CAPACITOR WITH NON-NOBLE METAL ELECTRODES AND METHOD OF MAKING THE SAME

CONDENSATEUR A ELECTRODES EN METAL NON NOBLE ET METHODE DE FABRICATION

English Abstract

CAPACITOR WITH NON-NOBLE METAL
ELECTRODES AND METHOD OF MAKING THE SAME
Abstract of Disclosure
A ceramic capacitor having electrodes. The capacitor
is formed by cosintering layers of ceramic dielectric and
layers of non-noble metal material indifferent to the dielectric
layers corresponding in area and position to the electrodes.
The indifferent layers are converted to a conductive state,
for example, by chemical conversion and used as such or are
removed and replaced by metal or conductive material. One
example in which the indifferent layers comprise nickel oxide
involves stacking layers of green ceramic coated with nickel
oxide in the desired electrode pattern, sintering the stacked
layers to produce a monolith, reducing the nickel oxide in the
monolith to metallic nickel in a hydrogen atmosphere at a tem-
perature low enough to have minimal effect upon the dielectric
properties of the ceramic and using the metallic nickel as
reduced for the ceramic capacitor electrodes. In another ex-
ample, after the reduction step ( which may be at high tempera-
ture) the metallic nickel is dissolved, for example by sulfuric
acid, the ceramic monolith is reozidized by firing in an oxi-
dizing atmosphere such as air, and the voids left by removal
of the dissolved metallic nickel are provided with suitable
electrodes. In still another example, in which the indifferent
layers comprise oxidizable material such as carbon, the stacked
layers are sintered in an inert atmosphere to produce a mono-
lith of matured ceramic and the indifferent layers are removed
by subsequent firing in an oxidizing atmosphere to produce the
voids for receiving conductive electrode material.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A monolithic structure comprising: a sintered
unitary body in the as sintered state.
a. said body having a matrix of a dielectric
ceramic composition, and
b. a plurality of vertically spaced solid non-
metallic strata in said matrix, each stratum
extending to one of a pair of edge regions of
said body, alternate strata extending to the
same edge region, said nonmetallic strata having
been positioned in said matrix prior to the
sintering of said body and being further defined
as a material which remains solid and nonmetallic
and in place and indifferent to said ceramic
composition during the sintering of said body and
after said sintering is capable of being chemically
converted to or replaced by conductive material.
2. A multilayer structure comprising a sintered unitary
body in the as sintered state, said body having a matrix of
an electrically insulating composition, and at least one
internal area extending to an edge region of said body com-
posed of a ceramic composition, and at least one other internal
area extending to an edge region of said body composed of a
solid nonmetallic material, said internal areas of ceramic
composition and of nonmetallic material having been positioned
in said matrix prior to the sintering of said body and said
nonmetallic material being further defined as a material which
remains solid and nonmetallic and in place and indifferent to
said ceramic composition during the sintering of said body and
after said sintering is capable of being chemically converted
to or replaced by conductive material.
3. The structure of claim 1 which has been further
processed to provide conducting material in the sites of
said strata.

4. The structure of Claim 1 in which said nonmetallic
strata comprise nickel oxide.
5. The structure of Claim 1 in which said nonmetallic
strata are selected from the group consisting of NiO, FeO,
CoO, Sno2, MnO, CrO, Bi2O3, C, combustible material.
6. The structure of Claim 1 in which said nonmetallic
strata are combustible.
7. The structure of Claim 1 in which said nonmetallic
strata comprise carbon.
8. The structure of Claim 2 which has been further
processed to provide electrical conductive material in said
other internal area.
9. A process of providing electrodes or conductors in
sintered ceramic bodies which comprises providing sheets of
a finely divided insulating or dielectric ceramic composition
bonded with a temporary binder, which composition forms a
dense layer when fired to sintering temperature; forming a
stack of said sheets, there being between at least one pair
of said sheets a deposit of a second composition of solid
nonmetallic material suspended in a vehicle which is elimin-
ated during said firing, consolidating a plurality of said
sheets and intervening deposits whereby to obtain a bonded,
self-sustaining body; heating said body to eliminate said
temporary binder and said vehicle; firing said body to
sintering temperature in an oxidizing atmosphere to produce
a sintered monolithic body having first areas of dense cera-
mic material and second areas of said second composition,
said second composition being further defined as a material
which remains solid and nonmetallic and in place and is

