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Claims  |
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What is claimed is:
1. A monolithic ceramic capacitor comprising a laminate of a plurality of
dielectric ceramic layers, at least internal electrodes between adjacent
dielectric ceramic layers in such a manner that one end of each internal
electrode is exposed at different ends of the dielectric ceramic layer
alternately, and a pair of external electrodes each electrically connected
to different exposed internal electrodes, in which said dielectric ceramic
layers comprise (a) barium titanate having an alkali metal oxide impurity
content of not more than about 0.02% by weight, (b) at least one member
selected from the group consisting of scandium oxide and yttrium oxide,
(c) at least one member selected from the group consisting of gadolinium
oxide, terbium oxide and dysprosium oxide, (d) manganese oxide, (e) cobalt
oxide and (f) nickel oxide, and is a material containing
(1) 100 mol of a main component represented by the compositional formula:
(1-.alpha.-.beta.){BaO}.sub.m .cndot.TiO.sub.2 +.alpha.{(1-x)M.sub.2
O.sub.3 +xRe.sub.2 O.sub.3 }+.beta.(Mn.sub.1-y-z Ni.sub.y Co.sub.z)O
wherein M.sub.2 O.sub.3 represents at least one member selected from the
group consisting of Sc.sub.2 O.sub.3 and Y.sub.2 O.sub.3 ; Re.sub.2
O.sub.3 represents at least one member selected from the group consisting
of Gd.sub.2 O.sub.3, Tb.sub.2 O.sub.3 and Dy.sub.2 O.sub.3 ;
0.0025.ltoreq..alpha..ltoreq.0.025; 0.0025.ltoreq..beta..ltoreq.0.05;
.beta./.alpha..ltoreq.4; 0<x.ltoreq.0.50; 0.ltoreq.y.ltoreq.1.0;
0.ltoreq.z.ltoreq.1.0; 0.ltoreq.y+z<1.0; and 1.000<m.ltoreq.1.035,
(2) about 0.5 to 5.0 mol, in terms of MgO, of magnesium oxide and
(3) about 0.2 to 3.0 parts by weight, per 100 parts by weight of the total
weight of said main component (1) and said magnesium oxide (2), of
SiO.sub.2 -TiO.sub.2 -MO-based oxide glass, wherein MO represents at least
one member selected from the group consisting of BaO, CaO, SrO, MgO, ZnO
and MnO.
2. A monolithic ceramic capacitor according to claim 1, wherein the
internal electrodes are of nickel or a nickel alloy.
3. A monolithic ceramic capacitor according to claim 2, wherein the alkali
metal oxide impurity content of not more than about 0.012% by weight;
M.sub.2 O.sub.3 represents Y.sub.2 O.sub.3 ; Re.sub.2 O.sub.3 comprises
Dy.sub.2 O.sub.3 ; 0.006.ltoreq..alpha..ltoreq.0.015;
0.005.ltoreq..beta..ltoreq.0.03; .beta./.alpha..ltoreq.3;
0.1.ltoreq.x.ltoreq.0.3; 0.1.ltoreq.y.ltoreq.0.2; 0.1.ltoreq.z.ltoreq.0.5;
0.1.ltoreq.y+z<0.5; and 1.005.ltoreq.m.ltoreq.1.02; the amount of MgO is
about 0.8-1.5 mol; the amount of glass is about 1-1.5 parts; and MO
comprises CaO.
4. A monolithic ceramic capacitor according to claim 3, wherein the
composition of said SiO.sub.2 -TiO.sub.2 -MO-based oxide glass is, when
plotted on a triangular mol % diagram of (SiO.sub.2, TiO.sub.2, MO) in the
area surrounded by, or on, four straight lines connecting four points: A
(85,1,14), B (35,51,14), C (30,20,50), and D (39,1,60) and contains at
least one of Al.sub.2 O.sub.3 and ZrO.sub.2 in a total amount of not more
than 15 parts by weight per 100 parts by weight of the (SiO.sub.2,
TiO.sub.2, MO) component, provided that the amount of ZrO.sub.2 is not
more than 5 parts by weight.
