U.S. patent application number 11/607374 was filed with the patent office on 2007-06-28 for solid electrolytic capacitor element, solid electrolytic capacitor, and manufacturing method therefor.
This patent application is currently assigned to SANYO Electric Co., Ltd.. Invention is credited to Takahisa Iida, Hiroshi Nonoue, Kazuhiro Takatani, Mutsumi Yano.
Application Number | 20070146970 11/607374 |
Document ID | / |
Family ID | 38193408 |
Filed Date | 2007-06-28 |
United States Patent
Application |
20070146970 |
Kind Code |
A1 |
Iida; Takahisa ; et
al. |
June 28, 2007 |
Solid electrolytic capacitor element, solid electrolytic capacitor,
and manufacturing method therefor
Abstract
The objective of the current invention is to provide a solid
electrolytic capacitor element with low equivalent series
resistance. In this solid electrolytic capacitor element, an anode
comprising a porous sintered body, and a dielectric layer are
sequentially formed on an anode lead so as to cover a portion of
the anode lead. An intermediate layer comprising polyethylene
glycol is formed on the dielectric layer so as to cover an area
around the dielectric layer. An electrolyte layer comprised of
polypyrrole is formed on the intermediate layer so as to cover an
area around the intermediate layer. A cathode comprised of: a first
electrically conductive layer mainly comprising graphite particles
and a second electrically conductive layer mainly comprising silver
particles is formed on the electrolyte layer so as to cover an area
surrounding the electrolyte layer.
Inventors: |
Iida; Takahisa; (Tottori,
JP) ; Yano; Mutsumi; (Osaka, JP) ; Takatani;
Kazuhiro; (Osaka, JP) ; Nonoue; Hiroshi;
(Osaka, JP) |
Correspondence
Address: |
MASUVALLEY & PARTNERS
8765 AERO DRIVE, SUITE 312
SAN DIEGO
CA
92123
US
|
Assignee: |
SANYO Electric Co., Ltd.
|
Family ID: |
38193408 |
Appl. No.: |
11/607374 |
Filed: |
December 1, 2006 |
Current U.S.
Class: |
361/523 |
Current CPC
Class: |
H01G 9/15 20130101; H01G
9/07 20130101; H01G 9/0036 20130101; H01G 9/042 20130101 |
Class at
Publication: |
361/523 |
International
Class: |
H01G 9/00 20060101
H01G009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2005 |
JP |
2005-379645 |
Claims
1. A solid electrolytic capacitor element comprising: an anode
using a valve metal or an alloy consisting mainly of a valve metal;
a dielectric layer formed by anodizing said anode; an electrolyte
layer including a conductive polymer, formed on said dielectric
layer; a cathode formed on said electrolyte layer; and an
intermediate layer including polyethylene glycol between said
dielectric layer and electrolyte layer.
2. The solid electrolytic capacitor element according to claim 1,
wherein a molecular weight of said polyethylene glycol is no less
than 400 and no more than 1200.
3. The solid electrolytic capacitor element according to claim 2,
wherein a molecular weight of said polyethylene glycol is no less
than 800 and no more than 1000.
4. The solid electrolytic capacitor element according to claim 1,
wherein a film thickness of said intermediate layer including
polyethylene glycol is from approximately 0.5 nm to approximately
20 nm.
5. A method of manufacturing a solid electrolytic capacitor
element, the method comprising the steps of: forming a dielectric
layer consisting mainly of an oxide of a valve metal or an alloy
consisting mainly of the valve metal by anodizing an anode using
the valve metal or an alloy consisting mainly of the valve metal;
coating a surface of said dielectric layer with a polyethylene
glycol layer by dipping said dielectric layer in a polyethylene
glycol solution; and forming an electrolyte layer including a
conductive polymer on a surface of said polyethylene glycol
layer.
6. The method for manufacturing the solid electrolytic capacitor
element according to claim 5, wherein a molecular weight of said
polyethylene glycol is no less than 400 and no more than 1200.
7. The method for manufacturing the solid electrolytic capacitor
element according to claim 6, wherein a molecular weight of said
polyethylene glycol is no less than 800 and no more than 1000.
