EP0594120A2 - Une méthode de fabrication d'une varistance type ZnO - Google Patents

Une méthode de fabrication d'une varistance type ZnO Download PDF

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Publication number
EP0594120A2
EP0594120A2 EP93116867A EP93116867A EP0594120A2 EP 0594120 A2 EP0594120 A2 EP 0594120A2 EP 93116867 A EP93116867 A EP 93116867A EP 93116867 A EP93116867 A EP 93116867A EP 0594120 A2 EP0594120 A2 EP 0594120A2
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EP
European Patent Office
Prior art keywords
zno
powders
varistor
producing
based varistor
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EP93116867A
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German (de)
English (en)
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EP0594120A3 (fr
Inventor
Atsushi Iga
Masahiro Ito
Hideyuki Okinaka
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Panasonic Holdings Corp
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Matsushita Electric Industrial Co Ltd
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Publication of EP0594120A2 publication Critical patent/EP0594120A2/fr
Publication of EP0594120A3 publication Critical patent/EP0594120A3/fr
Withdrawn legal-status Critical Current

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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
    • 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

  • the present invention relates to a method for producing a ZnO-based varistor used for absorbing a surge caused in an electrical circuit, and more particularly to a method for producing a low-voltage ZnO-based varistor widely used for protecting a semi-conductor device in an electronic circuit from various surges.
  • ZnO-based varistors are formed of a sintered body containing ZnO varistor materials (i.e., zinc oxide (ZnO), basic additives such as bismuth oxide (Bi2O3), manganese oxide (MnO2) and cobalt oxide (CoO), and various oxides to be added for the purpose of improving the performance of the varistors).
  • ZnO varistor materials i.e., zinc oxide (ZnO), basic additives such as bismuth oxide (Bi2O3), manganese oxide (MnO2) and cobalt oxide (CoO), and various oxides to be added for the purpose of improving the performance of the varistors.
  • the clamping voltage of each ZnO-based varistor is known to increase nearly in proportion to the number of grain boundaries present between electrodes. That is to say, the clamping voltage of the ZnO-based varistor increases by 3 to 4 V per one grain boundary.
  • a grain-growth-enhancing additive such as titanium oxide (TiO2) has been added to enhance the growth of ZnO grains.
  • the method for producing a ZnO-based varistor of the present invention includes the steps of: heat-treating a mixture of TiO2 powders and Bi2O3 powders to prepare composite powders; and adding the composite powders to ZnO varistor materials.
  • the above-mentioned method further includes the step of adding an aluminum component to the ZnO varistor materials.
  • the aluminum component is added to the ZnO varistor materials so that the weight ratio of Al2O3 powders to the ZnO powders is in the range of 0.00062 : 100.0 to 0.372 : 100.0.
  • the aluminum component is a solution of an aluminum salt.
  • the aluminum salt is aluminum nitrate.
  • the aluminum salt is aluminum acetate.
  • the above-mentioned method further includes the step of adding an antimony component to the ZnO varistor materials.
  • the antimony component is added to the ZnO varistor materials so that the weight ratio of Sb2O3 powders to the ZnO powders is in the range of 0.018 : 100.0 to 0.72 : 100.0.
  • the above-mentioned method further includes the step of adding a tin component to the ZnO varistor materials.
  • the tin component is added to the ZnO varistor materials so that the weight ratio of SnO2 powders to the ZnO powders is in the range of 0.005 : 100.0 to 0.37 : 100.0.
  • the above-mentioned method further includes the step of adding a chrome component to the ZnO varistor materials.
  • the chrome component is added to the ZnO varistor materials so that the weight ratio of Cr2O3 powders to the ZnO powders is in the range of 0.005 : 100.0 to 0.18 : 100.0.
