JPH08134692A - High dielectric constant composite aluminum oxide coating film and its production - Google Patents

Abstract

PURPOSE: To obtain a composite aluminum oxide coating film contg. a specified amt. of central atoms of anions of an inorg. oxo acid salt by anodically oxidizing aluminum in a nonaq. electrolytic soln. contg. the inorg. oxo acid salt. CONSTITUTION: Aluminum is anodically oxidized in a nonaq. electrolytic soln. contg. about 0.1-2mol/l inorg. oxo acid salt and having <=5wt.%, preferably about <=2% water content. Ammonium salt, alkali metallic salt, phosphonium salt or sulfonium salt of nitric acid, phosphoric acid, boric acid, vanadic acid or tungstic acid is suitable for use as the inorg. oxo acid salt. Ethylene glycol or toluene may be used as a nonaq. solvent. By the anodic oxidation, the objective composite aluminum oxide coating film contg. 1-50% central atoms of anions of the inorg. oxo acid salt, e.g. N, P, B, V or W and having a relative dielectric constant of >=20 is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high dielectric constant composite aluminum oxide film and a method for producing the same. The high-dielectric-constant composite aluminum oxide film is an electrolytic capacitor that requires high capacitance, a printed capacitor on a printed board, a dielectric resonator for microwaves, an IC, a liquid crystal TFT dielectric,
Used as an insulator.

[0002]

2. Description of the Related Art The anodic oxidation of aluminum has been a well-known principle since ancient times and has been industrially used in various fields. It is known that anodization is usually carried out in an aqueous electrolytic solution, and two types of oxide films called porous type and barrier type are formed depending on the type of electrolytic solution used. Since the barrier type film is dense and has high electric insulation, it is applied to a dielectric film of an electrolytic capacitor, an insulating film of aluminum wiring on a semiconductor, and the like.

In an aluminum electrolytic capacitor, an aluminum foil whose surface is electrochemically or chemically roughened is anodized with an aqueous solution of boric acid, phosphoric acid or adipic acid to form an aluminum oxide film layer. Foil is used for the anode electrode (Handbook of Metal Surface Technology 67
Page 1 (1976) Nikkan Kogyo Shimbun, Experimental Surface Technology 35
(6), 261 (1988)).

Generally, the capacitance C of a parallel plate capacitor
Is defined by C = ε ₀ · ε _r · A / d (where, ε _{0 is a} vacuum permittivity, ε _{r is a} relative permittivity, A is an electrode area, and d is a dielectric thickness). In order to obtain a capacitor having a high capacitance, either (1) improving the relative permittivity of the dielectric material, or (2) expanding or thinning the surface area is used. Aluminum oxide has a relative permittivity of 7 to 10, and since the withstand voltage decreases when the oxide film is thinned, high electrostatic capacity has been achieved by increasing the electrode surface area by electrolytic etching.

[0005]

However, in the recent trend toward lighter, thinner, shorter, and smaller electronic devices, there is a strong demand for electrolytic capacitors to be made into chips and smaller in size. For that purpose, the electrostatic capacitance of electrode foils is further increased. Is desired. Further, a dielectric film or an insulating film on a printed circuit board or a semiconductor circuit has a similar problem. The present invention aims to provide a high-dielectric-constant composite aluminum oxide film and a method for producing the same, which can meet such demands.

[0006]

That is, the first aspect of the present invention is to:
The present invention provides a high dielectric constant composite aluminum oxide film containing a central atom of an anion of an inorganic oxoacid salt and having a relative dielectric constant of 20 or more. A second aspect of the present invention provides a method for producing a high dielectric constant composite aluminum oxide film by electrolytic anodizing aluminum in a non-aqueous electrolytic solution containing an inorganic oxo acid salt and having a water content of 5% or less. Is.

[0007]

In the anodic oxidation in a system in which water does not exist or in a trace amount, oxygen forming the anion of the inorganic oxo acid salt, which is the solute of the electrolytic solution, can be the oxygen source. Therefore, the central atom of the anion of the oxo acid salt is contained together with the oxygen atom forming the anion of the inorganic oxo acid salt by anodization, and the relative dielectric constant is twice or more higher than that of conventional aluminum oxide, that is, the relative dielectric constant is higher. Greatly increased to over 20.

(Summary of the Invention) Method for Producing High Dielectric Constant Composite Aluminum Oxide Film The high dielectric constant composite aluminum oxide film of the present invention comprises aluminum in a non-aqueous electrolyte containing an inorganic oxo acid salt and having a water content of 5% or less. Is obtained by electrolytic anodic oxidation.

