JP2009170871A - Porous valve metal electrode and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous valve metal electrode of which adhesiveness is stabilized in the porous valve metal electrode in which a valve metal porous layer is formed on a valve metal current collector, and to provide a method of manufacturing the same. <P>SOLUTION: In the porous valve metal electrode including the valve metal current collector and the valve metal porous layer formed on the valve metal current collector, when the valve metal porous layer is formed, a low voidage layer is formed at a valve metal current collector side, with a thickness of 1/100 to 1/10 to a total thickness of the valve metal porous layer, wherein the low voidage layer is 1 to 30 vol% in voidage, and its voidage is lower than other portions of the valve metal porous layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a porous valve metal electrode and a method for manufacturing the same, and more particularly to a porous valve metal electrode made of tantalum or niobium.

  A tantalum electrolytic capacitor and a niobium electrolytic capacitor have features of small size, large capacity, and high reliability, and are indispensable electronic components for small electronic devices typified by mobile phones and notebook personal computers. With the recent reduction in height and functionality of electronic devices, tantalum electrolytic capacitors and niobium electrolytic capacitors are also strongly required to have low height and high capacity.

  Conventional tantalum and niobium electrolytic capacitors use porous pellets obtained by compacting and sintering tantalum or niobium powder as the anode body, but there are limits to the reduction in the height of the anode body due to restrictions in these manufacturing methods. However, there is a limit in reducing the height of the obtained tantalum electrolytic capacitor or niobium electrolytic capacitor.

  On the other hand, a mixed film composed of a valve metal and a different phase component not compatible with the valve metal is formed on a tantalum foil or niobium foil, which is a valve metal current collector, by sputtering or the like. Alternatively, Patent Document 1 and Non-Patent Document 1 disclose a method for producing a foil-like valve metal anode body having a valve metal porous layer by a method of performing heat treatment in an inert gas and then selectively removing only the heterogeneous components. It is described in Patent Document 1. The foil-like porous valve metal anode body obtained by this method enables a further reduction in the height of the capacitor, which can be said to be an effective method.

By the way, the demand for higher capacity of electronic devices has become more severe, and for example, realization of a higher capacity of 150 kCV / g or more has been demanded. In this foil-like porous valve metal anode body, when aiming at a high capacity of 150 kCV / g or more, the porous layer has a finer structure, so the adhesion between the valve metal current collector and the valve metal porous layer There is a problem that becomes unstable. Such instability of adhesion is not preferable because it causes variations in anode body characteristics, increases leakage current during the capacitor manufacturing process, and impairs capacitor reliability.
JP 2006-049816 A "Preparation of porous tantalum foil electrode and its anode properties" (Tetsufumi Komukai, Toshiyuki Osako, 73rd Annual Meeting of the Electrochemical Society, p. 287, published on April 1, 2006)

  The present invention has been made in view of such a problem, and is a porous valve metal electrode in which a valve metal porous layer is formed on a valve metal current collector. And it aims at providing the manufacturing method.

  The porous valve metal electrode according to the present invention comprises a valve metal current collector and a valve metal porous layer formed on the valve metal current collector, and the valve metal porous layer includes the valve metal electrode. A low porosity layer is formed on the metal current collector side, and the porosity of the low porosity layer is lower than the porosity of the other part of the valve metal porous layer and is 1 to 30% by volume. is there.

  The thickness of the low porosity layer is preferably 1/100 to 1/10 with respect to the thickness of the valve metal porous layer.

  In addition, the valve metal of the valve metal porous layer is preferably any one selected from Nb, Ta, Nb alloy, and Ta alloy.

  The method for producing a porous valve metal electrode according to the present invention comprises forming a mixed thin film composed of a valve metal and a heterogeneous component on a valve metal current collector, performing a heat treatment, and then removing the heterogeneous component. According to a method for manufacturing a valve metal electrode, when forming the mixed thin film, the mixing ratio of the different phase components is lower than the mixing ratio of the different phase components in other parts of the mixed thin film on the valve metal current collector side. A low heterogeneous component layer having a ratio of 1 to 30% by volume is formed.

  The thickness of the low heterogeneous component layer is preferably 1/100 to 1/10 of the thickness of the mixed thin film.

  The mixed thin film is preferably formed by co-sputtering or co-evaporation using a valve metal and a heterogeneous component.

