U.S. patent application number 11/803952 was filed with the patent office on 2008-11-20 for use of conjugated oligomer as additive for forming conductive polymers.
Invention is credited to Keith R. Brenneman, Qingping Chen, Randy S. Hahn, Philip M. Lessner, Yuhong Ma, Yongjian Qiu.
Application Number | 20080283409 11/803952 |
Document ID | / |
Family ID | 40026408 |
Filed Date | 2008-11-20 |
United States Patent
Application |
20080283409 |
Kind Code |
A1 |
Chen; Qingping ; et
al. |
November 20, 2008 |
Use of conjugated oligomer as additive for forming conductive
polymers
Abstract
A process for forming a capacitor. The process includes
providing an anode; providing a dielectric on the anode; exposing
the anode to a polymer precursor solution comprising monomer,
conjugated oligomer and optionally solvent and polymerizing the
polymer precursor. The ratio between monomer and conjugated
oligomer ranges from 99.9/0.1 to 75/25 by weight. The solvent
content in the polymer precursor solution is from 0 to 99% by
weight.
Inventors: |
Chen; Qingping;
(Simpsonville, SC) ; Brenneman; Keith R.;
(Simpsonville, SC) ; Ma; Yuhong; (Beijing, CN)
; Qiu; Yongjian; (Greenville, SC) ; Lessner;
Philip M.; (Newberry, SC) ; Hahn; Randy S.;
(Simpsonville, SC) |
Correspondence
Address: |
NEXSEN PRUET, LLC
P.O. BOX 10648
GREENVILLE
SC
29603
US
|
Family ID: |
40026408 |
Appl. No.: |
11/803952 |
Filed: |
May 16, 2007 |
Current U.S.
Class: |
205/317 |
Current CPC
Class: |
H01G 9/15 20130101; H01G
9/0036 20130101 |
Class at
Publication: |
205/317 |
International
Class: |
C25D 11/00 20060101
C25D011/00 |
Claims
1. A process for forming a capacitor comprising: providing an
anode; providing a dielectric on said anode; exposing said anode
comprising said dielectric to a solution of polymer precursor
comprising 75-99.9 wt % monomer and 0.1 to 25 wt % conjugated
oligomer; and polymerizing said polymer precursor.
2. The process for forming a capacitor of claim 1 wherein said
polymer precursor comprises 90-99.9 wt % monomer and 0.1 to 10 wt %
conjugated oligomer.
3. The process for forming a capacitor of claim 1 wherein said
polymer precursor comprises 95-99.5 wt % monomer and 0.5 to 5 wt %
conjugated oligomer.
4. The process for forming a capacitor of claim 1 comprising
exposing said anode comprising a dielectric to a solution
comprising 1-100% by weight of said polymer precursor and 0-99% by
weight solvent.
5. The process for forming a capacitor of claim 4 comprising 10-90%
by weight solvent.
6. The process for forming a capacitor of claim 1 wherein said
polymerizing said polymer precursor is by electrochemical
polymerization.
7. The process for forming a capacitor of claim 1 wherein said
polymerizing said polymer precursor is by chemical
polymerization.
8. The process for forming a capacitor of claim 7 wherein said
chemical polymerization is oxidative chemical polymerization.
9. The process for forming a capacitor of claim 1 wherein said
anode comprises a conductor.
10. The process for forming a capacitor of claim 9 wherein said
conductor comprises at least one material selected from niobium,
aluminum, tantalum, titanium, zirconium, hafnium, tungsten and
NbO.
11. The process for forming a capacitor of claim 10 wherein said
anode comprises at least one material selected from niobium,
tantalum and NbO.
12. The process for forming a capacitor of claim 1 wherein said
monomer is: ##STR00005## wherein: X is selected from S, Se and N;
R.sup.1 and R.sup.2 independently represent hydrogen, linear or
branched C.sub.1-C.sub.16 alkyl or C.sub.1-C.sub.18 alkoxyalkyl;
C.sub.3-C.sub.8 cycloalkyl; phenyl or benzyl which are
unsubstituted or substituted by C.sub.1-C.sub.6 alkyl,
C.sub.1-C.sub.6 alkoxy, halogen or --OR.sup.3; or R.sup.1 and
R.sup.2, taken together, are linear C.sub.1-C.sub.6 alkylene which
is unsubstituted or substituted by C.sub.1-C.sub.6 alkyl,
C.sub.1-C.sub.6 alkoxy, halogen, C.sub.3-C.sub.8 cycloalkyl,
phenyl, benzyl, C.sub.1-C.sub.4 alkylphenyl, C.sub.1-C.sub.4
alkoxyphenyl, halophenyl, C.sub.1-C.sub.4 alkylbenzyl,
C.sub.1-C.sub.4 alkoxybenzyl or halobenzyl, 5-, 6-, or 7-membered
heterocyclic structure containing two oxygen elements; and R.sup.3
represents hydrogen, linear or branched C.sub.1-C.sub.16 alkyl;
C.sub.1-C.sub.18 alkoxyalkyl; C.sub.3-C.sub.8 cycloalkyl, phenyl;
benzyl which are unsubstituted or substituted by C.sub.1-C.sub.6
alkyl.
