JP2008021761A - Bulb metal composite electrode foil and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrode foil for inexpensive electrolytic capacitor and its manufacturing method suitable for the manufacture of laminated solid state electrolytic capacitor, having a capacity density higher than that of etching aluminum foil, and further, having electrode resistance same as that of the etching aluminum foil and reduced in the using amount of Ta or Nb which is expensive rare metal. <P>SOLUTION: The precise layer (6) of Ta or Ta alloy is formed on the substrate (5) of aluminum foil or aluminum alloy foil. An alloy thin film is formed in which Ta and a constituent having different phase incompatible with Ta is distributed uniformly with a grain diameter of 1 nm-1 μm on the obtained precise layer (6). Then vacuum heat treatment is applied whereby the different phase constituent is molted and removed after the grain of the different phase constituent is regulated to form a porous layer (7) of Ta. In another case, Nb is employed instead of Ta. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrode foil and manufacturing method for a solid electrolytic capacitor.

  In recent years, along with miniaturization and high functionality of electronic devices, miniaturization, high integration, and high operating frequency of electronic circuits have been promoted. Similarly, passive components used in electronic circuits are also required to be smaller and have higher characteristics. For example, capacitors are also required to be as small, low profile, large capacity, and low impedance as possible. Yes.

As a capacitor having a large capacitance per volume, an electrolytic capacitor having a valve metal as an anode body and an anodic oxide film as a dielectric is widely used. For example, Al roughened by electrochemical etching. An Al electrolytic capacitor formed by anodizing a foil to form Al ₂ O ₃ , a Ta electrolytic capacitor formed by anodic oxidation of Ta porous pellets to form Ta ₂ O ₅ , and an anodizing of porous Nb pellets An Nb electrolytic capacitor in which Nb ₂ O ₅ is formed is mentioned. Among them, Ta ₂ O ₅ (dielectric constant 24-27) and Nb ₂ O ₅ (dielectric constant 41) have a higher dielectric constant than Al ₂ O ₃ (dielectric constant 7-10). Nb is more suitable than Al as a material for a small-capacity electrolytic capacitor.

  As shown in FIG. 5, a general Ta electrolytic capacitor or Nb electrolytic capacitor is manufactured by compacting and sintering Ta powder or Nb powder with a wire (2) made of Ta or Nb inserted. The made porous pellet (1) is used as an anode body. Porous pellets with a very large surface area can be obtained by using submicron Ta powder or Nb powder, but there is a limit to reducing the size and thickness of porous pellets from the manufacturing method, so the obtained Ta electrolytic capacitor Or, there is a limit to the reduction in size and height of the Nb electrolytic capacitor.

  On the other hand, for example, as disclosed in Patent Document 1 (US Pat. No. 3,889,357), Ta powder capacitors or Nb electrolytic capacitors have Ta powder or It has been attempted for some time to obtain a foil-like anode body by making Nb powder into a paste, applying it to Ta foil or Nb foil, and baking it. However, in this method, cracks are likely to occur in the sintered body due to sintering shrinkage. In addition, since the sintering of the powder is more likely to proceed than between the powder and the foil, sufficient adhesion at the interface between the sintered body and the foil cannot be obtained. The occurrence of cracks and insufficient adhesion as described above are not preferable because the sintered body is peeled off from the foil during handling in the capacitor manufacturing process or the leakage current characteristics are deteriorated.

  Moreover, in patent document 2 (Unexamined-Japanese-Patent No. 2006-49816), Ta and Nb and the heterophasic component which is not compatible with them are mixed, it forms into a film, and it heat-processes in a vacuum or inert gas After that, it is disclosed that a foil-like anode body having a porous layer made of Ta or Nb is produced by a method of selectively removing only the heterogeneous components. A cross-sectional view of the foil-like anode body manufactured in this way is shown in FIG. The obtained foil-like anode body is effective for further downsizing and lowering the capacitor. However, these foil-like anode bodies use rare metals such as Ta foil and Nb foil as the substrate (3) in addition to the porous layer (4), so compared to conventional compacted pellets, There is a problem that the amount of Ta and Nb used increases and the cost of the foil-like anode body increases.

  On the other hand, from the viewpoint of lowering the impedance of the electrolytic capacitor, it is effective to stack a plurality of thin solid electrolytic capacitor elements and electrically connect them. As a conventional multilayer solid electrolytic capacitor, for example, Patent Document 3 (Japanese Patent Laid-Open No. 11-135367) discloses a multilayer solid electrolytic capacitor obtained by stacking thin solid electrolytic capacitor elements. Although this method is effective for lowering the impedance of the capacitor, since an etched Al foil is used as the foil-like anode body, as described above, compared to a solid electrolytic capacitor made of Ta or Nb, There is a problem that the capacitance density per volume becomes low.

Further, as in the above-mentioned Patent Document 2 (Japanese Patent Laid-Open No. 2006-49816), using a thin solid electrolytic capacitor element using a foil-like anode body made of Ta or Nb is a static per volume. Although it is considered effective for improving the capacitance density, as described above, the amount of rare metals Ta and Nb increases, leading to an increase in the cost of the foil-like anode body. In order to reduce the impedance of the electrolytic capacitor, it is important to reduce the equivalent series resistance (ESR) of the capacitor, and it is desirable that the resistance of the foil-like anode body is as low as possible. However, since Ta and Nb have relatively high volume resistivity (Ta volume resistivity: 13.5 μΩcm, Nb volume resistivity: 14.5 μΩcm), the resistance of the foil-like anode body made of Ta or Nb is: There is also a problem that it becomes larger than the etched Al foil (volume resistivity of Al: 2.7 μΩcm).
U.S. Pat. No. 3,889,357 JP 2006-49816 A JP-A-11-135367

  The present invention has been made in order to solve such problems, and is suitable for the production of a multilayer solid electrolytic capacitor, has a higher capacity density than an etched Al foil, and has an equivalent electrode resistance, It is another object of the present invention to provide a low-cost electrode foil for electrolytic capacitors and a method for manufacturing the same, in which the amount of expensive rare metals Ta and Nb is reduced.

