Varistor compositions and multilayer varistor

Abstract

A varistor composition free of Sb comprising: (a) ZnO; (b) BBiZnPr glass, or BBiZnLa glass, or a mixture thereof; (c) a cobalt compound, a chromium compound, a nickel compound, a manganese compound, or mixtures thereof; (d) SnO.sub.2; and (e) an aluminum compound, a silver compound, or a mixture thereof. By adjusting the ratio between the components, the varistor composition may be made into a multilayer varistor with inner electrodes having a low concentration of noble metals at a sintering temperature less than 1200 C. The multilayer varistor made from the varistor composition has good maximum surge current, good ESD withstand ability, and low fabrication cost.

Claims

1. A varistor composition free of Sb comprising: zinc oxide; a first additive selected from the group consisting of: boron-bismuth-zinc-praseodymium glass (BBiZnPr glass), boron-bismuth-zinc-lanthanum glass (BBiZnLa glass), and a mixture thereof; a second additive selected from the group consisting of: a cobalt compound, a chromium compound, a nickel compound, a manganese compound, and mixtures thereof; a third additive comprising tin dioxide; and a fourth additive selected from the group consisting of: an aluminum compound, a silver compound, and a mixture thereof; wherein based on the total amount of B, Bi, Zn, and Pr contained in the BBiZnPr glass, the content of B in the BBiZnPr glass ranges from 20 at % to 70 at %, the content of Bi in the BBiZnPr glass ranges from 2 at % to 30 at %, the content of Zn in the BBiZnPr glass ranges from 10 at % to 60 at %, and the content of Pr in the BBiZnPr glass ranges from 5 at % to 30 at %; wherein based on the total amount of B, Bi, Zn, and La contained in the BBiZnLa glass, the content of B in the BBiZnLa glass ranges from 20 at % to 70 at %, the content of Bi in the BBiZnLa glass ranges from 2 at % to 30 at %, the content of Zn in the BBiZnLa glass ranges from 10 at % to 60 at %, and the content of La in the BBiZnLa glass ranges from 5 at % to 30 at %; wherein based on the total weight of the varistor composition, the total content of the first additive ranges from 0.05 wt % to 20 wt %, the individual content of the second additive ranges from 0.1 wt % to 5.0 wt %, the content of the third additive ranges from 0.1 wt % to 1.5 wt %, and the individual content of the fourth additive ranges from 0.001 wt % to 1.0 wt %.

2. The varistor composition free of Sb as claimed in claim 1, wherein the cobalt compound of the second additive is selected from the group consisting of: a cobalt oxide, cobalt hydroxide, a percobaltate, cobalt carbonate, cobalt phosphate, and mixtures thereof; the chromium compound of the second additive is selected from the group consisting of: a chromium oxide, a dichromate salt, a chromium boride compound, a chromium nitride compound, and mixtures thereof; the nickel compound of the second additive is selected from the group consisting of: a nickel oxide, nickel carbonate, nickel nitrate, and mixtures thereof; and the manganese compound of the second additive is selected from the group consisting of: a manganese oxide, manganese carbonate, manganese nitrate, manganese borohydride, and mixtures thereof.

3. The varistor composition free of Sb as claimed in claim 1, wherein the aluminum compound of the fourth additive is selected from the group consisting of: an aluminum oxide, aluminium nitrate, and a mixture thereof.

4. The varistor composition free of Sb as claimed in claim 2, wherein the aluminum compound of the fourth additive is selected from the group consisting of: an aluminum oxide, aluminium nitrate, and a mixture thereof.

5. The varistor composition free of Sb as claimed in claim 1, wherein the second additive is the mixture of the cobalt compound, the chromium compound, the nickel compound, and the manganese compound; and based on the total weight of the varistor composition, the total content of the second additive ranges from 0.4 wt % to 20.0 wt %.

6. The varistor composition free of Sb as claimed in claim 4, wherein the second additive is the mixture of the cobalt compound, the chromium compound, the nickel compound, and the manganese compound; and based on the total weight of the varistor composition, the total content of the second additive ranges from 0.4 wt % to 20.0 wt %.

7. The varistor composition free of Sb as claimed in claim 1, wherein the fourth additive is the mixture of the aluminum compound and the silver compound; and based on the total weight of the varistor composition, the total content of the fourth additive ranges from 0.002 wt % to 2.0 wt %.

