U.S. patent application number 15/623253 was filed with the patent office on 2017-12-28 for multilayer ceramic capacitor, ceramic powder, manufacturing method of multilayer ceramic capacitor and manufacturing method of ceramic powder.
The applicant listed for this patent is TAIYO YUDEN CO., LTD.. Invention is credited to Osamu HATTORI, Kazumichi HIROI, Chie KAWAMURA.
Application Number | 20170372841 15/623253 |
Document ID | / |
Family ID | 60677021 |
Filed Date | 2017-12-28 |
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United States Patent
Application |
20170372841 |
Kind Code |
A1 |
KAWAMURA; Chie ; et
al. |
December 28, 2017 |
MULTILAYER CERAMIC CAPACITOR, CERAMIC POWDER, MANUFACTURING METHOD
OF MULTILAYER CERAMIC CAPACITOR AND MANUFACTURING METHOD OF CERAMIC
POWDER
Abstract
A multilayer ceramic capacitor includes: a multilayer structure
in which ceramic dielectric layers and internal electrode layers
are alternately stacked, wherein: a main component of the ceramic
dielectric layer is barium titanate in which a donor element having
a larger valence than Ti is solid-solved and an acceptor element
having a smaller valence than Ti and larger ion radius than Ti and
the donor element is solid-solved; a solid-solution amount of the
donor element is 0.05 mol or more and 0.3 mol or less on a
presumption that an amount of the barium titanate is 100 mol and
the donor element is converted into an oxide; and a solid solution
amount of the accepter element is 0.02 mol or more and 0.2 mol or
less on a presumption that the amount of the barium titanate is 100
mol and the acceptor element is converted into an oxide.
Inventors: |
KAWAMURA; Chie;
(Takasaki-shi, JP) ; HIROI; Kazumichi;
(Takasaki-shi, JP) ; HATTORI; Osamu;
(Takasaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TAIYO YUDEN CO., LTD. |
Tokyo |
|
JP |
|
|
Family ID: |
60677021 |
Appl. No.: |
15/623253 |
Filed: |
June 14, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 35/4682 20130101;
C04B 2235/3267 20130101; C01P 2002/88 20130101; C04B 2235/3256
20130101; C04B 2235/3239 20130101; H01G 4/1227 20130101; C01G
23/006 20130101; C04B 2237/346 20130101; B32B 18/00 20130101; C01P
2002/72 20130101; C04B 2237/68 20130101; C04B 35/62685 20130101;
C04B 2235/5296 20130101; H01G 4/1218 20130101; C01P 2002/34
20130101; C04B 2235/3224 20130101; C04B 2235/3258 20130101; C01P
2002/50 20130101; C01P 2006/12 20130101; H01G 4/30 20130101; C04B
2235/3262 20130101; C04B 2235/5409 20130101; C04B 35/62655
20130101; C04B 2235/3418 20130101; C04B 2235/663 20130101 |
International
Class: |
H01G 4/30 20060101
H01G004/30; C04B 35/468 20060101 C04B035/468; H01G 4/12 20060101
H01G004/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 24, 2016 |
JP |
2016-125825 |
Claims
1. A multilayer ceramic capacitor comprising: a multilayer
structure in which ceramic dielectric layers and internal electrode
layers are alternately stacked, wherein: a main component of the
ceramic dielectric layer is barium titanate in which a donor
element having a larger valence than Ti is solid-solved and an
acceptor element having a smaller valence than Ti and larger ion
radius than Ti and the donor element is solid-solved; a
solid-solution amount of the donor element with respect to the
barium titanate is 0.05 mol or more and 0.3 mol or less on a
presumption that an amount of the barium titanate is 100 mol and
the donor element is converted into an oxide; and a solid solution
amount of the accepter element with respect to the barium titanate
is 0.02 mol or more and 0.2 mol or less on a presumption that the
amount of the barium titanate is 100 mol and the acceptor element
is converted into an oxide.
2. The multilayer ceramic capacitor as claimed in claim 1, wherein
the donor element is at least one of Mo and W.
3. The multilayer ceramic capacitor as claimed in claim 1, wherein
the acceptor element is Mn.
4. Ceramic powder comprising: barium titanate as a main component,
wherein: a donor element having a larger valence than Ti is
solid-solved in the barium titanate; an acceptor element having a
smaller valence than Ti and larger ion radius than Ti and the donor
element is solid-solved in the barium titanate, a solid solution
amount of the donor element with respect to the barium titanate is
0.05 mol or more and 0.3 mol or less on a presumption that an
amount of the barium titanate is 100 mol and the donor element is
converted into an oxide; a solid solution amount of the accepter
element with respect to the barium titanate is 0.02 mol or more and
0.2 mol or less on a presumption that the amount of the barium
titanate is 100 mol and the acceptor element is converted into an
oxide; and relationships y.gtoreq.-0.0003x+1.0106,
y.gtoreq.-0.0002x+1.0114, 4.gtoreq.x.gtoreq.25 and y.gtoreq.1.0099
are satisfied when a specific surface area of the ceramic powder is
"x" and an axial ratio c/a of the ceramic powder is "y".
5. The ceramic powder as claimed in claim 4, wherein the donor
element is at least one of Mo and W.
6. The ceramic powder as claimed in claim 4, wherein the acceptor
element is Mn.
7. A manufacturing method of a multilayer ceramic capacitor
comprising: synthesizing barium titanate powder by solid-solving a
donor element and an acceptor element in barium titanate, the donor
element having a larger valence than Ti, the acceptor element
having a smaller valence than Ti and having a larger ion radius
than Ti and the acceptor element; forming green sheets with use of
the barium titanate powder; forming a multilayer structure by
alternately stacking the green sheets and conductive pastes for
forming internal electrodes; and baking the multilayer structure;
wherein: a solid solution amount of the donor element with respect
to the barium titanate is 0.05 mol or more and 0.3 mol or less on a
presumption that an amount of the barium titanate is 100 mol and
the donor element is converted into an oxide; and a solid solution
amount of the accepter element with respect to the barium titanate
is 0.02 mol or more and 0.2 mol or less on a presumption that the
amount of the barium titanate is 100 mol and the acceptor element
is converted into an oxide.
