JP2001307961A - Solid electrolytic capacitor and manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor and its manufacturing method for reducing the size of the body and improving a capacity appearance ratio. SOLUTION: As a cathode foil, a TiN film is formed at an aluminum foil in a cathode arc plasma vapor deposition method. As an anode, aluminum foil is etched on its surface and treated with a conventional chemical formation step and thereby a dielectric film is formed on the surface. The anode foil is turned with the cathode foil and a separator to form a capacitor element. The capacitor element is impregnated with EDT monomer. The capacitor element is heated at 20 to 80 deg.C for 30 min or more after the capacitor element is impregnated with a butanol solution containing 40 to 60% ferric paratoluene sulfonate. The surface of the capacitor element is coated with resin and an aging step is carried out.

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 solid electrolytic capacitor improved in order to increase the rate of appearance of capacitance and to reduce the size of the capacitor. It relates to a manufacturing method.

[0002]

2. Description of the Related Art In an electrolytic capacitor using a metal having a valve action such as tantalum or aluminum, a valve action metal as an anode-side counter electrode is formed into a shape of a sintered body or an etching foil to expand a dielectric material. By using such a structure, it is possible to obtain a large capacity with a small size. In particular, a solid electrolytic capacitor using a solid electrolyte as an electrolyte has characteristics that it is small, large-capacity, low equivalent series resistance, easy to chip, and suitable for surface mounting. It is indispensable for miniaturization, high performance, and low cost of electronic devices.

In this type of solid electrolytic capacitor, for small size and large capacity applications, generally, an anode foil and a cathode foil made of valve metal such as aluminum are wound with a separator interposed therebetween to form a capacitor element. The capacitor element is impregnated with a driving electrolyte, and the capacitor element is housed in a metal case such as aluminum or a synthetic resin case, and has a sealed structure. Note that as the anode material, aluminum, tantalum, niobium, titanium, or the like is used, and as the cathode material, the same kind of metal as the anode material is used.

Incidentally, in order to increase the capacitance of an electrolytic capacitor, it is important to improve the capacitance of a cathode material together with the anode material. The capacitance of each electrode in an electrolytic capacitor depends on the type and thickness of the insulating film formed thin on the electrode surface, the surface area of the electrode, and the like. Assuming that t is t and the surface area of the electrode is A, the capacitance C is expressed by the following equation.

C = ε (A / t) As is apparent from this equation, in order to increase the capacitance, it is necessary to increase the electrode surface area, select an insulating film material having a high dielectric constant, and form a thin insulating film. Is effective. Of these,
It is not preferable to simply use a large electrode in order to increase the surface area of the electrode, because this simply causes an increase in the size of the electrolytic capacitor. Therefore, conventionally, the surface area of an aluminum foil, which is a base material of an electrode material, is subjected to an etching process to form irregularities, thereby substantially increasing the surface area.

[0006] Japanese Patent Application Laid-Open No. Sho 59-16709 discloses that
As a substitute for the above-mentioned etching treatment, a cathode material in which a metal film is formed on the surface of a base material by utilizing a metal deposition technique is disclosed. According to this technology,
It is said that by selecting the film forming conditions, fine irregularities can be formed on the film surface to increase the surface area and obtain a large capacitance. Further, if a metal such as Ti, which exhibits a high dielectric constant when converted to an oxide, is used as the metal film, the dielectric constant of the insulating film formed on the surface of the cathode material is increased to obtain a larger capacitance. It has been shown that it can.

Further, Japanese Patent Application Laid-Open No.
In -150825, the capacitance of the electrolytic capacitor is
Considering that the capacitance on the anode side and the capacitance on the cathode side are a combined capacitance connected in series, high-purity aluminum used for the cathode electrode was used to increase the capacitance value on the cathode side. A technique is disclosed in which a vapor deposition layer made of titanium nitride is formed on the surface by a cathodic arc vapor deposition method.

