JPH0677093A - Solid-state electrolytic capacitor and manufacture thereof - Google Patents

Abstract

PURPOSE:To produce a solid-state electrolytic capacitor excellent in characteristics by a method wherein conductive high molecular material soluble in solvent is used as a pre-electrode layer and doped with dopant, and a conductive layer of polypyrrole or the like is made to grow making the doped high molecular material serve as seed. CONSTITUTION:The surface of a valve metal 1 is anodized to form an oxide film 2, polyaniline is applied thereon and dried up for the formation of a pre- electrode layer 3, and the electrode layer 3 is enhanced in conductivity by doping. Thereafter, a conductive high molecular material (polypyrrole, polythiophene) film 4 is formed on the pre-electrode layer 3 through electrolytic polymerization making the pre-electrode layer 3 serve as an anode, and the high molecular material film 4 is made to serve as a cathode of a capacitor. By this setup, a pre-electrode layer can be easily and surely obtained as compared with a conventional process. As the pre-electrode layer is low in resistance, a capacitor of this design can be enhanced in characteristics and performance and lessened in size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor and a method of manufacturing the same, and more particularly to a small-sized solid electrolytic capacitor capable of easily forming a conductive polymer layer corresponding to an electrolyte portion in a conventional electrolytic capacitor. The present invention relates to a large capacity solid electrolytic capacitor and a method for manufacturing the same. 2. Description of the Related Art In recent years, highly advanced highly integrated devices represented by large scale integrated circuits (VLSI) have been realized due to remarkable progress in microelectronics, especially semiconductor element manufacturing technology. By adopting this in the control system of various devices, electronic devices have achieved dramatic miniaturization, and contributed greatly not only to various industries but also to miniaturization and multifunctionality of home appliances in general households. There is.

However, in an actual electronic circuit, not only semiconductor elements but also various passive elements, that is, resistors, capacitors, inductors and the like are indispensable.
Therefore, in order to reduce the size of the entire electronic circuit, not only the semiconductor device but also the elements of the peripheral circuits are required to be downsized. In particular, for capacitors, elements with a relatively large capacitance of several microfarads or more are required for switching regulators, transmission circuits, filter circuits in the video frequency band, etc. Becomes

A capacitor capable of realizing a relatively large capacity of several microfarads or more is a type of capacitor called an electrolytic capacitor. This is an extremely thin oxide layer with high insulating property formed by anodic oxidation etc. on the surface of valve metal (that is, metal such as aluminum, tantalum, titanium, etc. which electrochemically forms a passive film on the surface). Therefore, the valve metal is made to have a substantial surface area several times as large as the apparent surface area by etching or powder sintering.
The capacitance C per unit area of the capacitor is C = ε ₀ ε _r S / d ……………… (1) where ε _{0 is} the dielectric constant in vacuum, ε _r is the relative dielectric constant of the dielectric S: real electrode area, d: given by the thickness of the dielectric, d is small hundreds Å, if S is as large as several cm ^2, electrolytic capacitors large capacity of several to several hundred microfarads at a few cm ³ Can be realized. In order to increase the substantial surface area S, a conventional electrolytic capacitor uses an electrolyte solution in which an electrolyte such as ammonium chloride is dissolved in a mixed solvent of water and an organic solvent as a conductive layer of a cathode. However, in the electrolyte solution, the carrier responsible for its conductivity is ions, and its mass gives a long dielectric relaxation time, so when viewed as a capacitor, the frequency characteristics at high frequencies are not good, especially the equivalent series resistance. There is a problem that the (ESR) cannot be lowered sufficiently. In addition, since the electrolyte is basically a liquid, its vapor pressure rises at high temperatures, and the electrolyte solution gradually evaporates (drys up) during a long use time, so it is suitable for use at high temperatures. There is also a problem that it cannot withstand, or has a limited life even at room temperature.

From these backgrounds, ESR in a high frequency band
The solidification of the electrolyte portion is required in order to achieve a substantial miniaturization by lowering the temperature and extend the life at high temperature, which is a weak point of the conventional electrolytic capacitor.

