JP2009044021A - Solid electrolytic capacitor and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor capable of enhancing a withstand voltage characteristic, and to provide a manufacturing method thereof. <P>SOLUTION: The solid electrolytic capacitor includes: an anode body 1 composed of niobium; a dielectric layer 2 formed on the front surface of the anode body 1 and mainly composed of a niobium oxide; a conductive high molecular layer 3 formed on the dielectric layer 2; and a cathode layer 4 formed on the conductive high molecular layer 3. In the dielectric layer 2, fluorine (F) is doped by uneven distribution toward an anode and also metal, i.e., at least one of aluminum (Al) and tantalum (Ta) is solidly melted. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a solid electrolytic capacitor and a manufacturing method thereof, and more particularly to a solid electrolytic capacitor using niobium or a niobium alloy as an anode material and a manufacturing method thereof.

  In general, in a solid electrolytic capacitor, an anode made of a valve metal such as niobium (Nb) or tantalum (Ta) is anodized to form a dielectric layer mainly made of oxide on the surface thereof. It is configured by forming a cathode thereon. In particular, niobium is attracting attention as a material for next-generation high-capacity solid electrolytic capacitors because its dielectric constant is about 1.8 times as large as that of tantalum, which is a material of conventional solid electrolytic capacitors.

  Usually, when surface mounting a solid electrolytic capacitor on a substrate, it may be exposed to a high temperature in a reflow process. In a solid electrolytic capacitor using niobium or a niobium alloy as an anode material, a phenomenon occurs in which part of amorphous niobium oxide that functions as a dielectric layer is crystallized by such a thermal load. For this reason, there is a problem that the insulation property of the dielectric layer is lowered with the change of the state of niobium oxide from amorphous to crystalline, and the leakage current of the dielectric layer is increased.

In order to suppress such an increase in leakage current, an electrode (anode body) using a niobium alloy with aluminum added to niobium is anodized in an aqueous solution containing fluorine ions to form a dielectric layer. Has been proposed (see Patent Document 1). By doing so, the dielectric layer contains aluminum oxide together with niobium oxide, so that the crystallization of the dielectric layer is suppressed by the aluminum oxide, and the increase in leakage current is suppressed. Become. Further, the fluorine doped in the dielectric layer suppresses the diffusion of oxygen from the dielectric layer to the electrode (anode body) due to the thermal load, and the increase in leakage current can be suppressed even after the thermal load.
JP 2005-252224 A

  However, according to the method described in Patent Document 1, an increase in leakage current can be suppressed, but there is a problem that the withstand voltage characteristic of the dielectric layer cannot be improved. In particular, with the recent improvement in performance of solid electrolytic capacitors, it is strongly desired not only to suppress an increase in leakage current but also to improve the withstand voltage characteristics for the dielectric layer.

  This invention is made | formed in view of such a subject, The objective is to provide the solid electrolytic capacitor which can improve a withstand voltage characteristic, and its manufacturing method.

  To achieve the above object, a solid electrolytic capacitor according to the present invention includes an anode made of niobium or a niobium alloy, a dielectric layer containing niobium oxide formed on the surface of the anode, and a dielectric layer formed on the dielectric layer. And a region containing niobium oxide contains fluorine and at least one metal of aluminum and tantalum is solid-dissolved. Here, “metal is in solid solution” means that the metal is present in the dielectric layer in the state of a single metal.

In order to achieve the above object, a method for producing a solid electrolytic capacitor according to the present invention includes a dielectric containing niobium oxide by anodizing the surface of an anode made of niobium or a niobium alloy in an electrolyte containing fluorine ions. A first step of forming a layer and doping fluorine into the dielectric layer; and a second step of introducing at least one metal of aluminum and tantalum into a region containing niobium oxide using an ion implantation method to form a solid solution And a third step of forming a cathode layer on the dielectric layer.

  ADVANTAGE OF THE INVENTION According to this invention, the solid electrolytic capacitor which can improve a withstand voltage characteristic, and its manufacturing method are provided.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing the configuration of the solid electrolytic capacitor according to the first embodiment.

  The solid electrolytic capacitor of the first embodiment includes an anode body 1, a dielectric layer 2 formed on the surface of the anode body 1, a conductive polymer layer 3 formed on the dielectric layer 2, and this A cathode layer 4 formed on the conductive polymer layer 3.

  The anode body 1 is mainly composed of a porous sintered body of niobium metal particles, and a part of an anode lead 1a made of niobium metal is embedded therein. A niobium alloy may be adopted as niobium constituting the anode body 1 and the anode lead 1a.

