Self-limiting capacitor formed using a plurality of thin film semiconductor ceramic layers

Claim 2

A self-limiting ceramic capacitor having high capacitance and transient voltage protective properties, the capacitor comprising a plurality of thin film layers of semiconducting ceramic characterized by grain boundary equivalent circuitry, the ceramic having non-linear resistance characteristics and sintered together to form a laminated stack; the thin layers having a conductive coating on at least one surface thereof, some of the conductive coatings extending to a first edge of said stack and the remainder having the conductive coating extending to a second edge; conductive material on said first edge of said laminated stack of thin film ceramic layers and in electrical communication with a portion of the conductive coating extending to said first edge to provide a first connected electrode; and conductive material on said second edge of said plurality of layers and in electrical communication with a portion of the conductive coating extending to said second edge to provide a second connected electrode, said electrode and thin layers of ceramic in combination providing said self-limiting capacitor.

Claim 3

The self-limiting ceramic capacitor in accordance with claim 1 wherein the ceramic is a zinc oxide type material.

Claim 4

The self-limiting capacitor of claim 1 wherein each of said ceramic layers having a conductive coating extending to said first edge of said plurality of layers is interleaved with ceramic layers having a conductive coating extending to said second edge whereby said capacitor comprises a plurality of capacitors connected in parallel.

Claim 5

The self-limiting capacitor of claim 3 wherein the layers are connected in series in addition to being connected in parallel to increase voltage while maintaining high capacitance.

Claim 6

The self-limiting capacitor of claim 3 wherein said second edge of said plurality of layers is opposite said first edge.

Claim 7

The self-limiting capacitor of claim 5 wherein said capacitor is formed by coating each of said thin film ceramic layers with a conductive coating before said ceramic is fired and then firing said coated thin film ceramic layers in a stack to laminate said ceramic layers and said conductive coatings thereon.

Claim 8

The self-limiting capacitor of claim 6 wherein said ceramic material comprises ZnO.

Claim 9

The self-limiting capacitor of claim 6 wherein said ceramic material comprises at least about 60 mole % of ZnO.

Claim 10

The self-limiting capacitor of claim 8 wherein said ZnO comprises from about 90 to 96 mole % of said ceramic material.

Claim 11

The self-limiting capacitor of claim 9 wherein the balance of said ceramic material comprises one or more metal oxides selected from the class consisting of alkali metal oxides, boron oxide, bismuth oxide, cobalt oxide, aluminum oxide, silicon oxide, and mixtures thereof.

Claim 12

The self-limiting capacitor of claim 10 wherein said ceramic material has an average grain size of from about 1 to 50 microns.

Claim 13

The self-limiting capacitor of claim 11 wherein said ceramic material is formed into a green tape having a thickness of from about 10 to 250 microns.

Claim 14

The self-limiting capacitor of claim 12 wherein said green tape is coated with a conductive material capable of withstanding sintering temperatures above 1000° C.

Claim 15

The self-limiting capacitor of claim 11 wherein said ceramic material is formed into a green tape having a thickness of from about 12 to 35 microns.

Claim 18

The method of claim 15 wherein said step of forming said mixture of ceramic material exhibiting non-linear resistance characteristics further including forming a mixture comprising from 90 to 96 mole % ZnO having a particle size range of from about 0.1 to 1.0 microns.

Claim 19

The method of claim 16 wherein the balance of said non-linear ceramic material comprises one or more metal oxides selected from the class consisting of alkali metal oxides, boron oxide, bismuth oxide, cobalt oxide, aluminum oxide, silicon oxide, and mixtures thereof.

Claim 20

The method of claim 16 wherein said step of producing said green tape further comprises forming a slip having a thickness ranging from about 10 to 250 microns and cutting said tape into segments.

Claim 21

The method of claim 18 wherein said step of applying a conductive coating on said segments of green ceramic tape further comprises applying a conductive material capable of withstanding subsequent exposure to a sintering temperature of at least 1000° C.

Claim 22

The method of claim 19 wherein said conductive coating comprises one or more of the platinum metals.

