U.S. patent application number 15/889071 was filed with the patent office on 2018-08-16 for multilayer ceramic capacitor and manufacturing method of multilayer ceramic capacitor.
The applicant listed for this patent is TAIYO YUDEN CO., LTD.. Invention is credited to Katsuya TANIGUCHI.
Application Number | 20180233284 15/889071 |
Document ID | / |
Family ID | 63105875 |
Filed Date | 2018-08-16 |
United States Patent
Application |
20180233284 |
Kind Code |
A1 |
TANIGUCHI; Katsuya |
August 16, 2018 |
MULTILAYER CERAMIC CAPACITOR AND MANUFACTURING METHOD OF MULTILAYER
CERAMIC CAPACITOR
Abstract
A multilayer ceramic capacitor includes: a multilayer structure
in which each of a plurality of ceramic dielectric layers and each
of a plurality of internal electrode layers are alternately
stacked, wherein: (a current value at 10 V/.mu.m when a direct
voltage is applied to the plurality of the ceramic dielectric
layers at 125 degrees C.)/(a current value at 10 V/.mu.m when a
direct voltage is applied to the plurality of the ceramic
dielectric layers at 85 degrees C.) is more than 5 and less than
20; and a donor element concentration in the plurality of ceramic
dielectric layers is 0.05 atm % or more and 0.3 atm % or less.
Inventors: |
TANIGUCHI; Katsuya;
(Takasaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TAIYO YUDEN CO., LTD. |
Tokyo |
|
JP |
|
|
Family ID: |
63105875 |
Appl. No.: |
15/889071 |
Filed: |
February 5, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 2235/3256 20130101;
H01G 4/30 20130101; B32B 2315/02 20130101; C04B 2235/78 20130101;
H01G 4/1209 20130101; B32B 2457/16 20130101; C04B 2235/3251
20130101; C04B 2235/3239 20130101; C04B 2235/3206 20130101; C04B
2235/3258 20130101; H01G 4/1227 20130101 |
International
Class: |
H01G 4/12 20060101
H01G004/12; H01G 4/30 20060101 H01G004/30 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2017 |
JP |
2017-027330 |
Claims
1. A multilayer ceramic capacitor comprising: a multilayer
structure in which each of a plurality of ceramic dielectric layers
and each of a plurality of internal electrode layers are
alternately stacked, wherein: (a current value at 10 V/.mu.m when a
direct voltage is applied to the plurality of the ceramic
dielectric layers at 125 degrees C.)/(a current value at 10 V/.mu.m
when a direct voltage is applied to the plurality of the ceramic
dielectric layers at 85 degrees C.) is more than 5 and less than
20; and a donor element concentration in the plurality of ceramic
dielectric layers is 0.05 atm % or more and 0.3 atm % or less.
2. The multilayer ceramic capacitor as claimed in claim 1, wherein
an average grain diameter of the plurality of ceramic dielectric
layers is 80 nm or more and 200 nm or less.
3. The multilayer ceramic capacitor as claimed in claim 1, wherein
the donor element is at least one of V, Mo, Nb, La, W and Ta.
4. The multilayer ceramic capacitor as claimed in claim 2, wherein
the donor element is at least one of V, Mo, Nb, La, W and Ta.
5. The multilayer ceramic capacitor as claimed in claim 1, wherein
a thickness of the plurality of ceramic dielectric layers is 1
.mu.m or less.
6. The multilayer ceramic capacitor as claimed in claim 1, where a
main component ceramic of the plurality of ceramic dielectric
layers has a perovskite structure.
7. A manufacturing method of a multilayer ceramic capacitor
comprising: forming a green sheet of which a concentration of a
donor element with respect to a main component ceramic is 0.05 atm
% or more and 0.3 atm % or less; forming a multilayer structure by
alternately stacking the green sheet and a conductive paste for
forming an internal electrode; and baking the multilayer structure,
wherein the multilayer structure is sintered in the baking so that,
in the multilayer structure after the baking, (a current value at
10 V/.mu.m when a direct voltage is applied to the plurality of the
ceramic dielectric layers at 125 degrees C.)/(a current value at 10
V/.mu.m when a direct voltage is applied to the plurality of the
ceramic dielectric layers at 85 degrees C.) becomes more than 5 and
less than 20.