The dielectric layer 2 is made of a dielectric made of niobium oxide (Nb ₂ O ₅ ), which is an oxide of niobium metal, and is provided on the surfaces of the anode body 1 and the anode lead 1a. In the present embodiment, at least one of aluminum (Al) and tantalum (Ta) is dissolved in the dielectric layer 2. The dielectric layer 2 is doped with fluorine (F), and the fluorine is unevenly distributed on the anode side of the dielectric layer 2. Specifically, the fluorine has a concentration distribution in the thickness direction of the dielectric layer 2 (the direction from the cathode side to the anode side of the dielectric layer 2), and the fluorine concentration varies between the dielectric layer 2 and the anode body 1 and It is the largest at the interface.

  The conductive polymer layer 3 functions as an electrolyte layer and is provided on the surface of the dielectric layer 2. The material of the conductive polymer layer 3 is not particularly limited as long as it is a polymer material having conductivity, but materials such as polypyrrole, polyaniline, and polythiophene having excellent conductivity are employed.

  The cathode layer 4 is composed of a laminated film of a carbon layer 4 a made of a layer containing carbon particles and a silver paste layer 4 b made of a layer containing silver particles, and is provided on the conductive polymer layer 3. The cathode layer 4 and the conductive polymer layer 3 constitute a cathode.

  In this embodiment, a flat cathode terminal 6 is further connected to the cathode layer 4 via a conductive adhesive 5, and a flat anode terminal 7 is connected to the anode lead 1a. And the mold exterior body 8 which consists of an epoxy resin etc. is formed in the form with which the anode terminal 7 and a part of cathode terminal 6 were pulled out outside like FIG. As a material for the anode terminal 7 and the cathode terminal 6, a conductive material such as nickel (Ni) can be used. It functions as a terminal for electrolytic capacitors.

(Production method)
Next, the manufacturing method of the solid electrolytic capacitor of 1st Embodiment shown in FIG. 1 is demonstrated.

  Step 1: Anode body 1 made of a porous sintered body is sintered in a vacuum by sintering a molded body made of niobium metal particles molded so as to embed a part of anode lead 1a around anode lead 1a. Form. At this time, the niobium metal particles are fused.

  Step 2: The anode body 1 is anodized in an electrolytic solution containing fluorine ions to form a dielectric layer 2 mainly made of niobium oxide so as to cover the periphery of the anode body 1. At this time, fluorine is taken into the dielectric layer 2, and the fluorine is unevenly distributed on the anode side of the dielectric layer 2 (interface between the dielectric layer 2 and the anode body 1).

  Step 3: At least one metal of aluminum and tantalum is implanted into the dielectric layer 2 doped with fluorine by ion implantation. Thereby, the metal injected into the dielectric layer 2 is dissolved in the dielectric layer 2 in the state of a single metal.

  Step 4: A conductive polymer layer 3 such as polypyrrole is formed on the surface of the dielectric layer 2 using a chemical polymerization method, an electrolytic polymerization method, or the like. Specifically, as a first step, a first conductive polymer layer is formed by oxidative polymerization of a monomer with an oxidizing agent using a chemical polymerization method. Subsequently, as the second step, by using the electropolymerization method, the first electroconductive polymer layer is used as the anode, and the second electroconductive polymer layer is electropolymerized with the external cathode in the electrolytic solution containing the monomer and the electrolyte. A molecular layer is formed. In this way, the conductive polymer layer 3 composed of a laminated film of the first conductive polymer layer and the second conductive polymer layer is formed on the surface of the dielectric layer 2.

  Step 5: Carbon layer 4a is formed by applying a carbon paste on conductive polymer layer 3 and drying. Furthermore, a silver paste layer 4b is formed by applying and drying a silver paste on the carbon layer 4a. In this way, the cathode layer 4 made of a laminated film of the carbon layer 4a and the silver paste layer 4b is formed on the conductive polymer layer 3.

  Step 6: After applying the conductive adhesive 5 on the flat cathode terminal 6, the cathode layer 4 and the cathode terminal 6 are dried while being in contact with each other via the conductive adhesive 5. The layer 4 and the cathode terminal 6 are connected. Further, a flat anode terminal 7 is connected to the anode lead 1a by spot welding.

  Step 7: Molding is performed by a transfer method, and a mold outer package 8 made of an epoxy resin is formed around the periphery. At this time, the anode lead 1a, the anode body 1, the dielectric layer 2, the conductive polymer layer 3, and the cathode layer 4 are housed inside, and the end portions of the anode terminal 7 and the cathode terminal 6 are externally (opposite directions). ) To be pulled out.