8. The method as claimed in claim 7, wherein relationships
y.gtoreq.-0.0003x+1.0106, y.gtoreq.-0.0002x+1.0114,
4.gtoreq.x.gtoreq.25 and y.gtoreq.1.0099 are satisfied when a
specific surface area of the barium titanate powder is "x" and an
axial ratio c/a of the barium titanate powder is "y".
9. The method as claimed in claim 7, wherein the barium titanate
powder is synthesized by solid-phase synthesizing barium carbonate
and titanium dioxide together with the donor element and the
acceptor element.
10. The method as claimed in claim 7, wherein the donor element is
at least one of Mo and W.
11. The method as claimed in claim 7, wherein the acceptor element
is Mn.
12. A manufacturing method of ceramic powder comprising:
synthesizing barium titanate powder by solid-solving a donor
element and an acceptor element in barium titanate, the donor
element having a larger valence than Ti, the acceptor element
having a smaller valence than Ti and having a larger ion radius
than Ti and the acceptor element, wherein: a solid solution amount
of the donor element with respect to the barium titanate is 0.05
mol or more and 0.3 mol or less on a presumption that an amount of
the barium titanate is 100 mol and the donor element is converted
into an oxide; a solid solution amount of the accepter element with
respect to the barium titanate is 0.02 mol or more and 0.2 mol or
less on a presumption that the amount of the barium titanate is 100
mol and the acceptor element is converted into an oxide; and
relationships y.gtoreq.-0.0003x+1.0106, y.gtoreq.-0.0002x+1.0114,
4.gtoreq.x.gtoreq.25 and y.gtoreq.1.0099 are satisfied when a
specific surface area of the ceramic powder is "x" and an axial
ratio c/a of the ceramic powder is "y".
13. The method as claimed in claim 12, wherein the barium titanate
powder is synthesized by solid-phase synthesizing barium carbonate
and titanium dioxide together with the donor element and the
acceptor element.
14. The method as claimed in claim 12, wherein the donor element is
at least one of Mo and W.
15. The method as claimed in claim 12, wherein the acceptor element
is Mn.
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. 2016-125825,
filed on Jun. 24, 2016, 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, ceramic powder, a manufacturing
method of a multilayer ceramic capacitor and a manufacturing method
of ceramic powder.
BACKGROUND
[0003] Recently, downsizing of electronic components is needed, as
an electronic circuit used for digital electronic devices such as
mobile phones and tablet terminals is highly densified. Therefore,
downsizing and capacitance enlargement of the multilayer ceramic
capacitors (MLCC) structuring the circuit is rapidly
progressed.
[0004] The capacitance of the multilayer ceramic capacitor is
proportional to dielectric constant of a material of the dielectric
layer structuring the capacitor and the number of stacked
dielectric layers, and is inversely proportional to a thickness of
each dielectric layer. And so, in order to satisfy the demand of
the downsizing, it is needed that the dielectric constant of the
material is enlarged, the thickness of the dielectric layer is
reduced, and the number of the stacked layers is increased.
[0005] However, when the dielectric layer becomes thinner, a
voltage applied per unit thickness increases and the life time of
the dielectric layer is reduced. Moreover, reliability of the
multilayer ceramic capacitor is degraded. And so, in order to
improve the life, it is supposed that Mo or W acting as a donor
element is added to dielectric material.
[0006] Distribution of existence ratio of additive element such as
the donor element in ceramic powder structuring the dielectric
layer has an influence on property of the multilayer ceramic
capacitor. For example, Japanese Patent Application Publication No.
10-330160 discloses dielectric porcelanic that is capable of
improving insulation breakdown, in which an additive element such
as Mn, V, Cr, Co, Ni, Fe, Nb, Mo, Ta, W or the like is evenly
dispersed in all regions from grain boundary to grain center. In
examples of the publication, barium carbonate, titanium oxide and
the additive element are mixed and are calcined at 1200 degrees C.
Another additive element is added, and the mixed materials are
calcined in oxidizing atmosphere at 1000 degrees C. A green sheet
is made with use of the resulting porcelanic material. The green
sheets are stacked, and are baked for 2 hours at 1200 degrees C.
And, a multilayer capacitor is formed by thermally treating the
green sheets for 30 minutes in oxidizing atmosphere at 600 degrees
C. Although it is expected that the distribution of the additive
element in the dielectric porcelanic of the multilayer capacitor
formed in this manner is even, the publication discloses that
actually, there is a difference of 7 times between a grain boundary
and center of a grain.
[0007] Japanese Patent Application Publication No. 2001-230150
discloses, as a multilayer ceramic capacitor having a small size
and large capacitance without life degradation caused by insulation
break down even if a thickness of dielectric layers is reduced and
the dielectric layers are stacked, a multilayer ceramic capacitor
that has ceramic grains having crystalline core to which an
additive element such as Mn, V, Cr, Mo, Fe, Ni, Cu or Co is added
and a shell surrounding the core, in which a concentration of these
additive elements increases from the center of the core to the
shell. In examples of the publication, barium carbonate, titanium
oxide and the additive element are mixed and are calcined for two
hours at 200 degrees C. And, barium titanate including the additive
element is synthesized. Then, another additive element is added,
and the mixed materials are calcined at 1000 degrees C. A green
sheet is made with use of the resulting mixed material. The green
sheets are stacked, and are calcined for 3 hours at 1130 degrees C.
