JPH11233368A - Capacitor and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small size and large capacity organic film capacitor with small current leakage and a method of manufacturing the same. SOLUTION: A thin film, comprising a carboxylic resin is formed by electrodeposition on a surface of an etched aluminum foil electrode 1, a conductor with coarse surface, a dielectric layer of a carboxylic resin thin film 2 having a hydrophobic layer with an increased hydrophobicity is formed, and a first polypyrrole layer 3, a second polypyrrole layer 4, and a current collector layer 5 are formed on the surface of the dielectric layer above as an oppositely faced electrode. This, enables formation of a small and large organic film capacitor with a small current leakage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitor used for an electronic circuit of electric equipment, electronic equipment, and audio equipment.

[0002]

2. Description of the Related Art In recent years, devices have become smaller, thinner and lighter.
With the increase in the density and digitalization of electric device circuits, there is an increasing demand for miniaturization, higher performance, and higher reliability of electronic components. Under such circumstances, there is a strong demand for a capacitor having a small size, a large capacity, and a low impedance in a high frequency region.

[0003] Capacitors having a low impedance in a high frequency region include various types of ceramic capacitors and film capacitors using a ceramic or polymer film as a dielectric material. Will also be higher.

On the other hand, an aluminum electrolytic capacitor using an aluminum oxide film as a dielectric has a small size and a large capacity, but is inferior in impedance and dielectric characteristics in a high frequency region as compared with the above-mentioned ceramic capacitors and film capacitors. Therefore, in order to improve high-frequency characteristics, aluminum solid electrolytic capacitors have been developed in which the driving electrolyte portion of the aluminum electrolytic capacitor is replaced with a solid material having higher conductivity, such as manganese dioxide or polypyrrole.
However, in any case, it is difficult to use an aluminum electrolytic capacitor in an AC circuit because the dielectric oxide film has polarity.

Furthermore, a new type of small-sized and large-capacity film in which a polyimide film is formed on an etched aluminum foil surface by an electrodeposition method instead of an aluminum oxide film, and a conductive polymer is formed on the surface. A method of manufacturing a capacitor is also provided (for example, see
-87312). The present invention is intended to increase the capacitance while maintaining the advantages of non-polarity and low dielectric loss tangent of polyimide as a dielectric.

[0006]

However, in the above invention, an organic solvent such as dimethylformamide or methanol is used as a solvent for the polyamic acid salt solution when forming the polyimide film. Applying a voltage to an electrodeposition solution containing a large amount of such an organic solvent has a problem in safety, and it is necessary to consider the harmfulness of the organic solvent to the human body. Furthermore, it is often unsuitable for industrial mass production, which is more expensive than water.

Accordingly, the present inventors have developed a conductive electrode obtained by roughening a polyacrylic acid resin dielectric, which is a typical polycarboxylic acid resin, using an aqueous electrodeposition solution which is industrially easy to use. A capacitor formed on the surface and provided with a counter electrode on the surface of the dielectric layer and a method of manufacturing the same have been proposed (Japanese Patent Application Laid-Open No.
-115767).

In the method of the present invention, a hole having a large aspect ratio (pore diameter: 1 to 3 μm, hole length: 30 to 50)
A polycarboxylic acid-based resin is formed on the surface of an etched aluminum foil (thickness: about 100 μm) having a large number of μm), and various evaluations of the characteristics as a capacitor have been made. As a result, there remains a problem that the disadvantage that the leakage current is large must be improved.

As a result of measuring a large number of leakage current characteristics of the prototype capacitor before the resin sheathing, it was found that the leakage current increased when drying was insufficient, and decreased when drying was sufficiently performed. In addition, it was found that moisture was adsorbed in a short period of time even when drying was sufficiently performed, and the leakage current increased.

It is considered that the reason why the leakage current is increased by the minute adsorbed water as described above is that hydrogen ions (H ⁺ ) in the water adsorbed on the dielectric surface are involved in electric conduction. Hydrogen-bonding hydrogen in the polymer structure also
It is known that it easily participates in electric conduction. The structure and properties of the electrodeposited film largely reflect on such water adsorption capacity and hydrogen ion conduction.