  The valve metal composite electrode foil of the present invention comprises an Al foil or an Al alloy foil as a base material, a dense layer of Ta or Ta alloy formed on one or both surfaces of the base material, and formed on the dense layer, It has a laminated structure composed of a Ta or Ta alloy porous layer, and the porous layer has a surface area that is twice or more the apparent area.

  Alternatively, an Al foil or Al alloy foil is used as a base material, a dense layer of Nb or Nb alloy formed on one or both sides of the base material, and a porous layer of Nb or Nb alloy formed on the dense layer The porous layer has a surface area that is at least twice as large as the apparent area.

  It is preferable to provide a barrier layer that is thermodynamically stable against Ta, Ta alloy, Nb, Nb alloy, Al, and Al alloy between the base material and the dense layer.

  The barrier layer is preferably any one selected from TiN, ZrN, and HfN.

  The thickness of the substrate is preferably 100 μm or less.

  Furthermore, the porosity of the porous layer is preferably in the range of 30 to 70%.

  The method for producing a valve metal composite electrode foil of the present invention comprises forming a Ta or Ta alloy dense layer on an Al foil or Al alloy foil base material, Ta or Ta alloy on the obtained dense layer, and After forming the alloy thin film in which the heterogeneous component incompatible with Ta is uniformly distributed with a particle diameter of 1 nm to 1 μm and subjecting the Ta or Ta alloy and the heterogeneous component to grain adjustment by vacuum heat treatment, It is characterized by dissolving and removing heterogeneous components.

  Alternatively, a dense layer of Nb or Nb alloy is formed on the base material of Al foil or Al alloy foil, and Nb or Nb alloy and a different phase component incompatible with Nb are formed on the obtained dense layer. An alloy thin film having a diameter of 1 nm to 1 μm that is uniformly distributed is formed, and vacuum heat treatment is performed to adjust Nb or Nb alloy and the heterogeneous component, and then dissolve and remove the heterogenous component. .

  It is preferable to form a thermodynamically stable barrier layer with respect to Ta, Ta alloy, Nb, Nb alloy, Al and Al alloy between the base material and the dense layer.

  The barrier layer is preferably any one selected from TiN, ZrN, and HfN. Further, the barrier layer is preferably formed by reactive sputtering or reactive vapor deposition in which nitrogen gas is introduced.

  The amount of the heterogeneous component added to the alloy thin film is preferably in the range of 30 to 70% by volume. Moreover, it is preferable to use a sputtering method or a vacuum evaporation method for forming the alloy thin film.

  The heterogeneous component is preferably Cu or Ag. Alternatively, the heterogeneous component is preferably Mg, Ca, or an oxide thereof.

  The solid electrolytic capacitor of the present invention is characterized in that a valve metal composite electrode foil according to the present invention is subjected to constant voltage conversion treatment as an anode body.

  Since the valve metal composite electrode foil of the present invention uses Ta, Ta alloy, Nb or Nb alloy for the porous layer, the capacitance density per volume is larger than the etching Al foil. In addition, since Al or Al alloy is used as the base material, the electrode resistance can be lowered compared with the electrode foil of Ta alone or Nb alone, which is advantageous in reducing the equivalent series resistance of the electrolytic capacitor. Furthermore, since the usage amount of rare metals Ta and Nb can be reduced, the cost of the electrode foil can be reduced as compared with the electrode foil made of Ta alone or Nb alone.

  From the above, the valve metal composite electrode foil of the present invention can be suitably used as a cathode and an anode foil of an electrolytic capacitor. It is also suitable as an anode foil for thin solid electrolytic capacitors and multilayer solid electrolytic capacitors.

  For manufacturing a small, thin, and large-capacity capacitor, an electrode foil made of Ta or Nb is more advantageous than an etched Al foil because of the difference in dielectric constant. On the other hand, in order to reduce the equivalent series resistance of the capacitor, it is advantageous to use a metal having a volume resistivity lower than that of Ta or Nb as the base material of the electrode foil. By using such a metal, a rare metal is used. Since the amount of Ta and Nb used can be reduced, the electrode foil can be manufactured at a lower cost.

  The inventors of the present invention have made extensive studies based on such knowledge, and have Ta or Nb porous on an Al foil base material having a volume resistivity several times smaller than Ta and Nb and low cost. A method for forming the layer was found. As a result, it has been found that a composite electrode foil of a valve metal having a higher capacity density than conventional etching Al foil, a lower electrode resistance than an electrode foil made of Ta alone or Nb alone, and an inexpensive valve metal can be obtained. The present invention has been completed.

  In FIG. 1, the one aspect | mode of the valve metal composite electrode foil of this invention is shown with sectional drawing. The valve metal composite electrode foil of this aspect has a laminated structure comprising a dense layer (6) of Ta or Ta alloy and a porous layer (7) of Ta or Ta alloy formed on the dense layer (6). This laminated structure is formed on one side or both sides of the Al foil or Al alloy foil substrate (5), and the porous layer (7) has a surface area that is twice or more the apparent area.

  In FIG. 2, the different aspect of the valve | bulb metal composite electrode foil of this invention is shown with sectional drawing. The valve metal composite electrode foil of this embodiment is formed on a barrier layer (8) thermodynamically stable against Ta, Ta alloy, Al and Al alloy, and on the barrier layer (8). The layered structure (6) and a layered structure formed on the layer (6) and made of Ta or a Ta alloy porous layer (7) have an Al foil or Al alloy foil. The porous layer (7) is formed on one side or both sides of the substrate (5) and has a surface area that is twice or more the apparent area.

  In any embodiment, Nb or Nb alloy can be used instead of Ta or Ta alloy.

