JP2006339680A - Solid electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor having good capacitance characteristics. <P>SOLUTION: In the solid electrolytic capacitor comprising a capacitor element where an anode electrode foil and a cathode electrode foil are wound through a separator and conductive polymer is held by the separator, the cathode electrode foil employs an etching foil where a chemical conversion film is formed on the surface and a metal carbide coating is formed thereon, or a plane foil where a chemical conversion film is formed on the surface and a metal carbide coating is formed thereon, and the conductive polymer and the cathode electrode foil are brought into conducting state thus attaining good capacitance and ESR characteristics. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a solid electrolytic capacitor, and more particularly to a solid electrolytic capacitor using a conductive polymer as an electrolyte.

  An electrolytic capacitor is made of a valve action metal such as tantalum or aluminum, and has a structure in which an oxide film layer serving as a dielectric is formed on the surface of an anode electrode having fine holes and etching pits, and an electrode is drawn from the oxide film layer. Become. And the extraction of the electrode from the oxide film layer is performed by the electrolyte layer having conductivity. Therefore, in the electrolytic capacitor, the electrolyte layer serves as a true cathode. Such an electrolyte layer functioning as a true cathode is required to have adhesion, denseness, and uniformity with the oxide film layer. In particular, the adhesion within the fine holes of the anode electrode and the etching pits has a great influence on the electrical characteristics, and a number of electrolyte layers have been proposed in the past.

  By the way, in recent years, with the digitization and high frequency of electronic equipment, a capacitor having a small size and a large capacity and a low impedance in a high frequency region is required.

In response to these requirements, a capacitor element in which a cathode foil and an anode foil are wound through a separator is housed in a metal case, and a small and large capacity is realized by a wound type electrolytic capacitor sealed with a sealing rubber. Can do. And it can respond to low impedance by using a solid electrolyte as an electrolyte. As such a solid electrolyte, conductive polymers having high conductivity such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex, polypyrrole, and polythiophene are known. Attention is now focused on polyethylenedioxythiophene (PEDT), which has a slow reaction rate and excellent adhesion to the oxide film layer of the anode electrode (see Patent Document 1), and as a result, the anode electrode foil and the cathode electrode Capacitor element wound with foil through a separator is impregnated with a monomer and an oxidant, and then polyethylenedioxythiophene, which is a solid electrolyte, is formed inside the capacitor element through a chemical polymerization reaction between the monomer and the oxidant that occurs slowly. (See Patent Document 2).
JP-A-2-15611 Japanese Patent Laid-Open No. 10-340829

  By the way, in recent years, electronic information devices have been digitized, and the driving frequency of the microprocessor which is the heart of these electronic information devices has been increased. Along with this, the power consumption has been increasing and the problem of reliability due to heat generation has become obvious. Therefore, the drive voltage has been reduced as a countermeasure.

  In order to reduce the drive voltage, a large number of capacitors having low ESR are used as output-side capacitors of a power supply that supplies highly accurate power to the microprocessor. As the capacitor having such a low ESR characteristic, the solid electrolytic capacitor as described above is used.

  However, the increase in the driving frequency of the microprocessor is remarkable, and accordingly, the power consumption further increases, and further increase in the power supplied from the capacitor is required. For this reason, the solid electrolytic capacitor is required to have a large capacity. ing.

  Therefore, an object of the present invention is to provide a solid electrolytic capacitor having a high capacitance in order to solve the above-described problems.

    The present invention forms a chemical conversion film on a surface as a cathode electrode foil in a solid electrolytic capacitor having a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator and a conductive polymer is held by the separator. Further, the conductive polymer and the cathode electrode using an etching foil having a metal carbide film formed thereon or a plain foil having a chemical film formed on the surface and a metal carbide film formed thereon. The foil is in a conductive state.

  The solid electrolytic capacitor of the present invention will be described. An anode electrode foil made of a valve action metal such as aluminum and having an oxide film layer formed on the surface thereof and a cathode electrode foil are wound through a separator to form a capacitor element. The conductive polymer is held in the separator of the capacitor element.

  The anode electrode foil is made of a valve action metal such as aluminum, and an oxide film layer serving as a dielectric is formed on the surface of the anode electrode foil by applying a voltage in an aqueous solution of ammonium adipate or the like. The cathode electrode foil is made of aluminum or the like like the anode electrode foil, and the surface is subjected to etching treatment.

  Anode extraction means and cathode extraction means for connecting the respective electrodes to the outside are connected to the anode electrode foil and the cathode electrode foil by known means such as stitching and ultrasonic welding. These electrode lead-out means are led out from the end face of the wound capacitor element.

  The capacitor element is formed by winding the anode electrode foil and the cathode electrode foil with a separator interposed therebetween. The dimensions of the bipolar electrode foil are arbitrary depending on the specifications of the solid electrolytic capacitor to be manufactured, and the separator having a slightly larger width may be used depending on the dimensions of the bipolar electrode foil.

  A conductive polymer is formed in this capacitor element. When polyethylenedioxythiophene (PEDT) is used as the conductive polymer, a solid electrolytic capacitor having a large capacity and low ESR characteristics can be obtained. This PEDT can be obtained by polymerizing 3,4-ethylenedioxythiophene (EDT) as a monomer with ferric p-toluenesulfonate as an oxidizing agent. Polymerization can be performed by injecting EDT or an EDT solution and an oxidant solution into a capacitor element and heating, or by injecting a mixed liquid of EDT and an oxidant into the capacitor element, or immersing the capacitor element in a mixed solution. It can also be performed by heating.