8. The method as claimed in claim 7, wherein in the forming of the
green sheet, a green sheet of a main component ceramic in which the
donor element of 0.05 atm % or more and 0.3 atm % or less is
solid-solved in advance is formed.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Patent Application No. 2017-027330,
filed on Feb. 16, 2017, the entire contents of which are
incorporated herein by reference.
FIELD
[0002] A certain aspect of the present invention relates to a
multilayer ceramic capacitor and a manufacturing method of a
multilayer ceramic capacitor.
BACKGROUND
[0003] A thickness of a dielectric layer is being reduced because
downsizing and enhancement of a capacitance of a multilayer ceramic
capacitor are demanded. As a result, electric field intensity
applied to the dielectric layer increases. Thereby, life property
of the dielectric layer is degraded. And so, it is proposed that a
donor element such as Mo (molybdenum), W (tungsten) or the like is
added to a dielectric layer in order to improve life property (for
example, see Japanese Patent Application Publications No.
2016-139720 and No. 2016-127120).
SUMMARY OF THE INVENTION
[0004] However, in the technologies, a position of the donor
element in the dielectric layer is not defined. When the donor
element exists in a crystal grain of main component ceramic of the
dielectric layer, the donor element contributes to the life
property of the dielectric layer. A donor element existing in a
crystal boundary does not contribute to the life property of the
dielectric layer. Therefore, even if a concentration of the donor
element of a whole of the dielectric layer is defined, preferable
life property is not achieved.
[0005] The present invention has a purpose of providing a
multilayer ceramic capacitor and a manufacturing method of the
multilayer ceramic capacitor that are capable of achieving
preferable life property of a dielectric layer.
[0006] According to an aspect of the present invention, there is
provided a multilayer ceramic capacitor including: a multilayer
structure in which each of a plurality of ceramic dielectric layers
and each of a plurality of internal electrode layers are
alternately stacked, wherein: (a current value at 10 V/.mu.m when a
direct voltage is applied to the plurality of the ceramic
dielectric layers at 125 degrees C.)/(a current value at 10 V/.mu.m
when a direct voltage is applied to the plurality of the ceramic
dielectric layers at 85 degrees C.) is more than 5 and less than
20; and a donor element concentration in the plurality of ceramic
dielectric layers is 0.05 atm % or more and 0.3 atm % or less.
[0007] According to another aspect of the present invention, there
is provided a manufacturing method of a multilayer ceramic
capacitor including: forming a green sheet of which a concentration
of a donor element with respect to a main component ceramic is 0.05
atm % or more and 0.3 atm % or less; forming a multilayer structure
by alternately stacking the green sheet and a conductive paste for
forming an internal electrode; and baking the multilayer structure,
wherein the multilayer structure is sintered in the baking so that,
in the multilayer structure after the baking, (a current value at
10 V/.mu.m when a direct voltage is applied to the plurality of the
ceramic dielectric layers at 125 degrees C.)/(a current value at 10
V/.mu.m when a direct voltage is applied to the plurality of the
ceramic dielectric layers at 85 degrees C.) becomes more than 5 and
less than 20.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 illustrates a partial perspective view of a
multilayer ceramic capacitor;
[0009] FIG. 2 illustrates a flowchart of a manufacturing method of
a multilayer ceramic capacitor;
[0010] FIG. 3A and FIG. 3B illustrate a relationship between
temperature change coefficients (125 degrees C./85 degrees C.) and
accelerated life values of examples 1 to 5 and comparative examples
1 and 2.
[0011] FIG. 4 illustrates a relationship among a temperature
change, a leak current value and an applied voltage of a multilayer
ceramic capacitor of a comparative example 1;
[0012] FIG. 5 illustrates a relationship among a temperature
change, a leak current value and an applied voltage of a multilayer
ceramic capacitor of an example 1; and
[0013] FIG. 6 illustrates a relationship among a temperature
change, a leak current value and an applied voltage of a multilayer
ceramic capacitor of an example 4.
