U.S. patent application number 14/063000 was filed with the patent office on 2014-02-13 for manufacturing method for laminated ceramic capacitor, and laminated ceramic capacitor.
This patent application is currently assigned to MURATA MANUFACTURING CO., LTD.. The applicant listed for this patent is MURATA MANUFACTURING CO., LTD. Invention is credited to Makoto Matsuda, Tomoyuki Nakamura.
Application Number | 20140043725 14/063000 |
Document ID | / |
Family ID | 43627692 |
Filed Date | 2014-02-13 |
United States Patent
Application |
20140043725 |
Kind Code |
A1 |
Matsuda; Makoto ; et
al. |
February 13, 2014 |
MANUFACTURING METHOD FOR LAMINATED CERAMIC CAPACITOR, AND LAMINATED
CERAMIC CAPACITOR
Abstract
A method for manufacturing a laminated ceramic capacitor by
firing a laminated body which includes dielectric ceramic layers
containing a dielectric ceramic raw material powder and internal
electrodes. The firing is carried out in accordance with a
temperature profile in which the average rate of temperature rise
is 40.degree. C./second or more from room temperature to a maximum
temperature. The dielectric ceramic raw material powder contains a
BaTiO.sub.3 system as its main constituent, and contains R (R is
Sc, etc.), M (M is Mn, etc.), and Mg as accessory constituents, in
which, when the total amount of the accessory constituents
contained is denoted by D parts by mol with respect to 100 parts by
mol of the main constituent, an the specific surface area of the
main constituent is denoted by E m.sup.2/g, then D/E is 0.2 to
0.8.
Inventors: |
Matsuda; Makoto;
(Nagaokakyo-Shi, JP) ; Nakamura; Tomoyuki;
(Nagaokakyo-Shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MURATA MANUFACTURING CO., LTD |
Nagaokakyo-Shi |
|
JP |
|
|
Assignee: |
MURATA MANUFACTURING CO.,
LTD.
Nagaokakyo-Shi
JP
|
Family ID: |
43627692 |
Appl. No.: |
14/063000 |
Filed: |
October 25, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13403019 |
Feb 23, 2012 |
8609564 |
|
|
14063000 |
|
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PCT/JP2010/062213 |
Jul 21, 2010 |
|
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13403019 |
|
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Current U.S.
Class: |
361/321.4 |
Current CPC
Class: |
H01G 4/1227 20130101;
H01G 4/30 20130101; H01G 4/10 20130101 |
Class at
Publication: |
361/321.4 |
International
Class: |
H01G 4/10 20060101
H01G004/10 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 27, 2009 |
JP |
2009-196346 |
Claims
1. A laminated ceramic capacitor comprising: a laminated body
configured by a plurality of dielectric ceramic layers stacked, and
a plurality of internal electrodes formed along specific interfaces
between the dielectric ceramic layers; and a plurality of external
electrodes formed in different positions from each other on an
outer surface of the laminated body and electrically connected to
specific one of the internal electrodes, wherein a dielectric
ceramic constituting the dielectric ceramic layers contains
ABO.sub.3 as a main constituent thereof, and contains R, M, and Mg
as accessory constituents thereof, and the dielectric ceramic
constituting the dielectric ceramic layers has an average grain
size of 100 nm or less, wherein A contains Ba, B contains Ti, R is
at least one element selected from Sc, Y, La, Ce, Pr, Nd, Pm, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and M is at least one
element selected from Mn, Cr, Co, and Fe.
2. The laminated ceramic capacitor according to claim 1, wherein
the average grain size is 50 nm or less.
3. The laminated ceramic capacitor according to claim 1, wherein A
further contains at least one of Ca and Sr.
4. The laminated ceramic capacitor according to claim 3, wherein B
further contains at least one of Zr and Hf.
5. The laminated ceramic capacitor according to claim 1, wherein B
further contains at least one of Zr and Hf.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional of application Ser.
