JP5274344B2 - Solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a solid electrolytic capacitor reducing ESR (Equivalent Series Resistance). <P>SOLUTION: A solid electrolytic capacitor has: an anode 2; a dielectric layer 3 provided on a surface of the anode 2; a solid electrolyte layer 4 provided on the dielectric layer 3; and a cathode layer 6 provided on the solid electrolyte layer 4. The cathode layer 6 has: an oxide layer 5a consisting of oxide of a valve action metal; and a metal layer 5b consisting of a metal with a standard electrode potential of 0 V and more or an alloy of the metal. The oxide layer 5a is formed partially between the solid electrolyte layer 4 and the metal layer 5b. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a solid electrolytic capacitor using an anode made of a valve metal or an alloy containing a valve metal as a main component.

  In recent years, along with the reduction in size and weight of electronic devices, a capacitor having a low impedance, a small size and a large capacity has been required. It is desired to reduce the resistance component as much as possible for the solid electrolytic capacitor. The resistance component in the solid electrolytic capacitor includes 1 / ωC (ω = 2πf, f is a frequency), ESR (equivalent series resistance), and ESL (equivalent series inductance). ESR is the sum of the resistance values of the anode, the solid electrolyte layer, and the cathode layer, and the contact resistance between them, constituting the solid electrolytic capacitor.

  As the solid electrolyte layer of the solid electrolytic capacitor, a conductive polymer has been used. As a method for forming the conductive polymer, there are a chemical polymerization method and an electrolytic polymerization method. In general, a conductive polymer film formed by an electrolytic polymerization method is superior in conductivity to a conductive polymer film formed by a chemical polymerization method, and can form a strong film. When a conductive polymer layer formed by an electropolymerization method is used as a solid electrolyte layer, the surface tends to be smooth, the adhesion of the cathode layer formed thereon is poor, and causes an increase in ESR. . Further, the contact resistance between the solid electrolyte layer and the cathode layer is mainly affected by the surface shape of the solid electrolyte layer, that is, the surface roughness, and causes an increase in ESR.

  In a solid electrolytic capacitor, as a method for reducing ESR, improving the adhesion between the solid electrolyte layer and the cathode layer is performed. In Patent Document 1, it is proposed to form a metal layer serving as a current collector layer on a solid electrolyte layer. In Patent Document 2, it is proposed that conductive powder is attached to a capacitor element to provide unevenness on the surface of a solid electrolyte layer formed by electrolytic polymerization or chemical polymerization, thereby improving adhesion with the cathode layer. In Patent Document 3, it is proposed that a conductive polymer layer formed by chemical polymerization is formed on a conductive polymer layer formed by electrolytic polymerization to improve the adhesion with the cathode layer.

  Further, as a method for improving the withstand voltage of the capacitor element and suppressing the leakage current, Patent Document 4 proposes forming an island-like insulating portion on the surface of the solid electrolyte layer using alumina hydrate or the like. Has been.

Japanese Patent Laid-Open No. 2005-45007 JP-A-7-94368 JP 2000-133549 A JP 2008-198681 A

  An object of the present invention is to provide a solid electrolytic capacitor capable of reducing ESR.

  The solid electrolytic capacitor of the present invention includes an anode, a dielectric layer provided on the surface of the anode, a solid electrolyte layer provided on the dielectric layer, and a cathode layer provided on the solid electrolyte layer, The cathode layer has an oxide layer made of an oxide of a valve action metal and a metal layer made of a metal having a standard electrode potential of 0 V or more or an alloy of the metal, and the oxide layer is made up of a solid electrolyte layer and a metal layer. It is characterized by being partially formed between.

  In the present invention, the cathode layer has an oxide layer that partially covers the surface of the solid electrolyte layer, and a metal layer that is provided so as to cover the oxide layer. The metal layer is provided on the oxide layer in the region where the oxide layer is formed, and is provided on the solid electrolyte layer in the region where the oxide layer is not formed.

  According to the present invention, when the cathode layer includes the oxide layer and the metal layer, the contact resistance between the solid electrolyte layer and the cathode layer can be reduced, and the ESR can be reduced.