13. The process for forming a capacitor of claim 12 wherein neither
R.sup.1 nor R.sup.2 are hydrogen.
14. The process for forming a capacitor of claim 12 wherein R.sup.1
and R.sup.2 independently of one another, represent --OCH.sub.3 or
--OCH.sub.2CH.sub.3.
15. The process for forming a capacitor of claim 2 wherein R.sup.1
and R.sup.2 are taken together to represent
--OCH.sub.2CH.sub.2O--.
16. The process for forming a capacitor of claim 12 wherein X is
selected from S and N.
17. The process for forming a capacitor of claim 16 wherein X is
S.
18. A capacitor formed by the process of claim 1.
19. An electronic device comprising the capacitor of claim 18.
20. The process for forming a capacitor of claim 1 wherein said
conjugated oligomer is: ##STR00006## wherein: Y is independently
selected from S, Se and N; R.sup.4, R.sup.5, R.sup.6, R.sup.7,
R.sup.8 and R.sup.9 independently represent hydrogen, linear or
branched C.sub.1-C.sub.16 alkyl or C.sub.1-C.sub.18 alkoxyalkyl;
C.sub.3-C.sub.8 cycloalkyl, phenyl or benzyl which are
unsubstituted or substituted by C.sub.1-C.sub.6 alkyl,
C.sub.1-C.sub.6 alkoxy, halogen or --OR.sup.3; or R.sup.4 and
R.sup.5, R.sup.6 and R.sup.7 or R.sup.8 and R.sup.9, taken
together, are linear C.sub.1-C.sub.6 alkylene which is
unsubstituted or substituted by C.sub.1-C.sub.6 alkyl,
C.sub.1-C.sub.6 alkoxy, halogen, C.sub.3-C.sub.8 cycloalkyl,
phenyl, benzyl, C.sub.1-C.sub.4 alkylphenyl, C.sub.1-C.sub.4
alkoxyphenyl, halophenyl, C.sub.1-C.sub.4 alkylbenzyl,
C.sub.1-C.sub.4 alkoxybenzyl or halobenzyl, 5-, 6-, or 7-membered
heterocyclic structure containing two oxygen elements. R.sup.3
represents hydrogen, linear or branched C.sub.1-C.sub.16 alkyl;
C.sub.1-C.sub.18 alkoxyalkyl; C.sub.3-C.sub.8 cycloalkyl, phenyl;
benzyl which are unsubstituted or substituted by C.sub.1-C.sub.6
alkyl; and n is an integer selected from 0-3.
21. The process for forming a capacitor of claim 20 wherein none of
R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8 and R.sup.9 are
hydrogen.
22. The process for forming a capacitor of claim 20 wherein n is an
integer selected from 0 and 1.
23. The process for forming a capacitor of claim 20 wherein
R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8 and R.sup.9),
independently of one another, represent --OCH.sub.3 or
--OCH.sub.2CH.sub.3.
24. The process for forming a capacitor of claim 20 wherein at
least one of R.sup.4 and R.sup.5, R.sup.6 and R.sup.7; and R.sup.8
and R.sup.9 is taken together to represent
--OCH.sub.2CH.sub.2O--.
25. The process for forming a capacitor of claim 20 wherein at
least one Y is selected from S and N.
26. The process for forming a capacitor of claim 25 wherein at
least one Y is S.
27. A capacitor formed by the process of claim 20.
28. An electronic device comprising the capacitor of claim 27.
29. A capacitor formed by the process of: providing an anode;
providing a dielectric on said anode; exposing said anode
comprising said dielectric to a solution comprising polymer
precursor comprising 75-99.9 wt % monomer and 0.1 to 25 wt %
conjugated oligomer; and polymerizing said polymer precursor.
30. The capacitor of claim 29 wherein said polymer precursor
comprises 90-99.9 wt % monomer and 0.1 to 10 wt % conjugated
oligomer.
31. The capacitor of claim 30 wherein said polymer precursor
comprises 95-99.5 wt % monomer and 0.5 to 5 wt % conjugated
oligomer.
32. The capacitor of claim 29 wherein said anode comprises at least
one material selected from niobium, aluminum, tantalum, titanium,
zirconium, hafnium, tungsten and NbO.
33. The capacitor of claim 32 wherein said anode comprises at least
one material selected from niobium, tantalum and NbO.
34. The capacitor of claim 29 comprising exposing said anode to a
solution comprising 1-100% by weight of said polymer precursor and
0-99% by weight solvent.