DETAILED DESCRIPTION
[0014] A description will be given of an embodiment with reference
to the accompanying drawings.
Embodiment
[0015] FIG. 1 illustrates a partial perspective view of a
multilayer ceramic capacitor 100 in accordance with an embodiment.
As illustrated in FIG. 1, the multilayer ceramic capacitor 100
includes a multilayer chip 10 having a rectangular parallelepiped
shape, and a pair of external electrodes 20a and 20b that are
respectively provided at two edge faces of the multilayer chip 10
facing each other. In four faces other than the two edge faces of
the multilayer chip 10, two faces other than an upper face and a
lower face of the multilayer chip 10 in a stacking direction are
referred to as side faces. The external electrodes 20a and 20b
extend to the upper face, the lower face and the two side faces.
However, the external electrodes 20a and 20b are spaced from each
other.
[0016] The multilayer chip 10 has a structure designed to have
dielectric layers 11 and internal electrode layers 12 alternately
stacked. The dielectric layer 11 includes ceramic material acting
as a dielectric material. The internal electrode layers 12 include
a base metal material. End edges of the internal electrode layers
12 are alternately exposed to a first edge face of the multilayer
chip 10 and a second edge face of the multilayer chip 10 that is
different from the first edge face. In the embodiment, the first
face faces with the second face. The external electrode 20a is
provided on the first edge face. The external electrode 20b is
provided on the second edge face. Thus, the internal electrode
layers 12 are alternately conducted to the external electrode 20a
and the external electrode 20b. Thus, the multilayer ceramic
capacitor 100 has a structure in which a plurality of dielectric
layers 11 are stacked and each two of the dielectric layers 11
sandwich the internal electrode layer 12. In the multilayer chip
10, the internal electrode layer 12 is positioned at an outermost
layer. The upper face and the lower face of the multilayer chip 10
that are the internal electrode layers 12 are covered by cover
layers 13. A main component of the cover layer 13 is a ceramic
material. For example, a main component of the cover layer 13 is
the same as that of the dielectric layer 11.
[0017] For example, the multilayer ceramic capacitor 100 may have a
length of 0.2 mm, a width of 0.125 mm and a height of 0.125 mm. The
multilayer ceramic capacitor 100 may have a length of 0.4 mm, a
width of 0.2 mm and a height of 0.2 mm. The multilayer ceramic
capacitor 100 may have a length of 0.6 mm, a width of 0.3 mm and a
height of 0.3 mm. The multilayer ceramic capacitor 100 may have a
length of 1.0 mm, a width of 0.5 mm and a height of 0.5 mm. The
multilayer ceramic capacitor 100 may have a length of 3.2 mm, a
width of 1.6 mm and a height of 1.6 mm. The multilayer ceramic
capacitor 100 may have a length of 4.5 mm, a width of 3.2 mm and a
height of 2.5 mm. However, the size of the multilayer ceramic
capacitor 100 is not limited.
[0018] A main component of the internal electrode layers 12 is a
base metal such as nickel (Ni), copper (Cu), tin (Sn) or the like.
The internal electrode layers 12 may be made of a noble metal such
as platinum (Pt), palladium (Pd), silver (Ag), gold (Au) or alloy
thereof. The dielectric layers 11 are mainly composed of a ceramic
material that is expressed by a general formula ABO.sub.3 and has a
perovskite structure. The perovskite structure includes
ABO.sub.3-.alpha. having an off-stoichiometric composition. For
example, the ceramic material is such as BaTiO.sub.3 (barium
titanate), CaZrO.sub.3 (calcium zirconate), CaTiO.sub.3 (calcium
titanate), SrTiO.sub.3 (strontium titanate),
Ba.sub.1-x-yCa.sub.xSr.sub.yTi.sub.1-zZr.sub.zO.sub.3
(0.ltoreq.x.ltoreq.1, 0.ltoreq.y.ltoreq.1, 0.ltoreq.z.ltoreq.1)
having a perovskite structure. For example, the dielectric layer 11
has a thickness of 1 .mu.m or less or a thickness of 0.8 .mu.m or
less.