indifferent to and supports said ceramic during said sintering,
each such second area extending to a region on an outer face
of said monolithic body; and providing a conductive material
in the site of said second area by chemical conversion or
replacement of said second composition.
10. The process of Claim 9 in which the second composi-
tion and its vehicle is deposited on said sheets as a paint
suspended in a vehicle which is eliminated during said firing.
11. A process for forming a monolithic capacitor which
comprises:
a. providing a plurality of this leaves of finely
divided ceramic dielectric composition bonded with
a temporary binder, said composition forming a
dense layer when fired to sintering temperature
b. superposing a plurality of said leaves and
providing, between at least some of said leaves,
layers of a second nonmetallic composition sus-
pended in a vehicle which is eliminated during
firing, said layers being so arranged and placed
that alternate layers extend to one of two different
edge portions of said leaves while being spaced from
the other edge portions thereof.
c. forming a bonded, self-sustaining body from
said stack;
d. heating said self-sustaining body to eliminate
said temporary binder and said vehicle;
e. firing said self-sustaining body to sintering
temperature in an exidizing atmosphere whereby to
produce a monolithic body having strata of dense
dielectric, ceramic composition and strata of said
second composition, said second composition being

further defined as a material which remains solid
and nonmetallic and in place and is indifferent
to said ceramic dielectric during said sintering;
and
f. thereafter providing conductive material in
said strata of said second composition by chemical
conversion or replacement of said second composition.
12. A sintered unitary body comprising in the as
sintered state a plurality of superposed strata, said strata
including strata consisting of a dense, impervious, dielectric
or insulating ceramic composition; and second strata consist-
ing of a solid nonmetallic material, said second strata being
interposed between said dense strata and being exposed on at
least one surface of said body whereby a conductive material
may be introduced into the site thereof, and wherein each of
said second strata is smaller in area than the dense strata
above and below it, said second strata having been positioned
in said body prior to the sintering of said body, said
second composition being further defined as a material which
remains solid and nonmetallic and in place and is indifferent to
and supports said ceramic during said sintering and after said
sintering is capable of being replaced by conductive material.
13. A self-sustaining, green ceramic body comprising a
plurality of strata of a dielectric or insulating composition
having a temporary bond, said composition forming a dense
layer when fired to sintering temperature; and strata, inter-
posed between said first mentioned strata of a second solid
nonmetallic material, said second material suspended in a
vehicle which is eliminated during said firing, said second
material being further defined as a material which remains
solid and nonmetallic and in place and is indifferent to
first mentioned strata when fired to said temperature and

wherein each stratum of said second material is smaller in
area than said first mentioned strata above and below it and
after said sintering is capable of being chemically converted
to or replaced by conductive material.
14. A structure as set forth in Claim 1 in which said
ceramic composition comprises Ba Ti O.
15. A sintered monolith comprising ceramic dielectric
material and solid nonmetallic material embedded in and
margined inward from edges of the monolith in the positions
and of the shapes and sizes required for electrodes in
capacity relation to each other through portions of said
dielectric material, said nonmetallic material being further
defined as a material which remains solid and nonmetallic and
in place and is indifferent to the ceramic during said sinter-
ing and is convertible to conductive electrodes after said
sintering by chemical conversion or replacement of said non-
metallic material.
16. The method of making a monolithic capacitor with-
out high temperature noble metal electrodes which comprises
the steps of superposing layers of green ceramic dielectric
material having thereon patterns of nonmetallic material,
the patterns being in the positions and of the shapes and
sizes required for electrodes in capacity relation to each
other through portions of the dielectric and being margined
inward from edges of the layers, firing the superposed layers
into a sintered monolith, the nonmetallic material being
further defined as a material which is solid and in place
and is indifferent to said dielectric throughout said firing,
and changing the nonmetallic material into conductive elect-
rodes after said firing by chemical conversion or replacement
of said non metallic material.
17. An intermediate product comprising a sintered
monolith of ceramic dielectric material as one component
and non noble metallic oxide material as another component,
11