35. The capacitor of claim 34 comprising 10-90% by weight
solvent.
36. The process for forming a capacitor of claim 29 wherein said
polymerizing said polymer precursor is by electrochemical
polymerization.
37. The process for forming a capacitor of claim 29 wherein said
polymerizing said polymer precursor is by chemical
polymerization.
38. The process for forming a capacitor of claim 37 wherein said
chemical polymerization is oxidative chemical polymerization.
39. The capacitor of claim 29 wherein said monomer is: ##STR00007##
wherein: X is selected from S, Se and N; R.sup.1 and R.sup.2
independently represent hydrogen, linear or branched
C.sub.1-C.sub.16 alkyl or C.sub.1-C.sub.18 alkoxyalkyl;
C.sub.3-C.sub.8 cycloalkyl; phenyl or benzyl which are
unsubstituted or substituted by C.sub.1-C.sub.6 alkyl,
C.sub.1-C.sub.6 alkoxy, halogen or --OR.sup.3; or R.sup.1 and
R.sup.2, taken together, are linear C.sub.1-C.sub.6 alkylene which
is unsubstituted or substituted by C.sub.1-C.sub.6 alkyl,
C.sub.1-C.sub.6 alkoxy, halogen, C.sub.3-C.sub.8 cycloalkyl,
phenyl, benzyl, C.sub.1-C.sub.4 alkylphenyl, C.sub.1-C.sub.4
alkoxyphenyl, halophenyl, C.sub.1-C.sub.4 alkylbenzyl,
C.sub.1-C.sub.4 alkoxybenzyl or halobenzyl, 5-, 6-, or 7-membered
heterocyclic structure containing two oxygen elements; and R.sup.3
represents hydrogen, linear or branched C.sub.1-C.sub.16 alkyl;
C.sub.1-C.sub.18 alkoxyalkyl; C.sub.3-C.sub.8 cycloalkyl, phenyl;
benzyl which are unsubstituted or substituted by C.sub.1-C.sub.6
alkyl.
40. The capacitor of claim 39 wherein neither R.sup.1 nor R.sup.2
are hydrogen.
41. The capacitor of claim 39 wherein R.sup.1 and R.sup.2
independently of one another, represent --OCH.sub.3 or
--OCH.sub.2CH.sub.3.
42. The capacitor of claim 39 wherein R.sup.1 and R.sup.2 are taken
together to represent --OCH.sub.2CH.sub.2O--.
43. The capacitor of claim 39 wherein X is selected from S and
N.
44. The capacitor of claim 43 wherein X is S.
45. The process for forming a capacitor of claim 29 wherein said
conjugated oligomer is: ##STR00008## wherein: Y is independently
selected from S, Se and N; R.sup.4, R.sup.5, R.sup.6, R.sup.7,
R.sup.1 and R.sup.9 independently represent hydrogen, linear or
branched C.sub.1-C.sub.16 alkyl or C.sub.1-C.sub.18 alkoxyalkyl;
C.sub.3-C.sub.8 cycloalkyl, phenyl or benzyl which are
unsubstituted or substituted by C.sub.1-C.sub.6 alkyl,
C.sub.1-C.sub.6 alkoxy, halogen or --OR.sup.3; or R.sup.4 and
R.sup.5, R.sup.6 and R.sup.7 or R.sup.8 and R.sup.9, taken
together, are linear C.sub.1-C.sub.6 alkylene which is
unsubstituted or substituted by C.sub.1-C.sub.6 alkyl,
C.sub.1-C.sub.6 alkoxy, halogen, C.sub.3-C.sub.8 cycloalkyl,
phenyl, benzyl, C.sub.1-C.sub.4 alkylphenyl, C.sub.1-C.sub.4
alkoxyphenyl, halophenyl, C.sub.1-C.sub.4 alkylbenzyl,
C.sub.1-C.sub.4 alkoxybenzyl or halobenzyl, 5-, 6-, or 7-membered
heterocyclic structure containing two oxygen elements; R.sup.3
represents hydrogen, linear or branched C.sub.1-C.sub.16 alkyl;
C.sub.1-C.sub.18 alkoxyalkyl; C.sub.3-C.sub.8 cycloalkyl, phenyl;
benzyl which are unsubstituted or substituted by C.sub.1-C.sub.6
alkyl; and n is an integer selected from 0-3.
46. The process for forming a capacitor of claim 45 wherein none of
R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8 and R.sup.9 is
hydrogen.
47. The process for forming a capacitor of claim 45 wherein n is an
integer selected From 0 and 1.
48. The process for forming a capacitor of claim 45 wherein
R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8 and R.sup.9,
independently of one another, represent --OCH.sub.3 or
--OCH.sub.2CH.sub.3.
