JPH03201416A - magnetic thin film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magnetic materials for high frequency transformers, mag-amps, and other high frequency electronic components used particularly at high frequencies.

[Conventional technology]

In recent years, technological innovation in electronics has been remarkable, and in particular, miniaturization, weight reduction, and higher density of electronic devices have become central technological issues. One element of miniaturizing electronic devices is improving inductor elements. For example, in a switching power supply using a magnetic amplifier, it is expected that the power supply can be dramatically downsized by increasing the switching frequency. Magnetic materials constituting inductor elements are required to have better high frequency characteristics than ever before.

Magnetic permeability is a parameter that characterizes soft magnetic materials. FIG. 1 shows the dependence of frequency f on the relative permeability μ of magnetic materials that have been put into practical use. (Yamauchi, '89 Switching Power Supply System Symposium Proceedings, 5-2-1) As the frequency increases, the relative magnetic permeability decreases, and regardless of the magnitude of the relative magnetic permeability due to the difference in materials, the decreases are almost on the same line. are doing. In this way, the characteristics of magnetic materials deteriorate at high frequencies. Beyond this limit, attempts were made to develop magnetic materials that could be used at higher frequencies, such as the Ferrox planer (Perrox
A material called plana has been developed. (G, Ho
Jonker etal: Ph1lips, Tech,
Rev. 1B (1956) 145) However, it is difficult to increase the electrical resistivity sufficiently, the eddy current loss is large, and the manufacturing method is difficult because it requires special crystal growth, so it is not currently used in practical use. Not yet.

Recently, various methods for producing amorphous alloys have been developed, and materials with excellent soft magnetism can now be obtained. In particular, very thin materials can be obtained using the spuckling method. CoZr
Some amorphous alloys with a thickness exceeding this limit have been announced. (Shimada, Institute of Electronics and Communication Engineers Parts and Materials Study Group sample, CPM 8111 (1981)) However, since Zr is used, the saturation magnetic flux density is low, and as a result, it exceeds this limit line. It is not possible to obtain a high absolute value of magnetic permeability.

[Problem to be solved by the invention]

The present inventors have arrived at the present invention as a result of extensive research into materials that have high electrical resistivity, high magnetic permeability, and exhibit little deterioration in characteristics at high frequencies.

[Means to solve the problem]

The gist of the present invention is to provide an amorphous alloy mainly composed of iron and cobalt, which has an electrical resistivity of 5 at room temperature.
0 μΩ・(2) or more, and a magnetic thin film with good high frequency magnetic properties characterized by the existence of a high μ that satisfies the following formula between the initial magnetic permeability μ and the excitation frequency f (Hz). be.

log+oμ>8.9 0.9 log+of i.e.
The present invention is based on the discovery of a material that has a high electrical resistivity and a high initial magnetic permeability μ at high frequencies.

In order to obtain the magnetic thin film of the present invention, the following conditions must be satisfied at the same time.

(1) The alloy composition has excellent soft magnetism. In order to have low loss and excellent high frequency characteristics, it is necessary to minimize magnetostriction, which is a magnetic property parameter. The magnitude of magnetostriction is closely related to its alloy composition. For example, among elements that exhibit ferromagnetism, the composition that gives (magnetostriction) -0 is Fe.
/Co=6/94, Re/N1=18/82
, Co/N1=46154 is well known. The magnetic thin film of the present invention mainly contains Fe and Co, which provide a high saturation magnetic flux density.

However, other elements may also be contained in small amounts depending on the purpose.

(2) It must be an alloy with high electrical resistivity. Common metal materials have low electrical resistivity and cause loss due to eddy currents. In order to obtain the magnetic thin film of the present invention, it is preferable to use an amorphous alloy. Amorphous alloys usually have an electrical resistivity that is about two orders of magnitude higher than that of crystalline alloys. Electrical resistivity at room temperature is 5
It is preferably 0 μΩ·cm or more, preferably 100 μΩ·Cl11 or more.

(3) Thin film. Magnetic loss at high frequencies is dominated by eddy current loss. As can be seen from this equation, the eddy current loss (W) is smaller when the thickness is thinner. In order to obtain the magnetic thin film of the present invention, the magnetic thin film must be 1° or less, preferably 5° or less, more preferably 2I! m or less is better.

(4) The surface of the thin film is smooth. In particular, at high frequencies, domain walls are likely to be pinned due to surface irregularities, reducing magnetic properties. According to the theory of Gyorgy et al. (E, M, G
yorgy: Metallic Glasses,
American Society for Metal
S 275 (1978)), the coercive force (Hc) was calculated by approximating the surface roughness to a triangular pyramid with a width of 2χ and a depth of a.

