JP2010232699A - Solid electrolytic capacitor, and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the capacitance of a solid electrolytic capacitor while suppressing the cracking or crystallization of a dielectric layer and preventing increase in leakage current when a heat treatment process such as a reflow process is performed for the solid electrolytic capacitor. <P>SOLUTION: In the solid electrolytic capacitor including an anode 1 formed of a valve action metal or an alloy containing a valve action metal as a main constituent, a dielectric layer 2 formed by anodizing the anode, and a cathode 4 formed on the dielectric layer, the dielectric layer includes a first dielectric layer 21 located on the anode side, and a second dielectric layer 22 formed on the first dielectric layer, and an oxygen concentration in the second dielectric layer is decreased from the first dielectric layer side toward the cathode side. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an anode made of a valve action metal or an alloy containing a valve action metal as a main component, a dielectric layer formed by anodizing the anode, and a cathode formed on the dielectric layer. In particular, when a heat treatment process such as a reflow process is performed, an increase in leakage current is suppressed and a capacitance of the solid electrolytic capacitor is increased. It has characteristics.

  In general, as a solid electrolytic capacitor, an anode made of a valve action metal such as titanium, niobium or tantalum or an alloy mainly composed of this valve action metal is anodized in a phosphoric acid aqueous solution, and an oxide is formed on the surface of the anode. A dielectric layer comprising: an electrolyte layer composed of a conductive oxide or a conductive polymer on the dielectric layer; a carbon layer and a silver paint layer as a cathode on the electrolyte layer; Have been proposed (for example, see Patent Documents 1 and 2).

  However, the dielectric layer made of an oxide provided in the above-mentioned solid electrolytic capacitor is easily affected by heat, and in particular, the dielectric layer formed by anodizing an anode using niobium or titanium has a large effect of heat. It is easy to receive, and when a heat treatment process such as a reflow process is performed, a leakage current increases due to a crack in the dielectric layer due to the expansion and contraction of the electrolyte layer or a crystallization of the dielectric layer. There was a problem.

  In recent years, in a solid electrolytic capacitor using niobium as an anode, a dielectric layer having a niobium oxide layer and a niobium nitride region is provided on the surface of the anode, and the capacitance is increased by heating in the reflow process. A solid electrolytic capacitor that suppresses the change has also been proposed (see, for example, Patent Document 3).

However, even in a solid electrolytic capacitor in which a dielectric layer having a niobium oxide layer and a niobium nitride region is provided on the surface of the anode using niobium as described above, when a heat treatment step such as a reflow step is performed, There is a problem in that cracks in the dielectric layer and crystallization of the dielectric layer cannot be sufficiently suppressed, and leakage current still increases.
JP-A-6-151258 JP 2004-18966 A JP 11-329902 A

  The present invention suppresses the occurrence of cracks in the dielectric layer or crystallization of the dielectric layer when the solid electrolytic capacitor is subjected to a heat treatment step such as a reflow step, and the leakage current in the solid electrolytic capacitor is reduced. It is intended to increase the electrostatic capacity of the solid electrolytic capacitor by increasing the surface area of the anode while sufficiently suppressing the increase of.

  In the present invention, in order to solve the above-described problems, an anode made of a valve metal or an alloy mainly containing a valve metal, a dielectric layer formed by anodizing the anode, and the above In the solid electrolytic capacitor including the cathode formed on the dielectric layer, the dielectric layer is formed on the first dielectric layer located on the anode side and on the first dielectric layer. A second dielectric layer, and the oxygen concentration in the second dielectric layer decreases from the first dielectric layer side toward the cathode side.

  Here, in the above solid electrolytic capacitor, the second dielectric layer contains nitrogen and fluorine, and at least one element selected from silicon, phosphorus, titanium, niobium and germanium. In particular, it is preferable to contain silicon or germanium.

  Furthermore, in the above solid electrolytic capacitor, it is preferable that fluorine is contained in the first dielectric layer, and the fluorine concentration in the first dielectric layer is increased toward the anode side.

  Further, in the method for producing a solid electrolytic capacitor according to the present invention, an anode made of a valve metal or an alloy containing the valve metal as a main component, a dielectric layer formed by anodizing the anode, and the above In manufacturing a solid electrolytic capacitor including a cathode formed on a dielectric layer, the above anode is anodized in an electrolytic solution containing hexafluoride ions.