In the electrodeposition method, a polymer in a solution is ionized (charged) and electrophoresed to deposit a film on the surface of a conductor electrode. Therefore, in the anion electrodeposition method, a polycarboxylic acid resin having at least one carboxylic acid group that is negatively charged in a solution is generally used. Polycarboxylic acid-based resin dielectric film formed by electrodeposition method has strong ionicity because it has polar groups such as hydroxyl group and carboxylic acid group, compared with polypropylene etc. used for ordinary film capacitors. It also has strong hydrogen bonding properties. These polar groups can be somewhat reduced by a crosslinking reaction with a curing agent during heat treatment, but the electrodeposited dielectric film still has hydrogen bonding hydrogen compared to pure polypropylene. It is also easy to adsorb moisture.

The above factors are considered to be the main causes of increasing the contribution of hydrogen ion conduction and increasing the leakage current.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a new type of film capacitor having small leakage current, non-polarity, small size and large capacity, and a method of manufacturing the same.

[0014]

In order to achieve the above object, a capacitor according to the present invention comprises a polymer thin film dielectric layer formed by electrodeposition on a roughened or porous conductive electrode surface. And a conductor layer as a counter electrode on the surface of the dielectric layer, wherein the dielectric layer has a hydrophobic layer with increased hydrophobicity.

The roughened conductor electrode is preferably an etched aluminum foil. It is also characterized in that the dielectric layer is a polycarboxylic acid resin.

For the counter electrode, a conductive polymer is preferable, and among them, polypyrrole is preferable. Further, it is characterized by using a coupling agent to increase the hydrophobicity of the dielectric layer. It is also characterized by enhancing hydrophobicity by a silylation or alkylation reaction.

In order to achieve the above object, a method of manufacturing a capacitor according to the present invention comprises the steps of: using a solution containing a polymer as an electrodeposition liquid; A step of forming a thin dielectric layer, a step of heat-treating the dielectric layer, a step of increasing the hydrophobicity of the dielectric layer, and a step of forming a conductive layer as a counter electrode on the surface of the dielectric layer. Forming step.

Further, a method of manufacturing a capacitor according to the present invention comprises:
It is characterized in that the chemical reaction that occurs during the treatment for increasing the hydrophobicity is a silylation or alkylation reaction.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention has a dielectric layer of an organic polymer thin film formed on a roughened or porous conductive electrode surface by an electrodeposition method, By having a conductor layer as a counter electrode on the surface of the dielectric layer, it has the effect of realizing a small and large-capacity capacitor, and by having a hydrophobic layer with increased hydrophobicity on the dielectric layer, hydrogen The number of hydrogen ions contributing to ion conduction is extremely small.

According to the second aspect of the present invention, since an etched aluminum foil is used as the roughened conductor, the electrode has a large surface area and is suitable for capacity expansion.

According to the third aspect of the present invention, since a polycarboxylic acid resin is used as the dielectric, the surface of the conductive electrode having a complicated surface shape such as an etched aluminum foil is tracked by an electrophoretic electrodeposition method. It has an effect that a thin film can be formed efficiently.

According to a fourth aspect of the present invention, since the counter electrode is a conductive polymer, a conductive material having high conductivity is easily formed on the surface of the dielectric layer by chemical polymerization or a combination of chemical polymerization and electrolytic polymerization. It has the function of forming a layer.

The fifth aspect of the invention has the effect of using polypyrrole among conductive polymers to achieve excellent conductivity and thermal stability.

According to a sixth aspect of the present invention, since the dielectric layer has a hydrophobic layer whose hydrophobicity is increased by using a coupling agent, the number of active hydrogen ions involved in hydrogen ion conduction in the dielectric is reduced. Has the effect of reducing

The seventh aspect of the present invention has a hydrophobic layer whose hydrophobicity is increased by a silylation or alkylation reaction, and thus has an effect of remarkably improving the hydrophobicity of the dielectric after the reaction.

According to the present invention, a dielectric layer of an organic polymer thin film is formed by electrodeposition on a surface of a roughened or porous conductor electrode by using a solution containing an organic polymer as an electrodeposition solution. Forming, and heat treating the dielectric layer,
Since it has a process of performing a process of increasing the hydrophobicity of the dielectric layer and a process of forming a conductor layer as a counter electrode on the surface of the dielectric layer, it is possible to ensure a dielectric material having a small leakage current and a high withstand voltage. Can be formed.

According to the ninth aspect of the present invention, the treatment for increasing hydrophobicity is a silylation or alkylation reaction.
This has the function of manufacturing a capacitor having a dielectric having a small hydrogen ion conductivity.

Embodiment 1 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram of a cross section of a capacitor described in the present embodiment, and FIG. 2 is a flowchart showing a method of manufacturing the capacitor of the present embodiment.

