JPH05112895A - Composite consisting of metallic substrate and dielectric and its production - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention aims to reduce the size of a capacitor, to make it into a chip,
In order to cope with high capacity, a micron-order film of high dielectric constant material is formed on various metal substrates including complicated shaped products. [Structure] Capacitance can be increased by increasing the electrode area, thinning the dielectric, and using high dielectric constant materials. In the present invention, a thin film of a high dielectric constant material is used to expand the capacitance. Specifically, stainless steel, Fe, Ni, C
One of u and Al metals is used as an electrode, and barium ion, strontium ion, or barium ion and strontium ion are combined in an amount of 0.1 mol / mol.
l or more and titanium ion of 0.01 mol / l or more in an acidic aqueous solution to obtain an electrodeposition product by an electrochemical treatment, and heat treatment at a temperature of 800 ° C. or more to form a titanium oxide film. Let it form. This is a composite of the metal substrate and titanium oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitor element, more specifically, a novel composite material formed on a metal substrate by coating barium titanate or strontium titanate or barium strontium titanate, which is often used as a capacitor material. The present invention relates to a manufacturing method thereof.

[0002]

2. Description of the Related Art In order to realize the miniaturization, thinness, weight reduction and high performance of electronic equipment, various electronic parts are
There is a strong demand for weight reduction, high performance, and high frequency.
For this reason, capacitors, which are one of the electronic components, are required to be downsized, made into chips, and have high capacity.

A capacitor has a structure in which a dielectric is sandwiched between electrodes, where ε and d (cm) are the permittivity and thickness of the dielectric, and S (cm ² ) is the surface area of the electrode. , The capacitance C (μF) of the capacitor is given by the following equation. C = 8.855 × 10 ⁻⁸ × ε × S / d From this equation, it can be seen that C can be increased by increasing ε or S or decreasing d.

An electrolytic capacitor, which is a type of capacitor, uses a metal such as Al or Ta as an anode electrode, and uses a dense and corrosion-resistant oxide film formed on these metals by an anodic oxidation method as a dielectric. Is forming. In the electrolytic capacitor, conventionally, the capacitance C has been increased by increasing the surface area S of the electrode. The expansion of the surface area S is performed by etching the foil which will be the electrode and sintering the fine powder. However, the recent etching technology has no breakthrough invention, and the surface area S is increased in the order of several percent by the improvement next to the improvement, and a significant area expansion cannot be expected. In addition, if the powder is too fine, it is naturally oxidized in the air to generate heat, and there is a problem in handling such as a decrease in dust collection efficiency. Therefore, it is difficult to dramatically increase the surface area S in the future by these methods. In other words, there is a limit to the increase in capacitance C due to the increase in surface area S. In addition, since the conventional electrolytic capacitor uses the oxide film of the anode electrode for the dielectric, the type of dielectric material depends on the type of electrode material, and the dielectric constant, which is the intrinsic value of the material, also depends on the type of electrode material. It is uniquely determined. For example, in the case of an aluminum electrolytic capacitor, the dielectric constant of alumina (Al ₂ O ₃ ) which is its oxide film is about 10, and in the case of a tantalum electrolytic capacitor,
The oxide film, tantalum pentoxide (Ta ₂ O ₅ ) has a dielectric constant of about 30. However, if a high dielectric constant material having a large dielectric constant ε can be used for the dielectric, the capacitance C will increase. Examples of the complex oxide having a high dielectric constant include compounds having a perovskite structure such as barium titanate.

Here, a general method for producing a barium titanate film will be described. This is a method used for producing a dielectric film of a ceramic multilayer capacitor, and is a film-drawing method typified by a doctor blade method. In this method, a dielectric raw material powder, a binder, and a solvent are mixed to form a paste, which is thinly spread on a film to form a film. However, with this method, it is difficult to form a film having a thickness of 10 μm or less after firing. From the above equation, the smaller the film thickness d is, the better. Considering that the current oxide film has a thickness of several hundred nm, 10 μm is too thick. Further, in the electrolytic capacitor, the electrode has a complicated shape in order to make the surface area S large, but the film can be formed only on the smooth surface by the film-forming method. For the above reasons, the film produced by this method is not suitable for electrolytic capacitors.

Further, in order to obtain a thin film having good crystallinity at a low temperature, production of a barium titanate coating film by a hydrothermal electrochemical method has been attempted. In this method, a titanium metal substrate is immersed in a barium hydroxide solution placed under high pressure at about 200 ° C., and this is used as an anode to conduct electricity. The barium titanate film obtained by this method has good crystallinity despite a low temperature of 200 ° C. and a uniform interference color. However, since the anodic oxidation of titanium is used in this method, the substrate serving as the anode electrode is limited to titanium.

