JPH0917685A - Capacitor and its manufacture - Google Patents

Abstract

PURPOSE: To provide a capacitor, which excels in productivity, is small in size and has a large capacity, and its manufacture, without necessitating a complicated manufacturing process. CONSTITUTION: A capacitor is provided with a porous sintered body 2 composed of metal whose major component is titanium, a dielectric film 3, which is formed on the surface of the sintered body and contains composite oxide expressed by a general formula, ATiO3 , where A is Ba or Sr, as the major component, conductor or semiconductor formed on the surface of the dielectric film and a counter electrode which allows continuity with the conductor or semiconductor and faces the sintered body. The porosity of the sintered body is 20% or more. The composite oxide film expressed by the formula on the surface of the sintered body is formed as the dielectric film 3 by impregnating the sintered body in the aqueous solution that contains strontium or barium, performing hydrothermal treatment at a prescribed temperature. Then, the capacitor is formed by forming the conductor or semiconductor electrode 4 on the surface of the oxide film and forming the counter electrode that allows continuity with the electrode and faces the sintered body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a capacitor,
More specifically, the present invention relates to a compact capacitor capable of obtaining a large capacitance and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a conventional small-sized large-capacity capacitor,
For example, electrolytic capacitors such as tantalum electrolytic capacitors and aluminum electrolytic capacitors are known.

A tantalum electrolytic capacitor is a capacitor using a metal tantalum anodic oxide film as a dielectric and has a long life, good temperature characteristics, miniaturization, and relatively good frequency characteristics. It has features such as that.

Further, the aluminum electrolytic capacitor is characterized in that it can obtain a larger electrostatic capacity than the above-mentioned tantalum electrolytic capacitor, and is widely used in power supply circuits and the like.

In addition to the above-mentioned electrolytic capacitor, a monolithic ceramic capacitor is widely used as a small-sized large-capacity capacitor. This monolithic ceramic capacitor has features such as good frequency characteristics, high insulation resistance, and large capacitance per unit volume.

[0006]

However, in the tantalum electrolytic capacitor, there is a problem in that the tantalum metal is expensive, so that the capacitor that is a product is expensive. Since the oxide layer is used as the dielectric layer, it is difficult to increase the dielectric constant of the dielectric layer, and there is a problem that there is a limit to increase the capacity.

Further, in the aluminum electrolytic capacitor, the anodic oxide film of aluminum is used as the dielectric layer, but there is a problem that the leakage current is large and the life is short.

Further, all of the above electrolytic capacitors have polarities, and the direction (polarity) of the electrolytic capacitors must be identified in the process of assembling into an electric or electronic circuit, so that the workability in the mounting process is poor. There is a problem.

In the monolithic ceramic capacitor, attempts have been made to reduce the thickness of the dielectric in order to reduce the size and increase the capacity, but a good laminated structure is realized with a dielectric thickness of less than 1 μm. I can't do it.

Therefore, an object of the present invention is to solve the above problems, and to provide a small-capacity large-capacity capacitor which is excellent in productivity without requiring a complicated manufacturing process and a manufacturing method thereof. With the goal.

[0011]

According to a first aspect of the present invention, a capacitor is formed on at least a part of a surface of a porous sintered body made of a metal containing titanium as a main component. A dielectric film mainly composed of a perovskite-type complex oxide represented by the general formula ATiO ₃ (where A is Ba or Sr), a conductor or semiconductor formed on the surface of the dielectric film, It is characterized in that the porous sintered body is provided with a counter electrode which is electrically connected to a conductor or a semiconductor and faces the sintered body, and the porosity of the porous sintered body is 20% or more.

According to a second aspect of the present invention, in the method for producing a capacitor, a porous sintered body made of a metal containing titanium as a main component is used, and the porous sintered body has a pH of 13 or more containing at least 0.1 mol / liter of strontium or barium. A perovskite represented by the general formula ATiO ₃ (where A is Ba or Sr) is formed as a dielectric film on the surface of the sintered body by immersing in an aqueous solution and applying hydrothermal treatment at a temperature of 100 ° C. or higher. Forming a complex-type composite oxide film, forming a conductor or semiconductor electrode on the surface of the perovskite-type complex oxide film, and then forming a counter electrode electrically connected to the electrode and facing the sintered body. It is characterized by.

According to a third aspect of the present invention, in the method for manufacturing a capacitor, in the step of immersing the sintered body in an aqueous solution and subjecting it to hydrothermal treatment, electricity is applied between the electrode arranged in the aqueous solution and the sintered body. The electrolytic treatment is performed together with the hydrothermal treatment.