No. 13/403,019, filed Feb. 23, 2012, which is a continuation of
International application No. PCT/JP2010/062213, filed Jul. 21,
2010, which claims priority to Japanese Patent Application No.
2009-196346, filed Aug. 27, 2009, the entire contents of each of
which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to a method for manufacturing a
laminated ceramic capacitor and the laminated ceramic capacitor,
and more particularly, an improvement in a method for manufacturing
a laminated ceramic capacitor, and an improvement in the
composition of a BaTiO.sub.3 based dielectric ceramic for use in a
laminated ceramic capacitor which is suitable for the improved
manufacturing method.
BACKGROUND OF THE INVENTION
[0003] In laminated ceramic capacitors, for the purpose of
reduction in size (reduction in thickness), it is effective to
attempt to reduce in thickness not only of dielectric ceramic
layers, but also of internal electrodes. However, when the internal
electrodes are further reduced in thickness, electrode
disconnection is likely to be caused as a result of a firing step
for sintering of a raw laminated body. For example, the following
technique has been proposed as a technique which can prevent the
electrode disconnection.
[0004] In Japanese Patent Laid-Open Publication No. 2008-226941
(Patent Document 1), the rate of temperature rise adjusted to
500.degree. C./hour to 5000.degree. C./hour in a firing step
prevents electrode disconnection to achieve an electrode thickness
of 0.8 to 1 .mu.m.
[0005] In Japanese Patent Laid-Open Publication No. 2000-216042
(Patent Document 2), structural defects such as cracks are
prevented to increase the reliability of a laminated ceramic
capacitor obtained, in such a way that the rate of temperature rise
is adjusted to 500.degree. C./hour or more at 700.degree. C. to
1100.degree. C. in a temperature rising process for firing, the
oxygen partial pressure in the atmosphere is adjusted to 10.sup.-8
atm or less at 1100.degree. C. or more, and the oxygen partial
pressure is adjusted to 10.sup.-8 atm or more partially at
1100.degree. C. or less in a temperature falling process.
[0006] In Korean Patent Laid-Open Publication No. 10-2006-0135249
(Patent Document 3), the temperature is increased at a rate of
temperature rise of 10.degree. C./second up to a temperature
20.degree. C. lower than the maximum temperature to achieve a
balance between the prevention of electrode disconnection and the
prevention of overshoot during the temperature rise (reaching a
temperature higher than a desired firing temperature during the
temperature rise).
[0007] While the prior art described in any of Patent Documents 1
to 3 achieves the effect of allowing the internal electrodes to be
reduced in layer thickness by means such as increasing the rate of
temperature rise, the effect has a limitation, and for example, in
a laminated ceramic capacitor including internal electrodes
containing Ni as a conductive component, it is extremely difficult
to achieve 0.3 .mu.m or less as an electrode thickness after
firing.
[0008] In addition, the atmosphere for firing a raw laminated body
including internal electrodes using a base metal as a conductive
component is, for example, a N.sub.2/H.sub.2/H.sub.2O system which
needs to be controlled on a more reducing side than a Ni/NiO
equilibrium oxygen partial pressure, and this need will restrict
the equipment and the material design.
[0009] In addition, when the ceramic contains, for example, a
volatile component such as Li, this volatile component is likely to
scatter during firing. Further, the residual volume of the volatile
component is likely to vary depending on the size of the raw
laminated body to be fired, that is, the chip size, and the amount
of charging a firing furnace, and it is difficult to suppress the
variation in this residual volume.
[0010] On the other hand, laminated ceramic capacitors have been
progressively reduced in size (reduced in thickness), and the
dielectric ceramic layers are becoming 0.5 .mu.m or less in
thickness. In order to respond to this reduction in thickness of
the dielectric ceramic layers, there is a need for size reduction
of the dielectric ceramic grains constituting the dielectric
ceramic layers. Therefore, there is also a need for microscopic
grains of a dielectric ceramic raw material powder.
