US3632529A - Strontium-modified zinc oxide voltage variable resistor - Google Patents

Strontium-modified zinc oxide voltage variable resistor Download PDF

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Publication number
US3632529A
US3632529A US866819A US3632529DA US3632529A US 3632529 A US3632529 A US 3632529A US 866819 A US866819 A US 866819A US 3632529D A US3632529D A US 3632529DA US 3632529 A US3632529 A US 3632529A
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United States
Prior art keywords
oxide
mole percent
strontium
value
voltage variable
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Expired - Lifetime
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US866819A
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English (en)
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Michio Matsuoka
Takeshi Masuyama
Yoshio Iida
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Panasonic Holdings Corp
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Matsushita Electric Industrial Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01C—RESISTORS
    • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
    • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
    • H01C7/105—Varistor cores
    • H01C7/108—Metal oxide
    • H01C7/112—ZnO type

Definitions

  • a voltage variable resistor ceramic composition consisting essentially of zinc oxide and, as an additive, strontium oxide.
  • the strontium-modified zinc oxide voltage variable resistor has improved voltage nonlinear properties due to the further additon of bismuth oxide, lead oxide, calcium oxide and cobalt oxide.
  • This invention relates to compositions of voltage variable resistor ceramics having non-ohmic resistance, and more particularly to compositions of varistors comprising zinc oxide having non-ohmic resistance due to the bulk thereof.
  • n a numerical value greate; than 1.
  • V and V are the voltages at given currents I and Iz, respectively.
  • the desired value of C depends upon the kind of application to which the resistor is to be put. It is ordinarily desirable that the Value of n be as large as possible since this exponent determines the extent to which the resistors depart from ohmic characteristics.
  • varistors comprising germanium or silicon p-n junction diodes
  • it is diflicult to control the C-value over a wide range because the voltage variable property of these Varistors is not attributed to the bulk, but to the p-n junction.
  • silicon ca'bide varistors have voltage variable properties due to the contacts among the individual grains of silicon carbide bonded together by a ceramic binding material, and the C-value is controlled by changing a dimension in a direction in which the current flows through the varistors.
  • Silicon carbide varistors however, have a relatively low n-value and are prepared hy firing in non-oxidizing atmosphere, especially for the purpose of obtaining a lower C-value.
  • An object of the present invention is to provide a composition of a voltage variable resistor having non-ohmic properties due to the bulk thereof and having a controllable C-value.
  • Another object of the present invention is to provide a composition of a voltage variable resistor characterized by a high n-value.
  • reference character 10 designates, as a whole, a voltage variable resistor compn'sing, as its active element, a sintered body having a pair of electrodes 2 and 3 applied to opposite surfaces thereof.
  • Said sintered body 1 is prepared in a manner hereinafter set forth and is in any form such as circular, square or rectangular plate form.
  • Wire leads 5 and ⁇ 6 are attached conductively to the electrodes 2 and 3, respectively, by a connection means 4 such as solder or the like.
  • a voltage variable resistor according to the invention comprises a sintered body of a composition consisting essentially of 90.0 to 99.95 mole percent of zinc oxide and 0.05 to 10.0 mole percent of strontium oxide.
  • Such a voltage variable resistor has non-ohmic resistance due to the bulk itself. Therefore, its C-value can be changed without impairing the n-value by changing the distance between said opposite surfaces. The shorter distance results in the lower C-value.
  • n-value can be obtained when said sintered body consisting essentially of 97.0 -to 99.9 mole percent of zinc oxide and 0.1 to 3.0 mole percent of strontium oxide in accordance with the invention.
  • the C-value can be lowered without changing the dimension or lowering n-value when said sintered body is of a composition consisting essentially of 82.0 to 99.9 mole percent of zinc oxide, 0.05 to 10.0 mole percent of strontium oxide and 0.05 to 8.0 mole percent of bismuth oxide.
  • a combination of a low C-value and a high n-value can be obtained when said sintered body consists essentially of 94.0 to 99.8 mole percent of zinc oxide, 0.1 to 3.0 mole percent of strontium oxide and 0.1 to 3.0 mole percent of bismuth oxide.
  • the stability for ambient temperature and the electric load life test can be improved when said sintered body consists essentially of 82.0 to 99.9 mole percent of zinc oxide, 0.05 to 10.0 mole percent of strontium oxide and 0.05 to 8.0 mole percent of calcium oxide.
  • said sintered body consists essentially of 94.0 to 99.8 mole percent of zinc oxide, 0.1 to 3.0 mole percent of strontium oxide and 0.1 to 3.0 mole percent of calcium oxide.
  • the n-value is elevated when said sintered body consists essentially of 82.0 to 99.9 mole percent of zinc oxide, 0.05 to 10.0 mole percent of strontium oxide and 0.05 to 8.0 mole percent of one oxide selected from the group consisting of lead oxide and cobalt oxide.
  • n-value is further elevated when said sintered body is of a composition consisting essentially of 94.0 to 99.8 mole percent of zinc oxide, 0.1 to 3.0 mole percent of strontium oxide and 0.1 to 3.0 mole percent of one oxide selected from the group consisting of lead oxide and cobalt oxide.
  • the resistor has the high n-value when said sintered body is of a composition consisting essentially of 74.0 to 99.85 mole percent of zinc oxide, 0.05 to 10.0 mole percent of strontium oxide, 0.05 to 8.0 mole percent of lead oxide and 0.05 to 8.0 mole percent of cobalt oxide.
  • the n-value is extremely elevated when said sintered body is of a composition consisting essentially of 94.0 to 99.8 mole percent of zinc oxide, 0.1 to 3.0 mole percent of strontium oxide, 0.1 to 3.0 mole percent of lead oxide and 0.1 to 3.0 mole percent of cobalt oxide.
  • both the high nvalue and the low C-value can be obtained when said sintered body is of a composition consisting essentially of 74.0 to 99.85 mole percent of zinc oxide, 0.05 to 10.0 mole percent of strontium oxide, 0.05 to 8.0 mole percent of bsmuth oxide and 0.05 to 8.0 mole percent of cobalt oxide.
  • the C-value is lowered and the n-Value is extremely elevated when said sintered body is of a composition consisting essentially of 91.0 to 99.7 mole percent of zinc oxide, 0.1 to 3.0 mole percent of strontium oxide, and 0.1 to 3.0 mole percent of bsmuth oxide and 0.1 to 3.0 mole percent of cobalt oxide.
  • both the high nvalue and the low C-value also can be obtained when said sintered body is of a composition consisting essentially of 74.0 to 99.7 mole percent of zinc oxide, 0.05 to 10.0 mole percent of strontium oxide, 0.05 to 8.0 mole percent of bsmuth oxide and 0.05 to 8.0 mole percent of lead oxide.