  Step 8: The tip portions of the anode terminal 7 and the cathode terminal 6 exposed from the mold exterior body 8 are bent downward and arranged along the lower surface of the mold exterior body 8. The tips of both terminals function as terminals of the solid electrolytic capacitor, and are used to electrically connect the solid electrolytic capacitor to the mounting substrate.

  Through the above steps, the solid electrolytic capacitor of the first embodiment of the present invention is manufactured.

(Second Embodiment)
Similar to the first embodiment, the solid electrolytic capacitor according to the second embodiment includes an anode body 1, a dielectric layer 2 formed on the surface of the anode body 1, and a conductive material formed on the dielectric layer 2. A polymer layer 3 and a cathode layer 4 formed on the conductive polymer layer 3 are provided. In the dielectric layer 2, fluorine is unevenly distributed on the anode side, and at least one metal of aluminum and tantalum is dissolved. A difference from the first embodiment is that the dielectric layer 2 further contains nitrogen (N). The rest is the same as in the first embodiment.

  Such a solid electrolytic capacitor is formed by employing a nitrided anode body (a porous sintered body of nitrided niobium metal particles) as the anode body 1. Note that the nitrided anode body can be easily formed by pre-treating niobium metal particles with a heat treatment in a nitrogen atmosphere and sintering them.

  In the following examples and comparative examples, a capacitor is simply produced using an anode body made of niobium foil instead of an anode body made of a porous sintered body of niobium metal particles, and a dielectric corresponding to the above embodiment The layer characteristics were evaluated.

Example 1
In Example 1, capacitor A1 was manufactured through the following steps.

  Step 1A: A niobium foil having a thickness of 0.05 mm is cut into 1 cm × 5 cm to form anode body 1 made of niobium foil.

  Step 2A: The anode body 1 is anodized for 1 hour at a constant voltage of 50 V in a 0.05 wt% aqueous ammonium fluoride solution maintained at about 45 ° C. Thereby, the dielectric layer 2 made of niobium oxide containing fluorine is formed so as to cover the periphery of the anode body 1. At this time, fluorine has a concentration distribution in the thickness direction of the dielectric layer 2, and the concentration of fluorine becomes maximum at the interface between the dielectric layer 2 and the anode body 1.

Step 3A: Aluminum is implanted into the dielectric layer 2 using an ion implantation method. The conditions for aluminum implantation are an acceleration voltage of 100 kV and a dose of 4 × 10 ¹⁵ / cm ² . Thereby, aluminum is dissolved in the dielectric layer 2 in a state of aluminum alone. Thereafter, heat treatment is performed at a temperature of 250 ° C. for 30 seconds.

  In this way, the capacitor A1 in Example 1 is manufactured.

(Example 2)
In Example 2, a capacitor A2 was produced in the same manner as in Example 1 except that tantalum was used instead of the aluminum to be injected in Step 3A. The tantalum implantation conditions are an acceleration voltage of 300 kV and a dose amount of 7 × 10 ¹⁵ / cm ² .

(Example 3)
In Example 3, a capacitor A3 was produced in the same manner as in Example 1 except that aluminum was injected in Step 3A and tantalum was further injected. The tantalum implantation conditions are the same as in Example 2.

(Comparative Example 1)
In Comparative Example 1, Example 1 was used except that a 0.1% by weight nitric acid aqueous solution was used instead of the 0.05% by weight ammonium fluoride aqueous solution in Step 2A, and that no ion implantation was performed in Step 3A. A capacitor X1 was produced in the same manner as described above.

(Comparative Example 2)
In Comparative Example 2, capacitor X2 was manufactured through the following steps.

  Step 1B: A niobium / aluminum alloy foil having a thickness of 0.05 mm is cut into 1 cm × 5 cm to form anode body 1 made of the alloy foil. The aluminum content is 1% by weight based on the total weight of the alloy foil.

  Step 2B: The anode body 1 is anodized for 1 hour at a constant voltage of 50 V in a 0.05 wt% ammonium fluoride aqueous solution kept at about 45 ° C.

  Step 3B: Heat treatment is performed at a temperature of 250 ° C. for 30 seconds.

  In this way, the capacitor X2 in Comparative Example 3 is manufactured.

(Comparative Example 3)
In Comparative Example 3, a capacitor X3 was manufactured through the following steps.

  Step 1C: A niobium foil having a thickness of 0.05 mm is cut into 1 cm × 5 cm, and an aluminum foil of the same size is placed on the surface and held at 750 ° C. for 2 hours in an argon (Ar) gas atmosphere. Then, it is immersed in an aqueous nitric acid solution to dissolve excess aluminum. As a result, the anode body 1 made of a niobium foil having aluminum taken into the surface is formed.

