JPWO2014091744A1 - Solid electrolytic capacitor - Google Patents

Abstract

Anode (1), dielectric layer (2) formed on the surface of anode (1), intermediate layer (3) formed on the surface of dielectric layer (2), and intermediate layer (3 ) On the surface of the solid electrolytic capacitor (10). The intermediate layer (3) contains an n-type organic semiconductor having the lowest vacant orbit smaller than the work function of the solid electrolyte layer (4), and an amorphous insulating polymer. Further, an intermediate layer (30) containing an amorphous charge transfer complex is provided in place of the intermediate layer (3).

Description

  The present invention relates to a solid electrolytic capacitor used for electronic equipment and the like.

  In recent years, along with the downsizing and weight reduction of electronic devices, there has been a demand for small, high-capacity high-frequency capacitors, and as such capacitors, solids in which a solid electrolyte layer is formed using a conductive polymer compound. Electrolytic capacitors have been proposed. In such a solid electrolytic capacitor, capacitance, tan δ, equivalent series resistance, leakage current, etc. are the main performance indicators, and the reliability of the capacitor has little change in the above performance indicators over a long period of time. There is a need for capacitors with very low current.

  However, the dielectric oxide film formed on tantalum, niobium, titanium, or aluminum used for solid electrolytic capacitors has defects, and high reliability cannot be obtained due to increase in leakage current and decrease in voltage resistance. There was a problem. Therefore, in order to solve this problem, one method is generally used in which the thickness of the dielectric oxide film is increased to suppress the leakage current. However, when the dielectric oxide film is thickened, the electrostatic capacity, which is the main performance, is lowered as shown in the following equation. For example, in the following formula, when d is doubled, C is reduced by a factor of 1/2. Therefore, increasing the thickness of d greatly reduces the performance of C.

(C: electrostatic capacity, d: film thickness, S: area, ε0: dielectric constant of vacuum, εr: relative dielectric constant of dielectric)
Therefore, there is a method of forming a material layer between the dielectric and the cathode as a means for solving the above-described problems. For example, in Patent Document 1, after a dielectric is formed by anodic oxidation, the element is immersed in a PVA solution, thereby forming a PVA film on the dielectric, thereby realizing high withstand voltage. However, in this method, when the PVA film is formed uniformly, the PVA having a low dielectric constant is formed as the insulator layer, so that the capacity may be reduced. In Patent Documents 2 and 3, a technique is proposed in which an insulating thin film layer is locally formed on the defective portion of the dielectric layer by electrodeposition, and the defective portion of the dielectric layer is repaired by this insulating thin film layer. Has been. However, in this method, although locally, the insulating thin film layer is formed as an insulator layer, the capacity may be reduced.

  Further, in the method disclosed in Patent Document 1, even when the PVA film is formed uniformly, the ESR (equivalent series resistance) may increase because the resistance of the material layer (PVA film) is high.

JP 2007-173454 A JP 2002-343684 A Japanese Patent Laid-Open No. 10-247612

  This invention is made | formed in view of said point, and it aims at providing the solid electrolytic capacitor which can suppress a leakage current effectively.

  A solid electrolytic capacitor according to the present invention includes an anode, a dielectric layer formed on the surface of the anode, an intermediate layer formed on the surface of the dielectric layer, and a solid electrolyte formed on the surface of the intermediate layer. And the intermediate layer includes an n-type organic semiconductor having a minimum vacant orbit smaller than a work function of the solid electrolyte layer, and an amorphous insulating polymer. It is characterized by that.

  In the present invention, the n-type organic semiconductor is preferably an aromatic compound containing an electron withdrawing group such as a cyano group, a nitro group, or a sulfo group.

  In the present invention, the n-type organic semiconductor is preferably tetracyanoquinodimethane and its derivatives.

  In the present invention, the insulating polymer is preferably a soluble non-aromatic polymer.

  In the present invention, the insulating polymer is preferably polymethyl methacrylate.

  The solid electrolytic capacitor according to the present invention is formed on the anode, the dielectric layer formed on the surface of the anode, the intermediate layer formed on the surface of the dielectric layer, and the surface of the intermediate layer. A solid electrolytic capacitor comprising a solid electrolyte layer, wherein the intermediate layer contains an amorphous charge transfer complex.

  In the present invention, the amorphous charge transfer complex contains an n-type organic semiconductor having a lowest vacant orbit smaller than a work function of the solid electrolyte layer, and a polymer p-type semiconductor. Is preferred.

  In the present invention, it is preferable that the polymer p-type semiconductor has a lowest empty orbit higher than a bottom of a conduction band of a dielectric constituting the dielectric layer.

  In the present invention, the polymer p-type semiconductor is preferably an arylamine organic material.

