Title of Invention

A SEMI CONDUCTOR CERAMIC COMPRISING A STRONTIUM TITANIUM OXIDE BASED GRAIN BOUNDARY INSULATION TYPE SEMICONDUCTOR CERAMIC

Abstract In a semiconductor ceramic according to the present invention, a donor element within the range of 0.8 to 2.0 mol relative to 100 mol of Ti element is contained as a solid solution with crystal grains, an acceptor element in an amount less than the amount of the donor element is contained as a solid solution with the crystal grains, an acceptor element within the range of 0.3 to 1.0 mol relative to 100 mol of Ti element is present in crystal grain boundaries, and the average grain size of the crystal grains is 1.0 µm or less. A monolithic semiconductor ceramic capacitor is obtained by using this semiconductor ceramic. At that time, in a first firing treatment to conduct reduction firing, a cooling treatment is conducted while the oxygen partial pressure at the time of starting the cooling is set at 1.0 x 104 times or more the oxygen partial pressure in the firing process. In this manner, a SrTiO3 based grain boundary insulation type semiconductor ceramic having a large apparent relative dielectric constant εrAPP of 5,000 or more and a large resistivity logρ (ρ: Ω.cm) of 10 or more even when crystal grains are made fine to have an average grain size of 1.0 µm or less, a monolithic semiconductor ceramic capacitor including the semiconductor ceramic, and methods for manufacturing them are realized.
Full Text — 1 —
DESCRIPTION
SEMICONDUCTOR CERAMIC, MONOLITHIC SEMICONDUCTOR CERAMIC
CAPACITOR, METHOD FOR MANUFACTURING SEMICONDUCTOR CERAMIC,
AND METHOD FOR MANUFACTURING MONOLITHIC SEMICONDUCTOR
CERAMIC CAPACITOR
Technical Field
The present invention relates to a semiconductor
ceramic, a monolithic semiconductor ceramic capacitor, a
method for manufacturing a semiconductor ceramic, and a
method for manufacturing a monolithic semiconductor ceramic
capacitor. In particular, the present invention relates to
a SrTiO3 based grain boundary insulation type semiconductor
ceramic, a monolithic semiconductor ceramic capacitor
including the semiconductor ceramic, and methods for
manufacturing them.
Background Art
In recent years, miniaturization of electronic
components have been advanced rapidly as the electronics
technology has been developed. In the field of monolithic
ceramic capacitor as well, demands for miniaturization and
increases in capacity have intensified. Therefore,
development of ceramic materials having high relative
dielectric constants and reduction in thickness and
multilayering of dielectric ceramic layers have been

- 2 —
advanced.
For example, Patent Document 1 proposes a dielectric
ceramic represented by a general formula:
{Ba1-x-yCaxReyO}mTiO2 + αMgO + βMnO (where Re is a rare earth
element selected from the group consisting of Y, Gd, Tb, Dy,
Ho, Er, and Yb, and α, β, m, x, and y satisfy 0.001 0.05, 0.001 and 0.001 Patent Document 1 discloses a monolithic ceramic
capacitor including the above-described dielectric ceramic.
The monolithic ceramic capacitor having a thickness of 2 µm
per ceramic layer, the total number of effective dielectric
ceramic layers of 5, a relative, dielectric constant εr of
1,200 to 3,000, and a dielectric loss of 2.5% or less can be
obtained.
The monolithic ceramic capacitor of Patent Document 1
takes advantage of a dielectric action of the ceramic itself.
On the other hand, research and development on semiconductor
ceramic capacitors based on a principle different from this
have also been conducted intensively.
Among them, a SrTiO3 based grain boundary insulation
type semiconductor ceramic is produced by firing (primary
firing) a ceramic compact in a reducing atmosphere to
convert the ceramic compact to a semiconductor, coating the
ceramic compact with an oxidizing agent containing Bi2O3 or

- 3 -
the like and, thereafter, conducting firing (secondary
firing (reoxidation)) in an oxidizing atmosphere to convert
crystal grain boundaries to insulators. The relative
dielectric constant εr of SrTiO3 itself is about 200 and,
therefore, is small. However, since the crystal grain
boundaries have got a capacitance, the apparent relative
dielectric constant εrAPP can be increased by increasing the
crystal grain size and reducing the number of crystal grain
boundaries.
For example, in Patent Document 2, a SrTiO3 based grain
boundary insulation type semiconductor ceramic element
assembly having an average grain size of crystal grains of
10 µm or less and a maximum grain size of 20 µm or less is
proposed. This is a semiconductor ceramic capacitor having
a single-layered structure. In the case where the average
grain size of crystal grains is 8 µm, a semiconductor
ceramic element assembly having an apparent relative
dielectric constant εrAPP of 9,000 can be obtained.
Patent Document 1: Japanese Unexamined Patent
Application Publication No. 11-302072
Patent Document 2: Japanese Patent No. 2689439
Disclosure of Invention
Problems to be solved by the invention
However, if reduction in thickness and multilayering of
ceramic layers are pushed forward by using the dielectric

- 4 -
ceramic described in Patent Document 1, there are problems
in that the relative dielectric constant sr decreases, the
temperature characteristic of the capacitance deteriorates,
and short-circuit failures sharply increase.
Consequently, in the case where it is attempted to
obtain a thin monolithic ceramic capacitor having a large
capacity of, for example, 100 µF or more, the thickness of
the dielectric ceramic layer is required to be about 1 µm
per layer and the number of laminated layers is required to
be about 700 layers to 1,000 layers, so that commercial
application is difficult in this situation.
On the other hand, the SrTiO3 based grain boundary
insulation type semiconductor ceramic described in Patent
Document 2 has good frequency characteristic and temperature
characteristic and a small dielectric loss tanδ. The
electric field dependence of the apparent relative
dielectric constant εrAPP is small and, furthermore, a
varistor characteristic is provided, so that breakage of the
element can be avoided even when a high voltage is applied.
Consequently, an application to the field of capacitors is
expected.
However, regarding this type of semiconductor ceramic,
a large apparent relative dielectric constant εrAPP is
obtained by increasing the grain sizes of crystal grains, as
described above. Therefore, if the grain sizes of crystal

- 5 -
grains decrease, the apparent relative dielectric constant
εrAPP becomes small so as to cause deterioration of the
dielectric characteristic. Consequently, there is a problem
in that it is difficult to allow the facilitation of
reduction in layer thickness and the improvement of
dielectric characteristic to become mutually compatible.
Furthermore, in order to commercially apply the
semiconductor ceramic to a monolithic ceramic capacitor, it
is required to ensure a sufficient insulating property even
when the layer thickness is reduced. However, regarding the
monolithic semiconductor ceramic capacitor, the insulating
property comparable to that of the monolithic ceramic
capacitor is not ensured in practice in the present
situation.
The present invention has been made in consideration of
the above-described circumstances. It is an object of the
present invention to provide a SrTiO3 based grain boundary
insulation type semiconductor ceramic having a large
apparent relative dielectric constant εrAPP even when crystal
grains are made fine to have an average grain size of 1.0 urn
or less and exhibiting an excellent insulating property, a
monolithic semiconductor ceramic capacitor including the
semiconductor ceramic, a method for manufacturing the above-
described semiconductor ceramic, and a method for
manufacturing the above-described monolithic semiconductor

- 6 -
ceramic capacitor.
Means for Solving the Problems
Regarding the SrTiO3 based grain boundary insulation
type semiconductor ceramic, a donor element is allowed to
form a solid solution with crystal grains in order to
convert the ceramic to a semiconductor. On the other hand,
it is believed that if an acceptor element is allowed to
form a solid solution with crystal grains, the influence of
the donor element is canceled. Consequently, regarding the
semiconductor ceramic, a technical idea that the acceptor
element is allowed to form a solid solution with crystal
grains together with the donor element has not occurred.
On the other hand, the inventors of the present
invention conducted intensive research by trial and error on
formation of a solid solution between a donor element, an
acceptor element in addition to the donor element, and
crystal grains. As a result, it was found that when a solid
solution was formed from a predetermined amount of donor
element, the acceptor element in an amount less than the
amount of the above-described donor element, and crystal
grains, and a predetermined amount of acceptor element
(irrespective of whether the acceptor element was the same
as the acceptor element which formed the solid solution with
the crystal grains or not) was allowed to present in crystal
grain boundaries, a SrTiO3 based grain boundary insulation

