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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric ceramic composition used to
obtain a monolithic type electronic component constructed by cofiring
inner electrodes and ceramics, for example, a ceramic capacitor.
2. Description of the Prior Art
In a monolithic type electronic component such as a multilayer capacitor, a
sintered body obtained by cofiring an electrode material constituting
inner electrodes and dielectric ceramics is used. Meanwhile, when the
multilayer capacitor is fabricated, a conventional dielectric material
mainly composed of BaTiO.sub.3 is sintered at temperatures from
1300.degree. to 1500.degree. C. Accordingly, a noble metal such as Pd
which is not melted at such sintering temperatures has been used as an
electrode material constituting inner electrodes. However, the noble metal
such as Pd is very high in cost. Consequently, when the number of inner
electrodes is increased so as to achieve large capacity, the cost
significantly rises, so that a cost reduction has been demanded.
Therefore, an attempt to use a low-cost base metal such as nickel as the
electrode material constituting inner electrodes has been made. When inner
electrodes constituted by the base metal such as nickel are used, however,
the electrode material constituting the inner electrodes is liable to be
oxidized. Accordingly, the dielectric material must be sintered in a
reducing atmosphere. Consequently, if the dielectric material is sintered
in such an atmosphere, an oxygen deficiency occurs, resulting in decreased
insulation resistance.
In order to solve such a problem, a non-reduction type dielectric ceramic
composition in which oxygen deficiency does not easily occur even if it is
sintered in a reducing atmosphere by adding MgO and a rare earth oxide to
BaTiO.sub.3 -CaZrO.sub.3 is proposed (Japanese Patent Laid-Open Gazette
No. 157603/1987).
However, the dielectric ceramic composition disclosed in Japanese Patent
Laid-Open Gazette No. 157603/1987 has a disadvantage in terms of sintering
properties. More specifically, it is difficult to sinter the dielectric
ceramic composition unless it is sintered at temperatures of not less than
1300.degree. C.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a non-reduction type
dielectric ceramic composition capable of obtaining a dielectric ceramic
composition which can be sintered at relatively low temperatures and has
sufficient resistance to humidity.
The dielectric ceramic composition according to the present invention
contains as a main component a component expressed by the following
composition formula:
(1-x-y-z-t)BaTiO.sub.3 +xCaZrO.sub.3 +yMgO+zMnO+tRe.sub.2 O.sub.3
x.ltoreq.0.06
0.005.ltoreq.y.ltoreq.0.08
0.005.ltoreq.z.ltoreq.0.02
0.005.ltoreq.t.ltoreq.0.02.
In the composition formula, Re indicates at least one of Y, Gd, Dy, Ho, Er
and Yb.
Furthermore, the non-reduction type dielectric ceramic composition
according to the present invention contains 0.3 to 5.0 parts by weight of
an additive composed of at least one of SiO.sub.2, Li.sub.2 O and B.sub.2
O.sub.3 per 100 parts by weight of the above described main component.
The reason why x is not more than 0.06 in the above described composition
formula is that the rate of variation with temperature of the dielectric
constant in the temperature range of -55.degree. C. to +125.degree. C.
exceeds .+-.15% if the mixture ratio of CaZrO.sub.3 is more than 6 mole %.
x is preferably set to not less than 0.01 nor more than 0.04. The reason
for this is that the CR product is lowered, i.e., not more than 2000 when
x is less than 0.01 and the change in capacitance at a high temperature
(at 85.degree. C.) becomes large when x exceeds 0.04.
Furthermore, the reason why y is not less than 0.005 nor more than 0.08 is
that the CR product is lowered to not more than 1000 .OMEGA..multidot.F.,
resulting in insufficient insulation resistance, thereby to make it
impossible to use the dielectric ceramic composition as a multilayer
capacitor if the mixture ratio of MgO is outside of this range.
y is preferably set to not less than 0.02. The reason for this is that the
CR product is lowered, i.e., not more than 2000 when y is less than 0.02.
Additionally, the reason why z is not less than 0.005 nor more than 0.02 is
that the rate of variation with temperature of the dielectric constant in
the temperature range of -55.degree. C. to +125.degree. C. exceeds .+-.15%
if the mixture ratio of MnO is less than 0.5 mole %, while the CR product
is lowered if it exceeds 2.0 mole %. z is preferably set to not more than
0.015. The reason for this is that the CR product is lowered, i.e., not
more than 2000 when y exceeds 0.015.