  The thickness of the base material of the valve metal composite electrode foil of the present invention is preferably 100 μm or less. This is because the electrostatic capacity per apparent area of the electrode foil increases in proportion to the thickness of the porous layer, so that the thinner the base material and the thicker the porous layer, the electrostatic capacity per apparent area. This is based on the reason that an electrode foil having a large capacity can be obtained. When the thickness of the base material exceeds 100 μm, it is not preferable because the superiority of the capacitance density is reduced with respect to the conventional etching Al foil.

  The “apparent area” in this specification refers to the area of the electrode foil on the assumption that the surface of the electrode foil is not uneven, and is substantially equal to the surface area of the substrate. When the porous layer is formed on one side, the apparent area on one side is the standard, and when it is formed on both sides, the apparent area on both sides is the standard.

  The porous layer of the valve metal composite electrode foil of the present invention preferably has a porosity in the range of 30 to 70%. As an electrode foil of an electrolytic capacitor, the porous layer needs to have sufficient strength and surface area. When the porosity is less than 30%, the strength of the porous layer is sufficient, but when the surface area per apparent area becomes small, the residual of different phase components in the porous layer increases, or when an electrolytic capacitor is formed. It becomes difficult to impregnate the cathode. On the other hand, if the porosity exceeds 70%, a sufficient strength of the porous layer cannot be obtained, and the porous structure is easily broken, which is not preferable.

  Next, the manufacturing method of the valve metal composite electrode foil of this invention is demonstrated in detail for every process divided | segmented as follows.

  The method for producing a valve metal composite electrode foil of the present invention includes: [1] a first step of forming a dense layer of Ta or Ta alloy on a base material of an Al foil or an Al alloy foil, and [2] the obtained dense layer. On top of this, a second step of forming an alloy thin film in which Ta or Ta alloy and a different phase component incompatible with Ta are uniformly distributed with a particle diameter of 1 nm to 1 μm, [3] By performing vacuum heat treatment, Or it consists of a Ta alloy and a third step for grain growth of the different phase component, and [4] a fourth step for selectively dissolving and removing the different phase component. Alternatively, Nb or Nb alloy can be used instead of Ta or Ta alloy.

Note that Ta alloys and Nb alloys include valve metals such as Zr, Ti, Hf, and Al that improve the leakage current and thermal stability of Ta ₂ O ₅ and Nb ₂ O ₅ films that serve as dielectrics for electrolytic capacitors. And a material containing a trace amount of a dopant such as P, N or B.

[1] First step of forming a dense layer of Ta or Ta alloy (Nb or Nb alloy) on a substrate of Al foil or Al alloy foil:
The dense layer serves as a bonding layer between the porous layer and the substrate, and also serves to prevent alloying between a heterogeneous component, which will be described later, and an Al foil or an Al alloy foil. Without providing a dense layer, for example, when Cu or Ag is used as a heterogeneous component and an alloy film is directly formed on an Al foil or an Al alloy foil and heat treatment is performed, Cu or Ag is directly applied to the substrate. Since it is in contact with the Al foil or Al alloy foil, a reaction product is formed during the subsequent vacuum heat treatment, making it difficult to remove, and a porous layer cannot be obtained, or many different phase components remain in the porous layer. As a result, the capacitor characteristics are affected.

  Even if a dense layer is formed, depending on the quality and thickness of the dense layer and the heat treatment temperature, interdiffusion of Al and heterogeneous components occurs during the subsequent vacuum heat treatment, resulting in the formation of a compound. There is. For this, a barrier layer that is thermodynamically stable against Ta, Ta alloy, Al and Al alloy, or Nb, Nb alloy, Al, and Al alloy on Al foil or Al alloy foil. Form. The resulting barrier layer is less likely to react with Ta, Ta alloy, Al and Al alloy, or Nb, Nb alloy, Al and Al alloy during vacuum heat treatment. Can be prevented. As the barrier layer, TiN, ZrN or HfN is preferably used. These are preferable because they are thermodynamically stable and have a relatively high conductivity such that the volume resistivity is several hundred μΩcm. The barrier layer is preferably as dense as possible from the viewpoint of the barrier effect. Further, from the viewpoint of suppressing the increase in electrode resistance as much as possible, it is preferable that the barrier layer having a relatively high resistivity is thinner. As described above, the dense and thin barrier layer is preferably formed by reactive sputtering or reactive vapor deposition in which nitrogen gas is introduced. As the barrier layer, other nitrides such as Ta nitride and Nb nitride can be used.

[2] On the obtained dense layer, Ta or Ta alloy (Nb or Nb alloy) and an alloy thin film in which a different phase component incompatible with Ta (Nb) is uniformly distributed with a particle diameter of 1 nm to 1 μm Second step of film formation:
Ta or Ta alloy, and heterogeneous component not compatible with Ta, or Nb or Nb alloy, and heterophasic component not compatible with Nb are not in the range of 1 nm to 1 μm in particle diameter, or the distribution is not uniform. If so, the particle size and pore distribution of the finally obtained porous layer become non-uniform, leading to deterioration of the characteristics of the electrolytic capacitor. The uniformity of the particle diameter range and distribution can be easily confirmed with a scanning electron microscope or the like when the particle diameter is 100 nm or more. Even when the particle diameter is as fine as 100 nm or less, it can be confirmed with a transmission electron microscope.

  The addition amount of the heterophasic component is determined by the volume fraction and is preferably in the range of 30 to 70% by volume. The porous layer of the valve metal composite electrode foil of the present invention can be obtained by finally removing the heterogeneous component. In order to completely remove the heterogeneous component, it is necessary that the heterophasic component is completely connected. However, when the added amount of the heterophasic component is less than 30% by volume, the heterophasic component is completely eliminated. However, it becomes difficult to remove, and it remains in the porous layer, and the surface area per apparent area becomes small, or impregnation with the cathode when forming an electrolytic capacitor becomes difficult. If the added amount of the heterogeneous component is determined by volume fraction and exceeds 70% by volume, after removing the heterophasic component, the bonding strength of the particles is weak or the particles are not completely connected and the porous structure is maintained. become unable. However, the range of the added amount of the heterophasic component is a guide and does not absolutely limit the added amount of the heterophasic component. Depending on the degree of orientation of the film and the purpose of use, an additive amount outside the above range may be employed.

