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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a multilayer ceramic chip capacitor and more
particularly, to a multilayer ceramic chip capacitor having improved
dielectric layers.
2. Prior Art
Multilayer ceramic chip capacitors are generally fabricated by layering an
internal electrode-forming paste and a dielectric layer-forming paste by
sheeting, printing and similar techniques followed by integral co-firing.
Generally the internal electrodes have been formed of Pd and Pd alloys
although the use of relatively inexpensive Ni and Ni alloys instead of
expensive Pd is expanding.
Internal electrodes of Ni and Ni alloys are oxidized if fired in ambient
air.
In this regard, after binder removal, firing is typically carried out at an
oxygen partial pressure which is lower than the equilibrium oxygen partial
pressure between Ni and NiO.
To consolidate the dielectric material in this case, it is a common
practice to add SiO.sub.2 sintering aid.
Another approach for preventing dielectric layers from lowering their
insulation resistance due to reduction is Mn addition or Ca replacement.
Multilayer chip capacitors having internal electrodes of Ni or Ni alloys,
however, suffer from the problems of an extremely short life of insulation
resistance and low reliability as compared with multilayer chip capacitors
having internal electrodes of Pd which are prepared by firing in ambient
air.
Nevertheless, these problems were almost overcome by the multilayer ceramic
chip capacitor which the inventors proposed and in which a dielectric
material containing a dielectric oxide having a specific composition
having added thereto a specific amount of at least one member selected
from the group consisting of oxides of Y, Gd, Tb, Dy, Zr, V, Mo, Zn, Cd,
Tl, Sn and P and/or compounds which will convert to the oxides upon
firing, and an internal electrode-forming material in the form of Ni or Ni
alloy are layered and fired (see Japanese Patent Application Kokai No.
133116/1991).
That is, it was found that by adding yttrium or similar elements, an about
2 to 10 times extended life and fairly improved reliability are obtained
as compared with prior art chip capacitors free of such elements.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a multi-layer ceramic chip
capacitor which has a further increased life and further improved
reliability as compared with the above-mentioned capacitors having yttrium
or similar elements added thereto.
Another object of the present invention is to provide a multilayer ceramic
chip capacitor wherein an initial loss of insulation resistance is
minimized when dielectric layers have a thickness of 10 .mu.m or less.
These and other objects are attained by the present invention which is
defined below as (1) to (23).
(1) A multilayer ceramic chip capacitor having internal electrodes and
dielectric layers, characterized in that
a dielectric material containing a dielectric oxide having a composition of
the following formula:
[(Ba.sub.1-x-y Ca.sub.x Sr.sub.y)O].sub.m (Ti.sub.1-z Zr.sub.z)O.sub.2
wherein 0.ltoreq.x.ltoreq.0.25, 0.ltoreq.y.ltoreq.0.05,
0.1.ltoreq.z.ltoreq.0.3, and 1.000.ltoreq.m.ltoreq.1.020 and having added
thereto an oxide of Mn and/or a compound which converts to the oxide upon
firing in an amount of 0.01 to 0.5% by weight calculated as oxide (MnO),
an oxide of Y and/or a compound which converts to the oxide upon firing in
an amount of 0.05 to 0.5% by weight calculated as oxide (Y.sub.2 O.sub.3),
an oxide of V and/or a compound which converts to the oxide upon firing in
an amount of 0.005 to 0.3% by weight calculated as oxide (V.sub.2
O.sub.5), and an oxide of W and/or a compound which converts to the oxide
upon firing in an amount of 0.005 to 0.3% by weight calculated as oxide
(WO.sub.3), and an internal electrode-forming material in the form of Ni
or a Ni alloy are successively layered and co-fired.
(2) The multilayer ceramic chip capacitor of claim 1 wherein the dielectric
material has further added thereto up to 0.25% by weight of SiO.sub.2.
(3) The multilayer ceramic chip capacitor of claim 1 or 2 wherein the
dielectric material has further added thereto at least one oxide of Eu and
Mo and/or a compound which converts to the oxide upon firing in an amount
of up to 0.3% by weight calculated as oxide.