  By providing the oxide layer according to the present invention, charges are accumulated on the surface of the oxide layer, and the electric field is concentrated at the interface between the solid electrolyte layer and the cathode layer. By promoting the charge injection due to this electric field concentration, it is considered that the contact resistance between the solid electrolyte layer and the cathode layer can be reduced and the ESR can be reduced.

  The oxide layer in the present invention is formed from an oxide of a valve action metal. Examples of the valve metal include molybdenum, vanadium, tungsten, titanium, tantalum, niobium, hafnium, and zirconium.

  The metal layer in the present invention is formed of a metal having a standard electrode potential of 0 V or higher or an alloy of the metal. By forming a metal layer from such a metal or alloy, a metal layer in which a natural oxide film is difficult to form in the atmosphere can be obtained. Examples of metals having a standard electrode potential of 0 V or higher include rhenium (Re), ruthenium (Ru), rhodium (Rh), platinum (Pt), gold (Au), silver (Ag), iridium (Ir), osmium (Os), Examples include mercury (Hg).

  The relative dielectric constant of the material forming the oxide layer in the present invention is preferably 10 or more. By forming the oxide layer using a material having a relative dielectric constant of 10 or more, ESR can be further reduced.

  The oxide layer in the present invention is preferably formed of an oxide of at least one metal selected from the group consisting of molybdenum, tungsten, and vanadium. ESR can be further reduced by using oxides of these metals. The relative dielectric constant of molybdenum oxide is about 39, the relative dielectric constant of tungsten oxide is about 41, and the relative dielectric constant of vanadium oxide is about 12.

  In the present invention, the solid electrolyte layer can be formed from a conductive polymer. Examples of the conductive polymer include at least one selected from the group consisting of polyethylene dioxythiophene and derivatives thereof, and polypyrrole and derivatives thereof.

  According to the present invention, the contact resistance between the solid electrolyte layer and the cathode layer can be reduced, and the ESR can be reduced.

The typical sectional view showing the solid electrolytic capacitor of one embodiment of the present invention. The expanded sectional view which shows the interface vicinity of the solid electrolyte layer and cathode layer in the solid electrolytic capacitor of embodiment shown in FIG.

  Hereinafter, the present invention will be described with reference to specific embodiments, but the present invention is not limited to the following embodiments.

  FIG. 1 is a schematic cross-sectional view showing a solid electrolytic capacitor according to an embodiment of the present invention.

  As shown in FIG. 1, an anode lead 1 is embedded in the anode 2. The anode 2 is produced by molding a powder made of a valve action metal or an alloy containing the valve action metal as a main component and sintering the formed body. Therefore, the anode 2 is formed from a porous body. Although not shown in FIG. 1, this porous body has a large number of fine holes communicating from the inside to the outside. In this embodiment, the anode 2 manufactured in this way is manufactured so that the outer shape is a substantially rectangular parallelepiped.

  The valve metal that forms the anode 2 is not limited as long as it can be used for a solid electrolytic capacitor, and examples thereof include tantalum, niobium, titanium, aluminum, hafnium, and zirconium. Among these, tantalum, niobium, aluminum, and titanium, in which the oxide as the dielectric is relatively stable even at high temperatures, are particularly preferable. Moreover, as an alloy which has a valve action metal as a main component, the alloy of valve action metals which consist of 2 or more types, such as a tantalum and niobium, is mentioned.

  A dielectric layer 3 is formed on the surface of the anode 2. The dielectric layer 3 is also formed on the surface of the hole of the anode 2. In FIG. 1, the dielectric layer 3 formed on the outer peripheral side of the anode 2 is schematically shown, and the dielectric layer formed on the surface of the hole of the porous body is not shown. The dielectric layer 3 can be formed by oxidizing the anode 2 by anodic oxidation or the like.

