United States Patent O’
lCC
3,268,783
Patented August 23, 1956
1
2
3,268,783
addition of the additive are set forth below Equation A
Examples of this manner of controlling valence by the
CAPACITOR COMPRISING AN N-TYPE SEMICON
representing the situation where the alkaline earth ma
DUCTOR METALLIC UXIDE AND A LAYER 0F
terial
E is the host element and Equation B representing
COMPENSATED MATERIAL
5
the
situation
where the metal material is the host element.
()samu Saburi, Kyoto-fir, Japan, assigner to Murata
Manufacturing Co., Ltd., Otokuni-gun, Kyoto-fa, Japan,
a corporation of Japan
Filed Oct. 5, 1%5, Ser. No. 493,008
5 Claims. (Cl. 317-237)
This application is a continuation-in-part of my ap
plication Serial No. 123,054, ?led July 10, 1961 which
has become abandoned.
This invention relates to ceramic capacitors utilizing
dielectric ?lms formed on controlled valency type semi
Where the ceramic material is barium titanate and the
additive materials for valence control are lanthanum or
tantalum, Equations A and B can be written as follows:
conductor metal oxides by a method in which the con
trolled valence is compensated by the addition of ‘an ele
ment thereto so as to change the semiconductor to a
dielectric, and to the methods of manufacturing the said
capacitors.
I
The invention will be understood more fully by refer
ence to the following speci?cation and claims, taken to
gether with the accompanying drawings, in which:
20 The Equations A and A’ illustrate the case where some
sites of the alkaline earth material, e.g. the barium ions
in barium titanate, are occupied by the ions of the addi—
tive A having a valance a higher than that of the host
ions, so that in the valence controlled material, which can
has one surface which has a valence compensated layer 25 be represented by the right hand side of the equations, a
part of the metal, e.g. titanium ions, of valence four
thereon;
change to those of valence three to maintain the electric
FIG. 2 is a view similar to FIG. 1 of a capacitor hav
FIG. 1 is a cross sectional view of a capacitor which
ing opposite surfaces which have valence compensated
layers thereon;
FIG. 3 is a sectional view of a speci?c form of a ca
pacitor body having a valence compensated layer on the
outer surface thereof; and
FIG. 4 is a schematic view, on a greatly enlarged scale,
of a part of the capacitor of FIG. 3.
It is known that the resistivities of barium-titanates
which are usually higher than 1011 ohm-cm. can be greatly
reduced by introducing proper additives. This phenom
enon is understood to be caused because the additives
cause titanium having a valence of three to be produced
neutrality of the crystals. The Equations B and B’ illus
trate the case where some sites of the metal material ions,
30 e.g. the titanium ions in barium titanate, are occupied by
the ions of the additive B having a valence 1) higher than
that of the host ions, so that the valence controlled ma
terial, which can be represented by the right hand side of
the equations, a part of the metal, e.g. titanium ions, of
valence four change to those of valence three to maintain
the electric neutrality of the crystals.
Each of three valent metal material, e.g. titanium, ions
thus produced consists of a trapped electron and a four
valent metal material, e.g. titanium, ion. The trapped
from the titanium ions in the titanate. Hence, the semi 40 electrons can easily move to other metal material, e.g.
titanium, ions when excited ‘with a low voltage electric
conductive barium titanates produced by the above treat
?eld. The controlled valency type ceramic materials are
ment are called controlled valency semiconductive bar
thus semiconductive due to the available electrons thus
ium titanates.
produced.
The production of semiconductive ceramic material
It has now been discovered that this semiconductive
by this type of valency control can be carried out with 45
material can be made highly dielectric by compensating
all the members of the family of materials which can be
for the controlled valence by the addition of a com
generically designated E2+M4+O32*, one of which is bar
pensating material.
ium titanate, where E is an alkaline earth element ma
As the additives for compensating the controlled valence
terial taken from the group consisting of barium, magne
sium, calcium, strontium, lead ‘and mixtures thereof, and
there can be used at least one material C having a
M is a metal element from the group consisting of tita
valence c less than the valence of the alkaline earth
nium, tin, zirconium and solid solutions consisting of at
least two of the above mentioned substances, and in
sodium, potassium, copper, rubidium, silver, cesium, gold,
material E .and taken from the group consisting of
which 0 is oxygen.
and mixtures thereof or at least one material D having
As the additives for controlling valence there can be 55 a valence a’ less than the valence of the metal material
and taken from the group consisting of aluminum, scan
used at least one material A having a valence a greater
dium, chromium, molybdenum, manganese, iron, cobalt,
than 2 and an ionic radius close to that of the material
nickel, magnesium, and mixtures thereof.
