JP4973229B2 - Electrolytic capacitor and manufacturing method thereof - Google Patents

Description

  The present invention generally relates to an electrolytic capacitor, and more particularly to an electrolytic capacitor having an increased capacitance and a method for manufacturing the same.

  An electrolytic capacitor uses an oxide film formed by anodic oxidation on an anode made of metal, for example, aluminum, as a dielectric, contacts an electrolytic solution constituting the cathode, and an apparent cathode made of aluminum or the like in contact with the electrolytic solution. Is a large-capacitance capacitor having a configuration in which is contacted as an extraction electrode, and is widely used in various electronic devices.

The electrolytic solution is generally used in the form of impregnated electrolytic paper, but recently, an electrolytic polymer film is often used instead of electrolytic paper.
Patent No. 3040113 Nikkei Electronics June 5, 2006 issue p. 132-137

  In order to increase the capacitance of the electrolytic capacitor, conventionally, the surface of the anode is electrochemically etched in an aqueous chloride solution to form irregularities to increase the surface area of the anode. In that case, the oxide film constituting the capacitor dielectric film is formed on the surface of the anode on which the irregularities are formed, in a shape consistent with the irregularities and with a substantially constant film thickness.

  On the other hand, when the metal constituting the anode is aluminum, the oxide film to be formed has a relative dielectric constant of only about 7 to 10, so that even if the surface area is increased by forming irregularities on the anode surface, the obtained electrostatic capacitance can be obtained. Capacity is limited.

According to one aspect, the present invention is an electrolytic capacitor comprising a metal substrate constituting an anode, a dielectric film formed on the anode, a cathode made of an electrolyte medium and in contact with the dielectric film. The dielectric film is made of an oxide film of a metal element constituting the metal substrate, and the dielectric film is an oxide, nitride or carbide containing a metal element other than the metal element constituting the metal substrate. The oxide film is formed on the metal substrate, and the particles made of an oxide, nitride, or carbide containing a metal element other than the metal element constituting the metal substrate are formed on the oxide film. The surface of the metal substrate is uneven, the dielectric film has a shape that matches the unevenness, and more particles are present in the vicinity of the top than in the vicinity of the bottom of the unevenness in the previous item. exist To provide an electrolytic capacitor, characterized by and.

According to another aspect, the present invention provides a step of forming irregularities on the surface of a metal substrate that constitutes an anode, and then a metal constituting the metal substrate by an aerosol deposition method on the surface of the metal substrate on which the irregularities are formed. Depositing particles comprising an oxide, nitride or carbide containing a metal element other than the element, and then anodizing the surface of the metal substrate on which the irregularities have been formed after the particle deposition step, Forming a composite dielectric film made of an oxide of a constituent metal element and supporting the particles, and depositing the particles in a region near the top rather than a region near the bottom of the irregularities. be performed as many present, the step of forming the composite dielectric film, and wherein the thickness of said composite dielectric layer is performed such that 100nm with flat surface surface in terms To provide a method of manufacturing that the electrolytic capacitor.

  According to the present invention, the high dielectric particles are formed on the metal substrate constituting the anode of the electrolytic capacitor by the aerosol deposition method, and then the metal substrate is anodized to constitute the capacitor insulating film of the electrolytic capacitor. The dielectric film can be a composite film with high dielectric particles, and the capacitance of the electrolytic capacitor can be increased.

  FIG. 1 shows a schematic configuration of an electrolytic capacitor 10 according to an embodiment of the present invention.

  Referring to FIG. 1, an electrolytic capacitor 10 is typically composed of an Al foil, a Ta foil, a Ti foil, and a metal foil 11A that constitutes an anode, and a metal foil 11B that, for example, comprises an Al foil and constitutes an apparent cathode. Are separated with separators 11C made of electrolytic paper, electrolyte polymer membranes, etc. constituting the cathode and wound together, and the lead electrode 12A is connected to the metal foil 11A. A lead electrode 12B is provided in connection with the metal foil 11B.

  As the metal foil 11A, Ta or Ti that can be anodized can be used in addition to Al.

  In the following description, the anode 11A is made of Al foil, but may be made of Ta foil, Ti foil, or the like.

  FIG. 2 shows an enlarged part of such an electrolytic capacitor 10.

  Referring to FIG. 2, an uneven pattern is formed by etching on the surfaces of the metal foils 11A and 11B sandwiching the separator 11C, so that the substantial surface area of the metal hacks 11A and 11B is reduced. The number is increased several tens of times when the structure is not formed.