8. The method for manufacturing the solid electrolytic capacitor
element according to claim 5, wherein a film thickness of said
polyethylene glycol layer is from approximately 0.5 nm to
approximately 20 nm.
9. The method for manufacturing the solid electrolytic capacitor
element according to claim 5, wherein said polyethylene glycol
solution is a solution of polyethylene glycol dissolved with any of
a water, an ethanol or an acetone.
10. A solid electrolytic capacitor comprising: an anode using a
valve metal or an alloy consisting mainly of the valve metal; a
dielectric layer formed by anodizing said anode; an electrolyte
layer including a conductive polymer, formed on said dielectric
layer; a cathode formed on said electrolyte layer; an intermediate
layer including a polyethylene glycol located between said
dielectric layer and said electrolyte layer; and wherein, an anode
terminal is formed on said anode, a cathode terminal is formed on
said cathode, and a mold resin is formed such that respective edges
of the anode terminal and the cathode terminal are located outside
the mold resin.
Description
TECHNICAL FIELD
[0001] The current invention relates to a solid electrolytic
capacitor element having an anode using a valve metal or an alloy
consisting mainly of valve metal, a dielectric layer formed by
anodizing the anode above, specifically, the current invention
relates to, a solid electrolytic capacitor element with low
equivalent series resistance (hereinafter referred as ESR), a solid
electrolytic capacitor, and manufacturing method therefor.
BACKGROUND OF INVENTION
[0002] Solid electrolytic capacitors have widely been used for
various electronic devices, specially in recent years, due to the
necessity for instantaneously supplying current to a signal process
circuit along with speed-up of signal process circuits of
electronic devices, such as personal computers A solid electrolytic
capacitor with lower ESR value at high-frequency area is desired.
However, due to high contact resistance between a solid electrolyte
layer and a dielectric layer, there is a problem of increasing
ESR.
[0003] To decrease this contact resistance, a solid electrolytic
capacitor element having an intermediate layer comprised of organic
silane between a solid electrolyte and a dielectric layer has been
developed. An example of such solid electrolytic capacitor element
is in Japanese published unexamined patent application No.
1993-234826. However, sufficient reduction of contact resistance
could not be reached even with such structure, and there has been a
limit in reducing ESR of a solid electrolytic capacitor
element.
[0004] The objective of the current invention is to reduce ESR of a
solid electrolytic capacitor element and to provide a manufacturing
method of a solid electrolytic capacitor element able to reduce
ESR.
BRIEF SUMMARY OF THE INVENTION
[0005] To solve such issues described above, the solid electrolytic
capacitor element relating to the current invention is a solid
electrolytic capacitor element comprising an anode using a valve
metal or an alloy consisting mainly of valve metal, a dielectric
layer formed by anodizing the anode, an electrolyte layer including
a conductive polymer formed on the dielectric layer, and a cathode
formed on the electrolyte layer, and characterized by an
intermediate layer including polyethylene glycol between the
dielectric layer and the electrolyte layer.
[0006] For example, tantalum, niobium, and titanium can be used as
a valve metal.
[0007] In the above embodiment, adhesiveness of the dielectric
layer and electrolyte layer including the conductive polymer can be
increased, and this can reduce the contact resistance between the
dielectric layer and the electrolyte layer, therefore the ESR of a
solid electrolytic capacitor element can be reduced. It is thought
that the reason the adhesiveness can be increased is that the
polyethylene glycol forms chemical bonding, such as hydrogen
bonding, between the dielectric and the conductive polymer.
[0008] The molecular weight of the polyethylene glycol can be no
less than 400 and no more than 1200.
[0009] The molecular weight of the polyethylene glycol can
preferably be no less than 800 and no more than 1000.
[0010] The film thickness of the intermediate layer described above
including polyethylene glycol, can be from approximately 0.5 nm to
approximately 20 nm.
[0011] In this structure, adhesiveness of the dielectric layer and
the electrolyte layer comprising the conductive polymer can be
increased, and this allows further reduction of the contact
resistance between the dielectric layer and the electrolyte layer,
therefore the solid electrolytic capacitor element with lower ESR
can be provided.