Moreover, the reason why t is not less than 0.005 nor more than 0.02 is
that the rate of variation with temperature of the dielectric constant in
the temperature range of -55.degree. C. to +125.degree. C. exceeds .+-.15%
if the mixture ratio of Re.sub.2 O.sub.3 is less than 0.5 mole %, while
the sintering properties are degraded, thereby to make it difficult to
sinter the dielectric ceramic composition at temperatures of not more than
1250.degree. C. if it exceeds 2.0 mole %.
In the present invention, the dielectric ceramic composition contains an
additive composed of at least one of SiO.sub.2, LiO.sub.2 and B.sub.2
O.sub.3 to enhance the sintering properties. However, if the content of
the additive per 100 parts by weight of the main component is less than
0.3 parts by weight, the dielectric ceramic composition is not sintered at
a temperature of 1250.degree. C. Consequently, not less than 0.3 parts by
weight of the additive must be mixed with 100 parts be weight of the main
component.
On the other hand, when the content of the additive per 100 parts by weight
of the main component is more than 5.0 parts by weight, the dielectric
constant .epsilon. is significantly lowered. Consequently, the upper limit
of the content of the additive per 100 parts by weight of the main
component is 5.0 parts by weight. Further, the content of the additive is
preferably not more than 2.0 parts by weight per 100 parts by weight of
the main component. The reason for this is that the CR product is lowered,
i.e., not more than 2000 when the content of the additive exceeds 2.0
parts by weight.
In the present invention, 0.3 to 5.0 parts by weight of the above described
particular additive is mixed with 100 parts by weight of the above
described particular main component, thereby to obtain a dielectric
ceramic which can be sintered at temperatures of not more than
1250.degree. C, and shows a decreased rate of the variation with
temperature of dielectric constant and a sufficiently large CR product as
obvious from the embodiment as described later.
The foregoing and other objects, features, aspects and advantages of the
present invention will become more apparent from the following detailed
description of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Description is now made of a non-restrictive embodiment of the present
invention.
First, BaTiO.sub.3, CaZrO.sub.3, MgCO.sub.3 and MnCO.sub.3 and a rare earth
oxide are weighed on the basis of respective compositions shown in Table 1
and Table 2, and an additive shown in Table 3 and Table 4 is weighed at
ratios shown in the tables 3 and 4, to obtain starting materials for
samples Nos. 1 to 39.
5% by weight of a water-soluble vinyl acetate binder is added to each of
the starting materials for the samples Nos. 1 to 38 prepared in the above
described manner, followed by wet blending for 16 hours.
A ceramic slurry obtained by the above described blending is dried at a
temperature of 150.degree. C. and then, is classified using a 60-mesh
screen. Ceramic particles obtained by the classification are formed by
applying a pressure of 2 t/cm.sup.2, to fabricate a disk-shaped disk
having a diameter of 10 mm.
The disk-shaped disc obtained is calcined at a temperature of 300.degree.
C. and in an atmosphere of air for two hours to remove the binder and
then, is sintered in an atmosphere of N.sub.2 /H.sub.2 /H.sub.2 O at each
of the sintering temperatures shown in the tables 3 and 4 for two hours.
An In-Ga alloy is applied to both major surfaces of each of the obtained
sintered bodies of the samples and is dried, to form electrodes for
measurement.
Measurements are made of the dielectric constant .epsilon., tan .delta.,
the rate of variation with temperature of the dielectric constant Tc, and
the insulation resistance IR of the ceramic sintered body having the above
described electrodes for measurement formed therein. The conditions for
the measurements are as follows:
The measurement of the dielectric constant .epsilon. is made by causing an
AC current of 1.0 Vrms and 1.0 KHz to flow.
The measurement of tan .delta. is made by causing an AC current of 1.0 Vrms
and 1.0 KHz to flow.
The measurement of the rate of variation with temperature of the dielectric
constant Tc is made in the temperature range of -55.degree. C. to
+125.degree. C. and causing an AC current of 1.0 Vrms and 1.0 KHz to flow.
The measurement of the insulation resistance IR is made after an elapse of
two minutes since a current of 50 V was caused to flow.
The results of the measurements are shown in Table 5 and Table 6 as
described later. In addition, the CR product is also shown in the tables 5
and 6.