  In the present invention, the n-type organic semiconductor contained in the amorphous charge transfer complex is preferably tetracyanoquinodimethane and its derivatives.

  In the present invention, the polymer p-type semiconductor is preferably polyvinyl carbazole.

  The present invention effectively suppresses leakage current by including an n-type organic semiconductor having the lowest vacant orbit smaller than the work function of the solid electrolyte layer and an amorphous insulating polymer in the intermediate layer. A solid electrolytic capacitor that can be obtained is obtained.

  Moreover, this invention can obtain the solid electrolytic capacitor which can suppress a leakage current effectively by containing an amorphous charge-transfer complex in an intermediate | middle layer.

FIG. 1 is a schematic sectional view showing an example of an embodiment of the present invention. FIG. 2 is a schematic sectional view showing a part of the microscopic structure. FIG. 3A is a schematic diagram illustrating the operation of Comparative Examples 1 and 4, and FIG. 3B is a schematic diagram illustrating the operation of Examples 1 to 4.

  Hereinafter, a first embodiment for carrying out the present invention will be described.

  As shown in FIG. 1, solid electrolytic capacitor 10 of the present embodiment includes anode 1, dielectric layer 2 formed on the surface of anode 1, and intermediate layer 3 formed on the surface of dielectric layer 2. And a solid electrolyte layer 4 formed on the surface of the intermediate layer 3. Further, the solid electrolytic capacitor 10 of the present embodiment can be provided with the cathode layer 5 formed on the surface of the solid electrolyte layer 4. Furthermore, the solid electrolytic capacitor 10 of the present embodiment is covered with a mold exterior resin 6 around the periphery thereof. The mold exterior resin 6 covers the anode 1, the dielectric layer 2, the intermediate layer 3, the solid electrolyte layer 4, and the cathode layer 5. An anode lead 7 is embedded and connected to the anode 1. An anode terminal 11 is connected to the anode lead 7. A cathode terminal 8 is bonded and connected to the cathode layer 5 with an adhesive 9. The anode terminal 11 and the cathode terminal 8 are drawn out of the mold exterior resin 6 and exposed to the outside of the solid electrolytic capacitor 10.

  The anode 1 can be produced by molding a powder made of a valve metal (valve action metal) or an alloy containing the valve metal as a main component, and sintering the molded body. In this case, the anode 1 is formed from a porous body. Although not shown in FIG. 1, the anode 1, which is a porous body, has a large number of fine holes communicating from the inside to the outside. The anode 1 produced in this way can be produced so that the outer shape is a substantially rectangular parallelepiped. Examples of the valve metal include tantalum, niobium, titanium, aluminum, hafnium, and zirconium. Among these, tantalum, niobium, aluminum, and titanium, in which an oxide that is a dielectric is relatively stable even at high temperatures, are particularly preferably used. As an alloy having a valve metal as a main component, an alloy of two or more kinds of valve metals such as tantalum and niobium can be cited.

  The dielectric layer 2 is interposed between the anode 1 and the intermediate layer 3. The dielectric layer 2 can be formed from, for example, a valve metal or an oxide of an alloy containing the valve metal as a main component. The dielectric layer 2 can also be formed on the surface of the hole when the anode 1 is a porous body. In FIG. 1, the dielectric layer 2 formed on the outer peripheral side of the anode 1 is schematically shown, and the dielectric layer formed on the surface of the hole of the porous body is not shown. The dielectric layer 2 can be formed, for example, by anodizing the surface of the anode 1.

  The intermediate layer 3 functions as an electron trap layer, and is interposed between the dielectric layer 2 and the solid electrolyte layer 4. The intermediate layer 3 includes an n-type organic semiconductor having a lowest unoccupied molecular orbital (LUMO) smaller than the work function of the conductive polymer constituting the solid electrolyte layer 4, an amorphous insulating polymer, Contains.

  The n-type organic semiconductor (acceptor of the charge transfer complex) is preferably an aromatic compound containing an electron-withdrawing group such as a cyano group, a nitro group, or a sulfo group. This is because a cyano group, a nitro group, and a sulfo group have a large inducing effect among electron withdrawing groups, and thus have a great effect on lowering the LUMO level. The n-type organic semiconductor is, for example, 7,7,8,8-tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, 2,5-bis (2-hydroxyethoxy) -7,7,8. , 8-tetracyanoquinodimethane, tetracyanoethylene, 11,11,12,12-tetracyanonaphtho-2,6-quinodimethane, 1,4-benzoquinone, 2tetrafluoro-1,4-benzoquinone, 2,3 -Dichloro-5,6-dicyano-1,4-benzoquinone, 4,7-trinitro-9-fluorenone, 2,4,7-trinitro-9-fluorenylidenemalononitrile and the like. Among these, tetracyanoquinodimethane (TCNQ) and its derivatives are preferable. This is because TCNQ has high solubility in an organic solvent and can be easily formed, and has a low LUMO level among n-type organic semiconductors. Such an n-type organic semiconductor having the lowest vacant orbit can be used if it is smaller than the work function of the conductive polymer of the solid electrolyte layer 4, but is lower than the work function of the conductive polymer of the solid electrolyte layer 4. It preferably has a LUMO level lower than 0.2 eV.

