JP4545204B2 - Solid electrolytic capacitor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a solid electrolytic capacitor and a method for manufacturing the same.

  Amorphous niobium oxide has high insulation and has a dielectric constant of about 1.8 times that of tantalum oxide, which is the material of conventional solid electrolytic capacitors. It is attracting attention as a dielectric material.

This is because conventional solid electrolytic capacitors using niobium oxide are easily affected by heat treatment such as the reflow process, and the stability of capacitance is inferior to solid electrolytic capacitors using other dielectric materials such as tantalum oxide. In order to suppress this, a solid electrolytic capacitor in which a niobium nitride region is formed in niobium oxide constituting the dielectric layer has been proposed (see, for example, Patent Document 1).
JP 11-329902 A

  However, even in a conventional solid electrolytic capacitor using niobium oxide having a niobium nitride region formed as described above as a dielectric layer, a part of amorphous niobium oxide is crystallized by heat treatment such as a reflow process. The phenomenon that occurs. As a result, since the dielectric layer contains niobium oxide crystals having low insulation, there is a problem in that the insulation of the dielectric layer is lowered. Furthermore, since niobium oxide undergoes a volume change as the state changes from amorphous to crystalline, cracks are likely to occur in the dielectric layer due to crystallization of niobium oxide. As a result, there is a problem that the anode and the cathode formed on the surface of the dielectric layer are easily short-circuited. In addition, even in a solid electrolytic capacitor using niobium oxide having a conventional niobium nitride region as a dielectric layer, the diffusion of oxygen in the dielectric layer cannot be sufficiently suppressed, so that the thickness of the dielectric layer is reduced. There was a problem that it was easy. As a result, the conventional solid electrolytic capacitor has a problem that the leakage current between the anode and the cathode cannot be sufficiently reduced.

  An object of the present invention is to provide a solid electrolytic capacitor with reduced leakage current and a method for manufacturing the same.

In order to achieve the above object, a solid electrolytic capacitor according to a first aspect of the present invention is an anode made of niobium or a niobium alloy, niobium and oxygen formed on the anode as main components, and contains a fluorine . A dielectric layer; a second dielectric layer containing sulfur in addition to niobium and oxygen formed on the first dielectric layer; and a cathode formed on the second dielectric layer. In the present invention, “having niobium and oxygen as main components” means a state containing niobium and oxygen and having niobium or oxygen as main components. The dielectric layer is made of niobium oxide containing either one of niobium or oxygen as a main component. In the present invention, “ containing sulfur in addition to niobium and oxygen” means a state containing sulfur together with niobium oxide, and the second dielectric layer is composed of niobium oxide containing sulfur . .

In the solid electrolytic capacitor according to the first aspect, as described above, of the first dielectric layer and the second dielectric layer made of niobium oxide constituting the dielectric layer, the solid electrolytic capacitor is positioned on the surface side where the cathode and the like are formed. Since the second dielectric layer contains sulfur, niobium oxide on the surface of the dielectric layer is difficult to crystallize. As a result, even when heat treatment such as a reflow process is performed, crystalline niobium oxide having low insulating properties is not easily generated in the second dielectric layer, and it is possible to suppress a decrease in insulating properties on the surface of the dielectric layer. it can. In addition, since crystallization of niobium oxide on the surface of the dielectric layer is suppressed, cracks are unlikely to occur on the surface of the dielectric layer. That is, the second dielectric layer functions as a surface protective layer for the dielectric layer. As a result, cracks reaching the inside of the dielectric layer are less likely to occur, so that it is possible to suppress a short circuit between the anode and the cathode formed on the surface of the dielectric layer. Therefore, in the first aspect of the invention, it is possible to obtain a solid electrolytic capacitor in which a decrease in insulation of the dielectric layer and cracking of the dielectric layer are suppressed, and leakage current is reduced.

The first dielectric layer of a solid electrolytic capacitor according to the first aspect includes fluorine. Fluorine can suppress crystallization of niobium oxide as in the case of the above-described sulfur , so that leakage current can be reduced.

  In the solid electrolytic capacitor according to the first aspect, preferably, the concentration of fluorine increases from the cathode side to the anode side in the first dielectric layer. With this configuration, since the fluorine concentration on the anode side in the first dielectric layer is increased, a region containing niobium fluoride is easily formed on the anode side in the first dielectric layer. In the dielectric layer composed of niobium oxide containing niobium fluoride, oxygen is difficult to diffuse, so the region containing niobium fluoride at the interface between the dielectric layer and the anode suppresses the diffusion of oxygen from the dielectric layer to the anode. It functions as an oxygen blocking layer. As a result, since it is difficult for oxygen to decrease from the dielectric layer, it is possible to suppress a decrease in the thickness of the dielectric layer. Therefore, it can suppress that the insulation of a dielectric material layer falls.

