Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2001-03-19
2003-11-11
Brunsman, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
Reexamination Certificate
active
06645895
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a dielectric ceramic composition used, for example, as a dielectric layer of a multi-layer ceramic capacitor and a method of producing an electronic device using the dielectric ceramic composition as a dielectric layer.
2. Description of the Related Art
A multi-layer ceramic capacitor as an example of electronic devices is formed by printing a conductive paste on a green sheet comprised of a predetermined dielectric ceramic composition, layering a plurality of the green sheets printed the conductive paste thereon and firing the green sheet and internal electrodes as one body.
A dielectric ceramic composition had a characteristic that it was reduced and became semiconductive when fired in a neutral or reducing atmosphere having a low oxygen partial pressure. Therefore, when producing a multi-layer ceramic capacitor, it was inevitable to fire in an oxidizing atmosphere having a high oxygen partial pressure. Accordingly, as an internal electrode material to be fired at a time with the dielectric ceramic composition, it is necessary to use an expensive noble metal, such as palladium and platinum, which does not melt at a temperature of sintering the dielectric ceramic composition and is not oxidized when being fired in an oxidizing atmosphere, so it has been a large obstacle for lowering the cost of the multi-layer ceramic capacitor to be produced.
On the other hand, to use an inexpensive base metal, such as nickel and copper, as an internal electrode material, it is necessary to develop a dielectric ceramic composition having characteristics of not becoming semiconductive by being fired at a low temperature in a neutral or reducing atmosphere, that is having excellent resistance to reducing, showing sufficient specific dielectric constant and excellent dielectric characteristics (for example, having a small capacity-temperature change rate) after firing.
A variety of proposals have been made for dielectric ceramic composition wherein a base metal can be used as an internal electrode material in the related art.
For example, The Japanese Unexamined Patent Publication No. 1988-224108 discloses a dielectric ceramic composition containing as a main component a dielectric oxide having a composition expressed by (Sr
1-x
Ca
x
)
m
(Ti
1-y
Zr
y
)O
3
(note that 0.30≦x≦0.50, 0.03≦y≦0.20, 0.95≦m≦1.08) and containing as subcomponents 0.01 to 2.00 parts by weight of Mn (converted to MnO
2
) and 0.10 to 4.00 parts by weight of SiO
2
with respect to 100 parts by weight of the main component.
The Japanese Unexamined Patent Publication No. 1988-224109 discloses a dielectric ceramic composition further containing ZnO in an amount of 0.01 to 1.00 parts by weight with respect to the above main component in addition to the above Mn and SiO
2
.
The Japanese Unexamined Patent Publication No. 1992-206109 discloses a dielectric ceramic composition containing as a main component a dielectric oxide having a composition expressed by (Sr
1-x
Ca
x
)
m
(Ti
1-y
Zr
y
)O
3
(note that 0.30≦x≦0.50, 0.00≦y≦0.20, 0.95≦m≦1.08) and the particle diameter is made to be in the range of 0.1 to 1.0 &mgr;m.
The Japanese Examined Patent Publication No. 1987-24388 discloses a dielectric ceramic composition containing as a main component a dielectric oxide having a composition expressed by MeO
k
TiO
2
(note that Me is a metal selected from Sr, Ca and Sr+Ca, and k is 1.00 to 1.04) and 0.2 to 10.0 parts by weight of a glass component with respect to 100 parts by weight of the main component wherein Li
2
O, M (note that M is at least one kind of metal oxide selected from BaO, CaO and SrO) and SiO
2
are used at a predetermined mole ratio.
The Japanese Unexamined Patent Publication No. 1984-227769 discloses a dielectric ceramic composition containing as a main component a dielectric oxide having a composition expressed by {(Sr
1-x
Ca
x
)O}
k
•TiO
2
(note that 0≦x≦1.00, 1.00≦k≦1.04) and 0.2 to 10.0 parts by weight of a glass component with respect to 100 parts by weight of the main component wherein Li
2
O, M (note that M is at least one kind of metal oxide selected from BaO, Cao and SrO) and SiO
2
are used at a predetermined mole ratio.
The Japanese Unexamined Patent Publication No. 1988-224106 discloses a dielectric ceramic composition containing as a main component a dielectric oxide having a composition expressed by (Sr
1-x
Ca
x
)
m
(Ti
1-y
Zr
y
)O
3
(note that 0.30≦x≦0.50, 0.03≦y≦0.20, 0.95≦m≦1.08) and containing as a subcomponent 0.01 to 2.00 parts by weight of Mn (converted to MnO
2
), 0.10 to 4.00 parts by weight of SiO
2
and 0.01 to 1.00 parts by weight of Mo (converted to MoO) with respect to 100 parts by weight of the main component.
The Japanese Unexamined Patent Publication No. 1992-14704 discloses a dielectric ceramic composition containing as a main component a dielectric oxide having a composition expressed by (Sr
x
Ca
1-x
)(Zr
y
Ti
1-y
)O
3
(note that 0.59≦x≦0.65, 0≦y≦0.1) and containing less than 3.0 parts by weight of SiO
2
(note that 0 part by weight is not included) with respect to 100 parts by weight of the main component.
There have been disadvantages, however, that when producing the dielectric ceramic composition described in the publications in a usual method, an accelerating lifetime of insulation resistance after firing is insufficient in all cases, while, when producing a multi-layer ceramic capacitor having an internal electrode made by a base metal, such as nickel, by using the dielectric ceramic composition, the multi-layer ceramic capacitor to be obtained has lower credibility.
Note that the present inventors have proposed to add a rare-earth component, such as yttrium, in a composition system expressed by {(Sr
1-x
Ca
x
)O}
m
. (Ti
1-y
Zr
y
)O
2
wherein the mole ratio m is relatively low so that the accelerating lifetime of insulation resistance is improved (The Japanese Patent Application No. 2000-187800). However, when producing in a usual method, it was difficult to attain a longer lifetime even by adding a rare-earth component in a range where the mole ratio m satisfies 0.995≦m<1.08 which is relatively high.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of producing a dielectric ceramic composition having excellent resistance to reducing during firing and excellent capacity-temperature characteristics after firing, which furthermore improves an accelerating lifetime of insulation resistance and a method of producing an electronic device, such as a chip capacitor, having improved credibility.
To attain the above object, according to the present invention, there is provided a method of producing a dielectric ceramic composition containing a main component expressed by a composition formula of {(Sr
1-x
Ca
x
)O}
m
. (Ti
1-y
Zr
y
)O
2
wherein the mole ratio m satisfies 0.94<m<1.08, the code x satisfies 0≦x≦1.00 and the code y satisfies 0≦y≦0.20; and
a fourth subcomponent including an oxide of R (note that R is at least one selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu);
characterized by producing the dielectric ceramic composition by using a composition source material wherein at least a part of a fourth subcomponent source material for the fourth subcomponent is brought to react in advance with a main component source material for the main component.
According to the present invention, there is provided a method of producing an electronic device comprising a dielectric layer constituted by a dielectric ceramic composition containing a main component expressed by a composition formula of {(Sr
1-x
Ca
x
)O}
m
. (Ti
1-y
Zr
y
)O
2
, wherein the mole ratio m satisfies 0.94<m<1.08, the code x satisfies 0≦x≦1.00 and the code y satisfies 0≦y≦0.20; and a fourth subcomponent including an oxide of R (note that R is at least one selected from Sc, Y, La,
Fukui Takashi
Sato Akira
Takahashi Mikio
Watanabe Yasuo
Brunsman David
TDK Corporation
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