First, the structure of a target capacitor is shown in FIG.
This will be described in detail with reference to FIG. In the figure, reference numeral 1 denotes an etched aluminum foil electrode having an average pore diameter of 2 μm generated by etching and having a surface area approximately 30 times roughened. A thin film made of a polycarboxylic acid-based resin as a dielectric is formed by electrodeposition so as to follow the surface shape of the electrode 1.

Further, by treating the thin film made of the polycarboxylic acid resin with a coupling agent (not shown), a polycarboxylic acid resin thin film 2 having a hydrophobic layer (not shown) is formed. . The hydrophobic layer is formed by replacing the hydrogen-bonding active hydrogen present in the polycarboxylic acid-based resin thin film with a hydrophobic group, and is formed not only on the surface of the polycarboxylic acid-based resin thin film 2 but also on the film. It also exists inside.

A counter electrode of the etched aluminum foil electrode 1 is provided with a first polypyrrole layer 3 of a conductive polymer and a second
And a current collector layer 5 attached to collect current. Reference numeral 6 denotes an epoxy resin attached for insulating the electrodes. Then, if a lead wire is provided on the two electrodes shown in this figure and the package is covered with epoxy resin, the structure of the capacitor of the present embodiment is obtained.

The term "polycarboxylic acid resin" as used herein means a resin having at least one carboxylic acid group in the main chain or side chain of a polymer. For example, polyacrylic acid, polymethacrylic acid, and the like. Of course, it is needless to say that copolymers of these or partially esterified ones can also be used. Preferably, an amino resin-based curing agent such as melamine is mixed and the insulating property is improved by a three-dimensional crosslinking reaction at the time of heat treatment. Among these, a polyacrylic acid resin which is water-soluble and excellent in workability, and excellent in adhesiveness to aluminum and flexibility is suitable for this purpose.

There are two types of electric conduction, electronic conduction and ionic conduction, depending on the charge carrier. However, since the leakage current is affected by humidity, the electric conduction in the thin film made of the polycarboxylic acid resin of the present embodiment is reduced. The conduction is considered to be mainly ionic conduction. The carrier ion at this time is
It is a hydrogen ion (H ⁺ ). The mechanism of hydrogen ion conduction of a polymer has been studied for a long time, and it is known that the presence of a large number of hydrogen-bonding hydrogens makes hydrogen ion conduction more likely to occur (for example, DA Senor,
Electrical Properties of
Ploymers, Academic Press, N
ew York, (1982) pp. 45-55. ).

Therefore, in the present invention, by replacing such hydrogen which is likely to participate in electric conduction with a hydrophobic group,
The purpose was to form a polycarboxylic acid-based resin thin film 2 as a dielectric to reduce hydrogen ion conductivity. Also,
The purpose was also to suppress moisture adsorption on the dielectric surface. Here, the hydrophobic group that replaces active hydrogen in the thin film made of the polycarboxylic acid resin by the coupling reaction includes an alkyl group, a silyl group, and an alkyl fluoride group.

The hydrophobic group which is substituted by active hydrogen in the thin film made of the polycarboxylic acid resin by the coupling reaction is not limited to the above-mentioned one. Anything that is not included will be effective.

For example, a typical reaction for increasing hydrophobicity is a trimethylsilylation reaction. The reaction can be represented by the following equation.

[0038]

Embedded image

As shown in the above formula, when the present invention is used, hydrogen of a hydroxyl group or an amino group which is easily involved in electric conduction can be selectively substituted. In addition, the coupling agent used for the reaction with the active hydrogen in the resin as described above is not limited to chlorotrimethylsilane, but other chloroalkylsilanes having different numbers of carbon atoms and chlorine atoms and their alkyl groups. It is needless to say that hydrogen may be replaced by fluorine, and those silicon atoms may be replaced by carbon atoms.

Next, an example of a method of manufacturing the above-structured capacitor will be described in detail with reference to FIG.

First, the step of synthesizing the electrodeposition solution in step 1 will be described. The aqueous solution containing the polycarboxylic acid used was an emulsion solution containing 10% by weight of solid content, 86% by weight of ion-exchanged water, and 4% by weight of butyl cellosolve. The solid content used here was a mixture of a copolymer of polyacrylic acid and polymethacrylic acid (molecular weight: about 20,000) (main ingredient) and a melamine resin (curing agent) in a weight ratio of 7: 3. . When dispersing the solids in the liquid, 50% of the carboxylic acid groups in the solids are neutralized by adding an appropriate amount of triethylamine to improve dispersibility, as is often done by the anion electrodeposition method. Was.

