, the low voltage type cannot control the number of barriers between the electrodes of the polycrystalline body of the element, and the value of the rising voltage varies widely, making it practical. Was difficult. In the present invention, a low-voltage varistor is obtained by using a Schottky-type barrier generated by bringing an electrode into contact with a high-density zinc oxide-based porcelain of a surface barrier type. Then, a zinc oxide varistor with a low capacitance and a low voltage was obtained by reducing the electrode area. In such a surface barrier type varistor, the effect of the additive added to the contacting electrode material on the varistor characteristics is great. In the first embodiment, two non-ohmic electrodes are formed on one surface of a plate-shaped zinc oxide ceramic, but two non-ohmic electrodes are formed on the upper and lower surfaces of the zinc oxide ceramic. Gave similar results. In the embodiment, silver which is easy to carry out is used as an electrode material, but a metal or an alloy which does not oxidize in an oxidizing atmosphere can be used. Further, in the examples, Bi ₂ O ₃ , Sb ₂ O ₃ , B _{2
Two or three of} O ₃ , Cr ₂ O ₃ , TiO ₂ , and SnO ₂ were selected and mixed and subjected to heat treatment, or a mixture of the heat-treated mixed powders was used, but PbO, SiO ₂ , SnO ₂ , Ta ₂ O ₅ ,
Choosing among GeO ₂ , BaO, SrO, Y ₂ O ₃ , Pr ₂ O ₃ , CoO, MnO, the leakage current is small, or the nonlinearity is excellent in the high current region, or Varistors each having characteristics such as being suitable for forming electrodes at low temperatures can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a zinc oxide varistor produced in Example 1 of the present invention.

FIG. 2 is a schematic cross-sectional view of a zinc oxide varistor prepared in Example 2 of the present invention.

FIG. 3 is a schematic cross-sectional view of a laminated zinc oxide varistor prepared in Example 3 of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 Non-ohmic electrode type zinc oxide varistor 11 Zinc oxide based porcelain 12, 13 Electrode 14, 15 Lead wire 20 One non-ohmic electrode type zinc oxide varistor 21 Zinc oxide based porcelain 22 -Oxide electrode 23 Ohmic electrode 24, 25 Lead wire 30 Laminated type zinc oxide varistor 31, 32, 33 Zinc oxide porcelain 34, 35 Non-ohmic electrode 36, 37 Ohmic electrode 38, 39 Lead wire

 ──────────────────────────────────────────────────の Continuing on the front page F-term (reference) 4G026 BA02 BB02 BG05 BH06 4G030 AA06 AA07 AA09 AA10 AA11 AA12 AA16 AA21 AA22 AA25 AA27 AA28 AA29 AA32 AA35 AA36 AA37 AA38 AA39 AA04 CA05 DA07 AA03 A07 A08 DC02 DC06 DE02

Claims (7)

