JPH0475645B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a small-sized, large-capacity capacitor.

(Prior art) With the development of ICs, LSIs, etc., electronic circuits are becoming smaller, and capacitors, which are one of the passive components, are also becoming smaller. Large capacity is required.

Electrolytic capacitors, in which an insulating layer is formed by electrochemically oxidizing the surface of a metal, have been put into practical use as capacitors that are small and have a large capacity.

Electrolytic capacitors are made by anodizing (chemically forming) so-called valve metals such as Ta, Al, V, Zr, Hf, and Ti in an electrolyte solution to form a dielectric layer on the surface. .

One electrode of an electrolytic capacitor is a valve metal with a dielectric layer formed on its surface, and the other electrode is a cathode material with manganese dioxide made by thermally decomposing manganese nitrate deposited on the dielectric layer. In some cases, an electrolyte solution is brought into contact with the dielectric layer and another metal is connected through the electrolyte solution, thereby forming an electrode.

Because of this structure, the capacitance of an electrolytic capacitor is determined by the dielectric constant of the metal oxide formed on the valve metal by anodizing, the thickness of the dielectric, and the surface area of the valve metal to be anodized.

In electrolytic capacitors, the thickness of the dielectric is adjusted by the formation voltage, and the formation voltage varies depending on the rated voltage of the capacitor. The surface area of the valve metal has also been increased by etching or sintering the metal foil to form a porous body.

Since the permittivity of a dielectric is a constant specific to the material,
The value is determined by the metal used, with the commonly used aluminum having a value of 11 and tantalum having a value of about 27.

In this way, in electrolytic capacitors, the type of metal forming the dielectric layer is limited to valve metals, so it is impossible to increase the dielectric constant of the dielectric layer. Therefore, in order to make the electrolytic capacitor more compact and increase its capacity, methods are being used to reduce the thickness of the dielectric layer by increasing the surface area of the metal that undergoes anodization or by lowering the anodization voltage. .

(Problem to be solved by the invention) However, in order to increase the surface area of the metal to be anodized, it is necessary to precisely control etching conditions, sintering conditions, etc. This is becoming technically difficult.

In addition, lowering the formation voltage reduces the thickness of the dielectric layer and lowers the withstand voltage of the capacitor, so once the rated voltage is determined, the formation voltage is also uniquely determined, which makes it difficult to increase the capacitance. It becomes difficult to measure.

As described above, it has been extremely difficult to technically respond to miniaturization and increase in capacity with the electrolytic capacitors that have been put into practical use to date.

Furthermore, because electrolytic capacitors have polarity in their structure, there are problems in that their applications are limited and that two capacitors must be used in series when used in alternating current circuits.

Furthermore, various methods such as sputtering, vapor deposition, and vapor phase growth have been attempted to form metal oxide thin films on metals.

In all of these methods, it is difficult to control the composition, and it is difficult to produce large-area products. Furthermore, there were technical problems such as difficulty in obtaining good film quality and narrow range of conditions.

In addition, there were also problems from an industrial perspective, such as low productivity, expensive equipment, and lack of mass production, so it was used only for special purposes.

(Object of the Invention) An object of the present invention is to provide a method for manufacturing a small-sized, large-capacity capacitor by eliminating the above-mentioned conventional drawbacks.

(Summary of the Invention) According to the present invention, a metal oxide thin film is formed on the surface of a metal by decomposing an organometallic compound, and then a conductive layer is formed on this thin film to form a small size. , which manufactures large capacity capacitors.

(Description of Configuration) The present invention solves the problems of the prior art by adopting the above-described configuration.

That is, a metal oxide layer with a high dielectric constant is formed on the surface of the metal by decomposition of an organometallic acid compound,
Furthermore, by adopting a manufacturing method that forms a conductor layer on this thin film, it is possible to form a dielectric layer with a higher dielectric constant than the dielectric layer formed by conventional anodic oxidation of valve metal. Capacity can be greatly increased depending on the shape. Further, when the capacity is kept constant, the volume can be reduced.

In particular, perovskite compounds, such as barium titanate and lead titanate, have a high dielectric constant, so they can make capacitors smaller and larger in capacity.