The manufacturing method of solid electrolytic capacitor according to a second aspect of the invention, the anode of niobium or niobium alloy, by anodizing the first aqueous solution containing fluoride ions, as a main component niobium and oxygen Then, following the step of forming the first dielectric layer containing fluorine and the step of forming the first dielectric layer, the first dielectric is formed by anodizing the anode in a second aqueous solution containing sulfate ions . Forming a second dielectric layer containing sulfur in addition to niobium and oxygen on the layer, and forming a cathode on the second dielectric layer.

In the method for manufacturing a solid electrolytic capacitor according to the second aspect, following the step of forming the first dielectric layer, the dielectric layer is configured by anodizing the anode in a second aqueous solution containing sulfate ions. Of the first dielectric layer and the second dielectric layer made of niobium oxide, sulfur can be contained in the second dielectric layer located on the surface side where the cathode or the like is formed. Thereby, since niobium oxide on the surface of the dielectric layer becomes difficult to crystallize, it is possible to suppress a decrease in insulation on the surface of the dielectric layer. In addition, since crystallization of niobium oxide on the surface of the dielectric layer can be suppressed, cracks are unlikely to occur on the surface of the dielectric layer. As a result, since cracks reaching the inside of the dielectric layer are less likely to occur, it is possible to suppress a short circuit between the anode and the cathode formed on the surface of the dielectric layer. Therefore, in the invention of the second aspect, it is possible to easily manufacture a solid electrolytic capacitor in which a decrease in the insulation property of the dielectric layer and cracking of the dielectric layer are suppressed and the leakage current is reduced.

The 1st aqueous solution in the manufacturing method of the solid electrolytic capacitor by the said 2nd aspect contains a fluorine ion. If comprised in this way, since the 1st dielectric material layer containing a fluorine can be formed easily, crystallization of the niobium oxide in a 1st dielectric material layer can be suppressed. Further, since the first dielectric layer can be formed such that the fluorine concentration increases from the cathode side toward the anode side, the fluorine concentration on the anode side in the first dielectric layer can be increased. Thus, a region containing niobium fluoride having a function as an oxygen blocking layer that suppresses diffusion of oxygen from the dielectric layer to the anode can be easily formed at the interface between the dielectric layer and the anode. As a result, oxygen is less likely to decrease from the dielectric layer, and thus the thickness of the dielectric layer is less likely to decrease. Therefore, the insulating property of the dielectric layer is not easily lowered, and the leakage current can be further reduced.

Furthermore, by performing anodic oxidation in the first aqueous solution containing fluorine ions, the surface of the anode made of niobium or a niobium alloy is dissolved so that the fluorine ions have an uneven shape, so that the surface area of the anode is increased. In general, the capacitance C of the capacitor is proportional to the surface area of the anode, and the equivalent series resistance (ESR) in the high frequency region is proportional to 1 / (2πfC) ^1/2 where the frequency is f. Therefore, since the capacitance increases as the surface area of the anode increases, a solid electrolytic capacitor capable of reducing ESR in the high frequency region can be easily manufactured.

  Hereinafter, the present invention will be described in more detail based on the embodiments. However, the present invention is not limited to the following embodiments, and can be appropriately modified and implemented without departing from the scope of the present invention. It is a thing.

  FIG. 1 is a cross-sectional structure diagram of a solid electrolytic capacitor according to an embodiment of the present invention.

  As shown in FIG. 1, in the solid electrolytic capacitor 100, the surface of the anode 1 is oxidized with high insulation so as to cover the periphery of the anode 1 made of a porous sintered body obtained by sintering and molding niobium particles in a vacuum. A dielectric layer 2 made of niobium is formed. The dielectric layer 2 is formed on the first dielectric layer 21 so as to cover the periphery of the first dielectric layer 21 and the first dielectric layer 21 formed on the anode 1 so as to cover the periphery of the anode 1. The second dielectric layer 22 is formed.

  The first dielectric layer 21 contains fluorine, and the fluorine concentration decreases from the anode 1 side toward the second dielectric layer 22 side. The second dielectric layer 22 contains phosphorus or sulfur.

  An electrolyte layer 3 is formed on the dielectric layer 2 so as to cover the periphery of the dielectric layer 2. A cathode 4 is formed on the electrolyte layer 3 so as to cover the periphery of the electrolyte layer 3. Here, the cathode 4 includes a first conductive layer 4a formed so as to cover the periphery of the electrolyte layer 3, and a second conductive layer 4b formed so as to cover the periphery of the first conductive layer 4a. Yes. For the electrolyte layer 3, a conductive polymer such as polypyrrole or polythiophene or a material such as manganese dioxide is used. Carbon paste or the like is used for the first conductive layer 4a. For the second conductive layer 4b, a silver paste made of silver particles, a protective colloid and an organic solvent is used. The protective colloid is a hydrocolloid added to increase the stability of the hydrophobic colloid to the electrolyte (Iwanami Dictionary of Physical and Chemical Dictionary, 5th edition, p1300).

  A conductive adhesive layer 5 is formed on the upper surface of the periphery of the cathode 4, and a cathode terminal 6 is formed on the conductive adhesive layer 5. A part of the anode lead 1a is embedded in the anode 1, and the anode terminal 7 is connected to the anode lead 1a exposed from the anode 1 by welding. Further, a mold exterior resin 8 is formed around the cathode 4, the cathode terminal 6, and the anode terminal 7 so that the ends of the cathode terminal 6 and the anode terminal 7 are drawn out to the outside. Thus, a solid electrolytic capacitor according to an embodiment of the present invention is configured.