said non noble material being layers in the positions and
of the shapes and sizes required for electrodes in capacity
relation to each other through portions of said dielectric
material, said ceramic dielectric material and non noble
material having been first positioned in said monolith
and then cofired or sintered into said monolith, said
ceramic having been matured by said sintering, said non
noble material comprising a material which remains in
place and is indifferent to the ceramic during said sinter-
ing and is a metal oxide at the end of said sintering and
after said sintering is capable of being chemically converted
to or replaced by conductive material.
18. An intermediate product comprising a sintered
monolith of reduced ceramic dielectric material as one
component and a solid non noble material as another compon-
ent, said non noble material being layers embedded in said
monolith in the positions and of the shapes and sizes re-
quired for electrodes in capacity relation to each other
through portions of said dielectric material, said reduced
ceramic dielectric material and non noble material having
been cofired or sintered into said monolith, said ceramic
having been matured by said sintering, said non noble
material being further defined as a material which remains
solid and in place and is indifferent to and supports the
ceramic during said sintering and is convertible to capaci-
tor electrodes after said sintering.
19. An intermediate product comprising an as sintered
monolith of reduced ceramic dielectric material in one compon-
ent and a combustible material as another component, said
combustible material being embedded in the monolith in the
positions and of the shapes and sizes required for electrodes
in capacity relation to each other through portions of said
12

dielectric material, said ceramic dielectric material and
combustible material having been cofired or sintered into
said monolith, said ceramic having been matured by said
sintering, said combustible material being further defined
as a solid material which remains solid and in place and
is indifferent to and supports reduced ceramic during said
sintering.
20. A sintered monolith comprising in the as sintered
state ceramic dielectric material and solid non noble mater-
ial embedded in the monolith in the positions and of the shape
and sizes required for electrodes in capacity relation to
each other through portions of said dielectric material,
said ceramic dielectric material and solid non noble material
having been first positioned in said monolith and then cofired
or sintered into said monolith, said non noble material being
further defined as a material which remains solid and in
place and indifferent to said ceramic dielectric during said
sintering and which is not an electrode material at the end
of said sintering and which is convertible to a conductive
electrode material after said sintering by chemical conversion
or replacement of said non noble material.
21. The method of making a monolithic capacitor with-
out high temperature noble metal electrodes which comprises
the steps of superposing layers of green ceramic dielectric
material and solid non noble material, the non noble material
being in the positions and of the shapes and sizes required
for electrodes in capacity relation to each other through
portions of the dielectric material and the non noble material
being further defined as a material which is indifferent to
the dielectric material at the firing conditions required to
mature green ceramic, firing the superposed layers into a
13

monolith at said firing conditions, said non noble material
being further defined as a material which remains solid and
in place in said monolith and indifferent to said ceramic during
said firing and which is not electrodes at the end of said
firing and changing the non noble material to conductive
electrodes after said firing by chemical conversion or re-
placement of said non noble material.
22. An as sintered monolith comprising ceramic
dielectric material and other material embedded in the
monolith in the positions required for electrodes in capa-
city relation to each other through portions of said
dielectric, said ceramic and other material having been
positioned in said monolith as discrete layers in the green
state prior to said sintering of said monolith and having
been cosintered to mature the ceramic, said other material
being further defined as a solid non-conductive material
which remains solid and in place and is indifferent to the
ceramic during said cosintering and is convertible to a
conductive material by chemical conversion after said
cosintering.
23. The monolith of Claim 22 in which the ceramic is
a titanate ceramic.
24. The monolith of Claim 22 in which the other
material comprises nickel oxide.
25. The monolith of Claim 24 in which the nickel oxide
is reduced to the metallic state to provide capacitor elect-
rodes.
26. An as sintered monolith comprising ceramic
dielectric material and non-conductive other material, said
other material being embedded in the monolith in the positions
required for electrodes in capacity relation to each other
14

through portions of said dielectric, said ceramic and other
material having been positioned in said monolith as discrete
layers in the green state prior to sintering of said monolith
and having been cosintered to mature the ceramic, said other
material being further defined as a material which remains
solid and in place and is indifferent to the ceramic during
said cosintering and is convertible to a conductive material
after said cosintering by removing said other material and
substituting conducting electrode material.
27. The monolith of Claim 26 in which the other material
comprises nickel oxide.
28. The monolith of Claim 27 in which the nickel oxide
is reduced to the metallic state after said sintering and is
dissolved to remove the same.
29. The method of making a monolithic capacitor with-
out high temperature noble metal electrodes which comprises
the steps of superposing layers of green ceramic dielectric
material and other solid material, the other material being
in the positions required for electrodes in capacity relation
to each other through portions of the dielectric and remain-
ing in place and being indifferent to the dielectric material
at the firing conditions to produce a sintered monolith, firing
the superposed layers into a sintered monolith in which said
other material constitutes discrete solid layers which are
non-conductive, and changing the other material to conductive
electrodes after said firing by chemical conversion or
replacement of said other material.
30. The method of Claim 29 in which the other material
in said sintered monolith comprises nickel oxide which is
changed to conductive electrodes by subjecting the sintered
monolith to a hydrogen atmosphere at temperatures reducing
the nickel oxide to metallic nickel and below temperatures
substantially affecting the dielectric properties of the
ceramic.