  A solid electrolyte layer 4 made of a conductive polymer layer is formed on the surface of the dielectric layer 3. The conductive polymer layer can be formed from at least one selected from the group consisting of polyethylene dioxythiophene and derivatives thereof, and polypyrrole and derivatives thereof. The conductive polymer layer may be composed of a plurality of layers. The solid electrolyte layer 4 made of a conductive polymer layer is also formed on the dielectric layer 3 on the surface of the hole of the anode 2.

  On the solid electrolyte layer 4, an oxide layer 5 a made of an oxide of a valve action metal is formed. The oxide layer 5 a is formed so as to partially cover the surface of the solid electrolyte layer 4. Therefore, the oxide layer 5 a is not provided so as to cover the entire surface of the solid electrolyte layer 4. In FIG. 1, such an oxide layer 5a is schematically shown.

  The oxide layer 5a is preferably formed by vapor phase epitaxy in a vacuum. Specifically, it can be formed by vacuum deposition methods such as resistance heating, flash evaporation, arc evaporation, laser heating, high frequency heating, and electron beam heating. Further, it may be formed by a sputtering method such as ECR or magnetron, an ion plating method, an MBE method, or a laser ablation method.

  The oxide layer 5a can be formed from oxides such as molybdenum, vanadium, tungsten, titanium, tantalum, niobium, hafnium, and zirconium. In the case of forming from an oxide such as molybdenum, tungsten, or vanadium, these oxides sublime at a relatively low temperature, and thus can be formed by a vapor deposition method using resistance heating. Therefore, it can be formed without damaging the solid electrolyte layer.

  In the case of an oxide such as tantalum, yttrium, zirconium, or hafnium, it can be formed by an electron beam heating method. In the case of niobium oxide, it can be formed by either resistance vapor deposition or electron beam heating.

  The thickness of the oxide layer 5a is preferably about 1 nm to 20 nm, for example. If the film thickness is larger than 20 nm, ESR may increase or the capacitance may decrease. In general, it is often difficult to form the film with a reproducibility of less than 1 nm. The film thickness of the oxide layer 5a can be measured by, for example, a film thickness meter using a crystal resonator, and the film thickness can be determined by comparing with the absolute value of the film thickness obtained by an ellipsometer or the like. .

  A metal layer 5b made of a metal having a standard electrode potential of 0 V or higher or an alloy of the metal is formed on the oxide layer 5a. Since the oxide layer 5a is partially formed on the surface of the solid electrolyte layer 4, the metal layer 5b is provided on the oxide layer 5a in the region where the oxide layer 5a is formed. Yes. In the region where the oxide layer 5 a is not formed, the metal layer 5 b is formed on the solid electrolyte layer 4.

  By forming the metal layer 5b from a metal having a standard electrode potential of 0 V or more or an alloy of the metal, an ohmic junction is formed between the oxide layer 5a and the metal layer 5b, so that the ESR reduction effect can be enhanced. it can. Further, since a natural oxide film is hardly formed on the metal layer 5b, the effect of reducing ESR can be enhanced.

  The metal layer 5b can be formed from a metal having a standard electrode potential of 0 V or higher or an alloy of the metal, and can be formed from, for example, silver, gold, or the like. The formation method of the metal layer 5b is not particularly limited, but a vapor deposition method by resistance heating, a vacuum vapor deposition method such as flash evaporation, arc evaporation, laser heating, high frequency heating, electron beam heating, ECR, magnetron, etc. It can be formed by sputtering, ion plating, MBE, laser ablation, or the like.

  Although the film thickness of the metal layer 5b is not specifically limited, For example, it can be in the range of about 10 nm-1000 nm.

  A carbon layer 5c is formed on the metal layer 5b. The carbon layer 5c can be formed by applying a carbon paste containing conductive carbon particles such as graphite and drying it.

  A silver layer 5d is formed on the carbon layer 5c. The silver layer 5d can be formed by applying a silver paste containing silver particles and then drying it.

  In the present embodiment, the cathode layer 6 includes an oxide layer 5a, a metal layer 5b, a carbon layer 5c, and a silver layer 5d.

