Dielectric ceramic compositions

This invention provides a dielectric ceramic composition which has a high dielectric constant and a high Q value, and also has lower temperature coefficient of resonance frequency. The dielectric ceramic composition is attained by sintering composition which comprises a first component from 40 to 98 wt % and a second component from 2 to 60 wt %. The first component is represented by the following formula, EQU Ca{(Mg.sub.1/3 Nb.sub.2/3).sub.1-x Ti.sub.x }O.sub.3 where 0.ltoreq.x.ltoreq.0.50. The second component includes at least one element selected from the group consisting of SiO.sub.2 and B.sub.2 O.sub.3.

FIELD OF THE INVENTION 
This invention relates to dielectric ceramic compositions which are used 
for filters and resonant devices that operate in the microwave region. 
BACKGROUND OF THE INVENTION 
Recently, along with the advancement in communication using electromagnetic 
waves in the microwave frequency region, for example, in automobile 
telephones, in portable telephones, or in satellite broadcasts, the 
terminal apparatus is required to be smaller. In order to attain this 
goal, each component comprising the terminal apparatus must be 
miniaturized. In those apparatus, a dielectric ceramic is inserted in 
filters or in resonant devices. When using the same resonance mode, the 
size of the dielectric resonator is inversely proportional to the square 
root of the dielectric constant (.epsilon..sub.r) attributed to the 
dielectric material. Therefore, a material having a high dielectric 
constant is needed to manufacture a compact-sized dielectric resonator. In 
addition, the dielectric material for the dielectric resonator must have 
low loss in the microwave region. In other words, the dielectric material 
must have a high Q value and a low temperature coefficient (.tau..sub.f) 
of a resonance frequency. Q value means reciprocal of dielectric loss tan 
.delta.. 
As materials with a high dielectric constant, (Pb,Ca) ZrO.sub.3 are 
disclosed in Published Examined Japanese Patent Application No. (Tokkai 
Hei) 4-65021. These materials have high dielectric constants over 100, 
high Q values of about 800 in 2-4 GHz, and lower temperature coefficients 
of resonance frequencies. 
On the other hand, conductors and dielectric ceramics are laminated to 
miniaturize a resonant device. The conductor should have a higher 
conductivity when used in a high frequency (e.g. microwave) region. 
Therefore Cu, Au, Ag, or alloys of such metals should be used. These 
metals must be sintered carefully in a condition where the metal of the 
conductor does not melt or oxize, because the dielectric ceramic need to 
be fired carefully along with the metal conductors to be laminated. The 
material must be fired at lower temperatures (for Cu, at 1083.degree. C. 
or less; Au, at 1063.degree. C. or less; Ag, at 961.degree. C. or less), 
and when using Cu for an electrode, the partial pressure of oxygen should 
be lower. Bi.sub.2 O.sub.3 --CaO--Nb.sub.2 O.sub.5 has been disclosed in 
U.S. Pat. No. 5,273,944, as a microwave dielectric ceramic. 
Though the above-mentioned ceramic made of Bi.sub.2 O.sub.3 --CaO--Nb.sub.2 
O.sub.5 can be sintered at about 1000.degree. C., the first component 
(Bi.sub.2 O.sub.3) evaporates when fired. Thus the dielectric properties, 
with regard to the firing temperature, are unstable. 
SUMMARY OF THE INVENTION 
It is an object of this invention to solve the above-mentioned problems by 
providing dielectric ceramic compositions that do not contain Bi.sub.2 
O.sub.3 as the first components and which can be sintered at a lower 
temperature. In addition, they have high dielectric constants and high Q 
values, and also satisfy the requirement of a lower temperature 
coefficient of a resonance frequency. 
In order to accomplish these and other objects and advantages, a first 
embodiment of the dielectric ceramic compositions of this invention shown 
in the following formula comprises as the first component calcium oxide, 
magnesium oxide, niobium oxide, titanium oxide, 
EQU Ca{(Mg.sub.1/3 Nb.sub.2/3).sub.1-x Ti.sub.x }O.sub.3 
wherein 0.ltoreq.x.ltoreq.0.50. The dielectric ceramic composition 
comprises as a second component at least one element selected from the 
group consisting of SiO.sub.2 and B.sub.2 O.sub.3. The first component is 
present in an amount of from 40 to 98 weight percent (wt %), and the 
second component is present in an amount of from 2 to 60 wt %. 