8. The varistor composition free of Sb as claimed in claim 6, wherein the fourth additive is the mixture of the aluminum compound and the silver compound; and based on the total weight of the varistor composition, the total content of the fourth additive ranges from 0.002 wt % to 2.0 wt %.

9. The varistor composition free of Sb as claimed in claim 1, wherein the particle size of the first additive ranges from 50 nm to 500 nm.

10. The varistor composition free of Sb as claimed in claim 8, wherein the particle size of the first additive ranges from 50 nm to 500 nm.

11. The varistor composition free of Sb as claimed in claim 1, wherein the total content of the first additive ranges from 1.5 wt % to 5.5 wt % based on the total weight of the varistor composition.

12. The varistor composition free of Sb as claimed in claim 10, wherein the total content of the first additive ranges from 1.5 wt % to 5.5 wt % based on the total weight of the varistor composition.

13. The varistor composition free of Sb as claimed in claim 1, wherein the third additive comprises silicon dioxide or germanium dioxide.

14. The varistor composition free of Sb as claimed in claim 12, wherein the third additive comprises silicon dioxide or germanium dioxide.

15. A multilayer varistor comprising: a sintered body comprising a first end and a second end opposite the first end; multiple inner electrodes arranged in the sintered body at spaced intervals, each two neighboring inner electrodes connected with the first end and the second end respectively; a first external electrode mounted in the first end and contacting corresponding inner electrodes; and a second external electrode mounted in the second end and contacting corresponding inner electrodes; wherein the sintered body is made from the varistor composition free of Sb as claimed in claim 1.

16. The multilayer varistor as claimed in claim 15, wherein the inner electrodes comprises a PtAg alloy having an amount of Pt less than or equal to 30 wt %, or a PdAg alloy having an amount of Pd less than or equal to 30 wt %.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a schematic cross-sectional view of a multilayer varistor in accordance with the present invention.

DETAILED DESCRIPTION

(2) An embodiment of a varistor composition comprised zinc oxide (ZnO), a first additive, a second additive, a third additive, and a fourth additive. The first additive was selected from the group consisting of: BBiZnPr glass, BBiZnLa glass, and a mixture thereof. The second additive was selected from the group consisting of: a cobalt compound, a chromium compound, a nickel compound, a manganese compound, and mixtures thereof. The third additive comprised SnO.sub.2. The fourth additive was selected from the group consisting of: an aluminum compound, a silver compound, and a mixture thereof. Based on the total weight of the varistor composition, the total content of the first additive ranged from 0.05 wt % to 20 wt %, the individual content of the second additive ranged from 0.1 wt % to 5.0 wt %, the content of the third additive ranged from 0.1 wt % to 1.5 wt %, and the individual content of the fourth additive ranged from 0.001 wt % to 1.0 wt %.

(3) An embodiment of a method of fabricating the said BBiZnPr glass was as follows: B.sub.2O.sub.3 powder, Bi.sub.2O.sub.3 powder, ZnO powder, and Pr.sub.6O.sub.11 powder were mixed, ground, and dried to obtain a pretreated powder.

(4) Based on the total amount of B.sub.2O.sub.3 powder, Bi.sub.2O.sub.3 powder, ZnO powder, and Pr.sub.6O.sub.11 powder, the amount of B.sub.2O.sub.3 powder was 10 wt % to 30 wt %, the amount of Bi.sub.2O.sub.3 powder was 10 wt % to 30 wt %, the amount of ZnO powder was 10 wt % to 30 wt %, and the amount of Pr.sub.6O.sub.11 powder was 10 wt % to 30 wt %. Then the pretreated powder was heated to 500 C. to 900 C. and transformed into a melted substance. The melt substance was sprayed under high pressure to form multiple droplets. The droplets were solidified rapidly and the said BBiZnPr glass was obtained. The particle size of the said BBiZnPr glass was 50 nm to 500 nm.

(5) An embodiment of a method of fabricating the said BBiZnLa glass was as follows. The method of fabricating the said BBiZnLa glass was similar to the method of fabricating the said BBiZnPr glass. However, the said BBiZnLa glass was made from B.sub.2O.sub.3 powder, Bi.sub.2O.sub.3 powder, ZnO powder, and La.sub.2O.sub.3 powder. In addition, based on the total amount of B.sub.2O.sub.3 powder, Bi.sub.2O.sub.3 powder, ZnO powder, and La.sub.2O.sub.3 powder, the amount of La.sub.2O.sub.3 powder was 10 wt % to 30 wt %.