  The amorphous insulating polymer contained in the intermediate layer 3 is preferably a non-aromatic polymer that is soluble in water or an organic solvent (for example, toluene or acetone). This is because the non-aromatic polymer has a relatively high solubility in a solvent and can be easily formed, and since it is non-aromatic, it hardly affects the electron conduction of TCNQ. Examples of the amorphous insulating polymer include polymethyl methacrylate, polypropylene, polystyrene, and polyethylene terephthalate. Among these, it is preferable to use polymethyl methacrylate. This is because polymethyl methacrylate has high solubility in a solvent and hardly deteriorates even under acidic conditions during the production process.

  The content ratio of the n-type organic semiconductor and the insulating polymer in the intermediate layer 3 is preferably 25 to 75 parts by mass of the insulating polymer with respect to 100 parts by mass of the n-type organic semiconductor. . With such a content ratio, it becomes easy to achieve both reduction of leakage current and suppression of capacity reduction.

  The solid electrolyte layer 4 is interposed between the intermediate layer 3 and the cathode layer 5. The solid electrolyte layer 4 can be formed of, for example, a conductive polymer layer made of a conductive polymer having a π-conjugated bond. Examples of the conductive polymer monomer for forming the conductive polymer include pyrrole, thiophene, aniline, and derivatives thereof. By polymerization of the monomer, a π-conjugated conductive polymer having a monomer repeating unit can be obtained. Therefore, by using the monomer, a conductive polymer composed of, for example, polypyrroles, polythiophenes, polyanilines, and copolymers thereof can be obtained. The π-conjugated conductive polymer can obtain sufficient conductivity even if it is not substituted, but in order to further increase the conductivity, an alkyl group, a carboxylic acid group, a sulfonic acid group, an alkoxyl group, a hydroxyl group It is preferable to introduce a functional group such as a cyano group into the π-conjugated conductive polymer.

  Specific examples of the π-conjugated conductive polymer include polypyrrole, poly (N-methylpyrrole), poly (3-methylpyrrole), poly (3-octylpyrrole), poly (3-decylpyrrole), poly (3 -Dodecylpyrrole), poly (3,4-dimethylpyrrole), poly (3,4-dibutylpyrrole), poly (3-carboxypyrrole), poly (3-methyl-4-carboxypyrrole), poly (3-methyl) -4-carboxyethylpyrrole), poly (3-methyl-4-carboxybutylpyrrole), poly (3-hydroxypyrrole), poly (3-methoxypyrrole), poly (3,4-ethylenedioxypyrrole), polythiophene , Poly (3-methylthiophene), poly (3-hexylthiophene), poly (3-heptylthiophene), poly (3-o Tilthiophene), poly (3-decylthiophene), poly (3-dodecylthiophene), poly (3-octadecylthiophene), poly (3-bromothiophene), poly (3,4-dimethylthiophene), poly (3 4-dibutylthiophene), poly (3-hydroxythiophene), poly (3-methoxythiophene), poly (3-ethoxythiophene), poly (3-butoxythiophene), poly (3-hexyloxythiophene), poly (3 -Heptyloxythiophene), poly (3-octyloxythiophene), poly (3-decyloxythiophene), poly (3-dodecyloxythiophene), poly (3-octadecyloxythiophene), poly (3,4-dihydroxythiophene) ), Poly (3,4-dimethoxythiophene), poly (3, 4-ethylenedioxythiophene), poly (3,4-propylenedioxythiophene), poly (3,4-butenedioxythiophene), poly (3-carboxythiophene), poly (3-methyl-4-carboxythiophene) ), Poly (3-methyl-4-carboxyethylthiophene), poly (3-methyl-4-carboxybutylthiophene), polyaniline, poly (2-methylaniline), poly (3-isobutylaniline), poly (2- Aniline sulfonic acid), poly (3-aniline sulfonic acid) and the like. Among them, from one or two kinds selected from polypyrrole, polythiophene, poly (N-methylpyrrole), poly (3-methylthiophene), poly (3-methoxythiophene), and poly (3,4-ethylenedioxythiophene). The (co) polymer is preferably used from the viewpoint of conductivity. Furthermore, polypyrrole and poly (3,4-ethylenedioxythiophene) are more preferable from the viewpoint of higher conductivity and improved heat resistance.