It is preferable in this invention that the second component comprises 
SiO.sub.2 in an amount of from 30 to 65 wt %, B.sub.2 O.sub.3 in an amount 
of from 10 to 35 wt %, Al.sub.2 O.sub.3 in an amount of from 5 to 30 wt %, 
ZrO.sub.2 in an amount of from 0 to 8 wt %, and MO in an amount of from 0 
to 13 wt %, where M is at least one element selected from the group 
consisting of Ca, Sr, and Ba. 
Also, it is preferable that the second component contains at least one 
oxide selected from the group consisting of Li.sub.2 O, Na.sub.2 O, 
K.sub.2 O, PbO, and ZnO in the amount of 0 to 3 wt %. 
Furthermore, it is preferable in this invention that the dielectric 
constant (.epsilon..sub.r) of the dielectric ceramic composition is from 
14 to 40, Qf product is from 1000 to 30000 GHz, and the temperature 
coefficient (.tau..sub.f) of the resonance frequency is from -50 to +50 
ppm/.degree.C. 
Next, a second embodiment of the dielectric ceramic compositions of the 
invention comprises calcium oxide, magnesium oxide, niobium oxide, and 
titanium oxide as the first component shown in the following formula, 
EQU Ca{Mg.sub.1/3 Nb.sub.2/3).sub.1-x Ti.sub.x }O.sub.3 
wherein 0.ltoreq.x.ltoreq.0.50. In the second embodiment, aluminum oxide is 
also comprised in the first component. The dielectric ceramic composition 
comprises at least one element selected from the group consisting of 
SiO.sub.2 and B.sub.2 O.sub.3 as a second component. The first component 
is present in an amount of from 30 to 98 wt %, and the second component is 
present in an amount of from 2 to 70 wt %. 
It is preferable in this invention that the second component comprises 
SiO.sub.2 in an amount of from 30 to 65 wt %, B.sub.2 O.sub.3 in an amount 
of from 10 to 35 wt %, Al.sub.2 O.sub.3 in an amount of from 5 to 30 wt %, 
ZrO.sub.2 in an amount of from 0 to 8 wt %, and MO in an amount of from 0 
to 13 wt %, where M is at least one element selected from the group 
consisting of Ca, Sr, and Ba, because when the second component is fired 
to be glass, the melting point can be lowered. 
Also it is preferable that the second component contains at least one oxide 
selected from the group consisting of Li.sub.2 O, Na.sub.2 O, K.sub.2 O, 
PbO, and ZnO, and the oxide is present in an amount of from 0 to 3 wt %. 
It is preferable in this invention that the dielectric constant 
(.epsilon..sub.r) of the dielectric ceramic composition is from 9 to 24, 
Qf product is from 1000 to 30000 GHz, and the temperature coefficient 
(.tau..sub.f) of the resonance frequency is from -50 to +50 ppm/.degree.C. 
The dielectric ceramic composition of the first embodiment of this 
invention comprises Ca{(Mg.sub.1/3 Nb.sub.2/3).sub.1-x Ti.sub.x }O.sub.3 
as the first component which has a high dielectric constant and superior 
microwave dielectric properties, where 0.ltoreq.x.ltoreq.0.50. As the 
second component, glass promotes sintering. Thus the dielectric ceramic of 
the invention sinters at about 1000.degree. C., and it has a high 
dielectric constant, a high Q value, and a low temperature coefficient of 
resonance frequency. Also, the dielectric ceramic composition does not 
comprise Bi.sub.2 O.sub.3 as the first component, so that it is stable in 
dielectrtic properties relative to the firing temperature. 
The dielectric ceramic composition of the second embodiment of this 
invention preferably comprises aluminum oxide as a first component because 
it has a lower dielectric constant. Thus it is possible to control 
dielectric constant without sacrificing sintering temperature, Q value, or 
temperature coefficient. Furthermore, glass is added as the second 
component of the embodiment. Thus the dielectric ceramic of the invention 
sinters at about 1000.degree. C., and it has a high dielectric constant, a 
high Q value, and a low temperature coefficient of resonance frequency. 