[0005]

2. Description of the Related Art In conventional solid electrolytic capacitors,
As the cathode layer, a solid electrolyte made of a metal oxide such as manganese dioxide was used. However, the cathode layer made of a metal oxide has a relatively low electrical conductivity (10 ⁻⁶ to 10 ^−3).
S / cm), it is difficult to reduce the ESR in the high frequency band. Therefore, it is known that it is effective to use an organic conductive material having a relatively high conductivity of about several S / cm as the cathode layer. As the organic conductive material, a charge transfer complex material such as an alkylquinolinium-tetracyanoquinodimethane (TCNQ) complex can be used. However, since the organic charge transfer complex generally has a low melting point, it has low soldering resistance, and it is difficult to form a so-called chip component effective for downsizing the device. Also in terms of manufacturing, since it is formed as a cathode layer of the element by melt impregnation, a part of the complex is decomposed in the melting step to form a high resistance layer portion, and it is difficult to reduce ESR.

Therefore, attempts have been made to apply a conductive polymer material having high heat resistance as the organic conductive material.
For example, it is known that a stable capacitor having high heat resistance can be obtained by forming a stable conductive polymer substance such as polypyrrole or polythiophene on an oxide layer of a valve metal such as tantalum or aluminum.

Since polypyrrole, polythiophene and the like need to use an electrolytic polymerization method to form a highly conductive film, a thin oxide layer is grown on a valve metal such as aluminum or tantalum by an anodic oxidation method. rear,
First, a thin conductive layer (preliminary electrode layer) is formed on the surface by manganese dioxide or chemical polymerization, and the conductive polymer layer described above is allowed to grow by the electrolytic polymerization method starting from this.

This manganese dioxide layer is formed by infiltrating an anodized valve metal (element) into an aqueous solution of manganese nitrate, and then 200
It is formed by firing at ~ 300 ° C. For the preliminary electrode layer formed by the chemical polymerization method, the element is repeatedly immersed in a solution of an oxidizing agent and a solution of a film forming material (including pyrrole and thiophene as monomers) to oxidatively polymerize polypyrrole and polythiophene. ing.

[0009]

However, when the above manganese dioxide layer is used as a preliminary electrode layer for electropolymerization of a conductive polymer film, manganese dioxide has a relatively high specific resistance of about 10 kΩcm. It has been difficult to reduce the ESR in the high frequency region, and it has been difficult to reduce the effective volume when used in the high frequency band. In addition, the heat applied during the formation of the manganese dioxide layer is liable to cause defects in the oxide layer of the valve metal, which is required to be electrically dense, due to thermal strain, which leads to a decrease in capacity and an increase in leakage current. However, there is a problem that an undesirable phenomenon may occur due to the characteristics of the electrolytic capacitor.

Further, when chemical polymerization is used in the preliminary electrode layer forming step, the number of time-consuming steps of repeated dipping in the oxidant solution and the film-forming substance solution increases, and improvement in productivity cannot be expected. As a result, there is a problem that it becomes a major obstacle in reducing the manufacturing cost. Furthermore, by immersing a valve metal element on which an oxide film of high quality is formed in a highly chemically reactive oxidant solution, the oxide film responsible for the capacitor characteristics deteriorates, and the capacitor characteristics of the product, such as leakage, are reduced. Current characteristics and loss tangent (ta
There was also a problem that nδ) and the like deteriorate.

Therefore, according to the present invention, a low ESR preliminary electrode layer is formed on a valve metal oxide layer by a simple process without using the above-mentioned materials such as manganese dioxide and a chemically polymerized film, and a high quality is obtained. The purpose is to obtain the solid electrolytic capacitor of.

[0012]

In order to achieve the above-mentioned object, the inventors of the present invention have made extensive studies as to the material of the preliminary electrode layer and a so-called doping method for imparting high conductivity to the preliminary electrode layer. , A conductive polymer material soluble in a solvent is used for the preliminary electrode layer, and by doping this with a dopant, a preliminary electrode layer having a high conductivity can be formed. It has been found that by growing a conductive layer having a high conductivity, a solid electrolytic capacitor having good characteristics can be manufactured, and in the manufacturing process thereof, it has good manufacturability. Particularly, in the present invention, polyaniline is used as such a solvent-soluble conductive polymer material.

