JP2018018930A - Solid electrolytic capacitor and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a solid electrolytic capacitor which enables the reduction in leak current in a solid electrolytic capacitor arranged to use a conductive polymer as a solid electrolyte, and enables the suppress of decrease in a capacitance per unit volume; and a method for manufacturing the solid electrolytic capacitor.SOLUTION: A solid electrolytic capacitor comprises a positive electrode conductor 1 made of a valve metal, a dielectric layer 2, a silane coupling agent layer 9, and a solid electrolyte layer 4 which are formed in turn. The silane coupling agent layer 9 overlies 75% or more of a surface region of the dielectric layer and has a thickness of 10 nm larger and smaller than 50 nm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a solid electrolytic capacitor using a conductive polymer as a solid electrolyte and a method for manufacturing the same.

  A solid electrolytic capacitor in which a dielectric layer is formed on a surface of an anode body made of a porous valve metal, a silane coupling agent layer is formed on the dielectric layer, and a solid electrolyte layer is formed on the silane coupling agent layer; The manufacturing method is disclosed in Patent Document 1.

JP 2012-174948 A

  In a solid electrolytic capacitor, if the silane coupling agent layer is formed thick for the purpose of suppressing leakage current, the film thickness tends to be non-uniform. If the silane coupling agent layer is excessively thick, electron potential barrier transmission due to the tunnel effect is hindered, and the characteristics of the dielectric layer cannot be fully utilized, resulting in a decrease in capacitance per capacitor volume. On the other hand, if the silane coupling agent layer is too thin, the leakage current increases due to the tunnel effect.

  Therefore, in the conventional solid electrolytic capacitor, there is a problem that it is difficult to reduce the leakage current and at the same time suppress the decrease in the capacity per volume.

  The present invention includes an anode conductor made of a porous valve metal, a dielectric layer disposed on the surface of the anode conductor, a silane coupling agent layer disposed on the surface of the dielectric layer, and the silane coupling. A solid electrolytic capacitor including a solid electrolyte layer disposed on a surface of the agent layer, wherein the silane coupling agent layer has a thickness of 10 nm or more and less than 50 nm in 75% or more of the region on the surface of the dielectric layer. The above-mentioned problem is solved by using a solid electrolytic capacitor characterized by being.

  In the solid electrolytic capacitor of the present invention, the silane coupling agent layer may be in a monomolecular state.

  In the solid electrolytic capacitor of the present invention, the silane coupling agent layer may have a nonionic functional group.

  Furthermore, in the solid electrolytic capacitor of the present invention, the silane coupling agent layer may also be disposed inside the dielectric layer and the solid electrolyte layer.

  According to the present invention, a step of forming a dielectric layer on the surface of an anode conductor made of a valve metal of a porous body, and applying and drying a solution of a silane coupling agent on the surface of the dielectric layer, A method for producing a solid electrolytic capacitor comprising the steps of forming a silane coupling agent layer and forming a solid electrolyte layer on the surface of the silane coupling agent layer is obtained.

  In the method for producing a solid electrolytic capacitor of the present invention, the pH of the solution of the silane coupling agent may be 3.0 or more and less than 6.0.

  In the method for producing a solid electrolytic capacitor of the present invention, the solution of the silane coupling agent may contain an aprotic polar solvent.

  In the method for producing a solid electrolytic capacitor of the present invention, the temperature of the silane coupling agent solution may be 10 ° C. or less.

  By setting the thickness of the silane coupling agent layer within a predetermined range in 75% or more of the area on the surface of the dielectric layer, the silane coupling agent layer itself can function as a part of the potential barrier on the outermost surface of the dielectric. It becomes possible. In particular, by setting the thickness of the silane coupling agent layer to 10 nm or more, not only the repair of the potential barrier but also the transmission of electrons due to the tunnel effect can be suppressed, and the leakage current of the solid electrolytic capacitor can be reduced. it can. Moreover, the fall of the capacity | capacitance of a solid electrolytic capacitor and the raise of ESR (equivalent series resistance) can be suppressed because the thickness of a silane coupling agent layer shall be less than 50 nm.