Here, examples of the hexafluoride added to the electrolytic solution include, for example, the general formula (NH ₄ ) _x MF _6.
(Wherein, M is an element selected from phosphorus, silicon, niobium, titanium, germanium, and zirconium). And as an electrolytic solution containing the above hexafluoride ions, specifically, ammonium hexafluorophosphate, ammonium hexafluorosilicate, ammonium hexafluorotitanate, ammonium hexafluoroniobate, ammonium hexafluorogermanate, etc. An electrolytic solution containing an ammonium salt can be used, and an electrolytic solution containing ammonium hexafluorogermanate is preferably used.

  Like the solid electrolytic capacitor in the present invention, the dielectric layer includes a first dielectric layer located on the anode side and a second dielectric layer formed on the first dielectric layer. If the oxygen concentration in the second dielectric layer is decreased from the first dielectric layer side toward the cathode side, the stretch response to heat in the second dielectric layer becomes lower as described above. It improves as it goes to the cathode side.

  As a result, when the solid electrolytic capacitor of the present invention is subjected to a heat treatment process such as a reflow process, even if the electrolyte layer expands and contracts and a thermal stress is applied as described above, the thermal stress is applied to the second dielectric. In the body layer, it gradually relaxes toward the first dielectric layer, the thermal stress acting on the first dielectric is relaxed, cracking in the dielectric layer is suppressed, and leakage current is reduced. The increase is prevented.

  Further, in the solid electrolytic capacitor of the present invention, when the second dielectric layer contains nitrogen and fluorine, and contains at least one element selected from silicon, phosphorus, titanium, niobium and germanium, When a heat treatment process such as a reflow process is performed, the second dielectric layer is suppressed from crystallization, and an increase in leakage current due to the crystallization of the dielectric layer is also suppressed. When contained, the increase in leakage current is further suppressed.

  Furthermore, in the solid electrolytic capacitor of the present invention, when fluorine is contained in the first dielectric layer, and the fluorine concentration in the first dielectric layer is increased toward the anode side, a reflow process or the like is performed. When the heat treatment step is performed, it is possible to suppress the diffusion of oxygen from the dielectric layer to the anode, thereby reducing the thickness of the dielectric layer, and further suppressing the increase in leakage current.

  Further, as in the method for producing a solid electrolytic capacitor in the present invention, when an anode made of a valve metal or an alloy mainly containing a valve metal is anodized in an electrolyte containing hexafluoride ions, the anode side And a second dielectric layer formed on the first dielectric layer, wherein the oxygen concentration in the second dielectric layer is the first dielectric layer. While decreasing from the dielectric layer side toward the cathode side, fluorine is contained in the first dielectric layer and the second dielectric layer.

  In addition, when anodizing an anode made of a valve metal or an alloy containing the valve metal as a main component as described above in an electrolyte containing hexafluoride ions, ammonium hexafluorophosphate, ammonium hexafluorosilicate When using an electrolyte containing at least one ammonium salt selected from ammonium hexafluorotitanate, ammonium hexafluoroniobate and ammonium hexafluorogermanate, nitrogen and fluorine are contained, and silicon, phosphorus, A second dielectric layer containing at least one element selected from titanium, niobium and germanium is formed.

  Moreover, when an anode made of a valve metal or an alloy containing a valve metal as a main component as described above is anodized in an electrolyte containing hexafluoride ions, a part of the surface of the anode is dissolved. Asperities are formed on the surface of the anode, which increases the surface area of the anode and increases the capacitance of the solid electrolytic capacitor. In particular, when an electrolytic solution containing ammonium hexafluorogermanate is used, since the oxidizing power of germanium fluoride is strong, the dissolution of the anode surface advances, the surface area of the anode greatly increases, and the capacitance of the solid electrolytic capacitor It is considered that the generation of defects in the dielectric layer is reduced and the leakage current is further suppressed.

  Hereinafter, the solid electrolytic capacitor and the manufacturing method thereof according to the embodiment of the present invention will be specifically described, and a comparative example will be given. In the solid electrolytic capacitor according to the embodiment of the present invention, a heat treatment process such as a reflow process is performed. Even in this case, it is clarified that the increase in leakage current is suppressed and the capacitance increases. The solid electrolytic capacitor and the method for manufacturing the same according to the present invention are not limited to those shown in the following examples, and can be implemented with appropriate modifications within a range not changing the gist thereof.

Example 1
A solid electrolytic capacitor of Example 1 will be described with reference to the accompanying drawings.

  In the solid electrolytic capacitor of Example 1, a niobium metal powder having an average particle diameter of 2 μm is sintered to produce an anode 1 made of a porous sintered body of niobium. The lead wire 11 is extended.