Furthermore, it is preferable that the dielectric ceramic compositions of 
the first and the second embodiments comprise SiO.sub.2 from 30 to 65 wt 
%, B.sub.2 O.sub.3 from 10 to 35 wt %, Al.sub.2 O.sub.3 from 5 to 30 wt %, 
ZrO.sub.2 from 0 to 8 wt %, and MO from 0 to 13 wt %, where M is at least 
one element selected from the group consisting of Ca, St, and Ba. Such 
dielectric ceramic compositions can be sintered at a lower temperature, 
and have a high dielectric constant, a high Qf product, and a low 
temperature coefficient of resonance frequency. In other words, they have 
excellent microwave dielectric properties. 
Also, it is preferable that the second component contains at least one 
oxide selected from Li.sub.2 O, Na.sub.2 O, K.sub.2 O, PbO, and ZnO in the 
amount of 0 to 3 wt %. Such dielectric ceramic compositions can be 
sintered at a relatively low temperature, and have a high dielectric 
constant, a high Qf product, and a low temperature coefficient of 
resonance frequency. In other words, they have excellent microwave 
dielectric properties. 
Furthermore, it is preferable in the dielectric ceramic compositions of 
this invention that the dielectric constant (.epsilon..sub.r) is from 14 
to 40, Qf product is from 1000 to 30000 GHz, and the temperature 
coefficient (.tau..sub.f) of the resonance frequency is from -50 to +50 
ppm/.degree.C. It is further preferable that the dielectric constant 
(.epsilon..sub.r) is from 9 to 24, Qf product is from 1000 to 30000 GHz, 
and the temperature coefficient (.tau..sub.f) of the resonance frequency 
is from -50 to +50 ppm/.degree.C. Such dielectric ceramic compositions can 
be applied to multilayer microwave resonant devices. As a result, 
high-frequency devices like filters and duplexers can have a compact size 
and high performance. 
Furthermore the dielectric ceramic compositions of this invention can be 
applied to multilayer microwave resonant devices using metals like Au, Ag, 
or Cu as inner conductors. As a result, high-frequency devices like 
filters and duplexers can be miniaturized and have excellent performance.

DETAILED DESCRIPTION OF THE INVENTION 
This invention will be described by referring to the following examples and 
attached figures. The examples are not intended to limit the invention in 
any way. 
Example 1 
Example 1 is an example of the first embodiment of this invention. 
Starting materials used for the first component were CaCO.sub.3, MgO, 
Nb.sub.2 O.sub.5, and TiO.sub.2 of high chemical purity (99 wt % or more). 
After the materials were purified, the composition was weighed so that x 
in the formula Ca{(Mg.sub.1/3 Nb.sub.2/3).sub.1-x Ti.sub.x }O.sub.3 could 
be predetermined. Then the powders of the above-mentioned materials were 
mixed with pure water and zirconia balls by using a ball mill for 17 
hours. The mixed slurry was dried and calcined in an alumina crucible for 
2 hours at 1000.degree. to 1300.degree. C. The calcination product was 
crushed and then pulverized in the ball mill for 17 hours, then dried to 
produce a powder of the first component. 
Powders to be used as the second component were produced as follows. 
Starting materials were SiO.sub.2, B.sub.2 O.sub.3, Al.sub.2 O.sub.3, 
ZrO.sub.2, BaCO.sub.3, SrCO.sub.3, CaCO.sub.3, Li.sub.2 O, ZnO and PbO of 
high chemical purity (99 wt % or more). After being purified, the 
materials were weighed so as to make the various compositions shown in 
Table 1, and mixed with ethanol as a solvent by using a ball mill and then 
dried. The mixed slurry was melted in a crucible at a temperature from 
1000.degree. to 1200.degree. C., and quenched. After being crushed, the 
product was pulverized by using the ball mill, then dried. The composition 
of the second component is shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Composition of second component (wt %) 
No. SiO.sub.2 
B.sub.2 O.sub.3 
Al.sub.2 O.sub.3 
ZrO.sub.2 
BaO SrO CaO Li.sub.2 O 
ZnO PbO 
__________________________________________________________________________ 
A 50 20 10 20 
B 60 10 20 
C 50 30 20 10 
D 45 27 20 3 5 
E 45 26 20 3 5 1 
__________________________________________________________________________ 
The powders of the first component and second component were wet-mixed in a 
ball mill and dried. Next, after adding 6 wt % of 5 wt % of aqueous 
solution made of polyvinyl alcohol into this powder as a binder, it was 
mixed, granuated through a 32 mesh screen and press-molded with 100 MPa 
into a cylindrical shape of 13 mm in diameter and about 5 mm in thickness. 