  Examples of the oxidizing agent used as the polymerization initiator for the conductive polymer monomer as described above include transition metal compounds such as ferric sulfate and ferric nitrate, and organic sulfonic acids such as iron paratoluenesulfonate. And transition metal salts.

  The cathode layer 5 can be formed, for example, by laminating a first layer 5a containing carbon particles and a second layer 5b containing silver particles. The first layer 5a can be formed by applying a carbon paste and then drying it. The second layer 5b can be formed by applying a silver paste and then drying it. The cathode layer 5 is disposed around the anode 1 with a gap from the dielectric layer 2. In the cathode layer 5, the first layer 5 a is disposed on the dielectric layer 2 side, and the second layer 5 b is disposed on the opposite side to the dielectric layer 2.

  The solid electrolytic capacitor 10 of the present embodiment formed as described above includes an n-type organic semiconductor having a LUMO smaller than the work function of the solid electrolyte layer 4 between the dielectric layer 2 and the solid electrolyte layer 4. The containing intermediate layer 3 is inserted. Therefore, the Schottky barrier at the interface between the dielectric layer 2 and the solid electrolyte layer 4 can be increased, and the leakage current flowing between the anode 1 and the cathode layer 5 can be reduced. Further, since the electrons move to the inserted intermediate layer 3 and act as a cathode, the capacitance is hardly lowered. Further, according to the present embodiment, since the amorphous intermediate layer 3 is formed by mixing the n-type organic semiconductor and the amorphous insulating polymer, the crystal grain boundary portion of the n-type organic semiconductor. In addition, the conductive polymer (for example, polypyrrole) contained in the solid electrolyte layer 4 penetrates, and the leakage current can be effectively reduced without forming a conductive path.

  FIG. 2 is an enlarged cross-sectional view of a part of the solid electrolytic capacitor 10 described above. The anode 1 is microscopically composed of a large number of powders, and a dielectric layer 2 is formed on the surface of these powders. Thus, the anode 1 and the dielectric layer 2 constitute one porous body. When the intermediate layer 3 is formed on the surface of the dielectric layer 2, the intermediate layer 3 penetrates into the pores of the porous body composed of the anode 1 and the dielectric layer 2. For this reason, the contact area between the intermediate layer 3 and the dielectric layer 2 is increased, thereby increasing the effective area of the anode 1. For this reason, it becomes easy to increase the electrostatic capacitance of the solid electrolytic capacitor 10.

  Next, a second embodiment for carrying out the present invention will be described.

  The solid electrolytic capacitor 10 of the second embodiment has the configuration shown in FIG. 1, similarly to the solid electrolytic capacitor 10 of the first embodiment.

  The solid electrolytic capacitor 10 of the second embodiment is different from the solid electrolytic capacitor 10 of the first embodiment in the configuration of the intermediate layer 30 (3), and the other components are the first embodiment. The same as the solid electrolytic capacitor 10 of FIG.

  In the solid electrolytic capacitor 10 of the second embodiment, the intermediate layer 30 is interposed between the dielectric layer 2 and the solid electrolyte layer 4 and functions as an electron trap layer, and the intermediate layer 30 is amorphous. It is formed containing a charge transfer complex. As this amorphous charge transfer complex, it is preferable to use an n-type organic semiconductor having a lowest unoccupied molecular orbital (LUMO) smaller than the work function of the conductive polymer constituting the solid electrolyte layer 4. . As a result, an intermediate layer 30 containing an n-type organic semiconductor having a LUMO smaller than the work function of the solid electrolyte layer 4 is inserted between the dielectric layer 2 and the solid electrolyte layer 4. Therefore, the Schottky barrier at the interface between the dielectric layer 2 and the solid electrolyte layer 4 can be increased, and the leakage current flowing between the anode 1 and the cathode layer 5 can be reduced. The n-type organic semiconductor (acceptor of the charge transfer complex) is preferably an aromatic compound containing an electron-withdrawing group such as a cyano group, a nitro group, or a sulfo group. The n-type organic semiconductor is, for example, 7,7,8,8-tetracyanoquinodimethane, tetrafluorotetracyanoquinodimethane, 2,5-bis (2-hydroxyethoxy) -7,7,8. , 8-tetracyanoquinodimethane, tetracyanoethylene, 11,11,12,12-tetracyanonaphtho-2,6-quinodimethane, 1,4-benzoquinone, 2tetrafluoro-1,4-benzoquinone, 2,3 -Dichloro-5,6-dicyano-1,4-benzoquinone, 4,7-trinitro-9-fluorenone, 2,4,7-trinitro-9-fluorenylidenemalononitrile and the like. Among these, tetracyanoquinodimethane (TCNQ) and its derivatives are preferable. This is because TCNQ has high solubility in an organic solvent and can be easily formed, and has a low LUMO level among n-type organic semiconductors. Such an n-type organic semiconductor having the lowest vacant orbit can be used if it is smaller than the work function of the conductive polymer of the solid electrolyte layer 4, but is lower than the work function of the conductive polymer of the solid electrolyte layer 4. It preferably has a LUMO level lower than 0.2 eV.