(4) The multilayer ceramic chip capacitor of any one of claims 1 to 3
wherein each said dielectric layer consists of grains and a grain boundary
phase and the ratio of the area of the grain boundary phase in a cross
section of said dielectric layer is up to 2%.
(5) The multilayer ceramic chip capacitor of claim 4 wherein said grain
boundary phase is an oxide phase containing oxides of Mn, Y, V and W.
(6) A multilayer ceramic chip capacitor which is prepared by successively
layering and co-firing a dielectric material having additives added to a
matrix of the following formula:
[(Ba.sub.1-x-y Ca.sub.x Sr.sub.y)O].sub.m (Ti.sub.1-z Zr.sub.z)O.sub.2
wherein 0.ltoreq.x.ltoreq.0.25, 0.ltoreq.y.ltoreq.0.05,
0.1.ltoreq.z.ltoreq.0.3, and 1.000.ltoreq.m.ltoreq.1.020, said additives
including an oxide of Mn and/or a compound which converts to the oxide
upon firing, an oxide of Y and/or a compound which converts to the oxide
upon firing, an oxide of V and/or a compound which converts to the oxide
upon firing, and an oxide of W and/or a compound which converts to the
oxide upon firing, and an internal electrode-forming material in the form
of Ni or a Ni alloy, wherein said additive powders have a mean particle
size of up to 3 .mu.m.
(7) The multilayer ceramic chip capacitor of claim 6 wherein said additive
powders have a maximum particle size of up to 5 .mu.m.
(8) The multilayer ceramic chip capacitor of claim 6 or 7 wherein said
additives have a mean particle size which is within 5 times the mean
particle size of the matrix.
(9) The multilayer ceramic chip capacitor of claim 8 wherein said additives
have a mean particle size which is within 3 times the mean particle size
of the matrix.
(10) The multilayer ceramic chip capacitor of claim 6 or 7 wherein said
additives have a maximum particle size which is within 3 times the maximum
particle size of the matrix.
(11) The multilayer ceramic chip capacitor of claim 6 wherein said oxide of
Mn and/or said compound which converts to the oxide upon firing is added
in an amount of 0.01 to 0.5% by weight calculated as oxide (MnO), said
oxide of Y and/or said compound which converts to the oxide upon firing is
added in an amount of 0.05 to 0.5% by weight calculated as oxide (Y.sub.2
O.sub.3), said oxide of V and/or said compound which converts to the oxide
upon firing is added in an amount of 0.005 to 0.3% by weight calculated as
oxide (V.sub.2 O.sub.5), and said oxide of W and/or said compound which
converts to the oxide upon firing is added in an amount of 0.005 to 0.3%
by weight calculated as oxide (WO.sub.3).
(12) The multilayer ceramic chip capacitor of claim 6 or 11 wherein the
dielectric material has further added thereto up to 0.25% by weight of
SiO.sub.2.
(13) The multilayer ceramic chip capacitor of claim 6, 11 or 12 wherein the
dielectric material has further added thereto at least one oxide of Eu and
Mo and/or a compound which converts to the oxide upon firing in an amount
of up to 0.3% by weight calculated as oxide.
(14) The multilayer ceramic chip capacitor of any one of claims 6 to 13
wherein each said dielectric layer consists of grains and a grain boundary
phase and the ratio of the area of the grain boundary phase in a cross
section of said dielectric layer is up to 2%.
(15) The multilayer ceramic chip capacitor of claim 14 wherein said grain
boundary phase is an oxide phase containing oxides of Mn, Y, V and W.
(16) A multilayer ceramic chip capacitor which is prepared by successively
layering and co-firing a dielectric material having additives added to a
matrix of the following formula:
[(Ba.sub.1-x-y Ca.sub.x Sr.sub.y)O].sub.m (Ti.sub.1-z Zr.sub.z)O.sub.2
wherein 0.ltoreq.x.ltoreq.0.25, 0.ltoreq.y.ltoreq.0.05,
0.1.ltoreq.z.ltoreq.0.3, and 1.000.ltoreq.m.ltoreq.1.020, said additives
including an oxide of Mn and/or a compound which converts to the oxide
upon firing, an oxide of Y and/or a compound which converts to the oxide
upon firing, an oxide of V and/or a compound which converts to the oxide
upon firing, an oxide of W and/or a compound which converts to the oxide
upon firing, and Al.sub.2 O.sub.3 sintering aid, and an internal
electrode-forming material in the form of Ni or a Ni alloy.