  Next, a method for manufacturing the solid electrolytic capacitor 100 according to the embodiment of the present invention shown in FIG. 1 will be described.

  First, the niobium particles formed so as to embed a part of the anode lead 1a on the anode lead 1a are sintered in vacuum to form the anode 1 made of a porous sintered body. In this case, the niobium particles are welded.

  Next, the anode 1 is anodized in a first aqueous solution containing fluorine ions such as an aqueous ammonium fluoride solution. As a result, a first dielectric layer 21 made of niobium oxide is formed on the anode 1 so as to cover the periphery of the anode 1. At this time, the first dielectric layer 21 also contains fluorine, and the fluorine concentration decreases from the anode 1 side toward the surface side of the first dielectric layer 1 (second dielectric layer 22 side). .

  Subsequently, the anode 1 is anodized in a second aqueous solution containing phosphate ions such as a phosphoric acid aqueous solution or sulfate ions such as a sulfuric acid aqueous solution. Thus, the second dielectric layer 22 made of niobium oxide containing phosphorus or sulfur is formed on the first dielectric layer 21 so as to cover the periphery of the first dielectric layer 21. As a result, the dielectric layer 2 made of niobium oxide having high insulating properties, in which the first dielectric layer 21 and the second dielectric layer 22 are sequentially laminated, is formed on the surface of the anode 1.

  Next, an electrolyte layer 3 made of a conductive polymer such as polypyrrole or polythiophene is formed on the dielectric layer 2 by polymerization or the like so as to cover the periphery of the dielectric layer 2. When the electrolyte layer 3 made of a conductive polymer or the like is used, the electrolyte layer 3 is formed on the dielectric layer 2 so as to fill the concave portion on the surface of the porous sintered body constituting the anode 1.

  Thereafter, a carbon paste or the like is applied onto the electrolyte layer 3 and dried at a predetermined temperature, thereby forming the first conductive layer 4a on the electrolyte layer 3 so as to cover the periphery of the electrolyte layer 3. Further, by applying a silver paste or the like on the first conductive layer 4a so as to cover the periphery of the first conductive layer 4a and drying at a predetermined temperature, the second conductive layer 4b is formed on the first conductive layer 4a. Form. Thereby, the cathode 4 composed of the first conductive layer 4 a and the second conductive layer 4 b is formed on the electrolyte layer 3.

  Next, after applying a conductive adhesive on the cathode terminal 6, the conductive adhesive layer 5 is formed by drying the cathode 4 and the cathode terminal 6 in contact with each other via the conductive adhesive. At the same time, the cathode 4 and the cathode terminal 6 are connected by the conductive adhesive layer 5. An anode terminal 7 is connected to the anode lead 1a of the anode 1 exposed from the dielectric layer 2, the electrolyte layer 3, and the cathode 4 by welding. Thereafter, the mold exterior resin 8 is formed around the cathode 4, the cathode terminal 6, and the anode terminal 7 so that the ends of the cathode terminal 6 and the anode terminal 7 are drawn out to the outside. With the above method, the solid electrolytic capacitor 100 according to one embodiment of the present invention is manufactured.

  In one embodiment of the present invention, a second dielectric layer 22 made of niobium oxide containing phosphorus or sulfur is formed on the surface side of the dielectric layer 2 on the side where the electrolyte layer 3 and the cathode 4 are formed. Therefore, even if heat treatment such as a reflow process is performed in the second dielectric layer 22, crystalline niobium oxide having low insulation is unlikely to be generated. As a result, it is possible to suppress a decrease in the insulating property of the second dielectric layer 22 on the surface side of the dielectric layer 2. In addition, since niobium oxide in the second dielectric layer 22 is difficult to crystallize, the second dielectric layer 22 is unlikely to crack. As a result, cracks reaching the inside of the dielectric layer 2 are less likely to occur, so that the short circuit between the anode 1 and the cathode 4 formed on the surface of the dielectric layer 2 can be suppressed. Therefore, a decrease in the insulating property of the dielectric layer 2 is suppressed, and a solid electrolytic capacitor with reduced leakage current can be obtained.

  In the above-described embodiment, the first dielectric layer 21 contains fluorine that can suppress crystallization of niobium oxide, so that leakage current can be reduced.

  In the above embodiment, the fluorine concentration in the first dielectric layer 21 increases from the cathode 4 side to the anode 1 side in the first dielectric layer 21. The fluorine concentration on the anode 1 side in 21 increases. Accordingly, a region containing niobium fluoride is easily formed at the interface between the first dielectric layer 21 and the anode 1. The region containing niobium fluoride at the interface between the first dielectric layer 21 and the anode 1 has a function as an oxygen blocking layer that suppresses the diffusion of oxygen from the first dielectric layer 21 to the anode 1. Therefore, it is difficult for oxygen to decrease from the dielectric layer 2. As a result, since the thickness of the dielectric layer 2 is difficult to decrease, it is possible to suppress a decrease in insulating properties of the dielectric layer 2 and to reduce a leakage current.