E and taken from the group consisting of yttrium, actini
Because there are two types of valence controlled
um, thorium, antimony, bismuth, the members of the
rare earth elements, and mixtures thereof, or at least one 60 material, depending on which of the parts of the original
ceramic material acts as the host element, there are four
material B having a valence b greater than'4 and an ionic
possible
ways in which compensation of the semicon
radius close to that of the metal material M and taken
ductive valence controlled material can be carried out.
from the group consisting of vanadium, niobium, tanta
Where the valence compensating additive has a valence
lum, selenium, tellurium, tungsten and mixtures thereof. 65 less than the alkaline earth material, it can be substituted
The total quantity of the additive is from 0.01 atomic
in the alkaline earth material E, which is the host element
percent to 0.5 atomic percent of the host material. The
therefor, in the material which has either a valence con
additive A is substituted in the alkaline earth material E,
trol additive substituted in the alkaline earth material
and in this case the material E is considered the host ma
E or in ‘the metal material M. Equations C and D rep
terial, and the additive B is substituted in the metal ma 70 resent these situations, and can be written as follows:
terial, and in such case the metal material M is considered
the host material.
3,268,783
3
titanates, when a compound containing at least one of
the above mentioned valence compensating elements is
placed on the surface of the semiconductive barium tita
nates by an appropriate method, such as coating, plating,
Where the ceramic material is barium titanate and the
additive materials for valence control are lanthanum or
vaporizing, spraying, or electrolytically, and then the semi
tantalum, and the valence compensating additive is
conductive body is ?red at a temperature of from 700°
sodium, Equations C and D can be written as follows:
C. to 1300° C.
FIG. 1 shows a semiconductive plate 3 which has one
surface thereof treated by the above method to form a
10 layer 2 of valence compensated material, and FIG. 2
shows a semiconductive plate 3 which ‘has both surfaces
treated to form valence compensated layers 2. Elec
trodes 1, 4 and 5 in FIGS. 1 and 2 are applied by conven
tional methods of ?ring, brushing, sputtering, or spray
Where the valence compensating additive has a valence
less than the metal material, it can be substituted in the
metal material M, which is the host element therefor, in 15 mg.
If the resisitivity of the semiconductive body is suffi
the material which has either a valence control additive
ciently low, the device shown in FIG. 1 works as a capaci
substituted in the alkaline earth material E or in the metal
tor consisting of a thin ceramic ?lm of high dielectric con
material M. Equations E and F represent these situ
stant.
And the device shown in FIG. 2 works as two
The thickness of
the thin ?lm of compensated barium titanate can be con
ations, and can be Written as follows:
20 capacitors which are series connected.
trolled by controlling the quantity of the valence com
pensating compound applied to the surface of the body
25
Where the ceramic material is barium titanate and the
2,000. This capacity is twenty times that of conventional
additive materials for valence control are ‘lanthanum or
tantalum, and the valence compensating additive is alum
inum, Equations E and F can be written as follows:
when the valence compensating method is carried out.
Capacitors whose capacity is more than 0.15 micro
farad/cm.2 can be produced when the thickness of the
?lm is 10 microns and the dielectric constant of the ?lm is
ceramic capacitors.
30
Much higher capacity per unit volume is obtainable
with the form of capacitor shown in FIG. 3. In FIG. 3,
the element 13 denotes a porous semiconductive titanate
which is treated by the valence compensation method of
the present invention; 12 denotes an inner lead which is
35 ohmicly connected to the porous semiconductive titanate,
The foregoing equations show that the controlled va
lence material is compensated when ions of a material
and 14 denotes the outer can which forms an outer elec
trode connected to the treated surface of the semiconduc
tive barium titanate.
having a valence lower than either the alkaline earth ma
A detail of FIG. 3 is shown schematically in FIG. 4
terial, such as barium, are substituted for a part of the 40 on an enlarged scale.
alkaline earth material, or when ions of a material hav
The porous semiconductive material has numerous
ing a valence lower than that of the metal material, such
bubbles 18 like a sponge. Each bubble, which is called
as titanium, are substituted for ‘a part of the metal ma
“a cell” has a wall with a certain area. In the present
terial.