[0011] However, when the dielectric ceramic raw material powder is
reduced in size, for example, to several nm level, grain growth is
likely to be developed during firing, and as a result, may lead to
a problem that the laminated ceramic capacitor is inferior in terms
of lifetime characteristics under a high temperature load
condition. [0012] Patent Document 1: Japanese Patent Laid-Open
Publication No. 2008-226941 [0013] Patent Document 2: Japanese
Patent Laid-Open Publication No. 2000-216042 [0014] Patent Document
3: Korean Patent Laid-Open Publication No. 10-2006-0135249
SUMMARY OF THE INVENTION
[0015] Therefore, an object of the present invention is to provide
a method for manufacturing a laminated ceramic capacitor, and the
laminated ceramic capacitor, which can solve the problems described
above.
[0016] This invention is first directed to a method for
manufacturing a laminated ceramic capacitor, which includes: a step
of preparing a raw laminated body including a plurality of stacked
dielectric ceramic layers containing a dielectric ceramic raw
material powder, and internal electrodes formed along the specific
interfaces between the dielectric ceramic layers; and a firing step
of subjecting the raw laminated body to a heat treatment in order
to carry out sintering of the raw laminated body, and
characteristically has the following configuration in order to
solve the technical problems described above.
[0017] More specifically, in this invention, a temperature profile
in which the average rate of temperature rise is 40.degree.
C./second or more from room temperature to a maximum temperature is
adopted in the firing step. Further, in order for the composition
and properties of the dielectric ceramic raw material powder to be
suitable for this high-rate temperature rise, the following
composition is adopted.
[0018] The dielectric ceramic raw material powder contains
ABO.sub.3 (A necessarily contains Ba, and may further contain at
least one of Ca and Sr; and B necessarily contains Ti, and may
further contain at least one of Zr and Hf) as its main constituent,
and contains R (R is at least one selected from Sc, Y, La, Ce, Pr,
Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu), M (M is at
least one selected from Mn, Cr, Co, and Fe), and Mg as accessory
constituents. Furthermore, when the total amount of the accessory
constituents contained is denoted by D parts by mol with respect to
100 parts by mol of the main constituent, whereas the specific
surface area of the ceramic raw material powder for providing the
main constituent is denoted by E m.sup.2/g, D/E is 0.2 to 0.8.
[0019] In the method for manufacturing a laminated ceramic
capacitor according to this invention, the firing step is
preferably carried out in accordance with a temperature profile in
which the average rate of temperature rise is 100.degree. C./second
or more from room temperature to the maximum temperature.
[0020] This invention is also directed to a laminated ceramic
capacitor including: a laminated body configured by a plurality of
dielectric ceramic layers stacked, and a plurality of internal
electrodes formed along the specific interfaces between the
dielectric ceramic layers; and a plurality of external electrodes
formed in different positions from each other on the outer surface
of the laminated body and electrically connected to specific one of
the internal electrodes.
[0021] In the laminated ceramic capacitor according to this
invention, a dielectric ceramic constituting the dielectric ceramic
layers contains ABO.sub.3 (A necessarily contains Ba, and may
further contain at least one of Ca and Sr; and B necessarily
contains Ti, and may further contain at least one of Zr and Hf) as
its main constituent, and contains R (R is at least one selected
from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,
and Lu), M (M is at least one selected from Mn, Cr, Co, and Fe),
and Mg as accessory constituents, and the dielectric ceramic
constituting the dielectric ceramic layers has an average grain
size of 100 nm or less.
[0022] In the laminated ceramic capacitor according to this
invention, the dielectric ceramic constituting the dielectric
ceramic layers has an average grain size of 50 nm or less.
[0023] In the method for manufacturing a laminated ceramic
capacitor according to this invention, the dielectric ceramic
layers contain the accessory elements which have the action of
inhibiting the ceramic grain growth, and sintering is completed in
a short period of time in the firing step. Thus, the segregation of
the accessory elements is prevented from being caused as much as
possible in the dielectric ceramic layers, and can be made present
homogeneously. Therefore, the grain growth during the firing is
made less likely to be developed, and the ceramic constituting the
obtained dielectric ceramic layers can be composed of microscopic
grains.