[0008]

However, the solid electrolytic capacitor using the cathode foil formed by the above-described conventional technique has the following problems. That is, conventionally, manganese dioxide formed mainly by thermal decomposition of manganese nitrate has been used for the solid electrolyte of a solid electrolytic capacitor, but in this manganese dioxide formation step, heat treatment at 200 to 300 ° C. is performed several times. Since it must be performed, an oxide film is formed on the surface of the metal nitride film formed on the surface of the cathode foil, thereby lowering the capacitance of the cathode foil and, consequently, the capacitance of the electrolytic capacitor. Was causing it.

The present invention has been proposed to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a solid electrolytic capacitor capable of improving the rate of appearance of capacitance and a method of manufacturing the same. Is to do.

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies on a solid electrolytic capacitor capable of improving the capacitance appearance rate and a method of manufacturing the same, and as a result, completed the present invention. It has been reached. In other words, in a wound solid electrolytic capacitor using a conductive polymer or lead dioxide as the electrolyte layer, forming a film made of a conductive material that is less oxidized on the surface of the cathode foil greatly increases the capacitance appearance rate. It has been found that it can be improved.

First, the present inventor has proposed a wound solid electrolytic capacitor using a conductive polymer having high conductivity and good adhesion to a dielectric film, which has recently attracted attention as an electrolyte layer. Various studies were conducted. Representative examples of the conductive polymer include polyethylene dioxythiophene (hereinafter referred to as PEDT), polypyrrole, polyaniline, TCNQ (7,7,8,8-tetracyanoquinodimethane), and dielectrics thereof. It has been known. Further, various studies were also conducted on a wound solid electrolytic capacitor using lead dioxide, which is known as an inorganic conductive compound.

Further, the present inventor has proposed that a TiN
Was formed by vapor deposition, and a capacitor was prepared using the cathode foil under the conditions described later. When the capacity of the cathode foil alone was measured, the capacity was infinite. That is, it was found that the TiN and the cathode foil metal were conducting. By the way, it is expressed by the following equation that the capacitance C of the electrolytic capacitor is a combined capacitance in which the capacitance Ca on the anode side and the capacitance Cc on the cathode side are connected in series.

(Equation 1) As is clear from the above equation, as long as Cc has a value (the cathode foil has a capacitance), the capacitance C of the capacitor is smaller than the capacitance Ca on the anode side. In other words, when TiN deposited on the surface of the cathode foil and the cathode foil metal become conductive and the capacitance Cc of the cathode foil becomes infinite as in the present invention, the capacitance component of the cathode foil disappears and the anode foil loses its capacity. The capacitance C of the capacitor, which is the combined capacitance of the cathode foils connected in series, is the capacitance Ca on the anode side.
Is equal to the maximum. This means that a conductive material that hardly oxidizes like TiN contributes to improving the performance of the capacitor.

[0013] As such a conductive material which is less likely to be oxidized, it is difficult to form an oxide film on the surface.
Metal nitrides such as N, ZrN, TaN, and NbN can be used. Further, the film formed on the surface of the cathode is not limited to the metal nitride, but may be another material as long as it is a conductive material that can form the film and is less likely to be oxidized. For example, Ti, Zr, Ta, Nb, etc. can be used.

As a method of forming a film made of a conductive material that is less likely to be oxidized on a cathode made of a valve metal, consideration is given to the strength of the formed film, adhesion to the cathode, control of film forming conditions, and the like. Then, a vapor deposition method is preferable, and among them,
Cathodic arc plasma deposition is more preferred. The application conditions of this cathodic arc plasma deposition method are as follows. That is, the current value is 80 to 300 A, and the voltage value is 15 to 20.
V. In the case of metal nitride, the cathode made of valve metal is heated to 200 to 450 ° C., and the total pressure including nitrogen is 1
It is performed in an atmosphere of × 10 ^-1 to 1 × 10 ^-4 Torr.