5. A monolithic ceramic capacitor according to claim 4, wherein said
external electrodes comprise a sintered layer of an electrically
conductive metal powder or an electrically conductive metal powder
containing glass frit.
6. A monolithic ceramic capacitor according to claim 4, wherein said
external electrodes comprise a first layer made of a sintered layer of an
electrically conductive metal powder or an electrically conductive metal
layer containing glass frit and a second layer of plating on said first
layer.
7. A monolithic ceramic capacitor according to claim 1, wherein the alkali
metal oxide impurity content of not more than about 0.012% by weight;
M.sub.2 O.sub.3 represents Y.sub.2 O.sub.3 ; Re.sub.2 O.sub.3 comprises
Dy.sub.2 O.sub.3 ; 0.006.ltoreq..alpha.0.015;
0.005.ltoreq..beta..ltoreq.0.03; .beta./.alpha..ltoreq.3;
0.1.ltoreq.x.ltoreq.0.3; 0.1.ltoreq.y.ltoreq.0.2; 0.1.ltoreq.z.ltoreq.0.5;
0.1.ltoreq.y+z<0.5; and 1.005.ltoreq.m.ltoreq.1.02; the amount of MgO is
about 0.8-1.5 mol; the amount of glass is about 1-1.5 parts; and MO
comprises CaO.
8. A monolithic ceramic capacitor according to claim 7, wherein the
composition of said SiO.sub.2 -TiO.sub.2 -MO-based oxide glass is, when
plotted on a triangular mol % diagram of (SiO.sub.2, TiO.sub.2, MO) in the
area surrounded by, or on, four straight lines connecting four points: A
(85,1,14), B (35,51,14), C (30,20,50), and D (39,1,60) and contains at
least one of Al.sub.2 O.sub.3 and ZrO.sub.2 in a total amount of not more
than 15 parts by weight per 100 parts by weight of the (SiO.sub.2,
TiO.sub.2, MO) component, provided that the amount of ZrO.sub.2 is not
more than 5 parts by weight.
9. A monolithic ceramic capacitor according to claim 8, wherein said
external electrodes comprise a sintered layer of an electrically
conductive metal powder or an electrically conductive metal powder
containing glass frit.
10. A monolithic ceramic capacitor according to claim 8, wherein said
external electrodes comprise a first layer made of a sintered layer of an
electrically conductive metal powder or an electrically conductive metal
layer containing glass frit and a second layer of plating on said first
layer.
11. A monolithic ceramic capacitor according to claim 1, wherein the
composition of said SiO.sub.2 -TiO.sub.2 -MO-based oxide glass is, when
plotted on a triangular mol % diagram of (SiO.sub.2, TiO.sub.2, MO) in the
area surrounded by, or on, four straight lines connecting four points: A
(85,1,14), B (35,51,14), C (30,20,50), and D (39,1,60) and contains at
least one of Al.sub.2 O.sub.3 and ZrO.sub.2 in a total amount of not more
than 15 parts by weight per 100 parts by weight of the (SiO.sub.2,
TiO.sub.2, MO) component, provided that the amount of ZrO.sub.2 is not
more than 5 parts by weight.
12. A monolithic ceramic capacitor according to claim 11, wherein said
external electrodes comprise a sintered layer of an electrically
conductive metal powder or an electrically conductive metal powder
containing glass frit.
13. A monolithic ceramic capacitor according to claim 11, wherein said
external electrodes comprise a first layer made of a sintered layer of an
electrically conductive metal powder or an electrically conductive metal
layer containing glass frit and a second layer of plating on said first
layer.
14. A monolithic ceramic capacitor according to claim 1, wherein said
external electrodes comprise a sintered layer of an electrically
conductive metal powder or an electrically conductive metal powder
containing glass frit.
15. A monolithic ceramic capacitor according to claim 1, wherein said
external electrodes comprise a first layer made of a sintered layer of an
electrically conductive metal powder or an electrically conductive metal
layer containing glass frit and a second layer of plating on said first
layer. |
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Claims |
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Description |
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FIELD OF THE INVENTION
This invention relates to a ceramic capacitor, more particularly a
monolithic ceramic capacitor having internal electrodes made of nickel or
a nickel alloy.