  Furthermore, it is preferable to use any one selected from Nb, Ta, Nb alloy, and Ta alloy as the valve metal used in the mixed thin film, and Cu as the heterogeneous component.

  Similarly, as the valve metal used for the valve metal current collector, any one selected from Nb, Ta, Nb alloy, and Ta alloy is preferably used. The type may be different from the valve metal in the quality layer.

  According to the present invention, the contact area between the valve metal current collector and the valve metal porous layer is increased, and stable adhesion can be obtained.

  In addition, the low porosity layer can be easily formed when forming a mixed thin film composed of a valve metal and a heterogeneous component, and further, the heterophasic component can be removed after heat treatment, increasing the number of manufacturing steps. Therefore, a suitable porous valve metal electrode can be manufactured at low cost.

  In applying the porous valve metal electrode as an anode body of an electrolytic capacitor, the adhesion between the current collector made of the valve metal and the porous layer is important. In order to improve such adhesiveness, a structure in which the contact area between the valve metal porous layer and the valve metal current collector is increased is ideal.

  The inventors of the present invention have made extensive studies in order to realize a porous valve metal electrode having such a structure. As a result, when forming a mixed thin film, a low heterogeneous component layer is formed on the side of the valve metal current collector. By forming, a low porosity layer is formed on the valve metal current collector side of the valve metal porous layer after heat treatment and removal of heterogeneous components, and the contact area between the valve metal porous layer and the valve metal current collector is increased. The present invention has been completed with the knowledge that a stable adhesion can be obtained between them.

  The valve metal for forming the mixed thin film, that is, the valve metal for forming the valve metal porous layer includes various materials such as Ti, Ti alloy, Al, Al alloy, Ta, Ta alloy, Nb, and Nb alloy. Conceivable. However, Ti has a problem in the insulating property of the anodic oxide film, and Al has a small dielectric constant and a small capacity density. Therefore, considering practicality as an electrolytic capacitor anode body, Ta and Ta alloys , Nb, or Nb alloy is preferable.

  The valve metal forming the valve metal current collector is also preferably selected from Ta, Ta alloy, Nb, and Nb alloy, but other valve metals may be used, and the valve metal of the valve metal porous layer may be used. And may be different.

  Hereinafter, a method for producing a porous valve metal thin film according to the present invention will be described.

  The method for producing a porous valve metal electrode according to the present invention includes: 1) forming a low heterogeneous component layer in which a mixing ratio of heterogeneous components is 1 to 30% by volume on a valve metal current collector; A step of forming a high-phase component layer in which the mixing ratio exceeds 30% by volume, 2) adjusting the particle diameter of the valve metal and the hetero-phase component by heat treatment, and sintering between the valve metal particle / valve metal current collector And 3) a step of removing a different phase portion. Hereinafter, each step will be described in detail.

1) On the valve metal current collector, a low heterogeneous component layer with a heterogeneous component mixing ratio of 1 to 30% by volume is formed, and then a high heterogeneous component layer with a heterogenous component mixing ratio exceeding 30% by volume is formed. Step of forming As the valve metal current collector, it is desirable to use a rolled foil made of the same material as the valve metal of the valve metal porous layer as the substrate because it is easy to handle in the process, but a combination of different materials (for example, Nb foil substrate) And Ta porous layer).

  When forming a mixed thin film of a valve metal and a different phase component on one or both sides of the valve metal current collector, the mixing ratio of the different phase component is 1 to 30% by volume on the valve metal current collector side in the mixed thin film. A low heterogeneous component layer is formed. The thickness of the low heterogeneous component layer is 1/100 to 1/10 with respect to the thickness of the mixed thin film.

  When the mixing ratio of the different phase components exceeds 30% by volume in the low heterogeneous component layer, the porosity of the low porosity layer becomes higher than 30% by volume in the finally obtained porous valve metal electrode. The contact area between the current collector and the valve metal porous layer becomes small, and stable adhesion cannot be obtained. On the other hand, if the mixing ratio of the different phase component is less than 1% by volume, the different phase component remains in the step of removing the different phase portion.