Examples of the present invention will be described in detail below.

(Example 1) The surface of a nickel foil was etched using hydrochloric acid to form pores on the surface of the foil to make it porous.

When this porous nickel foil is pyrolyzed,
It was immersed in an organometallic compound solution of lead and titanium (lead titanate formation precursor solution) that would become PbTiO ₃ , pulled up, and then dried.

The organometallic compound solution was synthesized as follows.

Weigh out lead propionate and tetrabutoxytitanium so that the metal ratio is PbTiO ₃ and add it to decalin.
The reaction was carried out at 130-140°C. The reaction product was dried under reduced pressure to obtain a powdery reaction product. This was dissolved in acetylacetone to give a PbTiO ₃ equivalent concentration of 12.5% by weight.
A lead titanate forming precursor solution was prepared.

After drying, heat treatment was performed in air at a temperature of 400°C to decompose the organometallic compound and form a PbTiO ₃ thin film.

Aluminum was vacuum-deposited on the surface of this thin film to form an electrode and a capacitor.

The capacitor thus obtained exhibited good characteristics: capacity: 1 μF/cm ² dielectric loss: 3.5%, resistance-capacitance product: 2000 MΩμF.

Here, the relative dielectric constant of PbTiO ₃ was calculated to be 150. Note that the PbTiO ₃ thin film was formed with a thickness of about 0.4 μm.

(Example 2) When a porous nickel block formed by a sintering method is decomposed _, an organic metal compound mixed solution (zircon/lead titanate precursor solution) has a composition of PbZr _{0.52 Ti 0.48} O ₃ After immersing it in water and degassing it in a vacuum,
It was pulled out, excess solution was removed, and then dried.

The organometallic compound solution used at this time was synthesized by the following process.

Lead oxide, zirconium acetylacetate, and tetrabutoxytitanium were weighed so that the PbTiO ₃ /PbZrO ₃ molar ratio was 48/52, heated in acetylacetone to a temperature of 100 to 110°C, and reacted to obtain the concentration in terms of composite metal oxide. 12.5% zircon by weight
A lead titanate precursor solution was prepared.

After drying, heat treatment is performed in air at a temperature of 400°C to decompose the organometallic compound, and the metal surface is coated with PbZr ₀ . ₅₂ Ti ₀ .
₄₈ O ₃ thin film was formed.

Next, this porous block was impregnated with a 50% methanol mixture of manganese nitrate hexahydrate and thermally decomposed at 230°C. Then graphite. Silver paste was applied to evaluate the capacitor characteristics.

As a result, capacitance: 100μF/ _cm ³ Dielectric loss: 7% Resistance-capacitance product: _600MΩμF Here, the dielectric constant of PbZr _0.52 Ti _0.48 O ₃ was approximately 540. The thickness of the dielectric layer formed was 0.64 μm.

(Example 3) The surface of a nickel foil was etched using hydrochloric acid to form pores on the surface of the foil to make it porous.

When this porous nickel foil is pyrolyzed,
It was immersed in an organometallic compound solution of lanthanum and titanium (lanthanum titanate formation precursor solution) that would become La ₂ Ti ₂ O ₇ , pulled up, and then dried.

Note that the organometallic compound solution was synthesized by the following process. Lanthanum acetate: La (CH ₃ COO) ₃ and tetrabutoxytitanium Ti (OC ₄ H ₉ ) are converted into oxides and weighed to a composition of La ₂ Ti ₂ O ₇ in xylene.
The reaction was carried out by heating to a temperature of 130°C to 140°C.

Next, xylene was distilled off under reduced pressure, acetylacetone was added, and the mixture was heated under reflux to obtain a lanthanum titanate forming precursor solution having a concentration of 10 wt% in terms of La ₂ Ti ₂ O ₇ .

After drying, heat treatment was performed in air at a temperature of 400°C to form a thin film of La ₂ Ti ₂ O ₇ on the nickel foil.

This nickel foil was brought into contact with another nickel foil through a separator impregnated with an electrolyte aqueous solution to form a capacitor.