  The intermediate layer 30 preferably further contains a polymer p-type semiconductor as an amorphous charge transfer complex. According to this aspect, the intermediate layer 30 is formed of an amorphous charge transfer complex in which an n-type organic semiconductor and a polymer p-type semiconductor are mixed. For this reason, the conductive polymer (for example, polypyrrole) contained in the solid electrolyte layer 4 penetrates into the crystal grain boundary of the n-type organic semiconductor, effectively reducing the leakage current without forming a conductive path. However, the equivalent series resistance (ESR) can be reduced by reducing the resistance from the formation of the charge transfer complex to the organic semiconductor layer (intermediate layer 30). In addition, when the LUMO of the polymer p-type semiconductor of the intermediate layer 30 is lower than the bottom of the conduction band of the dielectric constituting the dielectric layer 2, charges are injected into the dielectric layer 2 via the polymer p-type semiconductor. Therefore, it is effective for the polymer p-type semiconductor to have a LUMO higher than the bottom of the conduction band of the dielectric constituting the dielectric layer 2.

  The polymer p-type semiconductor (charge transfer complex donor) is preferably an arylamine organic material. This is because the arylamine-based material easily develops p-type due to the electron donating effect of amine. Examples of the polymer p-type semiconductor include polyvinyl carbazole, poly [bis (4-phenyl) (2,4,6-trimethylphenyl) amine], and poly [N, N′-bis (4-butylphenyl) -N. , N′-diphenyl-1,1′-biphenyl-4,4′-diamine], poly [2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylenevinylene], poly (3-hexylthiophene) -2,5-diyl), poly [N-9'-heptadecanyl-2,7-carbazole-alt-5,5- (4 ', 7'-di-2-thienyl-2', 1 ', 3' -Benzothiadiazole)], poly [[9- (1-octylnonyl) -9H-carbazole-2,7-diyl] -2,5-thiophendiyl-2,1,3-benzothiadiazole-4,7-diyl 2,5-thiophenediyl], and the like. Among these, polyvinyl carbazole (PVCz) is preferable. As a preferable reason, PVCz has a high LUMO of 2.3 eV, shows only hole conductivity and does not show electron conductivity, and therefore there is no electron transfer from PVCz to the dielectric. When a polymer p-type semiconductor having a LUMO higher than the bottom of the conduction band of the dielectric constituting the dielectric layer 2 is used, the polymer p is higher than the bottom of the conduction band of the dielectric constituting the dielectric layer 2. The LUMO of the type semiconductor is preferably 0.2 eV or higher.

  The content ratio of the n-type organic semiconductor and the polymer p-type semiconductor in the intermediate layer 30 is 25 to 75 parts by mass of the polymer p-type semiconductor with respect to 100 parts by mass of the n-type organic semiconductor. Is preferred. With such a content ratio, it is easy to achieve both low ESR and reduction of leakage current.

  In the solid electrolytic capacitor 10 of the second embodiment formed as described above, an intermediate layer 30 containing an amorphous charge transfer complex is inserted between the dielectric layer 2 and the solid electrolyte layer 4. Yes. Therefore, the Schottky barrier at the interface between the dielectric layer 2 and the solid electrolyte layer 4 can be increased, and the leakage current flowing between the anode 1 and the cathode layer 5 can be reduced.

  Note that the solid electrolytic capacitor 10 of the second embodiment also has the configuration shown in FIG. 2, and the anode 1 is microscopically composed of a large number of powders, and a dielectric is formed on the surface of these powders. A body layer 2 is formed. Thus, the anode 1 and the dielectric layer 2 constitute one porous body. When the intermediate layer 30 is formed on the surface of the dielectric layer 2, the intermediate layer 30 penetrates into the pores of the porous body composed of the anode 1 and the dielectric layer 2. For this reason, the contact area between the intermediate layer 30 and the dielectric layer 2 is increased, thereby increasing the effective area of the anode 1. For this reason, it becomes easy to increase the electrostatic capacitance of the solid electrolytic capacitor 10.

  Hereinafter, the present invention will be specifically described by way of examples.

Example 1
[Step 1]
The tantalum sintered body element (anode) was anodized at a constant voltage of 12 V in 0.017% by mass phosphoric acid to form a dielectric oxide film (dielectric layer).

