Multilayer varistor and method for manufacturing the same

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.

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.

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.