BACKGROUND OF THE INVENTION
A monolithic ceramic capacitor is generally produced according to the
following procedures. Dielectric ceramic layers in sheet form having
applied thereon an electrode material to serve as an internal electrode
are prepared. A ceramic material mainly comprising, e.g., BaTiO.sub.3 is
used as a dielectric ceramic layer. A plurality of the dielectric ceramic
layers with the electrode material are piled up and press-bonded under
heat into one body. The resulting laminate is calcined at 1250.degree. to
1350.degree. C. to obtain a ceramic laminate having internal electrodes.
An external electrode is baked onto both sides of the ceramic laminate to
make an electrical connection to the internal electrodes and obtain a
monolithic ceramic capacitor.
The material for the internal electrodes are required to satisfy the
following conditions:
1. To have a melting point at or above the calcining temperature of the
ceramic laminate because the internal electrodes and the ceramic laminate
are calcined simultaneously.
2. To be resistant to oxidation in a high-temperature oxidative atmosphere
and be unreactive with the dielectric ceramic layer.
Noble metals, such as platinum, gold, palladium and a silver-palladium
alloy, have been used as an electrode material satisfying these
requirements. While excellent in performance, these electrode materials
are so expensive that the proportion of the electrode material cost
reaches 30 to 70% of the entire material cost, which has been the greatest
factor of increasing the production cost of monolithic ceramic capacitors.
In addition to noble metals, base metals, such as Ni, Fe, Co, W and Mo,
also have a high melting point. However, these base metals are readily
oxidized in a high-temperature oxidative atmosphere, causing them to fail
to perform their function as an electrode. Therefore, calcination of the
base metal together with dielectric ceramic layers must be carried out in
a neutral or reducing atmosphere before they can be used as an internal
electrode of a monolithic ceramic capacitor. However, the problem is that
a conventional dielectric ceramic material undergoes vigorous reduction
into a semiconductor if calcined in a neutral or reducing atmosphere.
Dielectric ceramic materials which have been proposed in order to solve the
above problem include a dielectric ceramic material comprising a barium
titanate solid solution having a barium site to titanium site ratio in
excess of a stoichiometric one (see JP-B-5742588, the term "JP-B" as used
herein means an "examined published Japanese patent application") and a
dielectric ceramic material comprising a barium titanate solid solution
having incorporated therein an oxide of a rare earth metal, such as La,
Nd, Sm, Dy or Y (see JP-A-61101459, the term "JP-A" as used herein means
an "unexamined published Japanese patent application").
On the other hand, dielectric ceramic materials whose dielectric constant
has reduced temperature dependence, such as BaTiO.sub.3 -CaZrO.sub.3
-MnO-MgO system (see JPA-62-256422) and BaTiO.sub.3 - (Mg, Zn, Sr or
Ca)O-B.sub.2 O.sub.3 -SiO.sub.2 system (see JP-B-61-14611), have also been
proposed.
Use of these dielectric ceramic materials have made it possible to obtain a
ceramic laminate that is not transformed into a semiconductor even when
calcined in a reducing atmosphere, thereby making it feasible to produce a
monolithic ceramic capacitor in which a base metal, such as nickel, is
used as an internal electrode.
In recent years, size reduction of electronic components has accelerated
rapidly in the development of electronics. Monolithic ceramic capacitors
have also showed a remarkable tendency to reduction in size and increase
in capacity. There has thus been an increasing demand for a dielectric
ceramic material which has a high dielectric constant, shows reduced
variation in dielectric constant with temperature change, and is thereby
highly reliable.
The dielectric ceramic materials disclosed in JP-B-57-42588 and
JP-A-61-101459 exhibit a high dielectric constant but have a large crystal
grain size on calcination. When they are applied to a monolithic ceramic
capacitor in which each dielectric ceramic layer has a small thickness
such as 10 .mu.m or less, the number of crystal grains existing per layer
is decreased, resulting in diminished reliability. Besides, these
materials undergo considerable variation in dielectric constant with
temperature change and are not regarded to meet the demands of the market
sufficiently.