As the non-aqueous electrolytic solution used in the method of the present invention, a non-aqueous solvent solution of an inorganic oxo acid salt is used. Examples of the inorganic oxoacid salt include inorganic oxoacids 1, 2, 3
Alternatively, a quaternary ammonium salt, an alkali metal salt, a quaternary phosphonium salt, or a sulfonium salt can be exemplified. Examples of the inorganic oxo acid forming the anion of the inorganic oxo acid salt include chromic acid, vanadic acid, even if the central atom is a non-metal oxo acid such as nitrogen, phosphorus, or boron, such as nitric acid, phosphoric acid, and boric acid. Alternatively, an oxyacid having a central atom such as chromium, vanadium, or tungsten such as tungstic acid may be used. Further, the oxo acid may be a poly acid, and may be an isopoly acid or a heteropoly acid.

Examples of the non-aqueous solvent include alcohol solvents such as ethylene glycol and methyl cellosolve; lactone solvents such as γ-butyrolactone, γ-valerolactone and δ-valerolactone; carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate. System solvent; N-methylformamide, N-ethylformamide, N, N-dimethylformamide, N, N-diethylformamide, N-methylacetamide, N, N-
Amide solvents such as dimethylacetamide and N-methylpyrrolidinone; nitrile solvents such as 3-methoxypropionitrile and glutaronitrile; phosphate ester solvents such as trimethyl phosphate and triethyl phosphate; and two or more of these. Examples thereof include polar solvents such as a mixture of solvents, and nonpolar solvents such as hexane, toluene, and silicon oil, but polar solvents in which the inorganic oxo acid salt is easily dissolved are preferable.

The concentration of the inorganic oxo acid salt used varies depending on the conductivity and spark voltage of the electrolytic solution to be obtained, but is generally below the saturation concentration, preferably 0.1 to 2 mol / 〓. Further, in order to obtain a high dielectric constant composite aluminum oxide film, the electrolytic solution must be substantially anhydrous, and the water content of the electrolytic solution must be 5% by weight or less, preferably 2% by weight or less. . By reducing the water content, the relative dielectric constant of the high dielectric constant composite aluminum oxide film can be further increased. If the water content is too large, a conventional oxide film using water as an oxygen source is formed, so that the relative permittivity of the obtained oxide film is not improved. Anodization is generally carried out in the above electrolytic bath at a temperature range of room temperature to 150 ° C. and a current density of 0.5 to
It is performed in the range of 50 mA / cm ² . The electrolytic anodic oxidation time is determined by the electrode area.

High dielectric constant composite aluminum oxide film A high dielectric constant composite aluminum oxide film having a relative permittivity of 20 or more, preferably 30 or more, containing 1 to 50% by weight of the central atom of the anion of the inorganic oxoacid salt by the above method. Can be obtained. The film thickness of the high dielectric constant composite aluminum oxide film of the present invention is arbitrarily determined by the formation voltage,
A wavelength of 1000 nm is obtained.

The high-dielectric-constant composite aluminum oxide film obtained by the above-mentioned method has a central atom of the anion of the inorganic oxoacid salt which is the electrolyte used in the anodization, that is, nitrate, phosphate or borate. The oxo acid salts contain nitrogen, phosphorus, and boron, and the oxy acid salts such as vanadate and tungstate contain vanadium and tungsten, respectively.

[0014]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples below. (Example 1) An ethylene glycol solution containing 1 molar concentration of tetraethylammonium salt of nitric acid was prepared and dehydrated by heating under reduced pressure. The water content of the electrolyte at this time is 15 ppm
Met. Using this electrolyte, 5 aluminum foil
Anodized to 50 V with a constant current of mA / cm ² to obtain a formed foil.

As a result of observing the cross section of the obtained chemical conversion foil with a TEM (scanning transmission electron microscope), the film was almost smooth, the surface area was almost unchanged from that before anodic oxidation, and the film thickness was 20.
was nm. This formed foil was dipped in a 10 wt% aqueous solution of ammonium adipate, and the capacitance at 120 Hz was measured with an LCR meter. The capacitance at 120 Hz was 4.1 μF / cm ² . Table 1 shows the relative permittivity obtained from the capacitance and the film thickness.

(Example 2) An ethylene glycol solution containing a tetraethylammonium salt of boric acid at a molar concentration of 1 was prepared and dehydrated by heating under reduced pressure. The electrolytic solution had a water content of 500 ppm. Using this electrolytic solution, an aluminum foil was anodized to 38 V at a constant current of 5 mA / cm 2 to obtain a formed foil. The obtained formed foil was dipped in a 10% by weight aqueous solution of ammonium adipate, and was immersed in an LCR meter for 12 hours.
The capacitance at 0 Hz was measured. Table 1 shows the relative permittivity obtained in the same manner as in Example 1.

Example 3 An ethylene glycol solution containing 1 molar concentration of tetraethylammonium phosphate was prepared and heated under reduced pressure for dehydration. The electrolytic solution had a water content of 400 ppm. Using this electrolytic solution, an aluminum foil was anodized to 25 V at a constant current of 5 mA / cm 2 to obtain a chemical conversion foil. The obtained formed foil was dipped in a 10% by weight aqueous solution of ammonium adipate, and was immersed in an LCR meter for 12 hours.
The capacitance at 0 Hz was measured. Table 1 shows the relative permittivity obtained in the same manner as in Example 1.