[0015] As described above, as the conductive polymer, PEDT, polypyrrole, polyaniline, TCNQ, or a dielectric material thereof which does not require high-temperature treatment can be used. In the case of a round capacitor, it is desirable to use PEDT which is easy to control the temperature in the manufacturing process of the capacitor and has excellent heat resistance.

Next, a method of manufacturing a wound solid electrolytic capacitor using a conductive polymer as the electrolyte layer will be described. That is, as the cathode foil, a foil obtained by forming a TiN film on a etched aluminum foil by a cathode arc plasma deposition method is used. The conditions of the cathodic arc plasma deposition method are as follows: using a Ti target in a nitrogen atmosphere, heating the cathode made of valve metal to 200 to 450 ° C.
The total pressure including nitrogen is 1 × 10 ^-1 to 1 × 10 ^-4 Torr, 8
It is performed at 0 to 300 A and 15 to 20 V. Further, as the anode foil, a foil obtained by subjecting a surface of an etched aluminum foil to a chemical conversion treatment by a conventionally used method to form a dielectric film is used. This anode foil is wound together with a cathode foil and a separator to form a capacitor element, ethylenedioxythiophene (hereinafter referred to as EDT) is impregnated into the capacitor element, and 40 to 60% of ferric paratoluenesulfonate is added. 20 to 1
Heat at 80 ° C for 30 minutes or more. Thereafter, the surface of the capacitor element is covered with a resin, and aging is performed.

Here, EDT impregnated in the capacitor element
Can be used as an EDT monomer,
A monomer solution in which T and a volatile solvent are mixed at a volume ratio of 1: 1 to 1: 3 can also be used. As the volatile solvent, hydrocarbons such as pentane, ethers such as tetrahydrofuran, esters such as ethyl formate, ketones such as acetone, alcohols such as methanol, and nitrogen compounds such as acetonitrile can be used. Among them, methanol, ethanol, acetone and the like are preferable. As the oxidizing agent, ferric paratoluenesulfonate dissolved in butanol is used. In this case, the ratio between butanol and ferric paratoluenesulfonate may be arbitrary, but in the present invention, a 40 to 60% solution is used. The mixing ratio of EDT and oxidizing agent is preferably in the range of 1: 3 to 1: 6.

Further, similarly to the above-mentioned conductive polymer,
Various studies were also conducted on a wound solid electrolytic capacitor using lead dioxide, which can form a semiconductor layer at a low temperature, and as with a solid electrolytic capacitor with an electrolyte layer made of a conductive polymer, It has been found that the appearance rate can be improved. Since this lead dioxide forms a highly conductive semiconductor layer, a solid electrolytic capacitor having low ESR characteristics can be formed. In addition, a semiconductor layer using lead dioxide can be formed by oxidizing lead acetate at room temperature with an oxidizing agent such as ammonium persulfate, so that the anodic oxide film is less damaged than manganese dioxide formed at a high temperature. It is considered that the film has good properties, withstand voltage characteristics, leakage current characteristics, and the like, and can obtain characteristics equivalent to those of the conductive polymer.

However, lead dioxide has a drawback that its rated voltage is lower than the formation voltage of the anode foil, as compared with the above-mentioned PEDT. Therefore, in order to obtain the same rated voltage as that of PEDT, the formation voltage of the anode foil must be increased, and accordingly, the thickness of the chemical conversion film of the anode foil increases, and the capacitance of the anode foil decreases. The capacitance of the capacitor, which is a combined capacitance of the capacitance of the anode foil and the capacitance of the cathode foil, is reduced.