(17) The multilayer ceramic chip capacitor of claim 16 wherein the Al.sub.2
O.sub.3 sintering aid is added in an amount of 0.005 to 0.5% by weight.
(18) The multilayer ceramic chip capacitor of claim 16 wherein the Al.sub.2
O.sub.3 sintering aid is added in an amount of 0.01 to 0.3% by weight.
(19) The multilayer ceramic chip capacitor of claim 16 wherein the Al.sub.2
O.sub.3 sintering aid is added in an amount of 0.01 to 0.15% by weight.
(20) The multilayer ceramic chip capacitor of claim 16 wherein said oxide
of Mn and/or said compound which converts to the oxide upon firing is
added in an amount of 0.01 to 0.5% by weight calculated as oxide (MnO),
said oxide of Y and/or said compound which converts to the oxide upon
firing is added in an amount of 0.05 to 0.5% by weight calculated as oxide
(Y.sub.2 O.sub.3), said oxide of V and/or said compound which converts to
the oxide upon firing is added in an amount of 0.005 to 0.3% by weight
calculated as oxide (V.sub.2 O.sub.5), and said oxide of W and/or said
compound which converts to the oxide upon firing is added in an amount of
0.005 to 0.3% by weight calculated as oxide (WO.sub.3).
(21) The multilayer ceramic chip capacitor of claim 16 or 20 wherein the
dielectric material has further added thereto at least one oxide of Eu and
Mo and/or a compound which converts to the oxide upon firing in an amount
of up to 0.3% by weight calculated as oxide.
(22) The multilayer ceramic chip capacitor of any one of claims 16 to 21
wherein each said dielectric layer consists of grains and a grain boundary
phase and the ratio of the area of the grain boundary phase in a cross
section of said dielectric layer is up to 2%.
(23) The multilayer ceramic chip capacitor of claim 22 wherein said grain
boundary phase is an oxide phase containing oxides of Mn, Y, V and W.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross section of one exemplary multilayer ceramic chip
capacitor according to the invention.
FIG. 2 is a photomicrograph of a polished cross section of a dielectric
layer in a sintered body constituting one exemplary multilayer ceramic
chip capacitor according to the invention, showing a grain structure.
ILLUSTRATIVE CONSTRUCTION
The illustrative construction of the invention is described in further
detail.
Referring to FIG. 1, there is illustrated a multilayer ceramic chip
capacitor according to one preferred embodiment of the invention. The
multilayer chip capacitor 1 includes alternately stacked internal
electrodes 21, 25 and dielectric layers 3 and a pair of external
electrodes 41, 45 connected to the respective internal electrodes 21, 25.
According to the invention, the internal electrodes 21, 25 are formed of Ni
or a Ni alloy, the Ni alloy being preferably a nickel alloy consisting of
at least 95% by weight of Ni and at least one element of Mn, Cr, Co, Al,
etc.
These lead to a satisfactory life and reliability according to the
invention.
It is to be noted that Ni or Ni alloys may contain up to 0.1% by weight of
P or the like as a trace component.
Parameters associated with the internal electrodes 21, 25 including
thickness may be suitably determined in accordance with a particular
purpose and application although the thickness is typically about 1 to 5
.mu.m, especially about 2 to 3 .mu.m.
The dielectric layer 3 consists of grains and a grain boundary phase.
The material of which the dielectric layer 3 is made contains a dielectric
oxide having a composition of the following formula.
[(Ba.sub.1-x-y Ca.sub.x Sr.sub.y)O].sub.m (Ti.sub.1-z Zr.sub.z)O.sub.2
In the formula, x is from 0 to 0.25, preferably from 0.05 to 0.10, y is
from 0 to 0.05, preferably from 0 to 0.01, z is from 0.1 to 0.3,
preferably from 0.15 to 0.20, and m is from 1.000 to 1.020, preferably
from 1.002 to 1.015.