Then, when the anode 1 is anodized to form the dielectric layer 2 on the surface of the anode 1, a 0.1 wt% ammonium hexafluorosilicate aqueous solution is used as the electrolytic solution.
In this electrolytic solution heated to 0 ° C., a voltage of 8 V is applied between the anode 1 and the counter electrode for 10 hours to anodize the anode 1, and the dielectric layer 2 is formed on the surface of the anode 1. Formed.

  Then, an electrolyte layer 3 made of polypyrrole is formed on the dielectric layer 2 formed on the surface of the anode 1 as described above by chemical polymerization or the like, and further, a graphite layer 41 and a silver paste are formed on the electrolyte layer 3. The cathode 4 composed of the layer 42 was formed. In addition to the polypyrrole, a conductive polymer material such as polythiophene or polyaniline, or a conductive oxide such as manganese dioxide can be used as the material for the electrolyte layer 3.

  Next, the anode lead 5 is connected to the lead wire 11 extending from the anode 1, and the cathode lead 6 is connected to the silver paste layer 42 of the cathode 4, which is then covered with a resin layer 7 made of epoxy resin. The anode lead 5 and the cathode lead 6 were taken out through the resin layer 7 to produce a solid electrolytic capacitor.

  In addition, when the anode 1 is anodized as described above, the surface of the dielectric layer 2 formed on the surface of the anode 1 by the energy dispersive spectroscopy (EDX), that is, the anode 2 The content of each element in the depth direction from the opposite surface was measured, and the results are shown in FIG.

  As a result, the dielectric layer 2 includes a first dielectric layer 21 located on the surface of the anode 1 and a first dielectric layer 21 formed on the first dielectric layer 21 as schematically shown in FIG. The second dielectric layer 22 has a structure with a depth of about 4 nm from the surface opposite to the anode 2. In the second dielectric layer 22, the second dielectric layer 22 has a structure with a depth of about 4 nm. While the oxygen concentration decreased from the first dielectric layer 21 toward the surface, nitrogen, silicon, and fluorine were contained, and the concentrations of nitrogen and silicon increased toward the surface.

  On the other hand, the first dielectric layer 21 in the region where the depth from the surface of the dielectric layer 2 is in the range of about 4 nm to about 25 nm contains almost no nitrogen and silicon, and the anode 1 The fluorine concentration increased as the temperature approached, and when the depth of about 17 nm from the surface of the dielectric layer 2 was exceeded, the oxygen concentration decreased rapidly while the niobium concentration increased rapidly.

(Example 2)
In Example 2, an anode 1 made of a porous sintered body of titanium produced by sintering titanium metal powder having an average particle diameter of 2 μm is used, and otherwise, the case of Example 1 above is used. A solid electrolytic capacitor was produced in the same manner as described above.

Example 3
In Example 3, a niobium alloy mainly composed of niobium produced by sintering a mixture of niobium metal powder having an average particle diameter of 2 μm and aluminum powder mixed at a weight ratio of about 99: 1. A solid electrolytic capacitor was produced in the same manner as in Example 1 except that the anode 1 made of the porous sintered body was used.

  As for the solid electrolytic capacitors shown in Examples 2 and 3, the dielectric layer 2 formed on the surface of the anode 1 was examined in the same manner as in Example 1, and as a result, As in the case, the first dielectric layer 21 located on the surface of the anode 1 and the second dielectric layer 22 formed on the first dielectric layer 21 have a structure, In the second dielectric layer 22, the oxygen concentration decreases from the first dielectric layer 21 toward the surface, while nitrogen, silicon, and fluorine are contained, and the concentrations of nitrogen and silicon increase toward the surface. In addition, the first dielectric layer 21 contained almost no nitrogen and silicon, and the fluorine concentration increased as the anode 1 was approached.

(Comparative Example 1)
In Comparative Example 1, when anodizing the anode made of the same niobium porous sintered body as in Example 1 described above, a 0.1 wt% phosphoric acid aqueous solution was used as the electrolytic solution. In the same manner as in Example 1, a solid electrolytic capacitor having the structure shown in FIG. 1 was produced.

  Here, also in the comparative example 1, the dielectric layer formed at the stage where the anode was anodized in the electrolytic solution using the 0.1% by weight phosphoric acid aqueous solution as described above, As in the case of 1, the content of each element in the depth direction from the surface opposite to the anode, that is, the surface of the dielectric layer, was measured by energy dispersive spectroscopy (EDX), and the results are shown in FIG. It was shown to.