  • the present invention has been achieved as a result of the earnest study of a mechanism of grain-growth-enhancing by using TiO2. More specifically, the following was found: When TiO2 is reacted with ZnO, the growth of ZnO grains cannot be enhanced. On the other hand, when TiO2 is reacted with Bi2O3, the reaction product can enhance the growth of ZnO grains. Therefore, in the case where TiO2 is merely added as in the conventional method, in some parts of the sintered body, TiO2 is reacted with ZnO and in other parts thereof, TiO2 is reacted with Bi2O3.
  • the growth of ZnO grains are not enhanced, and in other parts of the sintered body, the growth of ZnO grains are enhanced.
  • a mixture of TiO2 and Bi2O3 is previously heat-treated to prepare composite powders.
  • the composite powders can uniformly enhance the growth of ZnO grains.
  • an antimony component, a tin component, or a chrome component together with an antimony component suppresses the abnormal growth of ZnO grains.
  • the addition of either of these components makes the ZnO grains twin crystal, thereby suppressing the abnormal growth of ZnO grains.
  • the ZnO grains having a large average grain size and a small distribution of grain sizes can be obtained.
  • These phenomenons were found by the inventors of the present invention as a result of their earnest study of a method for adding a bismuth component and a titanium component to ZnO varistor materials.
  • an aluminum component dissolves in the ZnO grains in a solid state to function as a donor, thereby decreasing electrical resistance.
  • the invention described herein makes possible the advantage of providing a method for producing a low-voltage ZnO-based varistor with high yield, which is excellent in electrical characteristics and reliability at a low voltage.
  • Figure 1 is a schematic view showing a ZnO-based varistor produced in the examples according to the present invention.
  • TiO2 fine powders and Bi2O3 powders were mixed in a weight ratio of 11.4 : 88.6.
  • the mixture thus obtained was heat-treated at 600°C for 5 hours. Then, the mixture was ground to obtain composite powders.
  • the composite powders thus obtained will be referred to as TiO2/Bi2O3 composite powders.
  • ZnO powders, TiO2/Bi2O3 composite powders, CoO powders and MnO2 powders were mixed in a weight ratio of 100.0 : 2.93 : 0.804 : 0.555 by a wet method and ground.
  • the resulting powders were dried and formed by pressure molding.
  • the molding thus obtained was provisionally sintered at 600°C and ground.
  • the ground molding was formed into a disk shape.
  • the disk-shaped molding was heated in the atmosphere at 100°C/hour and kept at 1250°C for 2 hours. Then, the molding was cooled at 100°C/hour to obtain a sintered body.
  • the sintered body had a thickness of 1.2 mm and a diameter of 14 mm.
  • the ZnO-based varistor was measured for V 1mA/mm and non-linear resistance index 0.1 ⁇ 1mA .
  • V 1mA/mm refers to a voltage with respect to 1 mm thickness of the ZnO-based varistor between electrodes, in a case where an electric current of 1 mA flows through the lead wire 13 ;
  • the non-linear resistance index 0.1 ⁇ 1mA refers to a value obtained by using V 1mA and V 0.1mA .
  • the ZnO-based varistor was evaluated for reliability with respect to a DC load.
  • the ZnO-based varistor was added with a DC load of 0.2 watts at 80°C for 500 hours.
  • the change rate ⁇ V 1mA /V 1mA (change rate due to a DC load) of a clamping voltage V 1mA of the ZnO-based varistor was measured.
  • the ZnO-based varistor was evaluated for reliability with respect to a surge.
  • the ZnO-based varistor was twice applied with a pulse of 0.5 kA for 8 x 20 ⁇ sec to obtain the change rate ⁇ V 1mA /V 1mA (change rate due to a surge).
  • Table 1 The composition of the specimen of the present example is shown in Table 1, and the evaluation results of the electrical characteristics thereof are shown in Table 2. The numerals representing the evaluation results are the maximum and the minimum values of in each lot.