  As a method for producing an alloy thin film in which the heterogeneous components are finely and uniformly distributed, a method in which particles having a particle size in the range of 1 nm to 1 μm are dispersed in a volatile binder and printed, or a chemical vapor deposition (CVD) method is used. Various methods such as thermal spraying, sputtering, and vapor deposition are conceivable.

  Various methods are conceivable as described above. In the present invention, it is preferable to use a co-sputtering method or a co-evaporation method. In these methods, the flying material adheres to the substrate at the atomic or cluster level to form a thin film. Therefore, a thin film having a fine particle size and uniformly dispersed can be easily obtained with good reproducibility. Further, the alloy composition can be easily changed by changing the electric power supplied to the target and the evaporation source, that is, the porosity of the porous layer finally obtained can be easily adjusted.

  As the heterogeneous component, it is preferable to use Ta and Ta alloy, or a metal or oxide that does not dissolve in Nb and Nb alloy. For example, the metal component is preferably Cu or Ag. Cu or Ag hardly dissolves in Ta, Ta alloy, Nb and Nb alloy. Moreover, Mg, Ca, or these oxides are also preferable. Mg and Ca hardly dissolve in Ta, Ta alloy, Nb, and Nb alloy, and these oxides are more thermodynamically stable than Ta oxide and Nb oxide.

[3] Third step of grain growth of Ta or Ta alloy (Nb or Nb alloy) and heterogeneous components by vacuum heat treatment:
Unless Ta or Nb is grain-grown, the integrity of the porous layer cannot be secured, and the different-phase component can be dissolved and removed by growing the different-phase ingredient and making it continuous.

  In general, as the heat treatment is performed at a higher temperature, grain growth proceeds and the structure of the finally obtained porous layer becomes rougher. The heat treatment temperature for grain growth is preferably 200 ° C. or higher and 670 ° C. or lower. The reason why the temperature is 200 ° C. or higher is that the lower the heat treatment temperature, the less likely the grain growth occurs, and the surface area of the resulting porous layer increases, but if it is too low, the integrity of the structure of the porous layer is lost. , Not to be a continuum. The reason why the temperature is 670 ° C. or lower is that the heat treatment temperature cannot be raised above the melting point of the substrate.

  In the case of performing sputtering or vacuum vapor deposition, grain growth can be performed simultaneously with film formation by forming an alloy film while heating the substrate.

[4] Fourth step of selectively dissolving and removing heterogeneous components:
As described above, after the grains are adjusted by heat treatment, the heterogeneous components are removed. Various methods can be used as a removal method. From the simplicity of operation, Ta, Ta alloy, Nb, Nb alloy, Al foil, or Al alloy foil, which is a constituent component of the electrode foil, It is preferable to dissolve and remove with an acid utilizing the difference in corrosion resistance. As the acid, an acid that selectively dissolves the heterogeneous component is selected. For example, sulfuric acid or hydrochloric acid to which nitric acid or hydrogen peroxide is added can be used. After removing the heterogeneous component, it is washed with water and dried to obtain a valve metal composite electrode foil.

  The valve metal composite electrode foil thus obtained has a uniform distribution of voids and a large surface area. Further, since the porous layer on which the dielectric film is formed by anodic oxidation is formed of Ta, Ta alloy, Nb, or Nb alloy particles, the capacitance is larger than that of the conventional etching Al foil. Become. Moreover, since Al with a small volume resistivity is used as a base material, electrode resistance can be made smaller than electrode foil formed only with Ta, Ta alloy, Nb, or Nb alloy. In addition, since the amount of rare metals Ta and Nb used is small, it is possible to produce an electrode foil at a lower cost.

  FIG. 3 and FIG. 4 are sectional views showing an example of an electrolytic capacitor using the valve metal composite electrode foil of the present invention.

FIG. 3 is a schematic cross-sectional view of a thin solid electrolytic capacitor. On the surface of the valve metal composite electrode foil (9) according to the present invention, a Ta or Nb oxide film (10) serving as a dielectric is formed by anodic oxidation, and a conductive material such as MnO ₂ or polypyrrole or polythiophene is formed thereon. It has a structure in which an electrically conductive layer (11) is formed by molecules, and a cathode layer (12) is formed thereon by graphite and silver base. Since the total thickness of the thin solid electrolytic capacitor mainly depends on the thickness of the electrode foil, the use of the valve metal composite electrode foil according to the present invention is effective for reducing the height of the thin solid electrolytic capacitor.

  FIG. 4 is a schematic cross-sectional view of a multilayer solid electrolytic capacitor. Three thin solid electrolytic capacitor elements (13) shown in FIG. 3 are laminated, and the anode part and the cathode part of each element are electrically insulated with an insulating resin (14), and then the anode part and the cathode part of each element. Are electrically connected by lead frames (15, 16), that is, each element is electrically connected in parallel. Each element has an electrode resistance, that is, an equivalent series resistance in addition to the dielectric component. However, by stacking, the equivalent series resistance component of each element is connected in parallel, and as a result, the equivalent series resistance of the entire multilayer element can be reduced. it can. Also, the greater the number of layers, the greater the equivalent series resistance reduction effect. Since the thin solid electrolytic capacitor element using the valve metal composite electrode foil according to the present invention can be made thinner than the conventional one, it is advantageous for stacking such elements.

  Hereinafter, the present invention will be described by way of examples.