  Furthermore, an aluminum oxide film 11a having a thickness of 0.1 μm or less is uniformly formed on the surface of the metal foil 11A by anodizing, that is, in a shape matched with the concavo-convex structure of the surface. The electrolytic solution impregnated in the separator 11C is in contact with the aluminum film 11a as a cathode. Examples of the electrolytic solution include, but are not limited to, ammonium borate, phosphoric acid, adipic acid, oxalic acid, sulfuric acid, sebacic acid, or ammonium salts thereof. The film thickness of the aluminum oxide film 11a is substantially proportional to the formation voltage during the anodic oxidation process, and a film having a film thickness of 0.0013 to 0.0015 μm per 1 V formation voltage is formed.

In the present embodiment, the aluminum oxide film 11a is made of a high-dielectric material typically having a perovskite structure such as anodized aluminum and BaTiO ₃ , SrTiO ₃ , or (Ba, Sr) TiO ₃ . It is formed as a composite with flat ceramic particles 11b having a particle size of about 5 to 500 nm.

  FIG. 3 shows the relative dielectric constant of the dielectric film 11a made of anodized aluminum in which high dielectric ceramic particles having various relative dielectric constants are combined at various ratios. In FIG. 3, the horizontal axis represents the volume fraction of the high dielectric particles in the dielectric film 11a based on anodized aluminum, and the parameter in the graph represents the relative dielectric constant of the high dielectric particles to be blended. Indicates.

  Referring to FIG. 3, it can be seen that the capacitance of the electrolytic capacitor can be greatly increased by combining high dielectric particles in the anodic oxide film 11a.

  2 will be described with reference to FIGS. 4A to 4C.

First, in the process of FIG. 4A, the aluminum foil 11A constituting the anode is heat-treated in an inert gas at a temperature of 300 ° C. Further, the heat-treated aluminum foil is subjected to an aqueous solution of nitric acid and AlCl ₃ . An alternating current is applied for 8 minutes at a current density of 0.2 A / m ² , and a surface roughening treatment is performed for 8 minutes. As a result, as shown in FIG. 4A, irregularities having a depth of, for example, 10 to 100 μm are formed on the aluminum foil 11A at a pitch of, for example, about 0.5 to 2 μm.

Next, in the process of FIG. 4 (B), using the aerosol deposition apparatus 60 shown in FIG. 5, high dielectric ceramic particles, for example, BaTiO ₃ particles 11b are applied to the surface of the aluminum foil 11A on which the irregularities shown in FIG. 4 (A) are formed. Flat BaTiO ₃ particles sprayed at high speed and plastically deformed by impact activation are deposited substantially parallel to the uneven surface of the aluminum foil 11A.

Although a description of the high dielectric ceramic particles 11b as a BaTiO ₃ in the following, the high dielectric ceramic particles 11b are not limited to BaTiO _3, SrTiO ₃ and BaSrTiO _3, further PZT or PLZT Typically, it may be a high dielectric material having a perovskite structure.

  FIG. 5 shows a schematic configuration of an aerosol deposition apparatus 60 used in the process of FIG.

  Referring to FIG. 5, the aerosol deposition apparatus 60 includes a processing container 61 that is evacuated by a mechanical booster pump 62 and a vacuum pump 62A. In the processing container 61, a substrate to be processed is placed on a stage 61A. W is held by the XY stage drive mechanism 61a and the Z stage drive mechanism 61b so that it can be driven in the XYZ-θ direction.

  A nozzle 61B is provided in the processing container 61 so as to face the substrate W to be processed on the stage 61A, and the nozzle 61B is supplied with an aerosol of a high dielectric ceramic material together with a dry carrier gas. A jet 61c is sprayed on the surface of the substrate W to be processed. That is, the jet 61c does not contain a liquid such as a solvent.

  The high dielectric ceramic particles constituting the aerosol sprayed in this manner have a particle size of about 10 to 100,000 nm, and are solidified by impact on the surface of the substrate W to be processed, resulting in plastic deformation. Flat high dielectric particles are deposited on the substrate W to be processed.

  In order to supply the aerosol to the nozzle 61B, the aerosol deposition apparatus 60 of FIG. 4 has a raw material container 63 holding a high dielectric powder raw material having an average particle size of about 10 to 100,000 nm, preferably about 0.5 μm or less. The carrier vessel 63 is supplied with a carrier gas such as an inert gas or high-purity oxygen from a high-pressure gas source 64 via a mass flow controller 64A. The raw material container 63 is held on a vibration table 63A to promote the generation of aerosol, and the water in the raw material is removed by the pumps 62 and 62A by opening the valve 63B prior to the generation of the aerosol.

