JP2008263167A - Solid electrolytic capacitor and method of producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor excellent in preservation characteristics reduced in ESR (equivalent series resistance). <P>SOLUTION: The solid electrolytic capacitor is provided with an anode 2 formed of a metal or an alloy having valve action, a dielectric layer 3 formed on the surface of the anode 2, and an electrolyte layer 4 composed of a conductive polymer layer 4a formed so as to contact with a portion of the region on the dielectric layer 3 surface and a manganese dioxide layer 4b formed so as to contact with the other portion of the region on the dielectric layer 3 surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  Niobium has attracted attention as a material for next-generation high-capacity solid electrolytic capacitors because its dielectric constant is about 1.8 times larger than that of tantalum, which is a material for conventional solid electrolytic capacitors. Patent Document 1 discloses a solid capacitor in which a solid electrolyte made of manganese dioxide and a cathode conductive layer are sequentially formed on an anode sintered body obtained by sintering a valve action metal powder such as tantalum or niobium.

  However, the solid electrolytic capacitor described in Patent Document 1 has a problem in that ESR (equivalent series resistance) increases because the conductivity of manganese dioxide is low.

Patent Document 2 discloses a technique for forming a conductive polymer layer on a manganese dioxide layer by an electrolytic polymerization method. However, even with such a technique, the reduction of ESR was not sufficient.
JP 07-153650 A JP-A-5-136005

  An object of the present invention is to provide a solid electrolytic capacitor having a low ESR (equivalent series resistance) and excellent storage characteristics, and a method for manufacturing the same.

  The solid electrolytic capacitor of the present invention includes an anode made of a metal or alloy having a valve action, a dielectric layer provided on the surface of the anode, and a conductive property provided in contact with a part of the region on the surface of the dielectric layer. It is characterized by comprising an electrolyte layer composed of a polymer layer and a manganese dioxide layer provided so as to be in contact with a region of another part on the surface of the dielectric layer.

In the present invention, the conductive polymer layer provided so that the electrolyte layer provided on the dielectric layer is in contact with a part of the region on the surface of the dielectric layer, and the region of the other part on the surface of the dielectric layer. And a manganese dioxide layer provided so as to be in contact with each other. The conductivity (10 ² (S / cm)) of the conductive polymer is larger than the conductivity (10 ⁻¹ (S / cm)) of manganese dioxide. In the present invention, since the conductive polymer layer having such a high conductivity is provided so as to be in contact with a part of the region on the surface of the dielectric layer, only the manganese dioxide layer is formed on the surface of the dielectric layer. Compared with the case where it is provided, ESR can be reduced.

  In the present invention, the manganese dioxide layer is provided so as to be in contact with the region of the other part on the surface of the dielectric layer. Since the manganese dioxide layer has better adhesion to the dielectric layer compared to the conductive polymer layer, the manganese dioxide layer is provided so as to be in contact with the region of the other part on the surface of the dielectric layer. As compared with the case where only the conductive polymer layer is provided on the surface of the dielectric layer, the storage characteristics can be improved.

  Therefore, according to the present invention, a solid electrolytic capacitor having low ESR and excellent storage characteristics can be obtained.

  In the present invention, the coverage of the conductive polymer layer, which represents the ratio of the area of the region where the conductive polymer layer and the dielectric layer are in contact with the entire surface of the dielectric layer, is in the range of 3 to 70%. Preferably there is. If the coverage of the conductive polymer layer is less than 3%, the effect of reducing ESR may not be sufficiently obtained. On the other hand, when the coverage of the conductive polymer layer exceeds 70%, the ESR is reduced, but the contact area between the manganese dioxide layer and the dielectric layer becomes relatively small, so that the storage characteristics tend to be lowered. . The coverage of the conductive polymer layer is more preferably in the range of 10 to 40%.