  • n-value and the low C-value also can be obtained when said sintered body is of a composition consisting essentially of 91.0 to 99.7 mole percent of zinc oxide, ⁇ 0.1 to 3.0 mole percent of strontium oxide, 0.1 to 3.0 mole percent of bsmuth oxide and 0.1 to 3.0 mole percent of lead oxide.
  • the sintered body 1 can be prepared by a per se well known ceramic technique.
  • the starting materials of the compositions described in the foregoing description are mixed in a wet mill so as to produce homogeneous mixtures.
  • the mixtures are dried and pressed in a mold into desired shapes at a pressure from 100 kg./cm. to 1000 kg./cm.
  • the pressed bodies are sintered in air at a given temperature for 1 to 3 hours, and then furnace-cooled to room temperature (about 15 to about 30 C.).
  • the available sintering temperature is determined in view of electrical resistvity, non-linearity and stability and ranges from 1000 to 1450 C.
  • the pressed bodies are preferably sintered in non-oxidizing atmosphere such as nitrogen and argon when it is desired to reduce the electrical resistivity.
  • the mixtures can be preliminarily calcined at 700 to 1000 C. and pulverized for easy fabrication in the subsequent pressing step.
  • the mixture to be pressed can be admixed with a suitable binder such as water, polyvinyl alcohol, etc.
  • the sintered body be lapped at the opposite surfaces by abrasive powder such as silicon carbide in a particle size of 300 meshes to 1500 meshes.
  • the sintered bodies are provided, at the opposite surfaces thereof, with electrodes in any available and suitable method such as electroplatng method, vacuum evaporatior method, metallizing method by spraying or silver painting method.
  • the voltage variable properties are not practically affected by the kinds of electrodes used, but are affected by the thickness of the sintered bodies. Particularly, the C- value varies in proportion to the thickness of the sintered bodies, while the n-value is almost independent of the thickness. This surely means that the voltage variable property is due to the bulk of the body, but not to the electrode.
  • Lead wires can be attached to the electrodes in a per se conventional manner by using conventional solder having a low melting point. It is convenient to employ a conductive adhesive comprising silver powder and resin in an Organic solvent in order to connect the lead wires to the electrodes.
  • Voltage Variable resistors according to this invention have a high stability to temperature and to the load life test, which is carried out at 70 C. at a rating power for 500 hours.
  • the -value and C-value do not change remarkably after heating cycles and load life test. It is ad- 4 vantageous for achievement of a high stability to humidity that the resultant voltage variable resistors are embedded in a humidity proof resin such as epoxy resin and phenol resin in a per se well known manner.
  • EXAMPLE 1 A mixture of zinc oxide and strontium oxide in a composition of Table 1 is mixed in a wet mill for 3 hours. The mixture is dried and then calcined at 700 C. for 1 hour. The calcined mxture is pulverized by the motor-driven ceramic mortar for 30 minutes and then pressed in a mold into a shape of 17.5 mm. in diameter and 2.5 mm. in thickness at a pressure of 500 kg./cm.
  • the pressed body is sintered in air at 1350 C. for 1 hour, and then furnace-cooled to room temperature (about 15 to about 30 C.).
  • the sintered disc is lapped at the opposite surfaces thereof by silicon carbide in a particle size of 600 meshes.
  • the resulting sintered disc has a size of 14 mm. in diameter and 1.5 mm. in thickness.
  • the silver paint electrodes commercially available are attached to the opposite surfaces of sintered disc by painting. Then lead wires are attached to the silver electrodes by soldering.
  • the electric characteristics of the resultant resistors are shown in Table 1. It will be readily understood that the zinc oxide sintered body incorporated with strontium oxide in an amount of 0.05 to 10.0 mole percent is available for the voltage variable resistor. Particularly, the addition of strontium oxide in an amount of 0.1 to 3.0 mole percent makes the voltage nonlinear property more excellent.
  • EXAMPLE 2 Starting materials composed of 99.5 mole percent of zinc oxide and 0.5 mole percent of strontium oxide are mixed, dried, calcined and pulverized in the same manner as those of Example 1. The pulverized mixture is pressed in a mold into a disc of 17.5 mm. in diameter and 5 mm. in thickness at a pressure of 500 kg./cm.
  • the pressed body is sintered in air at 1350 C. for 1 hour, and then furnace-cooled to room temperature.
  • the sintered disc is ground at the opposite surfaces thereof into the thickness shown in Table 2 by silicon carbide in a particle size of 600 meshes.
  • the ground disc is pro vided with the electrodes and lead wires at the opposite surfaces in a manner similar to that of Example 1.
  • the electric characteristics of the resultant resistors are shown in Table 2; the C-value varies approximately in proportion to the thickness of the sintered disc while the n-value is essentially independent of the thickness. It will be readily realized that the voltage nonlinear property of the resistors are attributed to the sintered body itself.
  • EXAMPLE 3 Zinc oxide incorporated with strontium oxide and bismuth oxide in the composition of Table 3 is fabricated into the voltage varable resistors by the same process as that of Example 1. The resulting properties are shown in Table 3. It can be easily understood that the combination of strontium oxide and bismuth oxide as additive effectively lowers the C-value without appreciably changing the n-value.
  • EXAMPLE 4 Zinc oxide incorporated with strontium oxide and calcium oxide in the composition of Table 4 is fabricated into voltage varable resistors by the same process as that of Example 1. The resulting resistors are tested according to the methods used in the electronic Components parts. The load life test is carried out at 70 C. ambient temperature at 0.5 watt rating power for 500 hours. The heating cycle test is carried out by repeating 5 times the cycle in which said resistors are kept at 85 C. ambient' temperature for 30 minutes, cooled rapidly to C. and then kept at such temperature for 30 minutes. Table 4 shows a difference in the C-value and n-value between resistors before and after the load life test. It can be readily realzed that the combination of strontium oxide and calcum oxide as additive is effective for electrical and environmental stability.
  • EXAMPLE 5 Zinc oxide containing the additions of Table 5 is fabricated into 'voltage varable resistors by the same process as that of Example 1. The n-values of the resulting resistors are shown in Table 5. It will be readily seen that the combnation of strontium oxide with lead oxide and/ or cobalt oxide as additives results in a remarkably excellent voltage-nonlinear property.
  • a voltage varable resistor cera mic composition con sisting essentially of zinc oxide and 0.05 to 10.0 mole percent of strontium oxide.

