US 6,184,770 B2 · Monolithic varistor

Abstract

A monolithic varistor which is small and inexpensive and has excellent varistor characteristics includes a layered ceramic body containing ZnO as a primary component and, based on 100 mol % ZnO, an Al component in an amount of about 100-350 ppm calculated as A12O3, a Bi component in an amount of about 1.0-3.0 mol % calculated as Bi2O3, a Co component in an amount of about 0.1-1.5 mol% calculated as Co2O3, an Mn component in an amount of about 0.1-1.0 mol % calculated as MnO, at least one Sb component and/or an Sn component in an amount of about 0.1-2.0 mol % calculated as SbO3/2 or SnO, a Y component in an amount of 0-about 3.0 mol % calculated as Y2O3, an Si component in an amount of about 0.1-1.0 mol % calculated as SiO2, and a B component in an amount of about 0.1-2.0 mol % calculated as B2O3; and an average grain size in a characteristic portion of the varistor is about 0.9-3.0 μm.

Claims19

Dependent claims

A monolithic varistor which comprises a monolithically sintered layered ceramic body having a plurality of internal electrodes, wherein the ceramic comprises ZnO and, based on 100 mol % ZnO, an Al component in an amount of about 100-350 ppm calculated as Al2O3, a Bi component in an amount of about 1.0-3.0 mol % calculated as Bi2O3, a Co component in an amount of about 0.1-1.5 mol % calculated as Co2O3, an Mn component in an amount of about 0.1-1.0 mol % calculated as MnO, at least one of an Sb component and an Sn component in an amount of about 0.1-2.0 mol % calculated as SbO3/2 or SnO, a Y component in an amount of 0.0 about 3.0 mol % calculated as Y2O3, an Si component in an amount of about 0.1-1.0 mol % calculated as SiO2, and a B component in an amount of about 0.1-2.0 mol % calculated as B2O3;

and which has an average grain size of about 0.9-3.0 μm at least in a portion which exhibits a varistor characteristic and is sandwiched by internal electrodes.

A method for producing a varistor which comprises the following steps:

mixing starting raw materials including ZnO, and a source of Al, Bi, Co, Mn, Y, Si, B and at least one of Sb and Sn;
calcining the resultant mixture;
forming ceramic green sheets containing the calcined product;
forming an electrode on at least two of the ceramic green sheets;
forming a laminate including the two green sheets with electrodes such that the electrodes are in the interior thereof and separated from one another;
sintering the layered product;
and
providing on outer surfaces of the sintered product metallized portions which are electrically connected to the internal electrodes.

5 more elements

Dependencies are inferred from the claim text.

Monolithic varistor

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Monolithic varistor

Life of this patent

Abstract

Claims19