  In the above embodiment, following the step of forming the first dielectric layer 21, the anode 1 is anodized in a second aqueous solution containing phosphate ions or sulfate ions to thereby form the dielectric layer 2. Of the first dielectric layer 21 and the second dielectric layer 22 made of niobium oxide to constitute, phosphorus or sulfur is contained in the second dielectric layer 22 located on the surface side where the electrolyte layer 3 and the cathode 4 are formed. It can be included. Thereby, since niobium oxide on the surface of the dielectric layer 2 becomes difficult to crystallize, it is possible to suppress a decrease in insulation on the surface of the dielectric layer 2. Further, since crystallization of niobium oxide on the surface of the dielectric layer 2 can be suppressed, cracks are hardly generated on the surface of the dielectric layer 2. As a result, cracks reaching the inside of the dielectric layer 2 are less likely to occur, so that the anode 1 and the electrolyte layer 3 and the cathode 4 formed on the dielectric layer 2 can be prevented from being short-circuited. Therefore, it is possible to easily manufacture a solid electrolytic capacitor in which the deterioration of the insulating property of the dielectric layer 2 and the occurrence of cracks in the dielectric layer 2 are suppressed, and the leakage current is reduced.

  Moreover, in the said one Embodiment, since the 1st dielectric material layer 21 is formed with the 1st aqueous solution containing a fluorine ion, the 1st dielectric material layer 21 can be made to contain a fluorine easily. Thereby, crystallization of niobium oxide in the first dielectric layer 21 can be suppressed. Further, since the first dielectric layer 21 can be formed so that the fluorine concentration contained in the first dielectric layer 21 increases from the cathode 4 side toward the anode 1 side, the first dielectric layer 21 The fluorine concentration on the anode 1 side can be increased. Thus, a region containing niobium fluoride having a function as an oxygen blocking layer for suppressing diffusion of oxygen from the dielectric layer 2 to the anode 1 can be easily formed at the interface between the dielectric layer 2 and the anode 1. Can do. As a result, since it is difficult for oxygen to decrease from the dielectric layer 2, the thickness of the dielectric layer 2 is difficult to decrease. Therefore, it is possible to suppress a decrease in the insulating property of the dielectric layer 2 and further reduce the leakage current.

  Furthermore, in the above embodiment, since the anodic oxidation is performed in the first aqueous solution containing fluorine ions, the surface of the anode 1 made of niobium is dissolved so that the fluorine ions have an uneven shape. Thereby, since the surface area of the anode 1 increases, the electrostatic capacity of the solid electrolytic capacitor can be increased, so that the ESR in the high frequency region can be reduced.

  In the above embodiment, since the anode 1 is made of a porous sintered body, the anode 1 has a large surface area and can have a large capacity. In the present embodiment, a porous sintered body is used as the anode 1, but the present invention is not limited to this, and for example, a metal foil made of niobium may be used. Further, the anode 1 may be composed of not only niobium alone but also a niobium alloy containing elements such as tungsten, vanadium, zinc, aluminum, molybdenum, hafnium and zirconium.

  In the above embodiment, the electrolyte layer 3 is formed between the dielectric layer 2 and the cathode 4, but the present invention is not limited to this, and the electrolyte layer 3 may be omitted. Good. In this case, the cathode 4 is directly formed on the dielectric layer 2.

  In the following examples, solid electrolytic capacitors were produced and evaluated.

( Reference Example 1)
FIG. 2 is a sectional structural view of a solid electrolytic capacitor according to Reference Example 1 of the present invention. In Reference Example 1, a solid electrolytic capacitor A shown in FIG. 2 was produced by the following method.

(Oxidation step 1)
First, a niobium porous sintered body having a height of about 2.8 mm, a width of about 3.3 mm, and a depth of about 1.7 mm formed so as to embed a part of the anode lead 1 a was used as the anode 1. Anodization is performed for about 10 hours at a constant voltage of about 10 V in an about 0.5 wt% ammonium fluoride aqueous solution (fluoric acid ion concentration: about 0.05 wt%) in which the anode 1 is held at about 60 ° C. Thus, the first dielectric layer 21 was formed on the anode 1 so as to cover the periphery of the anode 1. Here, the ammonium fluoride aqueous solution is an example of the “first aqueous solution” in the present invention.

(Oxidation step 2)
Subsequently, the periphery of the first dielectric layer 21 is formed by anodizing the anode 1 in a phosphoric acid aqueous solution of about 0.5% by weight maintained at about 60 ° C. at a constant voltage of about 10 V for about 2 hours. A second dielectric layer 22 was formed on the first dielectric layer 21 so as to cover it. Here, the phosphoric acid aqueous solution is an example of the “second aqueous solution” in the present invention. Thereby, the dielectric layer 2 composed of the first dielectric layer 21 and the second dielectric layer 22 formed on the anode 1 was formed so as to cover the periphery of the anode 1.