  If the thickness of the low heterogeneous component layer is less than 1/100 of the thickness of the mixed thin film, the contact area between the valve metal current collector and the valve metal porous layer cannot be increased sufficiently. Stable adhesion cannot be obtained. On the other hand, when the thickness of the low heterogeneous component layer is thicker than 1/10 of the thickness of the mixed thin film, the overall surface area of the valve metal porous layer is significantly reduced, resulting in an electrolytic capacitor. Capacitance will be insufficient.

  After the low heterogeneous component layer is formed, the high heterogeneous phase is the remainder of the mixed thin film in which the valve metal and the heterogeneous component are known in an appropriate ratio, for example, the mixing ratio is more than 30% by volume and not more than 70% by volume. A component layer is formed. The mixing ratio in the high heterogeneous component layer is appropriately determined according to the use of the obtained electrolytic capacitor. However, when the porosity of the obtained valve metal porous layer exceeds 70% by volume, the strength decreases. The mixing ratio of the different phase components is 70% by volume or less.

  As a method for producing a mixed thin film of a valve metal and a different phase component, a printing method may be considered in which particles of the valve metal and the different phase component are dispersed in a volatile binder and the binder component is evaporated and fixed after coating. In this case, a low heterogeneous component layer can be formed by changing the particle mixing ratio of the valve metal and the heterophasic component. Further, it is possible to form a film by a CVD (chemical vapor deposition) method, a sputtering method, a vacuum vapor deposition method, or the like. Also in these cases, the mixing ratio can be changed by changing the film forming conditions in the middle.

  Although various film forming methods can be selected as described above, in the present invention, it is preferable to form a mixed thin film by simultaneous sputtering or simultaneous vapor deposition of a valve metal and a different phase component. Specifically, an independent sputtering (deposition) source is prepared for the valve metal and the heterogeneous component, and the valve metal current collector is alternately passed over these sputtering (deposition) sources. A mixed thin film in which different phase components are mixed at a predetermined ratio is prepared. At this time, the mixing ratio of the valve metal and the heterogeneous component forming the mixed thin film can be adjusted by changing the respective sputtering (evaporation) rates.

  As described above, the valve metal constituting the porous valve metal electrode is preferably a kind selected from Ta, Ta alloy, Nb, and Nb alloy in consideration of practicality. In this case, the heterophasic component can be selected from a metal component that does not dissolve in these, or an oxide that is thermodynamically stable to the valve metal. Specifically, metals such as Ag and Cu, and oxides such as MgO and CaO can be used, but Cu is preferable in consideration of economy, ease of film formation, and ease of removal. .

  The preferable form of a low heterogeneous component layer is demonstrated using FIGS. Each of the figures is a graph showing the mixing ratio of the different phase components with respect to the thickness direction of the mixed thin film. The origin of the horizontal axis indicates the boundary between the valve metal current collector and the mixed thin film, and the left side of the figure is the side of the valve metal current collector. The figure shows an enlarged view of the vicinity of the valve metal current collector. The thickness of the low porosity layer is 1/100 to 1/10 with respect to the thickness of the valve metal porous layer.

  FIG. 1 shows a case where the mixing ratio is constant in the low heterogeneous component layer. FIG. 2 shows a case where the mixing ratio in the low heterogeneous component layer is changed stepwise, and the heterogeneous component is small on the valve metal current collector side. FIG. 3 shows a case where the mixing ratio in the low-phase component layer is continuously changed. The phase-phase component continuously increases from the side of the valve metal current collector, and the remaining portion of the mixed thin film exceeds the low-phase component layer. This is a case where the mixing ratio is changed stepwise. FIG. 4 also shows a case where the mixing ratio in the low-phase component layer is continuously changed. The mixing ratio of the heterophasic component is further continued following the portion where the mixing ratio of the heterophasic component is up to 30% by volume. This is a case where a predetermined ratio is maintained from a predetermined position.

2) A process of adjusting the particle diameter of the valve metal and the heterogeneous component by heat treatment and advancing the sintering between the valve metal particle / valve metal current collector. Heat treatment is performed therein, and sintering between the valve metal particles, between the valve metal particles and the valve metal current collector is promoted, and crystal grains of different phase components are also grown. The reason why it is necessary to proceed with the sintering of the valve metal particles is to ensure the integrity of the structure made of the valve metal, and it is possible to proceed with the sintering between the valve metal particles and the valve metal current collector. The necessary reason is that the valve metal porous layer of the finally obtained porous valve metal electrode and the valve metal current collector are brought into close contact with each other. In order to obtain a high capacity, it is necessary to suppress sintering in order to obtain a fine porous structure. At this time, since sintering between the valve metal particles and the valve metal current collector is also suppressed, the adhesion is insufficient. In the present invention, since the contact area between the valve metal component and the valve metal current collector in the low heterogeneous component layer is large, stable adhesion can be obtained.