The dielectric ceramic material disclosed in JP-A-62-256422, on the other
hand, exhibits a relatively high dielectric constant and provides on
calcination, a ceramic laminate having a small crystal grain size and
small variation of dielectric constant with temperature change. However,
CaZrO.sub.3 and CaTiO.sub.3 produced on calcination tend to form a
secondary phase together with MnO, etc., which has made the resulting
monolithic ceramic capacitor less reliable in high temperatures.
The dielectric ceramic material disclosed in JP-B-61-14611 exhibits a
dielectric constant of 2000 to 2800, which is disadvantageous for
achieving size reduction and capacity increase in a monolithic ceramic
capacitor. Moreover, the material fails to fulfill the requirement of X7R
characteristics specified by EIA (Electronic Industries Association)
standards that the percentage of change in electrostatic capacity be
within a range of .+-.15% in the temperature range of from -55.degree. C.
to +125.degree. C.
Although JP-A-5-9066, JP-A-5-9067, and JP-A-59068 have proposed ceramic
compositions in order to eliminate these problems, the ever-continuing
demand for size reduction and capacity increase has been producing a keen
demand for dielectric ceramic materials with greater reliability. At the
same time, demand for thickness reduction of a ceramic dielectric layer
has been getting intenser.
Thus, there has been the necessity for the development of a small-sized and
high-capacity monolithic ceramic capacitor having excellent reliability in
a high temperature and high humidity environment.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an economical, small-sized
and high-capacity monolithic ceramic capacitor which has a dielectric
constant of 3000 or higher and an insulation resistance as high as
6000M.OMEGA..cndot..mu.F or more at room temperature or
2000M.OMEGA..cndot..mu.F or more at 125.degree. C., as expressed in terms
of the product of capacitance and insulation resistance (CR product), and
whose capacity exhibits temperature characteristics satisfying the B
characteristics specified by JIS (Japanese Industrial Standards) and the
X7R characteristics specified by EIA standards, and which has excellent
weathering performance in, for example, loading in high temperature or
high humidity.
The present invention provides a monolithic ceramic capacitor having a
laminate of a plurality of dielectric ceramic layers, a plurality of
internal electrodes each formed between two adjacent dielectric ceramic
layers in such a manner that one end of each internal electrode is exposed
at one end of the dielectric ceramic layer alternately, and a pair of
external electrodes each electrically connected to the plurality of
exposed internal electrodes of the laminate, in which the dielectric
ceramic layer comprises (a) barium titanate having an alkali metal oxide
impurity content of not more than about 0.02% by weight, (b) at least one
member selected from the group consisting of scandium oxide and yttrium
oxide, (c) at least one member selected from the group consisting of
gadolinium oxide terbium oxide and dysprosium oxide, (d) manganese oxide,
(e) cobalt oxide and (f) nickel oxide, and is made up of a material
containing (1) 100 mol of a main component represented by the
compositional formula:
(1-.alpha.-.beta.){BaO}.sub.m .cndot.TiO.sub.2 +.alpha.{(1-x)M.sub.2
O.sub.3 +xRe.sub.2 O.sub.3 }+.beta.(Mn.sub.1-y-z Ni.sub.y Co.sub.z)O
wherein M.sub.2 O.sub.3 represents at least one member selected from the
group consisting of Sc.sub.2 O.sub.3 and Y.sub.2 O.sub.3 ; Re.sub.2
O.sub.3 represents at least one member selected from the group consisting
of Gd.sub.2 O.sub.3, Tb.sub.2 O.sub.3, and Dy.sub.2 O.sub.3 ;
0.0025.ltoreq..alpha..ltoreq.0.025; 0.0025.ltoreq..beta..ltoreq.0.05;
.beta./.alpha..ltoreq.4; 0<x.ltoreq.0.50; 0.ltoreq.y.ltoreq.1.0;
0.ltoreq.z.ltoreq.1.0; 0.ltoreq.y+z<1.0; and 1.000<m<1.035, (2) about 0.5
to 5.0 mol, in terms of MgO, of magnesium oxide as a secondary component,
and (3) about 0.2 to 3.0 parts by weight, per 100 parts by weight of the
total weight of the main component (1) and the secondary component (2), of
SiO.sub.2 -TiO.sub.2 -MO-based oxide glass (wherein MO represents at least
one member selected from the group consisting of BaO, CaO, SrO, MgO, ZnO,
and MnO), and the internal electrodes are made up of nickel or a nickel
alloy.