The pressed body was heated at a temperature of 600.degree. C. for 3 
hours, and when the binder was burnt, the pressed body was put into a 
magnesia vessel, lidded and fired at various temperatures of from 
800.degree. to 1400.degree. C. for 2 hours. A sintered body, which was 
fired at a temperature at which the density reached the highest value, was 
measured with respect to dielectric properties in the microwave region. 
Resonance frequency and Q value were measured by dielectric resonator 
method. Dielectric constant (.epsilon..sub.r) was calculated by the size 
of the sintered body and the resonance frequency. The resonance frequency 
was from 4 to 8 GHz. Furthermore, resonance frequencies at -25.degree. C., 
20.degree. C., and 85.degree. C. were measured, and the temperature 
coefficient of the resonance frequencies (.tau..sub.f) were calculated by 
the values using the method of least squares. The results are shown in 
Table 2. In Table 2, Qf product is the product of the Q value and 
frequency (f) measured. The frequency (f) varies in from 4 to 8 GHz, 
according to sizes and shapes of the samples. Therefore Qf product was 
used to calculate without being influenced by the sizes or shapes of the 
samples. This method is well known to those of ordinary skill in the art. 
TABLE 2 
__________________________________________________________________________ 
Composition Dielectric properties 
first second Sintering Qf 
Sample 
component 
component 
temperature 
product 
.tau.f 
No. x wt (%) 
type 
wt (%) 
.degree.C. 
.epsilon.r 
GHz ppm/.degree.C. 
__________________________________________________________________________ 
1 0.0 80 D 20 900 14 4500 -41 
2 0.3 80 D 20 900 22 3800 -3 
3 0.5 80 D 20 900 29 2400 +48 
4# 0.55 
80 D 20 900 32 1800 +79 
5# 0.3 100 D 0 1400 42 34000 -12 
6 0.3 98 D 2 1150 40 18000 -10 
7 0.3 70 D 30 875 19 2900 -8 
8 0.3 40 D 60 850 14 1200 -7 
9# 0.3 30 D 70 850 12 400 -7 
10 0.3 80 A 20 1075 23 4100 +2 
11 0.3 80 B 20 875 20 2700 +4 
12 0.3 80 C 20 950 23 3900 -2 
13 0.3 80 E 20 875 22 3700 -5 
__________________________________________________________________________ 
The numbers followed by a # show comparative examples. 
As shown in Table 2, it was confirmed that the ceramic compositions of this 
Example are sinterable at temperatures from 850.degree. to 1150.degree. 
C., in which the dielectric constants (.epsilon..sub.r) are from 14 to 40, 
the Qf products are from 1200 to 18000 GHz, the temperature coefficients 
of resonance frequency (.tau..sub.f) are from -41 to +48 ppm/.degree.C. 
Thus it was confirmed that the ceramic compositions have excellent 
microwave dielectric properties. With respect to second components, as 
shown in Samples Nos. 10 to 13, the various components were excellent in 
dielectric properties. As a result, it was demonstrated that at least 
either SiO.sub.2 or B.sub.2 O.sub.3 should be included in the composition. 
As shown in Sample No.4, if x in the formula Ca{(Mg.sub.1/3 
Nb.sub.2/3).sub.1-x Ti.sub.x }O.sub.3, which represents the first 
component, is over 0.5, it becomes unpractical because the temperature 
coefficient of the resonance frequency becomes larger than +50 
ppm/.degree.C. As shown in Sample No.5, if the quantity of the second 
component is less than 2 wt %, the purpose of the invention cannot be 
obtained because firing temperature is 1400.degree. C. As shown in Sample 
No.9, if the quantity of the second component is over 60 wt %, it is 
undesirable because the Qf product becomes 1000 GHz or less. 
Example 2 
Example 2 is a preferable example of the first embodiment of this 
invention. 