  When a monomolecular silane coupling agent is used to form the silane coupling agent layer, the thickness of the silane coupling agent layer can be made uniform. It is possible to suppress a problem that the current decreases due to a decrease or an excessively thin current.

  When the silane coupling agent layer has an ionic functional group, the potential barrier is narrowed by doping into the dielectric, so that it has a nonionic functional group to ensure a sufficient potential barrier. Is desirable.

  The silane coupling agent layer may be present between the layers of the solid electrolyte layer, or may be divided into two or more layers, such as the surface of the dielectric layer and the layer between the solid electrolyte layers. When divided, the total thickness of each layer may be 10 nm or more and less than 50 nm. By forming a silane coupling agent layer between the solid electrolyte layers, there is a possibility that the capacity reduction can be further suppressed.

  By setting the pH of the solution of the silane coupling agent to 3.0 or more and less than 6.0, the condensation reaction between the silane coupling agents, that is, the polymerization is suppressed, and the monomolecular state of the silane coupling agent is maintained. It is possible.

  Since the solution of the silane coupling agent contains the aprotic polar solvent, the concentration of protons as a catalyst is lowered, so that polymerization of the silane coupling agent can be suppressed.

  When the temperature of the solution of the silane coupling agent is 10 ° C. or lower, the chemical reaction is difficult to occur due to the low temperature, and the polymerization of the silane coupling agent can be suppressed.

  According to the present invention, the silane coupling agent layer has a thickness within a predetermined range in a predetermined region on the surface of the dielectric layer, so that the silane coupling agent layer itself suppresses transmission of electrons as a part of the potential barrier, and tunnel effect In addition to reducing the leakage current of the solid electrolytic capacitor due to the thickness and increasing the substantial potential barrier, in addition to contributing to the improvement of the withstand voltage of the solid electrolytic capacitor, suppressing the decrease in capacity per volume It is possible to provide a solid electrolytic capacitor that can be manufactured and a method for manufacturing the same.

Sectional drawing of the solid electrolytic capacitor of this invention. The enlarged view of the broken-line part of FIG.

  Hereinafter, embodiments of the present invention will be described in detail.

  FIG. 1 is a cross-sectional view of a solid electrolytic capacitor of the present invention, and FIG. 2 is an enlarged view of a broken line portion of FIG.

  As shown in FIG. 1, the anode conductor 1 made of a porous valve action metal, and the dielectric layer 2 is formed on the surface of the anode conductor 1, and 75% or more of the area on the surface of the dielectric layer 2, A silane coupling agent layer 9 having a thickness of 10 nm or more and less than 50 nm is formed, a solid electrolyte layer 4 is formed on the surface of the silane coupling agent layer 9, and a cathode layer 5 is formed on the surface of the solid electrolyte layer 4. Lead frames 71 and 72 are connected to the anode lead 3 and the cathode layer 5, respectively. Connection is performed using welding or conductive adhesive 6. A portion that becomes the external electrode of the lead frames 71 and 72 is exposed, and the whole is molded with the exterior resin 8 to obtain a solid electrolytic capacitor.

The dielectric layer 2 is formed by anodic oxidation of a valve metal (for example, Ta). The portion adjacent to the metal side is an n-type tantalum oxide layer containing excess tantalum atoms having a chemical equivalent of Ta ₂ O ₅ or more, and the subsequent layer is an intrinsic semiconductor having a composition equivalent to the chemical equivalent of Ta ₂ O _5. I layer. The i layer has a thickness proportional to the formation voltage (voltage for forming an oxide film). The outermost surface is induced by a p-type tantalum oxide layer by a solid electrolyte (conductive polymer, silane coupling agent, etc.) formed on the dielectric layer. An n-junction is formed and good insulation is obtained. However, when the conductive polymer is formed, the conductive polymer draws electrons from the oxide film and lowers the electron barrier.

  The silane coupling agent used for forming the silane coupling agent layer 9 is a silicon compound having an organic functional group having high affinity with an organic substance (conductive polymer) and a hydrolyzable OR group. The OR group is hydrolyzed to change to an OH group and reacted with the dielectric surface to form a chemical bond with the inorganic surface. In addition, since the organic functional group has a high affinity with the conductive polymer, there is an effect of improving the adhesion between the organic functional group and the conductive polymer, and the dielectric and the conductive polymer layer are interposed via a silane coupling agent. Can be tied together. In addition, since the OH group is electrophilic, there is an effect of repairing the electron barrier on the outermost surface of the dielectric that has been lowered by the formation of the conductive polymer.

