Multilayer capacitor and method of fabricating the same

• US 5,144,527 A
• Filed: 03/14/1991
• Issued: 09/01/1992
• Est. Priority Date: 08/24/1989
• Status: Expired due to Term

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Mori, Susumu, Amano, Toshinori
• Primary Examiner(s): GRIFFIN, DONALD
• Application Number:
  US07/663,942
• Time in Patent Office: 537 Days
• Field of Search: 29/25.42, 361/303-305, 361/320, 361/321, 361/328-330, 361/308-310
• US Class Current: 361/321.2
• CPC Class Codes: H01G 13/06 with provision for removing metal surfaces
• CPC Class Codes: H01G 4/012 Form of non-self-supporting electrodes
• CPC Class Codes: H01G 4/30 Stacked capacitors H01G4/33 takes precedence
• CPC Class Codes: Y10T 29/435 Solid dielectric type

Abstract

A multilayer capacitor constructed using a monolithic type dielectric body in which a plurality of dielectric layers are laminated with inner electrodes being interposed therebetween and having a structure in which the width of the inner electrodes is made smaller than that of the dielectric layers so that side margin regions are provided in side parts of the inner electrodes. In this multilayer capacitor, the inner electrodes originally have the same width as the dielectric layers and have side edges which are exposed at side surfaces of the above described monolithic type dielectric body. The exposed side edges of the inner electrodes are etched or physically removed to form the above described side margin regions. The side margin regions are formed by removing parts of the inner electrodes by etching or physical removal, so that the width of the side margin regions is accurately achieved. In addition, the multilayer capacitor is constructed by forming the above side margin regions after overlapping the inner electrodes while they still have the same width as the dielectric layers, so that the overlapping area of the inner electrodes is accurately controlled.

Claims

1. A multilayer capacitor which has a monolithic type dielectric body having respective opposed pairs of end surfaces, side surfaces, and top and bottom surfaces, in which a plurality of dielectric layers are laminated with inner electrodes being interposed therebetween and in which the width of said inner electrodes between said side surfaces is made smaller than that of said dielectric layers so that side margin regions are provided at side parts of the inner electrodes, and having a pair of outer electrodes formed on respective end surfaces of said monolithic type dielectric body which are conductively connected to predetermined ones of said inner electrodes;

the multilayer capacitor being characterized in that said side margin regions are formed by etching side edges of said inner electrodes, at said side surfaces of the monolithic type dielectric body;

wherein the inner electrodes initially have the same width as said dielectric layers, and the side edges of the inner electrodes are exposed at said side surfaces, before said etching;

each of said outer electrodes extending onto said side, top and bottom surfaces from the respective end surface so as to form a five-sided cap on said monolithic type dielectric body.

2. The multilayer capacitor according to claim 1, wherein at least the side edges of said inner electrodes, after forming the side margin regions, are oxidized to form oxide films which increase adhesive strength between said inner electrodes and said dielectric layers.

3. The multilayer capacitor according to claim 2, characterized in that cavities formed in the side margin regions by etching said exposed side edges of the inner electrodes are filled with sealing materials.

4. The multilayer capacitor according to claim 1 characterized in that cavities formed in the side margin regions by etching said exposed side edges of the inner electrodes are filled with sealing materials.

5. The multilayer capacitor according to claim 1, wherein said dielectric layers comprise dielectric ceramic layers, and said monolithic type dielectric body comprises a monolithic type sintered body in which inner electrodes are alternately led out to said pair of end surfaces.

6. A method of fabricating a multilayer capacitor which includes a monolithic type dielectric body having respective opposed pairs of end surfaces, side surfaces, and top and bottom surfaces, in which a plurality of dielectric layers are laminated with inner electrodes being interposed therebetween and in which the width of the inner electrodes between said side surfaces is made smaller than that of said dielectric layers so that side margin regions are provided at side parts of the inner electrodes, and having a pair of outer electrodes formed on said end surfaces of said monolithic type dielectric body which are conductively connected to predetermined ones of said inner electrodes, comprising the steps of:

obtaining a monolithic type dielectric body in which a plurality of dielectric layers are laminated with inner electrodes being interposed therebetween and the width of the inner electrodes being made equal to that of the dielectric layers;

forming a pair of outer electrodes said end surfaces of said monolithic type dielectric body which are conductively connected to predetermined ones of said inner electrodes, said outer electrodes extending onto said side, top and bottom surfaces from said end surfaces so as to form a 5-sided cap on said multilayer capacitor;

forming side margin regions at side parts of the inner electrodes by etching side edges of said inner electrodes at said side surfaces of the monolithic type dielectric body at which said side edges of said inner electrodes are exposed.

7. The method of fabricating a multilayer capacitor according to claim 6, characterized by further comprising the steps of

forming on one major surface of a rectangular mother dielectric sheet a plurality of mother inner electrode material layers in parallel spaced apart from each other by a predetermined distance so as to extend between opposed edges of the mother dielectric sheet,

laminating mother dielectric sheets each having said mother inner electrode material layers formed thereon to obtain a monolithic type mother dielectric body, and

cutting said monolithic type mother dielectric body in the direction of lamination, to obtain said monolithic type dielectric body.

