Dielectric ceramic composition for microwave

The present invention relates to a dielectric ceramic composition for microwave which consists of BaO, Sm.sub.2 O.sub.3, TiO.sub.2 and PbO, and has a compositional formula of x(Ba.sub.1-.alpha., Pb.sub..alpha.)O-- ySm.sub.2 O.sub.3 -zTiO.sub.2, wherein 6 mol % .ltoreq.x.ltoreq.20 mol %, 6 mol %.ltoreq.y.ltoreq.20 mol %, 60 mol %.ltoreq.z.ltoreq.75 mol % and 0 mol % .ltoreq..alpha..ltoreq.0.2 mol %. Accordingly, since the dielectric ceramic composition for microwave according to the present invention has the dielectric constant more than 85, the temperature factor of the resonant frequency within .+-.5 ppm/.degree.C., and the quality factor more than 6000 in 1 GHz, it can be utilized in the filter for microwave, the dielectric for the resonator, the laminated ceramic capacitor, the dielectric for the filter for electromagnetic wave obstacle and the dielectric for capacitor. And also, since it is possible to reduce the problems to the volatilization of the plumbic oxide and the bismuth oxide, the dielectric ceramic composition for microwave according to the present invention can be made by a general manufacturing process and can reduce the use of the elements detrimental to the human body.

BACKGROUND OF THE INVENTION 
The present invention relates to a dielectric ceramic composition for 
microwave frequency, and more particularly to a dielectric ceramic 
composition having a high dielectric constant, a low temperature 
coefficient of the resonant frequency and a high quality factor(Q) for 
microwave frequency. 
Recently, as radio communication means such as a car-phone, a portable 
telephone, a radio telephone, a satellite broadcasting receiver, etc. are 
used widely, microwave dielectric ceramics are also used widely for 
microwave components such as band-pass filters, substrates and voltage 
controlled oscillators(VCOs), etc with development of microwave integrated 
circuits. 
The basic materials for microwave components should have the high 
dielectric constant, the quality factor should be high more than 5000, and 
the temperature coefficient of the resonant frequency should be low to the 
extent of .+-.5 ppm/.degree.C. at microwave frequency. Therefore, 
microwave components using resonators, generally, are formed of the 
dielectric ceramics having the high dielectric constant such as 
BaO-Nd.sub.2 O.sub.3 -TiO.sub.2 system, BaO-Sm.sub.2 O.sub.3 -TiO.sub.2 
system, etc. 
The dielectric constant(.epsilon.) of dielectric ceramics such as 
BaO-Nd.sub.2 O.sub.3 -TiO.sub.2 system, BaO-SM.sub.2 O.sub.3 -TiO.sub.2 
system, etc. is within the extent of 60 to 80 and the quality factor(Q) is 
high to the extent of 5000 in 1 GHz, but the temperature coefficient of 
the resonant frequency(r.sub.f) is high to .+-.30 ppm/.degree.C. 
Accordingly, these dielectric ceramics had many problems for pratical 
materials at microwave frequency. 
PbO-ZrO.sub.2 -CaO system having the high dielectric constant is shown in 
JAPANESE JOURNAL OF APPLIED PHYSICS, VOL. 30, NO. 9B, pp. 
2343-2346(1991.11) by Junichi Kato, et al. The dielectric constant of 
PbO-ZrO.sub.2 -CaO system is high more than 90 but its quality factor is 
low to the extent of 1000 to 3500, and its loss factor is high at high 
frequency more than 3 GHz, and therefore it has a defect that a loss of 
microwave components such as band pass filters(BPFs) and a voltage 
controlled oscillators(VCOs) become raised. 
A composition of BaO-PbO-Nd.sub.2 O.sub.3 -TiO.sub.2 system is shown in 
JOURNAL OF AMERICA CERAMIC SOCIETY, VOL. 67, NO. 4, pp. 278-281 by Wakino 
et al. Said composition of BaO-PbO-Nd.sub.2 O.sub.3 -TiO.sub.2 system adds 
PbO to the composition of BaO-Nd.sub.2 O.sub.3 -TiO.sub.2 system and it 
has a composition ratio of 0.5BaO-0.5PbO-1.0Nd.sub.2 O.sub.3 
-5.0TiO.sub.2. Said composition of BaO-PbO-Nd.sub.2 O.sub.3 -TiO.sub.2 
system is its dielectric constant raised to the extent of 85-90 by said 
PbO and its quality factor also is high to the extent of 4000-5000. 
But, while the composition ratio of PbO of the composition of the 
BaO-PbO-Nd.sub.2 O.sub.3 -TiO.sub.2 system is very high, the PbO is very 
volatile strong and an amount being volatilized becomes much in proportion 
to a quantity of PbO. Accordingly, there is a problem that not only the 
components produced by composition is difficult to have an uniform 
composition ratio, but also they can exert a fatal influence upon the 
human body in the manufacturing process. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide the 
dielectric ceramic composition for microwave frequency in which the 
dielectric constant and the quality factor in the high frequency wave are 
high and the temperature coefficient of the resonant frequency is low so 
that the components for microwave can be produced. 
A further object of the invention is to provide the dielectric ceramic 
composition for microwave components which allows the composition ratio of 
PbO to be small and the volatilized quantity of Pb harmful to the human 
body to be small and thereby allows the elements having the uniform 
composition ratio to be produced. 
A dielectric ceramic composition for microwave components according to an 
embodiment of the present invention for achieving the said objects 
consists of BaO, Sm.sub.2 O.sub.3, TiO.sub.2 and PbO or a compound of 
them, and has a compositional formula of x(BaO).sub.1-.alpha. 
(PbO).sub..alpha. !-ySm.sub.2 O.sub.3 -zTiO.sub.2, wherein 6 mol 
%.ltoreq.x..ltoreq.20 mol %, 6 mol %.ltoreq.y.ltoreq.20 mol %, 60 mol 
%.ltoreq.z.ltoreq.75 mol % and 0 mol %.ltoreq..alpha..ltoreq.0.2 mol %. 
A dielectric ceramic composition for microwave frequency according to a 
further embodiment of the present invention for achieving said objects 
includes BaO, Sm.sub.2 O.sub.3, TiO.sub.2 and PbO as chief ingredients and 
further includes SrO, ZrO.sub.2, MnO.sub.2, MgO, ZnO, Bi.sub.2 O.sub.3, 
La.sub.2 O.sub.3, CeO.sub.2, etc. or the compound of them as additives to 
selectively add one or more of said additives into said chief ingredients, 
and thereby provides a compositional formula of 
x(BaO).sub.1-.alpha.-.beta. (PbO).sub..alpha. (MO).sub..beta. 
!-y(Sm.sub.2 O.sub.3).sub.1-.gamma.-.delta. (La.sub.2 
O.sub.3).sub..gamma. (CeO.sub.2).sub..delta. !-zTiO.sub.2, wherein 
(MO).sub..beta. is ZrO.sub.2, MnO.sub.2, MgO, ZnO or Bi.sub.2 O.sub.3, 6 
mol %.ltoreq.x.ltoreq.20 mol %, 6 mol %.ltoreq.y.ltoreq.20 mol %, 60 mol 
%.ltoreq.z.ltoreq.75 mol %, 0 mol %.ltoreq..alpha..ltoreq.0.2 mol %, 0 mol 
%.ltoreq..beta..ltoreq.0.3 mol %, 0 mol %.ltoreq..gamma..ltoreq.0.3 mol %, 
0 mol %.ltoreq..delta..ltoreq.0.3 mol %, and x+y+z=100 mol %. 
Other objects, features and advantages of the present invention will be 
apparent from the following description.