(6) With reference to FIG. 1, an embodiment of a multilayer varistor 10 comprised a sintered body 11, multiple inner electrodes 12, 13, a first external electrode 14, and a second external electrode 15. The sintered body 11 comprised a first end and a second end opposite the first end. The inner electrodes 12, 13 are arranged in the sintered body 11 at spaced intervals. Each two neighboring inner electrodes 12, 13 are connected with the first end and the second end respectively. The first external electrode 14 is mounted in the first end and contacts corresponding inner electrodes 12. The second external electrode 15 is mounted in the second end and contacts corresponding inner electrodes 13.

(7) The multilayer varistor was made by a low temperature sintering process. In addition, the multilayer varistor was made from the varistor composition above.

(8) An embodiment of a method of fabricating the multilayer varistor was as follows.

(9) The first additive, the second additive, the third additive, and the fourth additive were blended and an additive blend was obtained. The additive blend was calcined under 750 C. to 950 C. for 2 hours to obtain a calcined powder. The calcined powder was ground to obtain a composite mash. After the composite mash and ZnO powder were blended, a dispersion agent, a binder, a plasticizer, and an organic solvent were added into the composite mash, so as to obtain a ceramic slurry. The ceramic slurry was subjected to a doctor blade process to form green sheets having a thickness of 5 m to 150 m.

(10) Subsequently, a number of the green sheets were stacked in sequence to form a top cover having a thickness of 200 m and a bottom cover having a thickness of 200 m. One of the said inner electrodes was printed on the top cover and the printed top cover was dried. Multiple green sheets having a thickness of 30 m were stacked in sequence on the bottom cover, wherein the green sheets having the thickness of 30 m were printed with the other inner electrodes respectively before stacked on the bottom cover, and the inner electrodes were platinum (Pt), palladium (Pd), gold (Au), silver (Ag), nickel (Ni), or an alloy of any two of these metals. The printed top cover was covered on the uppermost green sheet having the thickness of 30 m; then the printed top cover, the green sheets having the thickness of 30 m, and the bottom cover were bonded by pressing, and thereby forming a laminate.

(11) Subsequently, the laminate was cut into multiple green compacts. The green compacts were baked at 300 C. to 600 C. to burn out the binder. After the binder was burnt out, the green compacts were sintered at 900 C. to 1200 C. to obtain the sintered body. The first external electrode and the second external electrode were burn-attached on two opposite ends of the sintered body respectively and the multilayer varistor was obtained. The first external electrode comprised silver (Ag) or copper (Cu). The second external electrode comprised Ag or Cu. Preferably, the burning out temperature was 400 C. and the sintering temperature was 950 C. to 1050 C.

(12) Hereinafter, one skilled in the arts can easily realize the advantages and effects of the instant disclosure from the following examples. Therefore, it should be understood that the descriptions proposed herein are just preferable examples for the purpose of illustrations only, not intended to limit the scope of the disclosure. Various modifications and variations could be made in order to practice or apply the instant disclosure without departing from the spirit and scope of the disclosure.

Example 1: Preparation of BBiZnPr Glass

(13) B.sub.2O.sub.3 powder, Bi.sub.2O.sub.3 powder, ZnO powder, and Pr.sub.6O.sub.11 powder were mixed, ground, and dried to obtain a pretreated powder. The weight ratio of B.sub.2O.sub.3 powder, Bi.sub.2O.sub.3 powder, ZnO powder, and Pr.sub.6O.sub.11 powder was 20:20:30:30. The pretreated powder was heated to 850 C. and transformed into a melt substance. The melt substance was sprayed under high pressure to form multiple droplets. The droplets were solidified rapidly and the BBiZnPr glass of the present example was obtained. The particle size of the BBiZnPr glass of the present example was 200 nm. The components of the BBiZnPr glass of the present example were shown in Table 1.