In a preferred embodiment of the monolithic ceramic capacitor of the
present invention, the composition of the SiO.sub.2 -TiO.sub.2 -MO-based
oxide glass is, when plotted on a triangular diagram of (SiO.sub.2,
TiO.sub.2, MO) (wherein MO is as defined above), in the area surrounded
by, or on, four straight lines connecting four points: A (85,1,14), B
(35,51,14), C (30,20,50), and D (39,1,60) (unit: mol %), and contains at
least one of Al.sub.2 O.sub.3 and ZrO.sub.2 in a total amount of not more
than about 15 parts by weight per 100 parts by weight of the (SiO.sub.2,
TiO.sub.2 MO) component, provided that the amount of ZrO.sub.2 is not more
than about 5 parts by weight.
In another preferred embodiment, the external electrode is made up of a
sintered layer of an electrically conductive metal powder which may
contain glass frit. In a still preferred embodiment, the external
electrode is composed of a first layer made of a sintered layer of an
electrically conductive metal powder which may contain glass frit and a
second layer that is formed on the first layer by plating.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross section of a monolithic ceramic capacitor
according to one embodiment of the present invention.
FIG. 2 is a schematic plan of a ceramic layer with an internal electrode
which is used in the monolithic ceramic capacitor of FIG. 1.
FIG. 3 is a perspective exploded view of the ceramic laminate used in the
monolithic ceramic capacitor of FIG. 1.
FIG. 4 is a triangular diagram of (SiO.sub.2, TiO.sub.2, MO) showing a
preferred range of the composition of SiO.sub.2 -TiO.sub.2 -MO-based oxide
glass.
DETAILED DESCRIPTION OF THE INVENTION
In the monolithic ceramic capacitor of the present invention, the
dielectric ceramic layers are obtained by calcining a dielectric ceramic
material comprising (1) (a) barium titanate, (b) at least one of scandium
oxide and yttrium oxide, (c) at least one of gadolinium oxide, terbium
oxide and dysprosium oxide, (d) manganese oxide, (e) cobalt oxide and (f)
nickel oxide at a ratio shown by the above-described compositional formula
having incorporated therein (2) magnesium oxide and (3) SiO.sub.2
-TiO.sub.2 -MO-based oxide glass (wherein MO represents at least one
member selected from the group consisting of BaO, CaO, SrO, MgO, ZnO, and
MnO). The dielectric ceramic material can be calcined in a reducing
atmosphere without suffering from deterioration of characteristics to
provide a highly reliable monolithic ceramic capacitor whose capacity
exhibits temperature characteristics satisfying the B characteristics
specified by JIS and the X7R characteristics specified by EIA standards,
and which exhibits high insulation resistance at room temperature and high
temperature.
In the resulting dielectric ceramic laminate, the crystal grains are as
small as 1 .mu.m or less so that the grains increase in number per layer.
This will secure a sufficient reliability even though the thickness of the
dielectric ceramic layer in the laminate is reduced.
The barium titanate constituting the main component (1) contains, as
impurities, alkaline earth metal oxides (e.g., SrO and CaO), alkali metal
oxides (e.g., Na.sub.2 O and K.sub.2 O), and other oxides (e.g., Al.sub.2
O.sub.3 and SiO.sub.2). Of these impurities, the alkali metal oxides, such
as Na.sub.2 O and K.sub.2 O, have been confirmed to be greatly influential
on the electrical characteristics. It was proved that a dielectric
constant of not smaller than 3000 can be obtained by using barium titanate
having an alkali metal oxide content of not more than about 0.02% by
weight and preferably about 0.012% or less.
It has also been found that incorporation of oxide glass mainly comprising
SiO.sub.2 -TiO.sub.2 -MO (wherein MO is at least one member selected from
the group consisting of BaO, CaO, SrO, MgO, ZnO, and MnO) into the
dielectric ceramic layers brings about improved sintering properties and
improved resistance to plating. Further, addition of Al.sub.2 O.sub.3
and/or ZrO.sub.2 to the oxide glass makes it possible to obtain higher
insulation resistance.