  • the ZnO-based varistor produced by the method of the present example has excellent reliability. That is to say, in the ZnO-based varistor of the present invention, the clamping voltage V 1mA was low and the absolute value of the change rate ⁇ V 1mA /V 1mA of the clamping voltage V 1mA with respect to the application of a DC load or a surge for a long period of time was not more than 5%. In addition, as shown in Table 2, the variation of the electrical characteristics between the ZnO-based varistors obtained from one lot was small.
  • the yield of the ZnO-based varistors were remarkably improved.
  • a ZnO-based varistor was produced by a conventional method, using a sintered body having the same composition as that of Example 1.
  • ZnO powders, Bi2O3 powders, TiO2 fine powders, CoO powders, and MnO2 powders were mixed in a weight ratio of 100.0 : 2.60 : 0.33 : 0.804 : 0.555 by a wet method and ground.
  • the powders thus obtained were dried and formed by pressure molding.
  • the molding thus obtained was provisionally sintered at 600°C and ground.
  • the ground molding was formed into a disk shape.
  • the disk-shaped molding was heated in the atmosphere at 100°C/hour and kept at 1250°C for 2 hours. Then, the molding was cooled at 100°C/hour to obtain a sintered body.
  • the sintered body had a thickness of 1.2 mm and a diameter of 14 mm.
  • Example 1 a ZnO-based varistor was produced. Also, in the same way as in Example 1, the ZnO-based varistor thus obtained was evaluated for electrical characteristics. Table 3 shows the composition of the specimen of this comparative example, and Table 4 shows the evaluation results of the electrical characteristics thereof.
  • the clamping voltage V 1mA after the application of a DC load of 0.2 watts was remarkably decreased, and the absolute value of the change rate ⁇ V 1mA /V 1mA of the clamping voltage V 1mA with respect to the application of a DC load was not less than 25%.
  • the absolute value of the change rate ⁇ V 1mA /V 1mA of the application of a surge was more than 40%.
  • the reliability of the ZnO-based varistor produced by the conventional method was remarkably low.
  • the variation of the electrical characteristics between the ZnO-based varistors obtained from one lot was large.
  • the variation of the electrical characteristics between the ZnO-based varistors obtained from different lots was larger than that from one lot (not shown in Table 4).
  • the ZnO-based varistors had V 1mA/mm and a non-linear resistance index 0.1 ⁇ 1mA lower than those shown in Table 4.
  • the ZnO-based varistor produced by the method of the present invention is more excellent than the ZnO-based varistor produced by the conventional method in the initial electrical characteristics, the reliability, and the variation of the electrical characteristics between the ZnO-based varistors obtained from one lot and between the ZnO-based varistors obtained from different lots.
  • TiO2 fine powders and Bi2O3 powders were mixed in a weight ratio of 20.5 : 79.5.
  • the mixture thus obtained was heat-treated at 800°C for 5 hours.
  • the mixture was ground to obtain TiO2/Bi2O3 composite powders.
  • the composite powders contained Bi4Ti3O12 as a main component thereof.
  • ZnO powders, TiO2/Bi2O3 composite powders, CoO powders and MnO2 powders were mixed in a weight ratio of 100.0 : 3.15 : 0.922 : 0.534 by a wet method and ground.
  • the resulting powders were dried and formed by pressure molding.
  • the molding thus obtained was provisionally sintered at 600°C and ground.
  • the ground molding was formed into a disk shape.
  • the disk-shaped molding was heated in the atmosphere at 100°C/hour and kept at 1250°C for 2 hours. Then, the molding was cooled at 100°C/hour to obtain a sintered body.
  • the sintered body had a thickness of 1.2 mm and a diameter of 14 mm.
  • Example 1 a ZnO-based varistor was produced in the same way as in Example 1. Moreover, in the same way as in Example 1, the ZnO-based varistor thus obtained was evaluated for electrical characteristics.
  • the composition of the specimen of the present example is shown in Table 5, and the evaluation results of the electrical characteristics thereof are shown in Table 6.