[0019] The dielectric layer 11 includes a donor element. The donor
element is an element that can be replaced with an A site of the
perovskite ABO.sub.3 and can become an ion of which valence is
three (a part of rare earth elements such as Y (yttrium), La
(lanthanum), Sm (samarium), Gd (gadolinium), Dy (dysprosium) or Ho
(Holmium)) or an element that can be replaced with a B site of the
perovskite ABO.sub.3 and can become ion of which valence is five or
more (a part of transition metals such as V (vanadium), Mo
(molybdenum), Nb (niobium), W (tungsten) or Ta (tantalum)). For
example, when the main component ceramic of the dielectric layer 11
is a perovskite, V (vanadium), Mo, Nb, La, Ta or the like can be
used as the donor element. When the dielectric layer 11 includes a
donor element, generation of an oxygen defect can be suppressed.
Therefore, life property of the dielectric layer 11 is improved.
When the donor element concentration of the dielectric layer 11 is
excessively low, it may not be possible to achieve the effect of
the donor element sufficiently. And so, in the embodiment, the
concentration of the donor element in the dielectric layer 11 is
0.05 atm % or more. On the other hand, when the donor element
concentration of the dielectric layer 11 is excessively high,
insulating property may be degraded or the bias property may be
degraded in accordance with solid-solution of the donor element.
And so, in the embodiment, the donor element concentration in the
dielectric layer 11 is 0.3 atm % or less. "atm %" means a
concentration "atm %" of the donor element on the presumption that
the B site is 100 atm %.
[0020] The main component ceramic of the dielectric layer 11 is not
structured with a single crystal grain but includes a plurality of
crystal grains. Therefore, the donor element may be equally
dispersed in crystal grains and crystal grain boundaries or may be
mainly dispersed in the crystal grain boundaries. When the donor
element exists in the crystal grains of the main component ceramic,
the donor element suppresses the oxygen defect. Therefore, even if
the donor element concentration in the dielectric layer 11 is 0.05
atm % or more and 0.3 atm % or less, the donor element does not
always contribute to the life property of the dielectric layer
11.
[0021] When a temperature increases, electrons are excited to a
conduction band in accordance with a donor level of the donor
element. In this case, a leak current also increases. When
temperature dependence of the leak current is large, the donor
element exists in the dielectric layer 11 and is solid-solved in
crystal grains of the main component ceramic. Therefore, when a
temperature change coefficient of the leak current is large, the
donor element contributes to the life property of the dielectric
layer 11. And so, the embodiment focuses on a temperature change
coefficient of a leak current.
[0022] In concrete, (a current value at 10 V/.mu.m when a direct
voltage is applied to the dielectric layer 11 at 125 degrees C.)/(a
current value at 10 V/.mu.m when a direct voltage is applied to the
dielectric layer 11 at 85 degrees C.) is used as the temperature
change coefficient of the leak current. In the following, the
temperature change coefficient is referred to as a temperature
change coefficient (125 degrees C./85 degrees C.).
[0023] When the temperature change coefficient (125 degrees C./85
degrees C.) is small, an amount of the donor element in the main
component ceramic grains of the dielectric layer 11 is small. In
this case, maybe, preferable life property of the dielectric layer
11 is not achieved. And so, the temperature change coefficient (125
degrees C./85 degrees C.) is increased to more than a predetermined
value. On the other hand, when the temperature change coefficient
(125 degrees C./85 degrees C.) is large, the amount of the donor
element in the main component ceramic grains of the dielectric
layer 11 is large. In this case, insulating property and bias
property of the dielectric layer 11 may be degraded. And so, the
temperature change coefficient (125 degrees C./85 degrees C.) is
decreased to less than a predetermined value. In the embodiment,
the temperature change coefficient (125 degrees C./85 degrees C.)
is more than 5 and less than 20. It is therefore possible to
suppress the leak current and improve the life property. And, it is
preferable that the temperature change coefficient (125 degrees
C./85 degrees C.) is more than 6 and less than 15.
[0024] It is possible to calculate the temperature change
coefficient by changing an ambient temperature with use of a
thermostatic chamber, applying a direct voltage of 10 V/.mu.m
between the external electrode 20a and the external electrode 20b,
and measuring a leak current after 60 seconds after the
applying.