And, a multilayer capacitor is formed by sintering the green sheets
for 30 minutes in oxidizing atmosphere at 600 degrees C. The
publication discloses that, in the resulting multilayer ceramic
capacitor, a concentration of the additive element of the core of
the ceramic grain structuring the dielectric layer is approximately
290 ppm, and the concentration of the additive element of the shell
is approximately 410 ppm.
[0008] Japanese Patent Application Publication No. 2011-256091
discloses barium titanate-based ceramic grains that have a core and
a shell, include rare earth element R and M (at least one of Mg,
Mn, Ni, Co, Fe, Cr, Cu, Al, Mo, W and V) as a sub component, in
which total concentration of R and M has a gradient from a grain
boundary to the core and a local minimum portion and a local
maximum portion, as a dielectric ceramic that achieves a multilayer
ceramic capacitor that has preferable capacitance-temperature
property and has excellent life property.
SUMMARY OF THE INVENTION
[0009] However, when the distribution of the additive element in
the ceramic grains has a high portion and a small portion, an
amount of oxygen defect becomes larger in a low concentration
portion, and the life property may be degraded. And so, it is
thought that barium titanate solid-solving at least one of Mo, Ta,
Nb and W and having a small concentration variability is used.
However, these elements act as a donor element, and a leak current
may be increased.
[0010] The present invention has a purpose of providing a
multilayer ceramic capacitor, ceramic powder and a manufacturing
method of the multilayer ceramic capacitor and the ceramic powder
that are capable of improving life property of a dielectric layer
and suppressing a leak current.
[0011] According to an aspect of the present invention, there is
provided a multilayer ceramic capacitor comprising: a multilayer
structure in which ceramic dielectric layers and internal electrode
layers are alternately stacked, wherein: a main component of the
ceramic dielectric layer is barium titanate in which a donor
element having a larger valence than Ti is solid-solved and an
acceptor element having a smaller valence than Ti and larger ion
radius than Ti and the donor element is solid-solved; a
solid-solution amount of the donor element with respect to the
barium titanate is 0.05 mol or more and 0.3 mol or less on a
presumption that an amount of the barium titanate is 100 mol and
the donor element is converted into an oxide; and a solid solution
amount of the accepter element with respect to the barium titanate
is 0.02 mol or more and 0.2 mol or less on a presumption that the
amount of the barium titanate is 100 mol and the acceptor element
is converted into an oxide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates a partial perspective view of a
multilayer ceramic capacitor;
[0013] FIG. 2 illustrates a manufacturing method of the multilayer
ceramic capacitor;
[0014] FIG. 3 illustrates a relationship between a specific surface
area and a c/a value; and
[0015] FIG. 4 illustrates measured results.
DETAILED DESCRIPTION
[0016] A description will be given of an embodiment with reference
to the accompanying drawings.
Embodiment
[0017] A description will be given of a multilayer ceramic
capacitor. FIG. 1 illustrates a partial perspective view of a
multilayer ceramic capacitor 100. 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 20 and 30 that are provided at edge faces of the
multilayer chip 10 facing each other.
[0018] 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. End edges of the internal electrode
layers 12 are alternately exposed to a first end face of the
multilayer chip 10 and a second end face of the multilayer chip 10
that is different from the first end face. In the embodiment, the
first face faces with the second face. The external electrode 20 is
provided on the first end face. The external electrode 30 is
provided on the second end face. Thus, the internal electrode
layers 12 are alternately conducted to the external electrode 20
and the external electrode 30. 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, both end faces in the stack direction of the dielectric layers
11 and the internal electrode layers 12 (hereinafter referred to as
stack direction) are covered by cover layers 13. For example,
material of the cover layer 13 is the same as that of the
dielectric layer 11.
[0019] For example, the multilayer ceramic capacitor 100 may have a
length of 0.2 mm, a width of 0.1 mm and a height of 0.3 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.
[0020] A main component of the external electrodes 20 and 30 and
the internal electrode layer 12 is a base metal such as nickel
(Ni), copper (Cu), tin (Sn) or the like. The external electrodes 20
and 30 and the internal electrode layers 12 may be made of noble
metal such as platinum (Pt), palladium (Pd), silver (Ag), gold (Au)
or alloy thereof. The dielectric layer 11 is mainly composed of
barium titanate (BaTiO.sub.3) having a perovskite structure. The
perovskite structure includes ABO.sub.3-.alpha. having an
off-stoichiometric composition.
[0021] For example, the dielectric layer 11 can be formed by baking
material powder of which main component is barium titanate. When
the material powder is baked, the material powder is exposed to
reductive atmosphere. Therefore, oxygen defect may occur in the
barium titanate. And so, in the embodiment, a donor element having
a larger valence than Ti is solid-solved in the barium titanate of
the dielectric layer. Thus, formation of the oxygen defect of the
barium titanate is suppressed. As a result, life property of the
dielectric layer 11 is improved, and reliability of the dielectric
layer 11 is improved. Therefore, a high dielectric constant is
achieved, and preferable bias property is achieved. It is
preferable that, as the donor element of which valence is larger
than that of Ti, at least one of Mo (molybdenum) and W (tungsten)
is solid-solved in the barium titanate. Mo and W (for example,
Mo.sup.6+ and W.sup.6+) having a larger valence than Ti (four) in
the barium titanate is replaced to Ti site and acts as the donor
element.
[0022] When total solid-solution amount of the donor element is
small, maybe, the oxygen defect is not sufficiently suppressed. And
so, in the embodiment, the total solid-solution amount of the donor
element has a lower limit. On the other hand, when the total
solid-solution amount of the donor element is large, a leak current
may be excessive. And so, in the embodiment, the total
solid-solution amount of the donor element has an upper limit. In
concrete, in the embodiment, the total solid-solution amount of the
donor element with respect to the barium titanate is 0.05 mol or
more and 0.3 mol or less, on a presumption that an amount of the
barium titanate is 100 mol and the donor element is converted into
an oxide. It is preferable that the total solid-solution amount is
0.1 mol or more and 0.25 mol or less. It is more preferable that
the total solid-solution amount is 0.1 mol or more and 0.2 mol or
less.