[0012] A method of manufacturing the solid electrolytic capacitor
element of the current invention comprises a process for forming a
dielectric layer consisting mainly of an oxide of a valve metal or
an alloy consisting mainly of a valve metal by anodizing an anode
using a valve metal or an alloy consisting mainly of valve metal, a
process for coating the surface of the dielectric layer with a
polyethylene glycol layer by dipping the dielectric layer in a
polyethylene glycol solution and a process for forming an
electrolyte layer including a conductive polymer on the surface of
the polyethylene glycol layer.
[0013] By using such a manufacturing method, the polyethylene
glycol layer can be evenly formed on the surface of the dielectric
layer, which enables adherence of the dielectric layer and
electrolyte layer including the conductive polymer layer adequately
across the whole area of that adhesion face, so that the interface
of the dielectric layer and the electrolyte layer with low contact
resistance can be formed, therefore, the solid electrolytic
capacitor element able to reduce ESR can be provided.
[0014] The molecular weight of this polyethylene glycol can be
comprised to no less than 400 and no more than 1200.
[0015] Further, the molecular weight of the polyethylene glycol can
preferably be no less than 800 and no more than 1000.
[0016] Still further, the film thickness of above polyethylene
glycol layer can be from approximately 0.5 nm to approximately 20
nm.
[0017] The polyethylene glycol solution above can be characterized
by dissolving polyethylene glycol with any of water, ethanol or
acetone.
[0018] As for other aspects of the invention, there is a solid
electrolytic capacitor comprising an anode using a valve metal or
an alloy consisting mainly of a valve metal, a dielectric layer
formed by anodizing said anode, an electrolyte layer including
conductive polymer formed on said dielectric layer, a cathode
formed on said electrolyte layer, and an intermediate layer
including polyethylene glycol between the dielectric layer and the
electrolyte layer, wherein on the solid electric capacitor element,
an anode terminal is formed on said anode, a cathode terminal is
formed on said cathode, and a mold resin is formed such that
respective edges of the anode terminal and the cathode terminal are
located outside the mold resin.
[0019] In the solid electrolytic capacitor element and the solid
electrolytic capacitor of the current invention, adhesiveness of
the dielectric layer and the electrolyte layer including conductive
polymer can be increased, and this can reduces the contact
resistance between the dielectric layer and the electrolyte layer,
therefore the ESR of the solid electrolytic capacitor element can
be reduced.
[0020] Also, according to the manufacturing method for solid
electrolytic capacitor element of the current invention, the
polyethylene glycol layer can be evenly formed on the surface of
the dielectric layer, which improves the adhesiveness of the
dielectric layer and the electrolyte layer including the conductive
polymer layer across the whole area of that adhesion face, so that
the interface of the dielectric layer and the electrolyte layer
with low contact resistance can be formed, therefore, the solid
electrolytic capacitor element able to reduce ESR can be
provided.
BREIF DISCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a cross section view of a solid electrolytic
capacitor element for embodiment 1 of the current invention.
DETAIELD DISCRIPTION OF INVENTION
[0022] Embodiments of the current invention will hereinafter be
described in reference to the drawing.
Embodiment 1
[0023] FIG. 1 is a cross section view of a solid electrolytic
capacitor element of the current invention. A structure of the
solid electrolytic capacitor element as it relates to the
embodiment 1 of the current invention is hereinafter described.
[0024] First, as shown in FIG. 1, in the solid electrolytic
capacitor element in the embodiment 1 of the current invention, a
virtually plate-like anode 1 comprised of a tantalum porous
sintered body that is fabricated by sintering tantalum powder with
an average grain size of approximately 2 .mu.m, in vacuum, is
formed on an anode lead la comprised of tantalum so as to cover a
portion of the anode lead 1a. At this time, the tantalum is an
example of a "valve metal" and comprises the anode of the current
invention.
[0025] A dielectric layer 2 consisting mainly of a tantalum oxide
is formed on the anode 1, so as to cover an area surrounding the
anode 1.
[0026] An intermediate layer 3 comprised of polyethylene glycol
(hereinafter referred as PEG) having a film thickness
(approximately 5 nm) is formed on the dielectric layer 2 so as to
virtually uniformly cover an area surrounding the dielectric layer
2
[0027] An electrolyte layer 4 comprised of polypyrrole is formed on
the intermediate layer 3 so as to cover an area surrounding the
intermediate layer 3.