(Formation of electrolyte layer and cathode)
Next, an electrolyte layer 3 made of polypyrrole is formed on the dielectric layer 2 by polymerization or the like so as to cover the periphery of the dielectric layer 2, and further, a carbon paste is applied and dried on the electrolyte layer 3. The first conductive layer 4a was formed on the electrolyte layer 3 so as to cover the periphery of the electrolyte layer 3. Moreover, the 2nd conductive layer 4b was formed on the 1st conductive layer 4a so that the circumference | surroundings of the 1st conductive layer 4a might be covered by apply | coating and drying a silver paste on the 1st conductive layer 4a. Thus, the electrolyte layer 3 and the cathode 4 made of the first conductive layer 4a and the second conductive layer 4b were formed on the dielectric layer 2. Thus, the solid electrolytic capacitor A of Reference Example 1 was produced.

(Comparative Example 1)
In Comparative Example 1, a solid electrolytic capacitor X1 was produced under the same conditions and method as in Reference Example 1 except that the oxidation step 2 of Reference Example 1 was not performed. That is, the dielectric layer of the solid electrolytic capacitor X1 of Comparative Example 1 is composed of only the first dielectric layer.

(Comparative Example 2)
In Comparative Example 2, the solid electrolytic capacitor was subjected to the same conditions and method as in Reference Example 1 except that the oxidation step 1 of Reference Example 1 was not performed and the anodization time in the oxidation step 2 was about 10 hours. X2 was produced. That is, the dielectric layer of the solid electrolytic capacitor X2 of Comparative Example 2 is composed of only the second dielectric layer.

(Comparative Example 3)
In Comparative Example 3, except that about 0.5% by weight of hydrochloric acid was used instead of the about 0.5% by weight of ammonium fluoride aqueous solution used in the production of the solid electrolytic capacitor X1 of Comparative Example 1 described above. A solid electrolytic capacitor X3 was produced under the same conditions and method as in Comparative Example 1.

(Comparative Example 4)
In Comparative Example 4, the anode was heat-treated at about 600 ° C. for about 5 minutes in a nitrogen atmosphere of about 300 Torr (about 4 × 10 ⁻⁴ Pa) before performing the oxidation step 2 in Comparative Example 2 above. A solid electrolytic capacitor X4 was produced under the same conditions and method as in Comparative Example 2 except for the above. Here, the niobium nitride layer can be formed on the anode so as to cover the periphery of the anode by performing the heat treatment in the nitrogen atmosphere on the anode made of niobium. Further, by performing oxidation step 2 on this anode, a dielectric layer made of niobium oxide having a niobium nitride region can be formed on the anode so as to cover the periphery of the anode. The solid electrolytic capacitor X4 corresponds to a solid electrolytic capacitor in which a niobium nitride region is formed in niobium oxide which is a dielectric described in Patent Document 1.

(Evaluation)
FIG. 3 is a diagram showing measurement results by ESCA (Electron Spectroscopy for Chemical Analysis) of the solid electrolytic capacitor A of Reference Example 1 of the present invention. In this measurement, a sample in which the electrolyte layer 3 and the cathode 4 were not formed was used. In FIG. 3, the vertical axis represents the content of elements in the solid electrolytic capacitor, and the horizontal axis represents the sputtering time. The sputtering time corresponds to the position in the thickness direction of the solid electrolytic capacitor, and the sputtering depth per sputtering time is about 10 nm.

As shown in FIG. 3, the dielectric layer 2 of the solid electrolytic capacitor A of Reference Example 1 is made of niobium oxide containing niobium (Nb) and oxygen (O) as main components. That is, the dielectric layer 2 contains niobium (Nb) and oxygen (O), and is made of niobium oxide containing either one of niobium (Nb) or oxygen (O) as a main component. The dielectric layer 2 has three regions (i), (ii), and (iii) in order from the surface.

  Region (i) having a thickness of about 1 nm on the surface side of dielectric layer 2 where electrolyte layer 3 and cathode 4 are formed contains niobium and oxygen, and is made of niobium oxide containing oxygen as a main component. Further, in the region (i), phosphorus (P) is contained in a maximum of about 2.5 atomic%, but fluorine (F) is hardly contained in about 0.5 atomic% or less. Thereby, it was found that the region (i) is the second dielectric layer 22 formed in the oxidation step 2. Further, it was found that the concentration of phosphorus (P) was high on the surface side and decreased toward the anode 1 side in the region (i).

  The region (ii) having a thickness of about 15 nm inside the region (i) (on the anode 1 side) contains niobium and oxygen and is made of niobium oxide containing oxygen as a main component. The region (iii) having a thickness of about 11 nm further inside the region (ii) contains niobium and oxygen, and is made of niobium oxide containing niobium as a main component. Regions (ii) and (iii) both contain fluorine (F). Thereby, it was found that the regions (ii) and (iii) were the first dielectric layer 21 formed in the oxidation step 1. Further, the region (ii) contains fluorine (F) having a concentration of approximately 0.5 atomic% that is substantially constant in the depth direction. In the region (iii), the fluorine concentration increases from the region (ii) side toward the anode 1 side. Thus, it was found that in the entire first dielectric layer 21 composed of the regions (ii) and (iii), the fluorine concentration increased from the region (i) side toward the anode 1 side. Further, since the region (iii) contains a maximum of about 1.8 atomic% of fluorine, the region (iii) is considered to contain niobium fluoride. The fluorine (F) inside the anode 1 is considered to have diffused from the first dielectric layer 21 (regions (ii) and (iii)).