According to the invention, the material further contains manganese oxide
and/or a compound which converts to the oxide upon firing in an amount of
0.01 to 0.5% by weight, preferably 0.1 to 0.4% by weight, more preferably
0.2 to 0.4% by weight calculated as oxide MnO, yttrium oxide and/or a
compound which converts to the oxide upon firing in an amount of 0.05 to
0.5% by weight, preferably 0.08 to 0.45% by weight, more preferably 0.2 to
0.4% by weight calculated as oxide Y.sub.2 O.sub.3, vanadium oxide and/or
a compound which converts to the oxide upon firing in an amount of 0.005
to 0.5% by weight, preferably 0.01 to 0.2% by weight, more preferably 0.01
to 0.1% by weight calculated as oxide V.sub.2 O.sub.5, and tungsten oxide
and/or a compound which converts to the oxide upon firing in an amount of
0.005 to 0.3% by weight, preferably 0.01 to 0.2 % by weight, more
preferably 0.01 to 0.1% by weight calculated as oxide WO.sub.3.
Preferably, the material may further contain SiO.sub.2 or Al.sub.2 O.sub.3
as a sintering aid.
In this regard, the content of SiO.sub.2 is preferably up to about 0.25% by
weight, especially about 0.05 to 0.25% by weight. The content of Al.sub.2
O.sub.3 is 0.005 to 0.5% by weight, preferably 0.01 to 0.3% by weight,
more preferably 0.01 to 0.15% by weight.
It is rather desirable to use Al.sub.2 O.sub.3 as the sintering aid because
multilayer ceramic chip capacitors which are improved in the accelerated
life of insulation resistance are obtained by low-temperature firing.
Also there may be contained up to about 0.3% by weight of at least one of
Eu oxides and Mo oxides. There may be further contained up to about 0.5%
by weight of a Ni oxide, Mg oxide, Co oxide, Hf oxide, etc.
None of the advantages of the invention are established with oxides of
elements other than the above-specified elements and addition amounts
outside the above-specified ranges.
In this regard, the additive powders as a whole should desirably have a
mean particle size of up to 3.0 .mu.m and additionally, a maximum particle
size of up to 5 .mu.m. Further the additive powders as a whole should
desirably have a mean particle size which is within 5 times the mean
particle size of the matrix powder. Moreover, the additive powders should
desirably have a maximum particle size which is within 3 times the maximum
particle size of the matrix powder. The additive powders should desirably
have a mean particle size of 0.3 to 1.5 .mu.m and a maximum particle size
of up to 3.5 .mu.m. Desirably the additive powders are previously
comminuted so as to meet the above-mentioned requirements. Where additive
powders larger than the selected particle size are used, chip capacitors
having thin dielectric layers have the problem that the local segregation
of the additives is found in the dielectric layers which would cause an
initial loss of insulation resistance. However, by comminuting additive
powders, especially by selecting a maximum particle size within the
above-mentioned range, the rejection rate of initial insulation resistance
of the resulting chip capacitors is minimized. Especially by selecting the
maximum particle size of the additives within the above-mentioned range,
the rejection rate of initial insulation resistance of the resulting chip
capacitors is dramatically minimized. It is to be noted that the matrix
powder should desirably have a mean particle size of up to 1.5 .mu.m and a
maximum particle size of up to 3 .mu.m.
Parameters associated with the dielectric layers 3 including the number of
layers and thickness may be suitably determined in accordance with a
particular purpose and application.
Also preferably, the grains in the dielectric layers 3 have a mean grain
size of about 1 to 5 .mu.m.
The ratio of the area of the grain boundary phase, which is the remainder
other than the grains forming the dielectric layer 3, in an arbitrary
cross section of the dielectric layer 3 is preferably up to about 2%, more
preferably about 0.5 to 1.0%.
Beyond this range, there is a likelihood of reducing the life and lowering
the reliability.
With an extremely low area ratio, there is a tendency that formation of
dielectric layers 3 is difficult and consolidation of dielectric layers 3
is insufficient.
Understandably, the area ratio of the grain boundary phase may be
determined from a photograph taken using a scanning electron microscope.
Some components of the grain boundary phase are oxides of materials
introduced as Mn, Y, V and W components.
The external electrodes 41, 45 typically use Cu and Cu alloys or Ni and Ni
alloys.