  As a result, the dielectric layer in Comparative Example 1 contained phosphorus in a depth range of about 4 nm from the surface of the dielectric layer. Unlike the above Example 1, nitrogen, silicon and fluorine It was not contained. Further, the oxygen concentration and niobium concentration are almost constant from the surface of the dielectric layer to a depth range of about 17 nm, and the oxygen concentration decreases on the surface side of the dielectric layer as in the first embodiment. There was no. The dielectric layer in Comparative Example 1 was also located in a range where the depth from the surface was about 25 nm.

(Comparative Example 2)
In Comparative Example 2, the same 0.1 wt% aqueous phosphoric acid solution as in Comparative Example 1 was used as the electrolytic solution when anodizing the anode made of the same porous sintered body of titanium as in Example 2 above. Otherwise, a solid electrolytic capacitor was produced in the same manner as in Example 2.

(Comparative Example 3)
In Comparative Example 3, the same 0.1 wt% aqueous phosphoric acid solution as in Comparative Example 1 was used as the electrolytic solution when anodizing the anode made of the porous sintered body of the same niobium alloy as in Example 3 above. Otherwise, a solid electrolytic capacitor was produced in the same manner as in Example 3.

  Further, for the solid electrolytic capacitors shown in Comparative Examples 2 and 3, the dielectric layer 2 formed on the surface of the anode 1 was examined in the same manner as in Example 1 above. Similarly, phosphorus was contained within a certain depth range from the surface of the dielectric layer, but nitrogen, silicon and fluorine were not contained, and oxygen from the surface of the dielectric layer to a certain depth was also included. The concentration and niobium concentration were substantially constant, and the oxygen concentration did not decrease on the surface side of the dielectric layer as in Example 1 above.

  In Example 1 and Comparative Example 1, the surface state after the anode was anodized as described above was observed with an electron microscope (SEM), and the observation results of Example 1 were compared with FIG. The observation results of Example 1 are shown in FIG. As a result, in Example 1, irregularities were formed on the surface of the anode after anodization, and the surface area was increased. On the other hand, in Comparative Example 1, unevenness on the surface of the anode after anodic oxidation was not observed. Even when the anode was anodized as shown in Example 2 and Example 3, as in Example 1, irregularities were formed on the surface of the anode after anodization and the surface area was increased. It was.

  And the leakage current in the case of reflowing each solid electrolytic capacitor of Examples 1-3 and Comparative Examples 1-3 produced as mentioned above was measured.

  Here, in reflowing each of the above solid electrolytic capacitors, heat treatment was performed at a peak temperature of 240 ° C. for 5 minutes by an air reflow method, and a voltage of 5 V was applied to each of the solid electrolytic capacitors thus reflowed, and 20 seconds later. The leakage current was measured and the results are shown in Table 1.

  Further, the electrostatic capacity at a frequency of 120 Hz was measured for each solid electrolytic capacitor after reflowing as described above, and the results are shown in Table 1.

  As is apparent from this result, the anode made of a valve metal such as niobium is anodized in an electrolytic solution made of an aqueous ammonium hexafluorosilicate solution, and the first dielectric layer located on the anode side as described above is used. And the solid electrolytic capacitors of Examples 1 to 3 in which a dielectric layer including the second dielectric layer formed on the first dielectric layer is formed, the anode made of a valve metal such as niobium, Compared with the solid electrolytic capacitors of Comparative Examples 1 to 3, which were anodized in an electrolytic solution made of an aqueous phosphoric acid solution to form a dielectric layer as described above, the leakage current after reflowing was significantly reduced.

  Moreover, the solid electrolytic capacitor of Example 1 and the solid electrolytic capacitor of Comparative Example 1 using the same valve metal as the anode, the solid electrolytic capacitor of Example 2, the solid electrolytic capacitor of Comparative Example 2, and the solid electrolytic capacitor of Example 3 When comparing the solid electrolytic capacitor of Comparative Example 3 with the solid electrolytic capacitor of Example, the capacitance of the solid electrolytic capacitor of Example was larger than that of the solid electrolytic capacitor of Comparative Example.

(Examples 4 to 7)
In Examples 4 to 7, when anodizing the anode 1 made of the same niobium porous sintered body as in Example 1 above, only the type of the electrolyte used was changed, and otherwise the above-described implementation was performed. A solid electrolytic capacitor was produced in the same manner as in Example 1.