Compositions A to C of the additive shown in the tables 3 and 4 are as
follows:
Composition A; 100 parts by weight of SiO.sub.2
Composition B; 20 parts by weight of B.sub.2 O.sub.3, 40 parts by weight of
BaO, 30 parts by weight of SiO.sub.2, and 10 parts by weight of Li.sub.2 O
Composition C; 50 parts by weight of SiO.sub.2, 20 parts by weight of
Li.sub.2 O, 10 parts by weight of BaO, 10 parts by weight of CaO, and 10
parts by weight of SrO
As can be seen from the tables 5 and 6, in the sintered body of the sample
No. 2, the mixture ratio of CaZrO.sub.3 in the main component is beyond
the scope of the present invention, so that the rate of variation with
temperature of dielectric constant Tc is very large.
Furthermore, in the sintered body of the sample No. 6, no additive is
added, so that the dielectric ceramic composition of the sample is not
sufficiently sintered even at a temperature of 1300.degree. C., thereby to
make it impossible to make the above described respective measurements.
It is found that in the sintered body of the sample No. 9, the content of
the additive is high, i.e., 6.0% by weight, so that the dielectric
constant .epsilon. is low, i.e., 2100 and the CR product is also low.
It is found that in the sintered body of the sample No. 15, the mixture
ratio of MgO in the main component is high, i.e., 9.0 mole %, so that the
CR product is low, i.e., 800 .OMEGA.F. In addition, it is found that in
the sintered body of the sample No. 16, MgO is not contained in the main
component, so that the CR product is further lowered, i.e., 500 .OMEGA.F.
In the sintered body of the sample No. 18, the mixture ratio of the rare
earth oxide in the main component is high, i.e., 2.5 mole %, so that the
dielectric ceramic composition of the sample is not sufficiently sintered
even at a temperature of 1300.degree. C.
In the sintered body of the sample No. 20, no rare earth oxide is
contained, so that the rate of variation with temperature of the
dielectric constant Tc is significantly large, i.e., -15.5% .DELTA.C at a
temperature of 125.degree. C. In addition, it is found that in the
sintered body of the sample No. 23, the mixture ratio of MnO in the main
component is high, i.e., 2.5 mole %, so that the CR product is also
lowered, i.e., 800 .OMEGA.F. It is found that in the sintered body of the
sample No. 25, MnO is not contained, so that the rate of variation with
temperature of the dielectric constant at a temperature of -55.degree. C.
is large, i.e., -16.2% .DELTA.C.
Additionally, it is found that in the sintered bodies of the samples Nos.
26 and 27, the rare earth oxides are respectively Ce.sub.2 O.sub.3 and
Sm.sub.2 O.sub.3, so that the rates of variation with temperature of the
dielectric constant are both very large. In addition, in the sintered body
of the sample No. 27, the CR product is also significantly lowered, i.e.,
700 .OMEGA.F.
On the other hand, it is found that with respect to any one of the sintered
bodies of the remaining samples within the scope of the present invention,
the dielectric constant .epsilon. is relatively high, tan .delta. is low,
i.e., not more than 0.9, the CR product representing the insulation
resistance is high, i.e., not less than 1100, and the rate of variation
with temperature of the dielectric constant is less than .+-.15%. More
specifically, any one of the sintered bodies of the samples within the
scope of the present invention has superior dielectric properties.