(14) TABLE-US-00001 TABLE 1 the components of the BBiZnPr glass of example 1 and the components of the BBiZnLa glass of example 1 Example No. B Bi Zn Pr La Total 1 47.68 at % 7.12 at % 30.58 at % 14.62 at % 0.00 at % 100 at % 2 47.36 at % 7.08 at % 30.38 at % 0.00 at % 15.18 at % 100 at %

Example 2: Preparation of BBiZnLa Glass

(15) B.sub.2O.sub.3 powder, Bi.sub.2O.sub.3 powder, ZnO powder, and La.sub.2O.sub.3 powder were mixed, ground, and dried to obtain a pretreated powder. The weight ratio of B.sub.2O.sub.3 powder, Bi.sub.2O.sub.3 powder, ZnO powder, and La.sub.2O.sub.3 powder was 20:20:30:30. The pretreated powder was heated to 850 C. and transformed into a melt substance. The melt substance was sprayed under high pressure to form multiple droplets. The droplets were solidified rapidly and the BBiZnLa glass of the present example was obtained. The particle size of the BBiZnLa glass of the present example was 200 nm. The components of the BBiZnLa glass of the present example were shown in Table 1.

Examples 3 to 8: Preparation of Multilayer Varistor

(16) In examples 3 to 8, the BBiZnPr glass of example 1, Co.sub.3O.sub.4, Cr.sub.2O.sub.3, Mn.sub.2O, NiO, SnO.sub.2, AgNO.sub.3, Al(NO.sub.3).sub.3, and ZnO according to the weight percentages shown in Table 2 were applied as the raw materials to prepare the multilayer varistors as follows.

(17) The BBiZnPr glass of example 1, Co.sub.3O.sub.4, Cr.sub.2O.sub.3, Mn.sub.2O, NiO, SnO.sub.2, AgNO.sub.3, and Al(NO.sub.3).sub.3 were blended and an additive blend was obtained. After grinding, the additive blend was calcined under 850 C. for 2 hours and a calcined powder was obtained. The calcined powder was ball-ground and a composite mash was obtained. After the composite mash and ZnO powder were blended, a dispersion agent, a binder, a plasticizer, and an organic solvent were added, so as to obtain a ceramic slurry. The ceramic slurry was subjected to a doctor blade process to form green sheets having a thickness of 30 m. The plasticizer was an alcohol plasticizer or an ester plasticizer. In examples 3 to 8, the binder was polyvinyl butyral and the plasticizer was triethylene glycol bis(2-ethylhexanoate). Based on the weight of the ceramic slurry, the amount of the dispersion agent was 1 wt %, the amount of the binder was 10 wt %, and the amount of the plasticizer was 2 wt %.

(18) Subsequently, a number of the green sheets were stacked in sequence to form a top cover having a thickness of 200 m and a bottom cover having a thickness of 200 m. One inner electrode was printed on the top cover and the printed top cover was dried. Multiple green sheets having a thickness of 30 m were stacked in sequence on the bottom cover, wherein the green sheets having the thickness of 30 m were printed with the other inner electrodes respectively before being stacked on the bottom cover. The printed top cover was covered on the uppermost green sheet having the thickness of 30 m; then the printed top cover, the green sheets having the thickness of 30 m, and the bottom cover were bonded by pressing, and thereby forming a laminate. In examples 3 to 8, each of the inner electrodes was an AgPd alloy having an Ag-to-Pd weight ratio of 70:30.

(19) Subsequently, the laminate was cut into multiple green compacts having a length of 1.0 millimeters (mm), a width of 0.55 mm and a height of 0.55 mm. The green compacts were baked at 400 C. for 24 hours to burn out the binder. After the binder was burnt out, the green compacts were sintered at 1000 C. for 2 hours and the sintered body was obtained. A first external electrode and a second external electrode were burn-attached on two opposite ends of the sintered body at 750 C. and the multilayer varistor was obtained. The first and the second external electrodes both comprised Ag.

Examples 9 to 14: Preparation of Multilayer Varistor

(20) In examples 9 to 14, multilayer varistors were prepared in the similar manner as examples 3 to 8 except that the BBiZnLa glass of example 2, Co.sub.3O.sub.4, Cr.sub.2O.sub.3, Mn.sub.2O, NiO, SnO.sub.2, AgNO.sub.3, Al(NO.sub.3).sub.3, and ZnO according to the weight percentages shown in Table 2 were used as the raw materials to prepare the multilayer varistors of examples 9 to 14.