[0024] Thus, in the laminated ceramic capacitor, even when the
dielectric ceramic layers are reduced in layer thickness, lifetime
characteristics can be made favorable in a high temperature loading
test. In addition, the properties can be stabilized which are
provided by the dielectric ceramic layers. Furthermore, even when
the additive amount of the accessory elements is relatively small,
the effect of the accessory elements can be produced
sufficiently.
[0025] In addition, according to this invention, in the internal
electrodes, changes in state such as electrode disconnection and
ball formation are prevented during the heat treatment in the
firing step, and the internal electrodes can be thus progressively
reduced in layer thickness while maintaining the coverage of the
internal electrodes at a high level, thereby making a contribution
to the reduction in size of and the increase in capacitance of the
laminated ceramic capacitor.
[0026] In addition, the reduced layer thickness and increased
coverage for the internal electrodes are produced as a result of
preventing the internal electrodes from being shrunk, and voids,
gaps, and the like at the ends of the internal electrodes can be
thus also prevented from being caused at the same time. Therefore,
the sealing property of the laminated body is improved after the
heat treatment, and the reliability of environment resistance can
be also improved as a laminated ceramic electronic component.
[0027] In addition, the shrinkage of the internal electrodes is
prevented as described above, and thus, in the case of extracting
the internal electrodes to a predetermined surface of the laminated
body, the degree of recess will be quite low at the extracted ends
of the internal electrodes. In addition, sintering is completed in
a short period of time in the firing step, and thus, almost no
movement or segregation of the glass phase onto the surface will be
caused due to the additive component to the ceramic constituting
the dielectric ceramic layers. Therefore, the step for exposing the
extracted ends of the internal electrodes can be skipped in the
formation of external electrodes electrically connected to the
internal electrodes.
[0028] In addition, even when the dielectric ceramic constituting
the dielectric ceramic layers contains volatile components
(sintering aids) such as Li, B, and Pb, the volatile components is
prevented from being scattered by the heat treatment in the firing
step, because sintering is completed in a short period of time in
the firing step. As a result, the residual volume of the volatile
components can be prevented from varying depending on changes in
the size of the laminated body and the amount of charging a firing
furnace.
[0029] In addition, in the case of the laminated ceramic capacitor
including internal electrodes containing, as a conductive
component, a base metal such as Ni, there is conventionally a need
in the heat treatment step to precisely control the oxygen partial
pressure in the atmosphere to near the equilibrium oxygen partial
pressure of the base metal in order to achieve a balance between
the prevention of the internal electrodes from being oxidized and
the prevention of the ceramic from being reduced, and this need
complicates the design of a firing furnace. In contrast, according
to this invention, the high rate of temperature rise in the firing
step can reduce the time for the heat treatment (ceramic sintering
shrinkage), and thus, even in a more oxidizing atmosphere than the
equilibrium oxygen partial pressure of the base metal, the heat
treatment can be carried out almost without oxidation. Therefore, a
laminated ceramic capacitor with high reliability can be
manufactured which has the dielectric ceramic less likely to be
reduced and requires no reoxidation treatment.
BRIEF EXPLANATION OF THE DRAWINGS
[0030] FIG. 1 is a cross-sectional view schematically illustrating
a laminated ceramic capacitor produced by a manufacturing method
according to an embodiment of this invention.
[0031] FIGS. 2(A) and 2(B) show mapping analysis images of an Mn
element by a wavelength-dispersive X-ray microanalyzer (WDX);
wherein FIG. 2(A) is sample 10 and FIG. 2(B) is sample 11 from
Table 1, which were obtained in order to assess dispersion states
of accessory constituents in dielectric ceramics constituting
dielectric ceramic layers included in a laminated ceramic capacitor
prepared in an experimental example.