  Step 2C: The anode body 1 is anodized at a constant voltage of 50 V in a 0.1 wt% aqueous phosphoric acid solution maintained at about 45 ° C. for 1 hour.

  Step 3C: Heat treatment is performed at a temperature of 250 ° C. for 30 seconds.

  In this way, the capacitor X3 in Comparative Example 3 is manufactured.

(Comparative Example 4)
In Comparative Example 4, a capacitor X4 was produced in the same manner as in Example 1 except that ion implantation was not performed in Step 3A.

(Comparative Example 5)
In Comparative Example 5, a capacitor X5 was produced in the same manner as in Example 1 except that in Step 2A, a 0.1 wt% nitric acid aqueous solution was used instead of the 0.05 wt% ammonium fluoride aqueous solution.

(Evaluation)
First, in order to evaluate the state of the metal (aluminum) introduced into the dielectric layer by ion implantation, each capacitor was analyzed by electron probe micro-analysis (EPMA). FIG. 2 is a diagram showing the result of state analysis by EPMA of each capacitor. 2A shows the Al-Kα spectrum of the capacitor X5 in Comparative Example 5, and FIG. 2B shows the Al-Kα spectrum of the capacitor X3 in Comparative Example 3 by EPMA.

  The Al-Kα spectrum for aluminum has different peak shapes in the metal state and the oxide state. In the spectrum of FIG. 2A, the two peak intensities are left <right, which is consistent with the peak shape in which aluminum is in a metal state. In the spectrum of FIG. 2B, the two peak intensities are in the left = right state, which matches the peak shape in which aluminum is in an oxide state. This indicates that the aluminum in the dielectric layer in each capacitor exists in the state of aluminum alone (metal) in the capacitor X5 and in the state of aluminum oxide in the capacitor X3.

  Further, according to the same analysis, in Example 1 (capacitor A1) and Example 3 (capacitor A3), aluminum in the dielectric layer exists in a state of aluminum alone, and in Comparative Example 2 (capacitor X2), aluminum is aluminum oxide. It was confirmed that it exists in the state. In Comparative Example 2 (Capacitor X2) and Comparative Example 3 (Capacitor X3), aluminum oxide is present in the dielectric layer because the aluminum added in the dielectric layer during the manufacturing process is anodized after the addition. It is assumed that it is sometimes oxidized.

  Further, tantalum was also analyzed by EPMA, and in Example 2 (capacitor A2) and Example 3 (capacitor A3), it was confirmed that tantalum in the dielectric layer was present in the state of tantalum alone (metal).

  On the other hand, in the quantitative analysis by EPMA, aluminum dissolved in the dielectric layer in Example 1 (capacitor A1), Example 3 (capacitor A3), and Comparative Example 5 (capacitor X5) The ratio of aluminum content (aluminum concentration) to niobium content (niobium concentration) was 15 atomic%. In Comparative Example 2 (capacitor X2) and Comparative Example 3 (capacitor X3), the aluminum oxide in the dielectric layer was 15 atomic% in the ratio of the aluminum content to the niobium content in the dielectric layer. In Example 2 (capacitor A2) and Example 3 (capacitor A3), tantalum dissolved in the dielectric layer has a ratio of tantalum content (tantalum concentration) to niobium content in the dielectric layer. It was 25 atomic%.

  Next, leakage current and withstand voltage were evaluated for each capacitor. Table 1 shows the evaluation results of leakage current and withstand voltage of each capacitor.

  Since each capacitor is in a state where each capacitor is formed up to the dielectric layer, as shown in FIG. 3, 0.5 wt% phosphoric acid aqueous solution 12 held at 60 ° C. is put in a SUS container 11, After immersing the capacitor 13 (capacitors A1 to A3, X1 to X5) prepared as described above, a voltage of 5 V was applied with the capacitor 13 being plus and the SUS container 11 being minus, and the current after 5 seconds was measured. did. In addition, the measured value of each leakage current is normalized with the measurement result of the leakage current in Comparative Example 1 (capacitor X1) as 100.

  The withstand voltage is measured by increasing the applied voltage by 1V to each capacitor and measuring the leakage current (leakage current 5 seconds after applying the voltage), leakage current [μA] ÷ (capacitance [μF] × The voltage when the value calculated from the measured voltage [V]) exceeded 0.1 was taken as the withstand voltage. The capacitance (capacitance at a capacitor frequency of 120 Hz) is a value measured using an LCR meter before withstand voltage evaluation.