[0025] It is preferable that at least a part of the dielectric
layer 11 in which a voltage difference occurs has preferable life
property. Therefore, at least a part of the dielectric layer 11
having an electrical capacity of the multilayer ceramic capacitor
100 has preferable life property. And so, the dielectric layer 11
in a region in which the internal electrode layer 12 connected to
the external electrode 20a faces with the internal electrode layer
12 connected to the external electrode 20b includes a donor element
of which concentration is 0.05 atm % or more and 0.3 atm % or less,
and has property of 5<the temperature change coefficient (125
degrees C./85 degrees C.)<20.
[0026] When an average grain diameter of the main component ceramic
of the dielectric layer 11 is small, a dielectric constant becomes
smaller. And, maybe, a preferable electrostatic capacitance is not
achieved. And so, it is preferable that an average grain diameter
of the main component ceramic of the dielectric layer 11 is 80 nm
or more. On the other hand, when the average grain diameter of the
main component ceramic of the dielectric layer 11 is large, an area
of grain boundaries acting as a movement barrier of oxygen defects
is reduced in the dielectric layer 11 having a thickness of 1 .mu.m
or less and the life property may be degraded. And so, it is
preferable that the average grain diameter of the main component
ceramic of the dielectric layer 11 is 200 nm or less. The grain
diameters are Feret diameters that are measured by adjusting a
scale factor so that a single image of a scanning electron
microscope or a transmission electron microscope includes 80 to 150
crystal grains, capturing a plurality of images so that a total
number of the crystal grains is 400 or more, and measuring all
Feret diameters of all of the crystal grains on the images. The
average grain diameter is an average of the Feret diameters.
[0027] Next, a description will be given of a manufacturing method
of the multilayer ceramic capacitor 100. FIG. 2 illustrates a
manufacturing method of the multilayer ceramic capacitor 100.
[0028] (Making process of raw material powder) A ceramic material
powder is prepared as a main component of the dielectric layer 11.
A donor element may be included in the dielectric layer 11 by
mixing a ceramic material and a donor element source. However, it
is preferable that a ceramic material in which a donor element is
solid-solved in advance is used. When the donor element is Mo, Mo
compound such as MoO.sub.3 may be used as the donor element
source.
[0029] Next, additive compound may be added to ceramic powder
material, in accordance with purposes. The additive compound may be
an oxide of Mg (magnesium), Mn (manganese), V (vanadium), Cr
(chromium) or a rare earth element (Y (yttrium), Dy (dysprosium),
Tm (thulium), Ho (holmium), Tb (terbium), Yb (ytterbium), Sm
(samarium), Eu (europium), Gd (gadolinium) and Er (erbium)), or an
oxide of Co (cobalt), Ni (nickel), Li (lithium), B (boron), Na
(sodium), K (potassium) and Si (silicon), or glass. For example,
compound including additive compound is added to a ceramic material
powder and is calcined. Next, the resulting ceramic material grains
are wet-blended with additive compound, is dried and is crushed.
Thus, the ceramic material powder is prepared.
[0030] (Stacking Process) Next, a binder such as polyvinyl butyral
(PVB) resin, an organic solvent such as ethanol or toluene, and a
plasticizer such as dioctyl phthalate (DOP) are added to the
resulting ceramic material powder and wet-blended. With use of the
resulting slurry, a strip-shaped dielectric green sheet with a
thickness of 0.8 .mu.m or less is coated on a base material by, for
example, a die coater method or a doctor blade method, and then
dried.
[0031] Then, a pattern of the internal electrode layer 12 is
provided on the surface of the dielectric green sheet by printing a
conductive paste for forming the internal electrode with use of
screen printing or gravure printing. The conductive paste includes
powder of the main component metal of the internal electrode layer
12, a binder, a solvent, and additives as needed. It is preferable
that the binder and the solvent are different from those of the
above-mentioned ceramic slurry. As a co-material, the ceramic
material that is the main component of the dielectric layer 11 may
be distributed in the conductive paste.