According to a fourth aspect of the present invention, in the method for producing a capacitor, the porous sintered body containing titanium as a main component is made of metal powder having an average particle size of 150 μm or less and a vacuum degree of 1 × 10 ⁻⁴ t.
It is characterized by being sintered at a temperature of 500 to 1000 ° C. in a vacuum of orr or lower.

[0015]

In the capacitor of the present invention, the perovskite-type composite oxide represented by the general formula ATiO ₃ (A is Ba or Sr) is formed on the surface of the porous sintered body made of a metal containing titanium as a main component. Since a dielectric film containing a substance as a main component is formed, and an electrode made of a conductor or a semiconductor is further formed on the dielectric film, the sintered body serving as an electrode can be formed without increasing the size of the sintered body. It is possible to increase the surface area and the surface area of electrodes made of conductors or semiconductors. Therefore, a large capacitance can be realized without increasing the size of the entire capacitor.

When the porosity of the porous sintered body is 20% or more, the substantial specific surface area is increased and the capacitance is increased. Further, it is possible to easily form a dielectric film or an electrode made of a conductor or a semiconductor. Further, in the method for producing a capacitor of the present invention, the sintered body is hydrothermally treated under predetermined conditions. By applying, it is possible to easily and reliably form the perovskite complex oxide having excellent dielectric properties on the surface of the sintered body having an arbitrary shape.

Further, in the step of hydrothermally treating the sintered body, the electrode is immersed in the hydrothermal treatment solution (alkaline aqueous solution), and an electrolytic treatment in which electricity is applied between the sintered body and the electrode is simultaneously applied with the hydrothermal treatment. Thereby, the perovskite composite oxide can be formed more efficiently.

[0018]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an enlarged cross-sectional view of a porous sintered body portion of a capacitor of the present invention. 1 is a buried titanium wire, 2 is a porous sintered body, 3 is a dielectric film formed on the surface of the sintered body,
Reference numeral 4 denotes an electrode made of a conductor or a semiconductor formed on the surface of the dielectric film.

FIG. 2 is a sectional view of the capacitor of the present invention. 1 is a titanium wire, 5 is a capacitor element made of a porous sintered body, 6 is a graphite layer, 7 is a silver electrode layer,
Reference numeral 8 is a lead wire, 9 is a solder, and 10 is an exterior resin.

FIG. 3 is a schematic view of an apparatus for forming a dielectric film on a porous sintered body. 2 is a porous sintered body, 11 is a fluororesin beaker, 12 is a hydrothermal treatment solution, 13 is a platinum plate, 14 is an autoclave, 15 is a DC power supply, and 16 is a platinum wire. Example 1 First, a porous sintered body made of titanium metal was obtained. That is, a titanium metal powder having an average particle size of 50 μm was formed into a cylindrical shape. At this time, a part of the titanium wire was embedded in titanium metal powder and molded as a lead wire for taking out one of the electrodes. Then, this molded body was subjected to 5 × 10 ^{−6 to} 3 × 10 ⁻⁷ to
It was fired at a temperature of 800 ° C. in a vacuum of rr to obtain a porous sintered body.

Next, the porous sintered body was immersed in a hydrothermal treatment solution in which a 0.5 mol / liter strontium hydroxide aqueous solution was adjusted to pH 14 with sodium hydroxide, and the temperature was raised to 60 ° C. at 60 ° C. A hydrothermal treatment was carried out by holding for a minute, and as shown in FIG. 1, a dielectric film 3 made of a strontium titanate polycrystal thin film having a thickness of about 0.3 μm was directly formed on the surface of the porous sintered body 2.

Further, the sintered body on which the strontium titanate thin film is formed is dipped in a manganese nitrate solution and then heat-treated at a temperature of 200 to 400 ° C. to form a manganese dioxide layer on the surface of the strontium titanate thin film, A capacitor element 5 composed of a porous sintered body 2, a dielectric film 3, an electrode 4 made of a conductor or a semiconductor and a titanium wire 1 was produced.

Thereafter, as in the case of a normal solid electrolytic capacitor, as shown in FIG. 2, a graphite layer 6 is sequentially provided on a capacitor element 5, and a silver electrode layer 7 is further provided to form a counter electrode, while the other electrode is formed. The lead wire 8 was attached by the solder 9 and the exterior resin 10 was applied to form a capacitor.

When the capacitance, tan δ, and insulation resistance of the capacitor thus manufactured were measured,
The following results were obtained.

Capacitance (frequency 1 kHz, voltage 1 Vrms): 10.2 μF tan δ (same as above): 5.6% Insulation resistance (voltage 6.3 Vdc, after 120 seconds): 1.3 × 10 ⁷ Ω (Example 2) ) First, a porous sintered body was obtained in the same manner as in Example 1.