  As shown in Table 1, in Example 1 (capacitor A1), the leakage current is greatly reduced and the withstand voltage is about twice that of Comparative Example 1 (capacitor A1) having the conventional dielectric layer. Has improved. Thus, by doping fluorine in the dielectric layer and dissolving aluminum, it is possible to suppress an increase in the leakage current of the capacitor as in the prior art and to improve the withstand voltage. . This is presumably because the coexistence of both suppresses crystallization of amorphous niobium oxide functioning as the dielectric layer 2.

  In Comparative Example 3 (capacitor X3) having aluminum oxide in the dielectric layer and Comparative Example 2 (capacitor X2) having aluminum oxide in the dielectric layer and further doped with fluorine, Comparative Example 1 (capacitor X1) Compared with, the leakage current is reduced, but the withstand voltage is hardly changed. On the other hand, in Example 1 (capacitor A1), the leakage current is further reduced as compared with Comparative Example 3 and Comparative Example 2, and the withstand voltage is improved about twice. Thus, by making aluminum dissolve in the dielectric layer, an increase in the leakage current of the capacitor can be suppressed and the withstand voltage can be further improved as compared with the case where aluminum is contained in the dielectric layer. In Comparative Example 2 and Comparative Example 3, the aluminum contained in the dielectric layer is oxidized to aluminum oxide. Compared to the case of aluminum alone as in Example 1, the dielectric made of niobium oxide is used. This is presumably because the effect of suppressing crystallization of the body layer is reduced.

  In Comparative Example 4 (capacitor X4) in which fluorine is doped in the dielectric layer and in Comparative Example 5 (capacitor X5) in which aluminum is dissolved in the dielectric layer, the leakage current is larger than that in Comparative Example 1 (capacitor X1). However, the withstand voltage has hardly changed. On the other hand, in Example 1 (capacitor A1), the leakage current is further reduced and the withstand voltage is improved about twice as compared with Comparative Example 4 and Comparative Example 5. From this, it is surmised that the increase in the leakage current of the capacitor is suppressed and the withstand voltage is further improved by the synergistic effect of fluorine and aluminum (aluminum in a metal state) present in the dielectric layer.

  In Example 2 (capacitor A2) in which fluorine and tantalum were added, and in Example 3 (capacitor A3) in which tantalum was further dissolved in addition to fluorine and aluminum, the leakage current was significantly reduced as in Example 1. The withstand voltage has been improved. Thus, even if tantalum is dissolved in the dielectric layer, the same improvement effect can be obtained.

  From the above, it can be seen that it is effective to dissolve aluminum (or tantalum) together with fluorine that is unevenly distributed in the dielectric layer in order to suppress an increase in the leakage current of the capacitor and improve the withstand voltage. .

  Next, the influence of the amount of aluminum or tantalum dissolved in the dielectric layer on the leakage current and withstand voltage was evaluated.

(Examples 4 to 8)
In Examples 4 to 8, the dose of aluminum in Step 3A was changed from 4 × 10 ¹⁵ / cm ² to 1 × 10 ¹⁴ / cm ² , 3 × 10 ¹⁴ / cm ² , 3 × 10 ¹⁵ / cm ² , 7 ×. Capacitors B1 to B5 were produced in the same manner as in Example 1 except that the injection was performed in place of 10 ¹⁵ / cm ² and 1 × 10 ¹⁶ / cm ² .

(Examples 9 to 14)
In Examples 9 to 14, the tantalum dose was changed from 7 × 10 ¹⁵ / cm ² to 1 × 10 ¹⁴ / cm ² , 3 × 10 ¹⁴ / cm ² , 3 × 10 ¹⁵ / cm ² , 6 × 10 ¹⁵ / Capacitors B6 to B11 were fabricated in the same manner as in Example 2 except that implantation was performed instead of cm ² , 1 × 10 ¹⁶ / cm ² , and 2 × 10 ¹⁶ / cm ² .

(Evaluation)
First, the amount of solid solution of aluminum or tantalum dissolved in the dielectric layer of each capacitor was evaluated by quantitative analysis of EPMA. Table 2 shows the result of the solid solution amount of aluminum, and Table 3 shows the result of the solid solution amount of tantalum.

  Next, leakage current and withstand voltage were evaluated for each of the above capacitors. Tables 2 and 3 show the evaluation results of leakage current and withstand voltage of each capacitor. The leakage current and withstand voltage were measured in the same manner as in the previous evaluation. In addition, the measured value of each leakage current is normalized with the measurement result of the leakage current in Comparative Example 1 (capacitor X1) as 100.