8. The method of fabricating a multilayer capacitor according to claim 6, which further comprises the steps of

forming on one major surface of a rectangular dielectric sheet an inner electrode material layer from one edge of the dielectric sheet toward the other edge opposed to the one edge so as not to lead to the other edge and over the entire width between a pair of side edges which connects said edges, and

laminating a plurality of dielectric sheets such that their respective one edges to which the inner electrode material layers are led out are alternately located on opposite sides, to obtain said monolithic type dielectric body.

9. The method of fabricating a multilayer capacitor according to claim 8, characterized in that said step of forming side margin regions comprises the steps of

coating first and second end surfaces of the monolithic type dielectric body which derive from the edges, to which the inner electrode materials are led out, of said dielectric sheets, with resist materials,

etching inner electrode material portions exposed to a pair of side surfaces of the monolithic type dielectric body which derives from the side edges of said dielectric sheets using etchant which does not attack said resist materials, to form side margin regions between said side surfaces and the inner electrodes, and

removing said resist materials.

10. The method of fabricating a multilayer capacitor according to claim 9, wherein said step of forming a pair of outer electrodes is performed after said step of forming side margin regions.

11. The method of fabricating a multilayer capacitor according to claim 10, characterized by further comprising the step of filling cavities formed after etching the exposed side edges of the inner electrodes on the side surfaces of said monolithic type dielectric body with sealing materials.

12. The method of fabricating a multilayer capacitor according to claim 9, characterized in that said step of forming side margin regions is performed after said step of forming a pair of outer electrodes.

13. The method of fabricating a multilayer capacitor according to claim 12, characterized by further comprising the step of filling cavities formed after etching the exposed side edges of the inner electrodes on the side surfaces of said monolithic type dielectric body with sealing materials.

14. The method of fabricating a multilayer capacitor according to claim 9, characterized by further comprising the step of filling cavities formed after etching the exposed side edges of the inner electrodes on the side surfaces of said monolithic type dielectric body with sealing materials.

15. The method of fabricating a multilayer capacitor according to claim 9, characterized by further comprising the step of heating said monolithic type dielectric body in an oxidation atmosphere and oxidizing at least the side edges of the inner electrodes to form oxide films after said step of forming side margin regions, so as to increase adhesive strength between said inner electrodes and said dielectric layers.

16. The method of fabricating a multilayer capacitor according to claim 9, wherein Ni paste containing Ni is used as said resist materials.

17. The method of fabricating a multilayer capacitor according to claim 9, which further comprises the step of heating or neutralizing etchant remaining in spaces where said side margin regions are formed not to act as an etching material after said step of forming side margin regions.

18. The method of fabricating a multilayer capacitor according to claim 6, characterized in that said step of obtaining a monolithic type dielectric body comprises the steps of

laminating a plurality of ceramic green sheets each having on its one major surface a first inner electrode material layer comprising a difficult etching material provided to the vicinity of its one edge along the edge and a second inner electrode material layer comprising an easy etching material provided so as to extend from one edge to the other edge opposed to said one edge and over the entire width on the side of an upper or lower surface of the first inner electrode material layer such that their respective one edges on the side of the first inner electrode material layers provided are alternately located on opposite end surfaces in the direction of thickness to obtain a monolithic type dielectric green chip, and

firing said monolithic type dielectric green chip to sinter the ceramic green sheets as well as baking the first and second inner electrode material layers to form a plurality of inner electrodes each having first and second inner electrode portions, to obtain a monolithic type laminated body, and

said process of forming side margin regions is performed by etching the monolithic type dielectric body by a chemical agent for selectively engraving said second inner electrode portions to remove at least portions, which are exposed to the side surfaces of the dielectric body, of the second inner electrode portions and their vicinities, and

characterized by further comprising the step of forming a pair of outer electrodes on opposed first and second end surfaces, to which said first inner electrode portions are exposed, of the dielectric body.

19. The method of fabricating a multilayer capacitor according to claim 6, characterized in that said step of obtaining a monolithic type dielectric body comprises the steps of

laminating a plurality of ceramic green sheets each having a first inner electrode material layer comprising a difficult etching material provided in the vicinity of its one edge along the edge and a second inner electrode material layer comprising an easy etching material provided over the entire width so as to be connected to the first inner electrode material layers and extend to an edge opposed to said one edge such that their respective edges on the side of the first inner electrode materials provided are alternately located on opposite end surfaces in the direction of thickness, to obtain a monolithic type dielectric green chip, and

firing said monolithic type dielectric green chip to sinter the ceramic green sheets as well as baking the first and second inner electrode material layers to form a plurality of inner electrodes each comprising first and second inner electrode portions, to obtain a monolithic type dielectric body, and

said step of forming side margin regions is performed by etching the side surfaces of said monolithic type dielectric body by a chemical agent for selectively engraving the second inner electrode portions to remove at least portions, which are exposed to the side surfaces of the dielectric body, of the second inner electrode portions and their vicinities, and

characterized by further comprising the step of forming outer electrodes on first and second end surfaces, to which said inner electrodes are led out, of the dielectric body.