[0028] A cathode 5 is formed on the electrolyte layer 4 so as to
cover an area surrounding the electrolyte layer 4. The cathode 5 is
comprised of: a first electrically conductive layer 5a consisting
mainly of graphite particles, which is formed so as to cover the
area surrounding the electrolyte layer 4; and a second electrically
conductive layer 5b consisting mainly of silver particles, which is
formed so as to cover an area surrounding the first electrically
conductive layer 5a
[0029] The top surface of an area surrounding the cathode 5 is
formed with an electrically conductive adhesive layer 6, through
which the cathode 5 and a cathode terminal 7 are interconnected.
The solid electrolytic capacitor element in the embodiment 1 of
current invention is thus formed. Also, an anode terminal 8 is
welded onto the anode lead la exposed from the anode 1. Further a
mold-packaging resin 9 is formed around the second electrically
conductive layer 5b, the cathode terminal 7 and an anode terminal 8
such that respective edges of the cathode and anode terminals 7 and
8 can be located outside the mold resin. The solid electrolytic
capacitor in embodiment 1 of the current invention is thus
configured.
[0030] Next, a manufacturing method of the solid electrolytic
capacitor element for embodiment 1 shown in FIG. 1 will be
described.
[0031] At first, a virtually plate-like anode 1 that is fabricated
by sintering tantalum powder with an average grain size of
approximately 2 .mu.m, in vacuum, is formed on an anode lead 1a
comprised of tantalum oxide so as to cover a portion of the anode
lead 1a.
[0032] Then, the anode 1 was anodized in an approximately 0.1 wt. %
phosphoric acid solution, which was held at approximately
60.degree. C., by applying a constant voltage of approximately 8 V
for approximately 10 hours. This allowed the dielectric layer 2
comprised of tantalum to be formed so as to cover the area
surrounding the anode 1.
[0033] Thereafter, by dipping the anode 1 formed with the
dielectric layer 2 into the aqueous solution containing PEG with
average molecular weight of 1000 and approximately 0.001 wt %,
uniformly deposited PEG onto the surface of the dielectric layer 2.
Then, dried the anode 1 at approximately 65.degree. C. for
approximately 10 minutes. An intermediate layer 3 comprised of PEG
with a film thickness of 5 nm was formed on the dielectric layer 2
so as to cover an area surrounding the dielectric layer 2.
[0034] Thereafter, an electrolyte layer 4 comprised of a
polypyrrole by chemical polymerization and so on is formed on the
intermediate layer 3.
[0035] Thereafter, the first electrically conductive layer 5a
consisting mainly of graphite particles was formed by coating a
graphite paste on the electrolyte layer 4 and then drying the paste
at approximately 80.degree. C. for approximately 30 minutes. Also,
the second electrically conductive layer 5b consisting mainly of
silver particles was formed by coating a silver paste on the first
electrically conductive layer 5a so as to cover the area
surrounding the first electrically conductive layer 5a and then
drying the paste at approximately 170.degree. C. for approximately
30 minutes. Thus, the cathode 5 wherein the first electrically
conductive layer 5a and the second electrically conductive layer 5b
were laminated was formed on the electrolyte layer 4 so as to cover
the area surrounding the intermediate layer 3.
[0036] And, after an electrically conductive adhesive had been
coated on the cathode terminal 7, the cathode 5 and the cathode
terminal 7 were brought into contact with each other through the
electrically conductive adhesive. The electrically conductive
adhesive layer 6 through which the cathode 5 and the cathode
terminal 7 were interconnected was formed by drying the
electrically conductive adhesive at approximately 60.degree. C. for
approximately 30 minutes while pressing it with the cathode 5 and
the cathode terminal 7. The solid electrolytic capacitor element in
embodiment 1 of the current invention was thus configured.
[0037] Subsequently, the anode terminal 8 was connected onto the
anode lead la by welding. Further, the mold-packaging resin 9 was
formed such that respective edges of the cathode terminal 7 and the
anode terminal 8 were able to be located outside the mold-packaging
resin 9. The solid electrolytic capacitor according to the
embodiment 1 of current invention was thus fabricated.