31. The method of making a monolith capacitor with-
out high temperature noble metal electrodes which comprises
the steps of superposing layers of green ceramic dielectric
material and combustible material, the combustible material
being in the positions required for electrodes in capacity
relation to each other through portions of the dielectric
and remaining in place and being indifferent to the
dielectric material at the firing conditions to produce a
sintered monolith, firing the superposed layers into a
monolith in a non oxidizing atmosphere, and thereafter
changing the material to conductive electrodes by burning
out the combustible material and substituting conductive
material.
32. The method of Claim 31 in which the firing atmo-
sphere is inert to said combustible material.
33. The method of Claim 31 in which said combustible
material is carbon.
34. An as sintered monolith comprising ceramic dielectric
material and non conductive other material embedded in the
monolith in the position required for conductors, said
ceramic and other material having been positioned in said monolith
in the green state and in discrete layers and said ceramic
and other material having been cosintered into said monolith,
said other material being further defined as a material which
remains solid and in place and indifferent to the ceramic
during said cosintering and which is nonmetallic at the end of
said cosintering and is capable of being changed to conductive
material after said cosintering by chemical conversion or
replacement of said other material.
16

35. The method of making a sintered monolithic capaci-
tor without high temperature noble material electrodes which
comprises the steps of superposing layers Or green ceramic
dielectric material and solid other material, the other
material being in the positions required for electrodes in
capacity related to each other through portions of the
dielectric and being further defined as a material which
remains solid and in place and indifferent to the dielectric
material at the firing conditions, firing the superposed
layers into a cosintered monolith, the other material being
further defined as a material which is non conductive and
solid at the end of said cosintering and is capable of being
changed to conductive material after said cosintering, and
changing the other material to conductive electrodes after
said sintering by chemical conversion or replacement of said other
material.
36. An as sintered, unitary, ceramic body having a
plurality of cosintered regions and comprising a plurality
of regions of dielectric ceramic composition and at least
one region of base metal oxide material which remains solid
and in place and indifferent to the ceramic during its
sintering and by processing subsequent to said sintering
and in reducible to the metallic state, the base metal
oxide material extending to a region on the outer face of
the body.
37. A process of providing electrodes or conductors
in sintered ceramic bodies which comprises providing sheets
of a finely divided insulating or dielectric ceramic composi-
tion bonded with a temporary binder, which composition forms
a dense layer when fired to sintering temperature, introduc-
ing between the sheets a deposit of a base metal oxide
17

composition, the base metal oxide composition being sus-
pended in a vehicle which is eliminated during firing, the
base metal oxide composition developing a base metal oxide
layer when fired, consolidating a plurality of these sheets
and intervening deposits whereby to obtain a self-sustaining
body, heating this body to eliminate the vehicle and tempor-
ary binder, firing the body to sintering temperature in an
oxidizing atmosphere to produce a sintered monolithic body
having regions of dense ceramic material and regions of
metal oxide material, each such region extending to a region
on an outer face of the monolithic body; and providing a
conductive material in the metal oxide regions.
38. A process for forming a monolithic capacitor which
comprises:
a. providing a plurality of thin leaves of finely
divided ceramic dielectric composition bonded with
a temporary binder, this composition forming a
dense layer when fired to sintering temperature;
b. providing, between the leaves, layers of a
base metal oxide composition suspended in a vehicle,
the base metal oxide composition developing a base
metal oxide layer when fired, the layers being so
arranged and placed that alternate layers extend
to one of two different portions of the leaves
while being spaced from the other edge portions
thereof;
c. forming a stack of the alternated leaves and
layers;
d. heating the stack to eliminate the temporary
binder and vehicle;
18