  In the formation of the silane coupling agent layer 9, the film is obtained by dipping in a solution containing the silane coupling agent and then drying. Since the resulting coating is extremely thin, it is repeatedly dipped and dried until the desired film thickness is obtained. It is difficult to obtain a uniform film thickness because the film is more likely to adhere to a place where it easily adheres, and a large difference in film thickness tends to occur between places where it is difficult to adhere. Moreover, since the lump which a part of silane coupling agent condensed will arise when an acidic solvent is used, it will become still more difficult to set it as a uniform film thickness.

  In order to uniformly form the film thickness of the silane coupling agent layer 9, it is preferable to immerse the film several times using a silane coupling agent aqueous solution in a monomolecular state of 5% or less. Further, the pH of the aqueous solution is preferably 3.0 or more and less than 6.0, and outside the range, the silane coupling agent is polymerized by condensation between the silane coupling agents, so the thickness of the silane coupling agent layer is There is a possibility of non-uniformity.

  The silane coupling agent is used after the OR group is replaced with an OH group by hydrolysis. It is preferable to mix an aprotic polar solvent after substitution with an OH group. This is because protons can be used as a catalyst to increase the polymerization of silane coupling agents having an OH group, so that the proton concentration can be suppressed. The aprotic polar solvent is preferably dimethyl sulfoxide, acetonitrile or acetone. Further, the liquid temperature of the silane coupling agent solution is preferably 10 ° C. or lower because the condensation between the silane coupling agents is suppressed.

  The silane coupling agent layer 9 may exist between the solid electrolyte layers 4 or may be divided into two or more layers such as the surface of the dielectric layer 2 and the solid electrolyte layer 4. When divided, the total thickness of each layer may be 10 nm or more and less than 50 nm. By forming the silane coupling agent layer 9 between the solid electrolyte layers 4, there is a possibility that the capacity reduction can be further suppressed.

  The thickness of the silane coupling agent layer 9 is determined by forming a cross section by polishing, processing the cross section with an ion milling apparatus to remove any slack in the cross section by polishing, bonding the silane coupling agents with an aqueous ammonia solution, and combining the SEM ( Observation is performed using a scanning electron microscope. If the silane coupling agent is not bonded with an aqueous ammonia solution, the silane coupling agent is volatilized by the electron beam of the SEM, and observation is hindered.

  The solid electrolyte layer 4 is formed by any one or more methods of chemical polymerization, electrolytic polymerization, or a method of applying and drying a conductive polymer solution, and it is necessary to fill at least a part of the porous body. The solid electrolyte layer 4 preferably includes a polymer composed of a monomer containing at least one kind of pyrrole, thiophene, aniline and derivatives thereof. In addition, it is preferable to include a sulfonic acid compound as a dopant. In addition to the above conductive polymer materials, oxide semiconductors such as manganese dioxide and ruthenium oxide, and organic semiconductors such as TCNQ (7,7,8,8, -tetracyanoquinodimethane complex salt) are included. It may be.

  A known method may be used to form the solid electrolyte layer 4. For example, the solid electrolyte layer 4 is obtained by applying or impregnating the conductive polymer composition onto the dielectric layer 2 formed on the surface of the anode conductor 1 and drying. The solid electrolyte layer 4 may be composed of two or more layers.

  The material of the cathode layer 5 is not particularly limited as long as it is made of a conductor. For example, a two-layer structure including a carbon layer made of graphite or the like and a silver conductive resin layer can be used.

Example 1
A Ta powder was molded into a rectangular parallelepiped having a length of 3.5 mm, a width of 3.0 mm, and a thickness of 1.5 mm, and a press body in which a Ta wire was embedded as the anode lead 3 was sintered to prepare a Ta sintered body. This sintered body was anodized in an aqueous phosphoric acid solution to form a dielectric layer 2.