When the materials have had their controlled valence
compensated, they turn from semiconductors to‘ insulating
dielectrics because they no longer have available free elec
embodiment, the wall surface is treated according to the
above described compensation method, and then, conduc
tive material 17 such as silver paint is impregnated to form
an electrode which covers and connects the wall surfaces.
trons. It follows that in order to achieve this state the
The semiconducting barium titanate body forms the
amount of valence compensating additive material C or
opposing electrode as shown schematically in FIG. 4,
D which is added must correspond to the amount of va 50 when the wall surface of each cell is compensated in
lence control additive material A or B which has been
valence, there is formed a thin dielectric ?lm 15. A
added to make the material semiconductive in the ?rst
capacity of 50 microfarads can be achieved with a porous
place. For example, when the valence of material A is
three and "the valence of material C is one in Equation
C, the amount of valence compensation additive is the 55
same as the amount of valence control additive; when the
valence of material A is four and the valence of ma
terial C is one in Equation C, the amount of valence com
semiconducting barium titanate block of 1 cm.3 treated
according to the present invention.
I claim:
1. A capacitor, comprising a body of controlled valence
n-type metallic oxide semiconductor of the general
formula
pensation additive is twice of the amount of valence
E2+M4+O32_
control additive; when the valence of material A is three 60
where
E
is
an
alkaline
earth material taken from the
and the valence of material D is two in Equation E, the
group consisting of barium, magnesium, calcium, stron
amount of valence compensation additive is one half of
tium and lead, and mixtures thereof, M is a metal material
the ‘amount of valence control additive. As the amount
taken from the group consisting of titanium, tin, and zir
of valence control additive ranges from 0.01 atomic per
cent to 0.5 atomic percent, the amount of valence com 65 conium, and mixtures thereof, and O is oxygen, one of
the positive valence elements of said semiconductor being
pensation additive thus ranges from 0.005 atomic percent
a host element and having therein a valence controlling
to 1.0 atomic percent.
additive material which when the alkaline earth material
The electric properties of the compensated material are
E is the host element is taken from the group consisting
similar to those of the usual barium titanate ceramics, as
they have high dielectric strength and a dielectric constant 70 of yttrium, 'actinium, thorium, antimony and bismuth, the
rare earth elements, and mixtures thereof, and which
as high as one to ten thousand.
when the metal material M is the host element is taken
A practical use of this valence compensated material
from the group consisting of vanadium, niobium, an
is in the making of capacitors. A thin insulating layer of,
for example, valence compensated, barium titanate is
timony, tantalum, bismuth, selenium, tellurium, tungsten,
formed on a valence controlled semiconductive barium 75 and mixtures thereof, for making said semiconductor semi
5
3,268,783
6
conductive, said additive material being present in an
material E and is a material taken from the group con
amount of x atomic percent of the host element, x having
a value of from 0.01 to 0.5, at least one surface layer of
sisting of sodium, potassium, copper, rubidium, silver,
cesium, gold, and mixtures thereof, and an electrode on
said body having therein x atomic percent of a compensat~
ing material which when the alkaline earth material E is
said one surface layer and a further electrode on a sur
face layer of said body which is spaced from said one
the host element therefor is taken from the group consist
surface layer.
ing of sodium, potassium, copper, rubidium, silver, cesium,
4. A capacitor, comprising a body of controlled valence
n-type metallic oxide semiconductor of the general
formula
gold, and mixtures thereof, and which when the metal
material M is the host element therefor is taken from the
group consisting of aluminum, scandium, chromium,
molybdenum, manganese, iron, cobalt, nickel, magnesium,
10
where E is an alkaline earth material taken from the
and mixtures thereof, which compensating material makes
the surface layer highly resistive by compensating the
group consisting of barium, magnesium, calcium, stron
tium and lead, and mixtures thereof, M (each occurrence)
semiconductive effect of said additive material, and an
electrode on said one surface layer and a further elec
is a metal material taken from the group consisting of
trode on a surface layer of said body which’ is spaced from
said one surface layer.