Next, the step of electrodepositing a thin film made of a polycarboxylic acid resin as a dielectric in step 2 will be described.

First, the electrodeposition solution synthesized in Step 1 is placed in a cylindrical step container (cathode) having a diameter of 80 mm. Next, the etched aluminum foil electrode 1 to which a lead wire was attached by welding was used as a dielectric forming portion (area: 10 mm × 10 mm) and immersed in an electrodeposition solution to form an anode.

Next, in step 2, a current is applied between both electrodes at an applied voltage of 40 V (constant) for 10 minutes, so that the surface of the etched aluminum foil electrode 1 is made of polycarboxylic acid resin as the first dielectric. A thin film was formed.

It is needless to say that the thickness of the polycarboxylic acid-based thin film can be adjusted by changing the magnitude of the applied voltage, the length of the electrodeposition time, the number of times of electrodeposition, and the like in step 2.

Next, in step 3, the sample on which the dielectric layer was formed in step 2 was washed with water, dried at 80 ° C. for 20 minutes, and heat-treated at 180 ° C. for 30 minutes to obtain a melamine resin and a polycarboxylic acid-based resin. A curing reaction was performed with the resin.

Next, in step 4, the device formed in step 3 is immersed in a 1% by weight chlorotrimethylsilane hexane solution at room temperature for 5 hours to cause a trimethylsilylation reaction to replace active hydrogen with a trimethylsilyl group. Thus, a polycarboxylic acid-based resin thin film 2 having a hydrophobic layer was formed. Thereafter, it was repeatedly washed with hexane and acetone several times and dried. In addition, as can be seen from the formula (1) during the trimethylsilylation reaction, a small amount of hydrochloric acid is generated, but immediately after the reaction, repeated washing with hexane and acetone several times does not adversely affect the properties. I did it.

In step 4, chlorotrimethylsilane was used as the coupling agent, but the number of carbon atoms was different.

[0049]

Embedded image

Alternatively, carbon of the formula (2) is replaced by carbon.

[0051]

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Needless to say, such a compound is a coupling agent suitable for the purpose of the present invention.

Nothing. Needless to say, even when at least one of the hydrogen atoms in (Chemical Formula 2) and (Chemical Formula 3) is replaced with a fluorine atom, the effect is exerted.

Next, in step 5, the element is set to 1.0 m
The operation of alternately immersing in a 2 mol / l ethanol solution of a cylindrical stainless steel container pyrrole and a 1.0 mol / l ammonium persulfate aqueous solution for 2 minutes alternately was repeated three times to obtain a first polypyrrole layer 3 which is a chemically oxidized polymer film of polypyrrole.
Was formed.

Subsequently, in step 6, the element on which the first polypyrrole layer 3 was formed was prepared by placing 1 part of pyrrole in a cylindrical stainless steel container, 1 part of a 40% by weight aqueous solution of sodium butylnaphthalenesulfonate, and 40 parts of distilled water. Part was immersed in a mixed solution to form an anode, and a cylindrical stainless steel container was used as a cathode. A current density of 2.5 mA / cm was applied between the two electrodes.
^{The second} polypyrrole layer 4 was formed by electrolytic polymerization at a constant current of ² for 30 minutes.

Next, in step 7, a current collector layer 5 is formed by applying a conductive material such as colloidal carbon or silver paint to the device. Thus, a counter electrode composed of the first polypyrrole layer 3 and the second polypyrrole layer 4 collected by the current collector layer 5 is formed. Here, a lead wire was soldered to complete the counter electrode.

Further, in step 8, the capacitor of the present embodiment was completed by packaging with an epoxy resin (not shown).

(Embodiment 2) Next, a second example of a method for manufacturing a capacitor according to the present invention will be described.

In the second embodiment, a capacitor is manufactured in the same manner as in the first embodiment except for step 4 in the first embodiment.

Hereinafter, the step (step 4) of increasing the hydrophobicity of the thin film made of the polycarboxylic acid resin according to the second embodiment will be described.

First, the device fabricated in Step 3 was
Place in a flask at reduced pressure to about orr. And
The vapor of a 20% by weight hexane solution of trimethylsilane is
It is introduced until the pressure in the flask reaches 300 Torr, and left for 30 minutes. In this case, the active hydrogen in the thin film made of the polycarboxylic acid-based resin is replaced with the trimethylsilyl group by the gas phase reaction, whereby the hydrophobicity is improved.