[0038] As other specimens relate to the embodiment 1, solid
electrolytic capacitor elements having similar structures to that
of above were fabricated respectively, except that instead of using
tantalum powder with average grain size of approximately 2 .mu.m as
a material of anode 1, using tantalum-niobium alloy powder with
average grain size of approximately 2 .mu.m, and niobium powder
with average grain size of approximately 2 .mu.m respectively, were
employed.
COMPARATIVE EXAMPLE 1
[0039] As a comparative example, a solid electrolytic capacitor
element which has a similar structure to that of above embodiment 1
was fabricated, except that there is no intermediate layer 3
between the dielectric layer 2 and the electrolyte layer 4.
COMPARATIVE EXAMPLE 2
[0040] As a comparative example 2, a solid electrolytic capacitor
element similar to a conventional solid electrolytic capacitor
element was fabricated. That is, the solid electrolytic capacitor
element similar to that of the embodiment 1 was fabricated, except
that instead of using the intermediate layer 3 comprising PEG, an
intermediate layer consisting mainly of organic silane which
comprises octadecyltriethoxysilane (hereinafter referred as OTES),
was used.
[0041] In this comparative example, the intermediate layer
consisting mainly of an organic silane comprised of OTES is formed
as follows.
[0042] After dipping into a n-hexane solution containing 0.1 wt %
of OTES, the anode 1 which has the dialectic layer 2 formed was air
dried for 60 minutes at 125.degree. C. This allowed an intermediate
layer having a film thickness of 1 nm comprising OTES to be formed
on the dielectric layer 2 so as to cover an area around the
dielectric layer 2.
[0043] ESR measurements were performed at a frequency of 100 kHz on
the solid electrolytic capacitor elements fabricated in the cases
of embodiment 1, 2, 3, and Comparative Example 1 and 2. The ESR
measurements were performed using an LCR meter by applying voltage
between the cathode terminal 7 and the anode terminal 8. The
measurement results are listed in Table 1. In addition, Table 1
lists values determined by normalizing the measurement results in
Embodiment 1 and 2 and using the measurement result in Comparative
Example 1 as a reference value of 100.
TABLE-US-00001 TABLE 1 Material of Material of Anode Intermediate
layer ESR Embodiment 1 Tantalum PEG 86 Tantalum--Niobium PEG 85
Alloy Niobium PEG 87 Comparative Example 1 Tantalum None 100
Comparative Example 2 Tantalum OTES 98
[0044] As listed in table 1, it turned out that the solid
electrolytic capacitor element of embodiment 1 has decreased ESR
lower than that of the solid electrolytic capacitor elements of
comparative example 1 and 2. It is thought that the reason for
decrease in ESR even with relatively high resistivity of PEG of
approximately 10.sup.4 .OMEGA.cm is because adhesiveness between
the dielectric layer 2 and the electrolyte layer 4 was able to
improve by virtually uniformly forming the intermediate layer 3
comprised of PEG having a small film thickness between the
electrolyte layer 4 and the cathode 5.
Embodiment 2
[0045] In this embodiment 2, a solid electrolytic capacitor element
having a similar structure to that of the embodiment 1 was
fabricated, except that instead of the intermediate layer 3
comprised of PEG with average molecular weight 1000 in embodiment 1
above using tantalum as an anode material, forming a intermediate
layer 3 comprised of PEG with different molecular weights
(molecular weights 100, 400, 800, 1200, 1500, 2000, 4000).
[0046] In this embodiment, solid electrolytic capacitor elements
having a intermediate layer 3 comprised of PEG having a film
thickness of between approximately 0.5 nm and approximately 20 nm
in-between the dielectric layer 2 and the electrolyte layer 4 were
fabricated respectively in the manner similar to that of embodiment
1, except that instead of using the aqueous solution containing PEG
with a molecular weight of 1000 and approximately 0.001 wt % used
in the embodiment 1, aqueous solutions containing PEG with
molecular weights of 100, 400, 800, 1200, 1500, 2000, 4000, and
approximately 0.001 wt % respectively, were used.