— 7 -
type semiconductor ceramic having a large apparent relative
dielectric constant εrAPP of 5,000 or more and a large
resistivity logp (ρ: Ω.cm) of 10 or more was able to be
obtained even when crystal grains were made fine to have an
average grain size of 1.0 µm or less.
The present invention has been made on the basis of the
above-described findings. A semiconductor ceramic according
to the present invention is a SrTiO3 based grain boundary
insulation type semiconductor ceramic and is characterized
in that a donor element within the range of 0.8 to 2.0 mol
relative to 100 mol of Ti element is contained as a solid
solution with crystal grains, an acceptor element in an
amount less than the amount of the above-described donor
element is contained as a solid solution with the above-
described crystal grains, an acceptor element within the
range of 0.3 to 1.0 mol relative to 100 mol of the above-
described Ti element is further present in crystal grain
boundaries, and the average grain size of the crystal grains
is 1.0 µm or less.
The semiconductor ceramic according to the present
invention is characterized in that the above-described donor
element includes at least one element selected from the
group consisting of La, Sm, Dy, Ho, Y, Nd, Ce, Nb, Ta, and W.
The semiconductor ceramic according to the present
invention is characterized in that the above-described

- 8 -
acceptor element includes at least one element selected from
the group consisting of Mn, Co, Ni, and Cr.
The semiconductor ceramic according to the present
invention is characterized in that the acceptor element
contained in the above-described crystal grains and the
acceptor element contained in the above-described crystal
grain boundaries are the same element.
The semiconductor ceramic according to the present
invention is characterized in that the acceptor element
contained in the above-described crystal grains and the
acceptor element contained in the above-described crystal
grain boundaries are different types of elements.
Segregation of the above-described acceptor element
into the crystal grain boundaries can be facilitated by
allowing a low-melting-point oxide within the range of 0.1
mol or less relative to 100 mol of the above-described Ti
element to be contained.
That is, the semiconductor ceramic according to the
present invention is characterized in that the low-melting-
point oxide within the range of 0.1 mol or less relative to
100 mol of the above-described Ti element is contained.
The semiconductor ceramic according to the present
invention is characterized in that the above-described low-
melting-point oxide is SiO2.
A monolithic semiconductor ceramic capacitor according

- 9 -
to the present invention is characterized in that a
component element assembly is formed from the above-
described semiconductor ceramic, internal electrodes are
disposed in the above-described component element assembly,
and external electrodes electrically connectable to the
above-described internal electrodes are disposed on a
surface of the above-described component element assembly.
A method for manufacturing a semiconductor ceramic
according to the present invention is a method for
manufacturing a SrTiO3 based grain boundary insulation type
semiconductor ceramic, and the method is characterized by
including the steps of weighing, mixing, and pulverizing a
predetermined amount of ceramic raw material containing a
donor compound and an acceptor compound and conducting a
calcination treatment so as to prepare a calcined powder in
a calcined powder preparation step, mixing a predetermined
amount of acceptor compound with the above-described
calcined powder and conducting a heat treatment so as to
prepare a heat-treated powder in a heat-treated powder
preparation step, and subjecting the above-described heat-
treated powder to a primary firing treatment in a reducing
atmosphere and conducting a secondary firing treatment in a
weak reducing atmosphere, an air atmosphere, or an oxidizing
atmosphere in a firing step, wherein the above-described
donor compound is weighed in such a way that a donor element

- 10 -
becomes within the range of 0.8 to 2.0 mol relative to 100
mol of the above-described Ti element, the above-described
predetermined amount of acceptor compound is weighed in such
a way that an acceptor element becomes within the range of
0.3 to 1.0 mol relative to 100 mol of the above-described Ti
element, and the donor compound and the acceptor compound
are mixed with the above-described calcined powder.
The inventors of the present invention further
conducted intensive research. As a result, it was found
that the resistivity was able to be further increased and
the insulating property was able to be further improved by
conducting a cooling treatment while the oxygen partial
pressure at the time of starting the cooling was set at 1.0
x 104 times or more the oxygen partial pressure in the
firing process regarding a reduction firing process, which
was an intermediate step for a monolithic semiconductor
ceramic capacitor, that is, a first firing treatment.
That is, a method for manufacturing a monolithic
semiconductor ceramic capacitor according to the present
invention is a method for manufacturing a SrTiO3 based grain
boundary insulation type semiconductor ceramic capacitor and
the method is characterized by including the steps of
weighing, mixing, and pulverizing a predetermined amount of
ceramic raw material containing a donor compound and an
acceptor compound and conducting a calcination treatment so

- 11 -
as to prepare a calcined powder in a calcined powder
preparation step, mixing a predetermined amount of acceptor
compound with the above-described calcined powder and
conducting a heat treatment so as to prepare a heat-treated
powder in a heat-treated powder preparation step, subjecting
the above-described heat-treated powder to molding to
prepare ceramic green sheets and, thereafter, laminating
internal electrode layers and the ceramic green sheets
alternately so as to form a ceramic laminate in a ceramic
laminate formation step, and subjecting the above-described
ceramic laminate to a primary firing treatment in a reducing
atmosphere and conducting a secondary firing treatment in a
weak reducing atmosphere, an air atmosphere, or an oxidizing
atmosphere in a firing step, wherein the above-described
first firing treatment is carried out on the basis of a
firing profile including a temperature raising process, a
firing process, and a cooling process and the oxygen partial
pressure at the time of starting the cooling is set at 1.0 x
104 times or more the oxygen partial pressure in the firing
process.
The above-described "time of starting the cooling"
includes not only the point in time when the cooling process
is started, but also a short time after the cooling process
is started until the temperature in a firing furnace
decreases by a predetermined temperature from a maximum

- 12 -
firing temperature.
Advantages
According to the SrTiO3 based grain boundary insulation
type semiconductor ceramic of the present invention, a donor
element, e.g., La and Sm, within the range of 0.8 to 2.0 mol
relative to 100 mol of Ti element is contained as a solid
solution with crystal grains, an acceptor element, e.g., Mn
and Co, in an amount less than the amount of the above-
described donor element is contained as a solid solution
with the above-described crystal grains, an acceptor element
within the range of 0.3 to 1.0 mol relative to 100 mol of
the above-described Ti element is present in the crystal
grain boundaries, and the average grain size of the crystal
grains is 1.0 µm or less. Therefore, a semiconductor
ceramic having a large apparent relative dielectric constant
εrAPP and a large resistivity and, therefore, exhibiting
excellent electrical characteristics can be obtained even
when the average grain size of crystal grains is 1.0 µm or
less. The apparent relative dielectric constant εrAPP is
5,000 or more and the resistivity logρ (ρ: Ω.cm) is 10 or
more.
The above-described operation and effect can be exerted
irrespective of whether the acceptor element contained in
the crystal grains and the acceptor element contained in the
crystal grain boundaries are the same element or different

- 13 -
types of elements.
Since the low-melting-point oxide, e.g., SiO2, within
the range of 0.1 mol or less relative to 100 mol of the
above-described Ti element is contained, segregation of the
acceptor element into the crystal grain boundaries is
facilitated and a monolithic semiconductor ceramic having
desired electrical characteristics can easily be obtained.
According to the monolithic semiconductor ceramic
capacitor of the present invention, the component element
assembly is formed from the above-described semiconductor
ceramic, the internal electrodes are disposed in the above-
described component element assembly, and the external
electrodes electrically connectable to the above-described
internal electrodes are disposed on a surface of the above-
described component element assembly. Therefore, even when
the layer thickness of the semiconductor ceramic layer
constituting the component element assembly is reduced to
about 1.0 urn, a large apparent relative dielectric constant
εrAPP is exhibited, a large resistivity is exhibited, and an
insulating property comparable to that of the known
monolithic ceramic capacitor can be ensured. Consequently,
a thin-layer, high-capacity monolithic semiconductor ceramic
capacitor having a high practical value can be realized.
The method for manufacturing a semiconductor ceramic
according to the present invention includes the steps of

- 14 -
weighing, mixing, and pulverizing the predetermined amount
of ceramic raw material containing the donor compound and
the acceptor compound and conducting the calcination
treatment so as to prepare the calcined powder in the
calcined powder preparation step, mixing the predetermined
amount of acceptor compound with the above-described
calcined powder and conducting the heat treatment so as to
prepare the heat-treated powder in a heat-treated powder
preparation step, and subjecting the above-described heat-
treated powder to the primary firing treatment in the
reducing atmosphere and conducting the secondary firing
treatment in the weak reducing atmosphere, the air
atmosphere, or the oxidizing atmosphere in the firing step,
wherein the above-described donor compound is weighed in
such a way that the donor element becomes within the range
of 0.3 to 2.0 mol relative to 1.00 mol of Ti element, the
above-described predetermined amount of acceptor compound is
weighed in such a way that the acceptor element becomes
within the range of 0.3 to 1.0 mol relative to 100 mol of
the above-described Ti element, and the donor compound and
the acceptor compound are mixed with the above-described
calcined powder. Therefore, a semiconductor ceramic, which
can have a larger resistivity while a desired large apparent
relative dielectric constant εrAPP is ensured, can be
obtained.

