Non-reducible dielectric ceramic material, making method,...

Details Non-reducible dielectric ceramic material, making method,... Non-reducible dielectric ceramic material, making method,...

2000-05-30

2001-12-11

Brunsman, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Titanate, zirconate, stannate, niobate, or tantalate or...

C501S135000, C361S321400, C361S321500

Reexamination Certificate

active

06329311

ABSTRACT:

TECHNICAL FIELD
This invention relates to a temperature-compensating dielectric ceramic material for used in multilayer ceramic capacitors having a base metal as the internal electrode, a method for preparing the same, and a multilayer ceramic capacitor using the same.
BACKGROUND OF THE INVENTION
Multilayer ceramic capacitors are widely utilized as electronic parts featuring a small size, high capacitance and high reliability, with a number of such capacitors being employed in one electronic equipment. In the recent drive toward small-size, high-performance equipment, there is an increasing requirement to develop multilayer ceramic capacitors to a smaller size, higher capacitance, lower cost, and higher reliability.
The multilayer ceramic capacitors are generally manufactured by alternately stacking layers of an internal electrode-forming paste and a dielectric layer-forming paste by a sheeting or printing method, followed by co-firing.
Dielectric ceramic materials used in prior art multilayer ceramic capacitors or the like have the nature that when fired in a reducing atmosphere, they are reduced into semiconductors. This required to use as the internal electrode material noble metals such as palladium, which do not melt at the temperature at which dielectric ceramic materials are sintered and are not oxidized when fired under an oxygen partial pressure high enough to prevent dielectric ceramic materials from converting into semiconductors. However, the noble metals such as Pd are expensive, imposing a substantial bar against reducing the cost and increasing the capacitance of multilayer ceramic capacitors.
Then, a study is being made on the use of relatively inexpensive base metals such as nickel and nickel alloys as the internal electrode material. In the event where base metals are used as the conductor of internal electrode, the internal electrodes can be oxidized upon firing in air. Therefore, co-firing of dielectric layers and internal electrodes must be effected in a reducing atmosphere. However, firing in a reducing atmosphere causes the dielectric layers to be reduced as mentioned above, resulting in a lower resistivity. Non-reducible dielectric ceramic materials were thus proposed.
Exemplary non-reducible dielectric ceramic materials are (Ca,Sr)(Ti,Zr)O
3
compositions with manganese oxide and silicon oxide added as disclosed in JP-A 63-126117, JP-A 63-289709, JP-A 5-217426, JP-B 5-51127, JP-B 5-51122, and JP-B 5-51124. In these patent publications, manganese oxide is added alone such that Mn substitutes for the (Ca,Sr) site whereas silicon oxide is added either alone or as one component of a compound oxide. Manganese oxide is an additive component for imparting reduction resistance whereas silicon oxide serves as a sintering aid. It is thus concluded that dielectric materials containing manganese oxide and silicon oxide are customarily used for ceramic capacitors having internal electrodes formed of noble metals such as nickel.
DISCLOSURE OF THE INVENTION
In multilayer ceramic capacitors, it sometimes happens that ends of internal electrodes are not exposed at the side surface of a capacitor chip at the end of firing because of the difference in shrinkage factor between internal electrodes and dielectric layers during firing. This requires to add a step of polishing a capacitor chip, as by barrel finishing, for exposing internal electrodes prior to the attachment of terminal electrodes to the side surface of a capacitor chip.
However, the inventors' research revealed that when dielectric ceramic materials containing manganese oxide and silicon oxide are co-fired with nickel internal electrodes in a reducing atmosphere and then subjected to re-oxidizing treatment, Mn—Ni compound oxide precipitates between nickel internal electrodes confined within the chip and the side surface of the chip. This Mn—Ni compound oxide is composed mainly of NiMn