(Example 1)
Using Ta and Cu targets of 99.99% purity (both φ152.4 mm, manufactured by High Purity Chemical Laboratory), multi-sputtering apparatus (manufactured by ULVAC, Inc., SH-450), 10 mtorr, 20 mm × 20 mm in Ar atmosphere X A dense layer made of Ta was formed in a thickness of about 1 μm on one surface of an Al foil (purity 99.9%) having a thickness of 50 μm, and subsequently a film having a composition of Ta-60 vol% Cu was formed in a thickness of 10 μm. Thereafter, the inside of the multi-source sputtering apparatus was turned over, and a dense layer made of Ta and a film having a composition of Ta-60 vol% Cu were similarly formed on the other surface.

The obtained sample was heat-treated at 500 ° C. × 1 hr in a vacuum of 3.0 × 10 ⁻³ Pa or less using a high-temperature vacuum furnace (Tokyo vacuum, turbo-vac). Thereafter, when immersed in a 6.7 mol / l nitric acid aqueous solution, Cu began to dissolve while generating bubbles. After 1 hour of immersion in an aqueous nitric acid solution to completely dissolve Cu, it was washed with water and dried to obtain a Ta / Al composite electrode foil.

  When the cross section of the obtained Ta / Al composite electrode foil was observed with a scanning electron microscope, a laminated structure composed of a dense Ta layer of 1 μm and a Ta porous layer of 10 μm was formed on both sides of a 50 μm thick Al foil. The total thickness of the formed Ta / Al composite electrode foil was 72 μm.

The obtained Ta / Al composite electrode foil was cut into a 10 mm square, and a Nb wire having a diameter of 0.2 mm was attached as a lead with a spot welder, and then a constant voltage of 5 V in phosphoric acid aqueous solution at 80 ° C. for 6 hours. By performing chemical conversion, a Ta ₂ O ₅ film serving as a dielectric was formed on the surface.

  Thereafter, the capacitance was measured in 30% by mass of sulfuric acid using an LCR meter (manufactured by Agilent, 4263B) with an applied bias of 1.5 V, a frequency of 120 Hz, and an effective value of 1.0 Vrms. The measurement results are shown in Table 1.

(Example 2)
Using Nb and Cu targets with a purity of 99.99% (both φ152.4 mm, manufactured by High Purity Chemical Laboratory), multi-sputtering apparatus (manufactured by ULVAC, SH-450), 10 mtorr, 20 mm × 20 mm in Ar atmosphere X Reactive sputtering was performed on one surface of an Al foil (purity 99.9%) having a thickness of 50 μm in an Ar + 5% N 2 atmosphere to form a TiN film having a thickness of 0.5 μm as a barrier film. Thereafter, a dense layer made of Nb was formed to a thickness of about 1 μm, and subsequently a film having a composition of Nb-60 vol% Cu was formed to a thickness of 10 μm. Thereafter, the inside of the multi-source sputtering apparatus was turned over, and similarly, a barrier layer, a dense layer made of Nb, and a film having a composition of Nb-60 vol% Cu were formed on the other surface.

The obtained sample was heat-treated at 600 ° C. × 1 hr in a vacuum of 3.0 × 10 ⁻³ Pa or less using a high-temperature vacuum furnace (manufactured by Tokyo Vacuum, turbo-vac). Thereafter, when immersed in a 6.7 mol / l nitric acid aqueous solution, Cu began to dissolve while generating bubbles. After being immersed in an aqueous nitric acid solution for 1 hr to completely dissolve Cu, it was washed with water and dried to obtain an Nb / Al composite electrode foil.

  When the cross section of the obtained Nb / Al composite electrode foil was observed with a scanning electron microscope, a TiN barrier layer of 0.5 μm, a dense Nb layer of 1 μm, and a porous Nb layer were formed on both sides of the 50 μm thick Al foil. A laminated structure composed of a porous layer of 10 μm was formed, and the total thickness of the Nb / Al composite electrode foil was 73 μm.

The obtained Nb / Al composite electrode foil was cut into a 10 mm square, and a Nb wire having a diameter of 0.2 mm was attached as a lead with a spot welder, and then a constant voltage of 10 V in phosphoric acid aqueous solution at 80 ° C. for 6 hours. By performing chemical conversion, an Nb ₂ O ₅ film serving as a dielectric was formed on the surface.

  Thereafter, the capacitance was measured in 30% by mass of sulfuric acid using an LCR meter (manufactured by Agilent, 4263B) with an applied bias of 1.5 V, a frequency of 120 Hz, and an effective value of 1.0 Vrms. The measurement results are shown in Table 1.

(Example 3)
An Nb / Al composite electrode foil was obtained in the same manner as in Example 2 except that the thickness of the Nb porous layer was 29 μm.

  The total thickness of the obtained Nb / Al composite electrode foil was 111 μm.

Thereafter, an Nb ₂ O ₅ film serving as a dielectric was formed on the surface in the same manner as in Example 2, and the capacitance was measured in the same manner as in Example 2. The results are shown in Table 1.

Example 4
Using Ta and Cu targets of 99.99% purity (both φ152.4 mm, manufactured by High Purity Chemical Laboratory), multi-sputtering apparatus (manufactured by ULVAC, Inc., SH-450), 10 mtorr, 20 mm × 20 mm in Ar atmosphere X Reactive sputtering was performed on one surface of an Al foil (purity 99.9%) having a thickness of 50 μm in an Ar + 5% N ₂ atmosphere to form a TiN film having a thickness of 0.5 μm as a barrier film. Thereafter, a dense layer made of Ta was formed to a thickness of about 1 μm, and subsequently a film having a composition of Ta-60 vol% Cu was formed to a thickness of 10 μm. Thereafter, the inside of the multi-source sputtering apparatus was turned over, and a barrier layer, a dense layer made of Ta, and a film having a composition of Ta-60 vol% Cu were similarly formed on the other surface.