  In the present invention, it is preferable that the conductive polymer layer is provided in an island shape on the surface of the dielectric layer so as to be in contact with a part of the region on the surface of the dielectric layer. In this case, the manganese dioxide layer is preferably provided so as to cover the conductive polymer layer provided in an island shape and the exposed dielectric layer surface around the conductive polymer layer. Therefore, in the present invention, the conductive polymer layer is provided in an island shape on the surface of the dielectric layer, and the manganese dioxide layer is provided so as to cover the surfaces of the conductive polymer layer and the dielectric layer. It is preferable. As a result, the manganese dioxide layer can more firmly adhere the conductive polymer layer to the dielectric surface, and suppress external influences such as humidity change on the conductive polymer layer. And storage characteristics can be further improved.

  In the present invention, the thickness of the manganese dioxide layer is preferably in the range of 10 to 100 nm. When the thickness of the manganese dioxide layer is less than 10 nm, it becomes difficult to obtain a manganese dioxide layer having a uniform thickness, and the storage characteristics may be deteriorated. On the other hand, if the thickness of the manganese dioxide layer exceeds 100 nm, the ESR may increase because the conductivity of the manganese dioxide layer is low. A more preferable thickness of the manganese dioxide layer is in the range of 20 to 70 nm.

  In the present invention, the anode is formed from a metal or alloy having a valve action. The metal having a valve action is not particularly limited as long as it can be used for a solid electrolytic capacitor. For example, niobium, tantalum, titanium, aluminum, hafnium, zirconium, zinc, tungsten, bismuth, Antimony etc. are mentioned. Among these, niobium, tantalum, and titanium, which have a high dielectric constant of an oxide and are readily available as raw materials, are preferable, and niobium whose dielectric constant is about 1.5 times that of tantalum is more preferable. As the alloy having a valve action, an alloy of metals having one or more kinds of valve actions such as niobium and tantalum is preferably used. Moreover, when it is an alloy of the metal which has a valve action, and the metal which does not have a valve action, it is preferable that the metal which has a valve action is contained 50weight% or more. In the present invention, the metal or alloy having a valve action for forming the anode is particularly preferably niobium or an alloy containing niobium as a main component (that is, containing niobium in an amount of 50% by weight or more).

  In the present invention, the conductive polymer layer is not particularly limited as long as it can form an electrolyte layer of a solid electrolytic capacitor. For example, a polythiophene polymer such as polyethylenedioxythiophene, polypyrrole, etc. And polypyrrole-based polymers. These conductive polymer layers can be formed in an island shape on the dielectric layer by, for example, chemical polymerization.

  In the present invention, the electrolyte layer is composed of the conductive polymer layer and the manganese dioxide layer as described above. In the present invention, a conductive polymer layer may be further provided on the surface of such an electrolyte layer. By further providing a conductive polymer layer, ESR can be further reduced. Thus, the conductive polymer layer further provided on the electrolyte layer surface is preferably formed by an electrolytic polymerization method from the viewpoint that the thin film formation speed is high.

  The production method of the present invention is a method by which the solid electrolytic capacitor of the present invention can be produced, and a step of forming a dielectric layer on the surface of the anode and a partial region on the surface of the dielectric layer And a step of forming a conductive polymer layer by a chemical polymerization method and a step of forming a manganese dioxide layer so as to cover at least the surface of the dielectric layer on which the conductive polymer layer is not formed. Yes.

  In the production method of the present invention, the conductive polymer layer is formed in a partial region on the surface of the dielectric layer by forming the conductive polymer layer on the surface of the dielectric layer by a chemical polymerization method. . The chemical polymerization method is a method of forming a conductive polymer layer on the surface of the dielectric layer. However, since the thin film formation speed is slow, by adjusting the thin film formation time, etc., a part of the surface of the dielectric layer is formed. A conductive polymer layer can be formed in an island shape over the region.

  In the manufacturing method of the present invention, after forming the conductive polymer layer as described above, the manganese dioxide layer is formed so as to cover at least the surface of the dielectric layer where the conductive polymer layer is not formed. A manganese dioxide layer is formed on the substrate. In general, the manganese dioxide layer is formed as a continuous thin film so as to cover the conductive polymer layer and the surface of the dielectric layer where the conductive polymer layer around the conductive polymer layer is not formed. A manganese dioxide layer is formed.