- 15 -
According to the method for manufacturing a monolithic
semiconductor ceramic capacitor of the present invention,
the oxygen partial pressure at the time of starting the
cooling is set at 1.0 x 104 times or more the oxygen partial
pressure in the firing process. Therefore, in the cooling
process of the primary firing, the cooling treatment can be
conducted while the oxygen partial pressure has increased.
Consequently, the resistivity can further increase while the
desired large apparent relative dielectric constant εrAPP is
ensured, so that a monolithic semiconductor ceramic
capacitor can be produced, wherein the insulating property
can be further improved.
Brief Description of the Drawings
[Fig. 1] Fig. 1 is a sectional view schematically
showing an embodiment of a monolithic semiconductor ceramic
capacitor produced by using a semiconductor ceramic
according to the present invention.
[Fig. 2] Fig. 2 is a diagram showing an example of a
firing profile and changes in electromotive force over time.
Reference Numerals
1: component element assembly
1a to 1g: semiconductor ceramic layer
2: internal electrode
Best Mode for Carrying Out the Invention
The embodiment of the present invention will be

- 16 -
described below in detail.
A semiconductor ceramic according to an embodiment of
the present invention is a SrTiO3 based grain boundary
insulation type semiconductor ceramic. A donor element
within the range of 0.8 to 2.0 mol relative to 100 mol of Ti
element is contained as a solid solution with crystal grains,
and an acceptor element in an amount less than the amount of
the above-described donor element is contained as the solid
solution with the above-described crystal grains.
Furthermore, an acceptor element in an amount less than the
amount of the above-described donor element and within the
range of 0.3 to 1.0 mol relative to 100 mol of the above-
described Ti element is present in the crystal grain
boundaries, and the average grain size of the crystal grains
is specified to be 1.0 µm or less.
It has been previously known that a donor element is
contained as a solid solution with crystal grains in order
to convert ceramic to a semiconductor. However, it is not
usually conducted to contain an acceptor element together
with the donor element as a solid solution with crystal
grains because the effect of the donor element is assumed to
be cancelled.
On the other hand, the inventors of the present
invention conducted intensive research by trial and error on
formation of a solid solution between a donor element, an

- 17 -
acceptor element in addition to the donor element, and
crystal grains. As a result, it was found that when a solid
solution was formed from a predetermined amount of donor
element, the acceptor element in an amount less than the
amount of the donor element, and crystal grains, and a
predetermined amount of acceptor element was allowed to
present in crystal grain boundaries, a SrTiO3 based grain
boundary insulation type semiconductor ceramic having a
large apparent relative dielectric constant εrAPP of 5,000 or
more and a large resistivity logρ (ρ: Ω.cm) of 10 or more
was able to be obtained even when crystal grains were made
fine to have an average grain size of 1.0 µm or less.
Consequently, even when the layer thickness is reduced
to 1.0 µm or less, a semiconductor ceramic having a large
apparent relative dielectric constant εrAPP as compared with
that of a known dielectric ceramic, having an insulating
property comparable to that of the known dielectric ceramic,
and exhibiting excellent electrical characteristics can be
obtained.
Here, the content of donor element is specified to be
0.8 to 2.0 mol relative to 100 mol of Ti element for the
following reasons.
The ceramic can be converted to a semiconductor by
allowing a donor element having the number of valences
larger than that of Sr element to be contained in a solid

- 18 -
solution with crystal grains and conducting a firing
treatment in a reducing atmosphere. However, the content
thereof in terms of mol has an influence on the apparent
relative dielectric constant εrAPP. That is, if the above-
described donor element is less than 0.8 mol relative to 100
mol of Ti element, a desired large apparent relative
dielectric constant εrAPP cannot be obtained. On the other
hand, if the donor element exceeds 2.0 mol relative to 100
mol of Ti element, the limit of solid solubility into the Sr
site is exceeded and the donor element deposits at grain
boundaries so as to cause significant reduction in the
apparent relative dielectric constant εrAPP and deterioration
of the dielectric characteristic.
Therefore, in the present embodiment, the content is
specified to be 0.8 to 2.0 mol relative to 100 mol of Ti
element, as described above.
Such a donor element is not specifically limited
insofar as the element is contained as a solid solution with
crystal grains and has a function as a donor. Examples of
usable elements include rare earth elements, e.g., La, Sm,
Dy, Ho, Y, Nd, and Ce; Nb; Ta; and W.
In the present embodiment, the acceptor element is also
contained as a solid solution with crystal grains and, in
addition, the acceptor element within the range of 0.3 to
1.0 mol relative to 100 mol of Ti element is present in

- 19
crystal grain boundaries as well. The acceptor element
contained as the solid solution in crystal grains and the
acceptor element present in crystal grain boundaries may be
the same element or different types of elements.
Such an acceptor element is not specifically limited
insofar as the element functions as an acceptor when being
contained as a solid solution with crystal grains, and
transition metal elements, e.g., Mn, Co, Ni, and Cr, can be
used.
Here, the content of acceptor element present in
crystal grain boundaries is specified to be 0.3 to 1.0 mol
relative to 100 mol of Ti element for the following reasons.
When the acceptor element is contained in the
semiconductor ceramic and is allowed to present in crystal
grain boundaries, oxygen is adsorbed by crystal grain
boundaries due to the above-described acceptor element
present in the crystal grain boundaries during the secondary
firing. Consequently, the dielectric characteristic can be
improved.
However, if the content of acceptor element present in
crystal grain boundaries is less than 0.3 mol relative to
100 mol of Ti element, the apparent relative dielectric
constant εrAPP cannot be improved satisfactorily, and the
resistivity is small. On the other hand, if the content of
acceptor element present in crystal grain boundaries exceeds

- 20 -
1.0 mol relative to 100 mol of Ti element, the average grain
size exceeds 1.0 µm as well. Consequently, crystal grains
are allowed to become coarse, desired reduction in layer
thickness becomes difficult and, furthermore, the
resistivity decreases.
Therefore, in the present embodiment, the content of
acceptor element present in crystal grain boundaries is
adjusted to be 0.3 to 1.0 mol relative to 100 mol of Ti
element.
In the crystal grains, the content in terms of mol of
acceptor element present as a solid solution with crystal
grains is not specifically limited insofar as the amount is
smaller than the amount of donor element. However, 0.008 to
0.08 mol relative to 100 mol of Ti element is preferable.
The reasons are as described below. If the content in terms
of mol of acceptor element present as a solid solution with
crystal grains is less than 0.008 mol relative to 100 mol of
Ti element, the content in terms of mol of acceptor element
in the crystal grains is too small and, thereby, the
resistivity may not be improved satisfactorily. On the
other hand, if the content exceeds 0.08 mol relative to 100
mol of Ti element, the acceptor element becomes excessive
relative to the donor element, and reduction in the apparent
relative dielectric constant εrAPP may result although the
resistivity increases.

— 21 —
If the content of acceptor element present as a solid
solution with the crystal grains is converted to a ratio of
the acceptor element to the donor element (acceptor
element/donor element), the ratio is 1/10 to 1/1000, and
preferably 1/10 to 1/100.
It is also preferable that a low-melting-point oxide
within the range of 0.1 mol or less relative to 100 mol of
Ti element is added to the above-described semiconductor
ceramic, in particular, crystal grain boundaries. By
addition of such a low-melting-point oxide, the
sinterability can be improved and, in addition, the
segregation of the above-described acceptor element at
crystal grain boundaries can be facilitated.
If the content in terms of mol of the low-melting-point
oxide relative to 100 mol of Ti element exceeds 0.1 mol, the
anparent relative dielectric constant εrAPP may decrease.
Therefore, in the case where the low-melting-point oxide is
added, 0.1 mol or less relative to 100 mol of Ti element is
preferable, as described above.
Such low-melting-point oxides are not specifically
limited, and glass ceramic containing SiO2, B, or an alkali
metal element (K, Li, Na, or the like), copper-tungsten
oxide, or the like can be used. Preferably, SiO2 is used.
The formulation mole ratio m of the Sr site to the Ti
site is not specifically limited insofar as the ratio is in

- 22 -
the vicinity of the stoichiometric composition (m = 1.000).
However, it is preferable that 0.995 satisfied. The reasons for this are as described below. If
the formulation mole ratio m becomes less than 0.995, the
grain sizes of crystal grains become large so that the
average grain size may exceed 1.0 µm. On the other hand, if
the formulation mole ratio m exceeds 1.020, the deviation
from the stoichiometric composition becomes large and
sintering may become difficult. More preferably,- the
formulation mole ratio m satisfies 0.995 further preferably 1.000 The average grain size of the semiconductor ceramic
crystal grains can be easily controlled at 1.0 µm or less by
controlling the manufacturing condition combined with the
above-described composition range.
Fig. 1 is a sectional view schematically showing an
embodiment of a monolithic semiconductor ceramic capacitor
produced by using a semiconductor ceramic according to the
present invention.
In the monolithic semiconductor ceramic capacitor,
internal electrodes 2 (2a to 2f) are embedded in a component
element assembly 1 formed from the semiconductor ceramic of
the present invention. In addition, external electrodes 3a
and 3b are disposed at two end portions of the component
element assembly 1.