[Step 2]
The device was immersed in a solution dissolved in toluene so that the PMMA concentration was 0.025% by mass and the TCNQ concentration was 0.025% by mass. Thereafter, drying was performed and the solvent was sufficiently removed to form a PMMA: TCNQ film (intermediate layer).

[Step 3]
Next, a polypyrrole layer (solid electrolyte layer) was formed on the PMMA: TCNQ film by chemical polymerization followed by electrolytic polymerization or the like. Further, a carbon paste and a silver paste were applied to form a cathode layer, thereby producing a capacitor element.

[Step 4]
After the capacitor element was placed on the lead frame, the capacitor cathode layer was bonded to the frame.

[Step 5]
Next, the capacitor element and the lead frame were molded with an epoxy mold resin, and then cut into capacitor element units to produce tantalum capacitors (solid electrolytic capacitors).

(Comparative Example 1)
A tantalum capacitor was manufactured in the same manner as in Example 1 except that the process of Step 2 was not performed in Example 1.

(Comparative Example 2)
In Step 2 of Example 1, the device was immersed in a solution in which PVA was dissolved in pure water so as to have a concentration of 0.05% by mass. Then, it dried and fully removed the solvent and formed the PVA film | membrane. Further, the device was immersed in a solution in which glutaraldehyde was dissolved in pure water so as to have a concentration of 0.56M. Thereafter, the PVA was pulled up and heated at 65 ° C. for 30 minutes to crosslink the PVA. Subsequently, the unreacted PVA and glutaraldehyde were removed by washing with pure water to form a crosslinked PVA film. Regarding the other steps, a tantalum capacitor was fabricated in the same manner as in Example 1.

(Comparative Example 3)
In Step 2 of Example 1, PMMA was not used. That is, the device was immersed in a solution dissolved in toluene so that the TCNQ concentration was 0.025% by mass. Thereafter, it was dried and the solvent was sufficiently removed to form a TCNQ film. A tantalum capacitor was fabricated in the same manner as in Example 1 except for this step.

  The structural formula of TCNQ, the unit structural formula of PMMA, and the unit structural formula of PVA are shown in the following chemical formulas.

(Evaluation)
The capacitance and leakage current value of 40 chip-shaped solid electrolytic capacitors produced in the above examples and comparative examples were measured, and the average values of the capacitance and leakage current value were obtained. The capacitance was measured at a frequency of 120 Hz using an LCR meter (inductance-capacitance-resistance measuring device). The leakage current was measured at 40 seconds after applying the rated voltage at room temperature. The results are shown in Table 1. Table 1 shows an index with the electrostatic capacity and leakage current of Comparative Example 1 as 100. Table 2 shows the work functions and electron affinity of tantalum (Ta), tantalum oxide (Ta2O5), polypyrrole (PPy), and TCNQ.

  As apparent from Table 1, the leakage current of the solid electrolytic capacitor is reduced by forming the intermediate layer (PMMA: TCNQ layer) since the leakage current of the capacitor of Example 1 is smaller than that of Comparative Example 1. I understand. This is presumably because the interface (Schottky) barrier was increased by forming TCNQ having a LUMO smaller than the work function of the solid electrolyte layer between the dielectric layer and the cathode layer (interface). FIG. 3A schematically shows the state of Comparative Example 1. A dielectric layer 2 made of Ta2O5 is formed between the anode 1 made of Ta and the solid electrolyte layer 4 made of PPy. Usually, the dielectric layer 2 having a work function larger than that of the solid electrolyte layer 4 serves as an energy barrier, but a leakage current may occur (indicated by an arrow a). On the other hand, FIG. 3B schematically shows the state of the first embodiment. A dielectric layer 2 made of Ta2O5 is formed between the anode 1 made of Ta and the solid electrolyte layer 4 made of PPy. Further, between the dielectric layer 2 and the solid electrolyte layer 4, an n-type organic semiconductor having an LUMO smaller than the work function of the conductive polymer constituting the solid electrolyte layer 4, and an amorphous insulating polymer An intermediate layer 3 containing is formed. In this case, since the intermediate layer 3 becomes an electron trap layer, an energy barrier easily acts and a leakage current is less likely to occur (indicated by an arrow b).

  Moreover, since the capacity | capacitance fall of the capacitor | condenser of Example 1 is small compared with the comparative example 2 which formed PVA which is an insulating polymer, it turns out that TCNQ which is an n-type organic semiconductor is functioning as a cathode.

  In addition, it can be seen that the capacitor of Example 1 has substantially the same decrease in capacitance but has a reduced leakage current as compared with Comparative Example 3 in which TCNQ, which is an n-type organic semiconductor, is formed. This is because since the intermediate layer contains an amorphous insulating polymer, the formation of the TCNQ complex in the intermediate layer 3 can be suppressed, and the effect of reducing the leakage current due to the energy barrier can be easily obtained. it is conceivable that.