  In the solid electrolytic capacitor of the present invention, the cathode layer is formed on the dielectric layer, as in the conventional solid electrolytic capacitor. The cathode layer is not particularly limited as long as it is used for a solid electrolytic capacitor, but is generally formed by laminating a carbon layer and a silver paste layer. The carbon layer can be formed, for example, by applying a carbon paste and then drying it, and the silver paste layer can be formed by applying a silver paste and then drying it.

  According to the present invention, a solid electrolytic capacitor having low ESR and excellent storage characteristics can be obtained.

  Further, according to the manufacturing method of the present invention, a solid electrolytic capacitor having a small ESR and excellent storage characteristics can be efficiently manufactured.

  Hereinafter, the present invention will be specifically described with reference to embodiments and examples, but the present invention is not limited to the following embodiments and examples.

  FIG. 1 is a cross-sectional view schematically showing a solid electrolytic capacitor of one embodiment according to the present invention. As shown in FIG. 1, niobium powder, which is a metal having a valve action, is sintered and molded to form a porous anode 2. A metal lead wire 1 made of niobium is embedded in the anode 2.

  A dielectric layer 3 is formed on the surface of the anode 2. Since the anode 2 is a porous body, a dielectric layer 3 is formed on the porous surface inside the anode 2. The dielectric layer 3 is generally formed by anodic oxidation. The dielectric layer 3 is a layer mainly composed of niobium oxide.

  A conductive polymer layer 4 a is formed in a partial region on the surface of the dielectric layer 3 so as to be in contact with the dielectric layer 3. The conductive polymer layer 4a is made of, for example, polyethylene dioxythiophene.

  A manganese dioxide layer 4b is formed so as to cover the surfaces of the conductive polymer layer 4a and the dielectric layer 3. The electrolyte layer 4 is composed of the conductive polymer layer 4a and the manganese dioxide layer 4b.

  A carbon layer 5a is formed on the manganese dioxide layer 4b, and a silver paste layer 5b is formed on the carbon layer 5a. The cathode layer 5 is composed of the carbon layer 5a and the silver paste layer 5b. On the cathode layer 5, a cathode terminal 7 is connected via a conductive adhesive layer 6.

  An anode terminal 8 is connected to the metal lead wire 1. Mold exterior resin 9 is formed so that the ends of anode terminal 8 and cathode terminal 7 are drawn out.

  The anode 2 is a porous body as described above, and the dielectric layer 3 and the electrolyte layer 4 formed on the surface of the anode 2 are formed on the surface of the porous body inside the anode 2. FIG. 2 is an enlarged cross-sectional view for explaining this state. The anode 2 is a porous body obtained by sintering powder. A dielectric layer 3 is formed on the surface of the anode 2, and a conductive polymer layer 4 a is formed on the dielectric layer 3 in an island shape. Further, a manganese dioxide layer 4b is formed so as to cover the island-shaped conductive polymer 4a and the dielectric layer 3. Therefore, the dielectric layer 3 and the electrolyte layer 4 on the surface of the anode 2 are not formed only on the outside of the anode 2 as shown in FIG. 1, but on the surface of the porous portion inside the anode 2. Is formed. The carbon layer 5a and the silver paste layer 5b are formed by applying a paste and do not penetrate into the inside of the porous body, and thus are formed on the outer surface of the porous body.

  In the above embodiment, the conductive polymer layer 4a is formed so as to be in contact with a part of the region on the surface of the dielectric layer 3, and the manganese dioxide is in contact with the region of another part on the surface of the dielectric layer 3. Layer 4b is formed. Since the electrolyte layer 4 is composed of a conductive polymer layer 4a having high conductivity and a manganese dioxide layer 4b having excellent adhesion to the dielectric layer 3, by providing such an electrolyte layer 4, , ESR can be reduced, and storage characteristics can be improved.

  A solid electrolytic capacitor as shown in FIGS. 1 and 2 was manufactured as follows.

Example 1
Step 1: By sintering a niobium metal powder having an average particle diameter of 2 μm, an anode 2 made of a porous sintered body having a metal lead wire 1 made of niobium embedded therein was formed. This was anodized in a 0.5 wt% phosphoric acid aqueous solution maintained at 60 ° C. at a constant voltage of 10 V for 10 hours, and a dielectric layer 3 mainly composed of niobium oxide was formed on the surface of the anode 2.