(Example 4) An ethylene glycol solution containing a tetraethylammonium salt of vanadic acid at a molar concentration of 1 was prepared and dehydrated by heating under reduced pressure. The electrolytic solution had a water content of 0.9% by weight. Using this electrolytic solution, an aluminum foil was anodized to 60 V at a constant current of 5 mA / cm 2 to obtain a formed foil. 10% by weight of the obtained formed foil
Was immersed in an aqueous solution of ammonium adipate and the capacitance at 120 Hz was measured with an LCR meter. Table 1 shows the relative permittivity obtained in the same manner as in Example 1. FESTEM
(Field Emission Scanning Transmission Electron Microscope) -The structure of the oxide film was examined by EDX (energy dispersive X-ray spectroscopy).

FIG. 1 is a sectional view of an oxide film by FESTEM. The elemental analysis of the parts shown in FIGS.
As a result of X, 1 in atomic ratio
(O; 75.30%, Al; 22.15%, V;
2.55%), 2 (O; 73.69%, Al; 25.
08%, V; 1.23%), 3 (O; 69.44%,
Al; 29.38%, V; 1.18%) and 4
(O; 3.56%, Al; 96.28%, V;
16%), and the oxide film contained vanadium, which is the central atom of vanadic acid.

(Embodiment 5) An ethylene glycol solution containing a tetraethylammonium salt of tungstic acid at a molar concentration of 1 was prepared and dehydrated by heating under reduced pressure. The electrolytic solution had a water content of 1% by weight. Using this electrolyte,
The aluminum foil was anodized at a constant current of 5 mA / cm 2 to 38 V to obtain a chemical conversion foil. The obtained formed foil was dipped in a 10% by weight aqueous solution of ammonium adipate, and 1
The capacitance at 20 Hz was measured. Table 1 shows the relative permittivity obtained in the same manner as in Example 1.

(Comparative Example 1) Used as a chemical conversion electrolytic solution in the production of a chemical conversion foil for aluminum electrolytic capacitors 1
The aluminum foil was anodized in the same manner as in Example 1 except that a 0% by weight ammonium adipate aqueous solution was used and the formation voltage was set to 75V. The obtained formed foil was dipped in a 10% by weight ammonium adipate aqueous solution, and the capacitance was measured with an LCR meter. The capacitance at 120 Hz is 0.
It was 088 μF / cm ² . Further, the film thickness of the film was 80 nm from the observation of the cross section by TEM, and the relative dielectric constant obtained from the capacitance and the film thickness was 8.0.

(Comparative Example 2) Concentration of 1 mol as an electrolytic solution for chemical conversion
With tetraethylammonium vanadate solution
Other than that, the same procedure as in Example 1 was performed on the aluminum foil up to 50V.
Anodized. 10% by weight of adipine obtained from the formed foil
Immersion in ammonium acid aqueous solution, capacitance by LCR meter
Was measured. The capacitance at 120Hz is 0.12
μF / cm ²And the relative permittivity is determined in the same manner as in Example 1.
The calculated value is 7.4, which is almost the same as the relative dielectric constant of Comparative Example 1.
Met.

[0023]

[Table 1]

[0024]

The high-dielectric-constant composite aluminum oxide film of the present invention is a film having a relative dielectric constant of 20 or more, which is at least twice as high as that of an oxide film formed by a conventional aqueous chemical conversion electrolyte solution. By using the high-dielectric-constant composite aluminum oxide film, it is possible to realize an electrolytic capacitor having the same size and high capacitance or the same capacitance and small size.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a cross section of a high dielectric constant composite aluminum oxide film obtained in Example 4. Reference numerals 1 to 4 in the figure indicate the points of elemental analysis by EDX.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sachie Sachie 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Mitsubishi Chemical Corporation Tsukuba Research Center

Claims (4)

[Claims] 1. A high dielectric constant composite aluminum oxide film having a relative dielectric constant of 20 or more, containing 1 to 50% by weight of the central atom of an anion of an inorganic oxoacid salt. 2. The high dielectric constant composite aluminum oxide film according to claim 1, wherein the anion of the inorganic oxoacid salt is selected from nitric acid, phosphoric acid, boric acid, vanadic acid or tungstic acid. 3. A method for producing a high dielectric constant composite aluminum oxide film, which comprises electrolytically anodizing aluminum in a nonaqueous electrolytic solution containing an inorganic oxoacid salt and having a water content of 5% by weight or less. 4. The method for producing a high dielectric constant composite aluminum oxide film according to claim 3, wherein the inorganic oxo acid salt is selected from nitrates, phosphates, borates, vanadates or tungstates.