Anti-reducing dielectric ceramic composition and monolithic...

Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor

Reexamination Certificate

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C361S321500, C501S134000

Reexamination Certificate

active

06233134

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a anti-reducing dielectric ceramic composition and a monolithic ceramic capacitor using the dielectric ceramic composition.
2. Description of the Related Art
When a dielectric material mainly containing a titanate is used to form a monolithic ceramic capacitor, there has been the problem that when such a dielectric material is sintered under a condition of a low concentration oxygen partial pressure (neutral or reductive atmosphere), the dielectric material is undesirably reduced and hence undesirably becomes a semi-conductor. Because of this, in order to form internal electrodes, it is necessary to employ a noble metal such as palladium and platinum which will not melt under the sintering temperature, nor will it cause the dielectric ceramic material to be converted to a semi-conductor and itself be oxidized under a high concentration oxygen partial pressure. As a result, it is difficult to manufacture a monolithic ceramic capacitor with a low cost.
It is usually desired to use, as an internal electrode material, inexpensive base metals such as nickel and copper. However, when such a base metal is used as an internal electrode material and is sintered under conventional conditions, said electrode material is oxidized. As a result, it is impossible to provide the desired function of an electrode. For this reason, in order for such base metal to be used as an internal electrode material, it is necessary to employ a dielectric material having an excellent dielectric property with its ceramic layer having resistance against becoming a semiconductor even under a neutral or reductive atmosphere having a low concentration oxygen partial pressure. In order to meet such a requirement, Japanese laid-open patent application Nos. 63-289707 and 63-224106 suggest an improved dielectric material which is (Ca
1−x
Sr
x
) (Zr
1−y
Ti
y
)O
3
composition. By using such improved dielectric material, it has become possible to obtain a dielectric ceramic which is not converted into a semiconductor even when being sintered in a reductive atmosphere, thereby rendering it possible to manufacture a monolithic ceramic capacitor using a base metal material such as nickel or copper for forming internal electrode.
With the anti-reducing dielectric ceramic composition disclosed in the above Japanese laid-open patent application No. 63-289707, there is a problem that although it has excellent capacity and temperature characteristics, its dielectric constant is as low as 46. With the anti-reducing dielectric ceramic composition disclosed in the above Japanese laid-open patent application No. 63-224106, there is a problem that if the thickness of laminated ceramic body is made quite thin for the purpose of producing a monolithic ceramic capacitor compact in size but large in capacity, it is difficult to ensure the desired reliability during a life measuring test under a high temperature load.
SUMMARY OF THE INVENTION
The present provides an improved anti-reducing dielectric ceramic composition having a dielectric constant of 100 or higher and an excellent reliability during a life test under a high temperature load, and provides a monolithic ceramic capacitor formed by using the improved anti-reducing dielectric ceramic composition.
In accordance with one aspect of the present invention, a anti-reducing dielectric ceramic composition comprises a composite oxide containing as metal elements M (M: Ca or Ca and Sr), Zr and Ti, when represented by a composition formula (Ca
1−x
Sr
x
)
m
(Zr
1−y
Ti
y
)O
3
, the values of x, y, and m satisfy the ranges of 0≦x<0.5, 0.60<y≦0.85, 0.85<m<1.30 as a main component, and at least one of a manganese compound and a magnesium compound incorporated as an accessory component in a range of about 0.1 to 6 mols in terms of MnO and MgO, respectively, for every 100 mols of the main component.
The composition may further contain a sintering aid agent. The sintering aid agent may preferably contain at least one of Si and B. Further, the sintering aid agent may be SiO
2
.
Moreover, the sintering aid agent may be a member of the Li
2
O—(Si, Ti)O
2
—MO series (where MO is at least one of Al
2
O
3
and ZrO
2
).
In addition, the sintering aid agent may be a member of the SiO
2
—TiO
2
—XO series (where XO is at least one substance selected from a group consisting of BaO, SrO, CaO, MgO, ZnO and MnO). Preferably, the agent is at least one selected from Al
2
O
3
and ZrO
2
.
Further, the sintering auxiliary material may be a member of the Li
2
O—B
2
O
3
—(Si, Ti)O
2
series. Preferably, the sintering auxiliary material contains at least one substance selected from Al
2
O
3
and ZrO
2
.
Moreover, the agent may be a member of the B
2
O
3
—Al
2
O
3
—XO series (where XO is at least one substance selected from a group consisting of BaO, SrO, CaO, MgO, ZnO and MnO).
The content of the agent may be about 20 parts by weight or lower with respect to 100 parts by weight in total of the main component and the accessory component.
A monolithic ceramic capacitor of the present invention includes a plurality of dielectric ceramic layers, internal electrodes formed between the dielectric ceramic layers, and external electrodes electrically connected with the internal electrodes, and is characterized in that the dielectric ceramic layers are made of the above dielectric ceramic compositions, and each of the internal electrodes contains a base metal as its main component. The base metal may preferably be nickel or copper.


REFERENCES:
patent: 4700266 (1987-10-01), Chazono et al.
patent: 4859641 (1989-08-01), Fujino et al.
patent: 0913843A1 (1999-05-01), None

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