[0023] On the other hand, when the donor element is solid-solved in
the barium titanate of the dielectric layer 11, the leak current
may increase. And so, an acceptor element having a smaller valence
than Ti (four) and having a larger ion radius than Ti and the donor
element is solid-solved in the barium titanate. The acceptor
element is replaced to the Ti site. Therefore, electrical neutral
is remained. Accordingly, the leak current is suppressed. It is
preferable that at least one of Mn (manganese), Ni, Cu, Fe (iron),
Cr (chromium), Co (cobalt), Zn (zinc), and a rare earth element (Y
(yttrium), Dy (dysprosium), Ho (holmium), Er (erbium)) is used. It
is specifically preferable that Mn (for example, Mn.sup.2+) is
used. The ion radius of Mo and W is smaller than the ion radius of
Ti. The ion radius of the acceptor element is larger than the ion
radius of Ti. Lattice strain is suppressed, a c/a value (axial
ratio) of the barium titanate increases and a value close to 1.0099
that is a theoretical value of the c/a value of the barium titanate
is achieved, when at least one of Mo and W is solid-solved in the
barium titanate together with the acceptor element. Therefore, a
crystalline of the barium titanate is improved, and the dielectric
constant of the dielectric layer 11 is improved.
[0024] The ion radius is as follows. 6-coordinated Ti (+4 valence):
0.605 .ANG., Mn (+2 valence): 0.67 .ANG., Mo (+6 valence): 0.59
.ANG., W (+6 valence): 0.6 .ANG., Ni (+2 valence): 0.69 .ANG., Cu
(+2 valence): 0.73 .ANG., Fe (+2 valence): 0.61 .ANG., Cr (+3
valence): 0.615 .ANG., Co (+2 valence): 0.65 .ANG., Zn (+2
valence): 0.74 .ANG., Y (+3 valence): 0.9 .ANG., Dy (+3 valence):
0.912 .ANG., Ho (+3 valence): 0.901 .ANG., and Er (+3 valence):
0.89 .ANG.. These values are disclosed in "R. D. Shannon, Acta
Crystallogr., A32, 751 (1976)".
[0025] When the total solid-solution amount of the acceptor element
is small, it is not possible to sufficiently remain electrical
neutral of the barium titanate. And so, in the embodiment, the
total solid-solution amount of the acceptor element has a lower
limit. On the other hand, when the total solid-solution amount of
the acceptor element is large, the dielectric constant of the
barium titanate may be reduced. And so, in the embodiment, the
total solid-solution amount of the acceptor element has an upper
limit. In concrete, in the embodiment, the total solid-solution
amount of the acceptor element with respect to the barium titanate
is 0.02 mol or more and 0.2 mol or less on a presumption that the
amount of the barium titanate is 100 mol and the acceptor element
is converted into an oxide. It is preferable that the total
solid-solution amount is 0.03 mol or more and 0.15 mol or less. It
is more preferable that the total solid-solution amount is 0.04 mol
or more and 0.15 mol or less.
[0026] When the c/a value of the barium titanate in which the donor
element and the acceptor element are solid-solved is small, the
crystalline may be degraded and maybe, a high dielectric constant
is not achieved. And so, in the embodiment, it is preferable that
the c/a value of the barium titanate has a lower limit. For
example, it is preferable that the c/a value of the barium titanate
is 1.003 or more and 1.0099 or less.
[0027] Next, a description will be given of a manufacturing process
of the multilayer ceramic capacitor 100. First, material powder for
forming the dielectric layer 11 is prepared. The dielectric layer
11 includes Ba and Ti. These elements are included in the
dielectric layer 11 in a shape of a sintered compact of the barium
titanate grains.
[0028] The barium titanate is tetragonal compound having a
perovskite structure and has a high dielectric constant. Generally,
the barium titanate is obtained by reacting a titanium material
such as titanium dioxide with a barium material such as barium
carbonate and synthesizing barium titanate. Various methods can be
used as a synthesizing method of the barium titanate. For example,
a solid-phase method, a sol-gel method, a hydrothermal method or
the like can be used.
[0029] In the embodiment, in order to evenly disperse the donor
element and the acceptor element in the barium titanate of the
dielectric layer 11, a compound (for example, oxide) including
additive element is mixed with titanium material and barium
material, and barium titanate grains in which the donor element and
the acceptor element are solid-solved are synthesized by
synthesizing the barium titanate. Alternatively, barium titanate of
which grain diameter is sufficiently fine (high specific surface
area) is synthesized in advance by a solid-phase method, a sol-gel
method, or a hydrothermal method. The donor element and the
acceptor element are mixed with the resulting barium titanate, and
barium titanate grains in which the donor element and the acceptor
element are evenly solid-solved are formed by growing the barium
titanate to grains having a desirable grain diameter (reducing the
specific surface area).
[0030] FIG. 2 illustrates a manufacturing method of the multilayer
ceramic capacitor 100. A description will be given of a concrete
manufacturing method.
[0031] (Mix and dispersion process) In a mix and dispersion
process, a compound of a donor element, a compound of an acceptor
element, a compound of Ba, and a compound of Ti are mixed and
dispersed in an aqueous solution. When Mo is used as the donor
element, ammonium molybdate
{(NH.sub.4).sub.6Mo.sub.7O.sub.24.4H.sub.2O}, a molybdenum oxide
(MoO.sub.3) or the like can be used. When W is used as the donor
element, tungsten oxide (WO.sub.3) or the like can be used. When Mn
is used as the acceptor element, manganese carbonate (MnCO.sub.3),
manganese oxide (Mn.sub.3O.sub.4), manganese citrate
(C.sub.12H.sub.10Mn.sub.3O.sub.14) or the like can be used. Barium
carbonate (BaCO.sub.3) or the like can be used as the Ba compound.