DETAILED DESCRIPTION OF THE INVENTION
[0032] With reference to FIG. 1, the structure of a laminated
ceramic capacitor 1 will be described to which this invention is
applied.
[0033] The laminated ceramic capacitor 1 includes a laminated body
2 as a component main body. The laminated body 2 includes a
plurality of dielectric ceramic layers 3 stacked, and a plurality
of internal electrodes 4 and 5 formed along the specific interfaces
between the dielectric ceramic layers 3. One and the other end
surfaces 6 and 7 of the laminated body 2 respectively have exposed
ends of the plurality of internal electrodes 4 and 5, and external
electrodes 8 and 9 are formed respectively so as to electrically
connect the respective ends of the internal electrodes 4 to each
other and the respective ends of the internal electrodes 5 to each
other.
[0034] For the manufacture of this laminated ceramic capacitor 1,
the laminated body 2 in a raw state is first prepared by a well
known method such as stacking ceramic green sheets with the
internal electrodes 4 and 5 printed thereon. Then, a firing step is
carried out for sintering of the raw laminated body. Then, the
external electrodes 8 and 9 are formed respectively on the end
surfaces 6 and 7 of the sintered laminated body 2 to complete the
laminated ceramic capacitor 1.
[0035] In this invention, a powder which has the following
composition and properties is used as a dielectric ceramic raw
material powder, which is included in the ceramic green sheets to
serve as the dielectric ceramic layers 3 included in the laminated
body 2 described above.
[0036] More specifically, the dielectric ceramic raw material
powder contains ABO.sub.3 (A necessarily contains Ba, and may
further contain at least one of Ca and Sr; and B necessarily
contains Ti, and may further contain at least one of Zr and Hf) as
its main constituent, and contains R (R is at least one selected
from Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,
and Lu) and M (M is at least one selected from Mn, Cr, Co, and Fe)
as accessory constituents. Furthermore, in this dielectric ceramic
raw material powder, when the total amount of the accessory
constituents contained is denoted by D parts by mol with respect to
100 parts by mol of the main constituent, whereas the specific
surface area of the ceramic raw material powder for providing the
main constituent is denoted by E m.sup.2/g, D/E is 0.2 to 0.8.
[0037] In addition, in the firing step described above, a heat
treatment step of applying a temperature profile in which the
average rate of temperature rise is 40.degree. C./second or more
from room temperature to the maximum temperature is carried out
according to this invention. Preferably, the temperature profile is
adjusted to 100.degree. C./second or more.
[0038] The raw laminated body is preferably subjected to a
degreasing treatment before the heat treatment step.
[0039] In addition, after reaching the maximum temperature, cooling
is preferably carried out immediately without keeping the
temperature in the heat treatment step.
[0040] When the laminated ceramic capacitor 1 is manufactured by
applying the high rate of temperature rise as described above while
using the dielectric ceramic raw material powder, which has the
composition and properties as described previously, the dielectric
ceramic constituting the dielectric ceramic layers 3 can have, as
microscopic grains, an average grain size of 100 nm or less,
preferably 50 nm or less.
[0041] It is to be noted that while the laminated ceramic capacitor
1 shown is a two-terminal type laminated ceramic capacitor
including the two external electrodes 8 and 9, this invention can
be also applied to multi-terminal type laminated ceramic electronic
components.
[0042] An experimental example will be described below which was
carried out for confirming the effects of this invention.
[0043] (A) Preparation of Ceramic Powder for Main Constituent
[0044] First, a barium titanate powder and a barium calcium
titanate powder were prepared. Predetermined amounts of BaCO.sub.3
powder and TiO.sub.2 powder for the barium titanate powder, and
predetermined amounts of BaCO.sub.3 powder, CaCO.sub.3 powder, and
TiO.sub.2 powder for the barium calcium titanate powder were each
weighed, then mixed in a ball mill for 42 hours, and subjected to a
heat treatment for a solid-phase reaction to obtain a BaTiO.sub.3
(hereinafter, "BT") powder and a (Ba.sub.0.90Ca.sub.0.10)TiO.sub.3
(hereinafter, "BCT") powder.
