Solid electrolytic capacitor

Details Solid electrolytic capacitor Solid electrolytic capacitor

2001-04-02

2002-10-08

Reichard, Dean A. (Department: 2831)

Electricity: electrical systems and devices

Electrolytic systems or devices

Solid electrolytic capacitor

C361S523000, C361S532000, C361S528000, C361S518000, C029S025030

Reexamination Certificate

active

06462936

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a solid electrolytic capacitor comprising a solid electrolytic layer of a conducting polymer formed on a dielectric film, and in particular, it relates to improvement of the solid electrolytic layer for the purpose of providing a solid electrolytic capacitor having large capacitance and exhibiting low impedance in a high frequency region.
BACKGROUND ART
In accordance with recent trend in reducing the size and weight of electronic equipment, there are increasing demands for a compact capacitor having large capacitance and exhibiting low impedance in a high frequency region.
Capacitors conventionally used in a high frequency region are a plastic capacitor, a mica capacitor and a laminated ceramic capacitor, all of which are large in size and have a capacitance difficult to increase.
As a capacitor having large capacitance, an electrolytic capacitor is well known. Examples of the electrolytic capacitor are an electrolytic capacitor using an electrolyte (such as an aluminum electrolytic capacitor) and a solid electrolytic
Recently, a conducting polymer prepared by doping a polymer, such as polypyrrole and polythiophene, which is obtained by electrolytically polymerizing a heterocyclic monomer such as pyrrole or thiophene, with BF
4
−
(borofluoride ions) or C10
4
−
(perchlorate ions) has been proposed as a solid electrolyte usable instead of manganese dioxide (Japanese Laid-Open Patent Publication No. 60-37114/1985).
The conducting polymer obtained by using the aforementioned halogen anions as a dopant, however, can easily degrade a dielectric film. In addition, the conducting property of the conducting polymer can be easily lowered because it is poor in thermal stability and can be easily undoped. The conducting polymer can be easily undoped particularly in fixing an electrode at a high temperature of approximately 200° C.
The degradation of the dielectric film and the lowering of the conducting property of the conducting polymer can increase a leakage current in a capacitor, resulting in reducing the capacitance and increasing the impedance.
A conducting polymer obtained by using aryl sulfonic acid ions such as dodecylbenzene sulfonic acid ions and naphthalene sulfonic acid ions, as a dopant has been proposed for overcoming the aforementioned disadvantages (Japanese Laid-Open Patent Publication No. 64-49211/1989).
The conducting polymer obtained by using aryl sulfonic acid ions as a dopant has still rather high electric resistance although the electric resistance is lower than that of the conducting polymer obtained by using BF
4
−
or C10
4
−
as a dopant. Therefore, even when this conducting polymer is used as a solid electrolyte, it is difficult to obtain a solid electrolytic capacitor exhibiting low impedance in a high frequency region.
The present invention was devised in view of these conventional disadvantages, and a main object of the invention is providing a solid electrolytic capacitor having large capacitance and exhibiting low impedance in a high frequency region.
DISCLOSURE OF THE INVENTION
A solid electrolytic capacitor of the invention (hereinafter referred to as a first capacitor) comprises an anode, a dielectric film formed on the anode by anodic oxidation, a solid electrolytic layer formed on the dielectric film made from a conducting polymer produced by doping a polymer including a heterocyclic monomer unit represented by the following general formula as a repeating unit with alkyl sulfonic acid ions and sulfuric acid ions, and a cathode connected with the solid electrolytic layer.
Another solid electrolytic capacitor of the invention (hereinafter referred to as a second capacitor) comprises an anode, a dielectric film formed on the anode by anodic oxidation, a solid electrolytic layer formed on the dielectric film made from a conducting polymer obtained by doping a polymer including a heterocyclic monomer unit represented by the following general formula as a repeating unit with alkyl sulfonic acid ions in a ratio of one of the alkyl sulfonic acid ions per 2 through 5 heterocyclic monomer units represented by the general formula, and a cathode connected with the solid electrolytic layer. In this specification, the first capacitor and the second capacitor may be generically referred to as the capacitors of the invention.
wherein R
1
and R
2
independently indicate an alkyl group or H, and X is S or NR
3
(wherein R
3
indicates an alkyl group or H).
The solid electrolytic layer is preferably formed by electrolytic polymerization using, as a solution for electrolytic polymerization, an aqueous solution including a heterocyclic monomer such as pyrrole or thiophene and an ionic dopant such as alkyl sulfonic acid ions, because the dopant can be uniformly doped in the polymer in this manner.
The conducting polymer used in the first capacitor is preferably doped in a ratio of one ion of the dopant per 2 through 5 heterocyclic monomer units each represented by the above-described formula. The molar ratio between sulfuric acid ions and alkyl sulfonic acid ions used for doping in electrolytic polymerization is not specified. It is, however, confirmed through experiments that the maximum molar ratio is 10:1. The sulfuric acid ions cannot be doped exceeding this molar ratio. ions such as dodecylbenzene sulfonic acid ions and naphthalene sulfonic acid ions, as a dopant has been proposed for overcoming the aforementioned disadvantages (Japanese Laid-Open Patent Publication No. 64-49211/1989).
The conducting polymer obtained by using aryl sulfonic acid ions as a dopant has still rather high electric resistance although the electric resistance is lower than that of the conducting polymer obtained by using BF
4
−
and C10
4
−
as a dopant. Therefore, even when this conducting polymer is used as a solid electrolyte, it is difficult to obtain a solid electrolytic capacitor exhibiting low impedance in a high frequency region.
The present invention was devised in view of these conventional disadvantages, and a main object of the invention is providing a solid electrolytic capacitor having large capacitance and exhibiting low impedance in a high frequency region.
DISCLOSURE OF THE INVENTION
A solid electrolytic capacitor of the invention (hereinafter referred to as a first capacitor) comprises an anode, a dielectric film formed on the anode by anodic oxidation, a solid electrolytic layer formed on the dielectric film made from a conducting polymer produced by doping a polymer including a heterocyclic monomer unit represented by the following general formula as a repeating unit with alkyl sulfonic acid ions and sulfuric acid ions, and a cathode connected with the solid electrolytic layer. Another solid electrolytic capacitor of the invention (hereinafter referred to as a second capacitor) comprises an anode, a dielectric film formed on the anode by anodic oxidation, a solid electrolytic layer formed on the dielectric film made from a conducting polymer obtained by doping a polymer including a heterocyclic monomer unit represented by the following general formula as a repeating unit with alkyl sulfonic acid ions, and a cathode connected with the solid electrolytic layer. In this specification, the first capacitor and the second capacitor may be generically referred to as the capacitors of the invention.
wherein R
1
and R
2
independently indicate an alkyl group or H, and X is S or NR
3
(wherein R
3
indicates an alkyl group or H).
The solid electrolytic layer is preferably formed by electrolytic polymerization using, as a solution for electrolytic polymerization, an aqueous solution including a heterocyclic monomer such as pyrrole or thiophene and an ionic dopant such as alkyl sulfonic acid ions, because the dopant can be uniformly doped in the polymer in this manner.
The conducting polymer is preferably doped in a ratio of one ion of the dopant per 2 through 5 heterocyclic monomer units each represented by the above-described formula. The molar ratio between sulfuric acid ions and alkyl sul

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