Titanium dioxide (TiO.sub.2) or the like can be used as the Ti
compound.
[0032] For example, the ammonium molybdate and tungsten oxide are
dispersed in water. Ammonium carbonate salt is added to the aqueous
solution as the dispersing agent. Barium carbonate (specific
surface area is 15 m.sup.2/g or more), titanium dioxide (specific
surface area is 20 m.sup.2/g or more) and manganese carbonate are
added to the aqueous solution, with a Ba/Ti mol ratio of 1.001 to
1.010. And slurry is obtained. Thus, the mix and dispersion process
is performed.
[0033] Total additive amount of the donor element to the barium
titanate is 0.05 mol to 0.3 mol, on a presumption that the amount
of the barium titanate is 100 mol and the donor element is
converted into an oxide. Total additive amount of the acceptor
element to the barium titanate is 0.02 mol to 0.2 mol, on a
presumption that the amount of the barium titanate is 100 mol and
the acceptor element is converted into an oxide. The slurry is
subjected to the mix and dispersion process. In the mix and
dispersion process, a ball mill, a planetary boll mill, a bead
mill, a wet jet mill or the like can be used. In any mix process,
it is preferable that the mixing is performed until a thermal
decomposition is finished at a predetermined temperature or less in
a thermal analysis measurement of the material mixed powder. When
the finishing temperature of the thermal decomposition of the
material mixed powder is low, it can be determined that the
titanium dioxide and the barium carbonate are evenly mixed. The
barium titanate having a desirable range of the specific surface
area and the c/a value can be synthesized.
[0034] (Calcination process) The slurry subjected to the mix and
dispersion process is dried in a temperature range of 100 to 300
degrees C. Thus, water is removed. The dried powder is calcined for
0.5 to 5 hours in a temperature range of 800 degrees C. to 1000
degrees C. Atmosphere of the calcination process is not limited.
When the calcination is performed under a nitrogen flow, under air
gas of which dew point is -65 degrees C. or less, under inert gas
flow such as N.sub.2 or He, or under a low pressure atmosphere from
10 Pa to 1000 Pa, carbonate gas generated through a solid-phase
reaction is effectively removed and the reaction is uniformed. By
the calcination, the donor element and the acceptor element are
solid-solved in the barium titanate. From a view point of
dielectric constant control, it is preferable that the c/a value
(axial ratio) measured by a powder X-ray diffraction method is
1.003 or more.
[0035] It is possible to determine whether the donor element and
the acceptor element are solid-solved in the barium titanate, by
DSC measurement (differential scanning colorimeter) of powder. It
is possible to determine that the donor element and the acceptor
element are solid-solved in the barium titanate, when a transition
peak temperature between a tetragonal and a cubic around 120
degrees C. is shifted toward low temperature side by 1 degrees C.
or more, compared to another barium titanate in which none of the
donor element and the acceptor element are solid-solved.
[0036] Additive compound may be added to the resulting barium
titanate powder, in accordance with purposes. The additive compound
may be MgO, MnCO.sub.3, oxide of rare earth element (Y, Dy,
Tm(thulium), Sm(samarium), Eu(europium) Gd(gadolinium),
Tb(terbium), Ho and Er), or oxide of Cr, V(vanadium), Co, Ni,
Li(lithium), B, Na(sodium), K(potassium) and Si(silicon) or the
like.
[0037] The grain diameter of the barium titanate powder may be
adjusted by crushing the barium titanate powder as needed.
Alternatively, the grain diameter of the barium titanate powder may
be adjusted by combining the crushing and classifying.
[0038] When the specific surface area of the barium titanate powder
is small, grains becomes rough, and the roughness of the green
sheet may be degraded. And so, it is preferable that the specific
surface area of the barium titanate powder has a lower limit. On
the other hand, when the specific surface area of the barium
titanate powder is large, baking may be unstable, and abnormal
growth of grains may occur during the sintering. And so, it is
preferable that the specific surface area of the barium titanate
powder has an upper limit. In concrete, in the embodiment, it is
preferable that the specific surface area of the barium titanate
powder is 4 m.sup.2/g or more and 25 m.sup.2/g or less.
[0039] When the specific surface area of the barium titanate powder
is small, maybe, the high dielectric constant is not achieved
unless the c/a value is high. On the other hand, when the specific
surface area is large, maybe, the c/a value is not sufficiently
high and a necessary dielectric constant is not achieved. When the
donor element is added in order to suppress oxygen defect, the c/a
may be further reduced. The present inventors have learned that
there is an optimal range of the specific surface area and the c/a
value. In concrete, when the specific surface area of the barium
titanate is "x" and the c/a value (axis ratio) is "y", the present
inventors have learned that high dielectric constant is achieved in
a case where the barium titanate powder has a crystal structure
satisfying y.gtoreq.-0.0003x+1.0106, y.gtoreq.-0.0002x+1.0114,
4.gtoreq.x.gtoreq.25 and y.gtoreq.1.0099. It is possible to achieve
the above-mentioned relationship between the specific surface area
and the c/a value when the acceptor element having a larger ion
radius than Ti is solid-solved in the barium titanate powder. The
range is illustrated in FIG. 3.
[0040] 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 barium
titanate powder and wet-blended. With use of the resulting slurry,
a strip-shaped dielectric green sheet substance with a thickness of
1.2 .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. Then, a
metal conductive paste for the internal electrode is printed on the
surface of the dielectric green sheet by screen printing or gravure
printing to arrange patterns of the internal electrode layers.