Polyaniline is a polymer obtained by oxidatively polymerizing aniline under specific oxidizing conditions, and is soluble in a general-purpose solvent (for example, N-methyl-2-pyrrolidone, dimethylformamide, pyridine, dimethylsulfoxide, etc.). . Although the molecular structure of polyaniline is not clear, it is presumed to be as follows.

[0014]

[Chemical 1]

The polyaniline used has a molecular weight of 30,000 to 10
10,000 (weight average molecular weight), and the ratio of m to n is m: n = 1:
It is preferably 1 to 2: 1. Since polyaniline is soluble in a solvent, it is possible to form a polyaniline layer on the surface of an element (oxide) simply by adjusting a polyaniline solution, applying the solution on the surface of the element (oxide), and drying. The concentration of the polyaniline solution is preferably about 2-5%. The coating method is not limited and may be dipping. Drying can be performed at a low temperature of 200 ° C. or lower.

The polyaniline layer thus formed can be used as it is as a preliminary electrode layer, but it is preferable to dope it with a dopant in order to further enhance the conductivity. As the dopant, aromatic sulfonic acid, aliphatic sulfonic acid, polymeric acid having a sulfonic acid group in the side chain, phosphoric acid and the like are suitable. Aromatic sulfonic acids include benzenesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid, alkylnaphthalenesulfonic acid, n-alkylbenzenesulfonic acid such as styrenesulfonic acid, dodecylbenzenesulfonic acid, and the like, and vinyl as an aliphatic sulfonic acid. Alkyl sulfonic acids such as sulfonic acid, methacryl sulfonic acid and dodecyl sulfonic acid, trifluoromethane sulfonic acid and the like, and polystyrene sulfonic acid and the like can be mentioned as the polymeric acid having a sulfonic acid group in the side chain.

As the doping method, the polyaniline layer may be dipped in a solution containing a dopant, and diffusion from the liquid phase into the film may be used. Further, a method of simultaneously dissolving the dopant in the polyaniline solution at the time of forming the polyaniline layer can also be adopted. The preliminary electrode layer for electrolytic polymerization of the conductive polymer layer has a specific resistance of 1 × 10 ³ to 1
It is desired to be 0 ⁴ Ωcm or less, and further 1 × 10 ² Ωcm or less. The film thickness is preferably in the range of 500Å to 10000Å, more preferably 1000Å to 5000Å. If the film thickness of the preliminary electrode layer is insufficient, the resistance value increases and it cannot be used as an electrode for electrolytic polymerization. On the other hand, if the film thickness increases, the ESR of the solid electrolytic capacitor increases, which is not desirable.

Next, the structure of the solid electrolytic capacitor of the present invention will be described. Referring to FIG. 1, 1 is a valve metal, 2
Is a valve metal oxide layer (anodic oxide film), 3 is a preliminary electrode layer made of a soluble conductive material (polyaniline), 4 is a cathode conductive layer (conductive polymer substance), 5 is a carbon conductive layer, and 6 is a silver paste layer. , 7 is a cathode extraction lead, and 8 is a molding resin.

As the valve metal 1, a metal such as aluminum, tantalum, titanium, zirconium, vanadium, niobium, indium, or tungsten which has a current rectifying action between the metal oxide layer and the solution layer is used. The soluble polymer material 3 is doped with a dopant in the polyaniline layer.

The cathode conductive layer 4 is a conductive polymer layer having a high conductivity, which is formed by an electrolytic polymerization method on a preliminary electrode layer made of the above-mentioned soluble polymer material (polypyrrole, polythiophene, etc.). Acts as the cathode electrode of a conventional capacitor. The carbon conductive layer 5 and the silver paste layer 6 are formed to make good contact with the cathode electrode layer 4 when the wiring by the cathode lead 7 is drawn.

