U.S. patent application number 09/824287 was filed with the patent office on 2001-09-06 for method for making conductive polymer capacitor.
Invention is credited to Bluvstein, Alexander, Osherow, Alexander, Strokhin, Vitaly, Vera, Gerovich.
Application Number | 20010018788 09/824287 |
Document ID | / |
Family ID | 23524735 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010018788 |
Kind Code |
A1 |
Bluvstein, Alexander ; et
al. |
September 6, 2001 |
Method for making conductive polymer capacitor
Abstract
A conductive polymer capacitor includes an anode formed from a
porous metal body having an anode lead extending therefrom. A
dielectric layer is formed by oxidizing a surface of the anode. A
solid electrolyte is formed on the dielectric layer and includes
first and second polymer layers. The second conductive polymer
layer includes a polyaniline layer formed by dipping the metal body
having the first conductive layer thereon into a solution of doped
polyaniline dissolved in an organic solvent.
Inventors: |
Bluvstein, Alexander;
(Dimona, IL) ; Vera, Gerovich; (Beer Sheva,
IL) ; Osherow, Alexander; (Beer Sheva, IL) ;
Strokhin, Vitaly; (Beer Sheva, IL) |
Correspondence
Address: |
ZARLEY MCKEE THOMTE VOORHEES & SEASE PLC
SUITE 3200
801 GRAND AVENUE
DES MOINES
IA
50309-2721
US
|
Family ID: |
23524735 |
Appl. No.: |
09/824287 |
Filed: |
April 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09824287 |
Apr 2, 2001 |
|
|
|
09386237 |
Aug 31, 1999 |
|
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Current U.S.
Class: |
29/25.03 ;
29/25.01 |
Current CPC
Class: |
H01G 11/56 20130101;
H01G 9/025 20130101; Y02E 60/13 20130101 |
Class at
Publication: |
29/25.03 ;
29/25.01 |
International
Class: |
H01G 009/00; H01L
021/00 |
Claims
What is claimed is:
1. A conductive polymer capacitor comprising: an anode comprising a
porous metal body having an anode lead extending therefrom; a
dielectric layer formed by oxidizing a surface of said anode; a
solid electrolyte formed on said dielectric layer comprised of a
first conductive polymer layer formed on said dielectric layer and
a second conductive polymer layer formed on said first conductive
polymer layer; said second conductive polymer layer comprising a
polyaniline layer formed by dipping said metal body having said
first conductive layer thereon into a solution of doped polyaniline
dissolved in an organic solvent.
2. A conductive polymer capacitor according to claim 1 wherein said
organic solvent is selected from the group consisting essentially
of m-Cresol, p-Cresol, O-Cresol, and Cl-Cresol.
3. A conductive polymer capacitor according to claim 1 wherein said
doped polyaniline is doped with a dopant selected from the group
consisting essentially of arylsulfonic acids and camphorsulfonic
acid.
4. A conductive polymer capacitor according to claim 1 and further
comprising an inorganic filler within said second conductive
layer.
5. A conductive polymer capacitor according to claim 4 wherein said
inorganic filler is selected from the group consisting essentially
of SiO.sub.2, Al.sub.2O.sub.3, SnO.sub.2, ZrO.sub.2, MgO, and
BeO.
6. A conductive polymer capacitor according to claim 4 wherein said
inorganic filler comprises graphite.
7. A conductive polymer capacitor according to claim 1 wherein said
first conductive polymer layer comprises a polypyrrole layer.
8. A method for forming a conductive polymer capacitor comprising:
forming an anode from a porous metal body; connecting an anode lead
to said porous metal body; oxidizing a surface of said anode to
form a dielectric layer thereon; forming a first conductive polymer
layer on said dielectric layer; forming a second conductive polymer
layer on said first conductive polymer layer by dipping said metal
body having said dielectric layer and said first conductive layer
thereon into a solution of doped polyaniline dissolved in an
organic solvent.
9. A method according to claim 8 and further comprising forming
said doped polyaniline by using a dopant selected from the group
consisting essentially of arylsulfonic acid and camphorsulfonic
acid.
10. A method according to claim 8 and further comprising dissolving
said doped polyaniline in said organic solvent wherein said organic
solvent is selected from the group consisting essentially of
m-Cresol, P-Cresol, o-Cresol, and Cl-Cresol.
11. A method according to claim 8 and further comprising forming
said first conductive polymer layer from polypyrrole.
12. A method according to claim 8 and further comprising placing an
inorganic filler within said organic solvent before said dipping
step whereby said inorganic filler is within said second conductive
polymer layer after said dipping step.
13. A method according to claim 12 wherein said inorganic filler is
selected from the group consisting essentially of SiO.sub.2,
Al.sub.2O.sub.3, SnO.sub.2, ZrO.sub.2, MgO, and BeO.