- 23 -
That is, the component element assembly 1 is composed
of a sintered laminate including a plurality of
semiconductor ceramic layers 1a to 1g and the internal
electrodes 2a to 2f laminated alternately. The internal
electrodes 2a, 2c, and 2e are electrically connected to the
external electrode 3a, and the internal electrodes 2b, 2d,
and 2f are electrically connected to the external electrode
3b. The capacitance is formed between facing surfaces of
the internal electrodes 2a, 2c, and 2e and the internal
electrodes 2b, 2d, and 2f.
The above-described monolithic semiconductor ceramic
capacitor can obtain an apparent relative dielectric
constant εrAPP of 5,000 or more and a resistivity logρ (ρ:
Ω.cm) of 10 or more because the component element assembly 1
is formed from the above-described semiconductor ceramic.
Therefore, the manufacturing method is not specifically
limited insofar as a semiconductor ceramic having the above-
described composition is obtained.
However, it is more preferable that the production is
conducted by the above-described manufacturing method
because a semiconductor ceramic capacitor ensuring an
apparent relative dielectric constant εrAPP of 5,000 or more
and having a larger resistivity can be produced by
conducting a cooling treatment while the oxygen partial
pressure at the time of starting the cooling is set at 1.0 x

- 24 -
104 times or more the oxygen partial pressure in the firing
process in the primary firing treatment conducted in a
reducing atmosphere.
This favorable manufacturing method will be described
below in detail.
Each of a Sr compound, e.g., SrCO3, as a ceramic raw
material, a donor compound containing a donor element, e.g.,
La or Sm, an acceptor compound, e.g., Mn or Co, and a Ti
compound, e.g., TiO2, having a specific surface area of
preferably 10 m /g or more (average grain size: about 0.1 µm
or less), is prepared. The donor compound is weighed in
such a way that the content of donor element becomes 0.8 to
2.0 mol relative to 100 mol of Ti element. Furthermore,
predetermined amounts of Sr compound and Ti compound are
weighed.
A oredetecmined amount of dispersing agent is added to
the weighed materials, and the resulting mixture is put into
a ball mill together with water and pulverizing media, e.g.,
PSZ (Partially Stabilized Zirconia) balls. Wet-mixing is
conducted in the ball mill sufficiently so as to prepare a
slurry.
The resulting slurry is dried by vaporization and is
subjected to a calcination treatment in an air atmosphere at
a predetermined temperature (for example, 1,300°C to
1,450°C) for about 2 hours so as to prepare a calcined

- 25 -
powder in which the donor element and the acceptor element
are contained as a solid solution.
A low-melting-point oxide, e.g., SiO2, is weighed in
such a way that the content thereof becomes 0 to 0.1 mol
relative to 100 mol of Ti element. Furthermore, the
acceptor compound is weighed in such a way that the content
of acceptor element, e.g., Mn or Co, becomes 0.3 to 1.0 mol
relative to 100 mol of Ti element. The low-melting-point
oxide and the acceptor compound are blended with the above-
described calcined powder, pure water, and a dispersing
agent, if necessary, and wet-mixing is conducted
sufficiently. Drying was conducted by vaporization and,
thereafter, a heat treatment is conducted in an air
atmosphere at a predetermined temperature (for example,
600°C) for about 5 hours so as to prepare a heat-treated
powder.
The resulting heat-treated powder is blended with
appropriate amounts of organic solvent, e.g., toluene or
alcohol, and dispersing agent, and is put into the ball mill
again together with the above-described pulverizing media so
as to be wet-milled in the ball mill sufficiently.
Appropriate amounts of organic binder and plasticizer are
added, wet-mixing is conducted sufficiently for a long time
period and, thereby, a ceramic slurry is obtained.
The ceramic slurry is subjected to molding by using a

- 26 -
molding method, e.g., a doctor blade method, a lip coating
method, or a die coating method so as to prepare ceramic
green sheets in such a way that the thickness after the
firing becomes a predetermined thickness (for example, about
1 to 2 µm).
An electrically conductive film with a predetermined
pattern is formed on a surface of the above-described
ceramic green sheet by screen-printing or gravure-printing
an electrically conductive paste for the internal electrode
on the ceramic green sheet or by conducting vapor deposition,
sputtering, or the like.
The electrically conductive material contained in the
electrically conductive paste for the internal electrode is
not specifically limited. However, it is preferable that a
base metal material, e.g., Ni or Cu, is used.
A plurality of ceramic green sheets provided with the
electrically conductive film are laminated in a
predetermined direction and, in addition, ceramic green
sheets for external layers provided with no electrically
conductive film are laminated, followed by press-bonding and
cutting into a predetermined dimension, so as to produce a
ceramic laminate.
Subsequently, a binder removal treatment is conducted
in an air atmosphere at a temperature of 200°C to 300°C and,
furthermore, in a weak reducing atmosphere at a temperature

- 27 -
of 700°C to 800°C, if necessary. A firing furnace with a
reducing atmosphere, in which the ratio of flow rate of a H2
gas to a N2 gas is specified to be a predetermined value
(for example, H2/N2 = 0.025/100 to 1/100), is used. Primary
firing is conducted in the firing furnace at a temperature
of 1,150°C to 1,300°C for about 2 hours so as to convert the
ceramic laminate to a semiconductor. That is, the primary
firing is conducted at a temperature lower than or equal to
the calcination temperature (1,300°C to 1,450°C) so as to
convert the ceramic laminate to a semiconductor.
In this primary firing treatment, the oxygen partial
pressure in the firing furnace is sharply increased at the
time of starting the cooling after the firing, the oxygen
partial pressure at the time of starting of the cooling (the
oxygen partial pressure during cooling) is set at 1.0 x 104
times or more the oxygen partial pressure during the firing
process (the oxygen partial pressure during firing), and the
cooling treatment is conducted. Consequently, a larger
resistivity is obtained.
That is, in the present embodiment, large amounts of
steam is supplied to the firing furnace at the time of
starting of the cooling after the firing, and furthermore,
the supply rate of the H2 gas in the firing furnace is
decreased by a predetermined amount (for example, 1/10) so
as to sharply increase the oxygen partial pressure in the

- 28 -
firing furnace, and the cooling treatment is conducted while
the ratio of the oxygen partial pressure during cooling to
the oxygen partial pressure during firing, that is, the
oxygen partial pressure ratio ∆PO2, is set at 1.0 x 104 or
more. Consequently, a still larger resistivity is obtained
while an apparent relative dielectric constant εrAPP of 5,000
or more is ensured.
The above-described "time of starting the cooling"
includes not only the point in time when the cooling process
is started, but also a short time after the cooling process
is started until the temperature in a firing furnace
decreases by a predetermined temperature (for example, 30°C
to 50°C) from a maximum firing temperature.
The reason the oxygen partial pressure during cooling
is set at 1.0 x 104 times or more the oxygen partial
pressure during firing will be described with reference to
Fig. 2.
Fig. 2 is a diagram showing the firing profile and
changes in electromotive force E over time. The horizontal
axis indicates the time (hr), the left vertical axis
indicates the temperature (°C), and the right vertical axis
indicates the electromotive force E (V). A solid line
indicates the firing profile and an alternate long and short
dash line indicates changes in electromotive force over time.
That is, according to the firing profile, the