[0045] In this case, each of the BT powder and the BCT powder was
prepared so as to have target grain size and specific surface area
(SSA) as shown in Table 1. It is to be noted that the grain size
refers to an average grain size in the case of converting a SEM
observation image to a spherical shape, whereas the SSA was
measured by an apparatus (Multisorb) using a nitrogen adsorption
method.
[0046] (B) Preparation of Dielectric Ceramic Raw Material
Powder
[0047] In order to obtain samples 1 to 17 shown in Table 1,
respective powders of MgO, MnO, Dy.sub.2O.sub.3, and SiO.sub.2 were
blended as follows with each of the BT powder and BCT powder
obtained in the way described above.
[0048] Samples 1, 2, and 7 to 9: 100BT (or
BCT)-1.0Dy-1.0Mg-0.3Mn-1.0Si
[0049] Samples 3 to 6: 100BT (or BCT)-10Dy-10Mg-3Mn-1.0Si
[0050] Samples 10 to 13, 16, and 17: 100BT (or
BCT)-2.5Dy-2.5Mg-0.8Mn-1.0Si
[0051] Sample 14: 100BT-3.0Dy-1.1Mg-0.8Mn-1.1Si
[0052] Sample 15: 100BT-7.4Dy-2.7Mg-2.0Mn-1.1Si.
[0053] Next, these blended materials were mixed in a ball mill for
5 hours. Then, drying and dry grinding were carried out to obtain a
dielectric ceramic raw material powder.
[0054] (C) Production of Laminated Ceramic Capacitor
[0055] The dielectric ceramic raw material powder obtained with the
addition of a polyvinyl butyral based binder and ethanol was
subjected to wet mixing in a ball mill for 5 hours to prepare a
ceramic slurry.
[0056] Next, this ceramic slurry was formed by a die coater into
the shape of a sheet to obtain ceramic green sheets.
[0057] Next, a conductive paste containing Ni as its main
constituent was applied by screen printing onto the ceramic green
sheets, thereby forming conductive paste films to serve as internal
electrodes.
[0058] In addition, as a measure for eliminating differences in
level on the principal surfaces of the ceramic green sheets, which
can be produced between the regions with the conductive paste films
and the regions without the conductive paste films, a dielectric
paste film of the same composition as the ceramic slurry was formed
on the regions without the conductive paste films so as to have a
thickness equivalent to that of the conductive paste film.
[0059] Next, the ceramic green sheets with the conductive paste
films and dielectric paste films formed were stacked alternately so
that the sides were alternated to which the conductive paste films
were extracted, thereby providing a raw laminated body including 5
effective layers.
[0060] Next, the raw laminated body was heated to a temperature of
300.degree. C. in an N.sub.2 atmosphere to burn the binder, and
then the binder was burned again at a temperature of 700.degree. C.
in an N.sub.2 atmosphere.
[0061] Then, in accordance with a conventional firing method, a
heat treatment of increasing the temperature at a rate of
temperature rise in Table 1 was carried out in a reducing
atmosphere composed of a H.sub.2--N.sub.2--H.sub.2O gas with an
oxygen partial pressure 10.sup.-10 MPa to obtain a sintered
laminated body. In this case, the conditions of the maximum
temperature in the firing step and of the time for keeping at the
maximum temperature were set up as follows, depending on the rate
of temperature rise.
[0062] The case of 50.degree. C./min for Rate of Temperature Rise:
keeping at a maximum temperature of 1200.degree. C. for 5
minutes.
[0063] The case of 40 to 200.degree. C./min for Rate of Temperature
Rise: maximum temperature of 1400.degree. C. without keeping.