14. A method according to claim 12 wherein said inorganic filler
comprises graphite.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a conductive polymer
capacitor and method for making same. Prior solid electrolytic
capacitors have been provided from a molded porous body of metal
such as tantalum, niobium, or aluminum which serves as an anode for
the capacitor. The metal is powdered and is formed by heat and
pressure into a solid porous body. An oxide coating is formed over
the metal and a solid electrolyte such as maganese dioxide
(MnO.sub.2) is formed over the dielectric and serves as the cathode
of the capacitor.
[0002] In recent years polymers have been used in forming the
cathode solid electrolyte. Examples of the use of polymers as a
solid cathode electrolyte are shown in U.S. Pat. Nos. 5,461,537;
4,780,796; and 5,457,862.
[0003] In these prior capacitors, two polymer layers are formed.
The first polymer is formed by using a chemical oxidant to
chemically oxidize and polymerize the polymer on the dielectric
layer of the capacitor. Then a second polymer layer is formed using
a solution containing an undoped polymer compound polymerized in
advance and soluble in an organic solvent. After the formation of
the second polymer compound, the second polymer compound is doped
to make the undoped polymer compound layer conductive.
[0004] Therefore, a primary object of the present invention is the
provision of an improved conductive polymer capacitor and method
for making same.
[0005] A further object of the present invention is the provision
of an improved conductive polymer capacitor which achieves very
high conductivity of the polymer layers, thereby resulting in a
capacitor with lower equivalent series resistance (ESR).
[0006] A further object of the present invention is the provision
of an improved conductive polymer capacitor and method for making
same which is more durable in use, more reliable in operation, and
more efficient to manufacture.
SUMMARY OF THE INVENTION
[0007] The foregoing objects may be achieved by a conductive
polymer capacitor having an anode formed from a porous metal body,
and including an anode lead extending therefrom. A dielectric layer
is formed on the surface of the anode by oxidizing the metal of the
anode. A solid electrolyte is formed on the dielectric layer
comprised of a first conductive polymer layer formed on the
dielectric layer and a second conductive polymer layer formed on
the first conductive polymer layer. The first conductive polymer
layer is preferably a polypyrrole layer. The second conductive
polymer layer comprises a polyaniline layer formed by dipping the
metal body having the first conductive polymer layer thereon into a
solution of doped polyaniline dissolved in an organic solvent.
[0008] As used herein the term "doped" refers to the use of a
dopant which is either an electron donor or acceptor in polymer
compounds such as polypyrrole, polythiophene, and polyaniline.
Numerous types of dopants are well known in the art of making
capacitors, and include, but are not limited to, naphtalenesulfonic
acid sodium salt, toluenesulfonic acid sodium salt, and
benzenesulfonic acid sodium salt. Other dopants capable of donating
or accepting electrons to the polymer compound may be used without
detracting from the invention.
[0009] Numerous organic solvents may be used for the dissolving of
the polyaniline before the dipping process. Examples include but
are not limited to m-Cresol, p-Cresol, o-Cresol, and Cl-Cresol.
[0010] In one form of the invention inorganic fillers may be
included within the polyaniline solution inorganic solvent so that
the second conductive layer, once formed by dipping, includes the
inorganic filler within the second conductive layer. The inorganic
filler may be selected from any of a number of inorganic fillers,
including but not limited to graphite, SiO.sub.2, Al.sub.2O.sub.3,
SrO.sub.2, ZrO.sub.2, MgO, BeO.
BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS
[0011] FIG. 1 is a sectional view of the capacitor of the present
invention.
[0012] FIG. 2 is an enlarged sectional view taken along line 2-2 of
FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0013] Referring to the drawings the numeral 10 generally
designates the capacitor of the present invention. Capacitor 10
includes an anode pellet 12 having an anode lead 14 connected
thereto by means of a weld 16. The anode pellet is formed from a
powdered metal such as tantalum, niobium, or aluminum. The method
for forming the pellet 12 is well known in the art and involves
compressing the powdered material into the pellet shape and
sintering the pellet to cause it to retain its shape. The pellet 12
includes a plurality of voids interspersed throughout the pellet
12. Coating the surface of the pellet 12 is an oxide coating 18.
While this oxide coating 18 is shown schematically in FIG. 2, the
oxide coating coats the exposed surfaces of the particles within
pellet 12 throughout the entire body 12.
[0014] A first polymer layer 20 is formed on the outer surface of
the oxide coating 18, and a second polymer layer 22 is formed on
the outside of the first polymer layer 20. A conductive cathode
material 24 is formed on the outside surface of the polyaniline
layer, and a dielectric coating 26 is formed around the outside of
the entire capacitor 10, leaving a portion of the cathode 24
exposed to provide a cathode connecting surface 28 at the bottom of
the capacitor.