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Compositions Of Oxide Ceramics (AREA)
  • Thermistors And Varistors (AREA)
  • Inorganic Insulating Materials (AREA)
US866819A 1968-10-22 1969-10-16 Strontium-modified zinc oxide voltage variable resistor Expired - Lifetime US3632529A (en)

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Application Number Priority Date Filing Date Title
JP43077735A JPS495555B1 (en]) 1968-10-22 1968-10-22

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US (1) US3632529A (en])
JP (1) JPS495555B1 (en])
CA (1) CA922888A (en])
DE (1) DE1952840C3 (en])
FR (1) FR2021230A1 (en])
GB (1) GB1285362A (en])
NL (1) NL142262B (en])

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2500291A1 (de) 1974-02-20 1975-08-21 Matsushita Electric Ind Co Ltd Spannungsabhaengiger widerstand

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS52135344U (en]) * 1976-04-08 1977-10-14
CH601135A5 (en]) * 1976-07-01 1978-06-30 Bbc Brown Boveri & Cie
CH596647A5 (en]) * 1976-07-01 1978-03-15 Bbc Brown Boveri & Cie
JPS5360651U (en]) * 1976-10-26 1978-05-23
JPS63169147U (en]) * 1987-04-22 1988-11-02

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2500291A1 (de) 1974-02-20 1975-08-21 Matsushita Electric Ind Co Ltd Spannungsabhaengiger widerstand
DE2500291B2 (de) 1974-02-20 1977-02-10 Matsushita Electric Industrial Co., Ltd., Kadotna, Osaka (Japan) Spannungsabhaengiger widerstand mit einer spannungsabhaengigkeit allein aufgrund der masse seines gesinterten koerpers

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NL142262B (nl) 1974-05-15
DE1952840C3 (de) 1973-10-11
NL6915954A (en]) 1970-04-24
JPS495555B1 (en]) 1974-02-07
FR2021230A1 (en]) 1970-07-17
DE1952840B2 (de) 1973-03-15
DE1952840A1 (de) 1970-07-09
GB1285362A (en) 1972-08-16
CA922888A (en) 1973-03-20

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