Further, conventionally, a method of forming a film of barium strontium titanate having a perovskite structure similar to that of barium titanate by anodic oxidation and sputtering has been tried. Method of forming titanium metal by anodizing in a strong alkaline aqueous solution containing barium ions and strontium ions to form a Ba-Sr-Ti-based oxide layer having a specific composition on the surface (Patent Publication: Sho 61-30678) Is based on the anodization of titanium, and the substrate serving as the anode electrode is limited to titanium. Further, it is difficult to form a thin film having a desired composition by sputtering, and it has not yet been put to practical use.

As mentioned above, there is currently no suitable method for forming a sufficiently thin film of high electrical conductivity material on various metal substrates, including complex shaped articles.

[0009]

As described above, there is a demand for miniaturization, chipping, and high capacitance in capacitors, and in order to improve those characteristics, electrolytic capacitors have a high dielectric constant. It is conceivable to use a rate material. Further, the thickness of the film of the high dielectric constant material needs to be on the order of nm to μm in consideration of the capacitance formula and the electrode shape. However, there is no suitable method for forming a sufficiently thin film of a high dielectric constant material on various metal substrates including complicated shaped products.

An object of the present invention is to overcome the above-mentioned problems by a new manufacturing method for forming a film of high dielectric constant material of the order of μm on various metal substrates including complicated shaped products.

[0011]

In the present invention, for the above-mentioned purpose, a novel method for producing a film of barium titanate, strontium titanate, or barium strontium titanate by an electrochemical method was devised. That is, barium, or strontium as ions, or barium and strontium and titanium are present in the electrolytic solution to put an electrode and apply a voltage to move the metal ions to the cathode side to obtain an electrodeposition product, which is obtained. The barium titanate, strontium titanate, or barium strontium titanate crystal is obtained by heat-treating the deposited material. This reaction utilizes an electrochemical reaction on the cathode side, unlike anodization which is an electrochemical reaction on the anode side. In the case of anodization, it is necessary to use a material containing the constituent elements of the target coating film for the electrode. For example, in Japanese Patent Laid-Open No. Sho 61-30678, the anodization of titanium is used, so the electrode material is limited to titanium. However, according to the present invention, it is not necessary to use the material containing the constituent component of the target coating film for the electrode. That is, the electrode used when forming the barium titanate coating, the strontium titanate coating, or the barium strontium titanate coating is not limited to titanium. However, as a matter of course, when the titanium metal plate is used as the electrode, the barium titanate coating, the strontium titanate coating, or the barium strontium titanate coating can be formed.

Specifically, SU is used for stainless steel.
S416, SUS304, SUS430, SUSSP
(20Cr-5Al) is used, Fe is a metal plate having a purity of 99.9%, Ni is a metal plate having a purity of 99.9%, and Cu is a purity of 9.
A metal plate having a purity of 99.9% and a metal plate having a purity of 99.9% were used. One of these metals is used as an electrode, and the metal is used as an electrode, and barium ion, strontium ion, or barium ion and strontium ion are combined in an amount of 0.01 mol / l or more, and titanium ion is 0.01 mol / l. A barium titanate film, a strontium titanate film, or a barium strontium titanate film is obtained by applying an electric current to the above-prepared acidic aqueous solution to obtain a deposit, and heat-treating the resulting deposit at a temperature of 800 ° C. or higher. It is to obtain a composite of a metal substrate and barium titanate, strontium titanate, or barium strontium titanate by forming a film.

[0013]

As described above, the present invention provides a barium titanate film, a strontium titanate film, or a complex of barium strontium titanate formed on various metal substrates including complicatedly shaped products, and a complex of this composite. It is a manufacturing method that can be formed for the first time by a mechanical method.
By using the composite of the present invention, it is possible to make the capacitor smaller, lighter, and larger in capacity.

As a result of experiments, the metal used for the cathode was found to be capable of producing a film by using any one of the metals of stainless steel, Fe, Ni, Cu and Al. The metal has the advantage that it is cheaper than Ti. No electrodeposition product was obtained when Pt was used as the electrode.