The steps for manufacturing the solid electrolytic capacitor having this structure will be described below. First, after bonding the lead to the sintered body of the valve metal, the sintered body is immersed in an electrolytic solution and constant current electrolysis is performed with the side of the sintered body of the valve metal as an anode to form an oxide layer on the metal surface. Next, the valve metal sintered body is immersed in the solution of the soluble conductive material 3 and the solvent is dried to form a preliminary electrode layer on the oxide surface. The soluble conductive material to be the preliminary electrode layer is doped with a dopant to improve conductivity. As described above, the doping can be performed by forming a layer of the soluble conductive material and then immersing it in a solution containing a dopant.

After forming the preliminary electrode layer 3, a solution of an electropolymerized material of a conductive polymer substance (pyrrole as a monomer, thiophene, etc.) is used as an electrolytic solution, and the element having the preliminary electrode layer is immersed in the electrolytic solution to prepare a preliminary electrode layer. The electrode layer is used as an anode for electrolysis, and a platinum plate, a copper plate, a stainless plate, a carbon rod or the like is used as a cathode, and electrolytic polymerization is performed to form the conductive polymer substance film 4 on the surface of the preliminary electrode. Colloidal graphite and silver paste are sequentially applied to the surface of the conductive polymer substance 4 to form a cathode, and at the same time, a cathode lead is attached.

[0023]

In the present invention, as described above, a soluble conductive material soluble in an organic solvent is used as a preliminary electrode layer when forming a cathode conductive layer on the thin oxide layer formed on the valve metal surface. I am using some polyaniline. The formation of the preliminary electrode layer of the soluble conductive material is completed simply by immersing it in the solution and drying it. Therefore, it is easier and more efficient than the conventional method of forming a conductive thin film by the chemical polymerization method. Good nature. Further, in the chemical polymerization method, a strong oxidizing agent such as sulfuric acid may adversely affect the oxide layer, but in the present invention, since such a strong reagent is not used, the product is stable. Can be manufactured.

Further, since the drying at the time of forming the preliminary electrode layer can be performed at a relatively low temperature of usually 200 ° C. or lower, compared with the method of forming the preliminary electrode layer using manganese dioxide or the like, the dielectric film formed of the oxide layer can be formed. It does not cause defects and does not impair the characteristics of the capacitor. Therefore, it is possible to further simplify the process and provide a product with excellent characteristics, as compared with the conventional method.

[0025]

EXAMPLES Examples according to the present invention are shown below. Example 1 A tantalum sintered body (substantial area 10 cm ² ) was anodized at 41 V in a 0.05% phosphoric acid electrolyte solution to obtain a capacitor element. This capacitor element was immersed once in a 5% N-methyl-2-pyrrolidone solution of polyaniline represented by Structural Formula 1 and dried at 80 ° C. for 30 minutes under reduced pressure.

Next, p-toluenesulfonic acid (pTS)
Or naphthalenesulfonic acid (NS) or alkylnaphthalenesulfonic acid (ANS) or benzenesulfonic acid (BS) or n-alkylbenzenesulfonic acid (n
This element was immersed in a 1% aqueous solution of ABS) or styrene sulfonic acid (SS) for 10 minutes for doping treatment, and then dried at 150 ° C.

In order to form a cathode conductive layer on this, electrolytic polymerization was carried out under the following conditions. Electrolyte solution is 0.06 mol /
It is an aqueous solution of 1-pyrrole and an equimolar dopant, sodium p-toluenesulfonate. In this solution, 1
A constant current electrolysis was performed for 1 hour by applying a current of 0.4 mA per device. After forming the cathode conductive layer, a carbon paste and a silver paste were applied and dried at 120 ° C. for 20 minutes, and the whole was epoxy-molded to complete a device.

The characteristic of this capacitor element is the capacitance, t
An δ and ESR were measured. These characteristics were measured by the following methods in all of the following examples and comparative examples. In addition, Hewlett Packard impedance analyzer H
With P6194A, the capacity while sweeping the frequency,
Each parameter of tan δ and ESR was sequentially measured. The results are shown in Table 1. Example 2 A tantalum sintered body (substantial area 10 cm ² ) was anodized in 0.05% phosphoric acid electrolyte at 41 V to obtain a capacitor element. This capacitor element was immersed once in a 5% N-methyl-2-pyrrolidone solution of polyaniline represented by Structural Formula 1 and dried at 80 ° C. for 30 minutes under reduced pressure.