TABLE 1
______________________________________
MAIN COMPONENT (MOLE %)
Re.sub.2 O.sub.3
SAMPLE MOLE
NUMBER BaTiO.sub.3
CaZrO.sub.3
MgO MnO TYPE %
______________________________________
1 94 1.0 3.0 0.5 Y.sub.2 O.sub.3
1.0
2 93 2.0 3.0 1.0 Y.sub.2 O.sub.3
1.0
3 91 4.0 3.0 1.0 Y.sub.2 O.sub.3
1.0
4 90 5.0 3.0 1.0 Y.sub.2 O.sub.3
1.0
5 93 2.0 3.0 1.0 Y.sub.2 O.sub.3
1.0
6 93 2.0 3.0 1.0 Y.sub.2 O.sub.3
1.0
7 93 2.0 3.0 1.0 Y.sub.2 O.sub.3
1.0
8 93 2.0 3.0 1.5 Y.sub.2 O.sub.3
1.0
9 93 2.0 3.0 1.0 Y.sub.2 O.sub.3
1.0
10 89.5 2.0 6.0 0.5 Y.sub.2 O.sub.3
1.5
11 90 2.0 6.0 0.5 Y.sub.2 O.sub.3
1.5
12 87.5 2.0 8.0 1.0 Y.sub.2 O.sub.3
1.5
13 95.5 2.0 0.5 1.0 Y.sub.2 O.sub.3
1.0
14 95 2.0 1.0 1.0 Y.sub.2 O.sub.3
1.0
15 86.5 2.0 9.0 1.0 Y.sub.2 O.sub. 3
1.5
16 96 2.0 -- 1.0 Y.sub.2 O.sub.3
1.0
17 92 2.0 3.0 1.0 Y.sub.2 O.sub.3
2.0
18 91.5 2.0 3.0 1.0 Y.sub.2 O.sub.3
2.5
19 93.5 2.0 3.0 1.0 Y.sub.2 O.sub.3
0.5
______________________________________
TABLE 2
______________________________________
MAIN COMPONENT (MOLE %)
Re.sub.2 O.sub.3
SAMPLE MOLE
NUMBER BaTiO.sub.3
CaZrO.sub.3
MgO MnO TYPE %
______________________________________
20 96 0 3.0 1.0 Y.sub.2 O.sub.3
--
21 92.5 2.0 3.0 1.5 Y.sub.2 O.sub.3
1.0
22 92 2.0 3.0 2.0 Y.sub.2 O.sub.3
1.0
23 91.5 2.0 3.0 2.5 Y.sub.2 O.sub.3
1.0
24 90 2.0 6.0 0.5 Y.sub.2 O.sub.3
1.5
25 90.5 2.0 6.0 -- Y.sub.2 O.sub.3
1.5
26 93 2.0 3.0 1.0 Ce.sub.2 O.sub.3
1.0
27 93 2.0 3.0 1.0 Sm.sub.2 O.sub.3
1.0
28 93 2.0 2.0 0.5 Er.sub.2 O.sub.3
1.0
29 91 4.0 3.0 1.0 Er.sub.2 O.sub.3
1.0
30 89.5 2.0 6.0 1.0 Er.sub.2 O.sub.3
1.5
31 93 2.0 3.0 1.0 Gd.sub.2 O.sub.3
1.0
32 91 4.0 3.0 1.0 Gd.sub.2 O.sub.3
1.0
33 93 2.0 3.0 1.0 Dy.sub.2 O.sub.3
1.0
34 92 2.0 3.0 1.0 Ho.sub. 2 O.sub.3
1.0
35 93 2.0 3.0 1.0 Yb.sub.2 O.sub.3
1.0
36 89 6.0 3.0 1.0 Y.sub.2 O.sub.3
1.0
37 88.5 6.5 3.0 1.0 Y.sub.2 O.sub.3
1.0
38 89 6.0 3.0 1.0 Er.sub.2 O.sub.3
1.0
39 95 0 3.0 1.0 Er.sub.2 O.sub.3
1.0
______________________________________
TABLE 3
______________________________________
ADDITIVE SINTERING
SAMPLE % BY TEMPERATURE
NUMBER COMPOSITION WEIGHT (.degree.C.)
______________________________________
1 C 0.5 1250
2 C 0.5 1250
3 C 0.5 1250
4 C 0.5 1250
5 A 0.3 1250
6 -- -- 1300
7 C 1.0 1250
8 C 5.0 1250
9 C 6.0 1250
10 C 2.0 1250
11 C 1.0 1250
12 C 3.0 1250
13 B 0.5 1250
14 B 0.5 1250
15 C 2.0 1250
16 C 0.5 1250
17 B 0.5 1250
18 B 2.0 1300
19 B 0.5 1250
______________________________________
TABLE 4
______________________________________
ADDITIVE SINTERING
SAMPLE % BY TEMPERATURE
NUMBER COMPOSITION WEIGHT (.degree.C.)
______________________________________
20 A 0.5 1250
21 A 0.5 1250
22 A 0.5 1250
23 A 0.5 1250
24 B 1.0 1250
25 C 1.0 1250
26 C 1.0 1250
27 C 0.5 1250
28 C 0.5 1250
29 C 0.3 1250
30 C 0.5 1250
31 A 0.5 1250
32 A 0.5 1250
33 B 0.5 1250
34 C 0.5 1250
35 C 0.5 1250
36 B 0.5 1250
37 B 0.5 1250
38 B 0.5 1250
39 B 0.5 1250
______________________________________
TABLE 6
__________________________________________________________________________
SAMPLE tan.delta.