e. firing the self-sustaining stack to sintering
temperature in an oxidizing atmosphere so as to
produce a monolithic body having alternate strata
of dense, dielectric, ceramic composition and of
a base metal oxide; and
f. providing a conductive material in the base
metal oxide strata.
39. A method of making a capacitor without high tempera-
ture noble metal electrodes which comprises the steps of
superposing layers of green ceramic dielectric material and
base metal oxide material, the base metal oxide material
being in the position required for electrodes in capacity
relation to each other through portions of the dielectric
material and being further defined as a material which re-
mains solid and in place and is indifferent to the dielectric
material at the firing conditions required for maturing the
dielectric material, firing the superposed layers into a
monolith, and changing the base metal oxide material to
conductive electrodes by a process which includes reduction
of the base metal oxide to the metallic state.
40. An as sintered, unitary, ceramic body comprising
a plurality of regions of dense insulating or dielectric
ceramic composition and at least one region of solid combust-
ible material which remains in place and is indifferent to
the ceramic during its sintering and by processing subsequent
to said sintering is removable to provide at least one void
for receiving conductive material, the combustible material
extending to a region on the outer face of the body.
41. An as sintered, unitary, ceramic body comprising
a plurality of regions of dense insulating or dielectric
19

ceramic composition and at least one region of carbon material
which remains solid and in place and is indifferent to the
ceramic during its sintering and by processing subsequent to
said sintering is removable to provide at least one void for
receiving conductive material, the carbon material extending
to a region on the outer face of the body.
42. A process of providing electrodes or conductors
in sintered ceramic bodies which comprises providing sheets
of a finely divided insulating or dielectric ceramic composi-
tion bonded with a temporary binder, which composition forms
a dense layer when fired to sintering temperature, introduc-
ing between the sheets a deposit of a combustible composition,
the combustible composition being suspended in a vehicle
which is eliminated during firing, the combustible composition
developing a combustible layer when fired, consolidating a
plurality of these sheets and intervening deposits whereby
to obtain a self-sustaining body; heating this body to
eliminate the vehicle and temporary binder, firing the body
to sintering temperature in a non oxidizing atmosphere to
produce a sintered monolithic body having regions of dense
ceramic material and regions of combustible material, each
such region extending to a region on an outer face of the
monolithic body; and provided a conductive material in the
combustible regions.
43. A process for forming a monolithic capacitor
which comprises:
a. providing a plurality of thin leaves of finely
divided ceramic dielectric composition bonded with
a temporary binder, this composition forming a
dense layer when fired to sintering temperature;

b. providing, between the leaves, layers of a
combustible composition suspended in a vehicle,
the combustible composition developing a combust-
ible layer when fired in a non oxidizing atmosphere,
the layers being so arranged and placed that alter-
nate layers extend to one of two different portions
of the leaves while being spaced from the other
edge portions thereof;
c. forming a stack of the alternated leaves and
layers;
d. heating the stack to eliminate the temporary
binder vehicle
e. firing the self-sustaining stack to sintering
temperature in a non oxidizing atmosphere so as
to produce a monolithic body having alternate
strata of a dense, dielectric, ceramic composition
and of a combustible composition; and
f. providing a conductive material in the combust-
ible composition strata.
44. The method of making a monolithic capacitor with-
out high temperature noble metal electrodes which comprises
the step of superposing layers of green ceramic dielectric
material and other material, the other material being in the
position required for electrodes in capacity relation to each
other through portions of the dielectric and remaining in
place and being indifferent to the dielectric material at
21

the firing conditions to produce a sintered monolith, firing
the superposed layers into a sintered monolith in which said
other material constitutes discrete layers which are non
conductive and comprises nickel oxide which is changed to
conductive electrodes by subjecting the sintered monolith
to a reducing atmosphere at temperatures reducing the nickel
oxide to metallic nickel and below temperatures substantially
affecting the dielectric properties of the ceramic.
22