[0032] Then, the dielectric green sheet on which the internal
electrode layer pattern is printed is stamped into a predetermined
size, and a predetermined number (for example, 200 to 500) of
stamped dielectric green sheets are stacked while the base material
is peeled so that the internal electrode layers 12 and the
dielectric layers 11 are alternated with each other and the end
edges of the internal electrode layers 12 are alternately exposed
to both edge faces in the length direction of the dielectric layer
so as to be alternately led out to a pair of external electrodes of
different polarizations.
[0033] Cover sheets, which are to be the cover layers 13, are
compressed on the stacked green sheets and under the stacked
sheets. The resulting compact is cut into a predetermined size (for
example, 1.0 mm.times.0.5 mm). Thus, a ceramic multilayer structure
having a rectangular parallelepiped shape is obtained.
[0034] (Baking process) Next, after removing the binder in N.sub.2
atmosphere at 250 degrees C. to 500 degrees C., the resulting
ceramic multilayer structure is baked for ten minutes to 2 hours in
a reductive atmosphere in a temperature range of 1100 degrees C. to
1300 degrees C. Thus, each compound structuring the dielectric
green sheet is sintered. In this manner, a sintered structure
having the multilayer chip 10 having the multilayer structure in
which the sintered dielectric layers 11 and the sintered internal
electrode layers 12 are alternately stacked and having the cover
layers 13 formed as outermost layers of the multilayer chip 10 in
the stack direction is obtained.
[0035] (Re-oxidizing process) After that, a re-oxidizing process
may be performed at 600 degrees C. to 1000 degrees C. in N.sub.2
gas atmosphere.
EXAMPLES
Example 1
[0036] In an example 1, barium titanate was used as the main
component ceramic of the dielectric layer 11. Mo was used as the
donor element. MoO.sub.3 was added to the main component ceramic
powder so that Mo is 0.2 atm % on a presumption that Ti of the main
component ceramic powder is 100 atm %. The resulting main component
ceramic powder was sufficiently wet-blended and crushed with a ball
mil. Thus, the dielectric material was obtained. An organic binder
and a solvent were added to the dielectric material. And dielectric
green sheets were made by a doctor blade method. The organic binder
was polyvinyl butyral (PVB) resin or the like. The solvent was
ethanol, toluene or the like. And a plasticizer and so on were
added. Next, the conductive paste for forming the internal
electrode layer 12 was made by mixing powder acting as a main
component metal of the internal electrode layer 12, a binder, a
solvent and an additive as needed. The organic binder and the
solvent were different from those of the dielectric green sheet.
The conductive paste was screen-printed on the dielectric sheet.
500 of the dielectric green sheets on which the conductive paste
for forming the internal electrode layer were stacked, and cover
sheets were stacked on the stacked dielectric green sheets and
under the stacked dielectric green sheets. After that, a ceramic
multilayer structure was obtained by a thermal compressing. And the
ceramic multilayer structure was cut into a predetermined size. The
thickness of the dielectric layer 11 after the baking was 0.8
.mu.m.
Example 2
[0037] In an example 2, a main component ceramic powder in which
0.05 atm % of Mo was solid-solved in advance was used as the
dielectric material. A Mo source was not added to the main
component ceramic powder. Other conditions were the same as those
of the example 1.
Example 3
[0038] In an example 3, a main component ceramic powder in which
0.1 atm % of Mo was solid-solved in advance was used as the
dielectric material. A Mo source was not added to the main
component ceramic powder. Other conditions were the same as those
of the example 1.
Example 4
[0039] In an example 4, a main component ceramic powder in which
0.2 atm % of Mo was solid-solved in advance was used as the
dielectric material. A Mo source was not added to the main
component ceramic powder. Other conditions were the same as those
of the example 1.
Example 5
[0040] In an example 5, a main component ceramic powder in which
0.3 atm % of Mo was solid-solved in advance was used as the
dielectric material. A Mo source was not added to the main
component ceramic powder. Other conditions were the same as those
of the example 1.
Comparative Example 1
[0041] In a comparative example 1, a Mo source was not added to a
main component ceramic powder. Other condition were the same as
those of the example 1.
Comparative Example 2
[0042] In a comparative example 2, a main component ceramic powder
in which 0.35 atm % of Mo was solid-solved in advance was used as
the dielectric material. A Mo source was not added to the main
component ceramic powder. Other conditions were the same as those
of the example 1.