- 29 -
temperature in the furnace is raised as indicated by an
arrow A at the time of starting the firing treatment
(temperature raising process), a maximum firing temperature
Tmax (in the present embodiment, 1,150°C to 1,300°C) is
maintained for about 2 hours as indicated by an arrow B
(firing process), and the temperature in the furnace is
lowered to cool the fired product as indicated by an arrow C
(cooling process).
On the other hand, as shown by Mathematical expression
(1), the Nernst equation holds between the electromotive
force E (V) and the oxygen partial pressure PO2 (atm) in the
firing furnace.
E = (2.15 x 10-5 x T) x ln(PO2/0.206) (1)
where T indicates an absolute temperature (K) in the
tiring furnace.
Therefore, the oxygen partial pressure PO2 can be
determined by measuring the electromotive force E.
Steam was supplied to the firing furnace at the time of
starting of the cooling process, and furthermore, the supply
rate of the H2 gas to the firing furnace was decreased, if
necessary, while changes in the electromotive force E in the
firing furnace over time were measured with a direct-insert
type zirconia oxygen sensor. Consequently, as shown by the
alternate long and short dash line in Fig. 2, it was found
that the electromotive force E always became at a local

- 30 -
minimum at the point in time when the temperature in the
furnace was lowered by a predetermined temperature AT (for
example, 30°C to 50°C) from the maximum firing temperature
Tmax and, thereafter, the electromotive force E increased
gradually. Therefore, the oxygen partial pressure PO2
becomes at a local maximum at the point in time when the
temperature in the furnace is lowered by a predetermined
temperature AT from the maximum firing temperature Tmax on
the basis of Mathematical expression (1).
The inventors of the present invention conducted
experiments repeatedly in such a way that the oxygen partial
pressure during cooling was specified to be the local
maximum oxygen partial pressure PO2, the oxygen partial
pressure during firing was specified to be the oxygen
partial pressure at the maximum firing temperature Tmax, and
the supply rate of the steam and the supply rate of the H2
gas to the firing furnace were adjusted to variously
differentiate the oxygen partial pressure ratio ∆PO2 of the
two oxygen partial pressures (= oxygen partial pressure
during cooling/oxygen partial pressure during firing). As a
result, it was found that a still larger resistivity was
able to be obtained while an apparent relative dielectric
constant εrAPP of 5,000 or more was ensured by setting the
oxygen partial pressure ratio ∆PO2 at 1.0 x 10 or more.
From these reasons, in the present embodiment, the

- 31 -
cooling treatment is conducted while the above-described
oxygen partial pressure ratio ∆PO2 is set at 1.0 x 10 times
or more.
After the ceramic laminate is converted to the
semiconductor by the primary firing as described above, the
secondary firing is conducted in a weak reducing atmosphere,
an air atmosphere, or an oxidizing atmosphere at a low
temperature of 600°C to 900°C not to oxidize the internal
electrode material, e.g., Ni or Cu, for 1 hour. In this
manner, the semiconductor ceramic is reoxidized and a grain
boundary insulating layer is formed, so that the component
element assembly 1, in which the internal electrodes 2 are
embedded, is produced.
An electrically conductive paste for external electrode
is applied to both end surfaces of the component element
assembly 1, a baking treatment is conducted, so as to form
external electrodes 3a and 3b. In this manner, a monolithic
semiconductor ceramic capacitor is produced.
The electrically conductive material contained in the
electrically conductive paste for external electrode is not
specifically limited as well. However, it is preferable to
use a material, such as Ga, In, Ni, or Cu. Furthermore, a
Ag electrode may be formed on the electrode.
Alternatively, the external electrodes 3a and 3b may be
formed by a method in which the electrically conductive

- 32 -
paste for external electrode is applied to both end surfaces
of a ceramic laminate and, thereafter, the firing treatment
is conducted simultaneously with the ceramic laminate.
As described above, in the present embodiment, the
monolithic semiconductor ceramic capacitor is produced by
using the above-described semiconductor ceramic. Therefore,
the layer thickness of each of semiconductor ceramic layers
1a to 1g can be reduced to 1 µm or less. Furthermore, a
small, high-capacity monolithic semiconductor ceramic
capacitor can be obtained, which has a large apparent
relative dielectric constant εrAPP of 5,000 or more per layer
even after the layer thickness is reduced, a large
resistivity logp (ρ: Ω.cm) of 10 or more, and a good
insulating property comparable to that of the known
monolithic ceramic capacitor. Moreover, in contrast to a
high-capacity tantalum capacitor, ease of handling is
exhibited because the polarity needs not be taken into
consideration, and the resistance is low even in a high
frequency range. Therefore, the effectiveness as an
alternative to the tantalum capacitor is high.
It is known that the SrTiO3 based grain boundary
insulation type semiconductor ceramic has a varistor
characteristic, as is also described in the item "Problems
to be solved by the invention". In the present embodiment,
since the average grain size of crystal grains is 1.0 µm or

- 33 -
less and, therefore, the crystal grains are fine grains, the
varistor voltage can increase. Consequently, the use as a
capacitor in a usual field strength region (for example, 1
V/µm) , in which the voltage-current characteristic exhibits
linearity, broadens the versatility of application as the
capacitor. In addition, since the varistor characteristic
is provided, breakage of the element can be prevented even
when an abnormally high voltage is applied to the element,
and a capacitor exhibiting excellent reliability can be
obtained.
Since the varistor voltage can increase as described
above, a capacitor capable of avoiding breakage due to a
surge voltage and the like can be realized. Since the
breakage voltage is high, it is possible to use for the
application to an ESD-resistant capacitor, although a low-
capacity capacitor to be used for the purpose of ESD
(electro-static discharge) is required to have a surge-
resistant characteristic.
The present invention is not limited to the above-
described embodiment. Fig. 1 shows the monolithic
semiconductor ceramic capacitor including the plurality of
semiconductor ceramic layers 1a to 1g and the internal
electrodes 2a to 2f laminated alternately. However, a
monolithic semiconductor ceramic capacitor having a
structure, in which an internal electrode is formed on a

- 34 -
surface of a single plate (for example, thickness is about
200 µm) of semiconductor ceramic through evaporation or the
like and several layers (for example, two or three layers)
of the single plate are bonded together with an adhesive,
can also be used. Such a structure is effective for a
monolithic semiconductor ceramic capacitor to be used for a
low-capacitor application, for example.
In the above-described embodiment, the solid solution
is prepared by a solid phase method. However, the method
for preparing the solid solution is not specifically limited.
Any method, for example, a hydrothermal synthesis method, a
sol.gel method, a hydrolysis method, and a coprecipitation
method, can be used.
In the above-described embodiment, the secondary firing
(reoxidation treatment) is conducted in the air atmosphere
to form the grain boundary insulating layer. However,
desired operation and effect can be obtained even when the
oxygen concentration is somewhat lower than that in the air
atmosphere, if necessary.
Furthermore, in the primary firing treatment of the
above-described method for manufacturing a monolithic
semiconductor ceramic capacitor, the cooling treatment is
conducted while the oxygen partial pressure at the time of
starting the cooling is set at 1.0 x 104 times or more the
oxygen partial pressure in the firing process. However,

- 35 -
even when the primary firing treatment is conducted without
specifically changing the above-described oxygen partial
pressure in the firing furnace, an apparent relative
dielectric constant εrAPP of 5,000 or more and a large
resistivity logρ (ρ: Ω.cm) of 10 or more can be obtained.
In this case, the semiconductor ceramic can be produced
usually as described below.
That is, a donor compound is weighed in such a way that
a donor element becomes within the range of 0.8 to 2.0 mol
relative to 100 mol of Ti element, and a predetermined
amount of predetermined ceramic raw material containing an
acceptor compound is weighed. After mixing and pulverizing,
a calcining treatment is conducted so as to prepare a
calcined powder. Subsequently, the acceptor compound is
weighed in such a way that an acceptor element becomes
within the range of 0.3 to 1.0 mol relative to 100 mol of
the above-described Ti element, and if necessary, a low-
melting point oxide, e.g., SiO2, is weighed. They are mixed
with the above-described calcined powder and a heat
treatment is conducted so as to prepare a heat-treated
powder. The resulting heat-treated powder is subjected to a
primary firing treatment in a reducing atmosphere and,
thereafter, is subjected to a secondary firing treatment in
a weak reducing atmosphere, an air atmosphere, or an
oxidizing atmosphere, so that a semiconductor ceramic can be

- 36 -
produced.
The examples of the present invention will be
specifically described below.
EXAMPLE 1
In Example 1, a semiconductor ceramic capacitor having
a single-layered structure was produced, and electrical
characteristics were evaluated.
Each of SrCO3, LaCl3, MnCl2, and TiO2 having a specific
surface area of 30 m2 /g (average grain size: about 30 nm)
was prepared as a ceramic raw material. The ceramic raw
materials were weighed in such a way that the semiconductor
ceramic had the composition shown in Table 1. Furthermore,
2 parts by weight of ammonium polycarboxylate relative to
100 parts by weight of the weighed material was added as a
dispersing agent. The resulting mixture was put into a ball
mill together with pure water and PSZ balls having a
diameter of 2 mm. Wet-mixing was conducted in the ball mill
for 16 hours so as to prepare a slurry.
The resulting slurry was dried by vaporization and was
subjected to a calcination treatment in an air atmosphere at
a temperature of l,400°C for about 2 hours so as to prepare
a calcined powder in which the La element and the Mn element
were contained in a solid solution.
A MnCl2 aqueous solution and a SiO2 sol solution were
added to the above-described calcined powder in such a way