  The carbon layer 5c and the silver layer 5d are current collecting layers provided to improve current collecting properties. As the current collecting layer, it is not always necessary to provide both the carbon layer 5c and the silver layer 5d, and only one of the carbon layer 5c and the silver layer 5d may be formed. Further, a current collecting layer other than the carbon layer 5c and the silver layer 5d may be formed.

  A cathode terminal 9 is connected on the cathode layer 6 via a conductive adhesive layer 7. An anode terminal 8 is connected to the anode lead 1. Mold exterior resin 10 is formed so that the ends of anode terminal 8 and cathode terminal 9 are drawn out to the outside.

  As described above, the solid electrolytic capacitor of the present embodiment is configured.

  FIG. 2 is an enlarged schematic cross-sectional view showing the vicinity of the interface between the solid electrolyte layer 4 and the cathode layer 6 in the solid electrolytic capacitor of the embodiment shown in FIG.

  As shown in FIG. 2, the anode 2 is a porous body, and has a hole communicating from the inside to the outside. A dielectric layer 3 is formed on the surface of the anode 2. A solid electrolyte layer 4 is formed on the dielectric layer 3, and the solid electrolyte layer 4 is also formed on the dielectric layer 3 of the pores of the porous body as shown in FIG. .

  As shown in FIG. 2, an oxide layer 5 a is formed on the solid electrolyte layer 4 so as to partially cover the surface of the solid electrolyte layer 4. The oxide layer 5 a may be formed in an island shape on the surface of the solid electrolyte layer 4. Therefore, the region where the oxide layer 5a is formed may be an island shape. Conversely, the region where the oxide layer 5a is not formed may have an island shape, and the oxide layer 5a may be continuously formed around the region.

  A metal layer 5b is directly formed on the oxide layer 5a. Since the oxide layer 5a is partially formed as described above, the metal layer 5b is formed directly on the oxide layer 5a in the region where the oxide layer 5a is formed. In the region where the oxide layer 5 a is not formed, the metal layer 5 b is formed directly on the solid electrolyte layer 4.

  A carbon layer 5c and a silver layer 5d are formed in this order on the metal layer 5b.

  In the present invention, the oxide layer 5 a is provided so as to partially cover the surface of the solid electrolyte layer 4. Since the oxide layer 5a is formed of an oxide of a valve metal, electric charges are accumulated on the surface, and an electric field is concentrated on the interface. By concentrating the electric field, charge injection can be promoted, and the contact resistance between the interface between the metal layer 5b and the solid electrolyte layer 4 can be reduced. As a result, it is considered that ESR can be reduced. Even when a high frequency is applied, the ESR can be reduced although the reduction rate is somewhat reduced.

  Therefore, according to the present invention, the contact resistance between the cathode layer 6 and the solid electrolyte layer 4 can be reduced, and the ESR can be greatly reduced.

  In the present embodiment, the solid electrolyte layer 4 is formed from a conductive polymer, but the present invention is not limited to this, and may be formed from other materials such as manganese dioxide.

  Further, in the present embodiment, the anode 2 is formed from a porous body obtained by sintering a valve action metal powder. However, the present invention is not limited to this, for example, from a foil-like substrate. It may be formed.

  Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to the following examples.

Example 1
<Step 1>
A porous sintered body in which a tantalum powder having an average particle diameter of about 2 μm is used, a molded body in which a lead wire made of tantalum is embedded, and the anode lead made of tantalum is embedded by sintering the molded body. An anode comprising: This anode was anodized in an about 0.1 wt% phosphoric acid aqueous solution maintained at about 60 ° C. at a constant voltage of about 8 V for about 10 hours to form a dielectric layer on the surface of the anode.

<Step 2>
A solid electrolyte layer made of polypyrrole (Ppy) was formed on the surface of the dielectric layer on the anode 2 produced in Step 1 by chemical polymerization and electrolytic polymerization.

<Step 3>
Next, molybdenum oxide was deposited on the solid electrolyte layer in a vacuum of about 10 ⁻⁵ Pa by a resistance heating vapor deposition method so as to have a thickness of 1 nm, thereby forming an oxide layer. Next, silver was vapor-deposited by a resistance heating vapor deposition method so as to have a film thickness of 100 nm to form a metal layer.