Samples were prepared and their properties were varied in accordance with 
Example 1. Only the second components were replaced by those shown in 
Table 3. The results are shown in Table 4. 
TABLE 3 
______________________________________ 
Composition of second component (wt %) 
No. SiO.sub.2 
B.sub.2 O.sub.3 
Al.sub.2 O.sub.3 
ZrO.sub.2 
BaO SrO CaO 
______________________________________ 
F 45 27 20 3 5 
G 55 20 15 4 6 
H 35 30 25 6 1 1 
I 25 35 30 4 3 3 
J 70 15 10 2 3 
K 60 7 30 3 5 
L 35 40 17 3 5 
M 60 27 2 5 3 3 
N 40 20 35 2 1 2 
O 45 20 20 10 5 
P 40 25 17 3 5 10 
______________________________________ 
TABLE 4 
__________________________________________________________________________ 
Composition Dielectric properties 
first second Sintering Qf 
Sample 
component 
component 
temperature 
product 
.tau.f 
No. x wt % type 
wt % .degree.C. 
.epsilon.r 
GHz ppm/.degree.C. 
__________________________________________________________________________ 
14 0.3 80 F 20 900 22 3800 -3 
15 0.3 80 G 20 950 24 4000 -2 
16 0.3 65 G 35 875 19 3300 -5 
17 0.45 
65 G 35 875 23 2800 +41 
18 0.3 90 H 10 900 33 5100 -10 
19 0.3 80 H 20 875 21 3100 -4 
20# 0.3 90 I 10 950 32 500 -10 
21# 0.3 60 J 40 1100 20 2900 -7 
22# 0.3 60 K 40 1125 21 3100 -3 
23# 0.3 90 L 10 925 31 200 -11 
24# 0.3 80 M 20 950 22 400 -3 
25# 0.3 60 N 40 1150 19 1900 -1 
26# 0.3 55 O 45 1125 17 1700 +1 
27# 0.3 60 P 40 1125 17 2000 +2 
__________________________________________________________________________ 
The numbers followed by a # show examples that are within the scope of 
claim 1, but not within the scope of the preferred embodiment of claim 2. 
As shown in Table 4, dielectric ceramic compositions within the scope of 
claim 2 are sinterable at the temperatures from 875.degree. to 950.degree. 
C., and the dielectric constants (.epsilon..sub.r) are from 21 to 33, the 
Qf products are from 2800 to 5100 GHz, the temperature coefficients of the 
resonance frequency (.tau..sub.f) are from -10 to +41 ppm/.degree.C. In 
other words, the dielectric ceramic compositions have superior microwave 
dielectric properties. 
Sample No.20 comprises second component I in which SiO.sub.2 is less than 
30 wt %. Sample No.23 comprises second component L in which B.sub.2 
O.sub.3 is more than 35 wt %. Sample No.24 comprises second component M in 
which Al.sub.2 O.sub.3 is less than 5 wt %. These samples were not 
preferable because Qf products become smaller than 1000 GHz. Sample No.21 
comprises second component J in which SiO.sub.2 is more than 65 wt %. 
Sample No.22 comprises second component K in which B.sub.2 O.sub.3 is less 
than 10 wt %. Sample No.25 comprises second component N in which Al.sub.2 
O.sub.3 is more than 30 wt %. Sample No.26 comprises second component O in 
which ZrO.sub.2 is more than 8 wt %. Also, Sample No. 27 comprises second 
component P in which MO is more than 13 wt %, where M is at least one 
element selected from the group consisting of Ca, Sr, and Ba. These 
samples were not preferable embodiments because the firing temperatures 
were 1100.degree. C. or more. 
Example 3 
Example 3 is an example of the second embodiment of this invention. 
Samples were prepared and their properties were varied in accordance with 
Example 1. The first component of Example 3 comprises not only 
Ca{(Mg.sub.1/3 Nb.sub.2/3).sub.1-x Ti.sub.x }O.sub.3 but also Al.sub.2 
O.sub.3. Only the second components were replaced by those shown in Table 
1. The results are shown in Table 5. 
TABLE 5 
__________________________________________________________________________ 
Compositions Dielectric properties 
first second Sintering 
Qf 
Sample 
component component 
temp. product 
.tau.f 
No. x w wt % type 
wt % .degree.C. 