The obtained sample was heat-treated at 600 ° C. × 1 hr in a vacuum of 3.0 × 10 ⁻³ Pa or less using a high-temperature vacuum furnace (manufactured by Tokyo Vacuum, turbo-vac). Thereafter, when immersed in a 6.7 mol / l nitric acid aqueous solution, Cu began to dissolve while generating bubbles. After 1 hour of immersion in an aqueous nitric acid solution to completely dissolve Cu, it was washed with water and dried to obtain a Ta / Al composite electrode foil.

  When a cross section of the obtained Ta / Al composite electrode foil was observed with a scanning electron microscope, a TiN barrier layer of 0.5 μm, a Ta dense layer of 1 μm, and a porous Ta layer were formed on both sides of a 50 μm thick Al foil. A laminated structure composed of a porous layer of 10 μm was formed, and the total thickness of the Ta / Al composite electrode foil was 73 μm.

Thereafter, a Ta ₂ O ₅ film serving as a dielectric was formed on the surface in the same manner as in Example 1, and the capacitance was measured in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
Film formation was performed in the same manner as in Example 1 except that heat treatment was performed at 180 ° C. for 2 hours in a vacuum of 3.0 × 10 ⁻³ Pa or less in a high-temperature vacuum furnace (manufactured by Tokyo Vacuum, turbo-vac). After performing, it was immersed in a 6.7 mol / l nitric acid aqueous solution for 1 hr, but no bubbles were generated and Cu was not dissolved. Thereafter, it was washed with water and dried, and the cross section of the obtained sample was observed with a scanning electron microscope, but the whole was a dense layer, and no porous layer was confirmed.

(Comparative Example 2)
A film having a composition of Ta-60 vol% Cu was formed in the same manner as in Example 1 except that the film having a composition of Ta-75 vol% Cu was used, and then a 6.7 mol / l nitric acid aqueous solution was added. When immersed for 1 hr, black fibrous detachment was observed from the surface during dissolution. Thereafter, the sample was washed with water and dried, and the cross section of the obtained sample was observed with a scanning electron microscope.

  When the cross section of the obtained Ta / Al composite electrode foil was observed with a scanning electron microscope, a laminated structure consisting of a 1 μm thick Ta layer and a porous Ta layer was formed on both sides of the 50 μm thick Al foil. However, the porous layer did not become a complete continuum, and peeling occurred in some places.

(Comparative Example 3)
Using Ta and Cu targets of 99.99% purity (both φ152.4 mm, manufactured by High Purity Chemical Laboratory), multi-sputtering apparatus (manufactured by ULVAC, Inc., SH-450), 10 mtorr, 20 mm × 20 mm in Ar atmosphere X A dense layer made of Ta was formed in a thickness of about 1 μm on one surface of a 110 μm thick Al foil (purity 99.9%), and subsequently a film having a composition of Ta-60 vol% Cu was formed in a thickness of 5 μm. Thereafter, the inside of the multi-source sputtering apparatus was turned over, and a dense layer made of Ta and a film having a composition of Ta-60 vol% Cu were similarly formed on the other surface.

The obtained sample was heat-treated at 500 ° C. × 1 hr in a vacuum of 3.0 × 10 ⁻³ Pa or less using a high-temperature vacuum furnace (Tokyo vacuum, turbo-vac). Thereafter, when immersed in a 6.7 mol / l nitric acid aqueous solution, Cu began to dissolve while generating bubbles. After 1 hour of immersion in an aqueous nitric acid solution to completely dissolve Cu, it was washed with water and dried to obtain a Ta / Al composite electrode foil.

  When a cross section of the obtained Ta / Al composite electrode foil was observed with a scanning electron microscope, a laminated structure composed of a dense Ta layer of 1 μm and a Ta porous layer of 5 μm was formed on both sides of an Al foil having a thickness of 110 μm. The total thickness of the formed Ta / Al composite electrode foil was 122 μm.

Thereafter, a Ta ₂ O ₅ film serving as a dielectric was formed on the surface in the same manner as in Example 1, and the capacitance was measured in the same manner as in Example 1. The results are shown in Table 1.

(Conventional example 1)
An AC-etched Al foil having a total thickness of 110 μm consisting of a base material having a thickness of about 30 μm and an etching layer having a thickness of about 40 μm on both sides is cut into 10 cm square and has a diameter of 0.2 mm. After attaching the Nb wire as a lead, an anodization treatment was performed in an aqueous solution of ammonium borate at 85 ° C. for 5 hours at a voltage of 6 hours, thereby forming an Al ₂ O ₃ film serving as a dielectric on the surface.

  The obtained sample was measured for its capacitance in 30% by mass sulfuric acid using an LCR meter (manufactured by Agilent, 4263B) at an applied bias of 1.5 V, a frequency of 120 Hz, and an effective value of 1.0 Vrms. The measurement results are shown in Table 1.

(Conventional example 2)
A sample was obtained and the capacitance was measured in the same manner as in Conventional Example 1 except that the anodizing voltage was 10 V. The results are shown in Table 1.

(Conventional example 3)
Using Ta and Cu targets of 99.99% purity (both φ152.4 mm, manufactured by High Purity Chemical Laboratory), multi-sputtering apparatus (manufactured by ULVAC, Inc., SH-450), 10 mtorr, 20 mm × 20 mm in Ar atmosphere × Ta-60 vol% Cu was deposited in a thickness of 10 μm on both sides of a 50 μm thick Ta foil (manufactured by Tokyo Electrolytic Co., Ltd., purity 99.9% or more). The obtained sample was heat-treated at 500 ° C. × 1 hr in a vacuum of 3.0 × 10 ⁻³ Pa or less using a high-temperature vacuum furnace (Tokyo vacuum, turbo-vac). Thereafter, Cu was completely dissolved by immersing in a 6.7 mol / l nitric acid aqueous solution for 1 hour, and then washed with water and dried to obtain a Ta electrode foil.