49. The process for forming a capacitor of claim 45 wherein one of
R.sup.4 and R.sup.5, R.sup.6 and R.sup.7 or R.sup.8 and R.sup.9 is
taken together to represent --OCH.sub.2CH.sub.2O--.
50. The process for forming a capacitor of claim 45 wherein at
least one Y is selected from S and N.
51. The process for forming a capacitor of claim 50 wherein at
least one Y is S.
52. An electronic device comprising the capacitor of claim 45.
53. A process for forming a capacitor comprising: providing an
anode comprising a material selected from niobium, aluminum,
tantalum, titanium, zirconium, hafnium, tungsten and NbO; providing
a dielectric on said anode; exposing said anode comprising said
dielectric to a polymer precursor comprising 75-99.9 wt % monomer
defined as: ##STR00009## and 0.1 to 25 wt % conjugated oligomer
defined as: ##STR00010## and polymerizing said polymer
precursor.
54. The process for forming a capacitor of claim 53 wherein said
polymer precursor comprises 90-99.9 wt % monomer and 0.1 to 10 wt %
conjugated oligomer.
55. The process for forming a capacitor of claim 53 wherein said
polymer precursor comprises 95-99.5 wt % monomer and 0.5 to 5 wt %
conjugated oligomer.
56. The process for forming a capacitor of claim 53 comprising
exposing said anode to a solution comprising 1-100% by weight of
said polymer precursor and 0-99% by weight solvent.
57. The process for forming a capacitor of claim 56 comprising
10-90% by weight solvent.
58. The process for forming a capacitor of claim 53 wherein said
anode comprises at least one material selected from niobium,
aluminum, tantalum, titanium, zirconium, hafnium, tungsten and
NbO.
59. The process for forming a capacitor of claim 58 wherein said
anode comprises at least one material selected from niobium,
tantalum and NbO.
60. The process for forming a capacitor of claim 53 wherein said
polymerizing said polymer precursor is by electrochemical
polymerization.
61. The process for forming a capacitor of claim 53 wherein said
polymerizing said polymer precursor is by chemical
polymerization.
62. The process for forming a capacitor of claim 53 wherein said
chemical polymerization is oxidative chemical polymerization.
Description
FIELD OF THE INVENTION
[0001] This invention relates to methods for improving the
conductivity of intrinsically conductive organic polymers and
capacitors prepared by using such methods which exhibit reduced
equivalent series resistance (ESR) and robust performance during
the surface mounting process of the capacitor to a circuit board.
More specifically, the invention relates to a method of forming a
capacitor wherein a conductive polymer is formed by a combination
of monomers, and conjugated oligomers with no more than five
repeating units.
BACKGROUND OF THE INVENTION
[0002] Electrolytic capacitors having valve metal anodes
impregnated with a highly conductive liquid electrolyte such as an
aqueous solution of sulfuric acid have been in commercial use for
many years. There are many liquid electrolyte solutions which have
been used in electrolytic capacitors. The liquid electrolytes
conduct current by an ionic conduction mechanism and tend to have
high resistance. Haring et. al., in U.S. Pat. No. 3,093,883,
disclosed the use of pyrolytic manganese dioxide produced via the
pyrolysis of aqueous manganese nitrate solutions as the cathode
material. Manganese dioxide as a solid state conductor with lower
resistivity (1-3 orders of magnitude lower than liquid electrolyte
solutions) substantially reduced the resistance of the cathode
layer and overall resistance of these devices.
[0003] With the continuing development of ever-faster
microprocessors and lower-voltage logic circuits, the demand for
lower ESR capacitors for use in conjunction with faster
microprocessors has motivated capacitor manufacturers to develop
solid state cathode materials which are more conductive, less
electrically resistive, than manganese dioxide.
[0004] In the early 1980's, electrolytic capacitors were introduced
which were fabricated having a tetracyanoquinodimethane amine
complex acting as the cathode. These capacitors established the
stability and high conductivity achievable with solid-state organic
cathode materials. The ongoing effort to increase the maximum
temperature capability of organic cathode electrolytic capacitors
has led to the development of methods of capacitor fabrication
employing intrinsically conductive organic polymers, such as
polypyrrole, polythiophenes, polyanilines and their derivatives.
Numerous substituted monomers, or derivatives, are useful as are
mixtures of two or more monomers from different types, i.e.,
mixtures. High electric conductivity, good thermal stability and
benign failure mode led to the widespread use of these
intrinsically conductive organic polymers in solid electrolytic
capacitors since the 1990s.
[0005] Both chemical and electrochemical polymerization has been
used to form intrinsically conductive polymers for electrolytic
capacitors. Chemical polymerization is well described in U.S. Pat.
No. 4,910,645, to Jonas et. al., U.S. Pat. No. 6,136,176 to D.