  In particular, when niobium or titanium is used as the valve metal, the dielectric layer 2 becomes Nb2O5 or TiO2, so that the energy barrier becomes small. This is considered to be because the dielectric constant of Ta2O5 is about 3.0, whereas the dielectric constant of Nb2O5 or TiO2 is about 4.5, which increases the dielectric constant. Therefore, when the intermediate layer 3 of the present invention is provided as shown in FIG. 3B, an energy barrier is easily applied and a leakage current is hardly generated (indicated by an arrow c). Therefore, when niobium or titanium is used as the valve metal, the effect of the present invention is further increased.

(Example 2)
[Step 1]
The tantalum sintered body element (anode) was anodized at a constant voltage of 12 V in 0.017% by mass phosphoric acid to form a dielectric oxide film (dielectric layer).

[Step 2]
The element was immersed in a solution dissolved in toluene so that the PVCz concentration was 0.025% by mass and the EtO-TCNQ concentration was 0.025% by mass. Thereafter, drying was performed to sufficiently remove the solvent, and a PVCz: EtO-TCNQ film (intermediate layer) was formed. EtO-TCNQ is 2,5-bis (2-hydroxyethoxy) -7,7,8,8-tetracyanoquinodimethane.

[Step 3]
Next, a polypyrrole layer (solid electrolyte layer) was formed on the PVCz: EtO-TCNQ film by chemical polymerization, followed by electrolytic polymerization or the like. Further, a carbon paste and a silver paste were applied to form a cathode layer, thereby producing a capacitor element.

[Step 4]
After the capacitor element was placed on the lead frame, the capacitor cathode layer was bonded to the frame.

[Step 5]
Next, the capacitor element and the lead frame were molded with an epoxy mold resin, and then cut into capacitor element units to produce tantalum capacitors (solid electrolytic capacitors).

(Example 3)
In Step 2 of Example 2, TCNQ (7,7,8,8-tetracyanoquinodimethane) was used instead of EtO-TCNQ. That is, the device was immersed in a solution dissolved in toluene so that the PVCz concentration was 0.025% by mass and the TCNQ concentration was 0.025% by mass. Thereafter, it was dried and the solvent was sufficiently removed to form a PVCz: TCNQ film (intermediate layer). A tantalum capacitor was produced in the same manner as in Example 2 except for this step.

Example 4
In Step 2 of Example 2, F4-TCNQ (tetrafluorotetracyanoquinodimethane) was used instead of EtO-TCNQ. That is, the device was immersed in a solution dissolved in toluene so that the PVCz concentration was 0.025% by mass and the F4-TCNQ concentration was 0.025% by mass. Thereafter, it was dried and the solvent was sufficiently removed to form a PVCz: F4-TCNQ film (intermediate layer). A tantalum capacitor was produced in the same manner as in Example 2 except for this step.

(Comparative Example 4)
A tantalum capacitor was fabricated in the same manner as in Example 2 except that the process of Step 2 was not performed in Example 2.

(Comparative Example 5)
In Step 2 of Example 2, EtO-TCNQ was not used. That is, the device was immersed in a solution dissolved in toluene so that the PVCz concentration was 0.025% by mass. Thereafter, it was dried and the solvent was sufficiently removed to form a PVCz film. A tantalum capacitor was produced in the same manner as in Example 2 except for this step.

(Comparative Example 6)
In Step 2 of Example 3, PVCz was not used. That is, the device was immersed in a solution dissolved in toluene so that the TCNQ concentration was 0.025% by mass. Thereafter, it was dried and the solvent was sufficiently removed to form a TCNQ film. A tantalum capacitor was produced in the same manner as in Example 2 except for this step.

  The structural formula of EtO-TCNQ, TCNQ, and F4-TCNQ and the unit structural formula of PVCz are shown in the following chemical formula.

(Evaluation)
The ESR and leakage current value of 40 chip-shaped solid electrolytic capacitors produced in the above examples and comparative examples were measured, and the average values of the ESR and leakage current value were obtained. The ESR was measured at a frequency of 100 kHz using an LCR meter (inductance-capacitance-resistance measuring device). The leakage current value was measured at 40 seconds after applying the rated voltage at room temperature. The results are shown in Table 3. In Table 3, for the leakage current, a ratio with the leakage current value of Comparative Example 1 as 100 is indicated by an index. Regarding ESR, it shows by the difference which made ESR of the comparative example 4 0. Table 4 shows the work function and electron affinity of tantalum (Ta), tantalum oxide (Ta2O5), polypyrrole (PPy), TCNQ, F4-TCNQ, EtO-TCNQ, and PVCz.