  When the cross section of the obtained Ta electrode foil was observed with a scanning electron microscope, a Ta porous layer of 10 μm was formed on both sides of the 50 μm thick Ta foil, and the total thickness of the Ta electrode foil was 70 μm. there were.

Thereafter, a Ta ₂ O ₅ film serving as a dielectric was formed on the surface in the same manner as in Example 1, and the capacitance was measured in the same manner as in Example 1. The results are shown in Table 1.

  In Example 1 and Conventional Example 1 having the same anodic oxidation voltage, and in Examples 2, 3, 4 and Conventional Example 2 having the same anodic oxidation voltage, the valve metal composite electrode of the present invention was compared based on the comparison of the respective area capacitance densities. It can be seen that the foil has an area capacitance density several times that of the conventional AC-etched Al foil, and is advantageous in reducing the size and capacity of the capacitor.

  Further, in Comparative Example 1 where the heat treatment temperature was low, a porous layer was not obtained, and in Comparative Example 2 where the film-forming composition was outside the scope of the present invention, although it was made porous, peeling occurred.

  In Comparative Example 3 in which a 110 μm Al foil was used as the base material, the area capacitance density was the same as that of the conventional AC-etched Al foil, and a large capacity could not be obtained.

  From the comparison between Example 1 and Conventional Example 3, it was confirmed that even if an Al foil substrate was used, an area capacitance density equivalent to that using a conventional Ta foil substrate could be obtained. It was shown that it is possible to use Al which is inexpensive and has low resistance, instead of Ta, which is rare and has a relatively large volume resistivity.

(Example 5)
The Nb / Al composite electrode foil obtained in Example 3 was anodized in a phosphoric acid aqueous solution at 80 ° C. for 10 hours and for 6 hours to form an Nb ₂ O ₅ film serving as a dielectric on the surface. did. Polypyrrole was formed on the obtained sample by chemical polymerization, and then a carbon paste and an Ag paste were applied to produce a thin solid electrolytic capacitor. The capacitor cross-sectional structure has a structure in which a polypyrrole layer 15 μm, a carbon paste and an Ag paste layer 30 μm are formed on both surfaces of a 110 μm thick Nb / Al composite electrode foil, and the total thickness is about 200 μm. .

  About the obtained solid electrolytic capacitor, the electrostatic capacitance was measured by the applied bias 1.5V, the frequency 120Hz, and the effective value 1.0Vrms using the LCR meter (The product made from Agilent, 4263B). The measurement results are shown in Table 2.

(Example 6)
The Nb / Al composite electrode foil obtained in Example 2 was anodized in a phosphoric acid aqueous solution at 80 ° C. for 10 hours and for 6 hours to form a Nb ₂ O ₅ film serving as a dielectric on the surface. did. Polypyrrole was formed on the obtained sample by chemical polymerization, and then a carbon paste and an Ag paste were applied to produce a thin solid electrolytic capacitor. The capacitor cross-sectional structure has a structure in which a polypyrrole layer 15 μm, a carbon paste and an Ag paste layer 30 μm are formed on both surfaces of a 72 μm thick Nb / Al composite electrode foil, and the total thickness is about 162 μm. .

  About the obtained solid electrolytic capacitor, the electrostatic capacitance was measured by the applied bias 1.5V, the frequency 120Hz, and the effective value 1.0Vrms using the LCR meter (The product made from Agilent, 4263B). The measurement results are shown in Table 2.

(Comparative Example 4)
A voltage of 10 V in an aqueous solution of ammonium borate at 85 ° C. was formed on an AC-etched Al foil consisting of a substrate having a thickness of about 30 μm and an etching layer having a thickness of about 40 μm on both sides and a total thickness of 110 μm. An anodizing treatment for 6 hours was performed, and an Al ₂ O ₃ film serving as a dielectric was formed on the surface. Polypyrrole was formed on the obtained sample by chemical polymerization, and then a carbon paste and an Ag paste were applied to produce a thin solid electrolytic capacitor. The capacitor cross-sectional structure has a structure in which a polypyrrole layer 15 μm, a carbon paste, and an Ag paste layer 30 μm are formed on both surfaces of an AC-etched Al foil having a thickness of 110 μm, and the total thickness is about 200 μm.

  About the obtained solid electrolytic capacitor, the electrostatic capacitance was measured by the applied bias 1.5V, the frequency 120Hz, and the effective value 1.0Vrms using the LCR meter (The product made from Agilent, 4263B). The measurement results are shown in Table 2.

  From the comparison between Example 5 and Comparative Example 4, it can be seen that by using the composite electrode foil of the present invention, the area capacitance density can be increased several times with the same thickness as the conventional one. In addition, although Example 6 is thinner than Comparative Example 4, a capacitance density that is twice or more is obtained. From this, it can be seen that a thinner and larger capacity solid electrolytic capacitor can be produced by the present invention. Further, since the capacitor element can be thinned, more elements can be stacked with the same thickness. This leads to an improvement in capacitance density and a reduction in ESR of the capacitor. Therefore, the solid electrolytic capacitor using the valve metal composite electrode foil of the present invention is useful as an element of a multilayer solid electrolytic capacitor.

  As described above, the valve metal composite electrode foil of the present invention has a capacitance density several times that of the conventional etching Al foil, and is an electrode as compared with the electrode foil of Ta alone and Nb alone. Resistance becomes low. Moreover, since Al is used as a base material, and it becomes possible to produce an electrode foil at a low cost compared to an electrode foil using rare metals Ta and Nb alone, it is possible to use for an electrolytic capacitor. It is useful as an electrode foil.