  Next, the Ta sintered body covered with the dielectric layer 2 is immersed in a 5% by mass aqueous solution of 3-glycidoxypropyltrimethoxysilane whose pH is adjusted to 3.0 or more and less than 6.0 with acetic acid, It dried at 120 degreeC for 60 minutes. By repeating this operation three times, a silane coupling agent layer 9 was formed. The film thickness of the silane coupling layer was 10 nm or more and less than 50 nm, and the area of the region was 75% of the whole.

  The anode conductor 1 includes a monomer solution containing 3,4-ethylenedioxythiophene, 1,3,6-naphthalene trisulfonic acid as a dopant, and an oxidizing agent solution containing ammonium peroxodisulfate as an oxidizing agent. It was immersed in the solution. The immersion was repeated, and the conductive polymer layer, which is the solid electrolyte layer 4 containing poly 3,4-ethylenedioxythiophene, was formed by chemical oxidative polymerization.

  After forming the cathode layer 5 using graphite paste and silver paste as the conductive paste, connecting the lead frame 71 and the cathode layer 5 via the conductive adhesive 6, and connecting the anode lead 3 and the lead frame 72 by welding, The whole except for the external electrode was molded with the exterior resin 8 to obtain a solid electrolytic capacitor.

(Example 2)
In the same manner as in Example 1, a Ta sintered body was produced, anodized, and the dielectric layer 2 was formed. Thereafter, the Ta sintered body covered with the dielectric layer 2 is immersed in a 5% by mass aqueous solution of 3-glycidoxypropyltrimethoxysilane whose pH is adjusted to 3.0 or more and less than 6.0 with acetic acid. Dry at 60 ° C. for 60 minutes. The aqueous silane coupling agent solution was controlled at 5 ± 1 ° C. in order to promote uniform film thickness.

  By repeating the above operation three times, a silane coupling agent layer 9 was formed. The film thickness of the silane coupling layer was 10 nm or more and less than 30 nm, and the area of the region was 80% of the whole.

  Further, the solid electrolyte layer 4 was formed in the same manner as in Example 1, the cathode layer 5 was formed, and lead frames 71 and 72 were connected to the cathode layer 5 and the anode lead 3 using the conductive adhesive 6 and welding, respectively. Thereafter, the whole was molded with the exterior resin 8 to obtain a solid electrolytic capacitor.

(Example 3)
In the same manner as in Example 1, a Ta sintered body was produced, anodized, and the dielectric layer 2 was formed. Thereafter, the pH was adjusted to 3.0 or more and less than 6.0 with acetic acid, and the dielectric layer 2 was coated with a 5% by mass aqueous solution of 3-glycidoxypropyltrimethoxysilane containing 30% by mass of dimethyl sulfoxide. The Ta sintered body was immersed and dried at 120 ° C. for 60 minutes.

  By repeating the above operation three times, a silane coupling agent layer 9 was formed. The film thickness of the silane coupling layer was 10 nm or more and less than 30 nm, and the area of the region was 80% of the whole.

  Further, the solid electrolyte layer 4 was formed in the same manner as in Example 1, the cathode layer 5 was formed, and lead frames 71 and 72 were connected to the cathode layer 5 and the anode lead 3 using the conductive adhesive 6 and welding, respectively. Thereafter, the whole was molded with the exterior resin 8 to obtain a solid electrolytic capacitor.

Example 4
In the same manner as in Example 1, a Ta sintered body was produced, anodized, and the dielectric layer 2 was formed. Thereafter, the tantalum sintered body covered with the dielectric layer 2 is immersed in a 5% by mass aqueous solution of 3-glycidoxypropyltrimethoxysilane whose pH is adjusted to 3.0 or more and less than 6.0 with acetic acid. Dry at 60 ° C. for 60 minutes.

  The anode conductor 1 includes a monomer solution containing 3,4-ethylenedioxythiophene, 1,3,6-naphthalene trisulfonic acid as a dopant, and an oxidizing agent solution containing ammonium peroxodisulfate as an oxidizing agent. It was immersed in the solution. Then, it was immersed in a 5% by mass aqueous solution of 3-glycidoxypropyltrimethoxysilane whose pH was adjusted to 3.0 or more and less than 6.0 with acetic acid. This operation was repeated twice.