  Here, as an electrolytic solution, 0.1 wt% ammonium hexafluorophosphate aqueous solution was used in Example 4, 0.1 wt% ammonium hexafluoroniobate aqueous solution was used in Example 5, and 0.1 wt% ammonium hexafluoroniobate aqueous solution was used in Example 6. In Example 7, a 0.1% by weight ammonium hexafluorogermanate aqueous solution was used as a weight% ammonium hexafluorotitanate aqueous solution.

  For the solid electrolytic capacitors in Examples 4 to 7, the dielectric layer 2 formed on the surface of the anode 1 was examined in the same manner as in Example 1 above. As a result, as in the case of the first embodiment, the first dielectric layer 21 located on the surface of the anode 1 and the second dielectric layer 22 formed on the first dielectric layer 21 are configured. In the second dielectric layer 22, the oxygen concentration decreased from the first dielectric layer 21 side toward the surface of the dielectric layer 2. In addition to the nitrogen and fluorine, the second dielectric layer 22 contains phosphorus in Example 4, titanium in Example 5, niobium in Example 6, and germanium in Example 7. In the first dielectric layer 21, the fluorine concentration increased as the anode 1 was approached.

  Next, each of the solid electrolytic capacitors of Examples 4 to 7 was also heat-treated at a peak temperature of 240 ° C. for 5 minutes by the air reflow method in the same manner as described above, and each solid electrolytic capacitor thus reflowed was subjected to heat treatment. On the other hand, a voltage of 5 V was applied and the leakage current after 20 seconds was measured, and the capacitance at a frequency of 120 Hz was measured. The result was combined with that of Example 1 above, and the results are shown in Table 2 below. It was shown to.

As a result, also in each of the solid electrolytic capacitors of Examples 4 to 7, the leakage current after reflowing is remarkably higher than that of each of the solid electrolytic capacitors of Comparative Examples 1 to 3, as in the case of Examples 1 to 3. In particular, the anode 1 made of a porous sintered body of niobium is anodized in an aqueous solution of ammonium hexafluorophosphate or an aqueous solution of ammonium hexafluorogermanate, and silicon in the second dielectric layer 22 is obtained. Example 1 and Example 7 containing
In the solid electrolytic capacitor, the leakage current after reflowing was greatly reduced.

Further, in the solid electrolytic capacitor of Example 7 in which the anode 1 made of a porous sintered body of niobium was anodized in an aqueous ammonium hexafluorogermanate solution, the capacitance was greatly increased.

It is a section explanatory view of the solid electrolytic capacitor concerning the example of the present invention. In the solid electrolytic capacitor in Example 1 of this invention, it is the figure which showed the result of having measured the content of each element in the depth direction from the surface on the opposite side to an anode about the dielectric material layer formed in the surface of the anode. . In the solid electrolytic capacitor in the Example of this invention, it is the schematic sectional drawing which showed the state of the dielectric material layer formed in the surface of the anode. In the solid electrolytic capacitor in the comparative example 1, it is the figure which showed the result of having measured the content of each element in the depth direction from the surface on the opposite side to an anode about the dielectric material layer formed in the surface of the anode. In Example 1, it is the figure which showed the surface state after anodizing the anode. In the comparative example 1, it is the figure which showed the surface state after anodizing an anode.

DESCRIPTION OF SYMBOLS 1 Anode 2 Dielectric layer 3 Electrolyte layer 4 Cathode 5 Anode lead 6 Cathode lead 7 Resin layer 11 Lead wire 21 1st dielectric layer 22 2nd dielectric layer 41 Graphite layer 42 Silver paste layer

Claims (7)

A solid electrolytic capacitor comprising an anode made of a valve metal or an alloy containing a valve metal as a main component, a dielectric layer formed by anodizing the anode, and a cathode formed on the dielectric layer In
The dielectric layer includes a first dielectric layer located on the anode side, and a second dielectric layer formed on the first dielectric layer,
A solid electrolytic capacitor, wherein silicon is contained in the second dielectric layer.   The solid electrolytic capacitor according to claim 1, wherein the first dielectric layer does not contain silicon.   The solid electrolytic capacitor according to claim 1, wherein the valve metal is niobium.   The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the second dielectric layer further contains nitrogen.   The solid electrolytic capacitor according to claim 1, wherein the second dielectric layer further contains fluorine.   The fluorine is contained in the said 1st dielectric material layer, The density | concentration of the said fluorine is increasing toward the said anode side, The Claim 1 characterized by the above-mentioned. Solid electrolytic capacitor. Forming a dielectric layer on the anode by anodizing a valve action metal or an anode made of an alloy containing a valve action metal as a main component in an electrolyte containing silicon;
And a step of forming a cathode on the dielectric layer.

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