  On the other hand, the reason why it is necessary to grow the crystal grains of the different phase component is that the electrolyte cannot be filled unless the size of the voids after the removal of the different phase component is larger than a certain level.

  The heat treatment atmosphere and temperature are determined by the type of the valve metal and the different phase component and the particle diameter of the finally obtained valve metal porous layer. When the valve metal is selected from Ta, Ta alloy, Nb, and Nb alloy, the heat treatment atmosphere deteriorates leakage current characteristics and the like due to oxidation. Alternatively, heat treatment can be performed in an Ar atmosphere where Mg vapor or the like coexists.

  The higher the heat treatment temperature, the more the grain growth of the valve metal and the different phase component proceeds, and the particle diameter of the finally obtained valve metal porous layer becomes coarse. Moreover, when a heterophasic component is Cu, it is preferable that it is 400 to 1050 degreeC. When the temperature is lower than 400 ° C., valve metal and heterogeneous phase component grain growth occur, but the sintering of the valve metal particles and the valve metal current collector does not proceed sufficiently, and the finally obtained valve metal porous layer and valve metal current collector are obtained. Insufficient adhesion of electrical conductors. If it exceeds 1050 ° C., it becomes higher than the melting point of Cu which is a heterogeneous component, which is not preferable.

3) Step of removing the heterogeneous portion After adjusting the particle size by heat treatment, the heterogeneous component is removed. Various methods can be used as the removal method, but it is preferable to dissolve and remove with an acid or the like from the viewpoint of ease of operation. As the type of acid, one that selectively dissolves only the heterogeneous component is selected. For example, when one kind selected from Ta, Ta alloy, Nb, and Nb alloy is used as the valve metal and Cu is used as the heterogeneous component, nitric acid, hydrogen peroxide, or the like can be used. A valve metal porous layer can be obtained by dissolving and removing the heterogeneous components with these solutions, followed by washing with water and drying. The low heterogeneous component layer becomes a low porosity layer in this step.

  The porosity of the low porosity layer is 1 to 30% by volume depending on the mixing ratio of the low-phase component layer in the mixed thin film. In addition, the porosity in the low porosity layer is changed stepwise or continuously depending on the mixing ratio of the low-phase component layer. Even in the high porosity layer, there may be a layer in which the porosity is changed stepwise or continuously on the valve metal current collector side.

  In the porous valve metal electrode of the present invention, the presence of such a low porosity layer increases the contact area between the valve metal porous layer and the valve metal current collector, and thus has excellent adhesion between them. There is a feature in the point.

  Hereinafter, the present invention will be described in detail by way of examples. In the examples, Nb and Ta, which are highly practical as thin film capacitors, are used for the valve metal current collector and the valve metal porous layer. However, the present invention is characterized in that the contact area between the valve metal porous layer and the valve metal current collector is increased, thereby improving the adhesion between the two. The present invention is also suitably applied to the case where is used for the current collector and the porous layer.

Example 1
A mixed thin film was formed by sputtering using a Ta target having a purity of 99.99% and a Cu target (both of which were φ152.4 mm, manufactured by High Purity Chemical Laboratory) as targets. A multi-source sputtering apparatus (manufactured by ULVAC, Inc., SH-450) was used as the sputtering apparatus.

A Ta foil and an Nb foil (both made by Tokyo Electrolytic Co., Ltd.) having a thickness of 50 μm are fixed to the substrate holder, both are evacuated to 5 × 10 ⁻⁵ Pa, the Ar gas pressure is 1 Pa, Ta— The target input power with respect to each of the Ta target and the Cu target was adjusted so as to be 10 vol% Cu, and a low-phase component layer having a thickness of 0.2 μm was formed on the substrate.

  Subsequently, the target input power for each of the Ta target and the Cu target is readjusted so that Ta-60 volume% Cu is obtained, and a Ta-60 volume% Cu layer is formed on the low heterogeneous component layer to a thickness of 9. A mixed thin film having a total film thickness of 10 μm was formed by laminating 8 μm.