The characteristics of this capacitor were as follows.

Capacity: 1μF/ ^cm2 Dielectric loss: 3.0% Resistance-capacitance product: 500MΩμF Here, the dielectric constant of La ₂ Ti ₂ O ₇ formed on the nickel foil is 90, and the thickness of the La ₂ Ti ₂ O ₇ layer is is 0.4μm
It was hot.

(Example 4) When an aluminum foil whose surface was made porous by forming pores by an etching method was thermally decomposed, PbTiO ₃
It was immersed in an organometallic compound solution of lead and titanium, pulled out, and dried.

Note that the organometallic compound solution was synthesized using the same process as in Example 1.

After drying, heat treatment is performed at a temperature of 400℃ in air.
After decomposing organic matter, heat at 500℃ for 30 minutes.
A PbTiO ₃ thin film was formed.

A PbTiO ₃ thin film was formed on the aluminum foil, and aluminum was vacuum-deposited on the surface of the aluminum foil to form an electrode, thereby forming a capacitor.

The capacitor thus obtained exhibited good characteristics: capacitance: 2 μF/cm ² dielectric loss: 3.0%, resistance-capacitance product: 3000 MΩμF.

Here, the dielectric constant of PbTiO ₃ is 150,
The thickness of the PbTiO ₃ thin film was approximately 0.4 μm.

(Example 5) _A porous aluminum block formed by a sintering method was decomposed to _prepare an organometallic compound solution (zirconium titanate precursor solution) having a composition of PbZr _0.52 Ti _0.48 O ₃ . After degassing in vacuum, the sample was taken out, excess solution was removed, and the sample was dried.

The organometallic compound solution used at this time was Example 2.
It was synthesized by a similar process.

After drying, organic compounds were decomposed in air at a temperature of 400℃, and then heat treated at 500℃ for 10 minutes to produce PbZr ₀ .
₅₂ Ti ₀ . ₄₈ O ₃ thin film was formed on the aluminum porous surface.

Next, this porous block was impregnated with an electrolyte solution and sealed in an aluminum case via a separator to form a capacitor between the outer case and the porous aluminum.

The results of evaluating the characteristics of this capacitor were as follows: Capacity: 100μF/cm ³ Dielectric loss: _{8% Resistance-capacitance product: 500MΩμF Here, the dielectric constant of PbZr 0.52 Ti 0.48 O 3} was approximately 500.

(Example 6) A porous tantalum block sintered by powder metallurgy was decomposed to produce Pb (Fe1/2Nb1/2) _{0.67 (} Fe2/3W
1/3) Immerse it in an organometallic compound solution (iron niobate/lead iron tungstate precursor solution) with a composition of _{0.33 O 3} , degas it in a vacuum, and then pull it up and remove the excess solution. It was then dried.

The organometallic compound solution used at this time was synthesized by the following process.

Pb( _{Fe1 / 2}
Nb1/2) _0.67 (Fe2/3W1/3) _{0.33 O3} , heated in acetylacetone to a temperature of 100 to ₁₁₀ °C, reacted, and calculated as composite metal oxide equivalent concentration _. , a 12.5 wt % iron niobate/iron tungstate lead precursor solution was prepared.

After drying, the organic matter was decomposed in air at a temperature of 400°C, and then heat treatment was performed at 550°C for 10 minutes.
Pb (Fe1/2Nb1/ _{2) 0.67 (} Fe2/3W1/3) ₀ .
A thin film of ₃₃ O ₃ was formed.

Next, this porous block was impregnated with a 50% methanol mixture of manganese nitrate hexahydrate and thermally decomposed at 230°C. Thereafter, graphite and silver paste were applied to evaluate the capacitor characteristics.

As a result, capacitance: 500μF/cm ³ Dielectric loss: 5% Resistance-capacitance product: _1000MΩμF Here, Pb (Fe1/2Nb1/2) _0.67 (Fe2/3W1/3) _{0.33 O 3}
The dielectric constant was about 13000, and the thickness of the dielectric layer formed was 0.8 μm.