As an aqueous solution, for example, BaCl ₂ , Ba
(NO ₂ ) ₃ , Ba (CH ₃ COO) ₂ , Ba (OH)
₂ · 8H ₂ O and the like soluble Ba salt or for example SrCl,
₂ , Sr (NO ₂ ) ₃ , Sr (CH ₃ COO) ₂ , Sr
Soluble Sr salt such as (OH) ₂ .8H ₂ O and, for example, Ti
A mixed aqueous solution of a soluble Ti salt such as Cl ₃ or TiCl ₄ was used. Barium ion, or strontium ion,
Alternatively, the total concentration of barium ions and strontium ions must be at least 0.01 mol / l or more, and the titanium ion concentration must be at least 0.01 mol / l or more. Further, when the pH of the aqueous solution was less than 0, no electrodeposit was observed, so the pH of the aqueous solution must be 0 or higher.

FIG. 1 shows changes in the concentration ratio of barium ions and titanium ions due to changes in current value, and FIG. 2 shows changes in the concentration ratio between barium ions and titanium ions due to changes in voltage value. The concentration ratio of this barium ion and titanium ion is
The obtained electrodeposit was dissolved in hydrochloric acid and analyzed by ICP (fluorescent X-ray analysis). As a result, the constant current value ^{-10mA / cm 2 ~-50mA /} cm 2, a constant voltage -
0.6 to -2.0V V. S. The Ag / AgCl range has been found to be desirable. Further, FIG. 3 shows changes in the concentration ratio of barium ions and titanium ions depending on the energization time.

If the time is less than 1 minute, the titanium ion concentration is high,
It can be seen that the barium ion concentration increases after 1 minute. This means that only titanium ions are trapped in the cathode and barium ions are not trapped in the initial stage of energization. Therefore, the energization time is preferably 1 minute or more.

Further, when the temperature of the electrochemical treatment is 70 ° C. or higher, the solubility increases and the electrodeposit cannot be obtained because of the high temperature. Then, at 80 ° C. or higher, a reaction occurs in the electrolytic solution to precipitate the reaction product, and the electrodeposit does not reach the electrode. Therefore, the temperature during the electrochemical treatment needs to be less than 70 ° C. Further, it is desirable to perform heat treatment at a temperature of 800 ° C. or higher for crystallization.

The same applies to strontium titanate or barium strontium titanate.

Here, the barium ion and the strontium ion are divalent cations. By using this method, various titanium oxides can be produced by using a solution containing various divalent metal ions, not limited to barium ions and strontium ions, as an electrolytic solution.

[0021]

【Example】

(Example 1) An electrolytic solution is placed in a container, an electrode is installed, and a voltage is applied. At this time, the electrolytic solution was set to about 300 ml, and the electrode was set so that the surface area on one surface was 1 cm ^{2 in} the electrolytic solution. Pt was used for the electrode on the anode side. The electrode on the cathode side was subjected to ultrasonic cleaning with acetone for 10 minutes and then ultrasonic cleaning with ethanol for 5 minutes.

In the above setting, the S on the cathode side electrode
0.3 mol / l of Ba (NO ₃ ) ₂ using US430
In a mixed solution of 0.05 mol / l TiCl ₃ and
A constant current of -25 mA / cm ² was applied for 3 minutes. The pH of this liquid was 1.1. Completed film with substrate 80
When baking was performed at 0 ° C., a film having a film thickness of 5 μm was obtained. FIG. 4 shows the X-ray diffraction result of this film. BaTiO ₃
It was found to be a single phase. When it was baked at 650 ° C and confirmed by X-ray diffraction, it was amorphous and was not crystallized.

(Embodiment 2) In the same setting as in Embodiment 1, SUSSP (20Cr-5A) is attached to the electrode on the cathode side.
l) and 0.3 mol / l of BaCl ₂ and 0.03
The electrochemical treatment was carried out in a mixed aqueous solution of mol / l TiCl ₃ . At this time, when a constant current of −25 mA / cm ² was applied for 2 minutes, a film of about 3 μm was formed.

(Example 3) In the same setting as in Example 1, 99.9% Fe was used for the electrode on the cathode side, and 0.
1 mol / l of Ba (CH ₃ COO) ₂ and 0.03mo
The electrochemical treatment was carried out in a mixed aqueous solution of 1 / l TiCl ₃ . At this time, when a constant current of -25 mA / cm ² was applied for 5 minutes, a film of about 5 μm was formed.

(Embodiment 4) In the same setting as in Embodiment 1, 99.9% Ni was used for the electrode on the cathode side and 0.
3 mol / l Ba (OH) ₂ .8H ₂ O and 0.03 m
The electrochemical treatment was carried out in a mixed aqueous solution of TiCl ₃ of ol / l. At this time, a constant current of -25 mA / cm ² was applied for 2 minutes. A film of about 2 μm was produced.