  • the ZnO-based varistor produced by the method of the present example has excellent reliability. That is to say, in the ZnO-based varistor of the present invention, the clamping voltage V 1mA was low and the absolute value of the change rate V 1mA /V 1mA of the clamping voltage V 1mA with respect to the application of a DC load or a surge for a long period of time was not more than 5%. In addition, as shown in Table 6, the variation of the electrical characteristics between the ZnO-based varistors obtained from one lot was small.
  • the yield of the ZnO-based varistors were remarkably improved.
  • TiO2 fine powders and Bi2O3 powders were mixed in a weight ratio of 11.4 : 88.6.
  • the mixture thus obtained was heat-treated at 600°C for 5 hours. Then, the mixture was ground to obtain TiO2/Bi2O3 composite powders.
  • the resulting powders were dried and formed by pressure molding.
  • the molding thus obtained was provisionally sintered at 600°C.
  • An aqueous solution of aluminum nitrate was added to the molding so that the weight ratio of the ZnO powders to Al2O3 was 100.0 : 0.007 and ground. Then, the ground molding was formed into a disk shape.
  • the disk-shaped molding was heated in the atmosphere at 100°C/hour and kept at 1200°C for 2 hours. Then, the molding was cooled at 100°C/hour to obtain a sintered body.
  • the sintered body had a thickness of 1.2 mm and a diameter of 14 mm.
  • a ZnO-based varistor was produced in the same way as in Example 1. Also, in the same way as in Example 1, the ZnO-based varistor was evaluated for electrical characteristics.
  • the composition of the specimen of the present example is shown in Table 7, and the evaluation results of the electrical characteristics thereof are shown in Table 8.
  • the ZnO-based varistor produced by the method of the present example has excellent reliability. That is to say, in the ZnO-based varistor of the present example, the non-linear resistance index 0.1 ⁇ 1mA was large in the case where the added amount of the TiO2/Bi2O3 composite powders was not less than 0.2 in a weight ratio (Specimen Nos. 012 - 018), and the absolute value of the change rate ⁇ V 1mA /V 1mA of the clamping voltage V 1mA with respect to the application of a DC load or a surge for a long period of time was not more than 5%.
  • the added amount of the TiO2/Bi2O3 composite powders was not less than 20 in a weight ratio (Specimen No. 019), if a plurality of moldings were sintered under the condition that the moldings were layered, the sintered bodies stuck to each other, decreasing mass production. Thus, this added amount was not suitable for mass production.
  • TiO2 fine powders and Bi2O3 powders were mixed so that the weight ratio of the Bi2O3 powders to the TiO2 fine powders was in the range of 1.5 to 59.
  • the mixture thus obtained was heat-treated at 500°C for 5 hours. Then, the mixture was ground to obtain TiO2/Bi2O3 composite powders.
  • ZnO powders, CoO powders, MnO2 powders, Sb2O3 powders, and TiO2/Bi2O3 composite powders were mixed in a weight ratio of 100.0 : 0.555 : 0.291 : 3.0 by a wet method and ground.
  • the resulting powders were dried and formed by pressure molding.
  • the molding thus obtained was provisionally sintered at 600°C.
  • An aqueous solution of aluminum nitrate was added to the molding so that the weight ratio of ZnO to Al2O3 was 100.0 : 0.001 and ground.
  • the ground molding was formed into a disk shape.
  • the disk-shaped molding was heated in the atmosphere at 100°C/hour and kept at 1200°C for 2 hours.
  • the molding was cooled at 100°C/hour to obtain a sintered body.
  • the sintered body had a thickness of 1.2 mm and a diameter of 14 mm.
  • the sintered body thus obtained was observed by a scanning electron microscope (SEM), revealing that the sintered body had a characteristic fine structure having twin crystal grains of ZnO.
  • a ZnO-based varistor was produced in the same way as in Example 1. Also, in the same way as in Example 1, the ZnO-based varistor was evaluated for electrical characteristics. In particular, in order to inspect the reliability of the ZnO-based varistor with respect to a surge in detail, the change rate ⁇ V 0.01mA /V 0.01mA of the clamping voltage V 0.01mA of the ZnO-based varistor was measured, since the change of the reliability at 0.01 mA with respect to a surge was remarkably exhibited.