- 37 -
that the contents of the Mn element and SiO2 in terms of mol
became those shown in Table 1 relative to 100 mol of Ti
element in the crystal grain boundaries. Pure water and a
dispersing agent, if necessary, were added and wet-mixing
was conducted for 16 hours. Drying was conducted by
vaporization and, thereafter, a heat treatment was conducted
in an air atmosphere at a temperature of 600°C for 5 hours
so as to prepare a heat-treated powder. A MnO2 sol may be
used instead of the MnCl2 aqueous solution, and
tetraethoxysilane (Si(OC2H5)4) may be used instead of the
SiO2 sol solution.
The above-described heat-treated powder was blended
with appropriate amounts of organic solvent, e.g., toluene
or alcohol, and dispersing agent, and was put into the ball
mill again together with the PSZ balls having a diameter of
2 mm. Wet-mixing was conducted for 6 hours in the bail mill.
Appropriate amounts of polyvinylbutyral (PVB) serving as a
binder and dioctyl phthalate (DOP) serving as a plasticizer
were added, wet-mixing was further conducted for 16 hours
and, thereby, a ceramic slurry was prepared.
The resulting ceramic slurry was subjected to molding
by using a doctor blade method so as to prepare ceramic
green sheets. The resulting ceramic green sheets were
stamped into a predetermined size, and were stacked on top
of each other to have a thickness of about 0.5 mm, followed

- 38 -
by thermal compression bonding, so that a ceramic compact
was prepared.
The resulting ceramic compact was cut into a size 5 mm
long and 5 mm wide and, thereafter, a binder removal
treatment was conducted in an air atmosphere, in an air
atmosphere at a temperature of 250°C and, furthermore, in a
weak reducing atmosphere at a temperature of 800°C for 5
hours. Primary firing was conducted in a strong reducing
atmosphere, in which the ratio of flow rate of a H2 gas to a
N2 gas was specified in such a way as to satisfy H2:N2 =
1:100, at a temperature of 1,200°C to 1,250°C for 2 hours
and, thereby, conversion to a semiconductor was effected.
Subsequently, the secondary firing was conducted in an air
atmosphere at a temperature of 800°C for 1 hour to apply a
reoxidation treatment so as to produce a grain boundary
insulation type semiconductor ceramic.
Both end surfaces were coated with In-Ga so as to
produce external electrodes. In this manner, samples of
Sample Nos. 1 to 15 were produced.
Each sample was observed with a scanning electron
microscope (SEM). SEM photographs of a sample surface and a
fracture surface were subjected to image analysis, and an
average grain size of crystal grains (average crystal grain
size) was determined.
The capacitance of each sample was measured by using an

- 39 -
impedance analyzer (HP4194A: produced by Hewlett-Packard
Company) under the condition of a frequency of 1 kHz and a
voltage of 1 V. The apparent relative dielectric constant
εrAPP was calculated from the raeasured capacitance and the
sample dimension.
Each sample of Sample Nos. 1 to 15 was applied with a
direct current voltage of 5 to 500 V for 2 minutes, and the
insulation resistance IR was measured on the basis of the
leakage current thereof. The resistivity logρ (ρ: Ω.cm)
under a field strength of 1 V/(im was determined on the basis
of the resulting insulation resistance IR and the sample
dimension.
Table 1 shows the compositions of crystal grains and
crystal grain boundaries of Sample Nos. 1 to 15 and the
measurement results thereof.
[Table 1]


- 40 -

*asterisked sample numbers indicate samples which are out of the
present invention
As is clear from this Table 1, regarding Sample No 11,
since Mn, which was an acceptor element, was not contained
in the crystal grains, the resistivity logρ was a low 9.5,
that is, 10 or less, although the apparent relative
dielectric constant εrAPP exceeded 5,000. Consequently, a
desired high resistivity was not able to be obtained.
Regarding Sample No. 12, the content in terms of mol of
La, which was a donor element, in the crystal grains was 0.6
mol relative to 100 mol of Ti element and, therefore, was
less than 0.8 mol. Consequently, the apparent relative
dielectric constant εrAPP was 4,500 and, therefore, decreased
to less than 5,000.
Regarding Sample No. 13, the above-described content in
terms of mol of La in the crystal grains was 2.5 mol
relative to 100 mol of Ti element and, therefore, was
excessive. Consequently, the apparent relative dielectric
constant εrAPP was 3,700 and, therefore, decreased
significantly.

- 41 -
Regarding Sample No. 14, the content in terms of mol of
Mn in the crystal grain boundaries was 0.25 mol relative to
100 mol of Ti element and, therefore, was less than 0.3 mol.
Consequently, the apparent relative dielectric constant εrAPP
was 2,840 and, therefore, decreased to less than 5,000. The
resistivity logρ was a low 8.7.
Regarding Sample No. 15, the content in terms of mol of
Mn in the crystal grain boundaries was 1.5 mol relative to
100 mol of Ti element and, therefore, exceeded 1.0 mol.
Consequently, the average crystal grain size was 1.8 µm and,
therefore, the grains became coarse. The resistivity logρ
was a low 8.1.
If the content in terms of mol of SiO2, which is a low-
melting-point oxide, exceeds 0.1 mol relative to 100 mol of
Ti element, the apparent relative dielectric constant εrAPP
may decrease. Therefore, it is preferable that the content
in terms of mol of SiO2 relative to 100 mol of Ti element is
0.1 mol or less.
On the other hand, regarding Sample Nos. 1 to 10, the
contents in terms of mol of La, which was a donor element,
in the crystal grains were 0.8 to 2.0 mol relative to 100
mol of Ti element, and Mn, which was an acceptor element,
was contained together with La as a solid solution with
crystal grains. Furthermore, 0.3 to 1.0 mol of Mn was
present relative to 100 mol of Ti element in crystal grain

- 42 -
boundaries as well. Moreover, SiO2 was contained, and the
content in terms of mol thereof was 0.1 mol or less relative
to 100 mol of Ti element. Consequently, the average crystal
grain size became 0.4 to 0.9 µm, the apparent relative
dielectric constant εrAPP became 5,010 to 6,310, and the
resistivity logρ became 10.0 to 10.4. That is, it was found
that a semiconductor ceramic having good electrical
characteristics, such as the apparent relative dielectric
constant εrAPP of 5,000 or more and the resistivity logp of
10 or more, was able to be obtained in spite of the fact
that the average crystal grain size was 1.0 µm or less.
Regarding Sample Mo. 7, the average crystal grain size
was 1.0 µm or less, but a somewhat large 0.9 µm. The reason
for this is believed that the formulation mole ratio m of
the Sr site to the Ti site (= Sr site/Ti site) was a small
0.995. That is, it is believed that if the formulation mole
ratio m is excessively deviated from the stoichiometric
composition and becomes too small, the average crystal grain
size tends to become coarse.
EXAMPLE 2
In Example 2, samples (semiconductor ceramic capacitors
having a single plate structure) of Sample Nos. 21 to 25
were produced by changing the oxygen partial pressure in the
cooling process of the primary firing, the samples having
the same compositions as those of Sample Nos. 1 and 2 in

- 43 -
[Example 1], and the effect of an increase in the oxygen
partial pressure was checked.
That is, ceramic compacts having the compositions shown
by Sample Nos. 21 to 25 in Table 2 were prepared by the
method and the procedure similar to those in [Example 1].
The resulting ceramic compact was cut into a size 5 mm long
and 5 mm wide and, thereafter, a binder removal treatment
was conducted in an air atmosphere at a temperature of 250°C
and, furthermore, in a weak reducing atmosphere at a
temperature of 800°C for 5 hours.
Primary firing was conducted in a strong reducing
atmosphere, in which the ratio of flow rate of a H2 gas to a
N2 gas was set in such a way as to satisfy H2:N2 = 1:100, at
a temperature of 1,200°C to 1,250°C for 2 hours. At this
time, the cooling treatment was conducted until the firing
furnace became 800°C while the oxygen partial pressure PO2
was adjusted in such a way that the oxygen partial pressure
ratio ∆PO2 (= oxygen partial pressure during cooling/oxygen
partial pressure during firing) became the value shown in
Table 2. That is, in the cooling treatment, steam was
supplied to the firing furnace at the time of starting of
the cooling process, and furthermore, the supply rate of the
H2 gas was decreased, if necessary, while a zirconia oxygen
sensor was inserted into the firing furnace and the
electromotive force E, that is, the oxygen partial pressure

- 44 -
PO2, in the firing furnace was measured so as to control the
oxygen partial pressure ratio ∆PO2 at the value shown in
Table 2.
Subsequently, the secondary firing was conducted in an
air atmosphere at a temperature of 800°C for 1 hour to apply
a reoxidation treatment so as to produce a grain boundary
insulation type semiconductor ceramic. Both end surfaces
were coated with In-Ga. In this manner, samples of Sample
Nos. 21 to 25 were produced.
Regarding each sample of Sample Nos. 21 to 25, the
average crystal grain size, the apparent relative dielectric
constant εrAPP, and the resistivity logp were determined by
the method and the procedure similar to those in [Example 1j.
Table 2 shows the compositions of crystal grains and
crystal grain boundaries of Sample Nos. 21 to 25 and the
measurement results. For purposes of comparison,. Sample Nos.
1 and 2 produced in [Example 1] are shown in Table 2 again.



