Stock material or miscellaneous articles – Composite – Of metal
Reexamination Certificate
1999-04-06
2001-07-10
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of metal
C428S432000, C501S119000, C501S152000, C501S153000
Reexamination Certificate
active
06258462
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a dielectric ceramic composition useful for a device used as a resonator, a filter, an antenna, a capacitor, an inductor, a circuit board or the like in a highly frequency band such as microwave, millimeter wave, etc. The present invention also relates to a device for a communication apparatus including such a dielectric ceramic composition.
BACKGROUND OF THE INVENTION
Recently, dielectric ceramics have been used widely as filter materials for communication apparatus with the spread of mobile communication. Such dielectric ceramics are required to have a high dielectric constant (&egr;
r
), a low dielectric loss (tan &dgr;), i.e. a high Q value that is an inverse number of the dielectric loss, and a small absolute value of the temperature coefficient at resonance frequency (TCF).
It is predicted that the frequency of communication systems will become higher and the shorter wavelength of the radio wave will be used. Therefore, when machining accuracy and conductor loss are taken into consideration, dielectrics having a low dielectric constant increasingly will be demanded. Conventional examples of a dielectric ceramic composition having a low dielectric constant include MgTiO
3
—CaTiO
3
based dielectric ceramic compositions, Al
2
O
3
based dielectric ceramic compositions or the like (disclosed in, for example, Japanese Patent Publication (Tokkai Hei) No. 6-92727). Furthermore, as the dielectric ceramic composition that has a low dielectric constant and can be sintered simultaneously with a conductor such as Ag having high conductivity at low temperature of 1100° C. or less, a composition in which glass is added to Al
2
O
3
is well known.
However, in the MgTiO
3
—CaTiO
3
based dielectric ceramic composition, the loss is low and the TCF is close to zero, but the dielectric constant is as high as about 20. Furthermore, in the Al
2
O
3
based dielectric ceramic composition, the loss is low and the dielectric constant is as small as about 10, but the TCF has a large negative value. Similarly, in the composition in which glass is added to Al
2
O
3
, the dielectric constant is as small as 10 or less, but the TCF has a large negative value. From such circumstances, dielectric ceramic compositions having a dielectric constant lower than that of the MgTiO
3
—CaTiO
3
based composition and a practical level of loss and TCF, and dielectric ceramic compositions having a dielectric constant as high as that of the composition in which glass is added to Al
2
O
3
and a TCF closer to zero have been demanded.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a dielectric ceramic composition having a low dielectric constant, low loss and further a small absolute value of the temperature coefficient at resonance frequency (TCF), and to provide a device for communication apparatus using the dielectric ceramic composition and suitably used in a high frequency band such as millimeter wave, microwave, etc.
In order to achieve the object, the dielectric ceramic composition of the present invention comprises Al
2
O
3
, MgO and RO
n
. The Al
2
O
3
, MgO and RO
n
are expressed by a composition formula: xAlO
3/2
—yMgO—zRO
n
, where x≧55, y≧0.5, z≧0.5 and x+y+z=100.
Herein, R is at least one element selected from La, Ce, Pr, Nd, Sm, Eu, Gd and Tb; and n is a value stoichiometrically determined in accordance with the valence of the selected R. The n is expressed by m/2 when the valence of R is m. For example, when the valence of R is 3, n is 3/2; and when the valence of R is 4, n is 2.
Such a dielectric ceramic composition makes it possible to produce various kinds of devices having a low dielectric constant, low loss and yet a small absolute value of the temperature coefficient at resonance frequency (TCF). It is preferable that the dielectric ceramic composition comprises the component expressed by the above-mentioned composition formula as a main component.
On the other hand, the dielectric ceramic composition can be used in a form in which a glass composition is added. In this case, it is preferable that the dielectric ceramic composition comprises a glass composition containing at least one selected from SiO
2
and B
2
O
3
in an amount of 70 weight % or less as a second component in addition to the first component expressed by the above-mentioned composition formula. Furthermore, it is preferable that the second component comprises at least one oxide selected from Al
2
O
3
, ZrO
2
, TiO
2
, BaO, SrO, CaO, MgO, La
2
O
3
, PbO, ZnO, Li
2
O, Na
2
O and K
2
O.
More specifically, it is preferable that the second component has any of the below mentioned compositions I to III. Moreover, % given herein means weight %.
[Composition I] SiO
2
: 20 to 70%, B
2
O
3
: 0 to 35%, Al
2
O
3
: 1 to 35%, MO: 0 to 50%
[Composition II] SiO
2
: 30 to 60%, B
2
O
3
: 2 to 8%, Al
2
O
3
: 2 to 10%, MO: 20 to 50%, La
2
O
3
: 5 to 15%
[Composition III] SiO
2
: 30 to 70%, B
2
O
3
: 10 to 35%, Al
2
O
3
: 5 to 30%, MO: 2 to 15%, ZrO
2
: 0.5 to 13%
In the above, M is at least one element selected from Ca, Sr and Ba.
Moreover, the R is preferably at least one element selected from La, Nd and Sm, although it is not limited thereto. Furthermore, x, y and z in the above-mentioned composition formula are preferably in the ranges: 65.0≦x≦98.5, 1.5≦y≦30.0 and 1.5≦z≦35.0.
Furthermore, it is preferable that the dielectric composition comprises a crystal phase comprising the first component and a glass phase comprising the second component. It is further preferable that the crystal phase comprises a magneto-plumbite phase and the magneto-plumbite phase comprises Al
2
O
3
.
With the foregoing in mind, according to another aspect of the present invention, the dielectric ceramic composition comprises a crystal phase and a glass phase. The crystal phase comprises a magneto-plumbite phase and the magneto-plumbite phase comprises Al
2
O
3
.
Furthermore, it is preferable that the crystal phase comprises at least one phase selected from a corundum phase, a spinel phase, a trydimite phase, a cristobalite phase and a perovskite phase. Furthermore, as mentioned above, it is preferable that the composition contains MgO, RO, and at least one selected from SiO
2
and B
2
O
3
. R and n herein are the same as in the above.
According to another aspect of the present invention, a device for communication apparatus of the present invention comprises the dielectric ceramic composition. This device is suitably used in a GHz band, in particular, microwave, millimeter wave, etc. Furthermore, the device is constituted appropriately in combination with a metal conductor. For example, the above-mentioned dielectric ceramic composition is laminated to one or more metal conductors, which is used as a laminated device. This laminated device preferably comprises a dielectric layer comprising the dielectric ceramic composition and a conductive layer comprising at least one metal selected from Ag, Au, Cu and Pd as a main component. Examples of the devices of the present invention include a dielectric filter, a dielectric resonator, a dielectric antenna, a capacitor, an inductor and a circuit board or the like.
REFERENCES:
patent: 5350639 (1994-09-01), Inoue et al.
patent: 0 582 274 A1 (1994-02-01), None
patent: 60-21854 (1983-07-01), None
Kagata Hiroshi
Katsumura Hidenori
Jones Deborah
Matsushita Electric - Industrial Co., Ltd.
McNeil Jennifer
Merchant & Gould P.C.
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