FIG. 4 is a view showing an SEM photograph of the surface of the dielectric layer 2 after performing the oxidation step 2 in Reference Example 1 of the present invention. FIG. 5 is a view showing an SEM photograph of the surface of the dielectric layer after performing oxidation step 2 in Comparative Example 2 of the present invention. As shown in FIG. 4, in Reference Example 1 using the ammonium fluoride aqueous solution in the oxidation step 1, an uneven shape is generated on the surface of the dielectric layer 2. In contrast, as shown in FIG. 5, in Comparative Example 2 where the oxidation step 1 is not performed, the surface of the dielectric layer is relatively smooth. Thus, in the solid electrolytic capacitor A of Reference Example 1, in the oxidation step 1, dissolved surface of the anode 1 of niobium by fluorine ions in the aqueous solution of ammonium fluoride is believed that the irregularities have occurred.

Next, the leakage current after heat treatment of each solid electrolytic capacitor produced as described above was measured. FIG. 6 is a schematic diagram showing a method for measuring the leakage current of the solid electrolytic capacitor of Reference Example 1 of the present invention.

First, the solid electrolytic capacitor A of Reference Example 1 was heat-treated for about 10 minutes in the air in a drying furnace set at about 250 ° C. Subsequently, as shown in FIG. 6, a constant voltage of about 5 V was applied between the anode lead 1a of the anode 1 and the cathode 3, and the leakage current after about 20 seconds was measured. Further, the ESR at about 100 kHz between the anode lead 1a and the cathode 3 was measured by an LCR meter. In addition, the temperature of this heat processing means the preset temperature of the drying furnace used for heat processing, and is the temperature in the drying furnace measured with the thermocouple installed in the vicinity of the sample holding jig in a drying furnace.

Moreover, also about the solid electrolytic capacitor X1-X4 of Comparative Examples 1-4, the leakage current and ESR after heat processing were measured with the same method. The measurement results are shown in Table 1. In Table 1, the measured values of each leakage current and ESR are normalized with the measurement result of the leakage current and ESR in the solid electrolytic capacitor A of Reference Example 100 being 100.

As shown in Table 1, the solid electrolytic capacitor X1 of Comparative Example 1 produced a leakage current about five times that of the solid electrolytic capacitor A of Reference Example 1. In addition, the solid electrolytic capacitor X2 of Comparative Example 2 produced a leakage current about 10 times that of the solid electrolytic capacitor A of Reference Example 1. Further, the solid electrolytic capacitor X3 of Comparative Example 3 produced a leakage current about 20 times that of the solid electrolytic capacitor A of Reference Example 1. In addition, the solid electrolytic capacitor X4 of Comparative Example 4 produced a leakage current about 9.8 times that of the solid electrolytic capacitor A of Reference Example 1. From these results, it was found that in the solid electrolytic capacitor A of Reference Example 1, the leakage current was greatly reduced as compared with the solid electrolytic capacitors X1 to X4.

Further, in the solid electrolytic capacitors A and X1 of Reference Example 1 and Comparative Example 1 in which the oxidation step 1 using the ammonium fluoride aqueous solution was performed, Comparative Example 2 in which the ammonium fluoride aqueous solution was not used for anodic oxidation at the time of forming the dielectric layer. It was found that the ESR was smaller than the solid electrolytic capacitors X2 to X4.

( Reference Example 2)
In Reference Example 2, the correlation between the aqueous solution used when forming the first dielectric layer of the present invention and the leakage current was verified.

Here, in Reference Example 2, in place of the approximately 0.5% by weight ammonium fluoride aqueous solution used in the oxidation step 1 of Reference Example 1 above, an approximately 0.16% by weight potassium fluoride aqueous solution, Solid electrolytic capacitors B1, B2 and B3 were produced under the same conditions and method as in Reference Example 1 except that an 11% by weight sodium fluoride aqueous solution and an approximately 0.05% by weight hydrofluoric acid aqueous solution were used, respectively. . The fluorine ion concentration in any of the above aqueous solutions is about 0.05% by weight. The potassium fluoride aqueous solution, the sodium fluoride aqueous solution, and the hydrofluoric acid aqueous solution are examples of the “first aqueous solution” of the present invention.