  • the ZnO-based varistor was applied with a pulse of 1.0 kA for 8 x 20 ⁇ sec to obtain the change rate ⁇ V 0.01mA /V 0.01mA of the clamping voltage V 0.01mA thereof.
  • the composition of the specimen of the present example is shown in Table 9, and the evaluation results of the electrical characteristics thereof are shown in Table 10.
  • TiO2 fine powders and Bi2O3 powders were mixed in a weight ratio of 25 : 75.
  • the mixture thus obtained was heat-treated at 650°C for 5 hours.
  • the mixture was ground to obtain TiO2/Bi2O3 composite powders.
  • the resulting powders were dried, and an aqueous solution of aluminum acetate was added to the dried powders so that the weight ratio of the ZnO powders to Al2O3 was 100.0 : 0.001.
  • the resulting powders were provisionally sintered at 600°C.
  • the molding was ground and mixed.
  • the resulting mixture was formed into a disk shape.
  • the disk-shaped molding was heated in the atmosphere at 100°C/hour and kept at 1200°C for 2 hours. Then, the molding was cooled at 100°C/hour to obtain a sintered body.
  • the sintered body had a thickness of 1.2 mm and a diameter of 14 mm.
  • the sintered body thus obtained was observed by a scanning electron microscope (SEM), revealing that the sintered body had a characteristic fine structure having twin crystal grains of ZnO.
  • a ZnO-based varistor was produced in the same way as in Example 1. Also, in the same way as in Example 1, the ZnO-based varistor was evaluated for electrical characteristics. In particular, in order to inspect the reliability of the ZnO-based varistor with respect to a surge in detail, the change rate ⁇ V 0.01mA /V 0.01mA of the clamping voltage V 0.01mA of the ZnO-based varistor was measured, since the change of the reliability at 0.01 mA with respect to a surge was remarkably exhibited.
  • the ZnO-based varistor was applied with a pulse of 1.0 kA for 8 x 20 ⁇ sec to obtain the change rate ⁇ V 0.01mA /V 0.01mA of the clamping voltage V 0.01mA thereof.
  • the composition of the specimen of the present example is shown in Table 11, and the evaluation results of the electrical characteristics thereof are shown in Table 12.
  • the resulting powders were dried, and an aqueous solution of aluminum acetate was added to the dried powders so that the weight ratio of the ZnO powders to Al2O3 was 100.0 : 0.001.
  • the resulting powders were provisionally sintered at 600°C. Then, the molding was ground and mixed. The resulting mixture was formed into a disk shape. The disk-shaped molding was heated in the atmosphere at 100°C/hour and kept at 1200°C for 2 hours. Then, the molding was cooled at 100°C/hour to obtain a sintered body.
  • the sintered body had a thickness of 1.2 mm and a diameter of 14 mm.
  • the sintered body thus obtained was observed by a scanning electron microscope (SEM), revealing that the sintered body had a characteristic fine structure having twin crystal grains of ZnO.
  • a ZnO-based varistor was produced in the same way as in Example 1. Also, in the same way as in Example 1, the ZnO-based varistor was evaluated for electrical characteristics. In particular, in order to inspect the reliability of the ZnO-based varistor with respect to a surge in detail, the change rate ⁇ V 0.01mA /V 0.01mA of the clamping voltage V 0.01mA of the ZnO-based varistor was measured, since the change of the reliability at 0.01 mA with respect to a surge was remarkably exhibited.
  • the ZnO-based varistor was applied with a pulse of 1.0 kA for 8 x 20 ⁇ sec to obtain the change rated ⁇ V 0.01mA /V 0.01mA of the clamping voltage V 0.01mA thereof.
  • the composition of the specimen of the present example is shown in Table 13, and the evaluation results of the electrical characteristics thereof are shown in Table 14.
  • composite powders obtained by previously heat-treating the mixture of TiO2 powders and Bi2O3 powders can uniformly enhance the growth of ZnO grains.
  • an antimony component, a tin component, or a chrome component together with an antimony component suppresses the abnormal growth of ZnO grains.
  • a ZnO grain having a large average grain size and a small distribution in grain size can be obtained. Namely, a ZnO-based varistor excellent in electrical characteristics and reliability can be produced with a high yield.