Understandably, Ag and Ag-Pd alloys are, of course, useful.
The thickness of the external electrodes 41, 45 is arbitrary and may be
determined in accordance with a particular purpose and application
although it typically ranges from about 10 to 50 .mu.m.
The shape and size of the multilayer chip capacitor 1 may be determined in
accordance with a particular purpose and application. For example,
rectangular shape capacitors are generally sized 1.6-3.2 mm.times.0.8-1.6
mm.times.0.6-1.2 mm.
Preferably the multilayer ceramic chip capacitor of the present invention
is fabricated as follows.
First prepared are a paste for forming the dielectric layers 3, a paste for
forming the internal electrodes 21, 25, and a paste for forming the
external electrodes 41, 45.
The paste for forming the dielectric layers 3 is obtained by mixing
previously comminuted additives in the form of single or composite oxides
of Ca, Mn, Y, V, W, Mo, Eu, Si, etc. and a matrix-forming material
selected from BaTiO.sub.3, BaZrO.sub.3, CaTiO.sub.3, CaZrO.sub.3, etc. in
accordance with the aforementioned dielectric oxide composition, drying
the mixture, and adding thereto additives such as binders, plasticizers,
dispersants, and solvents.
The above-mentioned additives of Ca or the like may be replaced by
compounds which will convert to oxides upon firing, for example,
carbonates, sulfates, nitrates, oxalates, and organometallic compounds.
Additionally, both an oxide and a compound which converts to the oxide upon
firing may be used.
The starting raw material for forming the matrix need not take the form of
BaTiO.sub.3, BaZrO.sub.3, CaTiO.sub.3, and CaZrO.sub.3 specified above,
but oxides of Ti, Ba, Zr, Ca, etc. or compounds which convert to the
respective oxides upon firing may be used in accordance with the desired
dielectric oxide composition.
From these source powders, a dielectric material is prepared by the
following procedure, for example.
First the starting raw materials are blended in a predetermined ratio and
wet milled, for example, in a ball mill.
Then the mixture is dried, for example, by a spray dryer, and then calcined
to form a dielectric oxide of the above-defined formula.
Calcination is generally effected in air at 800.degree. to 1300.degree. C.
for about 2 to 10 hours.
Thereafter, the product is ground in a jet mill or ball mill until a
predetermined particle size is reached, obtaining a dielectric material.
In the preparation of the dielectric layer-forming paste, any desired
additives such as binders, plasticizers, dispersants, and solvents may be
used. Addition of glass frit is also acceptable.
Examples of the binder include ethyl cellulose, abietic acid resin, and
polyvinyl butyral;
examples of the plasticizer include abietic acid derivatives, diethyl
oxalate, polyethylene glycol, polyalkylene glycols, phthalic esters, and
dibutyl phthalate;
examples of the dispersant include glycerin, octadecylamine,
trichloroacetic acid, oleic acid, octadiene, ethyl oleate, glycerol
monooleate, glycerol trioleate, glycerol tristearate, and menthadiene oil;
examples of the solvent include toluene, terpineol, butyl carbitol and
methyl ethyl ketone.
In preparing the paste, the proportion of the dielectric material in the
entire composition is about 50 to 80% by weight while using about 2 to 5%
by weight of the binder, about 0.01 to 5% by weight of the plasticizer,
about 0.01 to 5% by weight of the dispersant, and about 20 to 50% by
weight of the solvent.
A paste or slurry is obtained by mixing the dielectric material with these
additives and kneading the mixture, for example, in a three-roll mill.
The paste for forming the internal electrodes 21, 25 is prepared using Ni
or a Ni alloy or a mixture thereof as a conductor material.
The conductor material may be spherical or flake in shape or a mixture of
such shapes since its shape is not critical.
Any conductor material having a mean particle size of about 0.1 to 10
.mu.m, especially about 0.1 to 1 .mu.m may be used.
An organic vehicle contains a binder and a solvent.
Useful as the binder are any known binders such as ethyl cellulose, acrylic
resins, and butyral resins.
The binder content is about 1 to 5% by weight.
Useful as the solvent are any known solvents such as terpineol, butyl
carbitol, and kerosene.