  Next, the substrate is turned over, and the low-phase component layer is similarly formed on the back surface of the substrate to a thickness of 0.2 μm, and a Ta-60 volume% Cu layer is stacked to a thickness of 9.8 μm, for a total film thickness of 10 μm. A mixed thin film was formed.

  Therefore, the mixing ratio of the heterogeneous component is as shown in the graph of FIG. 1 with respect to the thickness direction of the mixed thin film.

In order to determine the composition of the film and the mass of Ta attached to the substrate by sputtering, the sample formed on the Nb foil was cut into 2 cm ² squares and subjected to chemical analysis. As a result, the amount of Ta deposited by sputtering was 14 mg / cm ² .

Then, it was charged into a high-temperature vacuum furnace (Tokyo Vacuum Co., Ltd., turbo-vac), started heating at a vacuum degree of 5 × 10 ⁻³ Pa or higher, and subjected to heat treatment at 700 ° C. × 60 min. It was immersed in 3 mol / L nitric acid to selectively dissolve Cu. Thereafter, pure water cleaning and vacuum drying were performed to obtain two types of porous valve metal electrodes according to the present example using Ta foil and Nb foil as substrates (current collectors).

The obtained two types of porous valve metal electrodes were cut into 10 mm squares, Nb wires with a diameter of 0.2 mm were attached with a spot welder, and the initial current density was measured in an aqueous phosphoric acid solution having an electric conductivity of 10 mS / cm and 80 ° C. A constant voltage was formed at 0.01 mA / μFV, a voltage of 10 V, and a time of 6 hours to form Ta ₂ O _{5 serving} as a dielectric. With respect to the sample subjected to the chemical conversion treatment, the capacitance was measured with an applied bias of 1.5 V, a frequency of 120 Hz, and an effective value of 1.0 Vrms using an LCR meter (manufactured by Agilent, 4263B) in 40% by mass of sulfuric acid. As a result of obtaining the capacity from the measured capacitance and formation voltage, and Ta adhesion weight by sputtering obtained after film formation, the capacity of the porous valve metal electrode sample using Ta foil and Nb foil is both 220 kCV / g. there were.

  Moreover, the cross section which cut | disconnected the obtained two types of porous valve metal electrodes with CP apparatus (the JEOL Co., Ltd. make, SM-09010) was observed by SEM.

  As a result, a low porosity layer having a thickness of 0.2 μm and a high porosity layer having a thickness of 9.8 μm were formed on the substrate. Moreover, the remaining Cu particle | grains were not recognized from the SEM image of the low porosity layer.

  Furthermore, as a result of obtaining the porosity from the SEM image using image analysis software (ImageJ, free software), the porosity of the low porosity layer is 10% by volume, and the porosity of the high porosity layer is 60% by volume. Met.

  Moreover, the adhesiveness of two types of porous valve metal electrodes was evaluated by a tape peeling test as follows. First, a double-sided tape (NW-10, manufactured by Nichiban Co., Ltd.) is used on one side and affixed to a flat plastic plate. On the other side, a 1 cm wide adhesive tape (polyimide tape KA00H, Electronic Trading Co., Ltd.). The product was attached, and one end of the pressure-sensitive adhesive tape was strongly peeled off to examine whether or not the valve metal porous layer adhered to the pressure-sensitive adhesive tape.

  As a result, for two types of porous valve metal electrodes, a total of 200 surfaces were tested on each of 100 surfaces, and as a result, adhesion of the valve metal porous layer to the adhesive tape was not observed.

(Example 2)
In forming the mixed thin film, first, a Ta-2 volume% Cu low-phase component layer having a thickness of 0.4 μm is formed on the substrate, and then a Ta-10 volume% Cu low-phase component layer is formed. A thickness of 0.4 μm was formed, and then a Ta-50 volume% Cu layer was laminated to a thickness of 9.2 μm, and a mixed thin film having a total film thickness of 10 μm was formed on both sides of the substrate. Similarly, a mixed thin film was formed on the substrate.

  Therefore, the mixing ratio of the different phase components with respect to the thickness direction of the mixed thin film is as shown in the graph of FIG.

As a result of chemical analysis in the same manner as in Example 1, the amount of Ta deposited by sputtering was 18 mg / cm ² .