Thus, patterns of the internal electrode layers alternately
extracted to the pair of the external electrodes are arranged. The
metal may be nickel from a view point of cost. The barium titanate
having an average grain diameter of 50 nm may be dispersed into the
metal conductive paste, as a co-material.
[0041] (Stack process) 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, 100 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 end 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. A cover sheet, which are to be the cover
layers 13, are stacked 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). After that, Ni conductive
pastes to be the external electrodes 20 and 30 are coated on both
edge faces of the cut stack structure and are dried. Thus, a
compact of the multilayer ceramic capacitor 100 is obtained.
[0042] (Bake process) The binder is removed from the resulting
compact of the multilayer ceramic capacitor in N.sub.2 atmosphere
of a temperature range of 250 degrees C. to 500 degrees C. After
that, the compact 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 of the dielectric green sheet
is sintered and grown into grains. In this manner, it is possible
to manufacture the multilayer ceramic capacitor 100 having the
multilayer structure in which the sintered dielectric layers 11 and
the sintered internal electrode layers 12 are alternately stacked
and the cover layers 13 formed as outermost layers in the stack
direction.
[0043] In the embodiment, a re-oxidizing process may be performed
in a temperature range of 600 degrees C. to 1000 degrees C.
[0044] In another embodiment of the manufacturing method of the
multilayer ceramic capacitor, the external electrodes 20 and 30 may
be baked separately from the dielectric layer 11. For example,
after baking a multilayer structure in which a plurality of
dielectric layers 11 are stacked, conductive pastes may be formed
on both edge faces by baking and the external electrodes 20 and 30
may be formed. Alternatively, the external electrodes may be formed
thickly on the both edge faces of the multilayer structure by a
sputtering method.
[0045] Here, the effect of the embodiment is described. In the
embodiment, the donor element having a larger valence than Ti is
solid-solved in the barium titanate of the dielectric layer 11. The
total solid-amount of the donor element solid-solved in the barium
titanate is 0.05 mol or more and 0.3 mol or less, on a presumption
that the amount of the barium titanate is 100 mol and the donor
element is converted into an oxide. In this case, formation of
oxygen defect of the barium titanate is suppressed. Thus, the life
property of the dielectric layer 11 is improved and the reliability
of the dielectric layer 11 is improved. And, a high dielectric
constant is achieved, and preferable bias property is achieved. The
acceptor element having a smaller valence than Ti and having a
larger ion radius than Ti and the donor element is solid-solved in
the barium titanate of the dielectric layer 11. The total
solid-solution amount of the acceptor element solid-solved in the
barium titanate is 0.02 mol or more and 0.2 mol or less, on a
presumption that the amount of the barium titanate is 100 mol and
the acceptor element is converted into an oxide. In this case, the
electrical neutral is remained. Therefore, the leak current can be
suppressed.
[0046] When the green sheet including the barium titanate powder in
which the donor element and the acceptor element are solid-solved
in advance is baked, variability of the additive element in the
barium titanate in the resulting dielectric layer 11 is suppressed.
Thus, the above-mentioned effect is sufficiently achieved. When the
specific surface area of the barium titanate powder is "x" and the
c/a value (axial ratio) of the barium titanate powder is "y", it is
preferable that the barium titanate powder has a crystal structure
having relationships of y.gtoreq.-0.0003x+1.0106.
y.gtoreq.-0.0002x+1.0114, 4.gtoreq.x.gtoreq.25 and
y.gtoreq.1.0099.
EXAMPLES
[0047] The multilayer ceramic capacitors were manufactured in
accordance with the embodiment. And, characteristics of the
multilayer ceramic capacitors were measured.
Example 1
[0048] Ammonium molybdate tetrahydrate
{(NH.sub.4).sub.6Mo.sub.7O.sub.24.4H.sub.2O} was dissolved in
deionized water. And solvent was added to the aqueous solution.
After that, barium carbonate (30 m.sup.2/g) and titanium dioxide
(50 m.sup.2/g) were added to the aqueous solution so that the Ba/Ti
molar ratio is 1. Thus, slurry was obtained. Manganese carbonate
was added to the slurry. And, the slurry was mixed and dispersed
with use of a bead mill. An additive amount of Mo was 0.05 mol and
an additive amount of Mn was 0.02 mol, on a presumption that an
amount of the barium titanate was 100 mol, Mo was converted into
MoO.sub.3and Mn was converted into MnO.sub.2. The resulting slurry
was dried, and water was removed. After that, the slurry was
calcined at a temperature of 900 degrees C., and crushing was
performed. Thus, barium titanate having a specific surface area of
10 m.sup.2/g in which Mo and Mn were solid-solved was made.
[0049] The powder was dried for twenty minutes or more by flowing
nitrogen gas to the powder at a temperature of 200 degrees C. After
that, BET specific surface area was measured by MACsorb (HM-model
1210). The BET specific surface area was 10 m.sup.2/g.
[0050] Powder XRD measurement of the barium titanate in which Mo
and Mn were solid-solved was performed with use of RIGAKU TTR III.
A profile fitting was performed by performing Reitveld analysis
with use of RIETAN 2000. And, the c/a value was calculated from
lengths of a c-axis and an a-axis. The c/a value was 1.0094. The
powder of 30 mg was tightly sealed in an aluminum pan. The
temperature of the powder was increased and decreased from 100
degrees C. to 150 degrees C. at a rate of 10 degrees C./min with
use of DSC (a differential scan calorimeter made by RIGAKU, thermo
plus DSC 8230). The peak position during temperature decreasing was
calculated. The peak position was 121 degrees C. The peak position
of the barium titanate in which none of Mo and Mn were not
solid-solved of a comparative example described later was 123.5
degrees C. Therefore, the peak temperature was shifted to lower
temperature side by 1 degrees C. or more. That is, it was confirmed
that Mo and Mn were solid-solved in the barium titanate powder.