CR PRODUCT
TC (% .DELTA.C)
NUMBER
.epsilon.
(%) (.OMEGA.F)
-55.degree. C.
-25.degree. C.
+85.degree. C.
+125.degree. C.
__________________________________________________________________________
1 3000
0.9 2100 -9.7 -8.0 -8.8 -7.2
2 2700
0.8 2300 -5.6 -4.7 -6.1 -5.4
3 3000
0.8 2000 -3.7 -2.0 -9.1 -8.0
4 3100
0.9 2000 -4.9 -0.8 -11.2
-10.6
5 3100
0.9 2400 -5.6 -4.6 -8.7 -7.2
6 INSUFFICIENTLY SINTERED
7 2800
0.8 2200 -7.1 -5.8 -6.9 -5.4
8 2600
0.8 1400 -7.0 -4.8 -5.0 -4.3
9 2100
0.6 1000 -6.6 -4.5 -4.2 -3.8
10 2700
0.8 2000 -7.2 -5.1 -6.4 -6.1
11 2800
0.7 2300 -8.8 -6.2 -5.6 -4.8
12 2700
0.7 1100 -7.9 - 5.5 -6.4 -5.0
13 2700
0.8 1500 -9.6 -7.5 -8.6 -7.2
14 2800
0.7 1800 -8.2 -6.3 -6.8 -5.2
15 2200
0.6 800 -7.3 -5.2 -6.8 -4.9
16 2500
0.6 500 -5.8 -4.8 -5.2 -4.0
17 2600
0.6 1200 -5.2 -3.8 -6.2 -5.1
18 INSUFFICIENTLY SINTERED
19 3000
0.8 2000 -5.8 -4.9 -8.8 -7.6
__________________________________________________________________________
TABLE 7
__________________________________________________________________________
SAMPLE tan.delta.
CR PRODUCT
TC (% .DELTA.C)
NUMBER
.epsilon.
(%) (.OMEGA.F)
-55.degree. C.
-25.degree. C.
+85.degree. C.
+125.degree. C.
__________________________________________________________________________
20 2900
0.7 2600 -4.2 -3.0 -12.5
-15.5
21 2800
0.6 2100 -5.6 -4.8 -6.9 -5.3
22 2500
0.5 1600 -5.3 -3.8 -8.8 -7.0
23 2100
0.5 800 -3.9 -3.0 -11.2
-10.6
24 2800
0.7 2400 -8.1 -6.2 -5.6 -4.2
25 3100
0.9 3000 -16.2
-12.0 -8.8 -7.8
26 3300
1.0 1300 -15.0
-12.1 -17.4
-15.1
27 3100
0.8 700 -15.8
-13.8 -14.6
-12.0
28 3000
0.7 2100 -7.2 -5.5 -7.7 -6.5
29 2700
0.7 2100 -4.8 -3.2 -8.7 -7.3
30 2600
0.6 1900 -6.8 -4.6 -6.2 -5.1
31 2700
0.6 1600 -9.6 -7.8 -7.2 -5.9
32 2800
0.8 1700 -9.2 -7.2 -8.6 -8.0
33 2700
0.7 1800 -5.9 -4.8 -7.7 -6.2
34 2600
0.6 1500 -6.8 -4.9 -7.0 -5.9
35 2800
0.7 1900 -6.9 -5.8 -6.8 -6.0
36 2900
0.8 2300 -3.4 -0.6 -13.8
-10.1
37 2800
0.8 2200 -4.8 -1.5 -15.6
-13.0
38 2900
0.7 1900 -6.8 -2.8 -14.0
-10.5
39 2800
0.8 1300 -10.0
-8.5 -9.0 -7.3
__________________________________________________________________________
As described in the foregoing, according to the present invention, 0.3 to
5.0 parts by weight of the above described particular additive is
contained per 100 parts by weight of the above described main component
having a particular composition, thereby to make it possible to provide a
dielectric ceramic which can be sintered at a temperature of 1250.degree.
C. and has sufficient dielectric properties.
Therefore, a base metal such as Ni can be used as a material constituting
inner electrodes if the dielectric ceramic composition according to the
present invention is used, thereby to make it possible to provide a
low-cost multilayer capacitor.
Although the present invention has been described and illustrated in
detail, it is clearly understood that the same is by way of illustration
and example only and is not to be taken by way of limitation, the spirit
and scope of the present invention being limited only by the terms of the
appended claims.
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