The solvent content is about 20 to 55% by weight.
Additionally, if desired, there may be added in an amount of up to about
10% by weight in total dispersants such as sorbitan fatty acid esters and
glycerin fatty acid esters, plasticizers such as dioctyl phthalate,
dibutyl phthalate, and butyl butylphthalylglycolate, and various ceramic
powders such as dielectric materials and insulating materials for the
purposes of anti-delamination and controlled sintering.
Also it is effective to add organometallic resinates.
The paste for forming the external electrodes 41, 45 may be a conventional
paste containing the aforementioned conductor material powder.
Using the internal electrode-forming paste and dielectric layer-forming
paste thus obtained, layers are successively formed by a printing,
transfer or green sheet technique.
Then the laminate is cut to a predetermined size to form a green chip. The
green chip is removed of the binder and fired. Heat treatment is then
carried out for re-oxidation of the dielectric layers 3.
Binder removal may be carried out under conventional conditions, preferably
under the following conditions.
Heating rate: 5.degree.-300.degree. C./hour, especially
10.degree.-50.degree. C./hour
Holding temperature: 200.degree.-400.degree. C., especially
250.degree.-350.degree. C.
Holding time: 1/2-5 hours, especially 1-3 hours
Atmosphere: air
Firing is preferably carried out at an oxygen partial pressure of up to
10.sup.-7 atm., especially 10.sup.-7 to 10.sup.-13 atm.
Above the range, the internal electrodes 21, 25 are likely to oxidize. At
an extremely low oxygen partial pressure, the electrode material tends to
be abnormally sintered and disconnected.
Remaining conditions for sintering are preferably as follows.
Heating rate: 50.degree.-500.degree. C./hour, especially
200.degree.-300.degree. C./hour
Holding temperature: 1200.degree.-1400.degree. C., especially
1250.degree.-1350.degree. C.
Holding time: 1/2-8 hours, especially 1-3 hours
Cooling rate: 50.degree.-500.degree. C./hour, especially
200.degree.-300.degree. C./hour
The atmospheric gas is preferably a humidified mixture of N.sub.2 and
H.sub.2 gases.
Heat treatment is preferably carried out with the holding or maximum
temperature set at 800.degree. to 1200.degree. C., more preferably
900.degree. to 1100.degree. C.
Below the range, there is a likelihood that the life be reduced because of
short oxidation of the dielectric material. Above the range, there is a
likelihood that Ni as the internal electrodes be not only oxidized to
reduce the capacity, but also reacted with the dielectric material to
reduce the life.
During the heat treatment, the oxygen partial pressure is preferably at
least 10.sup.-8 atm., more preferably 10.sup.-4 to 10.sup.-7 atm.
Below the range, it is difficult to re-oxidize the dielectric layers 3 and
oxide layers 4 whereas above the range, the internal electrodes 21, 25 are
likely to oxidize.
Remaining conditions for heat treatment are preferably as follows.
Holding time: 0-6 hours, especially 2-5 hours
Cooling rate: 50.degree.-500.degree. C./hour, especially
100.degree.-300.degree. C./hour
The atmospheric gas is preferably humidified N.sub.2 gas.
For humidifying N.sub.2 gas or mixture, a wetter may be used, for example.
In this regard, water temperature is preferably about 0.degree. to
75.degree. C.
The foregoing binder removal, firing and heat treatment may be carried out
either continuously or separately.
The thus obtained sintered body is polished at end faces by barrel tumbling
and sand blasting, for example, before the external electrode-forming
paste is baked to form external electrodes 41, 45.
If necessary, pads are formed on the external electrodes 41, 45 as by
plating.
The multilayer ceramic chip capacitors of the invention use a barium
titanate system dielectric material having specific compounds added
thereto.
They are prepared by removing the binder and carrying out firing and heat
treatment under predetermined conditions.