Next, this element was immersed in a 1% aqueous solution of vinyl sulfonic acid (VS), methacryl sulfonic acid (MS), dodecyl sulfonic acid (DDS), or trifluorosulfonic acid for 10 minutes for doping treatment. Then, it was dried at 150 ° C. In order to form a cathode conductive layer on this, electrolytic polymerization was performed under the following conditions. The electrolyte is
0.06 mol / l Pyrrole and equimolar dopant, p-
An aqueous solution of sodium toluene sulfonate.
In this solution, a constant current electrolysis was performed for 1 hour by applying a current of 0.4 mA per device.

After forming the cathode conductive layer, carbon paste and silver paste were applied and dried at 120 ° C. for 20 minutes, and the whole was epoxy-molded to complete the device. The characteristics of the obtained capacitor element were measured, and the results are shown in Table 1. Example 3 A tantalum sintered body (substantial area 10 cm ² ) was subjected to anodization treatment at 41 V in a 0.05% phosphoric acid electrolytic solution to obtain a capacitor element. This capacitor element was immersed once in a 5% N-methyl-2-pyrrolidone solution of polyaniline represented by Structural Formula 1 and dried at 80 ° C. for 30 minutes under reduced pressure.

Next, this element was immersed in a 1% aqueous solution of polyvinyl sulfonic acid (PVS), polystyrene sulfonic acid (PSS), or polyphosphoric acid (PPA) for 10 minutes for doping treatment, and then dried at 150 ° C. did.
In order to form a cathode conductive layer on this, electrolytic polymerization was performed under the following conditions. The electrolytic solution is an aqueous solution containing 0.06 mol / l of pyrrole and an equimolar dopant of sodium p-toluenesulfonate. In this solution, a constant current electrolysis was performed for 1 hour by applying a current of 0.4 mA per device.

After forming the cathode conductive layer, carbon paste and silver paste were applied and dried at 120 ° C. for 20 minutes, and the whole was epoxy-molded to complete the device. The results of measuring the characteristics of this capacitor element are shown in Table 1. [Comparative Example 1] A tantalum sintered body element similar to the element used in Example 1 was dipped in a 30% aqueous solution of manganese nitrate and then dried at 290 ° C for 20 minutes to form a preliminary electrode layer of manganese dioxide. .

Next, using an acetonitrile solution containing 0.06 mol / l pyrrole and an equimolar dopant, tetraethylammonium p-toluenesulfonate as an electrolytic solution, a current of 0.5 mA was applied to each element and a constant current was applied for 1 hour. Electrolysis was performed. After forming the cathode conductive layer, a carbon paste and a silver paste are applied and dried at 120 ° C. for 20 minutes,
The whole was epoxy-molded to complete the device.

The results of measuring the characteristics of this capacitor element are shown in Table 1. Comparative Example 2 The same tantalum sintered body element as that used in Example 1 was subjected to oxidative polymerization of pyrrole by the following method to form a preliminary electrode layer. First, 2% sulfuric acid and 2%
After immersing the element in an oxidizing agent aqueous solution containing hydrogen peroxide, it is immediately immersed in a 0.1 mol / l acetonitrile solution of pyrrole. After drying at 100 ° C. for 30 minutes, it is immersed again in the oxidant solution and the pyrrole solution, and this is repeated 4 times in total.

After that, an acetonitrile solution containing 0.06 mol / l pyrrole and equimolar dopant and tetraethylammonium p-toluenesulfonate was used as an electrolytic solution, and a current of 0.5 mA was applied to each element for a constant current for 1 hour. Electrolysis was performed. After forming the cathode conductive layer, a carbon paste and a silver paste are applied and dried at 120 ° C. for 20 minutes,
The whole was epoxy-molded to complete the device.

The results of measuring the characteristics of this capacitor element are shown in Table 1.