  As shown in Table 2, when aluminum is dissolved in the dielectric layer in the range of 0.5 atomic% to 40 atomic%, the solid solution amount (aluminum content relative to the niobium content) Similar to 1 (capacitor A1), an effect of suppressing the increase in leakage current and an effect of improving the withstand voltage are obtained. Both effects are more prominent when the solid solution amount of aluminum is in the range of 1 atomic% to 15 atomic%. Note that the effect of suppressing the increase in leakage current and the effect of improving the withstand voltage are reduced when the solid solution amount of aluminum is 0.5% by weight, because the solid solution effect of aluminum in the dielectric layer is not sufficiently obtained. This is probably because of this. Further, when the solid solution amount of aluminum is 25% by weight or more, the effect of suppressing the increase in leakage current and the effect of improving the withstand voltage are reduced because of the increase of the solid solution aluminum, an intermetallic (for example, between aluminum and niobium) compound. This is presumed to be due to the crystallization of the dielectric layer that became a nucleus.

  As shown in Table 3, in the case where tantalum is contained in the dielectric layer and its solid solution amount (tantalum content relative to niobium content) is in the range of 0.5 atomic% to 70 atomic%, Example 1 ( Similar to the capacitor A1), the effect of suppressing the increase in leakage current and the effect of improving the withstand voltage are obtained. In addition, when the tantalum solid solution amount is in the range of 1 atomic% to 50 atomic%, both effects are more prominent. It should be noted that the effect of suppressing the increase in leakage current and the effect of improving the withstand voltage are reduced when the solid solution amount of tantalum is 0.5% by weight, because the solid solution effect of tantalum in the dielectric layer is not sufficiently obtained. This is probably because of this. In addition, when the tantalum solid solution amount is 70% by weight, the effect of suppressing an increase in leakage current and the effect of improving the withstand voltage are reduced because a large number of defects are generated in the dielectric layer due to an increase in the amount of injected tantalum. This is probably because crystallization of the dielectric layer progressed.

  Next, the influence of the addition of nitrogen to the dielectric layer (nitriding treatment on the anode body) on leakage current and withstand voltage was evaluated.

(Examples 15 to 21)
In Examples 15 to 21, the temperature of 200 ° C., 300 ° C., 500 ° C., 700 ° C., 800 ° C., 900 ° C., 1000 ° C. in the nitrogen atmosphere with respect to the anode body 1 between Step 1A and Step 2A Capacitors C1 to C7 were produced in the same manner as in Example 1 except that heat treatment was performed for 30 minutes.

(Comparative Example 6)
In Comparative Example 6, the anode body 1 was subjected to a heat treatment at a temperature of 550 ° C. for 30 minutes in a nitrogen atmosphere between Step 1A and Step 2A, and 0.05% by weight of fluorination in Step 2A. A capacitor X6 was produced in the same manner as in Example 1 except that a 0.1 wt% phosphoric acid aqueous solution was used instead of the ammonium aqueous solution, and that ion implantation was not performed in Step 3A.

(Evaluation)
First, the content of nitrogen added in the dielectric layer of each capacitor was evaluated by ammonia distillation separation amide sulfuric acid titration method. Table 4 shows the results of the nitrogen content.

  Next, leakage current and withstand voltage were evaluated for each of the above capacitors. Table 4 shows the evaluation results of leakage current and withstand voltage of each capacitor. The leakage current and withstand voltage were measured in the same manner as in the previous evaluation. In addition, the measured value of each leakage current is normalized with the measurement result of the leakage current in Comparative Example 1 (capacitor X1) as 100.

  As shown in Table 4, withstand voltage was further improved in Example 15 (capacitor C1) to Example 21 (capacitor C7) in which nitrogen was further added to the dielectric layer as compared to Example 1 (capacitor A1). ing. In addition, when the nitrogen content is in the range of 50 ppm to 5000 ppm, the effect of improving the withstand voltage is more prominently obtained. In Comparative Example 6 (capacitor X6) in which nitrogen is contained in the dielectric layer, although the leakage current is reduced as compared with Comparative Example 1 (capacitor X1), the withstand voltage is hardly changed. From this, it is surmised that such an improvement effect is due to a synergistic effect with the solid solution aluminum. The reason why the effect of improving the withstand voltage is reduced when the nitrogen content is 30 ppm or less is presumed that the nitrogen content in the dielectric layer is not sufficiently obtained. Moreover, when the nitrogen content is 7500 ppm or more, the effect of improving the withstand voltage is reduced and the effect of suppressing the increase in leakage current is slightly deteriorated because NbN is formed in the dielectric layer due to the increase in the nitrogen content. This is presumably due to the progress of crystallization of the entire dielectric layer.