[0043] (Analysis) FIG. 3A illustrates a relationship between
temperature change coefficients (125 degrees C./85 degrees C.) and
accelerated life values of the examples 1 to 5 and the comparative
examples 1 and 2. In FIG. 3A, the accelerated life values are
expressed as MTTF (Mean Time To Failure). The accelerated life
value was measured by applying a direct voltage of 10 V between the
external electrode 20a and the external electrode 20b at 125
degrees C., measuring a leak current value with an ampere meter,
and measuring a time to a dielectric breakdown. The mean time to
failure is an average of times to the dielectric breakdown of 20
numbers of the multilayer ceramic capacitors.
[0044] As illustrated in FIG. 3A, a correlation occurs between the
temperature change coefficient (125 degrees C./85 degrees C.) and
the accelerated life values. In the comparative example 1 in which
a donor element was not added (barium titanate in which Mo was not
added), the temperature change coefficient (125 degrees C./85
degrees C.) was approximately 2 that was a small value. And the
accelerated life value was 200 min or less that was a small value.
Therefore, a preferable life value was not achieved. In the example
1 (barium titanate in which Mo was added) in which the main
component ceramic powder and the Mo source were mixed with each
other and were baked, the temperature change coefficient (125
degrees C./85 degrees C.) was approximately 5 that was a relatively
large value. The accelerated life value was approximately 200 min
to 300 min that was a long life property. In the examples 2 to 5
(barium titanate in which Mo was solid-solved) in which the main
component ceramic powder in which Mo was solid-solved in advance
was sintered, the temperature change coefficient (125 degrees C./85
degrees C.) was 7 to 20 that was a larger value than that of the
example 1. The accelerated life value was approximately 200 min to
1200 min that was a larger value than that of the example 1.
However, when the temperature change coefficient (125 degrees C./85
degrees C.) was more than 20 as in the case of the example 2, the
leak current value at 85 degrees C. increased by two orders or more
with respect to the barium titanate in which Mo was not added, as
illustrated in FIG. 3B.
[0045] From the results, it is demonstrated that when the donor
element concentration in the dielectric layer 11 is 0.05 atm % to
0.3 atm % and the temperature change coefficient (125 degrees C./85
degrees C.) is more than 5 and less than 20, it is possible to
suppress the leak current and it is possible to improve the life
property.
[0046] FIG. 4 illustrates a relationship among a temperature
change, a leak current value and an applied voltage of the
multilayer ceramic capacitor 100 of the comparative example 1. As
illustrated in FIG. 4, when a donor element was not added to the
dielectric layer 11, there was little changing of the leak current
value with respect to the temperature. It is thought that this is
because a donor element was not solid-solved in crystal grains of
the main component ceramic of the dielectric layer 11.
[0047] FIG. 5 illustrates a relationship among a temperature
change, a leak current value and an applied voltage in the
multilayer ceramic capacitor 100 of the example 1. As illustrated
in FIG. 5, when a donor element was added to the dielectric layer
11, a temperature change appears in the leak current value. It is
thought this because a part of donor elements were solid-solved in
crystal grains of the main component ceramic of the dielectric
layer 11.
[0048] FIG. 6 illustrates a relationship among a temperature
change, a leak current value and an applied voltage in the
multilayer ceramic capacitor 100 of the example 4. A total added
amount of Mo in the dielectric layer 11 in the example 1 was the
same as that in the example 4. However, as illustrated in FIG. 6,
the changing of the leak current value with respect to the
temperature became larger than FIG. 5. It is thought that this is
because the barium titanate in which a donor element was
solid-solved in advance was used, and a lot of donor elements exist
in crystal grains of the main component ceramic of the dielectric
layer 11. From the results of FIG. 4 to FIG. 6, it is demonstrated
that when the main component ceramic powder in which a donor
element was solid-solved in advance was used, a lot of donor
elements exist in crystal grains.
[0049] Although the embodiments of the present invention have been
described in detail, it is to be understood that the various
change, substitutions, and alterations could be made hereto without
departing from the spirit and scope of the invention.
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