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  • Microelectronics & Electronic Packaging (AREA)
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EP93116867A 1992-10-20 1993-10-19 Une méthode de fabrication d'une varistance type ZnO. Withdrawn EP0594120A3 (fr)

Applications Claiming Priority (4)

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JP28146992 1992-10-20
JP281469/92 1992-10-20
JP301965/92 1992-11-12
JP30196592 1992-11-12

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EP0594120A2 true EP0594120A2 (fr) 1994-04-27
EP0594120A3 EP0594120A3 (fr) 1995-07-26

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EP93116867A Withdrawn EP0594120A3 (fr) 1992-10-20 1993-10-19 Une méthode de fabrication d'une varistance type ZnO.

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0699641A1 (fr) * 1994-08-29 1996-03-06 Matsushita Electric Industrial Co., Ltd. Procédé de préparation d'un corps compact fritté à base d'oxide de zinc
EP0762438A2 (fr) * 1995-09-07 1997-03-12 Mitsubishi Denki Kabushiki Kaisha Elément de résistance électrique à caractéristiques de tension nonlinéaire et méthode de fabrication

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1988002921A2 (fr) * 1986-10-16 1988-04-21 Raychem Corporation Varistors a oxyde metallique, compositions pulverulentes de precurseurs et procede de preparation
JPH01289218A (ja) * 1988-05-17 1989-11-21 Matsushita Electric Ind Co Ltd バリスタの製造方法
EP0357113A2 (fr) * 1988-08-03 1990-03-07 Philips Patentverwaltung GmbH Procédé de production d'une résistance non linéaire dépendant de la tension
GB2242065A (en) * 1990-03-16 1991-09-18 Ecco Ltd Varistor composition

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1988002921A2 (fr) * 1986-10-16 1988-04-21 Raychem Corporation Varistors a oxyde metallique, compositions pulverulentes de precurseurs et procede de preparation
JPH01289218A (ja) * 1988-05-17 1989-11-21 Matsushita Electric Ind Co Ltd バリスタの製造方法
EP0357113A2 (fr) * 1988-08-03 1990-03-07 Philips Patentverwaltung GmbH Procédé de production d'une résistance non linéaire dépendant de la tension
GB2242065A (en) * 1990-03-16 1991-09-18 Ecco Ltd Varistor composition

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 014 no. 070 (E-0886) ,8 February 1990 & JP-A-01 289218 (MATSUSHITA ELECTRIC IND CO LTD) 21 November 1989, *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0699641A1 (fr) * 1994-08-29 1996-03-06 Matsushita Electric Industrial Co., Ltd. Procédé de préparation d'un corps compact fritté à base d'oxide de zinc
US5569414A (en) * 1994-08-29 1996-10-29 Matsushita Electric Industrial Co., Ltd. Method of manufacturing zinc oxide sintered compact body
US5811033A (en) * 1994-08-29 1998-09-22 Matsushita Electric Industrial Co., Ltd. Method of manufacturing zinc oxide sintered compact body
EP0762438A2 (fr) * 1995-09-07 1997-03-12 Mitsubishi Denki Kabushiki Kaisha Elément de résistance électrique à caractéristiques de tension nonlinéaire et méthode de fabrication
EP0762438A3 (fr) * 1995-09-07 1997-12-10 Mitsubishi Denki Kabushiki Kaisha Elément de résistance électrique à caractéristiques de tension nonlinéaire et méthode de fabrication
US5807510A (en) * 1995-09-07 1998-09-15 Mitsubishi Denki Kabushiki Kaisha Electric resistance element exhibiting voltage nonlinearity characteristic and method of manufacturing the same

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KR940010133A (ko) 1994-05-24
EP0594120A3 (fr) 1995-07-26

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