Description

-
8~6
CAPACITOR WITH NON-NOBLE METAL
ELECTRODES AND METHOD OF MAKING ~HE SAME
Capacltors have been made with titanate dlelectrics
and noble metal composition (e.g. platinum, palladium~ gold,
etc.) electrodes co~fired in an ox~d~zing atmosphere. These
capacitors are expenslve. Other capacitors have been pro-
posed with titanate dielectrics and base metal electrodes
te.g. Ni etc.) ~ired ln a non-oxidizing or reduclng atmos-
phere. These capacitors degrade the dielectric properties
because of the reduction of the ceramic or because o~ ad-
ditlves to the ceramic which present reduction.
Thi8 in~entlon iB intended to reduce the co~t of
ceramic ¢apa¢ltors without degrading the dlelectric properties
by ellminating the need for high temperature noble metal elec-
trodes such as platinum, palladium and the llke. In lieu of
-` such electrodes, the electrode patterns are made with layers
of material ~ndifferent to the ceramic which can be ~ired with
the ceramdc. During firing the ceramic and indifferent layers
are consolidated into a dense ceramic monolith. The indif~er-
ent material is then changed to conductive electrodes, for
example by chemical converæion of the material to a conductive
state or by removlng the indifferent material and substituting
conducting electrode material.
In the drawing, Fig. 1 ls a plan view of one of the
ceramlc layers used in maklng the capacitor wh~ch has been
coated with an electrode pattern of lndifferent material, Fig.
2 is a cross sectional view of the layers be~ore flring, Fig.
3 i8 a similar ~iew after firlng, Fig. 4 ls an enlarged section
-1-

~091~6
on line 4-4 of Fig. 3, Fig. 5 is a view similar to Fig. 4
af'ter reduction of the nickel to the metallic state, Fig. 6
i~ a view of Fig. 5 after removal o~ the metalllc nickel,
Fig. 7 is a vlew o~ Fig. 6 after coating of the surfaces of
the roids left by dissolving the metallic nickel wlth other
electrode material such a~ silver, Fig. 8 i3 a view similar to
Fig. 7 in which the voidæ are filled with conductive material
such as metal, Fig. 9 is a plan view of one of the ceramic
layers which has been coated with another electrode pattern
o~ indi~ferent material, and Fig. 10 ls a view like Fig. 9 with
still another electrode pattern.
The manufackure of the capacitor start~ with a layer 1
of green ceramic dielectric, for example a high K titanate.
Such ceramlcs cons~st of mlxture~ of barlum titanate with
other oxldes, tltanates, zlrconates, stannates, etc. or pre-
cursors thereo~. The layer also contains temporary binders
and other ingredients which ai~ in processing. These ceramics
are well known to the art and many variations are described
in the patent literature. The layer 1 has an electrode
pattern 2 which extends to one edge 3 and is margined inward
from khe other edges to provide an insulating border. The
layers 1 are stacked one on top Or the other with alternate
layers turned end for end as shown in Fig. 2. The stacked
layers are then pressed together and fired or sintered into a
monolith as shown in Fig. 3. The firlng temperatures are hlgh,
1000-1400C. The thickness of the layer 1 depends on the
voltage rating and may be from 1 to 3 mils or more. In the
prior art procedures, the electrode patterns have been formed
o~ noble metals such as platinum, palladlum, etc. which with-
stand the high ~iring temperatures in oxidizing atmospheres

L8~
needed to optimize the propertles o~ titanate dielectrics.
Instead of the high temperature metals~ the electrode patterns
2 are of a material which remains in place and is indifferent
to the ceramic at lts sintering temperature and is convertible
to a conductive material. For dielectrics which are sintered
in air or an oxidizing atmosphere, the indi~ferent material
may be a base metal oxides such as nickel oxide either alone
or mi~ed wlth compatible metal o~ides such as FeO, CoO, MnO,
CrO, V20s, SnO2, CuO, Bi203, etc. ~he lndifferent material
is applied as a paint and the vehicle in ~hich the material
is ~uspended is vaporized or burned during the early stages
of the flring. After ~ir1ng the layer of indifferent material
may ha~e a thickness of 2/10 mil or less. If the firing is
in an oxidizing atmosphere, the indifferent material may be
wholly or partially metal slnce the oxidizing atmosphere converts
the metal to the oxlde form. In Fig. 4, which is a diagrammatic
section of a ~ired monolith showing a nickel oxide layer 2
sandwiched between two titanate ceramic layers 1, the boundar-
ies 5, 6 between the nickel oxide and the titanate ceramic
are sharp and well defined. Thi~ monolith is non porous
throughout. The ceramic layers are uni~ormlY supported by the
nickel oxide layers. Porosity of the nickel oxide layer can
he tolerated.
Several procedures are available for converting the
monolith at the stage of Fig. 4 to a usable capacitor. Fig. 5
shows the condition o~ the monolith a~ter belng sub~ected to
low temperature reduction in a hydrogen atmosphere. At the
low temperature, the hydrogen reduces the nickel oxide to
metallic nickel but only sllghtly reduces the titanate ceramic.
For example, at a temperature of 280C, in 24 hours the nickel