.epsilon.r 
GHz ppm/.degree.C. 
__________________________________________________________________________ 
28 0.3 0 80 E 20 875 22 3700 -5 
29 0.3 10 80 E 20 875 21 3800 -7 
30 0.3 50 80 E 20 900 16 4100 -11 
31 0.3 50 80 A 20 1000 18 4300 -10 
32 0.3 50 80 C 20 950 17 4200 -8 
33# 0.3 60 100 E 0 no sinter 
34 0.3 60 98 E 2 1150 24 12000 -14 
35 0.3 60 80 E 20 900 13 4400 -13 
36 0.3 60 45 E 55 875 11 2800 -11 
37 0.3 60 60 E 70 850 9 1400 -10 
38# 0.3 60 25 E 75 850 8 
500 -8 
39 0.3 80 80 E 20 950 11 6000 -22 
40# 0.3 100 80 E 20 1050 7 8100 -55 
41 0.3 50 80 E 20 900 21 3000 +46 
42# 0.55 
50 80 E 20 900 23 2400 +70 
__________________________________________________________________________ 
The numbers followed by a # show comparative examples. 
"w" in the column of compositions is weight percent of Al.sub.2 O.sub.3 i 
the first components. 
As shown in Table 5, it was confirmed that the dielectric ceramic 
compositions of this example are sinterable at a temperature from 
850.degree. to 1150.degree. C., in which the dielectric constants 
(.epsilon..sub.r) are from 9 to 24, the Qf products are from 1400 to 12000 
GHz, the temperature coefficients of the resonance frequency (.tau..sub.f) 
are from -22 to +46 ppm/.degree.C. Thus, the dielectric ceramic 
compositions have superior microwave dielectric properties. The dielectric 
constant can be lowered by increasing the amount of Al.sub.2 O.sub.3 (w) 
which is included in the first component. 
Sample No.33 comprising the second component at less than 5 wt % does not 
sinter at 1400.degree. C. or less. Sample No.38 comprising the second 
component at more than 70 wt % is not satisfactory because the Qf product 
becomes smaller than 1000 GHz. Sample No.40 comprising only Al.sub.2 
O.sub.3 as the first component is not satisfactory because the temperature 
coefficient of the resonance frequency is less than -50 ppm/.degree.C. In 
the case of Sample No.42, in which x in the formula Ca{(Mg.sub.1/3 
Nb.sub.2/3).sub.1-x Ti.sub.x }O.sub.3 is over 0.5, the sample becomes 
unpractical because the temperature coefficient of the resonance frequency 
is over +50 ppm/.degree.C. 
Example 4 
Example 4 is a preferable example of the second embodiment of this 
invention. 
Samples were prepared and their properties were varied in accordance with 
Example 1. Only second components were replaced by those shown in Table 3. 
The results are shown in Table 6. 
TABLE 6 
__________________________________________________________________________ 
Composition Dielectric properties 
first second Sintering 
Qf 
Sample 
component component 
temp. product 
.tau.f 
No. x w wt % type 
wt % .degree.C. 
.epsilon.r 
GHz ppm/.degree.C. 
__________________________________________________________________________ 
43 0.3 50 80 F 20 900 16 4200 -10 
44 0.3 20 80 G 20 950 22 4000 -4 
45 0.3 50 80 G 20 975 18 4100 -6 
46 0.3 50 65 G 35 900 14 3600 -8 
47 0.45 
50 65 G 35 875 17 3200 +37 
48 0.3 80 65 G 35 875 11 4100 -16 
49 0.3 50 90 H 10 900 24 5300 -13 
50 0.3 50 80 H 20 900 15 3300 -8 
51# 0.3 50 90 I 10 950 23 400 -13 
52# 0.3 50 60 J 40 1100 15 3300 -9 
53# 0.3 50 60 K 40 1150 15 3600 -7 
54# 0.3 50 90 L 10 925 23 300 -15 
55# 0.3 50 80 M 20 950 16 400 -6 
56# 0.3 50 60 N 40 1150 14 2000 -6 
57# 0.3 50 55 O 45 1150 13 1900 -2 
58# 0.3 50 60 P 40 1125 14 2500 0 
__________________________________________________________________________ 
The numbers followed by a # show examples that are within the scope of 
claim 5 but outside the preferred embodiment of claim 6. 