  Step 2: The capacitor element on which the dielectric layer 3 was formed was immersed in an oxidizing agent aqueous solution made of 20% by weight of ferric p-toluenesulfonate for 5 minutes and reacted with the vapor of ethylenedioxythiophene monomer for 10 minutes. Thereafter, the conductive polymer layer 4a made of polyethylenedioxythiophene was formed in an island shape on the surface of the dielectric layer 3 by heat treatment at 130 ° C. for 20 minutes. Next, the anode 2 on which the conductive polymer layer 4a was formed was immersed in a 30 wt% manganese nitrate aqueous solution for 5 minutes, and the manganese nitrate aqueous solution was impregnated therein. Thereafter, heat treatment was performed at 170 ° C. for 10 minutes to form a manganese dioxide layer 4b. The manganese dioxide layer 4b having a sufficient thickness was formed by repeating this immersion in a manganese nitrate aqueous solution and heat treatment three times.

  As described above, after the island-shaped conductive polymer layer 4a is formed on the dielectric layer 3 by chemical polymerization, the manganese dioxide layer 4b is formed so as to cover the island-shaped conductive polymer layer 4a. An electrolyte layer 4 composed of a molecular layer 4a and a manganese dioxide layer 4b was formed.

Step 3: A paste containing graphite was applied to the surface of the anode 2 on which the electrolyte layer 4 was formed to form a carbon layer 5a. Next, a silver paste was applied thereon and dried to form a silver paste layer 5b. A conductive adhesive layer 6 was formed on the silver paste layer 5 b, and the cathode terminal 8 was connected via the conductive adhesive layer 6. Further, after the anode terminal 8 is connected to the metal lead wire 1 by resistance welding, transfer molding is performed using epoxy resin under molding conditions of a temperature of 160 ° C., a pressure of 150 kg / cm ² , and a time of 90 seconds. The exterior resin was cured by heat treatment at 4 ° C. for 4 hours to form a mold exterior resin 9.

  The solid electrolytic capacitor of Example 1 was produced as described above.

(Example 2)
In this example, a solid electrolytic capacitor was produced in the same manner as in Example 1 except that the conductive polymer layer 4a was formed from polypyrrole. Specifically, in Step 1 of Example 1, after forming the dielectric layer 3, the dielectric layer 3 was immersed in an oxidizing agent composed of 20% by weight of ferric p-toluenesulfonate for 5 minutes, and pyrrole monomer vapor and 10 By reacting for a minute, the conductive polymer layer 4 a made of polypyrrole was formed in an island shape on the surface of the dielectric layer 3. Other than that was carried out similarly to Example 1, and produced the solid electrolytic capacitor.

(Comparative Example 1)
Example 1 is the same as Example 1 except that, in Step 2 of Example 1, only the manganese dioxide layer 4b is formed on the surface of the dielectric layer 3 without forming the conductive polymer layer 4a made of polyethylenedioxythiophene. Similarly, the solid electrolytic capacitor of Comparative Example 1 was produced.

(Comparative Example 2)
A solid electrolytic capacitor of Comparative Example 2 was produced in the same manner as in Example 1 except that the manganese dioxide layer 4b was not formed on the conductive polymer layer 4a in Step 2 of Example 1.

[Measurement of coverage of conductive polymer layer]
The ratio of the area of the region where the conductive polymer layer and the dielectric layer surface are in contact with the entire area of the dielectric layer surface (coverage of the conductive polymer layer) was measured as follows.

  In Step 1 of Example 1, after forming the dielectric layer on the anode surface, the capacitor layer was formed without forming the electrolyte layer, the carbon layer, and the silver paste layer, and the capacitance of this capacitor element was C1.

  Further, in Step 2 of each Example and each Comparative Example, after forming the conductive polymer layer, without forming the manganese dioxide layer, the carbon paste and the silver paste were applied thereon, and the carbon layer and Capacitor elements on which a silver paste layer was formed were produced, and the capacitance of each capacitor element was C2. The coverage of the conductive polymer layer was calculated from the capacitances C1 and C2 thus measured as follows.