- 46 -
Comparisons are made between Sample No. 1 and Sample
Nos. 21 to 23. Regarding Sample No. 21, the oxygen partial
pressure ratio ∆PO2 was 2.3 x 103 and, therefore, was 1.0 x
104 or less in spite of the fact that the oxygen partial
pressure was increased during the cooling. Consequently,
the resistivity logρ was at the same level as that of Sample
No. 1 in which the oxygen partial pressure during the
cooling was not increased. As a result, an increase in
resistivity logρ based on the effect of an increase in
oxygen partial pressure did not occur.
On the other hand, regarding Sample No. 22, it was
found that the oxygen partial pressure ratio ∆PO2 was 1.0 x
104 and the resistivity logp increased to 10.8.
Furthermore, regarding Sample No. 23, the oxygen
partial pressure ratio ∆PO2 was a larger 2.7 x 10 and the
resistivity logp was 11.2. Therefore, it was found that the
resistivity logp further increased.
Likewise, comparisons were made between Sample No. 2
and Sample Nos. 24 and 25. Sample No. 2 was conducted in
the strong reducing atmosphere and the oxygen partial
pressure was not increased during the cooling of the primary
firing. Therefore, the resistivity logp did not exceed 10.0.
On the other hand, regarding Sample No. 24, the cooling
treatment was conducted while the oxygen partial pressure
ratio ∆PO2 was set at 1.8 x 104 and, therefore, the

- 47 -
resistivity logp increased to 10.5. Regarding Sample No. 25,
it was found that since the cooling treatment was conducted
while the oxygen partial pressure ratio ∆PO2 was set at a
larger 3.8 x 105 , the resistivity logp further increased to
10.7.
As described above, it was found that by setting the
oxygen partial pressure ratio ∆PO2 at 1.0 x 104 or more
during the cooling, the resistivity logp was able to further
increase while the apparent relative dielectric constant
εrAPP of 5,000 or more was ensured and, therefore, the
insulating property was able to be further improved. In
addition, it was found that a semiconductor ceramic
capacitor having a larger resistivity logp was able to be
obtained by further increasing the oxygen partial pressure
ratio ∆PO2 in the case where the composition and component
of dielectric ceramic remained unchanged.
EXAMPLE 3
In Example 3, semiconductor ceramic capacitors having a
laminated structure were produced by using samples having
the same composition as that of Sample No. 1 in [Example 1],
and electrical characteristics were evaluated. In [Example
3] as well, the treatment was conducted by changing the
oxygen partial pressure in the cooling process of the
primary firing.
That is, ceramic slurries having the compositions shown

- 48 -
by Sample Nos. 31 and 32 in Table 3 were prepared by the
method and the procedure similar to those in [Example 1].
The resulting ceramic slurry was subjected to molding by
using a lip coating method so as to prepare ceramic green
sheets having a thickness of about 3.2 µm.
An electrically conductive paste for internal electrode
containing Ni as a primary component was prepared. The
electrically conductive paste for internal electrode was
used and an electrically conductive film with a
predetermined pattern was formed on a surface of the ceramic
green sheet by a screen printing method.
One set of ceramic layers was prepared by sandwiching
five ceramic green sheets provided with no electrically
conductive film between the ceramic green sheets provided
with the electrically conductive film. Ten sets of the
ceramic layers were laminated, ceramic green sheets provided
with no electrically conductive film were disposed on the
top and the bottom of the resulting laminate, and thermal
compression bonding was conducted. In this manner, a
ceramic laminate was obtained.
The resulting ceramic laminate was cut into a
predetermined size and, thereafter, a binder removal
treatment was conducted in an air atmosphere at a
temperature of 250°C for 6 hours and, furthermore, in an
atmosphere under a reduced pressure of 1.4 x 10-15 MPa at a

- 49 -
temperature of 800°C for 5 hours.
Primary firing was conducted in a strong reducing
atmosphere, in which the ratio of flow rate of a H2 gas to a
N2 gas was set in such a way as to satisfy H2:N2 = 1:100, at
a temperature of 1,200°C to 1,250°C for 2 hours, so that
conversion to a semiconductor was effected. At this time,
the cooling treatment was conducted while the oxygen partial
pressure PO2 was adjusted in such a way that the oxygen
partial pressure ratio ∆PO2 (= oxygen partial pressure
during cooling/oxygen partial pressure during firing) became
the value shown in Table 3 by the method similar to that in
[Example 2].
Subsequently, the secondary firing was conducted in an
air atmosphere at a temperature of 800°C for 1 hour to apply
a reoxidation treatment so as to produce a grain boundary
insulation type semiconductor ceramic. The thus obtained
semiconductor ceramic had a length of 2.0 mm, a width of 1.2
mm, and a thickness of 1.0 mm, the thickness per
semiconductor ceramic layer was 13 µm, and the number of
laminated layers was 10 layers.
Both end surfaces of the semiconductor ceramic were
polished and, thereafter, both end surfaces were coated with
In-Ga so as to form external electrodes. In this manner,
samples of Sample Nos. 31 and 32 were produced.
Regarding each sample of Sample Nos. 31 and 32, the

- 50 -
average crystal grain size, the apparent relative dielectric
constant εrAPP, and the resistivity logp were determined by
the method and the procedure similar to those in [Example 1].
Table 3 shows the compositions of crystal grains and
crystal grain boundaries of Sample Nos. 31 and 32 and the
measurement results.



- 52 -
As is clear from Table 3, regarding each of Sample Nos.
31 and 32, the average crystal grain size was 1.0 µm or less,
the apparent relative dielectric constant εrAPP was 5,000 or
more, and the resistivity logp was 11.0 or more. That is,
it was found that the insulating property was able to be
further improved while a high apparent relative dielectric
constant εrAPP was ensured regarding the monolithic
semiconductor ceramic capacitor as well.

- 53 -
CLAIMS
1. A semiconductor ceramic comprising a SrTiO3 based
grain boundary insulation type semiconductor ceramic,
characterized in that
a donor element within the range of 0.8 to 2.0 mol
relative to 100 mol of Ti element is contained as a solid
solution with crystal grains, and an acceptor element in an
amount less than the amount of the donor element is
contained as the solid solution with the crystal grains,
an acceptor element within the range of 0.3 to 1.0 mol
relative to 100 mol of the Ti element is present in crystal
grain boundaries, and
the average grain size of the crystal grains is 1.0 urn
or less.
2. The semiconductor ceramic, according to Claim 1,
characterized in that the donor element comprises at least
one element selected from the group consisting of La, Sm, Dy,
Ho, Y, Nd, Ce, Nb, Ta, and W.
3. The semiconductor ceramic according to Claim 1 or
Claim 2, characterized in that the acceptor element
comprises at least one element selected from the group
consisting of Mn, Co, Ni, and Cr.
4. The semiconductor ceramic according to any one of
Claim 1 to Claim 3, characterized in that the acceptor
element contained in the crystal grains and the acceptor