  Thereafter, except for the heat treatment conditions of 750 ° C. × 60 min, the heat treatment, selective removal of Cu, pure water cleaning, and vacuum drying were performed in the same manner as in Example 1, and the Ta foil and Nb foil were removed. Two types of porous valve metal electrodes according to this example were used as substrates (current collectors).

  As a result of measuring the capacitance in the same manner as in Example 1, the Ta foil and the Nb foil were 170 kCV / g for both of the two types used as the substrate (current collector).

  As a result of SEM observation as in Example 1, two low porosity layers having a thickness of 0.4 μm and 0.4 μm and a high porosity layer having a thickness of 9.2 μm were formed on the substrate. Was formed. Moreover, the remaining Cu particle | grains were not recognized from the SEM image of the low porosity layer.

  Moreover, as a result of obtaining the porosity from the SEM image in the same manner as in Example 1, the porosity of the low porosity layer is 2% by volume and 10% by volume, and the porosity of the high porosity layer is 50% by volume. there were.

  Furthermore, as in Example 1, as a result of evaluation by a tape peeling test, adhesion of the valve metal porous layer to the adhesive tape was not observed.

(Example 3)
When the mixed thin film is formed, the target input power for each of the Ta target and the Cu target is adjusted so as to continuously change from Ta-2% by volume Cu to Ta-30% by volume. The component layer is formed to a thickness of 1.0 μm, and similarly, the layer in which the mixing ratio of the heterophasic component is inclined by changing continuously from Ta-30% by volume Cu to Ta-60% by volume is 1. After forming 0 μm, the substrate is the same as in Example 1 except that a Ta-60 volume% Cu layer is stacked to 8.0 μm and a mixed thin film having a total thickness of 10 μm is formed on both sides of the substrate. A mixed thin film was formed thereon.

  Therefore, the mixing ratio of the heterogeneous components with respect to the thickness direction of the mixed thin film is as shown in the graph of FIG.

As a result of chemical analysis in the same manner as in Example 1, the amount of Ta deposited by sputtering was 15 mg / cm ² .

  Thereafter, in the same manner as in Example 1, the heat treatment, selective removal of Cu, pure water cleaning, and vacuum drying were performed, and two types of this example in which Ta foil and Nb foil were used as substrates (current collectors). A porous valve metal electrode was obtained.

  As a result of measuring the capacitance in the same manner as in Example 1, the Ta foil and the Nb foil were 220 kCV / g for both of the two types used as the substrate (current collector).

  As a result of SEM observation in the same manner as in Example 1, a low porosity layer having a thickness of 1.0 μm with a continuously changing porosity and a thickness with continuously changing the porosity are formed on the substrate. A high porosity layer composed of a 1.0 μm layer and a layer having a constant porosity and a thickness of 8.0 μm was formed. Moreover, the remaining Cu particle | grains were not recognized from the SEM image of the low porosity layer.

  Further, as a result of obtaining the porosity from the SEM image in the same manner as in Example 1, the porosity of the low-porosity layer was continuously changed from 2% by volume to 30% by volume from the substrate side. The porosity of the layer was 60% by volume except that it continuously changed from 30% to 60% by volume on the substrate side.

  Furthermore, as in Example 1, as a result of evaluation by a tape peeling test, adhesion of the valve metal porous layer to the adhesive tape was not observed.

Example 4
As a target, an Nb target with a purity of 99.99% and a Cu target (both φ152.4 mm, manufactured by High Purity Chemical Research Laboratory) were used to form a mixed thin film, from Nb-2% by volume Cu to Nb-30% by volume. The target input power for each of the Nb target and the Cu target is adjusted so as to continuously change to a thickness of 1.0 μm in thickness on the substrate, and similarly, Nb− After continuously changing from 30% by volume Cu to Nb-60% by volume to form a 1.0 μm thick layer in which the mixing ratio of the different phase components is inclined, the Nb-60% by volume Cu layer is formed to a thickness of 8.0 μm. The mixed thin film was formed on the substrate in the same manner as in Example 1 except that the mixed thin film having a total film thickness of 10 μm was formed on both surfaces of the substrate.

  Therefore, the mixing ratio of the heterogeneous components with respect to the thickness direction of the mixed thin film is as shown in the graph of FIG.