2. A capacitor, comprising a body of controlled valence
n-type metallic oxide semiconductor of the general
titanium, tin, and zirconium, and mixtures thereof, A is
formula
a material having a valence a greater than 2 and an ionic
radius close to that of the alkaline earth material E, and
is taken from the group consisting of yttrium, actinium,
20 thorium, antimony, bismuth, the members of rare earth
elements, and mixtures thereof, and the material A being
present in an amount of x atomic percent of element E
and x lies between 0.01 and 0.5, and O is oxygen, at least
where E is an alkaline earth material taken from the
one surface layer of said body being a highly dielectric
group consisting of barium, magnesium, calcium, stron
tium and lead, and mixtures thereof, M (each occurrence) 25 material having a composition of the general formula
is a metal material taken from the group consisting of
titanium, tin, and zirconium, and mixtures thereof, A
is a material having a valence a greater than 2 and an
where E, A, M and O are the same materials as in the
ionic radius close to that of the alkaline earth material E,
?rst-mentioned general formula and D is a material hav
and is taken from the group consisting of yttrium, actin 30 ing a valence d lower than the valence of the metal
ium, thorium, antimony, bismuth, the members of rare
earth elements, and mixtures thereof, and the material A
material M and is a material taken from the group con
being present in an amount of x atomic percent of ele
manganese, iron, cobalt, nickel, magnesium, and mixtures
sisting of aluminum, scandium, chromium, molybdenum,
ment E and x lies between 0.01 and 0.5, and O is oxygen, , thereof, and an electrode on said one surface layer and a
at least one surface layer of said body being a highly di 35 further electrode on a surface layer of said body which
electric material having a composition of the general
formula
is spaced from said one surface layer.
5. A capacitor, comprising a body of controlled valence
n-type metallic oxide semiconductor of the general formula
where E, A, M and O are the same materials as in the
?rst mentioned general formula and C is a material hav 40
ing a valence lower than the valence of the alkaline earth
where E is an alkaline earth material taken from the group
material E and is a material taken from the group con
consisting of barium, magnesium, calcium, strontium and
sisting of sodium, potassium, copper, rubidium, silver,
lead, and mixtures thereof, M is a metal material taken
from the group consisting of titanium, tin, and zirconium,
cesium, gold, and mixtures thereof, and an electrode on
said one surface layer and a further electrode on a sur
45 and mixtures thereof, B is a material having a valence b
face layer of said body which is spaced from said one
surface layer.
greater than 4 and an ionic radius close to that of the
metal M, and is taken from the group consisting of vana
3. A capacitor, comprising a body of controlled valence
n-type metallic oxide semiconductor of the general formula
tellurium, tungsten, and mixtures thereof, and the material
dium, niobium, antimony, tantalum, bismuth, selenium,
50 B being present in an amount of x atomic percent of ele
where E is an alkaline earth material taken from the group
ment M and x lies between 0.01 and 0.5, and O is oxygen,
at least one surface layer of said body being a highly di
consisting of barium, magnesium, calcium, strontium and
electric material having a composition of the general
lead,, and mixtures thereof, M (each occurrence) is a
metal material taken from the group consisting of 55
titanium, tin, and zirconium, and mixtures thereof, B is
where E, M, B and O are the same materials as in the ?rst
mentioned general formula and D is a material having a
valence d lower than the valence of the metal material M
group consisting of vanadium, niobium, antimony, tanta
lum, bismuth, selenium, tellurium, tungsten, and mixtures 60 and is a material taken from the group consisting of alu
thereof, and the material B being present in an amount of
minum, scandium, chromium, molybdenum, manganese,
x atomic percent of element M and x lies between 0.01
iron, cobalt, nickel, magnesium, and mixtures thereof, and
an electrode on said one surface layer and a further elec
and 0.5, and O is oxygen, at least one surface layer of
trode on a surface layer of said body which is spaced from
said body being a highly dielectric material having a
composition of the general formula '
65 said one surface layer.
a material having a valence b greater than 4 and an ionic
radius close to that of the metal M, and is taken from the
E1-(b-4)x2+C(b-4)x1+M1-x4+Bxb+032_
No references cited.
where E, M, B and O are the same materials as in the
JOHN W. HUCKERT, Primary Examiner.
?rst-mentioned general formula and C is a material hav
ing a valence lower than the valence of the alkaline earth 70 J. D. KALLAM, Assistant Examiner.