Then, using the apparatus shown in FIG. 3, a dielectric film was formed on this porous sintered body by electrolytic treatment. That is, a hydrothermal treatment solution 12 in which a 0.5 mol / liter aqueous barium hydroxide solution was adjusted to pH 13.5 with sodium hydroxide was prepared. Next, in the fluororesin beaker 11, the porous sintered body 2 and the platinum plate 13 were immersed in the hydrothermal treatment solution 12. At the same time, even when the autoclave 14 is sealed, the external DC power source 15
In order to supply electric power to the porous sintered body 2 and the platinum plate 13, a pair of fluorocarbon resin-coated platinum wires 16 that are pre-wired are connected to the porous sintered body 2 and It was connected to a platinum plate 13. Then, the autoclave 14 was sealed while the porous sintered body 2 and the platinum plate 13 were immersed in the hydrothermal treatment solution 12 in the fluororesin beaker 11.

In this state, the temperature is raised to 150 ° C. and then 6
While maintaining this temperature for 0 minutes to perform the hydrothermal treatment, a DC voltage of 10 is applied between the porous sintered body 2 and the platinum plate 13.
A constant voltage electrolysis treatment was performed by applying V. Next, the treated porous sintered body 2 was sufficiently ultrasonically washed in distilled water and then dried at 120 ° C. for 60 minutes.

By this method, a barium titanate polycrystal thin film having a thickness of 1.0 μm, which is a dielectric film, was formed on the entire surface of the porous sintered body 2. In addition, in the method for forming a dielectric film only by hydrothermal treatment without electrolytic treatment as in Example 1,
While it takes several hours to several tens of hours to form a film having a thickness of about 0.5 μm or more, as in Example 2,
According to the method for forming a dielectric film involving electrolytic treatment, a dielectric film having a thickness of several μm could be formed in a few hours.

After forming the dielectric film in this way,
A capacitor was manufactured by the same method as in Example 1,
Then, when the electrostatic capacity, tan δ, and insulation resistance were measured, the following results were obtained.

Capacitance (frequency 1 kHz, voltage 1 Vrms): 6.1 μF tan δ (same as above): 7.4% Insulation resistance (voltage 6.3 Vdc, after 120 seconds): 1.1 × 10 ⁷ Ω (Example 3) ) First, porous sintered bodies made of titanium metal and having various porosities were obtained. That is, the average particle size is 5
A 0 μm titanium metal powder was formed into a columnar shape at the density shown in Table 1. At this time, a part of the titanium wire was embedded in titanium metal powder and molded as one of the lead wires. This compact was fired at a firing temperature shown in Table 1 in a vacuum of 5 × 10 ⁻⁶ torr or less to obtain a porous sintered body. The porosity was calculated by measuring the density of the obtained sintered body.

Next, a dielectric film was formed on the surface of this porous sintered body. That is, 0.5 mol / liter of barium hydroxide or strontium hydroxide, and an aqueous solution of barium hydroxide and strontium hydroxide mixed at 0.25 mol / liter were adjusted to pH 13.5 with sodium hydroxide. A hydrothermal treatment solution was prepared. Next, in the same manner as in Example 2, hydrothermal treatment and constant voltage electrolysis treatment were performed to form a strontium titanate thin film on the surface of the porous sintered body, and then ultrasonic cleaning was performed and then drying was performed. .

After forming the dielectric film in this way, a manganese dioxide layer of semiconductor was formed on the surface of the dielectric film as an electrode in the same manner as in Example 1 to manufacture a capacitor element.

Then, similarly to a normal solid electrolytic capacitor, a graphite layer and a silver electrode layer are sequentially provided to form an external electrode, and the other lead wire is attached by soldering,
Exterior resin was applied to make a capacitor.

The capacitance (frequency 1 kHz, voltage 1 Vrms), t
When an δ (frequency 1 kHz, voltage 1 Vrms) and insulation resistance (voltage 6.3 Vdc, after 120 seconds) were measured,
The results shown in Table 1 were obtained. The sample numbers with * are out of the scope of the present invention.

[0035]

[Table 1]

As is clear from Table 1, the porosity of the porous sintered body is preferably 20% or more. Since a porous sintered body having a porosity smaller than this has a substantially small specific surface area, the capacitance of a capacitor obtained by a dielectric film having the same composition becomes small, which is not preferable.

(Example 4) The average particle size is 30 μm
Porous sintered bodies were produced using titanium metal powders of m, 50 μm, 150 μm, and 300 μm at various firing temperatures and vacuum degrees shown in Table 2 and by the same method as in Example 1 except for the above.