(Evaluation)
For solid electrolytic capacitors B1 to B3 of Reference Example 2, measurement by ESCA was performed in the same manner as Reference Example 1. As a result, in any of the solid electrolytic capacitors B1 to B3, it was confirmed that the first dielectric layer 21 containing fluorine and the second dielectric layer 22 containing phosphorus were laminated on the anode 1 in this order. Moreover, the solid electrolytic capacitor B1~B3 of Reference Example 2, in the same manner as in Reference Example 1, about 250 ° C., was measured the leakage current after the heat treatment of about 10 minutes. The results are shown in Table 2. In Table 2, the measurement value of each leakage current is normalized with the measurement result of the leakage current in the solid electrolytic capacitor A of Reference Example 1 being 100.

As shown in Table 2, the solid electrolytic capacitors B1 to B3 of Reference Example 2 all have a smaller leakage current than the solid electrolytic capacitors X1 to X4 of Comparative Examples 1 to 4, and the solid electrolytic capacitors A of Reference Example 1 and Equivalent leakage current. The leakage current is smallest in the solid electrolytic capacitor A using an aqueous ammonium fluoride solution. Thus, it was found that in the oxidation step 1 for forming the first dielectric layer 21, an aqueous potassium fluoride solution, an aqueous sodium fluoride solution, and an aqueous hydrofluoric acid solution can be used in addition to the aqueous ammonium fluoride solution. Further, it is considered that an aqueous solution containing fluorine ions can be used for the oxidation step 1.

( Reference Example 3)
In Reference Example 3, in the above Reference Example 1, in place of the anode made of a porous sintered body of niobium, niobium and aluminum and about 99: of mixed at a weight ratio of the sintered formed niobium alloy porous A solid electrolytic capacitor C was produced under the same conditions and method as in Reference Example 1 except that an anode made of a sintered material was used.

(Evaluation)
The solid electrolytic capacitor C of Reference Example 3 was measured by ESCA as in Reference Example 1. As a result, also in the solid electrolytic capacitor C, it was confirmed that the first dielectric layer 21 containing fluorine and the second dielectric layer 22 containing phosphorus were laminated on the anode 1 in this order. For the solid electrolytic capacitor C of Reference Example 3, the leakage current after heat treatment at about 250 ° C. for about 10 minutes was measured by the same method as in Reference Example 1. The results are shown in Table 3. In Table 3, the measurement value of each leakage current is normalized with the measurement result of the leakage current in the solid electrolytic capacitor A of Reference Example 1 being 100.

As shown in Table 3, in the solid electrolytic capacitor C of Reference Example 3, the leakage current is smaller than that of the solid electrolytic capacitors X1 to X4 of Comparative Examples 1 to 4, and the leakage is equal to or less than that of the solid electrolytic capacitor A of Reference Example 1. Current. As a result, it was found that niobium alloy as well as niobium alloy can be used for the anode.

(Example 1 )
In Example 1 , the reference example 1 was used except that about 0.5% by weight sulfuric acid aqueous solution was used instead of the about 0.5% by weight phosphoric acid aqueous solution used in the oxidation step 2 of reference example 1. A solid electrolytic capacitor D was produced under the same conditions and method as in Example 1.

(Comparative Example 5)
In Comparative Example 5, the solid electrolytic capacitor was subjected to the same conditions and method as in Example 1 except that the oxidation step 1 of Example 1 was not performed and the anodization time of oxidation step 2 was about 10 hours. X5 was produced. That is, the dielectric layer of the solid electrolytic capacitor X5 of Comparative Example 5 is composed of only the second dielectric layer.

(Evaluation)
Solid electrolytic capacitor D of Example 1, was measured by similarly ESCA as in Reference Example 1. FIG. 7 is a diagram showing a measurement result by ESCA for the solid electrolytic capacitor D of Example 1 of the present invention. In this measurement, a sample in which the electrolyte layer 3 and the cathode 4 were not formed was used. In FIG. 7, the vertical axis indicates the content of elements in the solid electrolytic capacitor, and the horizontal axis indicates the sputtering time. The sputtering time corresponds to the position in the thickness direction of the solid electrolytic capacitor, and the sputtering depth per sputtering time is about 10 nm.

As shown in FIG. 7, the dielectric layer 2 of the solid electrolytic capacitor D of Example 1 is made of niobium oxide containing niobium (Nb) and oxygen (O) as main components. That is, the dielectric layer 2 contains niobium (Nb) and oxygen (O), and is made of niobium oxide containing either one of niobium (Nb) or oxygen (O) as a main component. The dielectric layer 2 has three regions (i), (ii), and (iii) in order from the surface.

  Region (i) having a thickness of about 1 nm on the surface side of dielectric layer 2 where electrolyte layer 3 and cathode 4 are formed contains niobium and oxygen, and is made of niobium oxide containing oxygen as a main component. In the region (i), sulfur (S) is contained at a maximum of about 2.5 atomic%, but fluorine (F) is hardly contained at about 0.5 atomic% or less. Thereby, it was found that the region (i) is the second dielectric layer 22 formed in the oxidation step 2. Moreover, in the area | region (i), it turned out that the density | concentration of sulfur (S) is high on the surface side, and is decreasing toward the anode 1 side.