  The carbon layer was formed by apply | coating carbon paste on a metal layer, and drying after application | coating. Moreover, the silver layer was formed by apply | coating a silver paste layer on a carbon layer, and drying after application | coating.

  A cathode terminal was bonded onto the silver layer via a conductive adhesive layer, and the anode terminal was connected to the anode lead, and then a mold exterior resin was coated to produce a solid electrolytic capacitor.

(Example 2)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the thickness of the oxide layer was 5 nm.

(Example 3)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the thickness of the oxide layer was 20 nm.

Example 4
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the thickness of the oxide layer was 10 nm.

(Example 5)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the metal layer was formed from gold so as to have a film thickness of 100 nm by vapor deposition using a resistance heating method.

(Example 6)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the oxide layer was formed from tungsten oxide having a thickness of 10 nm.

(Example 7)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the oxide layer was formed of vanadium oxide having a thickness of 10 nm.

(Example 8)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the silver layer was formed directly on the metal layer without forming the carbon layer.

(Comparative Example 1)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the carbon layer and the silver layer were formed on the solid electrolyte layer without forming the oxide layer and the metal layer.

(Comparative Example 2)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the metal layer, the carbon layer, and the silver layer were formed on the solid electrolyte layer without forming the oxide layer.

(Comparative Example 3)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the carbon layer and the silver layer were formed on the oxide layer without forming the metal layer.

(Comparative Example 4)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the thickness of the oxide layer was 50 nm. The oxide layer formed with a film thickness of 50 nm is formed so as to cover the entire surface of the solid electrolyte layer.

(Comparative Example 5)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that aluminum having a standard electrode potential of −1.68 V was formed to a thickness of 100 nm as the metal layer.

(Comparative Example 7)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the oxide layer was formed from aluminum oxide having a thickness of 10 nm.

(Comparative Example 6)
A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the metal layer was formed on the solid electrolyte layer without forming the oxide layer, the carbon layer, and the silver layer.

[Measurement of ESR and capacitance]
About each said solid electrolytic capacitor, ESR in frequency 100kHz and the electrostatic capacitance (Cp) in frequency 120Hz were measured with the LCR meter. The measurement results are shown in Table 1.

  The values of ESR and capacitance (Cp) shown in Table 1 are indices with the ESR value and Cp value of Comparative Example 1 as 100.

  As shown in Table 1, it can be seen that the solid electrolytic capacitors of Examples 1 to 8 according to the present invention have lower ESR than the solid electrolytic capacitor of Comparative Example 1 in which no oxide layer and metal layer are provided. .

  As is clear from Examples 1 to 4, the ESR reduction effect is recognized in the range where the thickness of the oxide layer is 1 nm to 20 nm. In such a film thickness range, the oxide layer is formed so as to partially cover the surface of the solid electrolyte layer.

  On the other hand, in Comparative Example 4 in which the thickness of the oxide layer is 50 nm, the effect of reducing ESR is not recognized. By forming the oxide with a thickness of 50 nm, the oxide layer covers the entire surface of the solid electrolyte layer. For this reason, there is no region where the metal layer is in contact with the solid electrolyte layer, and the contact resistance between the solid electrolyte layer and the cathode layer is increased, so it is considered that the ESR is increased.

  As shown in Example 5, even when gold is used for the metal layer, the effect of reducing ESR is obtained.

  In addition, as shown in Examples 6 and 7, even when tungsten oxide or vanadium oxide is formed as the oxide layer, the effect of reducing ESR is obtained.

  Moreover, as shown in Example 8, the effect of reducing ESR is also obtained when a silver layer is formed directly on a metal layer without forming a carbon layer.

  As is clear from Comparative Example 2, when the metal layer is formed without forming the oxide layer, the effect of reducing the ESR is not obtained.

  As is clear from Comparative Example 3, the effect of reducing ESR is not obtained even when only the oxide layer is formed without forming the metal layer.