(Embodiment 5) In the same setting as in Embodiment 1, SUS304 is used for the electrode on the cathode side, and 0.01
Electrochemical treatment was performed in a mixed aqueous solution of mol / l Ba (NO ₃ ) ₂ and 0.01 mol / l TiCl ₃ .
At this time, a constant voltage of -1.2V V.V. S. Ag / AgCl
Was applied for 5 minutes. A film of about 1 μm was produced.

Example 6 In the same setting as in Example 1, 99.9% Ni was used for the electrode on the cathode side,
3 mol / l Sr (NO ₃ ) ₂ and 0.05 mol / l
Electrochemical treatment was carried out in a mixed aqueous solution of TiCl ₃ . At this time, a constant voltage of -1.2V V.V. S. Ag / AgC
1 was applied for 5 minutes. The pH of this liquid was 0.8. When the resulting film was baked together with the substrate at 800 ° C, a film with a thickness of 5 µm was obtained.
It was found to be a TiO ₃ single phase.

(Embodiment 7) In the same setting as in Embodiment 1, 99.9% Cu was used for the electrode on the cathode side, and 0.
3 mol / l SrCl ₂ and 0.05 mol / l Ti
Electrochemical treatment was performed in a mixed aqueous solution of Cl ₃ . At this time, a constant voltage of -1.2V V.V. S. Ag / AgCl 5
It was applied for a minute. A film of about 5 μm was obtained.

(Embodiment 8) In the same setting as in Embodiment 1, 99.9% Al was used for the cathode side electrode, and
3mol / l of _{Sr (OH) 2 · 8H 2} O and 0.05m
The electrochemical treatment was carried out in a mixed aqueous solution of TiCl ₃ of ol / l. At this time, a constant voltage of -1.2V V.V. S. Ag
/ AgCl was applied for 3 minutes. A film of about 3 μm was obtained.

(Embodiment 9) In the same setting as in Embodiment 1, 99.9% Ni was used for the electrode on the cathode side and 0.
15 mol / l Ba (NO ₃ ) ₂ and 0.15 mol / l
l Sr (NO ₃ ) ₂ and 0.05 mol / l TiCl
Electrochemical treatment was performed in a mixed aqueous solution of ₃ . At this time,
Constant voltage -1.2V V. S. Ag / AgCl was applied for 5 minutes. The pH of this liquid was 0.98. The resulting film was dissolved in hydrochloric acid and analyzed by ICP to show Ba
It was found to be a -Sr-Ti based oxide.

[0031]

INDUSTRIAL APPLICABILITY As described above, the present invention provides a composite having a ferroelectric barium titanate coating film formed on a metal substrate and a method of manufacturing the composite for the first time by an electrochemical method. Is. By using the composite body of the present invention, it is possible to make the capacitor smaller, to have a chip, to have a larger capacity, and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing changes in the concentration ratio of barium ions and titanium ions due to changes in current value.

FIG. 2 is a diagram showing changes in the concentration ratio of barium ions and titanium ions due to changes in voltage value.

FIG. 3 is a diagram showing changes in the concentration ratio of barium ions and titanium ions depending on the energization time.

FIG. 4 is a diagram showing an X-ray diffraction result of a film after baking.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuichi Taniguchi 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Nippon Steel Corporation Advanced Technology Research Laboratories

Claims (5)

[Claims] 1. Stainless steel, Fe, Ni, C
A composite comprising a metal layer of any one of u and Al and a barium titanate coating, a strontium titanate coating, or a barium strontium titanate coating formed on the metal layer. 2. Stainless steel, Fe, Ni, C
u or Al, one of the metals is used as an electrode, the metal is used as an electrode, and an electrodeposit is obtained by energizing in an electrolytic solution containing the constituent metal ions of the target dielectric, and the obtained metal layer and A method for producing a composite of a metal substrate and a dielectric, comprising simultaneously heat treating an electrodeposit formed on a metal layer at a temperature of 800 ° C. or higher to form a dielectric. 3. The electrolytic solution according to claim 2, wherein barium ions are 0.01 mol / l or more and titanium ions are 0.0
A method for producing a composite comprising a metal substrate and a barium titanate coating, using an acidic aqueous solution containing 1 mol / l or more. 4. The metal substrate and the strontium titanate coating according to claim 2, wherein an acidic aqueous solution containing 0.01 mol / l or more of strontium ions and 0.01 mol / l or more of titanium ions is used as the electrolytic solution. Of producing the complex. 5. The electrolytic solution according to claim 2, wherein the total amount of barium ions and strontium ions is 0.01 mol.
/ L or more and an acidic aqueous solution containing 0.01 mol / l or more of titanium ions, and a method for producing a composite comprising a metal substrate and a barium strontium titanate coating.