  Then, the capacitor element in which the conductive polymer is formed is housed in a bottomed cylindrical metal case, and is swaged and sealed with a sealing rubber to form a solid electrolytic capacitor.

  Here, in the present invention, as the cathode electrode foil, a chemical conversion film is formed on the surface, and an etching foil in which a film made of a metal carbide is further formed thereon, or a chemical conversion film is formed on the surface, and a metal is further formed thereon. A plain foil on which a film made of carbide is formed is used. As the metal carbide, TiC, WC, ZrC, HfC, VC, TaC, NbC or the like having a low specific electric resistance is preferable, and 1 mΩ · cm or less is preferable. The thickness of the metal carbide film is preferably 0.01 to 3 μm, more preferably 0.03 to 2 μm. If it is less than this range, the effect of reducing ESR is small. In addition, when a plain foil is used, the thickness of the foil can be reduced as much as there is no etching portion compared to the etching foil, and the capacitance can be increased by increasing the foil area.

  As a method for forming a film made of metal carbide on the formed etching foil or the formed plain foil, a vapor deposition method is preferable. Examples of the vapor deposition method include a vacuum vapor deposition method, an ion plating method, a sputtering method, an ion beam sputtering method, and an ion beam assisted vapor deposition method. Of these, the ion plating method is preferable, and the arc ion plating method (cathode arc plasma deposition method) is more preferable. The conditions of this arc plasma deposition method are that a predetermined metal is a target, a current value is 60 to 300 A, and a voltage value is 15 to 25 V. In the case of a metal carbide, the total pressure including carbon-based gas such as methane, ethane, propane, acetylene, etc. is performed in an atmosphere of 1 × 10 −1 to 1 × 10 −4 Torr. The use of the vapor deposition method as described above is preferable because the compound ratio of metal to carbon of the metal carbide can be set to a desired compound ratio by changing the vapor deposition conditions such as gas concentration.

  In the above solid electrolytic capacitor, since the specific electric resistance of the metal carbide formed on the surface of the chemical conversion film is low, the conductive polymer and the cathode electrode foil are in a conductive state, the combined capacitance of the capacitor is maximized, and the electrostatic capacitance Will increase. Further, since the adhesion between the metal carbide and the conductive polymer is good, ESR is reduced.

    The present invention forms a chemical conversion film on a surface as a cathode electrode foil in a solid electrolytic capacitor having a capacitor element in which an anode electrode foil and a cathode electrode foil are wound via a separator and a conductive polymer is held by the separator. Further, the conductive polymer and the cathode electrode using an etching foil having a metal carbide film formed thereon or a plain foil having a chemical film formed on the surface and a metal carbide film formed thereon. Since the foil is in a conductive state, the capacitance characteristics and the ESR characteristics are good.

Next, the solid electrolytic capacitor of the present invention will be specifically described.
The anode electrode foil and the cathode electrode foil are made of a valve metal, such as aluminum or tantalum, and the surface thereof is preliminarily etched to increase the surface area. The anode electrode foil is further subjected to chemical conversion treatment, and an oxide film layer made of aluminum oxide is formed on the surface. The anode electrode foil and the cathode electrode foil are wound through a separator to obtain a capacitor element.

  Next, the capacitor element is impregnated with EDT and an oxidizing agent. As the oxidizing agent, a butanol solution of ferric p-toluenesulfonate is used and polymerized by heating at 150 ° C. for 1 hour to produce PEDT which is a conductive polymer.

  The capacitor element in which the conductive polymer layer is formed on the separator interposed between the anode electrode foil and the cathode electrode foil in this way is housed in a bottomed cylindrical case and sealed with a sealing rubber made of butyl rubber. A solid electrolytic capacitor is formed. The rating is 2.5 WV-820 μF.

  Here, as Example 1, a 50 μm 2V chemical etching foil having a 0.3 μm titanium carbide film formed thereon was used as a cathode electrode foil. In Example 2, a 30 μm 2V chemical conversion plain foil on which a 0.3 μm titanium carbide film was formed was used as the cathode electrode foil.

  Further, as Comparative Example 1, a 50 μm etching foil formed with a 0.3 μm titanium nitride film was used, and as Comparative Example 2, a 50 μm 2V chemical conversion etching foil formed with a 0.3 μm titanium nitride film was used.

  Next, initial characteristics of these solid electrolytic capacitors are shown in (Table 1).

As described above, the example has better electrostatic capacity and ESR than the comparative example.

Claims (3)

In a solid electrolytic capacitor having a capacitor element in which an anode electrode foil and a cathode electrode foil are wound through a separator and a conductive polymer is held by the separator, a chemical conversion film is formed on the surface as the cathode electrode foil, An etching foil having a metal carbide film formed thereon, or a plain foil having a chemical film formed on the surface and a metal carbide film formed thereon, and the conductive polymer and the cathode electrode foil are in a conductive state. Solid electrolytic capacitor. 2. The solid electrolytic capacitor according to claim 1, wherein the metal carbide is TiC, WC, ZrC, HfC, VC, TaC, or NbC. The solid electrolytic capacitor according to claim 1, wherein the coating made of the metal carbide is formed by cathodic arc plasma deposition.