That is, a polycarboxylic acid-based resin thin film 2 having a hydrophobic layer is formed. (Performance Study 1) Table 1 shows the data of the electrical characteristics of the capacitor obtained in this embodiment together with the data of the comparative example.

[0063]

[Table 1]

The comparative example is data of a capacitor manufactured by the same method except that the process for increasing the hydrophobicity of the dielectric in step 4 of the first and second embodiments was not performed. As is clear from Table 1, Embodiments 1 and 2
Has a smaller dielectric loss tangent and leakage current than those of the comparative example by replacing active hydrogen involved in hydrogen ion conduction with a hydrophobic group.

[0065]

As described above, the capacitor according to the present invention has a polymer thin film dielectric layer formed by electrodeposition on the roughened or porous conductive electrode surface. By providing a conductive layer as a counter electrode on the upper side and providing a hydrophobic layer on the dielectric layer with enhanced hydrophobicity, there is an effect that the size is small, the capacity is large, and the leakage current value is low.

Further, by using an etched aluminum foil as the roughened conductor, the surface area of the electrode is increased, and the capacitance of the capacitor can be easily increased.

Since a polycarboxylic acid resin is used as the dielectric, a thin film can be formed following the surface of a conductor electrode having a complicated surface shape, such as an etched aluminum foil, by electrophoretic electrodeposition. This has the effect of realizing a capacitor having a large capacity and excellent heat resistance.

Further, since the counter electrode is a conductive polymer, a conductive layer having high conductivity can be easily formed on the surface of the dielectric layer by chemical polymerization or a combination of chemical polymerization and electrolytic polymerization. A resistor capacitor can be realized.

In addition, by using polypyrrole among conductive polymers, a capacitor having excellent conductivity, thermal stability, heat resistance and frequency characteristics can be realized.

Further, by having a hydrophobic layer in which the hydrophobicity of the dielectric layer is increased by using a coupling agent and reducing the number of hydrogen-bonding active hydrogens involved in hydrogen ion conduction,
This has the effect of reducing the leakage current of the capacitor.

In addition, the presence of the hydrophobic layer whose hydrophobicity has been enhanced by the silylation or alkylation reaction has the effect of reducing the hydrogen ion conduction of the dielectric and significantly reducing the leakage current.

Further, a solution containing a polymer is used as an electrodeposition solution,
Forming a dielectric layer of an organic polymer thin film on the roughened or porous conductive electrode surface by electrodeposition, heat treating the dielectric layer, and increasing the hydrophobicity of the dielectric layer Since it has a step of performing the treatment and a step of forming a conductor layer as a counter electrode on the surface of the dielectric layer,
Dielectrics with small leakage current characteristics can be reliably formed,
Excellent small and large capacity capacitors can be manufactured.

Further, since the treatment for increasing the hydrophobicity is a silylation or alkylation reaction, a capacitor having a small leakage current can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a cross section of a capacitor according to an embodiment of the present invention.

FIG. 2 is a flowchart of a method for manufacturing the capacitor of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Etched aluminum foil electrode 2 Polycarboxylic acid resin thin film (dielectric) 3 First polypyrrole layer 4 Second polypyrrole layer 5 Current collector layer 6 Epoxy resin (for insulation)

Claims (9)

[Claims] 1. A polymer thin film dielectric layer formed by electrodeposition on a roughened or porous conductive electrode surface, and a conductive layer as a counter electrode on the dielectric layer surface. Wherein the dielectric layer has a hydrophobic layer with increased hydrophobicity. 2. The capacitor according to claim 1, wherein the roughened conductor electrode is an etched aluminum foil. 3. The capacitor according to claim 1, wherein the dielectric layer is a polycarboxylic acid resin. 4. The capacitor according to claim 1, wherein the counter electrode is a conductive polymer. 5. The capacitor according to claim 4, wherein the conductive polymer is polypyrrole. 6. The capacitor according to claim 1, further comprising a hydrophobic layer in which the hydrophobicity of the dielectric layer is increased by using a coupling agent. 7. The capacitor according to claim 1, further comprising a hydrophobic layer whose hydrophobicity is increased by a silylation or alkylation reaction. 8. A step of forming a dielectric layer of a polymer thin film by electrodeposition on a roughened or porous conductive electrode surface using a solution containing a polymer as an electrodeposition liquid; A step of heat-treating the substrate, a step of performing a treatment for increasing the hydrophobicity of the dielectric layer, and a step of forming a conductor layer as a counter electrode on the surface of the dielectric layer. . 9. The method according to claim 8, wherein the treatment for increasing hydrophobicity is a silylation or alkylation reaction.