The multilayer ceramic chip capacitors of the invention have a life which
is increased about 1.5 times or more over the life of conventional chip
capacitors having added thereto yttrium or the like. Therefore, a
satisfactory life is maintained even when the thickness of dielectric
layers is reduced from the conventional thickness 10 to 15 .mu.m to 6
.mu.m or less. By comminuting the additives to a mean particle size of 3
.mu.m or less, the initial loss of insulation resistance is minimized,
greatly contributing to the fabrication of compact size, high capacity
multilayer ceramic chip capacitors. Furthermore, addition of SiO.sub.2 or
Al.sub.2 O.sub.3 as a sintering aid allows for low-temperature firing and
especially the use of Al.sub.2 O.sub.3 improves the accelerated life of
insulation resistance.
EXAMPLE
Examples of the invention are given below by way of illustration.
EXAMPLE 1
The starting raw materials used for forming a matrix were BaTiO.sub.3,
BaZrO.sub.3 and CaTiO.sub.3 resulting from liquid phase synthesis.
The additives used were MnCO.sub.3, Y.sub.2 O.sub.3, V.sub.2 O.sub.5,
WO.sub.3, SiO.sub.2, MoO.sub.3, Eu.sub.2 O.sub.3, etc. and the amounts of
MnCO.sub.3, Y.sub.2 O.sub.3, V.sub.2 O.sub.5, WO.sub.3, MoO.sub.3, and
Eu.sub.2 O.sub.3 were changed as shown in Table 1. For each run, the
additives were milled for 24 hours in a ball mill to form a slurry of the
additives having a mean particle size of up to 3 .mu.m and a maximum
particle size of up to 5 .mu.m. To the additive slurry were added the
BaTiO.sub.3, BaZrO.sub.3 and CaTiO.sub.3. Each mixture was wet milled for
16 hours in a ball mill, and dried. There were obtained twenty one (21)
samples of dielectric material. Note that sample Nos. 1 to 13 are
inventive examples and sample Nos. 14 to 21 are comparative examples.
TABLE 1
__________________________________________________________________________
MnO Y.sub.2 O.sub.3
V.sub.2 O.sub.5
WO.sub.3
others
IR life
Initial properties (20.degree. C.)
Sample
(wt %)
(wt %)
(wt %)
(wt %)
(wt %)
(h) C(nF)
tan .delta. (%)
IR (.OMEGA.)
__________________________________________________________________________
1 0.2 0.1 0.05
0.05 8.7 205 4.8 5 .times. 10.sup.10
2 0.2 0.2 0.05
0.05 12.4
193 4.1 7 .times. 10.sup.10
3 0.2 0.3 0.05
0.05 14.6
170 3.7 7 .times. 10.sup.10
4 0.2 0.4 0.05
0.05 13.3
136 2.9 3 .times. 10.sup.10
5 0.1 0.3 0.05
0.05 9.3 218 5.8 1 .times. 10.sup.10
6 0.3 0.3 0.05
0.05 15.3
140 2.8 8 .times. 10.sup.10
7 0.2 0.3 0.01
0.05 12.7
173 4.3 9 .times. 10.sup.10
8 0.2 0.3 0.1 0.05 15.0
154 3.9 7 .times. 10.sup.10
9 0.2 0.3 0.2 0.05 10.1
125 3.5 8 .times. 10.sup.10
10 0.2 0.3 0.005
0.01 12.9
170 3.7 8 .times. 10.sup.10
11 0.2 0.3 0.05
0.1 13.7
162 3.1 7 .times. 10.sup.10
12 0.2 0.3 0.05
0.05
MoO.sub.3 0.05
13.8
220 5.1 9 .times. 10.sup.10
13 0.2 0.3 0.05
0.05
Eu.sub.2 O.sub.3 0.05
18.2
158 5.4 4 .times. 10.sup.10
14 0.2 0 0 0 0.01
251 5.7 8 .times. 10.sup.9
15 0.2 0.3 0 0 4.1 206 4.4 5 .times. 10.sup.10
16 0.2 0 0.04
0.05 0.18
232 5.1 2 .times. 10.sup.10
17 0 0.3 0.04
0.05 0.37
87 2.6 1 .times. 10.sup.8
18 1.0 0.3 0.04
0.05 3.8 113 5.8 2 .times. 10.sup.10
19 0.2 0.3 0.75
0.05 2.7 115 3.4 7 .times. 10.sup.10
20 0.2 0.8 0.04
0.05 4.9 88 8.6 4 .times. 10.sup.8
21 0.2 1.0 1.0 1.0 1.1 59 15.1 7 .times. 10.sup.7
__________________________________________________________________________
Matrix composition: [(Ba.sub.0.989 Ca.sub.0.01 Sr.sub.0.001) O].sub.1.004
(Ti.sub.0.92 Zr.sub.0.18)O.sub.2
From each of these dielectric materials, a dielectric layer-forming paste
was prepared by mixing it with additives at the blending ratio shown below
in a ball mill charged with alumina balls, thereby forming a slurry.