Dielectric ceramic layers made from the above-described dielectric ceramic
material provide a highly reliable, small-sized, and high-capacity
monolithic ceramic capacitor, the capacity of which shows reduced
variation with temperature. Use of the dielectric ceramic material makes
it feasible to use nickel or a nickel alloy as an internal electrode. It
is also possible to use nickel or a nickel alloy in combination with a
small amount of ceramic powder.
The external electrode is not particularly limited in composition. For
example, it can be a sintered layer of a conductive powder of various
metals (e.g., Ag, Pd, Ag-Pd, Cu and Cu alloys) or a sintered layer of a
mixture of such a conductive metal powder and glass frits of various kinds
(e.g., B.sub.2 O.sub.3 -Li.sub.2 O-SiO.sub.2 -BaO-based glass frits,
B.sub.2 O.sub.3 -SiO.sub.2 -BaO-based glass frits, Li.sub.2 O-SiO.sub.2
-BaO-based glass frits, B.sub.2 O.sub.3 -SiO.sub.2 -ZnO-based glass
frits). Ceramic powder may be used in a small proportion with the
conductive metal powder (and glass frits). It is preferable that the
sintered layer is plated with Ni, Cu, an Ni-Cu alloy, etc. The plated
layer may further be plated with solder, tin, etc.
A monolithic ceramic capacitor according to one embodiment of the present
invention will be described by referring to the accompanying drawings.
FIG. 1 is a schematic cross section of the monolithic ceramic capacitor.
FIG. 2 is a schematic plan of a ceramic layer having an internal electrode
used in the monolithic ceramic capacitor of this embodiment. FIG. 3 is a
perspective exploded view of the ceramic laminate used in the monolithic
ceramic capacitor of this embodiment.
As shown in FIG. 1, the monolithic ceramic capacitor 1 is of rectangular
chip type having a ceramic laminate 3 composed of a plurality of
dielectric ceramic layers 2a and 2b, with an internal electrode 4 being
interposed between every two ceramic layers. On each side of the ceramic
laminate 3 are formed an external electrode 5, a first plating layer 6
formed by plating with nickel, copper, etc., and a second plating layer 7
formed by plating with solder, tin, etc.
The monolithic ceramic capacitor 1 shown in FIG. 1 can be produced as
follows.
(1) A main component comprising (a) barium titanate, (b) at least one of
scandium oxide and yttrium oxide, (c) at least one of gadolinium oxide,
terbium oxide and dysprosium oxide, (d) manganese oxide, (e) cobalt oxide
and (f) nickel oxide, (2) magnesium oxide, and (3) SiO.sub.2 -TiO.sub.2
-MO-based oxide glass (wherein MO is as defined above) are compounded
together with a binder and a solvent into a slurry and molded to prepare a
dielectric ceramic layer 2 (green sheet). An internal electrode 4 of
nickel or a nickel alloy is formed on one side of the dielectric ceramic
layer 2 by screen printing, vacuum evaporation or plating to obtain a
dielectric ceramic layer 2b having an internal electrode 4 as shown in
FIG. 2.
A requisite number of the dielectric ceramic layers 2b are piled up and
press-bonded in between a pair of dielectric ceramic layers 2a having no
internal electrode to obtain a laminate as shown in FIG. 3. The laminate
of the dielectric ceramic layers 2a, 2b . . . 2b, 2a is calcined in a
reducing atmosphere at a prescribed temperature to form a ceramic laminate
3.
An external electrode 5 is then formed on each side of the ceramic laminate
3 to make an electrical connection to the internal electrodes 4. The
external electrodes 5 can be made of the same material as used for the
internal electrodes 4. In addition, silver, palladium, silver-palladium
alloy, copper, copper alloy, etc. are also useful. These metal powders may
be used in combination with glass frits, such as B.sub.2 O.sub.3
-SiO.sub.2 -BaO-based glass frits or Li.sub.2 O-SiO.sub.2 -BaO-based glass
frits. The material of the external electrode should be selected
appropriately taking into consideration the use of the resulting
monolithic ceramic capacitor, the place of use, and the like. The external
electrodes 5 can be formed by applying a paste of the metal powder
selected to the ceramic laminate 3 (i.e., a calcined laminate) followed by
baking. Alternatively, the paste may be applied to the laminate of the
green sheets before calcination and baked to form the electrodes 5 and the
ceramic laminate 3 simultaneously.