Thereafter, in order to obtain the composition of the film and the mass of Nb adhering to the substrate by sputtering, the sample formed on the Ta foil was cut into 2 cm ² squares and subjected to chemical analysis. As a result, the amount of Nb deposited by sputtering was 8 mg / cm ² .

  Thereafter, except for heat treatment conditions of 850 ° C. × 60 min, heat treatment, selective removal of Cu, pure water cleaning, and vacuum drying were performed in the same manner as in Example 1, and Ta foil and Nb foil were formed. Two types of porous valve metal electrodes according to this example were used as substrates (current collectors).

  As a result of measuring the capacitance in the same manner as in Example 1, the Ta foil and the Nb foil were 220 kCV / g for both of the two types used as the substrate (current collector).

  As a result of SEM observation in the same manner as in Example 1, a low porosity layer having a thickness of 1.0 μm with a continuously changing porosity and a thickness with continuously changing the porosity are formed on the substrate. A high porosity layer composed of a 1.0 μm layer and a layer having a constant porosity and a thickness of 8.0 μm was formed. Moreover, the remaining Cu particle | grains were not recognized from the SEM image of the low porosity layer.

  Further, as a result of obtaining the porosity from the SEM image in the same manner as in Example 1, the porosity of the low-porosity layer was continuously changed from 2% by volume to 30% by volume from the substrate side. The porosity of the layer was 60% by volume except that it continuously changed from 30% to 60% by volume on the substrate side.

  Furthermore, as in Example 1, as a result of evaluation by a tape peeling test, adhesion of the valve metal porous layer to the adhesive tape was not observed.

(Conventional example)
A mixed thin film was formed on a conventional Ta foil and Nb foil substrate in the same manner as in Example 1 except that the low heterogeneous component layer was not formed.

As a result of chemical analysis in the same manner as in Example 1, the amount of Ta deposited by sputtering was 13 mg / cm ² .

  Thereafter, similar to Example 1, heat treatment, selective removal of Cu, pure water cleaning, and vacuum drying were performed, and two types of conventional examples in which Ta foil and Nb foil were used as a substrate (current collector) were used. A porous valve metal electrode was obtained.

  The capacitance was measured in the same manner as in Example 1. As a result, the two types using Ta foil and Nb foil as the substrate (current collector) were both 220 kCV / g.

  As in Example 1, SEM observation was performed and the porosity was determined from the SEM image. As a result, residual Cu particles were not observed, and the porosity of the valve metal porous layer was 60% by volume.

  However, as in Example 1, as a result of evaluation in a tape peeling test, the porous metal valve layer was peeled off and adhered to the adhesive tape, and the adhesion was not stable.

(Comparative Example 1)
A mixed thin film was formed on a Ta foil and Nb foil substrate in the same manner as in Example 1 except that the composition of the low heterophase component layer was Ta-40 vol% Cu.

As a result of chemical analysis in the same manner as in Example 1, the amount of Ta deposited by sputtering was 20 mg / cm ² .

  Thereafter, in the same manner as in Example 1, heat treatment, selective removal of Cu, pure water cleaning, and vacuum drying were performed, and two types of this comparative example using Ta foil and Nb foil as a substrate (current collector) A porous valve metal electrode was obtained.

  As a result of measuring the capacitance in the same manner as in Example 1, it was 210 kCV / g for both of the two types using Ta foil and Nb foil as the substrate (current collector).

  As a result of SEM observation in the same manner as in Example 1, the boundary between the low porosity layer and the high porosity layer was unclear. The porosity in the vicinity of the substrate was 40% by volume, and the porosity at a position 0.3 μm from the substrate was 60% by volume. Moreover, the remaining Cu particle | grains were not recognized from a SEM image.

  In the same manner as in Example 1, as a result of evaluation by a tape peeling test, the valve metal porous layer was peeled off and adhered to the adhesive tape, and the adhesion was not stable.

(Comparative Example 2)
A mixed thin film was formed on a Ta foil and Nb foil substrate in the same manner as in Example 1 except that the composition of the low heterophase component layer was Ta-0.5 volume% Cu.

As a result of chemical analysis in the same manner as in Example 1, the amount of Ta deposited by sputtering was 14 mg / cm ² .

  Thereafter, except for the heat treatment conditions of 750 ° C. × 60 min, the heat treatment, selective removal of Cu, pure water cleaning, and vacuum drying were performed in the same manner as in Example 1, and the Ta foil and Nb foil were removed. Two types of porous valve metal electrodes according to this comparative example used as a substrate (current collector) were obtained.