Wheeler, et. al. and U.S. Pat. No. 6,334,966 to Hahn et al. The
process consists of immersing the anodized substrate first in a
solution of an oxidizing agent such as, but not necessarily limited
to, iron (III) p-toluenesulfonate. After a drying step the anode
bodies are then immersed in a solution of the monomer. Once the
solution of monomer, which may consist entirely of monomer, is
introduced into the capacitor anode bodies, the anodes are allowed
to stand to facilitate production of the intrinsically conductive
polymer material. Repeated dipping sequences may be employed to
more completely fill the pore structure of the anode bodies. In
practice, rinsing cycles are generally employed to remove reaction
by-products, such as ammonium sulfate, sulfuric acid, iron salts
(when an iron (I) oxidizer is employed), or other by-products
depending on the system employed. Chemical production of
intrinsically conductive organic polymers may also be carried-out
with capacitor anode bodies by first introducing the monomer to the
capacitor bodies, followed by introduction of the oxidizer and
dopant (the reverse order of polymer precursor introduction
described above). It is also possible to mix the dopant acid(s)
with the monomer solution rather than with the oxidizer solution if
this is found to be advantageous. U.S. Pat. Nos. 6,001,281 and No.
6,056,899 describe a chemical means of producing an intrinsically
conductive organic polymer through the use of a single solution
which contains both the monomer and the oxidizing agent, which has
been rendered temporarily inactive via complexing with a high vapor
pressure solvent. As the solution is warmed and the inhibiting
solvent evaporates, the oxidative production of conductive polymers
ensues. The dopant acid anion is also contained in the stabilized
poly-precursor solution.
[0006] The demand for capacitors exhibiting lower equivalent series
resistance (ESR) and dissipation factor, which has led to the
development of electrolytic capacitors based on conductive polymer
cathode materials, has been accompanied by a demand for capacitors
exhibiting higher reliability, particularly a lower incidence of
high leakage current/short circuit failures.
[0007] Intrinsically conductive organic polymers generally contain
one dopant anion for each 3 to 4 monomer units which have been
joined to form the polymer. The presence of a strong dopant acid
anion is thought to result in a delocalization of electric charge
on the conjugated molecular chain and therefore provides electrical
conductivity. In the case of ferric salt being used as the
oxidizer, the presence of an acid also keeps the Fe.sup.3+ ions
from precipitating out of the solution. In the sequential dipping
process the acid could accumulate in the monomer solution. It is
known that an acid can promote the formation of non-conjugated
dimers and trimers through acid catalyzed reaction. U.S. Pat. No.
6,891,016 to Rueter et al. disclosed the formation of
non-conjugated ethylenedioxythiophene (EDT) dimer, structure (I),
and trimer, structure (II), in the presence of an acid
catalyst.
##STR00001##
[0008] These non-conjugated dimers and trimers can result in a
decrease in conjugation length which deteriorates conductivity of
the polymer. This would cause an increase in ESR of conductive
polymer based solid electrolytic capacitors. In U.S. patent
application (docket number 31433-117 filed Apr. 16, 2007)
procedures to control the acid content in the monomer solution are
disclosed. Although the conductivity of polymer made according to
U.S. patent application (docket number 31433-117 filed Apr. 16,
2007) was maintained high, the growth rate of the conductive
polymer could be decreased. More production cycles may be required
to provide adequate polymer coverage.
[0009] There has been an ongoing, and increasing, desire to provide
a conductive polymer layer with improved conductivity. There has
also been a desire to provide a capacitor, comprising the
conductive polymer, with an improved ESR and reliability.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide an
improved polymer coating as indicated by a reduced resistance.
[0011] It is another object of the present invention to provide an
improved capacitor wherein the capacitor has a lower ESR due to a
lower resistance in the polymeric cathode layer.
[0012] A particular advantage of the present invention is the
ability to implement the improvement with minimal alterations to
existing manufacturing facilities or processes.
[0013] These and other advantages, as will be understood, are
provided in a process for forming a capacitor. The process includes
providing an anode; providing a dielectric on the anode such as by
anodizing the anode; exposing, such as by dipping, the anode into a
polymer precursor solution comprising monomers, conjugated
oligomers and optionally solvents and polymerizing the polymer
precursor. The ratio of monomers to conjugated oligomers ranges
from 99.9/0.1 to 75/25 by weight, the solvent content of the
solution of polymer precursor is from 0 to 99% by weight.
[0014] A preferred embodiment is provided in a capacitor formed by
the process of: providing an anode; forming a dielectric on the
anode; exposing the anodized anode into a polymer precursor
solution comprising monomer, conjugated oligomer and optionally
solvent and polymerizing the polymer precursor. The ratio between
monomers and conjugated oligomers ranges from 99.9/0.1 to 90/10 by
weight, the solvent content in the solution of precursors is
preferably from 10-90% by weight.