The external electrodes 5 are then plated with nickel, copper, etc. to form
a first layer 6. Finally, the first layer 6 is plated with solder, tin,
etc. to form a second layer 7, thereby to produce a monolithic ceramic
capacitor 1 of the chip type.
As described above, the ceramic material used in the present invention does
not undergo reduction and therefore does not change into a semiconductor
even if calcined in a reducing atmosphere, which allows use of a base
metal (nickel or a nickel alloy) as an electrode material. Further,
calcination of the ceramic material can be achieved at a relatively low
temperature of not higher than 1300.degree. C. As a result, both the
material cost and the process cost of monolithic ceramic capacitors can be
reduced.
The monolithic ceramic capacitor according to the present invention
exhibits excellent characteristics, having a dielectric constant of not
smaller than 3000, showing reduced variation in dielectric constant with
temperature change, having a high insulation resistance, and undergoing no
deterioration in characteristics under a high temperature or high humidity
condition.
The grain size of the dielectric ceramic material according to the present
invention is as small as about 1 .mu.m or less. Therefore, if the
thickness of dielectric ceramic layers constituting a monolithic ceramic
capacitor is reduced, each layer can have a greater number of crystal
grains than in conventional monolithic ceramic capacitors. There is thus
provided a highly reliable, small-sized, and yet high-capacity monolithic
ceramic capacitor.
The present invention will now be illustrated in greater detail with
reference to Examples, but it should be understood that the present
invention is not construed as being limited thereto.
EXAMPLE 1
TiCl.sub.4 and Ba(NO.sub.3).sub.2 both having varied purity were weighed
and treated with oxalic acid to precipitate barium titanyl oxalate
(BaTiO(C.sub.2 O.sub.4).cndot.4H.sub.2 O). The precipitate was thermally
decomposed at or above 1000.degree. C. to synthesize 4 species of barium
titanate (BaTiO.sub.3) shown in Table 1 below.
TABLE 1
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Content of Impurities (wt %)
Average
Alkali Particle
Kind of
Metal Size
BaTiO.sub.3
Oxide SrO CaO SiO.sub.2
Al.sub.2 O.sub.3
(.mu.m)
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A 0.003 0.012 0.001
0.010 0.005 0.60
B 0.020 0.010 0.003
0.019 0.008 0.56
C 0.012 0.179 0.018
0.155 0.071 0.72
D 0.062 0.014 0.001
0.019 0.004 0.58
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Oxides, carbonates or hydroxides of silicon, titanium, barium, strontium
and manganese were weighed and mixed so as to give an SiO.sub.2 :TiO.sub.2
:BaO:SrO:MnO molar ratio of 0.60:0.25:0.10:0.02:0.03. The mixture was
ground and evaporated to dryness to obtain powder. The powder was melted
by heating in an aluminum crucible at 1300.degree. C., quenched, and
ground to obtain powdered oxide glass having an average particle size of
not greater than 1 .mu.m.
The compositions shown in Table 2 below were compounded from (i) the barium
titanate of Table 1, (ii) the powdered oxide glass prepared above, (iii)
BaCO.sub.3 serving for adjustment of the Ba/Ti molar ratio of barium
titanate and (iv) Sc.sub.2 O.sub.3, Y.sub.2 O.sub.3, Gd.sub.2 O.sub.3,
Tb.sub.2 O.sub.3, Dy.sub.2 O.sub.3, MnCO.sub.3, NiO, Co.sub.2 O.sub.3 and
MgO, each having a purity of not lower than 99%.
TABLE 2
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Amount of
›(1 -.alpha. - .beta.){BaO}.sub.m .circle-solid.TiO.sub.2 + .alpha.{(1 -
x)M.sub.2 O.sub.3 + xReO.sub.3 } + .beta.(Mn.sub.1-y-z Ni.sub.y Co.sub.z)O
! MgO Oxide Glass
Sample
Kind of M Re (mol
(part by
No. BaTiO.sub.3
.alpha.