  Furthermore, it is immersed in a solution containing a monomer solution containing 3,4-ethylenedioxythiophene, 1,3,6-naphthalene trisulfonic acid as a dopant, and an oxidizing agent solution containing ammonium peroxodisulfate as an oxidizing agent. I let you. The immersion was repeated, and the conductive polymer layer, which is the solid electrolyte layer 4 containing poly 3,4-ethylenedioxythiophene, was formed by chemical oxidative polymerization.

  In addition, the film thickness of the silane coupling agent layer between the conductive polymer layers in this example and the silane coupling agent layer on the dielectric surface is 10 nm or more and less than 50 nm. Of 75%.

  Further, the cathode layer 5 is formed in the same manner as in Example 1, and the lead frames 71 and 72 are connected to the cathode layer 5 and the anode lead 3 using the conductive adhesive 6 and welding, respectively, and then the whole is covered with the exterior resin 8. The mold was packaged to obtain a solid electrolytic capacitor.

(Comparative example)
In the same manner as in Example 1, a Ta sintered body was produced, anodized, and the dielectric layer 2 was formed. Next, the Ta sintered body covered with the dielectric layer 2 was immersed in a 1% by mass aqueous solution of 3-glycidoxypropyltrimethoxysilane having a pH of 7, and dried at 120 ° C. for 60 minutes. By repeating this operation three times, a silane coupling agent layer 9 was formed. In addition, the area whose film thickness of a silane coupling agent layer was 10 nm or more and less than 50 nm was 50% of the whole.

  Further, the solid electrolyte layer 4 was formed in the same manner as in Example 1, the cathode layer 5 was formed, and lead frames 71 and 72 were connected to the cathode layer 5 and the anode lead 3 using the conductive adhesive 6 and welding, respectively. Thereafter, the whole was molded with the exterior resin 8 to obtain a solid electrolytic capacitor.

  As shown in Table 1, in Examples 1 to 4 of the present invention, the leakage current was significantly reduced as compared with the configuration of the comparative example. Also, the capacity was improved by about 5 to 8% compared to the comparative example.

  As mentioned above, although the Example of this invention was described, this invention is not limited to the said structure, A change and correction of a structure are possible in the range which does not deviate from the summary of this invention. That is, it goes without saying that various modifications and corrections that can be made by those skilled in the art are also included in the present invention.

DESCRIPTION OF SYMBOLS 1 Anode conductor 2 Dielectric layer 3 Anode lead 4 Solid electrolyte layer 5 Cathode layer 6 Conductive adhesive 8 Exterior resin 9 Silane coupling agent layer 71, 72 Lead frame

Claims (8)

  An anode conductor made of a porous metal valve, a dielectric layer disposed on the surface of the anode conductor, a silane coupling agent layer disposed on the surface of the dielectric layer, and a surface of the silane coupling agent layer A solid electrolytic capacitor including a solid electrolyte layer disposed on the dielectric layer, wherein the silane coupling agent layer has a thickness of 10 nm or more and less than 50 nm in 75% or more of the region on the surface of the dielectric layer. Solid electrolytic capacitor.   The solid electrolytic capacitor according to claim 1, wherein the silane coupling agent layer is in a monomolecular state.   The solid electrolytic capacitor according to claim 1, wherein the silane coupling agent layer has a nonionic functional group.   4. The solid electrolytic capacitor according to claim 1, wherein the silane coupling agent layer is also disposed inside the dielectric layer and the solid electrolyte layer. 5.   A step of forming a dielectric layer on the surface of the anode conductor made of a valve metal of the porous body, and applying and drying a solution of a silane coupling agent on the surface of the dielectric layer to form a silane coupling agent layer The manufacturing method of the solid electrolytic capacitor characterized by including the process of forming, and the process of forming a solid electrolyte layer on the surface of the said silane coupling agent layer.   The method for producing a solid electrolytic capacitor according to claim 5, wherein the pH of the solution of the silane coupling agent is 3.0 or more and less than 6.0.   The method for producing a solid electrolytic capacitor according to claim 5, wherein the solution of the silane coupling agent contains an aprotic polar solvent.   The method for producing a solid electrolytic capacitor according to any one of claims 5 to 7, wherein the temperature of the solution of the silane coupling agent is 10 ° C or lower.

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