~C~9~3~86
oxide is reduced to porous metallic nickel as shown at 7,
~hich forms a good capacitor electrode. At this low tempera-
ture there i3 some reduction of the tltanate which affects
the dielectric and insulating properties. The reduction, how-
ever, is only partial and is not sufficient to destroy the
utility of the capacitor. For example, with a ti~anate
ceramic capacitor dielectric having a normal K of 6000, the
low temperature reduction may reduce the K as much as 10 or 15%
and also lower the d.c. insulation resistance one order o~
magnitude wh~ch does not impair the use as a capacitor. The
power factor also remains at an acceptable 2%. The reduction
of the nickel o~ide is a time-temperature reaction, the lower
the temperature, the longer the time. By adding to the nickel
oxide other oxides such as tln oxide ln small proportion~,
1% or less, the reduction of the nickel oxide to the metallic
state at low temperatures can be speeded up or the reduction
temperature can be lowered.
Ano~her procedure for converting the monolith of Figs
3 and 4 to a usable capacitor is shown in Figs. 5, 6 and 7.
Fig. 5 shows the nickel oxide reduced to porous metallic
nlckel. Because of the succeeding steps illustrated in Figs.
6 and 7, there is no need for low temperature reduction so
that the reduction i8 carried out at hlgh temperatures which
not only cause the reduction to metallic nickel but also
cause reduction of the titanate ceramic to the semiconductor
state. After reaching the Fig. 5 state, the metalllc nickel
is removed by dissolving in a solution indif~erent to the
ceramlc, for example ln dllute sulfuric acid. The ceramic
body is reoxidized by firing ln an oxidizing atmosphere such
as air, restoring the ceramic to the dielectric state having
--4--

~1~9~8~;
:Lts origlnal dielectric properties. Thi~ leaves a void or
slot 8 in each location prevlously occupied by the nickel
oxlde powder. The slot 8 will ordlnarily be a few tenths
of a mil thick while the dlelectric layers l will ordinarily
have thicknesses of from one to three or four mils. The
manufacture is completed by filling the slots or by coating
the surfaces 9, lO of the slot 8 wlth suitable electrode
material. This, for example, could be silver paint intro-
duced into the slots 8 by a capillary action or by a com-
bination of capillary action and pressure. Many conductive
paint~ are known~ some conslstlng of metal plgments ~hich
~orm a conductive coatlng and others having metal compounds
which bre~k down into metallic coating. Fusible metal such
as solder may be used as shown ln Fig. 8.
The indlfferent materlal 2 1~ not limited to oxldes or
chemical compounds. When the monollth i3 sintered in an
inert atmosphere, oxidizable materials such as carbon may
be used ~or the layers 2. Carbon i8 suspended in a vehicle
slmilar to that u~ed for nickel oxide. After firing in an
inert atmosphere to mature the ceramic, refiring in an oxi-
dizing atmosphere will remove the carbon and supply any
oxygen deficiency in the dielectric. The voids left by the
removal o~ the carbon may be filled with conductiYe material
as shown in Figs. 7~ 8 as descrlbed above.
Figs. 9 and lO show layers 1 o~ green ceramic with
electrode patterns 2 of indifferent material which are open
at both ends to facilltate fllling by eliminatlng the need
for ventlng air during f~lling or for evacuating air before
filllng the voids with liquid conductive material. The
layers l of Figs. 9 and lO may be stacked and processed in

t;he manner shown in Figs. 1-8. -
Although the invention has been described in connec-
t;ion with titanate ceramlcs, lt is adYantageous ln other
c:eramlc dielectrics, particularly those requirin~ high firing
temperatures which can be wi~hstood only by the high tempera-
ture metals ~uch as platinum, palladium, etc. The materials
of the electrode patterns 2 should remaln in place and be
indlfferent to the ceramic dielectric at the firing tempera-
ture requlred to mature the ceramic, should not melt or sub-
lime at the ~iring ~emperature and should be convertible to
a conductive state either by chemical conversion in situ or
by removal to pro~ide voids for rece$ving conductive materials.
The indifferent material 2 supports the green ceramic 1 during
the initial ~lring or sintering to mature the cerami¢. There-
after the ceramlc is dimensionally stable and does not re~uire
such support during the subsequent firing in reducing or o~i-
dizing atmospheres.