______________________________________
Dielectric material:
100 parts by weight
Acrylic resin: 5.0 parts by weight
Benzylbutyl phthalate:
2.5 parts by weight
Mineral spirits: 6.5 parts by weight
Acetone: 4.0 parts by weight
Trichloroethane: 20.5 parts by weight
Methylene chloride:
41.5 parts by weight
______________________________________
Separately, an internal electrode-forming paste was prepared by milling the
following components in the blending ratio shown below in a three-roll
mill, thereby forming a slurry.
______________________________________
Ni: 44.6% by weight
Terpineol: 52% by weight
Ethyl cellulose: 3% by weight
Benzotriazole: 0.4% by weight
______________________________________
Using these pastes, a multilayer ceramic chip capacitor 1 as shown in FIG.
1 was fabricated as follows.
First using the dielectric layer-forming paste, a sheet of 10 .mu.m thick
was formed on a carrier film. Using the internal electrode-forming paste,
an internal electrode was printed thereon. A plurality of thus formed
sheets were stripped from the carrier films, stacked one on top of
another, and bonded under pressure.
The number of dielectric layers 3 was four layers.
The stack was cut to a predetermined size and then continuously subjected
to binder removal, firing and heat treatment under the following
conditions.
Binder removal
Heating rate: 20.degree. C./hr.
Holding temperature: 300.degree. C.
Holding time: 2 hours
Atmospheric gas: air
Firing
Heating rate: 200.degree. C./hr.
Holding temperature: 1340.degree. C.
Holding time: 2 hours
Cooling rate: 300.degree. C./hr.
Atmospheric gas: humidified N.sub.2 and H.sub.2 gas mixture
Oxygen partial pressure: 10.sup.-8 atm.
Heat treatment
Holding temperature: 1000.degree. C.
Holding time: 2 hours
Cooling rate: 300.degree. C./hr.
Atmospheric gas: humidified N.sub.2 gas
Oxygen partial pressure: 10.sup.-7 atm.
For humidifying the atmospheric gases, a wetter was used at a water
temperature of 5.degree. to 75.degree. C.
The sintered body thus obtained was polished at end faces by sand blasting
and In-Ga alloy was applied to form testing electrodes.
The thus prepared multilayer ceramic chip capacitor 1 had dimensions 3.2
mm.times.1.6 mm.times.0.6 mm, the dielectric layers 3 were 6 .mu.m thick,
and the internal electrodes 21, 25 were 2.5 .mu.m thick. The dielectric
layers 3 contained a dielectric oxide of a composition represented by the
formula:
[(Ba.sub.0.989 Ca.sub.0.01 Sr.sub.0.001)O].CT.sub.0.82 Zr.sub.0.18)O.sub.2
as a main ingredient. Note that strontium found in this composition
resulted from an impurity incidentally contained in the raw materials.
The photograph of FIG. 2 shows one exemplary fine structure appearing on a
polished surface of the dielectric layer 3 in the sintered body or
multilayer ceramic chip capacitor 1. The sintered body had a grain size of
1 to 3 .mu.m and the grain boundary had a thickness of up to 5 nm. Table 2
shows element distributions within grains, at the grain boundary and the
triple point as analyzed by means of a transmission type scanning electron
microscope. Note that in Table 2, A/B is a ratio of the component of the
formula at A site to that at B site. For all the samples, the area ratio
of the grain boundary phase in a cross section of the dielectric layer was
up to 2%.
TABLE 2
__________________________________________________________________________
Ti Ba Zr Al Si Ca Mn Y Ni W V O A/B
at %
__________________________________________________________________________
Within grain
14.5
19.7
3.47
0.65
0.54
0.14
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