Dielectric ceramic composition for microwave

Details Dielectric ceramic composition for microwave Dielectric ceramic composition for microwave

2000-11-21

2001-08-14

Brunsman, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

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

Reexamination Certificate

active

06274526

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric ceramic composition for microwave which has a high specific dielectric constant ∈
r
and a large Qf value and of which the temperature coefficient &tgr;
f
of resonant frequency (f
0
) can easily be controlled.
2. Description of the Related Art
With the recent rapid progress of size reduction and digitalization in electronic technology, particularly in the field of communication components using microwaves, such as comunications satellite systems, mobile phones, and portable personal telephones, a small-size, high-performance and high-reliability microwave resonator has been demanded.
Dielectric ceramics used in microwave resonators are required to have such characteristics as a high specific dielectric constant ∈
r
a large Qf value, and of which the temperature coefficient &tgr;
f
of resonant frequency (f
0
) can easily be controlled.
Known dielectric ceramics for microwave applications include BaO—TiO
2
—Nd
2
O
3
—Bi
2
O
3
ceramics (see Japanese Patent Laid-Open No. 102003/81) and BaO—TiO
2
—Sm
2
O
3
—Ce
2
O
3
—Bi
2
O
3
ceramics (see Japanese Patent Laid-Open No. 187162/87). The problems of these conventional materials are: that their Qf value is as low as 4000 to 6500 for use as a dielectric in microwave communication and that their frequency-temperature characteristics are not easy to control in conformity with various cavities.
Japanese Patent Laid-Open No. 169326/95 discloses BaO—TiO
2
—Ln
2
O
3
ceramics (wherein Ln
2
O
3
represents Nd
2
O
3
and Pr
6
O
11
) containing Cr
2
O
3
, which have a specific dielectric constant ∈
r
of 91 to 93. However, their Qf value is low as 5700 to 6000, and the temperature coefficient &tgr;
f
of resonant frequency (f
0
) is from 6 to 9 ppm/° C. Therefore, they are inapplicable to filters whose cavities are made of iron or copper and which have a large &tgr;
f
.
SUMMARY OF THE INVENTION
An object of the present invention is to eliminate the problems associated with conventional dielectric cramics for microwave and to provide a dielectric ceramic composition for microwave which has a high specific dielectric constant ∈
r
and a large Qf value, and of which the temperature coefficient &tgr;
f
of resonant frequency (f
0
) can easily be controlled.
The present invention relates to a dielectric ceramic composition for microwave which comprises a basic composition represented by compositional formula: 2aBaO—bLn
2
O
3
—cBi
2
O
3
—2dTiO
2
, wherein Ln
2
O
3
represents (eNd
2
O
3
+fSm
2
O
3
+gEu
2
O
3
); a+b+c+d=1; and e+f+g=1, in which 0.0913<a≦0.1429, 0.2098<b<0.3003, 0<c<0.0856, 0.5714≦d<0.6043, 0.27<e<0.80, 0.18<f<0.70, 0<g<0.20, and 0.15<a/d<0.25.
The present invention provides a dielectric ceramic composition for microwave which has a high specific dielectric constant ∈
r
and a large Qf value and of which the temperature coefficient &tgr;
r
of resonant frequency (f
0
) can easily be controlled.
DETAILED DESCRIPTION OF THE INVENTION
The grounds for limitations imposed on the composition of the present invention will be explained. In the compositional formula: 2aBaO—bLn
2
O
3
—cBi
2
O
3
—2dTiO
2
, wherein Ln
2
O
3
represents (eNd
2
O
3
+fSm
2
O
3
+gEu
2
O
3
); a+b+c+d=1; and e+f+g=1), if a is less than 0.0913, the dielectric has a reduced Qf value. If it exceeds 0.1429, the dielectric constant is reduced. If b is less than 0.2098, the dielectric constant is reduced. If it is more than 0.3003, the Qf value is reduced. The presence of Bi
2
O
3
increases the dielectric constant and lowers the sintering temperature. If c exceeds 0.0856, however, the Qf value is considerably reduced. If d is less than 0.5714, the dielectric constant is reduced, and if it exceeds 0.6043, the Qf value is reduced. If e is less than 0.27, the dielectric constant is reduced. If it is more than 0.80, the Qf value is reduced. If f is less than 0.18, the Qf value is reduced. If it is more than 0.70, the dielectric constant is reduced. Incorporation of Eu
2
O
3
brings about a reduction in sintering temperature, but if g is more than 0.20, the dielectric constant is reduced. Where a/d is less than 0.15, the Qf value is reduced. If a/d is more than 0.25, the dielectric constant is reduced.
It is preferred for the dielectric ceramic composition of the present invention to further comprise SiO
2
as an auxiliary component. A preferred SiO
2
content (symbolized by “h”) is less than 3% by weight based on the basic composition of the ceramic composition according to the present invention. Being added in an amount of less than 3% based on the basic composition, SiO
2
is effective in broadening the firing temperature range in which preferred dielectric characteristics can be secured. Addition of 3% or more of SiO
2
is unfavorable because both the dielectric constant and the Qf value are reduced.
The dielectric ceramic composition of the present invention is preferably prepared, for example, as follows. Raw materials providing barium oxide, neodymium oxide, samarium oxide, europium oxide, bismuth oxide, titanium oxide, and SiO
2
(auxiliary component) are weighed out and wet mixed together with a solvent, such as water or an alcohol. The solvent is removed, and the solid is ground to powder. The powder is uniformly mixed with an organic binder, such as polyvinyl alcohol, and the miture is dried, ground, and pressed under, e.g., 100 to 1000 kg/cm
2
. The resulting body is fired in an oxygen-containing gas, such as air, at 1200 to 1500° C. to obtain the ceramic composition as desired.
The ceramic composition of the present invention is processed into a part of a dielectric resonator, a dielectric substrate, a multilayer ceramic device, and the like in a manner selected for the purpose. For example, the ceramic (after firing) is processed into appropriate shape and size, or the composition in a slurry form is formed into sheeting by a doctor blade process, or the sheet of the ceramic is laminated with an electrode layer.
The raw materials supplying barium, neodymium, samarium, europium, bismuth, titanium and silicon include not only their oxides, i.e., BaO, Nd
2
O
3
, Sm
2
O
3
, Eu
2
O
3
, Bi
2
O
3
, TiO
2
, and SiO
2
, but those capable of becoming the corresponding oxides on being fired, such as corresponding nitrates, caionates, hydroxides, chlorides, and organometallic compounds.


REFERENCES:
patent: 1-128309 (1989-05-01), None
patent: 3-192606 (1991-08-01), None
patent: 4-265269 (1992-09-01), None
patent: 5-97508 (1993-04-01), None
patent: 406080467 (1994-03-01), None
patent: 08017243 (1996-01-01), None

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