[0064] Next, a Cu paste containing a
B.sub.2O.sub.3--Li.sub.2O--SiO.sub.2--BaO glass frit was applied to
both end surfaces of the sintered laminated body, and fired at a
temperature of 800.degree. C. in an N.sub.2 atmosphere to form
external electrodes electrically connected to the internal
electrodes, thereby providing laminated ceramic capacitors as
samples.
[0065] The laminated ceramic capacitors thus obtained had outside
dimensions of 0.5 mm in width and 1.0 mm in length, and the area of
the electrode opposed per dielectric ceramic layer was 0.3
mm.sup.2. In addition, the dielectric ceramic layers were 0.3 .mu.m
in thickness, and the internal electrodes were 0.3 .mu.m in
thickness.
[0066] (D) Evaluation
[0067] As shown in Table 1, evaluated were the grain size, the
degree of grain growth, and the number of defectives in a high
temperature load life test.
[0068] The measurement of the grain size was made in such a way
that the laminated ceramic capacitors according to each sample were
fractured and subjected to thermal etching at a temperature of
1000.degree. C., and the fractured surfaces were observed by using
a scanning microscope. More specifically, the observation images
were subjected to an image analysis to determine the equivalent
circle diameters as the grain sizes. The average value was
calculated for the number of grains measured of 300, as the "Grain
Size" shown in Table 1.
[0069] The degree of grain growth was calculated from the formula
of "Degree of Grain Growth"="Average Grain Size after
Firing"/"Grain Size of Ceramic Powder for Main Constituent".
[0070] In order to find the number of defects in a high temperature
load life test, the high temperature load life test was carried out
in which DC 4V was applied to the dielectric ceramic layers of 0.3
.mu.m in thickness at a temperature of 85.degree. C. to measure the
change in insulation resistance with time for the laminated ceramic
capacitors according to each sample. In this case, 100 samples for
each sample number were subjected to the high temperature load life
test, and the sample was determined as a defective if the
insulation resistance value was decreased to 100 k.OMEGA. or less
before a lapse of 2000 hours.
TABLE-US-00001 TABLE 1 Number of Defectives Grain Size SSA of Main
Total Amount in High Type of for Main Constituent of Accessory Rate
of Grain The Degree Temperature Sample Main Constituent Powder: E
Constituent: D Temperature Size of Grain Load Life Number
Constituent Powder (nm) (m.sup.2/g) (parts by mol) D/E Rise (nm)
Growth Test 1 BT 12 80 2.3 0.03 50.degree. C./min 273 22.8 100 2 BT
12 80 2.3 0.03 200.degree. C./second 197 16.4 100 3 BT 12 80 23
0.29 50.degree. C./min 260 21.7 100 4 BT 12 80 23 0.29 200.degree.
C./second 21 1.8 0 5 BCT 14 72 23 0.32 50.degree. C./min 245 17.5
100 6 BCT 14 72 23 0.32 200.degree. C./second 22 1.6 0 7 BT 42 24
2.3 0.10 50.degree. C./min 220 5.2 95 8 BT 40 25 2.3 0.09
50.degree. C./min 247 6.2 100 9 BT 40 25 2.3 0.09 200.degree.
C./second 153 3.8 50 10 BT 40 25 5.8 0.23 50.degree. C./min 215 5.4
92 11 BT 40 25 5.8 0.23 200.degree. C./second 45 1.1 0 12 BCT 43 23
5.8 0.25 50.degree. C./min 238 5.5 99 13 BCT 43 23 5.8 0.25
200.degree. C./second 49 1.1 0 14 BT 40 25 4.9 0.19 200.degree.
C./second 101 2.5 5 15 BT 40 25 12.1 0.49 200.degree. C./second 43
1.1 0 16 BT 40 25 5.8 0.23 40.degree. C./second 55 1.4 0 17 BT 40
25 5.8 0.23 100.degree. C./second 50 1.3 0
[0071] The following is determined from Table 1.
[0072] In the case of samples 1, 3, 5, 7, 8, 10, and 12 with
50.degree. C./min for the rate of temperature rise, the grain size
is much greater than 200 nm due to grain growth. Further, when the
grain size is increased as described above, the number of
defectives is also large in the high temperature load life
test.