In one example, BaTiO ₃ powder having an average particle size of 0.5 μm is held in the processing container, and the raw material container 63 is heated to a temperature of about 150 ° C. with the valve 63B open, The vacuum pumps 62 and 62A are driven while applying sound waves, and moisture is removed from the raw material powder for about 30 minutes.

Further, the valve 63B is closed, the inside of the processing vessel 61 is depressurized to a pressure of 10 Pa or less, and high-purity oxygen gas is supplied to the raw material vessel 63 from the high-pressure gas source 64 through a mass flow controller 64A. BaTiO ₃ aerosol is formed in the raw material container 63 and sprayed from the nozzle 61B to the substrate W to be processed. In this embodiment, this injection is performed for 20 seconds, and the pressure of the processing container 61 is maintained at 200 Pa during that time. By such an aerosol deposition method, a high dielectric film made of the BaTiO ₃ particles 11b is formed on the aluminum foil 11A to a thickness of about 100 nm in terms of a flat surface.

Referring to FIG. 4B again, as described above, the aluminum foil 11A has irregularities formed by chemical conversion treatment in the process of FIG. 4A. When the high dielectric particles 11b such as BaTiO ₃ are deposited in the position device 60, the high dielectric particles 11b are mostly deposited on the convex portions of the aluminum foil 11A, and few of them penetrate into the concave portions. That is, in the structure of FIG. 4B, metal Al is mainly exposed in the recesses of the aluminum foil 11A. Also in the convex portion, there is a gap between the high dielectric particles 11b into which the electrolytic solution used for the chemical conversion treatment enters.

  Therefore, in the step of FIG. 4C, the aluminum foil 11A is anodized, and the anodized aluminum film 11a is grown on the structure of FIG. 4B.

  More specifically, the structure shown in FIG. 4B is immersed in an electrolytic solution made of ammonium borate, phosphoric acid, adipic acid, oxalic acid, sulfuric acid, sebacic acid, or an ammonium salt thereof, and anodized at 5V. Executed. However, as described above, the applied voltage at the time of anodizing is set in accordance with the desired film thickness of the anodized aluminum film 11a.

As a result, the anodized aluminum film 11a grows from the surface of the aluminum foil 11A to the inside of the aluminum foil 11A, and the anodized aluminum film 11a as shown in FIG. 4C contains BaTiO ₃ particles. A composite dielectric film configured to carry is formed. At that time, the high dielectric particles such as BaTiO ₃ particles are in close contact with the underlying aluminum foil 11A by impact activation or by physical bite, and the surface of the aluminum foil 11A is anodized. Even if it is processed, strong adhesion to the aluminum foil 11A is maintained.

  Since the high dielectric ceramic particles 11b formed by the aerosol deposition method are crystalline, they have a large relative dielectric constant. In the electrolytic capacitor 10 shown in FIG. 1, the aluminum shown in FIG. By using the foil 11A as an anode, an electrolytic capacitor having a large capacitance can be obtained.

Table 1 below shows the leakage current and capacitance of the electrolytic capacitor of the present invention obtained in this way when BaTiO ₃ is used as the high dielectric particles, TiO ₂ is used, and BaSrTiO ₃ is used. In the case of using a conventional electrolytic capacitor in which high dielectric particles are not formed on the aluminum foil constituting the anode 11A, and a BaTiO ₃ film as a dielectric film on the anode 11A is sputtered. It is shown in comparison with the case where it is formed by the sol-gel method. However, the BaTiO ₃ film formed by the sputtering method and the sol-gel method is in an amorphous phase.

表１に示す実験では、電解質として導電性高分子膜ポリエチレンジオキシチオフェン（ＰＥＤＴ）を使っており、陰極１１Ｂは、前記陽極１１Ａと同様な凹凸処理を施したアルミ箔により構成している。なお図４（Ａ）〜（Ｃ）の工程以降の電解コンデンサの製造工程は、標準的な工程を使っており、説明を省略する。

In the experiment shown in Table 1, a conductive polymer film polyethylene dioxythiophene (PEDT) is used as an electrolyte, and the cathode 11B is made of an aluminum foil that has been subjected to the same uneven treatment as the anode 11A. In addition, the manufacturing process of the electrolytic capacitor after the process of FIG. 4 (A)-(C) uses the standard process, and abbreviate | omits description.

Referring to Table 1, the leakage current was measured 30 minutes after the voltage generated at both ends of the electrolytic capacitor reached 20 V. In the case of the conventional example, the leakage current was 1.9 μA / 5 cm ^2. It can be seen that the electrolytic capacitor of the present invention is reduced to 0.9 to 1.0 μA / 5 cm ² . Further, it can be seen that when the BaTiO ₃ film is formed by sputtering or sol-gel method, the leakage current deteriorates to 2.6 to 3 μA / 5 cm ² under the same conditions.