It is sectional drawing which shows one Example of the valve metal composite electrode foil of this invention. It is sectional drawing which shows the Example from which the valve metal composite electrode foil of this invention differs. It is sectional drawing which shows an example of the electrolytic capacitor which uses the valve metal composite electrode foil of this invention. It is sectional drawing which shows an example of the electrolytic capacitor which uses the valve metal composite electrode foil of this invention. It is sectional drawing which shows the anode body which consists of a porous pellet used for the conventional Ta electrolytic capacitor or Nb electrolytic capacitor. It is sectional drawing which shows the conventional foil-shaped anode body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous pellet 2 Wire 3 Base material 4 Porous layer 5 Base material 6 Dense layer 7 Porous layer 8 Barrier layer 9 Valve metal composite electrode foil 10 Oxide film 11 Electrically conductive layer 12 Cathode layer 13 Solid electrolytic capacitor element 14 Insulating layer 15 Anode lead frame 16 Cathode lead frame

Claims (19)

  An Al foil or an Al alloy foil as a base material, and a Ta or Ta alloy dense layer formed on one or both sides of the base material, and a Ta or Ta alloy porous layer formed on the dense layer. A valve metal composite electrode foil, characterized in that the porous layer has a surface area more than twice the apparent area.   An Al foil or an Al alloy foil as a base material, and a dense layer of Nb or Nb alloy formed on one or both sides of the base material, and a porous layer of Nb or Nb alloy formed on the dense layer A valve metal composite electrode foil, characterized in that the porous layer has a surface area more than twice the apparent area.   An Al foil or Al alloy foil as a base material, formed on one or both sides of the base material, and a thermodynamically stable barrier layer against Ta, Ta alloy, Al and Al alloy, and on the barrier layer And a laminated structure comprising a dense layer of Ta or Ta alloy and a porous layer of Ta or Ta alloy formed on the dense layer, wherein the porous layer has an apparent area of 2 A valve metal composite electrode foil characterized by having a surface area more than doubled.   An Al foil or an Al alloy foil as a base material, formed on one or both sides of the base material, and a thermodynamically stable barrier layer against Nb, Nb alloy, Al and Al alloy, and on the barrier layer And a laminated structure comprising a dense layer of Nb or Nb alloy and a porous layer of Nb or Nb alloy formed on the dense layer, wherein the porous layer has an apparent area of 2 A valve metal composite electrode foil characterized by having a surface area more than doubled.   The valve metal composite electrode foil according to claim 3 or 4, wherein the barrier layer is any one selected from TiN, ZrN, and HfN.   The valve metal composite electrode foil according to any one of claims 1 to 5, wherein the substrate has a thickness of 100 µm or less.   The valve metal composite electrode foil according to any one of claims 1 to 6, wherein the porosity of the porous layer is in the range of 30 to 70%.   A dense layer of Ta or Ta alloy is formed on the base material of Al foil or Al alloy foil, and Ta or Ta alloy and a different phase component incompatible with Ta are formed on the obtained dense layer with a particle diameter of 1 nm. A valve metal characterized by forming an alloy thin film uniformly distributed at ˜1 μm and performing vacuum heat treatment to dissolve and remove Ta or Ta alloy and the foreign phase component after adjusting the grain size of the foreign phase component. A method for producing a composite electrode foil.   A dense layer of Nb or Nb alloy is formed on the base material of Al foil or Al alloy foil. On the obtained dense layer, Nb or Nb alloy and a heterogeneous component incompatible with Nb have a particle diameter of 1 nm. A valve metal characterized by forming an alloy thin film uniformly distributed at ˜1 μm and performing vacuum heat treatment to dissolve and remove the Nb or Nb alloy and the heterogeneous component after adjusting the grains of the heterophasic component A method for producing a composite electrode foil.   A barrier layer which is thermodynamically stable against Ta, Ta alloy, Al and Al alloy is formed on the base material of Al foil or Al alloy foil, and a dense layer of Ta or Ta alloy is formed on the barrier layer. By forming a thin alloy film in which Ta or a Ta alloy and a heterophasic component incompatible with Ta are uniformly distributed with a particle diameter of 1 nm to 1 μm on the dense layer, vacuum heat treatment is performed. Alternatively, the method for producing a valve metal composite electrode foil is characterized by dissolving and removing the Ta component and the heterogeneous component after the grain adjustment of the heterogeneous component.   A barrier layer which is thermodynamically stable with respect to Nb, Nb alloy, Al and Al alloy is formed on the base material of Al foil or Al alloy foil, and a dense layer of Nb or Nb alloy is formed on the barrier layer. Nb or Nb alloy, and an alloy thin film in which a heterogeneous component incompatible with Nb is uniformly distributed with a particle diameter of 1 nm to 1 μm is formed on the dense layer, and vacuum heat treatment is performed. Alternatively, the method for producing a valve metal composite electrode foil is characterized by dissolving and removing the Nb alloy and the heterogeneous component after the grain adjustment of the heterogeneous component.   The method for producing a valve metal composite electrode foil according to claim 10 or 11, wherein the barrier layer is formed of any one selected from TiN, ZrN, and HfN.   The method for producing a valve metal composite electrode foil according to claim 12, wherein the barrier layer is formed by reactive sputtering or reactive vapor deposition in which nitrogen gas is introduced.   The method for producing a valve metal composite electrode foil according to any one of claims 8 to 13, wherein an amount of the heterogeneous component added to the alloy thin film is in a range of 30 to 70% by volume.   The method for producing a valve metal composite electrode foil according to any one of claims 8 to 14, wherein a sputtering method or a vacuum deposition method is used for forming the alloy thin film.   The method for producing a valve metal composite electrode foil according to any one of claims 8 to 15, wherein the heterogeneous component is Cu or Ag.   The method for producing a valve metal composite electrode foil according to any one of claims 8 to 15, wherein the heterogeneous component is Mg, Ca, or an oxide thereof.   8. An electrolytic capacitor using the valve metal composite electrode foil according to claim 1 as an electrode.   A thin solid electrolytic capacitor or a laminated solid electrolytic capacitor, wherein the valve metal composite electrode foil according to any one of claims 1 to 7 is anodized.