[0015] A particularly preferred embodiment is provided in a process
for forming a capacitor comprising: providing an anode comprising a
material selected from niobium, aluminum, tantalum, titanium,
zirconium, hafnium, tungsten and NbO; forming a dielectric on the
anode to form an anodized anode; dipping the anodized anode into a
polymer precursor solution comprising monomer, conjugated oligomers
and optionally solvents to form a polymer precursor coating and
polymerizing the polymer precursor coating. The ratio of monomers
to conjugated oligomers ranges from 99.9/0.1 to 75/25 by weight and
the solvent content in the solution of precursor is from 0 to 99%
by weight with the monomer defined as:
##STR00002##
[0016] and the conjugated oligomer is defined as:
##STR00003##
[0017] where n=0 to 3.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a schematic cross-sectional view of a capacitor of
the present invention.
[0019] FIGS. 2a and 2b provide Fourier transform infrared (FT-IR)
spectra of conjugated and nonconjugated EDT dimmers,
respectively.
[0020] FIGS. 3a and 3b provide proton nuclear magnetic resonance
(.sup.1H NMR) spectra of conjugated and nonconjugated EDT dimmers,
respectively.
[0021] FIG. 4 provides a .sup.1H NMR spectrum of an EDT sample used
to make poly-EDT (PEDT).
[0022] FIG. 5 provides scanning electron microscope (SEM) pictures
after deposition of polymer from various solutions.
DETAILED DESCRIPTION
[0023] An improvement in a conductive polymer, and capacitor formed
with the conductive polymer, is achieved by adding conjugated
oligomer, preferably conjugated dimer or conjugated trimer, to the
monomer solution. The addition of conjugated oligomer provides
adequate polymer growth rate for good polymer coverage of the
dielectric surface of the anode.
[0024] The invention will be described with reference to the FIG. 1
forming a part of the present application.
[0025] In FIG. 1, a cross-sectional view of a capacitor is shown.
The capacitor comprises an anode, 1. A dielectric layer, 2, is
provided on the surface of the anode, 1. The dielectric layer is
preferably formed as an oxide of the anode as further described
herein. Coated on the surface of the dielectric layer, 2, is a
conducting layer, 3. Layers 4 and 5 are conductive coating layers
comprising graphite and silver based materials and providing
connection to lead 7. Leads, 7 and 8, provide contact points for
attaching the capacitor to a circuit. The entire element, except
for the terminus of the leads, is then preferably encased in a
housing, 6, which is preferably an epoxy resin housing. The
capacitor may be attached to circuit traces, 9, of a substrate, 10,
and incorporated into an electronic device, 11.
[0026] The anode is a conductive material preferably comprising a
valve-metal preferably selected from niobium, aluminum, tantalum,
titanium, zirconium, hafnium, or tungsten or a conductive oxide
such as NbO. Aluminum, tantalum, niobium and NbO are most preferred
as the anode material. Aluminum is typically employed as a foil
while tantalum, niobium and NbO are typically prepared by pressing
a powder and sintering to form a compact. For convenience in
handling, the anode is typically attached to a carrier thereby
allowing large numbers of elements to be processed at the same
time.
[0027] The anode in the form of a foil is preferably etched to
increase the surface area. Etching is preferably done by immersing
the anode into at least one etching bath. Various etching baths are
taught in the art and the method used for etching the valve metal
is not limiting herein.
[0028] A dielectric is formed on the anode. In a preferred
embodiment the surface of the anode is coated with a dielectric
layer comprising an oxide. It is most desirable that the dielectric
layer be an oxide of the anode material. The oxide is preferably
formed by dipping the anode into an electrolyte solution and
applying a positive voltage. The process of forming the dielectric
layer oxide is well known to those skilled in the art. Other
methods of forming the dielectric layer may be utilized such as
vapour deposition, sol-gel deposition, solvent deposition or the
like. The dielectric layer may be an oxide of the anode material
formed by oxidizing the surface of the anode or the dielectric
layer may be a material which is different from the anode material
and deposited on the anode by any method suitable therefore.
[0029] The polymer precursors are polymerized to form the
conductive layer which functions as the cathode of the capacitor.
The polymer precursors are preferably polymerized by either
electrochemical or chemical polymerization techniques with
oxidative chemical polymerization being most preferred. In one
embodiment the conductive layer is formed by dipping the anodized
substrate first in a solution of an oxidizing agent such as, but
not necessarily limited to iron (III) p-toluenesulfonate. After a
drying step, the anode bodies are then immersed in a solution
comprising monomer and oligomer of the conductive polymer and
solvents.