Examples 15 to 19: Preparation of Multilayer Varistor

(21) In examples 15 to 19, the multilayer varistors were prepared in the similar manner as examples 3 to 8 except that the BBiZnPr glass of example 1, the BBiZnLa glass of example 2, Co.sub.3O.sub.4, Cr.sub.2O.sub.3, Mn.sub.2O, NiO, SnO.sub.2, AgNO.sub.3, Al(NO.sub.3).sub.3, and ZnO according to the weight percentages shown in Table 2 were used as the raw materials to prepare the multilayer varistors of examples 15 to 19.

Examples 20 to 26: Preparation of Multilayer Varistor

(22) In examples 20 to 26, the multilayer varistors were prepared in the similar manner as examples 3 to 8 except that the weight percentages of the components in the raw materials to prepare the multilayer varistors of examples 20 to 26 were shown in Table 3.

Examples 27 to 33: Preparation of Multilayer Varistor

(23) In examples 27 to 33, the multilayer varistors were prepared in the similar manner as examples 9 to 14 except that the weight percentages of the components in the raw materials to prepare the multilayer varistors of examples 27 to 33 were shown in Table 3.

Comparative Example: Preparation of Multilayer Varistor

(24) In the comparative example, a multilayer varistor was prepared in the similar manner as examples 3 to 26 except that the raw material of the comparative example did not comprise the BBiZnPr glass of example 1 and the BBiZnLa glass of example 2, and the weight percentages of the components in the raw material of the comparative example were shown in Table 4.

(25) TABLE-US-00002 TABLE 2 components in the raw materials of examples 3 to 19 BBiZnPr BBiZnLa Example No. ZnO glass glass Co.sub.3O.sub.4 Cr.sub.2O.sub.3 3 95.35 wt % 0.05 wt % 0 wt % 1.0 wt % 1.0 wt % 4 93.4 wt % 2.0 wt % 0 wt % 1.0 wt % 1.0 wt % 5 90.4 wt % 5.0 wt % 0 wt % 1.0 wt % 1.0 wt % 6 85.4 wt % 10.0 wt % 0 wt % 1.0 wt % 1.0 wt % 7 80.4 wt % 15.0 wt % 0 wt % 1.0 wt % 1.0 wt % 8 75.4 wt % 20.0 wt % 0 wt % 1.0 wt % 1.0 wt % 9 95.35 wt % 0 wt % 0.05 wt % 1.0 wt % 1.0 wt % 10 93.4 wt % 0 wt % 2.0 wt % 1.0 wt % 1.0 wt % 11 90.4 wt % 0 wt % 5.0 wt % 1.0 wt % 1.0 wt % 12 85.4 wt % 0 wt % 10.0 wt % 1.0 wt % 1.0 wt % 13 80.4 wt % 0 wt % 15.0 wt % 1.0 wt % 1.0 wt % 14 75.4 wt % 0 wt % 20.0 wt % 1.0 wt % 1.0 wt % 15 93.4 wt % 1.0 wt % 1.0 wt % 1.0 wt % 1.0 wt % 16 90.4 wt % 2.5 wt % 2.5 wt % 1.0 wt % 1.0 wt % 17 85.4 wt % 5.0 wt % 5.0 wt % 1.0 wt % 1.0 wt % 18 80.4 wt % 7.5 wt % 7.5 wt % 1.0 wt % 1.0 wt % 19 75.4 wt % 10 wt % 10 wt % 1.0 wt % 1.0 wt % Example No. Mn.sub.2O NiO SnO.sub.2 AgNO.sub.3 Al(NO.sub.3).sub.3 Total 3 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 4 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 5 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 6 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 7 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 8 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 9 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 10 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 11 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 12 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 13 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 14 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 15 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 16 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 17 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 18 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % 19 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt %

(26) TABLE-US-00003 TABLE 3 components in the raw materials of examples 20 to 33 BBiZnPr BBiZnLa Example No. ZnO glass glass Co.sub.3O.sub.4 Cr.sub.2O.sub.3 20 97.498 wt % 2.0 wt % 0 wt % 0.1 wt % 0.1 wt % 21 93.898 wt % 2.0 wt % 0 wt % 1.0 wt % 1.0 wt % 22 77.898 wt % 2.0 wt % 0 wt % 5.0 wt % 5.0 wt % 23 92.998 wt % 2.0 wt % 0 wt % 1.0 wt % 1.0 wt % 24 92.498 wt % 2.0 wt % 0 wt % 1.0 wt % 1.0 wt % 25 92.9 wt % 2.0 wt % 0 wt % 1.0 wt % 1.0 wt % 26 91 wt % 2.0 wt % 0 wt % 1.0 wt % 1.0 wt % 27 97.498 wt % 0 wt % 2.0 wt % 0.1 wt % 0.1 wt % 28 93.898 wt % 0 wt % 2.0 wt % 1.0 wt % 1.0 wt % 29 77.898 wt % 0 wt % 2.0 wt % 5.0 wt % 5.0 wt % 30 92.998 wt % 0 wt % 2.0 wt % 1.0 wt % 1.0 wt % 31 92.498 wt % 0 wt % 2.0 wt % 1.0 wt % 1.0 wt % 32 92.9 wt % 0 wt % 2.0 wt % 1.0 wt % 1.0 wt % 33 91 wt % 0 wt % 2.0 wt % 1.0 wt % 1.0 wt % Example No. Mn.sub.2O NiO SnO.sub.2 AgNO.sub.3 Al(NO.sub.3).sub.3 Total 20 0.1 wt % 0.1 wt % 0.1 wt % 0.001 wt % 0.001 wt % 100 wt % 21 1.0 wt % 1.0 wt % 0.1 wt % 0.001 wt % 0.001 wt % 100 wt % 22 5.0 wt % 5.0 wt % 0.1 wt % 0.001 wt % 0.001 wt % 100 wt % 23 1.0 wt % 1.0 wt % 1.0 wt % 0.001 wt % 0.001 wt % 100 wt % 24 1.0 wt % 1.0 wt % 1.5 wt % 0.001 wt % 0.001 wt % 100 wt % 25 1.0 wt % 1.0 wt % 1.0 wt % 0.05 wt % 0.05 wt % 100 wt % 26 1.0 wt % 1.0 wt % 1.0 wt % 1.0 wt % 1.0 wt % 100 wt % 27 0.1 wt % 0.1 wt % 0.1 wt % 0.001 wt % 0.001 wt % 100 wt % 28 1.0 wt % 1.0 wt % 0.1 wt % 0.001 wt % 0.001 wt % 100 wt % 29 5.0 wt % 5.0 wt % 0.1 wt % 0.001 wt % 0.001 wt % 100 wt % 30 1.0 wt % 1.0 wt % 1.0 wt % 0.001 wt % 0.001 wt % 100 wt % 31 1.0 wt % 1.0 wt % 1.5 wt % 0.001 wt % 0.001 wt % 100 wt % 32 1.0 wt % 1.0 wt % 1.0 wt % 0.05 wt % 0.05 wt % 100 wt % 33 1.0 wt % 1.0 wt % 1.0 wt % 1.0 wt % 1.0 wt % 100 wt %

(27) TABLE-US-00004 TABLE 4 components in the raw materials of comparative example BBiZnPr BBiZnLa ZnO glass glass Co.sub.3O.sub.4 Cr.sub.2O.sub.3 Comparative 95.4 wt % 0 wt % 0 wt % 1.0 wt % 1.0 wt % Example Mn.sub.2O NiO SnO.sub.2 AgNO.sub.3 Al(NO.sub.3).sub.3 Total Comparative 1.0 wt % 1.0 wt % 0.5 wt % 0.05 wt % 0.05 wt % 100 wt % Example

(28) Test: Varistor Characteristics

(29) Breakdown voltage: the breakdown voltage (V.sub.1 mA) of each of the multilayer varistors of examples 3 to 33 and the comparative example was measured under a current of 1 mA.

(30) Non-linear exponent: the non-linear exponent () of each of the multilayer varistors of examples 3 to 33 and the comparative example was calculated from the I-V characteristic curve of each of the multilayer varistors of examples 3 to 33 and the comparative example.

(31) Maximum surge current: The maximum surge current (I.sub.M) of each of the multilayer varistors of examples 3 to 33 and the comparative example was measured when an impulse current of 8/20 s was applied once and the permissible variation in the breakdown voltage change was 10%.