2
O
4
and more difficult to polish than dielectric ceramics. As a result, the polishing step for exposing ends of internal electrodes is prolonged. The long term of polishing step not only leads to a lowering of productivity, but also applies some load to the chip, causing defects such as cracks.
An object of the invention is, in the manufacture of a multilayer ceramic capacitor having nickel-containing internal electrodes, to prevent the polishing step for exposing ends of the internal electrodes from being prolonged.
This and other objects are achieved by any of the following embodiments of the present invention.
(1) A non-reducible dielectric ceramic material comprising
a compound oxide represented by the formula (I):
[(Ca
x
Sr
1−x
)O]
m
[(Ti
y
Zr
1−y
)O
2
]
 wherein 0≦x≦1, 0≦y≦0.10, and 0.75≦m≦1.04, as a main component,
0.5 to 15 mol % based on the main component of SiO
2
and BaO and/or CaO as an auxiliary component, these oxides being calculated as a compound oxide represented by the formula (II):
[(Ba
z
Ca
1−z
)O]
v
SiO
21
 wherein 0≦z≦1 and 0.5≦v≦4.0,
0.2 to 5 mol % based on the main component of MnO as an auxiliary component, and
0.001 to 10 mol % based on the main component of MgO as an additive component, the material having been prepared by adding a starting raw material for the additive component to a calcined material containing the main component, followed by firing.
(2) A non-reducible dielectric ceramic material comprising
a compound oxide represented by the formula (I):
[(Ca
x
Sr
1−x
)O]
m
[(Ti
y
Zr
1−y
)O
2
]
 wherein 0≦x≦1, 0≦y≦0.10, and 0.75 ≦m≦1.04, as a main component,
0.5 to 15 mol % based on the main component of SiO
2
as an auxiliary component,
0.2 to 5 mol % based on the main component of MnO as an auxiliary component, and
0.01 to 10 mol % based on the main component of at least one rare earth oxide selected from the group consisting of oxides of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, as an additive component.
(3) A non-reducible dielectric ceramic material according to (2) wherein the auxiliary component includes CaO and/or BaO, which are contained along with SiO
2
in such proportions as to provide a compound oxide represented by the formula (II):
[(Ba
z
Ca
1−z
)O]
v
SiO
2
 wherein 0≦z≦1 and 0.5≦v≦4.0.
(4) A non-reducible dielectric ceramic material according to (2) or (3) further comprising MgO.
(5) A non-reducible dielectric ceramic material according to any one of (1) to (4) further comprising up to 10 mol % based on the main component of Al
2
O
3
as an auxiliary component.
(6) A non-reducible dielectric ceramic material according to any one of (1) to (5) which includes a silicon rich phase having a SiO
2
concentration of at least 10 mol %.
(7) A method for preparing a non-reducible dielectric ceramic material comprising
a compound oxide represented by the formula (I):
[(Ca
x
Sr
1−x
)O]
m
[(Ti
y
Zr
1−y
)O
2
]
 wherein 0≦x≦1, 0≦y≦0.10, and 0.75≦m≦1.04, as a main component,
0.5 to 15 mol % based on the main component of SiO
2
and BaO and/or CaO as an auxiliary component, these oxides being calculated as a compound oxide represented by the formula (II):
[(Ba
z
Ca
1−z
)O]
v
SiO
2
 wherein 0≦z≦1 and 0.5≦v≦4.0,
0.2 to 5 mol % based on the main component of MnO as an auxiliary component, and
0.001 to 10 mol % based on the main component of MgO as an additive component, the method comprising the steps of adding a starting raw material for the additive component to a calcined material containing the main component, followed by firing.
(8) A multilayer ceramic capacitor comprising a non-reducible dielectric ceramic material according to any one of (1) to (6) as a dielectric material and internal electrodes containing at least nickel.


REFERENCES:
patent: 5204301 (1993-04-01), Ohkubo et al.
patent: 6118648 (2000-09-01), Kojima et al.
patent: 63-126117 (1987-05-01), None
patent: 63-254602 (1988-10-01), None
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