Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2000-11-29
2002-02-05
Brunsman, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C501S139000, C361S321200, C361S321300, C361S321400, C361S321500, C438S396000
Reexamination Certificate
active
06344427
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a dielectric ceramic composition to be used for dielectric layers of a multilayer ceramic capacitor having internal electrode layers composed of base metal such as nickel or the like, a capacitor using the same and a method of manufacturing the capacitor.
BACKGROUND ART
A conventional multilayer ceramic capacitor such as disclosed in Japanese Patent Laid-Open Publication No. 8-337471 (1996) is such that dielectric layers and internal electrode layers of nickel are alternately stacked, and sintered in an inert atmosphere or in a reducing atmosphere , and external electrodes are formed with silver or the like thereafter. The above-mentioned dielectric layers contain, as a main component, BaTiO
3
in which rare earth oxide(s) such as Dy
2
O
3
and the like and Co
2
O
3
are contained, and contain BaO, MnO, MgO, Al
2
O
3
and oxide glass mainly composed of Li
2
O—(Si, Ti)—Al
2
O
3
as sub components.
Generally, nickel and silver do not dissolve in each other. Accordingly, electrically connect the internal electrodes and the external electrodes without fail, it is preferable to form the external electrodes with, for example, copper or the like, a metal which dissolves completely in silver. However, to form with copper, the external electrodes should be formed in a non-oxidizing atmosphere. In the case of dielectric layers having the above-mentioned composition, the components of the dielectric layers are problematically reduced during formation of the external electrodes, and insulation resistance of the dielectric layers lowers accordingly.
Generally, in the case of manufacturing a multilayer capacitor using a dielectric ceramic composition mainly composed of barium titanate , when a molar ratio of Ba/Ti is less than 1, TiO
2
is apt to be reduced during the sintering process in the reducing atmosphere, or while organic binders contained in the dielectric layers are burned. Although the reduced TiO
2
is re-oxidized in some degree during a cooling process after sintering, the inside of each of the dielectric layers and the inside of each crystal grain resist being re-oxidized, and remain deficient in oxygen. As a result, the insulation resistance and dielectric breakdown voltage of the dielectric layers degrade.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a dielectric ceramic composition enabling obtainment of a multilayer capacitor whose dielectric layers are not reduced , and have high insulation resistance even if external electrodes are formed of base metal such as copper or the like, a capacitor using this composition and a method of manufacturing the capacitor.
The dielectric ceramic composition of the present invention contains barium titanate as a main component, and contains at least 0.5 to 5.0 mol of Mg in the form of MgO, 0.1 to 3.0 mol of Dy in the form of Dy
2
O
3
, 0.01 to 0.4 mol of Mn in the form of MnO
4/3
, 0.01 to 0.26 mol of V in the form of V
2
O
5
, 0.3 to 3.5 mol of Si in the form of SiO
2
and 0.01 to 3.0 mol of Al in the form of Al
2
O
3
as sub components per 100 mol of the barium titanate, and is characterized in that a molar ratio of Ba/Ti ranges between 1.001 and 1.05.
The dielectric ceramic composition of the present invention compensates oxygen defect occurring during sintering with making the Ba/Ti molar ratio ranging between 1.001 and 1.05, the molar ratio which is made to be larger than 1, and with cation holes each being caused by substituting a part of Ti having a valence of four with V having a valence of five. As a result, reduction of TiO
2
and decrease in insulation resistance of the dielectric ceramic composition can be prevented.
REFERENCES:
patent: 6058005 (2000-05-01), Matoba et al.
patent: 6291380 (2001-09-01), Yokoi et al.
Kobayashi Keiji
Komatsu Kazuhiro
Kuramitsu Hideki
Nagai Atsuo
Brunsman David
Parkhurst & Wendel L.L.P.
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