"w" in the column of compositions is weight percent of Al.sub.2 O.sub.3 i 
the first component. 
As shown in Table 6, it was confirmed that dielectric ceramics of the 
preferred embodiment of claim 6 are sinterable at a temperature from 
875.degree. to 975.degree. C., in which the dielectric constant 
(.epsilon..sub.r) is from 11 to 22, the Qf product is from 3300 to 5300 
GHz, and the temperature coefficient of the resonance frequency 
(.tau..sub.f) is from -16 to +37 ppm/.degree.C. Thus it was shown that the 
ceramic compositions have excellent microwave dielectric properties. 
Sample No.51 comprises second component I in which SiO.sub.2 is less than 
30 wt %. Sample No.54 comprises second component L in which B.sub.2 
O.sub.3 is more than 35 wt %. Sample No.55 comprises second component M in 
which Al.sub.2 O.sub.3 is less than 5 wt %. These samples were not 
preferable because Qf products become smaller than 1000 GHz. Sample No.52 
comprises second component J in which SiO.sub.2 is more than 65 wt %. 
Sample No.53 comprises second component K in which B.sub.2 O.sub.3 is less 
than 10 wt %. Sample No.56 comprises second component N in which Al.sub.2 
O.sub.3 is more than 30 wt %. Sample No.57 comprises second component O in 
which ZrO.sub.2 is more than 8 wt %. Also, Sample No. 58 comprises second 
component P in which MO is more than 13 wt %, where M is at least one 
element selected from the group consisting of Ca, Sr, and Ba. These 
samples were not preferable because the firing temperatures were 
1100.degree. C. or more. 
In addition, it is also possible to include elements other than those shown 
in the examples, as long as they are within the scope of the invention and 
do not negatively affect dielectric properties. 
Reference 1 
The following figures show one embodiment of a multilayer resonant device 
that employs a dielectric ceramic of the invention. FIG. 1 is a 
perspective view of a multilayer microwave resonant device using 
dielectric ceramic composition 1 of one embodiment of the invention. The 
device has inner conductors made of metals like Au, Ag, and Cu and also 
has outer conductors 5, 6, and 7. The multilayer microwave resonant device 
is 8 mm long, 5 mm wide and 2.5 mm high. FIG. 2 is a cross-sectional view 
taken on line I--I of FIG. 1. FIG. 3 is a cross-sectional view taken on 
line II--II of FIG. 1. FIG. 4(a) is a cross-sectional view taken on line 
III--III of FIG. 2. FIG. 4(b) is a cross-sectional view taken on line 
IV--IV of FIG. 2. FIG. 4(c) is a cross-sectional view taken on line V--V 
of FIG. 2. The figures show the arrangement of inner conductors made of 
metals like Au, Ag and Cu (2, 3, 4), and outer conductor 5 which are all 
attached to the dielectric ceramic composition 1. The inner conductor 3 is 
1 mm wide, 7 mm long and 0.03 mm (30 .mu.m) thick. The inner conductors 2 
and 3 were formed by screenprint method. The area between the inner 
conductors 2 and 3 works as a capacitor. Microwaves are introduced into 
the resonant device via the capacitor. Then only some waves which have the 
predetermined frequency will resonate. In this way the resonant device 
functions. 
As clearly described in the above-mentioned examples, a dielectric ceramic 
composition of this invention can be sintered at temperatures as low as 
1000.degree. C., and attain high Q values and small .tau..sub.f when the 
dielectric constants are as high as 15 or 25. Therefore this invention can 
be used in a multilayer resonant devices using metals like Cu, Au, or Ag 
as inner conductors. Consequently high-frequency devices like filters and 
duplexers can have a compact size and high performance. In addition, 
dielectric ceramics of this invention can be used not only for dielectric 
resonators, but also for microwave circuit substrates, multilayer ceramic 
capacitors etc, so that its industrial utility is high. 
The invention may be embodied in other forms without departing from the 
spirit or essential characteristics thereof. The embodiments disclosed in 
this application are to be considered in all respects as illustrative and 
not limitative, the scope of the invention is indicated by the appended 
claims rather than by the foregoing description, and all changes which 
come within the meaning and range of equivalency of the claims are 
intended to be embraced therein.