It was also confirmed that similar capacitors had good capacitor characteristics when similar capacitors were formed using thin or porous blocks of metals such as stainless steel, iron, cobalt, and niobium.

Furthermore, excellent capacitor characteristics were obtained by using an organometallic compound solution other than those in the examples as well, by using a precursor that would become a composite perovskite compound containing lead.

(Example 7) Nickel foil is etched with hydrochloric acid to form pores on the surface of the foil to make it porous. When this porous nickel foil is thermally decomposed, 0.15PbZrO ₃ −
0.35PbTiO ₃ −0.50Pb(Ni1/3Nb2/3)O ₃ immersed in a ternary PZT dielectric formation precursor solution,
Dry after lifting.

The three-component PZT dielectric precursor solution was synthesized using the following process.

In the reaction vessel, lead acetate Pb (CH ₃ COO) ₂ , tetrabutoxyzirconium Zr (OC ₄ H ₉ ) ₄ , tetrabutoxytitanium Ti (OCH ₄ H ₉ ) ₄ , nickel acetate Ni
( _CH3COO ) ₂ , pentabutoxyniobium Nb
(OC ₄ H ₉ ) ₅ converted to oxide is 0.15PbZrO ₃ −
It was weighed to give 0.35PbTiO ₃ −0.50Pb(Ni1/3Nb2/3)O ₃ and reacted in xylene. Acetylacetone was added to the reaction solution and heated under reflux to obtain a three-component PZT dielectric forming precursor solution with an oxide equivalent concentration of 10 wt%.

After drying and decomposing organic matter in the air at 400℃,
A three-component PZT thin film was formed on the nickel foil by heat treatment at 600°C for 10 minutes.

This nickel foil was brought into contact with another nickel foil via a separator impregnated with an aqueous electrolyte solution to form a capacitor.

The characteristics of this capacitor were as follows.

Capacity: 50μF/ ^cm2 Dielectric loss: 2.5% Resistance-capacitance product: 1000MΩ・μF Here, three-component PZT formed on nickel foil
The dielectric constant of the thin film was 4500, and the film thickness was about 0.4 μm.

(Effects of the present invention) Since the manufacturing method of the present invention forms a dielectric layer uniformly and inexpensively on metal, it is possible to significantly increase the capacitance compared to conventional electrolytic capacitors, and compared with the same capacitance. Then, the shape can be made smaller.

This makes it possible to downsize the capacitor and increase its capacity. Furthermore, among conventional electrolytic capacitors, the cost of electrode materials is an issue, such as tantalum capacitors, which are in practical use as small and large capacity capacitors, and Nickel. Since low-cost metals such as aluminum can be used as electrodes, and a dielectric layer with a high dielectric constant is formed, a low-cost, small-sized, large-capacity capacitor can be obtained.

In addition, once heat-treated at high temperature, a capacitor with lower leakage current and higher resistance than conventional electrolytic capacitors can be obtained, expanding the range of uses.

Furthermore, since the dielectric layer is not formed by anodic oxidation (chemical formation), there is no polarity of the capacitor, which means that the range of uses for electrolytic capacitors can be greatly expanded beyond those for which electrolytic capacitors have traditionally been used.

In addition, as a method for applying the organometallic compound, although the dip method is shown in the example, there are other methods such as the spray method and the spinner method that can be used to coat large areas at low cost. .

Furthermore, the composition of the dielectric layer can be adjusted with good reproducibility by controlling the composition of the organometallic compound to a constant value, making it possible to industrially supply capacitors with a high yield.

Furthermore, perovskite-based oxide dielectrics other than the oxide dielectrics shown in Examples “A ₂ B ₂ O ₇ -based oxides”
A thin film of tungsten bronze-based oxide can be formed by decomposition of this organometallic compound.

Claims (1)

[Claims] 1. A method comprising the steps of forming a metal oxide thin film on the surface of a metal by heat-treating an organometallic compound at a temperature of 600°C or less, and forming a conductive layer on this thin film. A method for manufacturing a capacitor characterized by: 2. The method for manufacturing a capacitor according to claim 1, wherein the metal is a porous metal or a metal foil with a porous surface.