  This is compared to the example in which an ohmic junction is formed between the metal layer and the oxide layer (particularly, the example 4 having the same oxide layer thickness as that in the comparative example 3). Since the carbon layer is formed directly on the layer by the carbon paste, it is considered that a good ohmic junction was not formed and the contact resistance could not be reduced.

  As is clear from Comparative Example 5, even when aluminum is formed as a metal layer having a standard electrode potential of less than 0 V, the effect of reducing ESR is not obtained.

  As is clear from Comparative Example 6, when the oxide layer, the carbon layer, and the silver layer are not formed, the effect of reducing the ESR is not obtained.

Example 9
Solid electrolysis was performed in the same manner as in Example 1 except that poly (3,4-ethylenedioxythiophene) (PEDOT) was formed by a chemical heavy method and an electropolymerization method instead of polypyrrole (Ppy) as the solid electrolyte layer. A capacitor was produced.

(Comparative Example 8)
A solid electrolytic capacitor was produced in the same manner as in Example 9 except that the carbon layer and the silver layer were formed on the solid electrolyte layer without forming the oxide layer and the metal layer.

[Measurement of ESR and capacitance]
In the same manner as above, the ESR and capacitance of the solid electrolytic capacitors of Example 9 and Comparative Example 7 were measured, and the measurement results are shown in Table 2.

  The ESR and Cp values shown in Table 2 are indices with the ESR value and Cp value of Comparative Example 7 as 100.

  As shown in Table 2, even when the solid electrolyte is formed from PEDOT, it can be seen that ESR can be reduced by providing the oxide layer and the metal layer according to the present invention.

  In Example 7 using vanadium oxide having a relative dielectric constant of about 12 as the oxide layer, the ESR reduction rate is about 4%. In Example 4 in which molybdenum oxide having a relative dielectric constant of about 39 was used as the oxide layer, the ESR reduction rate was about 15%. In Example 6 in which tungsten oxide having a relative dielectric constant of about 41 was used as the oxide layer, the ESR reduction rate was about 10%. On the other hand, in Comparative Example 7 in which the oxide layer was formed using aluminum oxide having a relative dielectric constant of about 9, ESR was increased, and the effect of reducing ESR was not recognized. From these, it can be seen that the relative dielectric constant of the material forming the oxide layer is preferably 10 or more.

(Measurement of leakage current)
About the solid electrolytic capacitor of each said Example and each comparative example, the leakage current was measured. As the leakage current, 2.5 V was applied and the current after 20 seconds was measured. In either case, the current value only changed in the range of 5%, and there was no significant difference in the leakage current between the example and the comparative example.

DESCRIPTION OF SYMBOLS 1 ... Anode lead 2 ... Anode 3 ... Dielectric layer 4 ... Solid electrolyte layer 5a ... Oxide layer 5b ... Metal layer 5c ... Carbon layer 5d ... Silver layer 6 ... Cathode layer 7 ... Conductive adhesive layer 8 ... Anode terminal 9 ... Cathode terminal 10 ... Mold exterior resin

Claims (4)

An anode, a dielectric layer provided on the surface of the anode, a solid electrolyte layer provided on the dielectric layer, and a cathode layer provided on the solid electrolyte layer,
The cathode layer has an oxide layer made of an oxide of a valve action metal, and a metal layer made of a metal having a standard electrode potential of 0 V or more or an alloy of the metal,
The solid electrolytic capacitor, wherein the oxide layer is partially formed between the solid electrolyte layer and the metal layer.   The solid electrolytic capacitor according to claim 1, wherein a relative dielectric constant of a material forming the oxide layer is 10 or more.   3. The solid electrolytic capacitor according to claim 1, wherein the oxide layer is formed of an oxide of at least one metal selected from the group consisting of molybdenum, tungsten, and vanadium. The said solid electrolyte layer is formed from at least 1 sort (s) chosen from the group which consists of a polyethylenedioxythiophene and its derivative (s), and a polypyrrole and its derivative (s), The any one of Claims 1-3 characterized by the above-mentioned. Solid electrolytic capacitor.

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