Sc Y 1 - x
Gd Tb Dy x .beta.
.beta./.alpha.
y z y + z
m %**)
weight***)
__________________________________________________________________________
1* A 0.0000 0.00300
0.10
0.30
0.40
1.015
1.00
0.80
2* A 0.0120 0.80
0.80
0.20 0.20
0.0000 1.010
1.20
1.00
3* A 0.0100 1.00
1.00 0.00
0.0200
2.0
0.10
0.10
0.20
1.005
0.80
1.00
4* A 0.0150 0.80
0.80 0.20
0.20
0.0300
2.0
0.20
0.20
0.40
0.990
1.00
1.00
5* A 0.0150 0.70
0.70 0.30
0.30
0.0450
3.0
0.20
0.30
0.50
1.000
0.80
1.00
6* A 0.0200 0.80
0.80 0.20
0.20
0.0200
1.0
0.30
0.10
0.40
1.015
0.20
0.80
7* A 0.0150
0.10
0.70
0.80 0.20
0.20
0.0300
2.0
0.10
0.10
0.20
1.005
1.20
0.00
8 A 0.0025 0.80
0.80
0.10 0.10
0.20
0.0025
1.0
0.10
0.10
0.20
1.010
1.00
0.20
9 A 0.0250 0.70
0.70 0.30
0.30
0.0500
2.0
0.10
0.30
0.40
1.005
0.80
1.20
10 A 0.0060
0.10
0.70
0.80 0.20 0.20
0.0240
4.0
0.10
0.30
0.40
1.010
1.20
1.00
11 B 0.0100
0.50 0.50 0.50
0.50
0.0150
1.5
0.20
0.30
0.50
1.020
1.50
1.20
12 C 0.0100 0.90
0.90 0.10
0.10
0.0050
0.5
0.00
0.50
0.50
1.010
1.00
1.00
13 A 0.0150 0.80
0.80
0.20 0.20
0.0300
2.0
0.10
0.00
0.10
1.005
0.50
1.00
14 A 0.0050 0.70
0.70 0.10
0.20
0.30
0.0150
3.0
0.00
0.00
0.00
1.005
5.00
1.20
15 A 0.0100 0.80
0.80
0.10
0.10 0.20
0.0300
3.0
0.10
0.30
0.40
1.035
0.80
1.20
16 A 0.0100 0.80
0.80
0.10
0.05
0.05
0.20
0.0200
2.0
0.10
0.10
0.20
1.010
1.00
3.00
17* A 0.0300 0.80
0.80
0.20 0.20
0.0450
1.5
0.10
0.10
0.20
1.010
1.00
1.50
18* A 0.0200 0.80
0.80 0.20
0.20
0.0700
3.5
0.20
0.40
0.60
1.010
0.80
1.00
19* A 0.0050 0.70
0.70
0.10 0.20
0.30
0.0300
6.0
0.10
0.10
0.20
1.015
1.00
0.80
20* A 0.0150 0.20
0.20
0.80 0.80
0.0150
1.0
0.10
0.30
0.40
1.010
1.00
1.20
21* A 0.0150 0.80
0.80 0.20 0.20
0.0300
2.0
0.00
1.00
1.00
1.010
1.00
1.00
22* A 0.0050
0.10
0.70
0.80
0.20 0.20
0.0150
1.5
0.40
0.60
1.00
1.010
1.20
1.20
23* A 0.0100 0.70
0.70 0.30
0.30
0.0150
1.5
0.40
0.60
1.00
1.010
1.20
1.20
24* A 0.0100
0.20
0.60
0.80 0.20
0.20
0.0300
3.0
0.20
0.20
0.40
1.050
0.80
1.20
25* A 0.0100 0.70
0.70
0.30 0.30
0.0250
2.5
0.10
0.10
0.20
1.005
7.00
1.00
26* A 0.0050 0.70
0.70 0.30 0.30
0.0150
3.0
0.30
0.10
0.40
1.010
0.80
5.00
27* D 0.0150 0.90
0.90
0.10 0.10
0.0300
2.0
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