[0051] The measurement condition of XRD is shown in Table 1.
TABLE-US-00001 TABLE 1 XRD MEASUREMENT CONDITION ScanningMode 2
Theta/Theta ScanningType FT X-Ray 50 kV/300 mA DIVERGENCE SLIT
1/3.degree. VERTICAL DIVERGENCE 10 mm LIMITATION SLIT SCATTERING
SLIT 1/3.degree. PHOTORECEPTION SLIT 0.15 mm MONOCHROME 0.8 mm
PHOTORECEPTION SLIT EMASUREMENT RANGE 20~85.degree. STEP 0.01
[0052] Next, additive material was added to the 100 mol of the
barium titanate in which Mo and Mn was solid-solved so that an
amount of Ho.sub.2O.sub.3 was 0.5 mol, an amount of MnCO.sub.3 was
0.2 mol together with the solid-solved Mn, an amount of
V.sub.2O.sub.5 was 0.1 mol, and an amount of SiO.sub.2 was 1.0 mol.
Barium carbonate was added to the barium titanate so that a Ba/Ti
molar ratio (a molar ratio of Ba to Ti in total of barium titanate
in which Mo and Mn were solid-solved, the added barium carbonate
and added titanium dioxide) was 1.000. And a solvent was added to
the barium titanate. And slurry was obtained. PVB binder was added
to the slurry. And a green sheet having a thickness of 1.2 .mu.m
was coated on a PET film.
[0053] Next, Ni conductive paste was printed on the green sheet, as
an internal electrode. With use of the printed green sheet, a
multilayer ceramic capacitor having 400 layers was manufactured.
The multilayer capacitor had a length of 1.0 mm, a width of 0.5 mm
and a height of 0.5 mm. After removing the binder, the printed
green sheets were baked in a reductive atmosphere of 1200 degrees
C. And a re-oxidizing process was performed in N.sub.2 atmosphere
at a temperature of 800 degrees C. A thickness of the dielectric
layer after the baking was 0.8 .mu.m, and a thickness of the
internal electrode was 0.9 .mu.m.
[0054] The amounts of Mo and Mn included in the dielectric layer
were measured by ICP. It was confirmed that an amount of Mo was
0.05 mol and an amount of Mn was 0.02 mol on a presumption that an
amount of the barium titanate was 100 mol, Mo was converted into
MoO.sub.3, and Mn was converted into MnO.sub.2.
Examples 2, 7 and 8
[0055] In examples 2, 7 and 8, the amounts of Mo and Mn that were
solid-solved in the barium titanate powder in advance were changed.
In the example 7, Mn was further added to the barium titanate
powder without solid-solving. Other conditions were the same as the
first embodiment. It was confirmed that the DSC peak temperature of
the barium titanate powder of the examples 2, 7 and 8 in which Mo
and Mn were solid-solved in advance was shifted toward lower
temperature side by 1 degrees C. or more, compared to the barium
titanate of the comparative example 1.
Examples 3 to 5
[0056] In examples 3 to 5, the amounts of Mo and Mn solid-solved in
the barium titanate powder in advance were 0.2 mol and 0.04 mol, on
a presumption that the amount of the barium titanate was 100 mol,
Mo was converted into MoO.sub.3, and Mn was converted into
MnO.sub.2. In the example 3, the temperature of synthesizing was
950 degrees C. In the example 4, the temperature of synthesizing
was 1000 degrees C. and the BET value was 4 by enhancing crushing.
In the example 5, the specific surface area of TiO.sub.2 was 300
m.sup.2/g and the temperature of synthesizing was 800 degrees C. In
the examples 3 to 5, Mn was further added to the barium titanate
powder without solid-solving. Other conditions were the same as the
example 1. It was confirmed that the DSC peak temperature of the
barium titanate powder of the examples 3 to 5 in which Mo and Mn
were solid-solved in advance was shifted toward lower temperature
side by 1 degrees C. or more, compared to the barium titanate of
the comparative example 1.
Example 6
[0057] In an example 6, WO.sub.3 powder was used instead of the Mo
material. The amounts of W and Mn solid-solved in the barium
titanate powder in advance were 0.2 mol and 0.04 mol, on a
presumption that the amount of the barium titanate was 100 mol, W
was converted into WO.sub.3, and Mn was converted into MnO.sub.2.
In the example 6, Mn was further added to the barium titanate
powder without solid-solving. Other conditions were the same as the
example 1.
Examples 9 to 11
[0058] In examples 9 to 11, the amounts of Mo and Mn solid-solved
in the barium titanate powder in advance were 0.2 mol and 0.04 mol,
on a presumption that the amount of the barium titanate was 100
mol, Mo was converted into MoO.sub.3, and Mn was converted into
MnO.sub.2. In the example 9, the temperature of synthesizing was
1020 degrees C. In the example 10, the barium titanate was
synthesized by using TiO.sub.2 having a specific surface area of 7
m.sup.2/g, and the temperature of synthesizing was 920 degrees C.
In the example 11, barium titanate having the specific surface area
of 50 m.sup.2/g was used as the raw material. The barium titanate
was not made from BaCO.sub.3 and TiO.sub.2 but made by hydrothermal
synthesizing. The raw material was thermally treated at a
temperature of 800 degrees C. And, barium titanate of 20 m.sup.2/g
in which Mo and Mn were solid-solved was made. In the examples 9 to
11, Mn was further added to the barium titanate powder without
solid-solving. Other conditions were the same as the first example
1.