  From the above, in order to reduce the leakage current of the capacitor and improve the withstand voltage, it is effective to contain nitrogen in the dielectric layer together with fluorine and solute aluminum that are unevenly distributed in the dielectric layer. I understand that there is.

  Next, the influence of the anodizing voltage on leakage current and withstand voltage was evaluated.

(Examples 22 to 27)
In Examples 22 to 27, capacitors D1 to D6 were formed in the same manner as in Example 1 except that the anodic oxidation voltage was changed from 50 V to 10 V, 20 V 100 V, 150 V, 175 V, and 200 V in Step 2A. Produced.

(Evaluation)
Leakage current and withstand voltage were evaluated for each of the above capacitors. Table 5 shows the evaluation results of leakage current and withstand voltage of each capacitor. The leakage current and the withstand voltage were measured in the same manner as in the previous evaluation, and the voltage at the time of measuring the leakage current was applied by applying a voltage 1/10 of each anodizing voltage. In addition, the measured value of each leakage current is normalized with the measurement result of the leakage current in Comparative Example 1 (capacitor X1) as 100.

  As shown in Table 5, when anodic oxidation is performed in the range of 20 to 150 V during the formation of the dielectric layer, the effect of greatly suppressing leakage current is obtained as in Example 1. Yes. Note that when the anodic oxidation voltage is 10 V, the effect of suppressing the increase in leakage current is reduced. This is presumably because the thickness of the dielectric layer itself is small because the thickness of the dielectric layer is proportional to the voltage applied during anodization (in the case of niobium oxide, 2.5 nm / V). . Further, even when the anodic oxidation voltage is 175 V or more, the effect of suppressing increase in leakage current is reduced. This is because the anodic oxidation at this voltage generates a crystalline oxide in the dielectric layer at the time of formation, so even if aluminum is subsequently dissolved, the oxide at this point affects it. It is guessed.

  Next, the influence of the electrolyte upon doping the fluorine in the dielectric layer on the leakage current and withstand voltage was evaluated.

(Examples 28 to 31)
In Examples 28 to 31, the electrolyte in Step 2A was changed from a 0.05% by weight ammonium fluoride aqueous solution to a 0.1% by weight potassium fluoride aqueous solution, a 0.1% by weight sodium fluoride aqueous solution, 0.1% by weight. Capacitors E1 to E4 were produced in the same manner as in Example 1 except that anodization was performed instead of an aqueous solution of 10% hydrofluoric acid, 0.05% by weight of ammonium fluoride + 0.05% by weight of potassium fluoride. did.

(Evaluation)
Leakage current and withstand voltage were evaluated for each of the above capacitors. Table 6 shows the evaluation results of leakage current and withstand voltage of each capacitor. The leakage current and withstand voltage were measured in the same manner as in the previous evaluation. In addition, the measured value of each leakage current is normalized with the measurement result of the leakage current in Comparative Example 1 (capacitor X1) as 100.

  As shown in Table 6, even when various electrolytes containing fluorine ions are used, as in Example 1 (capacitor A1), an increase in the leakage current of the capacitor can be suppressed and the withstand voltage can be improved. .

  From the above, according to the solid electrolytic capacitor and the manufacturing method thereof of the present embodiment, the following effects can be obtained.

  (1) The dielectric layer 2 made of niobium oxide contains fluorine, and at least one metal of aluminum and tantalum is dissolved, so that amorphous niobium oxide is applied when a thermal load is applied. Therefore, the increase in leakage current of the solid electrolytic capacitor is suppressed, and the withstand voltage can be improved.

  (2) By allowing fluorine in the dielectric layer 2 to be present near the anode side surface (near the interface between the dielectric layer 2 and the anode body 1), oxygen from the dielectric layer 2 to the anode body 1 Since the diffusion is suppressed and the reduction in the thickness of the dielectric layer 2 is suppressed, the effect of improving the withstand voltage can be enjoyed more effectively.

  (3) By making the aluminum content in the range of 1 atomic% to 15 atomic% with respect to the niobium content in the dielectric layer 2, the effect of the above (1) or (2) can be obtained more remarkably. it can.

  (4) By setting the tantalum content in the range of 1 atomic% to 50 atomic% with respect to the niobium content in the dielectric layer 2, the effect (1) or (2) can be obtained more remarkably. it can.

  (5) Nitrogen is further contained in the dielectric layer 2 made of niobium oxide together with fluorine unevenly distributed on the anode side and solid solution aluminum, whereby the withstand voltage improvement effect can be further enhanced.