[0037]

[Table 1]

As is apparent from this table, the frequency 120
The capacitance C at Hz is 4.5 to 4.6 μF in the solid electrolytic capacitors according to Comparative Examples 1 and 2, whereas that of Example 1 is different.
3 to 4.1 are solid electrolytic capacitors 4.1 to 4.7 μF
And is substantially equivalent. Also, ta representing the degree of heat generation
nδ (loss tangent) is 2.0 to 3.5% for the solid electrolytic capacitors according to Comparative Examples 1 and 2, while Example 1 to
The solid electrolytic capacitor according to No. 3 decreased to 1.1 to 1.4%.

The ESR at a frequency of 1 MHz is 0.4 to 0.6 for the solid electrolytic capacitors according to Comparative Examples 1 and 2.
In contrast to Ω, the solid electrolytic capacitors according to Examples 1 to 3 have decreased to 0.1 to 0.3Ω. Further, the total process time required for manufacturing the solid electrolytic capacitor is 7 to 8 H (hours) in Comparative Examples 1 and 2, whereas it is shortened to 4 H in Examples 1 to 3.

[0040]

As described above, according to the present invention, in the production of a solid electrolytic capacitor, polyaniline, which is a conductive material soluble in a solvent, is used in the preparation of a preliminary electrode layer for forming the cathode conductive layer. By doing so, there is an effect that the preliminary electrode layer can be formed in a short time, and the preliminary electrode layer can be obtained more simply and surely as compared with the conventional method.
In addition, since the resistance of the preliminary electrode layer is low, good capacitor characteristics can be obtained, which greatly contributes to downsizing and high performance of the capacitor.

[Brief description of drawings]

FIG. 1 is a diagram showing a principle configuration of a solid electrolytic capacitor of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Valve metal 2 ... Valve metal oxide layer (anodic oxide film) 3 ... Soluble conductive material (polyaniline layer) 4 ... Cathode conductive layer 5 ... Carbon conductive layer 6 ... Silver paste layer 7 ... Cathode extraction lead 8 ... Mold resin

Claims (10)

[Claims] 1. An anode made of a valve metal, a dielectric layer formed on the surface of the anode, a preliminary electrode layer made of polyaniline formed on the surface of the dielectric layer, and a conductive high layer formed on the preliminary electrode layer. A solid electrolytic capacitor comprising a cathode composed of a molecular substance layer. 2. The solid electrolytic capacitor according to claim 1, wherein the preliminary electrode layer contains a dopant. 3. The solid electrolytic capacitor according to claim 2, wherein the dopant is an aromatic sulfonic acid or an aliphatic sulfonic acid, or a polymer acid having a sulfonic acid group in a side chain. 4. The solid electrolytic capacitor according to claim 3, wherein the aromatic sulfonic acid is benzenesulfonic acid, p-toluenesulfonic acid, naphthalenesulfonic acid, alkylnaphthalenesulfonic acid, styrenesulfonic acid, or n-alkylbenzenesulfonic acid. . 5. The solid electrolytic capacitor according to claim 3, wherein the aliphatic sulfonic acid is vinyl sulfonic acid, methacrylic sulfonic acid, dodecyl sulfonic acid or trifluorosulfonic acid. 6. The solid according to claim 1, wherein the conductive polymer substance of the cathode is polypyrrole, polythiophene, polyaniline, polyfuran or a side chain-substituted derivative thereof produced by electrolytic polymerization. Electrolytic capacitor. 7. A valve metal surface forming an anode of a capacitor is anodized to form an oxide layer, a polyaniline solution is applied to the surface of the anodized film and dried to form a polyaniline layer, and the polyaniline layer is used as an electrode. And a step of forming a conductive polymer substance layer by electrolytic polymerization as a method for producing a solid electrolytic capacitor. 8. The method according to claim 7, further comprising a step of immersing the polyaniline layer in a solution containing a dopant after the formation of the polyaniline layer so that the dopant is contained in the polyaniline layer. 9. The method according to claim 7, wherein the dopant is an aromatic sulfonic acid or an aliphatic sulfonic acid, or a polymeric acid having a sulfonic acid group in a side chain. 10. The method according to claim 7, wherein the conductive polymer substance is polypyrrole, polythiophene, polyaniline, polyfuran or a side chain-substituted derivative thereof produced by electrolytic polymerization.