[0030] The present invention utilizes a polymer precursor
comprising a monomer and conjugated oligomer. The monomer
preferably represents 75-99.9 wt % of the polymer precursors and
the conjugated oligomer represents 0.1-25 wt % of the polymer
precursors. More preferably the monomer represents 90-99.9 wt % of
the polymer precursors and the conjugated oligomer represents
0.1-10 wt % of the polymer precursors. Even more preferably the
monomer represents 95-99.5 wt % of the polymer precursors and the
conjugated oligomer represents 0.5-5 wt % of the polymer
precursors. The preferred monomer is a compound of Formula I and
the preferred oligomer is a compound of Formula II.
[0031] The conducting polymer is preferably the polymer comprising
repeating units of a monomer and oligomer of Formula I and Formula
II:
##STR00004##
[0032] R.sup.1 and R.sup.2 of Formula I and R.sup.4-R.sup.9 of
Formula II are chosen to prohibit polymerization at the .beta.-site
of the ring. It is most preferred that only .alpha.-site
polymerization be allowed to proceed. Therefore, it is preferred
that R.sup.1 and R.sup.2 are not hydrogen. More preferably R.sup.1,
R.sup.2, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.1 and R.sup.9
are .alpha.-directors. Therefore, ether linkages are preferable
over alkyl linkages. It is most preferred that the groups are small
to avoid steric interferences. For these reasons R.sup.1 and
R.sup.2, R.sup.4 and R.sup.5, R.sup.6 and R.sup.7 or R.sup.8 and
R.sup.9 taken together as --O--(CH.sub.2).sub.2--O-- are most
preferred.
[0033] In Formula II n is an integer selected from 0-3.
[0034] In Formulas I and II, X and Y independently are S, Se or N.
Most preferably X and Y are S.
[0035] R.sup.1, R.sup.2, R.sup.4, R.sup.5, R.sup.6, R.sup.7,
R.sup.8 and R.sup.9 independently represent linear or branched
C.sub.1-C.sub.16 alkyl or C.sub.1-C.sub.18 alkoxyalkyl; or are
C.sub.3-C.sub.8 cycloalkyl, phenyl or benzyl which are
unsubstituted or substituted by C.sub.1-C.sub.6 alkyl,
C.sub.1-C.sub.6 alkoxy, halogen or OR.sup.3; or R.sup.1 and
R.sup.2, R.sup.4 and R.sup.5, R.sup.6 and R.sup.7 or R.sup.8 and
R.sup.9, taken together, are linear C.sub.1-C.sub.6 alkylene which
is unsubstituted or substituted by C.sub.1-C.sub.6 alkyl,
C.sub.1-C.sub.6 alkoxy, halogen, C.sub.3-C.sub.8 cycloalkyl,
phenyl, benzyl, C.sub.1-C.sub.4 alkylphenyl, C.sub.1-C.sub.4
alkoxyphenyl, halophenyl, C.sub.1-C.sub.4 alkylbenzyl,
C.sub.1-C.sub.4 alkoxybenzyl or halobenzyl, 5-, 6-, or 7-membered
heterocyclic structure containing two oxygen elements. R.sup.3
preferably represents hydrogen, linear or branched C.sub.1-C.sub.16
alkyl or C.sub.1-C.sub.18 alkoxyalkyl; or are C.sub.3-C.sub.8
cycloalkyl, phenyl or benzyl which are unsubstituted or substituted
by C.sub.1-C.sub.6 alkyl.
[0036] More preferably R.sup.1, R.sup.2, R.sup.4, R.sup.5, R.sup.6,
R.sup.7, R.sup.8 and R.sup.9, independently of one another,
represent --CH.sub.3, --CH.sub.2CH.sub.3; --OCH.sub.3;
--OCH.sub.2CH.sub.3 or most preferably R.sup.1 and R.sup.2, R.sup.4
and R.sup.5, R.sup.6 and R.sup.7 or R.sup.8 and R.sup.9 are taken
together to represent --CH.sub.2CH.sub.2-- wherein the hydrogen can
be replaced with a solubilizing group, a halide or an alkyl.
[0037] Terms and chemical formulas used herein to refer to alkyl or
aryl moieties refer to either the substituted or unsubstituted
unless specifically stated otherwise. A solvent is defined as a
single solvent or a mixture of solvents.
[0038] The synthesis of conjugated dimers and trimers is well known
in the literature. For example. The dimer of
3,4-ethylenedioxythiophene can be made through Ulmann coupling of
the monomers with alkyl lithium and cupric chloride [J. Kagan and
S. K. Arora, Heterocycles, 20 (1983) 1937].
[0039] Conjugated and non-conjugated dimers can be distinguished by
Fourier transform infrared (FT-IR) spectroscopy as illustrated in
FIG. 2, and by nuclear magnetic resonance (NMR) spectroscopy as
illustrated in FIG. 3. The presence of nonconjugated dimer in a
sample of EDT that was used in the manufacturing dip process of
making PEDT onto an anodized Ta surface is shown in FIG. 4. The
content of the conjugated as well as non-conjugated dimers in the
monomer can be measured by gas chromatograph (GC). Using
3,4-ethylenedioxythiophene (EDT) as an example, the peaks for the
monomer, non-conjugated dimer, and conjugated dimer are
distinguishable. It is observed over time that the non-conjugated
peak (dihydrothiophene) grows in intensity during usage.