Furthermore, from the formation of the dielectric film made of strontium titanate to the production of the capacitor, a capacitor was produced by the same method of forming the dielectric film as in Example 2 involving the electrolytic treatment.

Table 2 shows the measurement results of these capacitors. The sample numbers with * are out of the scope of the present invention.

[0040]

[Table 2]

As is clear from Table 2, the titanium metal powder used for producing the porous sintered body has an average particle size of 15
It is desirable that the thickness be 0 μm or less. If the powder has an average particle size larger than this, the surface area of the sintered body becomes small and the capacitance of the obtained capacitor becomes small, which is not preferable.

When firing, 1 × 10 ^-4 torr
The following vacuum degree is desirable. At a vacuum degree lower than this, reactions such as oxides occur on the metal surface during sintering,
It is not preferable because tan δ increases.

Further, the firing temperature is preferably 500 to 1000 ° C. If the temperature is lower than 500 ° C., it is difficult to obtain a sufficient sintered body, and if the temperature is higher than 1000 ° C., the surface area of the sintered body becomes small and the capacitance of the obtained capacitor becomes small, which is not preferable.

In this example, hydroxide was used as the ion source of barium or strontium, but it should not be limited to this, and the pH adjuster is not limited to sodium hydroxide, and other It is possible to use hydroxides such as potassium hydroxide or lithium hydroxide.

The electrode formed on the dielectric film may be not only the semiconductor manganese dioxide used in this embodiment, but also another conductor or semiconductor such as an electrolytic solution or an organic substance.

[0046]

As is apparent from the above description, the capacitor of the present invention comprises a porous sintered body, a dielectric film on the surface of the sintered body, a conductor or semiconductor on the surface of the dielectric film, a conductor or semiconductor. Since it is composed of the film and the counter electrode that is electrically connected to the film, a small-sized and large-capacity capacitor can be realized. And
Since the dielectric film contains the perovskite-type composite oxide as a main component, a dielectric film having a larger dielectric constant than that of a single oxide can be obtained, and a capacitor having a larger capacity can be obtained.

Further, in the manufacturing method, since the dielectric film can be directly formed on the porous sintered body, it is possible to easily manufacture at a low cost without requiring a complicated manufacturing process. Become.

[Brief description of the drawings]

1 is a partial cross-sectional view of a porous sintered body of a capacitor of the present invention.

FIG. 2 is a sectional view of a capacitor of the present invention.

FIG. 3 is a schematic view of an apparatus for forming a dielectric film on a porous sintered body.

[Explanation of symbols]

 1 Titanium Wire-2 Porous Sintered Body 3 Dielectric Film 4 Electrode Made of Conductor or Semiconductor 5 Capacitor Element 6 Graphite Layer 7 Silver Electrode Layer 8 Lead Wire 9 Solder 10 Exterior Resin

Claims (4)

[Claims] 1. A porous sintered body made of a metal containing titanium as a main component, and a general formula ATiO ₃ (where A is Ba or Sr) formed on at least a part of the surface of the sintered body.
And a conductor film or a semiconductor film formed on the surface of the dielectric film, a conductor film or a semiconductor film formed on the surface of the dielectric film film, and a conductor film or a semiconductor film formed on the surface of the dielectric film film. A capacitor comprising an electrode, wherein the porosity of the porous sintered body is 20% or more. 2. A porous sintered body made of a metal containing titanium as a main component is immersed in an aqueous solution containing at least 0.1 mol / liter of strontium or barium and having a pH of 13 or more, and a temperature of 100 ° C. or more. And hydrothermal treatment to form a perovskite-type complex oxide film represented by the general formula ATiO ₃ (where A is Ba or Sr) as a dielectric film on the surface of the sintered body,
A method of manufacturing a capacitor, comprising forming a conductor or semiconductor electrode on the surface of the perovskite type complex oxide film, and then forming a counter electrode which is electrically connected to the electrode and faces the sintered body. 3. In the step of immersing the sintered body in an aqueous solution for hydrothermal treatment, an electrolytic treatment in which an electric current is applied between the electrode arranged in the aqueous solution and the sintered body is performed together with the hydrothermal treatment. The method of manufacturing a capacitor according to claim 2, wherein the capacitor is manufactured. 4. The porous sintered body containing titanium as a main component is made of metal powder having an average particle size of 150 μm or less and a vacuum degree of 1 × 1.
The method for manufacturing a capacitor according to claim 2, wherein the capacitor is sintered at a temperature of 500 to 1000 ° C in a vacuum of 0 ^-4 torr or less.