  (6) By setting the content of nitrogen in the dielectric layer 2 in the range of 50 ppm to 5000 ppm, the effect of the above (5) can be more remarkably enjoyed.

  (7) According to this manufacturing method, fluorine is unevenly distributed in the vicinity of the anode side surface of the dielectric layer 2 (near the interface between the dielectric layer 2 and the anode body 1), and the dielectric layer 2 A solid electrolytic capacitor in which aluminum (or tantalum) is dissolved can be manufactured. This suppresses crystallization of amorphous niobium oxide functioning as a dielectric layer against a thermal load, suppresses an increase in leakage current of the solid electrolytic capacitor, and improves its withstand voltage. Therefore, an increase in leakage current due to a thermal load is suppressed, and a solid electrolytic capacitor with improved withstand voltage can be easily manufactured.

(8) After the anodization (after the formation of the dielectric layer 2), by implanting aluminum (or tantalum) using the ion implantation method, the aluminum (or tantalum) is not oxidized as in the prior art. In the dielectric layer 2, aluminum (or tantalum) can be present in a solid solution state. Therefore, an increase in leakage current due to a thermal load is suppressed, and a solid electrolytic capacitor with improved withstand voltage can be easily manufactured.

  (9) The anode body 1 is subjected to a heat treatment in a nitrogen atmosphere, and then anodized in an electrolytic solution containing fluorine ions, whereby the dielectric layer 2 is subjected to nitrogen in addition to the above-described fluorine. Can be easily contained. Thereafter, aluminum (or tantalum) is dissolved by ion implantation, whereby a solid electrolytic capacitor containing aluminum dissolved in the dielectric layer 2 together with fluorine and nitrogen can be manufactured. Therefore, according to this manufacturing method, a solid electrolytic capacitor having a further improved withstand voltage can be easily manufactured.

  The present invention is not limited to the above-described embodiments (examples), and various modifications such as design changes can be added based on the knowledge of those skilled in the art. The described embodiments (examples) can also be included in the scope of the present invention.

  In the above-described embodiment (example), as an example of the method for containing nitrogen in the dielectric layer, an example of nitriding an anode body made of a niobium metal particle porous sintered body or niobium foil has been shown. Not limited to this. For example, the dielectric layer may be formed by employing a porous sintered body made of niobium nitride particles or a niobium nitride foil as the anode body. Even in this case, the corresponding effect can be enjoyed.

1 is a schematic cross-sectional view showing a configuration of a solid electrolytic capacitor according to an embodiment. (A) Al-Kα spectrum by EPMA of Comparative Example 5 (capacitor X5), (B) Al-Kα spectrum by EPMA of Comparative Example 3 (capacitor X3). The block diagram at the time of the leakage current measurement of each capacitor | condenser which concerns on an Example and a comparative example.

Explanation of symbols

  1a anode lead, 1 anode body, 2 dielectric layer, 3 conductive polymer layer, 4 cathode layer, 4a carbon layer, 4b silver paste layer, 5 conductive adhesive, 6 cathode terminal, 7 anode terminal, 8 mold exterior Body, 11 container, 12 phosphoric acid aqueous solution, 13 capacitor.

Claims (6)

An anode made of niobium or a niobium alloy;
A dielectric layer comprising niobium oxide formed on the surface of the anode;
A cathode formed on the dielectric layer;
With
A solid electrolytic capacitor characterized in that the region containing niobium oxide contains fluorine, and at least one of aluminum and tantalum is dissolved therein.   2. The solid electrolytic capacitor according to claim 1, wherein the metal is aluminum and the content thereof is in the range of 1 atomic% to 15 atomic% with respect to the content of niobium in the dielectric layer.   2. The solid electrolytic capacitor according to claim 1, wherein the metal is tantalum and the content thereof is in the range of 1 atomic% to 50 atomic% with respect to the content of niobium in the dielectric layer.   The solid electrolytic capacitor according to claim 1, wherein the dielectric layer further contains nitrogen. First step of forming a dielectric layer containing niobium oxide by anodizing the surface of the anode made of niobium or niobium alloy in an electrolyte containing fluorine ions, and doping the fluorine into the dielectric layer When,
A second step of introducing at least one metal of aluminum and tantalum into the region containing niobium oxide using an ion implantation method to form a solid solution;
A third step of forming a cathode on the dielectric layer;
A method for producing a solid electrolytic capacitor, comprising:   6. The solid electrolytic capacitor according to claim 5, further comprising a fourth step of nitriding the anode by subjecting the anode to a heat treatment in a nitrogen atmosphere before the first step. Production method.

Images