In terms of the capacitance, in the present invention, the high dielectric particle 11b is about 90 to 120 μF / 0.1 cm ² regardless of whether BaTiO ₃ is used, TiO ₂ is used, or BaSrTiO ₃ is used. It can be seen that a substantially large relative dielectric constant is realized with respect to the capacitance of 80 μF / 0.1 cm ² of the electrolytic capacitor of the conventional configuration. On the other hand, when the BaTiO ₃ film is formed by the sputtering method or the CVD method, the capacitance is 40 to 60 μF / 0.1 cm ² , and it is understood that the capacitance is deteriorated as compared with the conventional configuration.

  As described above, according to the present invention, the high dielectric particles are formed on the metal substrate constituting the anode of the electrolytic capacitor by the aerosol deposition method, and then the metal substrate is anodized to obtain the capacitor insulating film of the electrolytic capacitor. Can be a composite film with high dielectric particles, and the capacitance of the electrolytic capacitor can be increased.

  As described above, in the present invention, the anode 11A is not limited to the aluminum foil, and other materials such as Ta foil and Ti foil can be used as long as they can be anodized.

The high dielectric particles 11b are not limited to BaTiO ₃ , SrTiO ₃ , and BaSrTiO ₃ , and other high dielectric materials having a perovskite structure such as PZT and PLZT can be used.

  Further, the aerosol deposition conditions for volumetric high dielectric particles 11b are not limited to the conditions described above, and the flat high dielectric particles are made in close contact with the concavo-convex formed anode by impact activation. Other conditions may be used as long as they can be formed by the composition and the compositional deformation accompanying this.

  As mentioned above, although this invention was described about preferable embodiment, this invention is not limited to this specific embodiment, A various deformation | transformation and change are possible within the summary described in the claim.

It is a figure which shows the structure of the electrolytic capacitor by one Embodiment of this invention. It is a figure which expands and shows the principal part of the electrolytic capacitor of FIG. It is a figure which shows the dielectric constant of the dielectric film in the electrolytic capacitor of FIG. 1 about the ratio of the high dielectric ceramic particle | grains deposited on an anode by the aerosol deposition method. (A)-(C) are figures which show a part of manufacturing process of the electrolytic capacitor of the said FIG. It is a figure which shows the structure of the aerosol deposition apparatus used by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Electrolytic capacitor 11A Anode 11a Anodized film 11b High dielectric ceramic particle 11B Cathode 11C Separator 12A, 12B Lead electrode 61 Processing container 61A Stage 61B Nozzle 61a XY stage drive mechanism 61b Z stage drive mechanism 61c Jet 62 Mechanical booster pump 63 Raw material container 63A Shaking table 63B Valve 64 High pressure gas source

Claims (5)

A metal substrate constituting the anode;
A dielectric film formed on the anode;
A cathode made of an electrolyte medium and in contact with the dielectric film;
An electrolytic capacitor comprising:
The dielectric film is made of an oxide film of a metal element constituting the metal substrate,
Furthermore, the dielectric film includes particles made of an oxide, nitride, or carbide containing a metal element other than the metal element constituting the metal substrate,
The oxide film is formed on the metal substrate;
Particles made of an oxide, nitride or carbide containing a metal element other than the metal element constituting the metal substrate are formed on the oxide film ,
Concavities and convexities are formed on the surface of the metal substrate, the dielectric film has a shape matched to the concavities and convexities, and the particles are present more in the vicinity of the top than in the vicinity of the bottom of the unevenness in the previous item. Electrolytic capacitor.   The electrolytic capacitor according to claim 1, wherein the particles have a flat shape.   3. The electrolytic capacitor according to claim 1, wherein the particles are high dielectric particles having a perovskite structure.   4. The electrolytic capacitor according to claim 1, wherein the particles include at least one of barium titanate, strontium titanate, titanium oxide, PZT, and PLZT. 5. Forming irregularities on the surface of the metal substrate constituting the anode;
Next, depositing particles made of an oxide, nitride, or carbide containing a metal element other than the metal element constituting the metal substrate by an aerosol deposition method on the surface of the metal substrate on which the irregularities are formed;
Next, the surface of the metal substrate on which the irregularities are formed is anodized after the step of depositing the particles to form a composite dielectric film made of an oxide of a metal element constituting the metal substrate and supporting the particles; ,
Including
The step of depositing the particles is performed such that the particles are present in a region near the top rather than a region near the bottom of the unevenness,
The method of manufacturing an electrolytic capacitor is characterized in that the step of forming the composite dielectric film is executed such that the thickness of the composite dielectric film is 100 nm in terms of a flat surface .

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