Next, a method for manufacturing a wound solid electrolytic capacitor using lead dioxide as the electrolyte layer will be described. That is, as the cathode foil, a foil obtained by forming a TiN film on a etched aluminum foil by a cathode arc plasma deposition method is used. The conditions for the cathodic arc plasma deposition method are as follows: a cathode made of a valve metal is heated to 200 to 450 ° C. using a Ti target in a nitrogen atmosphere, and the total pressure including nitrogen is 1 × 10 ⁻¹ to 1 × 10 ^{−. 4} Torr, 80-3
00A, 15-20V. Also, as the anode foil,
The surface of the etched aluminum foil subjected to a chemical conversion treatment by a conventionally used method to form a dielectric film is used. The anode foil is wound together with the cathode foil and the separator to form a capacitor element, and the capacitor element is immersed in an aqueous solution of lead acetate in a range of 0.05 mol / liter to a concentration that gives a saturated solubility. An aqueous solution of ammonium persulfate in the range of 0.1 to 5 mol per 1 mol of lead is added and left at room temperature for 30 minutes to 2 hours to form a lead dioxide layer on the dielectric layer. Next, the capacitor element is washed with water and dried, and then sealed with a resin to form a solid electrolytic capacitor.

Incidentally, even if the cathode foil according to the present invention is used for an electrolytic capacitor using a normal electrolytic solution, an electric double layer capacitor is formed at the interface between the electrolytic solution and the cathode foil and becomes a capacitance component. The capacity does not become zero and the maximum capacity as in the present invention cannot be obtained.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail based on embodiments.

[1. First Embodiment] The present embodiment relates to a wound solid electrolytic capacitor using a conductive polymer as an electrolyte layer. In addition, the cathode foil according to the present invention, in which a film made of a conductive material that hardly oxidized was formed, was prepared as in Example 1 below. Further, a conventional cathode foil was used as Conventional Example 1.

Example 1 A high-purity aluminum foil (purity 99%, thickness 50 μm) cut into a size of 4 mm × 30 mm was used as a material to be processed. After etching, a TiN film was formed by a cathodic arc plasma deposition method. Formed. Note that the conditions of the cathodic arc plasma deposition method are as follows: a high-purity aluminum foil is heated to 200 ° C. using a Ti target in a nitrogen atmosphere, and 5 × 10 ⁻³ Torr, 300
A, at 20V. Then, the cathode foil is wound together with the anode foil and the separator to form a capacitor element having a shape of 4φ × 7 L. The capacitor element is impregnated with an EDT monomer, and a 45% paratoluenesulfonic acid as an oxidizing agent solution. The solution was impregnated with a ferric butanol solution and heated at 100 ° C. for 1 hour. Thereafter, the surface of the capacitor element was covered with a resin, and aged to form a solid electrolytic capacitor. The rated voltage of this solid electrolytic capacitor is 6.3 WV and the rated capacity is 33 μF.

(Conventional Example 1) The same material as in Example 1 was used as a material to be treated, and a material having no surface formed of a metal nitride film was used as a cathode foil. Using this cathode foil, a solid electrolytic capacitor was formed in the same manner as in Example 1.

[Comparative Results] Table 1 shows the electrical characteristics of the solid electrolytic capacitors of Example 1 and Conventional Example 1 obtained by the above method.

[0027]

[Table 1]

As is clear from Table 1, in the conventional example 1 using the cathode foil having no metal nitride film formed on the surface, the capacitance (Cap) is as low as "30.2", The tan δ was as high as “0.120”. On the other hand, in Example 1, Cap was "47.8", which is about 1.6 times the value of Conventional Example 1, and tan δ was "0.027", which was about 22.5% of that of Conventional Example 1. Has dropped. The equivalent series resistance (ESR) was "49" and "47", respectively, and no significant difference was observed. Thus, in Example 1, C
The value of ap was about 1.6 times that of the conventional example 1 because the film made of metal nitride was formed on the surface of the cathode foil, the cathode foil and the metal nitride were conducted, and the capacity of the cathode foil portion was increased. It is considered that as a result, the capacitance component of the cathode foil disappeared, and the capacitance of the capacitor, which was the combined capacitance of the series connection of the anode foil and the cathode foil, became maximum.