Covering rate of conductive polymer layer (%) = (C2 / C1) × 100
As shown in FIG. 3, the capacitance of each capacitor element is obtained by immersing the capacitor element 12 in a cell 11 using an activated carbon electrode 10 as a counter electrode and a 30% by weight sulfuric acid aqueous solution as an electrolytic solution. The measurement was performed by measuring the capacitance at a frequency of 120 Hz with the meter 13.

[Measurement of film thickness of manganese dioxide layer]
The film thickness of the manganese dioxide layer in the solid electrolytic capacitors of each Example and each Comparative Example was measured as follows.

  The anode, dielectric layer and electrolyte layer of each solid electrolytic capacitor were measured for the concentration distribution of niobium and manganese while sputtering in the depth direction using an X-ray photoelectron spectroscopy (XPS) apparatus. The sputtering time until the sizes of the niobium and manganese compositions were reversed was measured, and the film thickness of the manganese dioxide layer was calculated from the sputtering rate (10 nm / min) of the silicon oxide used as a reference.

  FIG. 4 is a diagram showing an XPS profile. As shown in FIG. 4, here, the concentrations of manganese (Mn) and niobium (Nb) are reversed after a sputtering time of 3 minutes. Therefore, the sputtering time for reversing the composition of niobium and manganese is 3 minutes, and the film thickness of manganese dioxide is 30 nm from the sputtering rate of silicon oxide (10 nm / min).

[Measurement of ESR]
About the solid electrolytic capacitor of each Example and each comparative example, ESR in frequency 100kHz was measured with the LCR meter.

[Measurement of storage characteristics]
The solid electrolytic capacitors of each Example and each Comparative Example were each stored at 105 ° C. for 500 hours. The electrostatic capacity C3 before storage and the electrostatic capacity C4 after storage were measured at a frequency of 120 Hz using an LCR meter, and the capacity retention rate (%) in storage characteristics was determined by the following equation.

Capacity retention ratio in storage characteristics (%) = (C4 / C3) × 100
Table 1 shows measurement results of ESR and storage characteristics of the solid electrolytic capacitors of Examples 1 and 2 and Comparative Examples 1 and 2. In addition, the value of the capacity maintenance ratio in the ESR and the storage characteristics is a value normalized with the value of Example 1 as 100.

  As is apparent from the results shown in Table 1, in Examples 1 and 2 in which the electrolyte layer is composed of the conductive polymer layer and the manganese dioxide layer according to the present invention, the ESR is small and the capacity retention rate in the storage characteristics is low. It is getting bigger.

  In Comparative Example 1, since the electrolyte layer is formed only from the manganese dioxide layer, the capacity retention rate in the storage characteristics is large and good, but the ESR is increased.

  Moreover, in Comparative Example 2, since the electrolyte layer is formed only from the conductive polymer layer, the ESR is good, but the capacity retention rate in the storage characteristics is lowered.

(Examples 3 to 9)
Here, the relationship between the coverage of the conductive polymer layer, ESR, and storage characteristics was examined.

  In Step 2 of Example 1, the time (polymerization time) for immersion in an oxidizing agent composed of 20% by weight of ferric p-toluenesulfonate and reacting with the vapor of ethylenedioxythiophene monomer was 1 minute, 2 minutes. Solid electrolytic capacitors of Examples 3 to 9 were produced in the same manner as in Example 1 except that the time was changed to 5 minutes, 10 minutes, 15 minutes, 40 minutes, 90 minutes, and 120 minutes.

  In the same manner as described above, the capacity retention ratio in ESR and storage characteristics was measured, and the measurement results are shown in Table 2.

  As is clear from the results shown in Table 2, good results were obtained when the coverage of the conductive polymer layer was in the range of 3 to 70%.

(Examples 10 to 14)
Here, the relationship between the thickness of the manganese dioxide layer, ESR, and storage characteristics was examined.

  Example 2 is the same as Example 1 except that the number of steps for forming the manganese dioxide layer in Step 2 of Example 1 was set to 1, 2, 5, 10, and 15 times. 10 to 14 solid electrolytic capacitors were produced. Table 3 shows the measurement results of the obtained solid electrolytic capacitor. Table 3 also shows the results of Example 1.