[Claims] (1) Manganese oxide (MnO), cobalt oxide (Co)
O), iron oxide (Fe_TwoO_Three), Nickel oxide (NiO), Magne oxide
Cium (MgO), Aluminum oxide (Al_TwoO_Three) And oxidation
At least one oxide of beryllium (BeO)
Bismuth oxide on the surface of the zinc oxide (ZnO) -based porcelain
(Bi_TwoO_Three), Antimony oxide (Sb_TwoO_Three), Boron oxide (B
_TwoO_Three), Chromium oxide (Cr_TwoO_Three), Lead oxide (PbO), titanium oxide
 (TiO_Two), Silicon oxide (SiO_Two), Tin oxide (SnO_Two), Oxidation
(Ta_TwoO_Five), Germanium oxide (GeO_Two), Oxidation burr
(BaO), strontium oxide (SrO), yttrium oxide
Umm (Y_TwoO _Three), Praseodymium oxide (Pr_TwoO_Three), Oxidized edge
At least two of the following (CoO) and manganese oxide (MnO)
Electrodes containing two oxides
Zinc oxide varistor with poles. 2. MnO, CoO, Fe ₂ O ₃ , NiO, MgO, Al ₂ O ₃ , BeO
On at least one surface of the zinc oxide-based ceramics containing oxides _{of, Bi 2 O 3, Sb 2} O 3, B 2 O 3, Cr 2 O 3, PbO, Ti
O ₂ , SiO ₂ , SnO ₂ , Ta ₂ O ₅ , GeO ₂ , BaO, SrO, Y ₂ O ₃ , Pr
_An electrode containing at least two oxides of ₂ O ₃ , CoO, and MnO is formed, and one ohmic electrode is formed on another portion of the surface of the zinc oxide based porcelain. A zinc oxide varistor formed. 3. MnO, CoO, Fe ₂ O ₃ , NiO, MgO, Al ₂ O ₃ , BeO
And zinc oxide-based ceramics containing at least one oxide _{of, Bi 2 O 3, Sb 2} O 3, B 2 O 3, Cr 2 O 3, PbO, TiO 2, Si
O ₂ , SnO ₂ , Ta ₂ O ₅ , GeO ₂ , BaO, SrO, Y ₂ O ₃ , Pr ₂ O ₃ , Co
A zinc oxide varistor comprising a laminate in which electrodes containing at least two oxides of O and MnO and an electrode containing an oxide are alternately laminated. 4. An electrode-added oxide comprising Bi ₂ O ₃ , Sb ₂ O ₃ , B ₂ O ₃ ,
Cr ₂ O ₃ , PbO, TiO ₂ , SiO ₂ , SnO ₂ , Ta ₂ O ₅ , GeO ₂ , BaO, Sr
_{O, Y 2 O 3, Pr} 2 O 3, CoO, electrode containing the composite powder of the mixture 350 ° C. to 700 oxide obtained by applying heat treatment to the range of ° C. consisting of at least two oxides of MnO The zinc oxide varistor according to claim 1, 2 or 3, comprising an additional oxide. (5) ZnO contains MnO, CoO, Fe_TwoO_Three, NiO, MgO, Al_TwoO
_ThreeAdd and mix at least one oxide of BeO and BeO
Obtaining a zinc oxide-based porcelain to be sintered,_TwoO _Three, Sb_Two
O_Three, B_TwoO3, Cr_TwoO_Three, PbO, TiO_Two, SiO_Two, SnO_Two, Ta_TwoO_Five, GeO
_Two, BaO, SrO, Y_TwoO _Three, Pr_TwoO_Three, CoO, MnO
To form a mixture of two oxides
Oxide added to synthetic electrode by heat treatment in the range of 0 ° C and pulverization
And a metal mainly composed of silver or a silver alloy
Electrode additive oxidation containing powder and the synthetic electrode additive oxide
Mixing the material and resin / solvent to obtain the electrode material;
The above electrode material is applied in two places on the zinc oxide based porcelain
And then performing a heat treatment to form an electrode.
A method for manufacturing a zinc oxide varistor. 6. A method for producing ZnO by adding MnO, CoO, Fe_TwoO_Three, NiO, MgO, Al_TwoO
_ThreeAdd and mix at least one oxide of BeO and BeO
Obtaining a zinc oxide-based porcelain to be sintered,_TwoO _Three, Sb_Two
O_Three, B_TwoO_Three, Cr_TwoO_Three, PbO, TiO_Two, SiO_Two, SnO_Two, Ta_TwoO_Five, GeO
_Two, BaO, SrO, Y_TwoO _Three, Pr_TwoO_Three, CoO, MnO
To form a mixture of two oxides
Oxide added to synthetic electrode by heat treatment in the range of 0 ° C and pulverization
And a metal mainly composed of silver or a silver alloy
Electrode additive oxidation containing powder and the synthetic electrode additive oxide
Mixing the material and resin / solvent to obtain an electrode material; and
Apply the electrode material to one place on zinc oxide based porcelain
Forming a single electrode by performing a heat treatment;
A single ohmic electrode on a zinc oxide porcelain
Manufacture of a zinc oxide varistor comprising a step of forming a pole
Construction method. 7. MnO, CoO, Fe_TwoO_Three, NiO, MgO, Al_TwoO_Three, BeO
Oxide system containing at least one oxide of
The process of obtaining porcelain and Bi_TwoO_Three, Sb_TwoO_Three, B_TwoO_Three, Cr_TwoO _Three, PbO,
TiO_Two, SiO_Two, SnO_Two, Ta_TwoO_Five, GeO_Two, BaO, SrO, Y_TwoO_Three, Pr_Two
O_ThreeConsisting of at least two oxides of CoO, MnO
A mixture is prepared and subjected to a heat treatment in the range of 350 ° C to 700 ° C.
Grinding and pulverizing to produce a synthetic electrode additive oxide;
Or a metal powder mainly composed of silver alloy and the above-mentioned synthetic electrode
Mix electrode-added oxide containing oxide and resin / solvent
Obtaining an electrode material, the zinc oxide-based porcelain,
Forming a laminate by alternately laminating electrode materials;
Zinc oxide comprising a step of subjecting the laminate to a heat treatment
Varistor manufacturing method.