[0059] (Analysis) FIG. 4 illustrates measured results (the amounts
of Mo, W and Mn solid-solved in the barium titanate in advance, the
amounts of Mo and Mn added to the barium titanate without
solid-solving, the specific surface area, the c/a value, a relative
dielectric constant .epsilon., a high-temperature acceleration life
value, a leak current value). The relative dielectric constant
.epsilon. was calculated by calculating a capacitance of the
multilayer ceramic capacitor under conditions of 25 degrees C., 1
kHz and 0.55 Vrms/.mu.m. The life was high-acceleration life value
before insulation resistivity (.rho.) becomes 1.times.1010
.OMEGA.cm under a direct current electrical field of 10V/.mu.m at a
temperature of 125 degrees C. The leak current after five minutes
from the start of the high-temperature acceleration was
measured.
[0060] As illustrated in FIG. 4, in any of the examples 1 to 11,
high relative dielectric constant was achieved, and the life was
elongated. This is because the donor element of 0.05 mol or more
was solid-solved in the barium titanate of the dielectric layer 11
and the acceptor element of 0.2 mol or more was solid-solved in the
barium titanate of the dielectric layer 11, on a presumption that
the amount of the barium titanate was 100 mol and the donor element
and the acceptor element were converted into oxides. And, in any of
the examples 1 to 11, the leak current was suppressed. This is
because the acceptor element of 0.02 mol or more having a smaller
valence than Ti and having a larger ion radius than Ti and the
donor element was solid-solved in the barium titanate of the
dielectric layer 11, and the donor element of 0.3 mol or more
having a larger valence than Ti was solid-solved in the barium
titanate, on a presumption that the amount of the barium titanate
was 100 mol and the acceptor element and the donor element were
converted into oxides.
[0061] When the example 1 is compared with the example 2 of which
specific surface area is the same as the example 1, the total
additive amount of Mn of the example 1 (0.2 mol) is the same as
that of the example 2. However, the leak current of the example 2
was suppressed more than the example 1. When the example 7 is
compared with the example 8 of which specific surface area is the
same as the example 7, the total additive amount of Mn of the
example 7 (0.2 mol) is the same as that of the example 8. However,
the leak current of the example 8 was suppressed more than the
example 7. This is because the additive element was evenly diffused
in the barium titanate by solid-solving the additive element in the
barium titanate in advance.
[0062] Compared to the example 9, the life was further elongated to
20 thousands minutes or more in the other examples. This is because
degradation of the roughness of the green sheet was suppressed
because the specific surface area of the barium titanate powder was
4 m.sup.2/g or more.
[0063] Compared to the examples 10 and 11, the life was further
elongated and the relative dielectric constant was within the
preferable range of 2500 to 5000 in the other examples except for
the example 9. This is because the relationship between the c/a
value and the specific surface area was within the range of FIG. 3
and high crystalline was achieved.
Comparative Examples 1 and 2
[0064] In comparative examples 1 and 2, barium titanate, in which
none of the donor element having a larger valence than Ti and the
acceptor element having a smaller valence than Ti and having a
larger ion radius than Ti and the donor element were not
solid-solved, was used. In the comparative example 1, Mo and Mn
were added without solid-solving. In the comparative example 2,
only Mn was added without solid-solving. Other conditions were the
same as the example 1. In the comparative examples 1 and 2,
sufficient life was not achieved. This is because Mo was not
sufficiently solid-solved in the barium titanate even if Mo was
added to the barium titanate.
Comparative Example 3
[0065] In a comparative example 3, barium titanate in which only Mo
of Mo and Mn was solid-solved was made, and Mn was added to the
barium titanate without solid-solving. The other conditions were
the same as the example 1. In the comparative example 3, the leak
current was not sufficiently suppressed. This is because Mn was not
sufficiently solid-solved in the barium titanate even if Mn was
additionally added although Mo was solid-solved in the barium
titanate in advance.
Comparative Example 4
[0066] In a comparative example 4, the amounts of Mo and Mn that
were solid-solved in the barium titanate were 0.3 mol and 0.25 mol,
on a presumption that the amount of the barium titanate was 100
mol, Mo was converted into MoO.sub.3 and Mn was converted into
MnO.sub.2. The other conditions were the same as the example 1. In
the comparative example 4, high relative dielectric constant was
not achieved. This is because the amount of Mn solid-solved in the
barium titanate in advance was large.
Comparative Example 5
[0067] In a comparative example 5, the amounts of Mo and Mn that
were solid-solved in the barium titanate were 0.05 mol and 0.01
mol, on a presumption that the amount of the barium titanate was
100 mol, Mo was converted into MoO.sub.3 and Mn was converted into
MnO.sub.2. The other conditions were the same as the example 1. In
the comparative example 5, the leak current was not sufficiently
suppressed. This is because the amount of Mn solid-solved in the
barium titanate was small.
Comparative Example 6
[0068] In a comparative example 6, the amounts of Mo and Mn that
were solid-solved in the barium titanate were 0.04 mol and 0.04
mol, on a presumption that the amount of the barium titanate was
100 mol, Mo was converted into MoO.sub.3 and Mn was converted into
MnO.sub.2. The other conditions were the same as the example 1. In
the comparative example 6, long life was not achieved. This is
because Mn was not sufficiently solid-solved in the barium titanate
even if Mn was additionally added.
Comparative Example 7
[0069] In a comparative example 7, the amounts of Mo and Mn that
were solid-solved in the barium titanate were 0.35 mol and 0.04
mol, on a presumption that the amount of the barium titanate was
100 mol, Mo was converted into MoO.sub.3 and Mn was converted into
MnO.sub.2. Moreover, Mn was additionally added to the barium
titanate. The other conditions were the same as the example 1. In
the comparative example 7, the leak current was not sufficiently
suppressed. This is because the amount of Mo solid-solved in the
barium titanate in advance was large.
[0070] 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.
* * * * *