  As apparent from Table 3, the capacitors of Examples 2 to 4 have a smaller leakage current than Comparative Example 4, and therefore, by forming an intermediate layer containing PVCz and TCNQ or a derivative thereof, the leakage of the solid electrolytic capacitor It can be seen that the current decreases. This is thought to be due to the fact that the interface (Schottky) barrier is increased by forming TCNQ or a derivative thereof having a LUMO smaller than the work function of the solid electrolyte layer between the dielectric layer and the cathode layer (interface). It is done. FIG. 3A schematically shows the state of Comparative Example 4. A dielectric layer 2 made of Ta2O5 is formed between the anode 1 made of Ta and the solid electrolyte layer 4 made of PPy. Usually, the dielectric layer 2 having a work function larger than that of the solid electrolyte layer 4 serves as an energy barrier, but a leakage current may occur (indicated by an arrow a). On the other hand, FIG.3 (b) shows the state of Examples 2-4 typically. A dielectric layer 2 made of Ta2O5 is formed between the anode 1 made of Ta and the solid electrolyte layer 4 made of PPy. An intermediate layer 30 containing an amorphous charge transfer complex is formed between the dielectric layer 2 and the solid electrolyte layer 4. In this case, since the intermediate layer 30 serves as an electron trap layer, an energy barrier is likely to act, and a leakage current is less likely to occur (indicated by an arrow b).

  Moreover, since ESR of the capacitor | condenser of Examples 2-4 containing TCNQ or its derivative (s) and PVCz is falling compared with Comparative Examples 5 and 6, TCNQ or its derivative (s) and PVCz are amorphous. It is considered that the resistance is reduced by forming a charge transfer complex of

  Further, since the leakage current decreases as the LUMO decreases as in Examples 2 to 4, it is considered that the Schottky barrier at the interface increases. The decrease in ESR seems to be due to the large difference between PVCz and HOMO, which is likely to generate charges and lower the resistance.

  In particular, when niobium or titanium is used as the valve metal, the dielectric layer 2 becomes Nb2O5 or TiO2, so that the energy barrier becomes small. This is considered to be because the dielectric constant of Ta2O5 is about 3.0, whereas the dielectric constant of Nb2O5 or TiO2 is about 4.5, which increases the dielectric constant. Therefore, when the intermediate layer 30 of the present invention is provided as shown in FIG. 3B, an energy barrier is easily applied and a leakage current is hardly generated (indicated by an arrow c). Therefore, when niobium or titanium is used as the valve metal, the effect of the present invention is further increased.

DESCRIPTION OF SYMBOLS 1 Anode 2 Dielectric layer 3, 30 Intermediate layer 4 Solid electrolyte layer 10 Solid electrolytic capacitor

Claims (11)

  A solid electrolytic capacitor comprising an anode, a dielectric layer formed on the surface of the anode, an intermediate layer formed on the surface of the dielectric layer, and a solid electrolyte layer formed on the surface of the intermediate layer The intermediate layer contains an n-type organic semiconductor having a minimum vacant orbit smaller than a work function of the solid electrolyte layer, and an amorphous insulating polymer. Capacitor.   The solid electrolytic capacitor according to claim 1, wherein the n-type organic semiconductor is an aromatic compound including an electron-withdrawing group such as a cyano group, a nitro group, or a sulfo group.   The solid electrolytic capacitor according to claim 1, wherein the n-type organic semiconductor is tetracyanoquinodimethane and a derivative thereof.   The solid electrolytic capacitor according to any one of claims 1 to 3, wherein the insulating polymer is a soluble non-aromatic polymer.   The solid electrolytic capacitor according to claim 1, wherein the insulating polymer is polymethyl methacrylate.   A solid electrolytic capacitor comprising an anode, a dielectric layer formed on the surface of the anode, an intermediate layer formed on the surface of the dielectric layer, and a solid electrolyte layer formed on the surface of the intermediate layer A solid electrolytic capacitor, wherein the intermediate layer contains an amorphous charge transfer complex.   The amorphous charge transfer complex contains an n-type organic semiconductor having a lowest vacant orbit smaller than a work function of the solid electrolyte layer, and a polymer p-type semiconductor. The solid electrolytic capacitor described in 1.   8. The solid electrolytic capacitor according to claim 7, wherein the polymer p-type semiconductor has a lowest empty orbit higher than a bottom of a conduction band of a dielectric constituting the dielectric layer.   9. The solid electrolytic capacitor according to claim 7, wherein the polymer p-type semiconductor is an arylamine organic material.   The solid electrolytic capacitor according to claim 7, wherein the n-type organic semiconductor is tetracyanoquinodimethane and a derivative thereof.   The solid electrolytic capacitor according to claim 7, wherein the polymer p-type semiconductor is polyvinyl carbazole.

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