[0073] On the other hand, among samples 2, 4, 6, 9, 11, and 13 to
17 with 40.degree. C./second or more for the rate of temperature
rise, the grain size is also greater than 100 nm due to grain
growth for samples 2, 9, and 14 with D/E less than 0.2. Further,
when the grain size is increased as described above, the number of
defectives is also large in the high temperature load life
test.
[0074] In contrast to these samples, in the case of samples 4, 6,
11, 13, and 15 to 17 with 40.degree. C./second or more for the rate
of temperature rise and D/E of 0.2 to 0.8, the grain size is
reduced to 100 nm or less, and the number of defectives is even 0
in the high temperature load life test. In particular, among these
samples 4, 6, 11, 13, and 15 to 17, the grain size is further
reduced to 50 nm or less in the case of samples 4, 6, 11, 13, 15,
and 17 with 100.degree. C./second or more for the rate of
temperature rise.
[0075] Furthermore, for example, when a comparison is made among
samples 11, 16, and 17, the samples are different only in rate of
temperature rise: the rate of temperature rise of 200.degree.
C./second or more in the case of sample 11; the rate of temperature
rise of 40.degree. C./second or more in the case of sample 16; and
the rate of temperature rise of 100.degree. C./second or more in
the case of sample 17. As a result, the grain size is further
reduced as 55 nm, 50 nm, and 45 nm, in the order of increasing the
rate of temperature rise: samples 16, 17, and 11.
[0076] It is to be noted that although Table 1 shows no sample with
D/E greater than 0.8, it has been confirmed that the D/E greater
than 0.8 causes the segregation of the accessory constituent to
degrade the lifetime characteristics in the high temperature load
life test, even if firing is carried out with high-rate temperature
rise such as 40.degree. C./second or more, and further, 100.degree.
C./second for the rate of temperature rise in the firing step.
[0077] FIGS. 2(A) and 2(B) show mapping analysis images of an Mn
element by a wavelength-dispersive X-ray microanalyzer (WDX), which
were obtained in order to assess dispersion states of accessory
constituents in dielectric ceramics constituting dielectric ceramic
layers included in a laminated ceramic capacitor prepared in this
experimental example. FIG. 2(A) is an image for sample 10, and FIG.
2(B) is an image for sample 11.
[0078] It is to be noted that although FIGS. 2(A) and 2(B) are not
intended to indicate the mapping analysis of the Mn element
accurately because FIGS. 2(A) and 2(B) are not presented in full
color, it can be determined in the black and white representation
that the segregation of the Mn element is caused more strongly when
the contrast is greater.
[0079] Sample 10 and sample 11 are different from each other in the
firing conditions of the rate of temperature rise, maximum
temperature, and keeping time. In the case of sample 11 with the
high rate of temperature rise of 200.degree. C./second adopted, as
shown in FIG. 2(B), there is less segregation of the Mn element as
the accessory constituent, and the Mn element is dispersed almost
homogeneously. It is considered that this homogeneous dispersion
enhances the effect of inhibiting the grain growth. In contrast, in
the case of sample 10 with the low rate of temperature rise of
50.degree. C./second adopted, the segregation of the Mn element is
caused strongly as shown in FIG. 2(A).
[0080] It is to be noted that while Dy and Mn were used
respectively as the accessory constituent elements R and M in the
dielectric ceramic raw material powder in the experimental example,
it has been confirmed that a similar effect is produced even in the
case of using any of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Ho,
Er, Tm, Yb, and Lu except for Dy as the accessory constituent
element R, or in the case of using any of Cr, Co, and Fe except for
Mn as the accessory constituent element M.
DESCRIPTION OF REFERENCE SYMBOLS
[0081] 1 laminated ceramic capacitor [0082] 2 laminated body [0083]
3 dielectric ceramic layer [0084] 4, 5 internal electrode
* * * * *