  As is apparent from the results shown in Table 3, it can be seen that the thickness of the manganese dioxide layer is preferably in the range of 10 to 100 nm.

(Example 15)
In this example, an electrolytic polymerization film made of pyrrole was further formed on the manganese dioxide layer, and ESR and storage characteristics were measured.

  After Step 2 of Example 1, a polypyrrole layer was formed on the manganese dioxide layer by electrolytic polymerization so as to have a film thickness of 100 nm. Other than that was carried out similarly to Example 1, the solid electrolytic capacitor was produced, and ESR and the storage characteristic were measured. Table 4 shows the measurement results.

  As shown in Table 4, ESR can be further reduced by forming an electrolytic polymer film (PPy electrolytic polymer film) made of pyrrole on the manganese dioxide layer.

[Observation with a transmission electron microscope]
About the sample of Example 7, when the cross section was observed with a transmission electron microscope (TEM), the length A of the sintered body particle surface of the anode in the observed range and the conductive polymer layer were coated. When the length B of the portion was measured and the ratio of A to B was determined, it was about 40%. Therefore, it was confirmed that the observation result by the transmission electron microscope is almost the same as the coverage of the conductive polymer layer obtained from the above-mentioned capacitance.

  In the above embodiment, niobium is used as the valve metal that forms the anode. However, when tantalum is used as the valve metal, ESR can be similarly reduced and storage characteristics can be improved.

The typical sectional view showing the solid electrolytic capacitor of one embodiment according to the present invention. The typical sectional view showing the dielectric material layer and electrolyte layer inside the porous body of an anode. The perspective view for demonstrating the measuring method of the coverage of the conductive polymer layer in the dielectric material layer surface. The figure which shows the density | concentration distribution of Mn and Nb in the dielectric material layer and electrolyte layer on an anode surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Metal lead wire 2 ... Anode 3 ... Dielectric layer 4 ... Electrolyte layer 4a ... Conductive polymer layer 4b ... Manganese dioxide layer 5 ... Cathode layer 5a ... Carbon layer 5b ... Silver paste layer 6 ... Conductive adhesive layer 7 ... Anode terminal 8 ... Cathode terminal 9 ... Mold exterior resin 10 ... Activated carbon electrode 11 ... Cell 12 ... Capacitor element 13 ... LCR meter

Claims (8)

An anode made of a metal or alloy having a valve action;
A dielectric layer provided on the surface of the anode;
A conductive polymer layer provided in contact with a part of the region on the surface of the dielectric layer and a manganese dioxide layer provided in contact with a region of the other part on the surface of the dielectric layer. A solid electrolytic capacitor comprising an electrolyte layer.   The coverage of the conductive polymer layer, which represents the ratio of the area of the region where the conductive polymer layer and the dielectric layer are in contact with the entire surface of the dielectric layer, is in the range of 3 to 70%. The solid electrolytic capacitor according to claim 1.   The conductive polymer layer is provided in an island shape on the surface of the dielectric layer, and the manganese dioxide layer is provided so as to cover the surface of the conductive polymer layer and the dielectric layer. The solid electrolytic capacitor according to claim 1 or 2.   The thickness of the said manganese dioxide layer is the range of 10-100 nm, The solid electrolytic capacitor of any one of Claims 1-3 characterized by the above-mentioned.   5. The solid electrolytic capacitor according to claim 1, wherein the metal or alloy having a valve action is niobium or an alloy containing niobium as a main component.   The solid electrolytic capacitor according to claim 1, wherein the conductive polymer layer is formed of polyethylene dioxythiophene or polypyrrole.   The solid electrolytic capacitor according to claim 1, wherein a conductive polymer layer is further provided on the surface of the electrolyte layer. A method for producing the solid electrolytic capacitor according to any one of claims 1 to 7,
Forming the dielectric layer on the surface of the anode;
Forming the conductive polymer layer by a chemical polymerization method on a partial region on the surface of the dielectric layer;
And a step of forming the manganese dioxide layer so as to cover at least the surface of the dielectric layer where the conductive polymer layer is not formed.

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