Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2000-11-06
2003-11-04
Brunsman, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C174S12000C, C174S1100AR, C361S321400, C361S321500
Reexamination Certificate
active
06642167
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to dielectric ceramic compositions which are suitable for the use in high-frequency regions, such as the microwave region and millimeter-wave region. In particular, the present invention relates to a dielectric ceramic composition which is suitable for miniaturization of products by laminating metallic electrode layers and sintering the laminate. The present invention also relates to a monolithic ceramic substrate, a ceramic electronic component and a monolithic ceramic component using the dielectric ceramic composition.
2. Description of the Related Art
In recent years, high-frequency dielectric ceramics have been widely used in, for example, dielectric resonators and dielectric substrates for monolithic integrated circuits (MICs). Major requirements for achieving miniaturization of the high-frequency dielectric ceramics are large dielectric constants, large Q values and small dependencies of dielectric constants on temperature.
Japanese Unexamined Patent Application Publication No. 6-333426 discloses a dielectric ceramic composition having a high specific dielectric constant (&egr;
r
) and a high Q value in which 0.5 percent by weight or less of MnO
2
and 1.2 percent by weight or less of Ta
2
O
5
are added to a main component represented by BaO-x {(1-y)TiO
2
.yZrO
2
}. This dielectric ceramic composition is obtained by sintering at a high temperature of at least 1,300° C., and has a specific dielectric constant (&egr;
r
) of at least 38 and a Q value of at least 8,000.
It is necessary to use inexpensive metals having low resistance, such as Ag and Cu, as electrodes for use in high-frequency regions, such as dielectric resonators. Thus, the metal and ceramic must be sintered at a temperature which is lower than the melting point of the metal. The melting points of these metals, however, are in a range of 960° C. to 1063° C. and are significantly lower than the above-described sintering temperature, that is, at least 1,300° C., for the dielectric ceramic composition. Accordingly, the above dielectric ceramic composition suitable for high-frequency regions precludes use of these metals as internal electrode materials.
Japanese Unexamined Patent Application Publication No. 8-45344 discloses a dielectric ceramic composition in which at least one auxiliary component of 0.1 to 5 percent by weight of GeO
2
and 0.5 to 5 percent by weight of CuO is added to a major component represented by ×BaO-yTiO
2
wherein x is in a range of 0.18 to 0.20, y is in a range of 0.80 to 0.82 and x+y=1. The addition of CuO and GeO
2
facilitates sintering at a lower temperature, that is, 1000° C.
The GeO
2
used in the above composition is, however, relatively expensive and exhibits poor water resistance. Since silver has a high electrical conductivity and is relatively inexpensive, it is most suitable as an electrode material which can be sintered in air. Silver, however, has a melting point of 962° C. and thus cannot be simultaneously sintered together with this dielectric ceramic composition.
Japanese Unexamined Patent Application Publication No. 5-325641 discloses a B-TiO
2
-Zro
2
dielectric ceramic composition which can be sintered at a low temperature of 900° C. by adding B
2
O
3
. B
2
O
3
, however, is hygroscopic. Even when a glass component containing excess B
2
O
3
is used instead of the addition of the B
2
O
3
, the composition is chemically unstable due to elution of the B
2
O
3
from the glass component. Moreover, the use of the glass component increases cost. Since this composition exhibits relatively low sinterability, the raw materials must be pulverized to an average grain size of 0.6 &mgr;m or less before sintering. This is also a factor increasing the cost.
Japanese Unexamined Patent Application Publication No. 10-167817 discloses a dielectric ceramic composition containing 100 parts by weight of BaO-x(Ti
1-a
Zr
a
)O
2
as a major component wherein 3.5≦×≦4.5 and 0≦a≦0.20, 4 to 30 parts by weight, on a ZnO basis, of a zinc compound, 1 to 20 parts by weight, on a B
2
O
3
basis, of a boron compound, 1 to 10 parts by weight, on an alkali metal carbonate basis, of an alkali metal compound, and 0.01 to 7 parts by weight, on a CuO basis, of a copper compound. This dielectric ceramic composition can be sintered at 900° C. by the effects of these auxiliary components. This dielectric ceramic composition also contains the boron compound. Since B
2
O
3
in the composition is chemically unstable, the composition exhibits deterioration of insulation resistance in high-temperature, high-humidity environments.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a dielectric ceramic composition which can be sintered together with low-resistance electrode materials, such as silver and copper, at a low temperature of not more than 1,000° C., which exhibits a high dielectric constant, a high Q value, a small rate of change in dielectric property with temperature, superior high-frequency characteristics and superior reliability in high-temperature, high-humidity environments.
It is another object of the present invention to provide a monolithic ceramic substrate, a ceramic electronic component and a monolithic ceramic electronic component which use the above dielectric ceramic composition and exhibit superior high-frequency characteristics and superior reliability in high-temperature, high-humidity environments.
According to an aspect of the present invention, a dielectric ceramic composition comprises 100 parts by weight of major component represented by the formula BaO-x {(1-y)TiO
2
.yZrO
2
} wherein 3.5≦×≦4 and 0≦y≦0.2, a components added to the main component comprising about 5 to 30 parts by weight, on a ZnO basis, of a zinc compound, about 0.5 to 6 parts by weight, on a SiO
2
basis, of a silicon compound, about 0.1 to 3 parts by weight, on an oxide (R
2
O) basis, of an alkali metal compound wherein R is alkali metal, about 0.1 to 7 parts by weight, on a CuO basis, of a copper compound, and about 0.1 to 6 parts by weight of, on a V
2
O
5
basis, vanadium compound or on a Bi
2
O
3
basis, a bismuth compound.
In this dielectric ceramic composition, the specific amounts of the auxiliary components are compounded to the major component represented by the above formula. This dielectric ceramic composition can be sintered at 1,000° C. or less, and exhibits a high dielectric constant, that is, of approximately 30 or more, and a high Q value, that is, of approximately 2,000 or more at 8 GHz.
Since the dielectric ceramic composition does not contain B
2
O
3
, the composition exhibits high stability in high-temperature, high-humidity environments.
Since the dielectric ceramic composition can be sintered at lower temperatures, the composition can be simultaneously sintered together with a low-resistance inexpensive metals, such as silver and copper. Simultaneous sintering of the dielectric ceramic composition of the present invention and the low-resistance metals facilitates miniaturization of monolithic ceramic electronic components.
Reasons for the limitation of the composition in the present invention are as follows. At x<3.5 or x>4.5, the temperature coefficient of the resonant frequency significantly shifts to the positive side, and the dielectric ceramic composition exhibits a large dependence of the dielectric constant on the temperature.
When ZrO
2
is partially replaced with TiO
2
, the temperature coefficient of the resonant frequency shifts to the negative side. At y>0.2, however, the dielectric constant &egr; and the Q value decrease.
Preferably, 4.30≦×≦4.4 and 0<y≦0.1. In this case, the composition is composed of a Ba
2
Ti
9
O
20
single phase, and exhibits a higher Q value.
The zinc compound contributes to an increased Q value and enhanced sinterability at low temperatures. When the content of the zinc compound is less than about 5 parts by weight, the composition does not have thes
Sugimoto Yasutaka
Tsukizawa Takayuki
Brunsman David
Dickstein , Shapiro, Morin & Oshinsky, LLP
Murata Manufacturing Co. Ltd.
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