In Example 1, tan δ was reduced to about 22.5% of that of Conventional Example 1 because the high temperature treatment was not performed in the process of forming the capacitor, and the metal nitride deposited on the surface of the cathode foil was not treated. This is presumably because no oxide film was formed on the surface of the object, and the dielectric loss of the oxide film disappeared.

As described above, it is clear that in the solid electrolytic capacitor using the cathode foil having the surface formed of a film made of a conductive material which does not easily oxidize, the capacitance appearance rate can be greatly improved. Was. Incidentally, the present inventor, in a solid electrolytic capacitor using TiN deposited on the cathode foil and using manganese dioxide as a solid electrolyte,
It has been confirmed that the capacitance decreases after the heat treatment step.

[2. Second Embodiment] The present embodiment relates to a wound solid electrolytic capacitor using lead dioxide as an electrolyte layer. In addition, the cathode foil according to the present invention in which a film made of a conductive material that is less likely to be oxidized was formed as in Example 2 below. Further, a conventional cathode foil was used as Conventional Example 2.

Example 2 A high-purity aluminum foil (purity 99%, thickness 50 μm) cut into a size of 4 mm × 30 mm was used as a material to be processed. After etching, a TiN film was formed by a cathodic arc plasma deposition method. Formed. Note that the conditions of the cathodic arc plasma deposition method are as follows: a high-purity aluminum foil is heated to 200 ° C. using a Ti target in a nitrogen atmosphere, and 5 × 10 ⁻³ Torr, 300
A, at 20V. Then, the cathode foil was wound together with the anode foil and the separator to form a capacitor element having an element shape of 4φ × 7L. This capacitor element was immersed in a 3 mol / l aqueous lead acetate solution, and the same amount of a 3 mol / l aqueous ammonium persulfate solution was added thereto.
It was left at room temperature for 1 hour. Next, after washing and drying the capacitor element, a solid electrolytic capacitor having a rated voltage of 6.3 WV and a rated capacity of 22 μF was formed in the same manner as in Example 1.

In the second embodiment, the rated capacity is as small as 22 μF as compared with the first embodiment using PEDT, for the following reason. That is, lead dioxide has a lower rated voltage of the capacitor with respect to the formation voltage of the anode foil than PEDT. Therefore, for the same rated voltage, in the case of lead dioxide, the formation voltage of the anode foil must be increased. Therefore, the thickness of the anode foil increases, the capacitance of the anode foil decreases, and the capacitance of the capacitor, which is the combined capacitance of the capacitance of the anode foil and the capacitance of the cathode foil, decreases.

(Conventional Example 2) The same material as that of Example 2 was used as a material to be treated, and a material having no surface formed of a metal nitride film was used as a cathode foil. Then, using this cathode foil, a solid electrolytic capacitor was formed in the same manner as in Example 2.

[Comparative Results] Table 2 shows the electrical characteristics of the solid electrolytic capacitors of Example 2 and Conventional Example 2 obtained by the above method.

[0036]

[Table 2]

As is clear from Table 2, in the conventional example 2 using the cathode foil having no metal nitride film formed on the surface, the capacitance (Cap) is as low as "22.1". The tan δ was as high as “0.132”. On the other hand, in Example 2, Cap was "25.2", which was about 14% higher than that of Conventional Example 2, and tan δ was "0.042", which was about 30% of that of Conventional Example 2. Note that the equivalent series resistance (ES
R) were "159" and "156", respectively, and no significant difference was observed. Thus, in Example 2, Cap
Is about 1.14 times that of Conventional Example 2 because the film made of metal nitride is formed on the surface of the cathode foil, the cathode foil and the metal nitride conduct, and the capacity of the cathode foil portion is reduced. It is considered that as a result of the infinity, the capacitance component of the cathode foil disappeared, and the capacitance of the capacitor, which is the combined capacitance of the series connection of the anode foil and the cathode foil, became maximum.