[0047] As for the solid electrolytic capacitor elements fabricated
for the embodiment 2, ESR measurements at frequency of 100 kHz were
also performed using an LCR meter by applying voltage between the
cathode terminal 7 and the anode terminal 8. The measurement
results for the embodiment 1 above along with in case of
comparative example 1 and 2 are listed in Table 2. In addition,
Table 2 lists values determined by using the measurement result in
comparative example 1 as a reference value of 100 and normalizing
the measurement results in Embodiment 1, 2 and comparative example
2. Also, the anode materials for embodiment 1, 2, and comparative
example 1, 2 are tantalum.
TABLE-US-00002 TABLE 2 Intermediate Layer Average Molecular
Material Weight ESR Embodiment 2 PEG 100 96 PEG 400 90 PEG 800 88
PEG 1200 90 PEG 1500 95 PEG 2000 95 PEG 4000 96 Embodiment 1 PEG
1000 86 Comparative Example 1 None -- 100 Comparative Example 2
OTES -- 98
[0048] As listed in table 2, it turned out that when the average
molecular weight of PEG in the intermediate layer 3 is from 100 to
4000, the solid electrolytic capacitor element of embodiment 2 can
reduce ESR lower than that of the solid electrolytic capacitor
element of comparative example 1 not having an intermediate layer
and comparative example 2 having the intermediate layer comprised
of OTES. Further, when PEG with a molecular weight no less than 400
and no greater than 1200, a reduction in ESR grater than 10% has
been found.
[0049] In the embodiments 1 and 2, PEG can be virtually uniformly
deposited on the surface of dielectric layer 2 by dipping the
dielectric layer 2 into an aqueous solution containing PEG. Also,
the film thickness of the intermediate layer can be controlled by
repeatedly dipping into the above aqueous solution.
[0050] Also, the virtually plate-like anode 1 comprised of a porous
sintered body was used in Embodiments 1 and 2. Because this causes
a contact area between the dielectric layer 2 and the electrolyte
layer 4 to be increased, and also micro-irregularities are formed
on the surface of the dielectric layer 2, the adhesiveness between
the dielectric layer 2 and the electrolyte layer 4 is improved. As
a result, the ESR can be further reduced.
[0051] Further, the anode 1 comprised of tantalum that is a valve
metal is used in embodiments 1 and 2. For this reason, anodizing
the anode 1 enables a dielectric layer consisting mainly of
tantalum oxide to be readily obtained.
[0052] In addition, all of the examples disclosed herein are for
illustrative purposes in all aspects, and should not be considered
limiting. The scope of the current invention is defined not by the
description of the above-described examples but by the appended
claims, and includes all equivalents and variations that fall
within the scope of the claims.
[0053] Further, in the above-described embodiment, the intermediate
layer 3 was formed by dipping the dielectric layer 2 into an
aqueous solution containing PEG; however, the current invention is
not limited to this, and it may be formed by depositing PEG using a
method such as spraying the above aqueous solution onto the surface
of the dielectric layer 2.
[0054] Still further, in the above-described embodiment, the
electrolyte layer 4 was comprised of polypyrrole; however, the
current invention is not limited to this, and it may consist mainly
of other electrically conductive polymers.
[0055] Also, in the above-described embodiment, the first
electrically conductive layer 5a consisted mainly of graphite
particles; however, the current invention is not limited to this,
and it may contain carbon particles other than the graphite
particles.
[0056] Still further, in the above-described embodiment, the a node
1 was comprised of tantalum, tantalum-niobium alloy, or niobium
however, the current invention is not limited to this, and it may
consist mainly of another valve metal such as aluminum, titanium
or, alternatively, it may be an alloy consisting mainly of such a
valve metal.
[0057] Still further, in the above-described embodiment, the
phosphoric acid solution was used for anodizing the anode 1;
however, the current invention is not limited to this, an aqueous
solution containing fluorine such as ammonium fluoride solution,
potassium fluoride solution, sodium fluoride solution or
hydrofluoric acid solution or, alternatively, sulfuric acid may be
used.
[0058] Still further, in the above-described embodiment, the anode
1 was in the form of a virtual plate comprised of a porous sintered
body; however, the current invention is not limited to this, and it
may be comprised of a column-shape or a metal foil.
* * * * *