(32) ESD withstand ability: Each of the multilayer varistors of examples 3 to 33 and the comparative example was measured when applied with ESD 10 times based on the contact discharge mode of IEC 61000-4-2. According to the contact discharge mode, the test voltage was 8 kV to 30 kV. The ESD withstand ability of each of the multilayer varistors of examples 3 to 33 and the comparative example was evaluated by the highest test voltage while the variation in the breakdown voltage change of each of the same was within 10%.

(33) The breakdown voltage (V.sub.1 mA), the non-linear exponent (), the maximum surge current (I.sub.M), and the ESD withstand ability of each of the multilayer varistors of examples 3 to 33 and the comparative example were shown in Tables 5 and 6.

(34) TABLE-US-00005 TABLE 5 test results of the multilayer varistors of examples 3 to 33 Breakdown Maximum ESD Example voltage Non-linear surge withstand No. (V.sub.1mA) exponent () current (I.sub.M) ability 3 84.2 V 25.1 10 A 10 kV 4 30.4 V 45.4 20 A 30 kV 5 20.7 V 35.6 20 A 30 kV 6 18.5 V 28.5 20 A 25 kV 7 10.3 V 18.0 20 A 15 kV 8 7.6 V 12.7 15 A 10 kV 9 72.4 V 21.2 10 A 10 kV 10 26.1 V 41.2 20 A 30 kV 11 18.2 V 32.3 20 A 30 kV 12 15.4 V 24.4 20 A 25 kV 13 10.6 V 14.6 15 A 15 kV 14 8.4 V 10.4 15 A 10 kV 15 28.4 V 43.2 20 A 30 kV 16 17.7 V 32.4 20 A 30 kV 17 15.5 V 24.5 20 A 25 kV 18 9.3 V 14.6 20 A 15 kV 19 8.6 V 10.8 15 A 10 kV 20 20.3 V 34.2 20 A 30 kV 21 28.2 V 44.4 20 A 30 kV 22 42.6 V 36.8 20 A 30 kV 23 36.1 V 42.7 20 A 30 kV 24 36.8 V 41.2 20 A 30 kV 25 35.2 V 45.6 20 A 30 kV 26 36.0 V 38.4 20 A 30 kV 27 18.6 V 32.1 20 A 30 kV 28 27.8 V 42.2 20 A 30 kV 29 40.3 V 36.3 20 A 30 kV 30 34.6 V 41.5 20 A 30 kV 31 32.5 V 40.4 20 A 30 kV 32 34.0 V 42.5 20 A 30 kV 33 35.5 V 36.0 20 A 30 kV

(35) TABLE-US-00006 TABLE 6 test results of the multilayer varistor of comparative example Breakdown Non-linear Maximum ESD voltage exponent surge withstand (V.sub.1mA) () current (I.sub.M) ability comparative 2 V 0 0 A 0 kV example

(36) As mentioned above, compared to the raw materials of examples 3 to 33, the raw material of the comparative example did not comprise the BBiZnPr glass of example 1 and the BBiZnLa glass of example 2. As shown in Table 5, each of the multilayer varistors of example 3 to 33 had a breakdown voltage (V.sub.1 mA) more than 6 V, a non-linear exponent () more than 10, a maximum surge current (I.sub.M) more than or equal to 10 A, and an ESD withstand ability more than or equal to 10 kV.

(37) As shown in Table 6, the multilayer varistor of the comparative example had a breakdown voltage (V.sub.1 mA) of 2 V, a non-linear exponent () of 0, and a maximum surge current (I.sub.M) of 0 A; in addition, the multilayer varistor of the comparative example failed to pass the ESD withstand ability test, and therefore, the ESD withstand ability was recorded as 0 kV in Table 6. Accordingly, proof had been made that each of the multilayer varistors of examples 3 to 33 had good varistor characteristics, such as good breakdown voltage, non-linear exponent, maximum surge current, and ESD withstand ability.

(38) To sum up, the said varistor composition was capable of applying to the sintering process having the sintering temperature less than 1200 C. with inner electrodes made of PtAg alloy having the amount of Pt less than or equal to 30 wt %, or PdAg alloy having the amount of Pd less than or equal to 30 wt % to obtain the said multilayer varistor. As such, the fabrication cost of the said multilayer varistor was lowered. Further, the said multilayer varistor showed good breakdown voltage, good non-linear exponent, good maximum surge current, and good ESD withstand ability. Therefore, the said multilayer varistor had an extensive application.