- 54 -
element contained in the crystal grain boundaries are the
same element.
5. The semiconductor ceramic according to any one of
Claim 1 to Claim 3, characterized in that the acceptor
element contained in the crystal grains and the acceptor
element contained in the crystal grain boundaries are
different types of elements.
6. The semiconductor ceramic according to any one of
Claim 1 to Claim 5, characterized in that a low-melting-
point oxide within the range of 0.1 mol or less relative to
100 mol of the Ti element is contained.
7. The semiconductor ceramic according to Claim 6,
characterized in that the low-melting-point oxide is SiO2.
8. A monolithic semiconductor ceramic capacitor
characterized in that a component element assembly is formed
from the semiconductor ceramic according to any one of Claim
1 to Claim 7, internal electrodes are disposed in the
component element assembly, and external electrodes
electrically connectable to the internal electrodes are
disposed on a surface of the component element assembly.
9. A method for manufacturing a semiconductor ceramic,
which is a SrTiO3 based grain boundary insulation type
semiconductor ceramic, the method characterized by
comprising the steps of:
weighing, mixing, and pulverizing a predetermined

- 55 -
amount of ceramic raw material containing a donor compound
and an acceptor compound and conducting a calcination
treatment so as to prepare a calcined powder in a calcined
powder preparation step;
mixing a predetermined amount of acceptor compound with
the calcined powder and conducting a heat treatment so as to
prepare a heat-treated powder in a heat-treated powder
preparation step; and
subjecting the heat-treated powder to a primary firing
treatment in a reducing atmosphere and conducting a
secondary firing treatment in a weak reducing atmosphere, an
air atmosphere, or an oxidizing atmosphere in a firing step,
wherein the donor compound is weighed in such a way
that a donor element becomes within the range of 0.8 to 2.0
mol relative to 100 mol of Ti element, the predetermined
amount of acceptor compound is weighed in such a way that an
acceptor element becomes within the range of 0.3 to 1.0 mol
relative to 100 mol of the Ti element, and the donor
compound and the acceptor compound are mixed with the
calcined powder.
10. A method for manufacturing a monolithic semiconductor
ceramic capacitor, which is a SrTiO3 based grain boundary
insulation type semiconductor ceramic capacitor, the method
characterized by comprising the steps of:
weighing, mixing, and pulverizing a predetermined

- 56 -
amount of ceramic raw material containing a donor compound
and an acceptor compound and conducting a calcination
treatment so as to prepare a calcined powder in a calcined
powder preparation step;
mixing a predetermined amount of acceptor compound with
the calcined powder and conducting a heat treatment so as to
prepare a heat-treated powder in a heat-treated powder
preparation step;
subjecting the heat-treated powder to molding to
prepare ceramic green sheets and, thereafter, laminating
internal electrode layers and the ceramic green sheets
alternately so as to form a ceramic laminate in a ceramic
laminate formation step; and
subjecting the ceramic laminate to a primary firing
treatment in a reducing atmosphere and conducting a
secondary firing treatment in a weak reducing atmosphere, an
air atmosphere, or an oxidizing atmosphere in a firing step,
wherein the first firing treatment is carried out on
the basis of a firing profile including a temperature
raising process, a firing process, and a cooling process and
the oxygen partial pressure at the time of starting the
cooling is set at 1.0 x 104 times or more the oxygen partial
pressure in the firing process.

In a semiconductor ceramic according to the present
invention, a donor element within the range of 0.8 to 2.0
mol relative to 100 mol of Ti element is contained as a
solid solution with crystal grains, an acceptor element in
an amount less than the amount of the donor element is
contained as a solid solution with the crystal grains, an
acceptor element within the range of 0.3 to 1.0 mol relative
to 100 mol of Ti element is present in crystal grain
boundaries, and the average grain size of the crystal grains
is 1.0 µm or less. A monolithic semiconductor ceramic
capacitor is obtained by using this semiconductor ceramic.
At that time, in a first firing treatment to conduct
reduction firing, a cooling treatment is conducted while the
oxygen partial pressure at the time of starting the cooling
is set at 1.0 x 104 times or more the oxygen partial
pressure in the firing process. In this manner, a SrTiO3
based grain boundary insulation type semiconductor ceramic
having a large apparent relative dielectric constant εrAPP of
5,000 or more and a large resistivity logρ (ρ: Ω.cm) of 10
or more even when crystal grains are made fine to have an
average grain size of 1.0 µm or less, a monolithic
semiconductor ceramic capacitor including the semiconductor
ceramic, and methods for manufacturing them are realized.

Documents:

00614-kolnp-2008-abstract.pdf

00614-kolnp-2008-claims.pdf

00614-kolnp-2008-correspondence others.pdf

00614-kolnp-2008-description complete.pdf

00614-kolnp-2008-drawings.pdf

00614-kolnp-2008-form 1.pdf

00614-kolnp-2008-form 3.pdf

00614-kolnp-2008-form 5.pdf

00614-kolnp-2008-pct priority document notification.pdf

00614-kolnp-2008-pct request form.pdf

00614-kolnp-2008-translated copy of priority document.pdf

614-KOLNP-2008-(11-05-2012)-ABSTRACT.pdf

614-KOLNP-2008-(11-05-2012)-CORRESPONDENCE.pdf

614-KOLNP-2008-(11-05-2012)-DESCRIPTION (COMPLETE).pdf

614-KOLNP-2008-(11-05-2012)-DRAWINGS.pdf

614-KOLNP-2008-(11-05-2012)-FORM-1.pdf

614-KOLNP-2008-(11-05-2012)-FORM-2.pdf

614-KOLNP-2008-(11-05-2012)-OTHERS.pdf

614-KOLNP-2008-(14-10-2011)-ABSTRACT.pdf

614-KOLNP-2008-(14-10-2011)-AMANDED CLAIMS.pdf

614-KOLNP-2008-(14-10-2011)-CORRESPONDENCE.pdf

614-KOLNP-2008-(14-10-2011)-DESCRIPTION (COMPLETE).pdf

614-KOLNP-2008-(14-10-2011)-DRAWINGS.pdf

614-KOLNP-2008-(14-10-2011)-FORM 1.pdf

614-KOLNP-2008-(14-10-2011)-FORM 2.pdf

614-KOLNP-2008-(14-10-2011)-OTHERS.pdf

614-KOLNP-2008-(14-10-2011)-PA.pdf

614-KOLNP-2008-(14-10-2011)-PETION UNDER RULE 137.pdf

614-KOLNP-2008-(15-05-2012)-CORRESPONDENCE.pdf

614-KOLNP-2008-(15-05-2012)-OTHERS.pdf

614-KOLNP-2008-(16-05-2012)-CORRESPONDENCE.pdf

614-KOLNP-2008-(16-05-2012)-OTHERS.pdf

614-KOLNP-2008-ASSIGNMENT.pdf

614-KOLNP-2008-CORRESPONDENCE OTHERS 1.1.pdf

614-KOLNP-2008-CORRESPONDENCE.pdf

614-KOLNP-2008-EXAMINATION REPORT.pdf

614-KOLNP-2008-FORM 18 1.1.pdf

614-kolnp-2008-form 18.pdf

614-KOLNP-2008-FORM 3 1.2.pdf

614-KOLNP-2008-FORM 3-1.1.pdf

614-KOLNP-2008-FORM 5.pdf

614-KOLNP-2008-GPA.pdf

614-KOLNP-2008-GRANTED-ABSTRACT.pdf

614-KOLNP-2008-GRANTED-CLAIMS.pdf

614-KOLNP-2008-GRANTED-DESCRIPTION (COMPLETE).pdf

614-KOLNP-2008-GRANTED-DRAWINGS.pdf

614-KOLNP-2008-GRANTED-FORM 1.pdf

614-KOLNP-2008-GRANTED-FORM 2.pdf

614-KOLNP-2008-GRANTED-SPECIFICATION.pdf

614-KOLNP-2008-OTHERS.pdf

614-KOLNP-2008-REPLY TO EXAMINATION REPORT.pdf

614-KOLNP-2008-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf


Patent Number 254296
Indian Patent Application Number 614/KOLNP/2008
PG Journal Number 42/2012
Publication Date 19-Oct-2012
Grant Date 17-Oct-2012
Date of Filing 12-Feb-2008
Name of Patentee MURATA MANUFACTURING CO., LTD.
Applicant Address 10-1, HIGASHIKOTARI 1-CHOME, NAGAOKAKYO-SHI, KYOTO-FU
Inventors:
# Inventor's Name Inventor's Address
1 KAWAMOTO MITSUTOSHI C/O (A170) INTELLECTUAL PROPERTY DEPARTMENT, MURATA MANUFACTURING CO., LTD., 10-1, HIGASHIKOTARI 1-CHOME NAGAOKAKYO-SHI, KYOTO-FU 617-8555
PCT International Classification Number C04B 35/47
PCT International Application Number PCT/JP2007/060816
PCT International Filing date 2007-05-28
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2007-005522 2007-01-15 Japan
2 2006-152812 2006-05-31 Japan