  The region (ii) having a thickness of about 15 nm inside the region (i) (on the anode 1 side) contains niobium and oxygen, and is made of niobium oxide containing oxygen as a main component. The region (iii) having a thickness of about 11 nm further inside the region (ii) contains niobium and oxygen and is made of niobium oxide containing niobium as a main component. Regions (ii) and (iii) both contain fluorine (F). Thereby, it was found that the regions (ii) and (iii) were the first dielectric layer 21 formed in the oxidation step 1. Further, the region (ii) contains fluorine (F) having a concentration of about 0.5 atomic% that is substantially constant in the depth direction. In the region (iii), the fluorine concentration increases from the region (ii) side toward the anode 1 side. Thus, it was found that the fluorine concentration of the entire first dielectric layer 21 composed of the regions (ii) and (iii) increases from the region (i) side toward the anode 1 side. Further, since the region (iii) contains a maximum of about 1.8 atomic% of fluorine, the region (iii) is considered to contain niobium fluoride. The fluorine (F) inside the anode 1 is considered to have diffused from the first dielectric layer 21 (regions (ii) and (iii)).

Next, with respect to the solid electrolytic capacitors D and X5 of Example 1 and Comparative Example 5, the leakage current after heat treatment at about 250 ° C. for about 10 minutes, the anode lead 1a and the cathode 3 in the same manner as in Reference Example 1 And the ESR at about 100 kHz was measured. The results are shown in Table 4. In Table 4, the measured values of leakage current and ESR are normalized with the measurement result of leakage current and ESR in the solid electrolytic capacitor A of Reference Example 1 being 100.

As shown in Table 4, the solid electrolytic capacitor X5 of Comparative Example 5 generates about 12 times the leakage current of the solid electrolytic capacitor A of Reference Example 1, whereas the solid electrolytic capacitor D of Example 1 The leakage current is greatly reduced as compared with the solid electrolytic capacitors X1 to X5 of Comparative Examples 1 to 5, and the leakage current is equivalent to that of the solid electrolytic capacitor A of Reference Example 1. Thereby, even when the second dielectric layer 22 located on the surface side of the dielectric layer 2 contains sulfur, the solid electrolytic capacitor A of Reference Example 1 in which the second dielectric layer 22 contains phosphorus Similarly, it has been found that there is an effect of reducing leakage current.

Further, in the solid electrolytic capacitor D of Example 1, even less than the solid electrolytic capacitor X1~X5 of Comparative Examples 1 to 5 for the ESR, was found to be a solid electrolytic capacitor A equivalent ESR of Reference Example 1.

In the reference examples 1 and 4, the first dielectric layer 21 and the second dielectric layer 22 are composed of a region (iii) made of niobium oxide containing niobium as a main component and niobium oxide containing oxygen as a main component. However, the present invention is not limited to this. For example, even if all the regions are made of niobium oxide containing oxygen as a main component, the regions (i) and (ii) are made. Alternatively, the region (iii) may be made of niobium oxide mainly containing oxygen, and the regions (i) and (ii) may be made of niobium oxide mainly containing niobium.

1 is a cross-sectional structure diagram of a solid electrolytic capacitor according to an embodiment of the present invention. It is a cross-section figure of the solid electrolytic capacitor by the reference example 1 of this invention. It is a figure which shows the measurement result by ESCA about the solid electrolytic capacitor of the reference example 1 of this invention. In the reference example 1 of this invention, it is a figure which shows the SEM photograph of the surface of the dielectric material layer after performing the oxidation step 2. FIG. In the comparative example 2 of this invention, it is a figure which shows the SEM photograph of the surface of the dielectric material layer after performing the oxidation step 2. FIG. It is a schematic diagram which shows the measuring method of the leakage current of the solid electrolytic capacitor of the reference example 1 of this invention. It is a figure which shows the measurement result by ESCA about the solid electrolytic capacitor of Example 1 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anode 1a Anode lead 2 Dielectric layer 21 1st dielectric layer 22 2nd dielectric layer 3 Electrolyte layer 4 Cathode 4a 1st conductive layer 4b 2nd conductive layer 5 Conductive adhesive layer 6 Cathode terminal 7 Anode terminal 8 Mold Exterior resin 100 Solid electrolytic capacitor

Claims (3)

An anode made of niobium or a niobium alloy; a first dielectric layer mainly composed of niobium and oxygen formed on the anode and containing fluorine ; and niobium and oxygen formed on the first dielectric layer. In addition, a solid electrolytic capacitor comprising a second dielectric layer containing sulfur and a cathode formed on the second dielectric layer. The solid electrolytic capacitor according to claim 1, wherein the fluorine concentration increases from the cathode side to the anode side in the first dielectric layer. Forming a first dielectric layer containing niobium and oxygen as main components and containing fluorine by anodizing an anode made of niobium or a niobium alloy in a first aqueous solution containing fluorine ions ; Subsequent to the step of forming the dielectric layer, the anode is anodized in a second aqueous solution containing sulfate ions , whereby a second dielectric containing sulfur in addition to niobium and oxygen is formed on the first dielectric layer. A method for producing a solid electrolytic capacitor, comprising: forming a layer; and forming a cathode on the second dielectric layer.

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