[0015] The first step in the formation of cathode 10 is the
formation of the metal body 12. This metal body may comprise
tantalum, niobium, or aluminum powder which is compressed under
pressure and then is sintered to form the anode pellet 12. The
pellet 12 is then oxidized in accordance with the processes well
known in the art to form the dielectric layer 18 on the surface of
the pellet. The dielectric layer 18 is preferably an oxide of the
metal powder used for the pellet 12.
[0016] After the formation of the oxide layer 18, two polymer
layers 20, 22 are formed on the surface of the pellet 12. The
formation of the two layers 20, 22 will be described below in
detail by way of examples.
EXAMPLE 1
[0017] The first polymer layer 20 is formed by dipping the pellet
12 having the oxide coating 18 thereon into an iron (III) chloride
aqueous solution (2-20 wt. %) for 3-15 minutes at room temperature.
It is then permitted to dry for 10-20 minutes at
60.degree.-80.degree. C. The pellet is then dipped into a solution
of pyrrole (2-5 wt. %) and naphtalenesulfonic acid sodium salt (1-2
wt. %) for 5 minutes at 0.degree.-10.degree. C. The dipped pellet
is then permitted to dry for 10-20 minutes at 60.degree.-80.degree.
C.
[0018] After drying the pellet is washed with methanol at room
temperature for 5 minutes and is permitted to dry for 10-20 minutes
at 60.degree.-80.degree. C. After completion of this drying step a
polypyrrole layer is formed for the first polymer layer 20. This
polymerization procedure is repeated 5-7 times.
[0019] The second polymer layer 22 is formed by dipping the pellet
into a solution of doped polyaniline (2 wt. %) in m-Cresol for 5
minutes at room temperature. The dopant is camphorsulfonic acid. It
is then vacuum dried for 30-60 minutes at 60.degree.-90.degree. C.
This step is repeated 2-3 times. This results in the formation of
the second polymer layer 22 from as a polyaniline.
EXAMPLE 2
[0020] The formation of the pellet 12 having the oxide layer 18
thereon is the same as described above. Also, the formation of the
first polymer layer 20 of a polypyrrole material is the same as
described above.
[0021] After the formation of the polypyrrole layer the pellet is
dipped into a solution of doped polyaniline (2 wt. %) in m-Cresol
with inorganic fillers such as S.sub.iO.sub.2 or similar fillers
for 5 minutes at room temperature. The pellet is then vacuum dried
for 30-60 minutes at 60.degree.-90.degree. C.
EXAMPLE 3
[0022] The pellet 12, oxide layer 18, and first polymer layer 20
are formed in the manner described above in Examples 1 and 2. The
pellet, having the polypyrrole polymer layer formed on the outer
surface thereof is dipped into a solution of doped polyaniline (2
wt. %) in m-Cresol with graphite filler for 5 minutes at room
temperature, and the pellet is vacuum dried for 30-60 minutes at
60.degree.-90.degree. C.
[0023] The use of fillers as described above for Examples 2 and 3
permits the fillers to be dispersed throughout the polyaniline
layer 22, whereas prior art methods formed the fillers as separate
layers rather than embedding them within the polyaniline layer.
[0024] The oxidant used for forming the polypyrrole layer in the
above examples is preferably iron (III) chloride. However, also
ferric salts of arylsulfonic acids may be used as oxidant.
[0025] The preferred dopant for use in the formation of the
polyaniline layer in the above examples is camphorsulfonic acid.
However, other acids may be used, including but not limited to,
arylsulfonic acids.
[0026] The solvent for forming the polyaniline layer is preferably
m-Cresol, but other solvents may be used such as p-Cresol, o-Cresol
or Cl-Cresol.
[0027] The inorganic fillers described for Example 2 above
preferably include SiO.sub.2. However, other fillers such as
Al.sub.2O.sub.3, SnO.sub.2, ZrO.sub.2, MgO, and BeO may be
used.
[0028] In Examples 1-3 above, the process for forming the
polypyrrole impregnation is repeated 5-10 cycles so as to form
layer 20 of multiple polypyrrole layers. The formation of the
polyaniline layer 22 is preferably two cycles so as to form two
polyaniline based layers.
[0029] The above described method achieves a very high conductivity
of the multiple polyaniline based layers. This results in
capacitors with very low equivalent series resistance (ESR). Of
particular importance is the ability to disperse inorganic fillers
in the polyaniline layers so as to improve the electrical
conductivity of the polyaniline layers.
[0030] In the drawings and specification there has been set forth a
preferred embodiment of the invention, and although specific terms
are employed, these are used in a generic and descriptive sense
only and not for purposes of limitation. Changes in the form and
the proportion of parts as well as in the substitution of
equivalents are contemplated as circumstances may suggest or render
expedient without departing from the spirit or scope of the
invention as further defined in the following claims.
* * * * *