In the second embodiment, the rate of increase in capacitance (about 14%) is smaller than that in Example 1 using PEDT (about 60%). It is considered as follows. That is, as described above, in Example 2, when the same rated voltage as in Example 1 was used, the formation voltage of the anode foil had to be increased, so that the thickness of the anode foil was increased and the capacitance of the anode foil was increased. Becomes smaller. Therefore, even if the capacitance of the cathode foil becomes infinite due to the deposition of TiN, the contribution to the capacitance of the capacitor, which is a combined capacitance of the capacitance of the anode foil and the capacitance of the cathode foil, is expressed by PEDT. This is considered to be because the size is smaller than that in the first embodiment using.

In Example 2, the tan δ was reduced to about 30% of that in Conventional Example 2 because the high temperature treatment was not performed in the process of forming the capacitor, and the metal nitride deposited on the surface of the cathode foil was not treated. No oxide film is formed on the surface,
It is considered that the dielectric loss of the oxide film disappeared.

As described above, even when lead dioxide is used as the electrolyte, like the solid electrolytic capacitor provided with the electrolyte layer made of a conductive polymer, the withstand voltage characteristic, the leakage current characteristic, and the like are good, and the high capacity appearance is achieved. Rate was found to be obtained.

[0041]

As described above, according to the present invention,
By forming a film made of a conductive material that does not easily oxidize on the surface of the cathode foil, the capacity of the cathode foil part becomes infinite, so that the capacitance component of the cathode foil disappears, and the anode foil and the cathode foil are connected in series. Therefore, it is possible to provide a solid electrolytic capacitor capable of miniaturizing the capacitor and improving the rate of appearance of the capacitor, and a method of manufacturing the same.

Claims (9)

[Claims] 1. A capacitor element is formed by winding a cathode foil made of a valve metal and an anode foil made of a valve metal having an oxide film formed on a surface thereof through a separator, and forming a capacitor element between the cathode foil and the anode foil. A solid electrolytic capacitor having an electrolyte layer made of a conductive polymer, wherein a film made of a conductive material that is less likely to be oxidized is formed on the surface of the cathode foil. 2. A capacitor element is formed by winding a cathode foil made of a valve metal and an anode foil made of a valve metal having an oxide film formed on a surface thereof through a separator, and forming a capacitor element between the cathode foil and the anode foil. A solid electrolytic capacitor having an electrolyte layer made of lead dioxide, wherein a film made of a conductive material that is less likely to be oxidized is formed on the surface of the cathode foil. 3. The solid electrolytic capacitor according to claim 1, wherein the conductive polymer is polyethylene dioxythiophene. 4. The solid electrolytic capacitor according to claim 1, wherein the valve metal is aluminum. 5. The film according to claim 1, wherein the film made of a conductive material that is less likely to be oxidized is any of Ti, Zr, Ta, and Nb. Solid electrolytic capacitor. 6. The solid electrolytic capacitor according to claim 1, wherein the film made of a conductive material that hardly oxidizes is formed by a vapor deposition method. 7. The solid electrolytic capacitor according to claim 6, wherein the vapor deposition method is a cathodic arc plasma vapor deposition method. 8. A capacitor element is formed by winding a cathode foil made of a valve metal and an anode foil made of a valve metal having an oxide film formed on the surface thereof through a separator to form a capacitor element. A method for manufacturing a solid electrolytic capacitor, wherein an electrolyte layer made of a conductive polymer is formed, wherein a film made of a conductive material that is less likely to be oxidized is formed on the surface of the cathode foil. 9. A capacitor element is formed by winding a cathode foil made of a valve metal and an anode foil made of a valve metal having an oxide film formed on a surface thereof through a separator, thereby forming a capacitor element between the cathode foil and the anode foil. A method for manufacturing a solid electrolytic capacitor, wherein an electrolyte layer made of lead is formed, wherein a film made of a conductive material that is less likely to be oxidized is formed on the surface of the cathode foil.