Claim 23

The method of claim 20 wherein said stack of thin film ceramic layers having said conductive coating material thereon is sintered at a temperature of from about 1000° to 1200° C. for a period of from about 2 to 24 hours.

Claim 24

The method of claim 19 wherein said step of applying a conductive coating on a surface of said green ceramic tape segment includes extending said conductive coating on at least some of said segments to a single edge of said segment while terminating said coating at a point spaced from the remaining edges of said segment.

Claim 25

The method of claim 22 wherein said green tape segments having said conductive coating extending to a single edge of said segment are stacked in alternate fashion so that every other segment having said conductive coating applied to said single edge has a conductive coating extending to an opposite edge and said step of coating two edges of said laminated stack with conductive material comprises coating two opposite edges to interconnect respectively with said conductive coatings applied to a single edge of said segments.

Claim 26

The method of claim 23 wherein said step of applying said conductive coating on said surface of said green tape segments further comprises forming two discontinuous portions of a conductive coating on the surface of one or more segments with each of said discontinuous portions extending to an opposite edge of said tape segment to connect with said respective conductive coatings on the respective edges of said laminated stack.

Claim 27

The method of claim 24 wherein said step of applying said conductive coating to said green ceramic tape further comprises applying said coating to one or more segments while terminating said conductive coating at a point sufficiently spaced from all of the edges of said segment to prevent electrical contact with said conductive material applied to any of the edges of said laminated stack and said step of forming said stack further includes positioning said segment having a conductive coating thereon spaced from all of said edges adjacent a segment coated with said discontinuous conductive coating portions whereby said coated segments cooperate to form two capacitors in series with said conductive coating spaced from said edges acting as a common floating electrode of said two capacitors and said discontinuous conductive portions respectively acting as the other electrode of each of said two capacitors in series.

Claim 30

A self-limiting ceramic capacitor device having high capacitance and in situ transient voltage protection properties wherein said capacitor, when exposed to a voltage in excess of the safe operating voltage of said capacitor will act as a varistor and thus limit the voltage until said excess voltage is removed when said device will again act as a capacitor, said capacitor comprising a plurality of thin film layers of semiconducting ceramic characterized by grain boundary equivalent circuitry and non-linear resistance characteristics which permit it to function as a varistor upon exposure to a voltage in excess of the safe operating voltage of the capacitor; said thin film layers sintered together to form a laminated stack; said thin layers having a conductive coating on at least one surface thereof, some of said conductive coatings extending to a first edge of said stack and at least some of the remainder of said thin layers having said conductive coating extending to a second non-contiguous edge; conductive material on said first edge of said laminated stack of thin film ceramic layers and in electrical communication with said conductive coating extending to said first edge to provide a first connected electrode; and conductive material on said second edge of said laminated stack and in electrical communication with said conductive coating extending to said second edge to provide a second connected electrode, said electrodes and thin layers of ceramic in combination providing said self-limiting capacitor.

Claim 31

A self-limiting ceramic capacitor device having high capacitance and in situ transient voltage protection properties wherein said capacitor, when exposed to a voltage in excess of the safe operating voltage of said capacitor will act as a varistor and thus limit the voltage until said excess voltage is removed when said device will again act as a capacitor, said capacitor comprising a plurality of thin film layers of semiconducting ceramic characterized by grain boundary equivalent circuitry and non-linear resistance characteristics which permit it to function as a varistor upon exposure to a voltage in excess of the safe operating voltage of the capacitor; said thin film layers sintered together to form a laminated stack; said thin layers having a conductive coating on at least one surface thereof, some of said conductive coatings extending to a first edge of said stack and at least some of the remainder of said thin layers having said conductive coating extending to a second non-contiguous edge; conductive material on said first edge of said laminated stack of thin film ceramic layers and in electrical communication with said conductive coating extending to said first edge to provide a first connected electrode; and conductive material on said second edge of said laminated stack and in electrical communication with said conductive coating extending to said second edge to provide a second connected electrode, said electrodes and thin layers of ceramic in combination providing said self-limiting capacitor.