[0040] A complete coverage of the anodized surface by intrinsically
conductive polymer is desired to prevent the graphite and other
conductive layers of anode materials from contacting the bare
surface of dielectric. When high leakage occurs on the dielectric
surface intrinsically conductive polymers would degrade, lose the
dopant induced delocalized charges and therefore become
non-conductive. Through this mechanism intrinsically conductive
polymers provide a self-healing protection similar to MnO.sub.2
based solid electrolytic capacitors where MnO.sub.2 would convert
into the non-conductive Mn.sub.2O.sub.3 at elevated
temperature.
[0041] The polymer coated capacitor anode bodies, coated with an
intrinsically conductive organic polymer cathode layer, may then be
processed into completed capacitors by coating the conductive
polymer cathode coatings with graphite paint, conductive paint
comprising conductive fillers such as silver particles, attachment
of electrode leads, etc. as is well known to those skilled in the
art. The device is incorporated into a substrate or device or it is
sealed in a housing to form a discrete mountable capacitor as known
in the art.
[0042] Other adjuvants, coatings, and related elements can be
incorporated into a capacitor, as known in the art, without
diverting from the present invention. Mentioned, as a non-limiting
summary include, protective layers, multiple capacitive levels,
terminals, leads, etc.
EXAMPLES
Group A--Controls
[0043] 150 uF 6V rated anodized tantalum anodes were dipped into a
solution of Fe (III) p-toluenesulfonate (oxidant), dried and
subsequently dipped into fresh 3,4-ethylenedioxythiophene (monomer)
to initiate the polymerization reaction. Polymerization formed a
thin layer of conductive polymer (PEDT) on the dielectric surface
of the anodes. They were then washed to remove excess monomer and
by-products of the reactions. The anodes were then reformed by
subjecting to a DC voltage in a diluted phosphoric acid solution to
repair any damage to the dielectric and therefore, reducing the DC
leakage. This dipping-reforming process cycle was repeated until a
thick polymer layer was formed. Scanning electron microscope (SEM)
pictures were taken of the anode surface covered with conductive
polymer and are shown in FIG. 4.
[0044] Carbon and silver coatings were applied onto the anodes by
conventional process which is known to those skilled in the art.
The parts were then assembled onto leadframes and molded with epoxy
based encapsulant. The ESR of the capacitors was measured at 100
KHz. Leakage current under a DC bias was also measured. The number
of parts showing short was recorded. The results are listed in
Table 1.
Group B--Non-Conjugated Dimers as Additive
[0045] The same type of parts as in Group A were processed the same
as Group A with one difference. The fresh monomer used in Group A
was replaced with a monomer solution after a large number of dips.
It contained 2.3% non-conjugated dimer of EDT as measured by GC.
SEM picture of the anode surface covered by conductive polymer is
shown in FIG. 5. The ESR and the number of shorts shown after
molding are listed in Table 1.
Group C--Conjugated Dimers as Additive
[0046] The same type of parts as in Group A were processed the same
as Group A with one difference. The fresh monomer used in Group A
was replaced with a polymer precursor solution containing 2.3%
conjugated dimer of EDT. The conjugated dimer was made according to
the procedure in the literature [J. Kagan and S. K. Arora,
Heterocycles, 20 (1983) 1937]. The polymer precursor solution was
made with the conjugated dimer and fresh monomer liquid. SEM
picture of the anode surface covered by conductive polymer is shown
in FIG. 5. The ESR and the number of shorts shown after molding are
listed in Table 1.
[0047] The data in Table 1 clearly showed that the addition of
conjugated dimer into the monomer improved the polymer growth rate
and the polymer coverage of the dielectric surface of the anodes
while maintaining a low ESR. The improved coverage in turn helped
to reduce the number of shorts.
TABLE-US-00001 TABLE 1 ESR Values and Number of Shorts from Control
(Group A), Non-conjugated Dimer Solution in Monomer (Group B) and
Conjugated Dimer Solution in Monomer (Group C) ESR (m.OMEGA.)
Number of Shorts Group A (fresh monomer) 31.4 22 Group B (2.3%
non-conjugated dimer) 42.7 14 Group C (2.3% conjugated dimer) 32.2
3 *Total number of parts for each group was 333.
[0048] This invention has been described with particular reference
to the preferred embodiments without limit thereto. Additional
embodiments, alterations and improvements could be envisioned
without departure from the meets and bounds of the invention as
more specifically set forth in the claims appended hereto.
* * * * *