  The capacitance was measured in the same manner as in Example 1. As a result, the two types using Ta foil and Nb foil as the substrate (current collector) were 180 kCV / g.

  As a result of SEM observation in the same manner as in Example 1, a low porosity layer having a thickness of 0.2 μm and a high porosity layer having a thickness of 9.8 μm were formed on the substrate. From the image, it was observed that a large amount of Cu particles remained in the low porosity layer. For this reason, porosity analysis and tape peeling test were not performed.

(Comparative Example 3)
A mixed thin film was formed on a Ta foil and Nb foil substrate in the same manner as in Example 1 except that the thickness of the low heterogeneous component layer was 0.05 μm.

As a result of chemical analysis in the same manner as in Example 1, the amount of Ta deposited by sputtering was 13 mg / cm ² .

  Thereafter, in the same manner as in Example 1, heat treatment, selective removal of Cu, pure water cleaning, and vacuum drying were performed, and two types of this comparative example using Ta foil and Nb foil as a substrate (current collector) A porous valve metal electrode was obtained.

  The capacitance was measured in the same manner as in Example 1. As a result, the two types of Ta foil and Nb foil used as the substrate (current collector) were 210 kCV / g.

  As a result of SEM observation as in Example 1, the presence of a low porosity layer was not observed. Since the low heterogeneous component layer is extremely thin, it is considered that it disappeared in the heat treatment step.

  SEM observation was performed in the same manner as in Example 1, and the porosity was determined from the SEM image. As a result, the remaining Cu particles were not observed, but the porosity in the vicinity of the substrate was 60% by volume.

  In the same manner as in Example 1, as a result of evaluation by a tape peeling test, the valve metal porous layer was peeled off and adhered to the adhesive tape, and the adhesion was not stable.

  As shown in Table 1, in Examples 1 to 3 of the present invention, peeling of the valve metal porous layer from the valve metal current collector did not occur, and stable adhesion was obtained. For this reason, it is understood that the porous valve metal electrode according to the present invention is suitable as an anode body of a thin electrolytic capacitor.

It is a graph which shows the mixing ratio of a different phase component with respect to the thickness direction of a mixed thin film. It is a graph which shows the mixing ratio of a different phase component with respect to the thickness direction of a mixed thin film. It is a graph which shows the mixing ratio of a different phase component with respect to the thickness direction of a mixed thin film. It is a graph which shows the mixing ratio of a different phase component with respect to the thickness direction of a mixed thin film.

Claims (7)

  A porous valve metal electrode comprising a valve metal current collector and a valve metal porous layer formed on the valve metal current collector, wherein the valve metal current collector includes the valve metal current collector. A low porosity layer is formed on the body side, and the porosity of the low porosity layer is lower than the porosity of the other part of the valve metal porous layer and is 1 to 30% by volume. Characteristic porous valve metal electrode.   The porous valve metal electrode according to claim 1, wherein the thickness of the low porosity layer is 1/100 to 1/10 of the thickness of the valve metal porous layer.   The porous valve metal electrode according to claim 1, wherein the valve metal of the valve metal porous layer is any one selected from Nb, Ta, Nb alloy, and Ta alloy.   A method for producing a porous valve metal electrode in which a mixed thin film composed of a valve metal and a heterogeneous component is formed on a valve metal current collector, heat-treated, and then the heterophasic component is removed. In forming the low-phase component layer, on the valve metal current collector side, the lower-phase component layer is lower than the mixing rate of the different-phase component in the other part of the mixed thin film and the mixing rate of the different-phase component is 1 to 30% by volume Forming a porous valve metal electrode.   The method for producing a porous valve metal electrode according to claim 4, wherein the thickness of the low heterogeneous component layer is 1/100 to 1/10 of the thickness of the mixed thin film.   The method for producing a porous valve metal electrode according to claim 4, wherein the mixed thin film is formed by simultaneous sputtering or simultaneous vapor deposition using a valve metal and a heterogeneous component.   The valve metal used for the mixed thin film is any one selected from Nb, Ta, Nb alloy, and Ta alloy, and Cu is used as the heterogeneous component. Manufacturing method of porous valve metal electrode.

Images