Multilayer varistor and method for manufacturing the same

Patent metadata

Field	Value
Publication number	US-12580105-B2
Application number	US-202118252671-A
Country	US
Kind code	B2
Filing date	Nov 16, 2021
Priority date	Nov 25, 2020
Publication date	Mar 17, 2026
Grant date	Mar 17, 2026

Abstract

A multilayer varistor includes a sintered body, a first external electrode, a second external electrode, a first internal electrode, a second internal electrode, and a high-resistivity portion. The first internal electrode is provided inside the sintered body and electrically connected to the first external electrode. The second internal electrode is provided inside the sintered body and electrically connected to the second external electrode. The high-resistivity portion includes: a surface high-resistivity portion provided to cover a surface of the sintered body; and an inner high-resistivity portion extended inward from the surface high-resistivity portion inside the sintered body.

First claim

The invention claimed is:

1 . A multilayer varistor comprising:
a sintered body; a first external electrode and a second external electrode both provided outside the sintered body; a first internal electrode provided inside the sintered body and electrically connected to the first external electrode; a second internal electrode provided inside the sintered body and electrically connected to the second external electrode; and a high-resistivity portion provided in a surface region of the sintered body, the high-resistivity portion including: a surface high-resistivity portion provided to cover a surface of the sintered body; and an inner high-resistivity portion extended inward from the surface high-resistivity portion inside the sintered body, the inner high-resistivity portion having a maximum length equal to or greater than 10 μm, and the inner high-resistivity portion being in contact with neither the first internal electrode nor the second internal electrode.

2 . The multilayer varistor of claim 1 , wherein
the sintered body contains zinc oxide as a main component thereof, and the high-resistivity portion contains zinc silicate.

3 . The multilayer varistor of claim 1 , wherein
the surface high-resistivity portion has an average thickness equal to or greater than 0.3 μm and equal to or less than 10 μm.

4 . A multilayer varistor comprising:
a sintered body; a first external electrode and a second external electrode both provided outside the sintered body; a first internal electrode provided inside the sintered body and electrically connected to the first external electrode; and a second internal electrode provided inside the sintered body and electrically connected to the second external electrode, the sintered body including: a surface region including a surface of the sintered body; and a facing region where the first internal electrode and the second internal electrode face each other, the surface region including a high-resistivity portion, the high-resistivity portion forming at least part of the surface region, a porosity in the surface region being smaller than a porosity in the facing region, and the porosity in the facing region being equal to or greater than 2% by volume and less than 6% by volume.

5 . The multilayer varistor of claim 4 , wherein
the high-resistivity portion includes: a surface high-resistivity portion provided to cover the surface of the sintered body; and a first inner high-resistivity portion extended inward from the surface high-resistivity portion inside the sintered body.

6 . The multilayer varistor of claim 4 , wherein
the high-resistivity portion includes: a surface high-resistivity portion provided to cover the surface of the sintered body; and a second inner high-resistivity portion provided inside the sintered body to be out of contact with the surface high-resistivity portion.

7 . The multilayer varistor of claim 4 , wherein
the high-resistivity portion is absent from the facing region inside the sintered body.

8 . The multilayer varistor of claim 4 , wherein
the porosity in the surface region is equal to or greater than 0% by volume and less than 2% by volume.

9 . A method for manufacturing a multilayer varistor, the method comprising:
a first step including providing a sintered body containing zinc oxide as a main component thereof and including a first internal electrode and a second internal electrode inside; a second step including impregnating, at a reduced pressure, the sintered body with a solution containing silicon; a third step including conducting, after the second step, heat treatment on the sintered body to form a high-resistivity portion, containing zinc silicate, in at least part of a surface region of the sintered body; and a fourth step including forming, on end faces of the sintered body, a first external electrode to be electrically connected to the first internal electrode and a second external electrode to be electrically connected to the second internal electrode, the high-resistivity portion including: a surface high-resistivity portion provided to cover a surface of the sintered body; and an inner high-resistivity portion extended inward from the surface high-resistivity portion inside the sintered body, and the solution containing silicon is a sodium silicate solution.

10 . The method of claim 9 , wherein
in the sodium silicate solution, a molar ratio of SiO 2 to Na 2 O is equal to or greater than 23 and equal to or less than 29.

11 . The method of claim 9 , wherein
the solution containing silicon has a viscosity equal to or greater than 1 mPa's and equal to or less than 20 mPa·s at 20° C.

12 . The method of claim 9 , wherein
the second step includes impregnating the sintered body at a reduced pressure equal to or higher than 0.1 kPa and equal to or lower than 50 kPa.

13 . The method of claim 9 , wherein
the third step includes conducting the heat treatment at a temperature equal to or higher than 825° C. and equal to or lower than 900° C.

14 . A method for manufacturing a multilayer varistor, the method comprising:
a first step including providing a sintered body including a first internal electrode and a second internal electrode inside; a second step including impregnating the sintered body with a solution containing a component to form a high-resistivity portion when introduced into the sintered body; and a third step including conducting heat treatment on the sintered body to form the high-resistivity portion in at least part of a surface region of the sintered body, a porosity in the surface region after the third step being smaller than a porosity in a facing region where the first internal electrode and the second internal electrode face each other, the solution being a sodium silicate solution.

15 . The method of claim 14 , wherein
in the sodium silicate solution, a molar ratio of SiO 2 to Na 2 O is equal to or greater than 23 and equal to or less than 29.

16 . The method of claim 14 , wherein
the porosity in the surface region after the third step is equal to or greater than 0% by volume and less than 2% by volume.

17 . The method of claim 14 , wherein
the porosity in the facing region after the third step is equal to or greater than 2% by volume and less than 6% by volume.

18 . The method of claim 14 , wherein
the porosity of the sintered body in the first step is equal to or greater than 4% by volume and less than 20% by volume.

Assignees

• Panasonic Ip Man Co Ltd

Inventors

• Kawajiri Keiji
• Mutou Naoki
• Motomitsu Hironori
• WATANABE Michiya
• Yamagishi Yuji
• Nishimura Yasuhiro

Classifications

• H01C17/30

  adapted for baking · CPC title

• H01C17/28

  adapted for applying terminals · CPC title

• H01C7/112

  ZnO type · CPC title

• H01C1/148

  the terminals embracing or surrounding the resistive element (H01C1/142 takes precedence) · CPC title

• H01C17/06546

  Oxides of zinc or cadmium · CPC title