The smaller the width χ and the larger the depth a, the larger the Hc, that is, the larger the surface unevenness, the larger the loss. Figure 2(a)
Figure 2 shows the surface condition of a commercially available amorphous alloy obtained by the rapid cooling method using the stylus method. A material with such severe surface irregularities does not have excellent high frequency characteristics. The preferred surface roughness is 1. It should have an average surface roughness of less than On, more preferably less than 0.5 tnn.

(5) A large number of domain walls. It is necessary to increase the number of domain walls by having a dense microstructure inside the magnetic film. The equation below shows that eddy current loss is affected by the number of domain walls.

(6) Small magnetic anisotropy. The initial magnetic permeability assuming a rotational magnetization process is (near angle, "Physics of Ferromagnetic Materials" Shokabo) The smaller K, the higher the magnetic permeability. A method of drawing at a high speed, such as a rapid cooling method, is undesirable because magnetic anisotropy occurs due to internal stress.

The present inventors have discovered that by simultaneously satisfying the above conditions, high electrical resistivity and high magnetic permeability at high frequencies can be obtained, and have arrived at the present invention.

Means for specifically realizing the present invention will be described below, but it is not necessarily necessary to use the following means, and any means may be used as long as it satisfies the above conditions.

The magnetic thin film of the present invention is suitably formed by plating. In order to obtain a single thin film by plating, the surface must be
．． It is preferable to use an electrode polished to a surface roughness of 1 μm or less. By using such an electrode, a film with a very smooth surface can be electrolytically deposited. Also,
The alloy thin film can be easily peeled off from the electrode. On the other hand, when plating a substrate such as an electrical conductor such as copper or iron or a semiconductor such as a metal oxide, and forming the magnetic thin film of the present invention and using it integrally with the substrate, the surface of the substrate should be covered as much as possible. A smooth one is preferable. The technique of depositing an amorphous alloy by plating is disclosed in Japanese Patent Application Laid-open No. 140403/1983.
This method is known in Japanese Patent Publications No. 55-164092 and No. 60-33382, and involves methods such as depositing a metalloid together with a metal, or depositing under a high overvoltage using a pulse voltage. The electrolytically deposited amorphous alloy must have excellent soft magnetic properties. The soft magnetic properties of magnetic materials are better if they have lower magnetostriction. The iron-cobalt system has a high saturation magnetic flux density, and those containing 90% or more of cobalt in terms of atomic ratio have very low magnetostriction. In particular, when the cobalt content is 94%, the magnetostriction constant becomes almost zero, so it is preferable to electrolytically deposit a material having this atomic ratio. In order to stabilize the amorphous state, it is necessary to eutectoid metalloid elements. The metalloid element that can be easily eutectoided by the plating method is P (phosphorus), and phosphorous acid, phosphite, or a mixture thereof, or hypophosphorous acid or hypophosphite is used in the plating film. It is preferable. In particular, if phosphorous acid or phosphites are used, a foil with very good film-forming properties and high flexibility can be obtained. Since it is a plating method, the film thickness can be easily controlled by changing the electrolysis time. If the above-mentioned phosphorous acid or phosphite is used, a very thin film can be easily obtained because of its good film-forming property, and it is possible to obtain a film with a thickness of 2 or less.

The content of P is preferably from 5.0 at% to 30 at%.

(Patent Application No. 1-263975 and No. 1-263976
According to the plating method, no excessive external force is applied during manufacturing, so magnetic anisotropy due to internal stress does not occur. A highly isotropic film is obtained.

On the other hand, when considering the alloy precipitation process due to the plating method, a large number of atomic nuclei are formed immediately after electrolysis, and alloy precipitation progresses around these nuclei. This indicates that a dense and fine morphology is formed in the plating film. Amorphous alloys produced by the rapid cooling method do not have such a structure because they are solidified from a molten liquid state. The dense and fine morphology created by the plating method increases the number of domain walls. Hereinafter, a plating method will be explained as a specific example for carrying out the present invention.

In a plating bath containing at least divalent cobalt ions and divalent iron ions, phosphorous acid and/or
Alternatively, electrodeposition is performed in an acidic plating bath containing phosphite and at least one of a reducing agent and a complexing agent. To explain in more detail, divalent cobalt ions include cobalt sulfate,
Cobalt chloride, cobalt sulfamate, cobalt nitrate, and the like may be used as long as they supply divalent cobalt ions, and mixtures of these salts may also be used.

Preferably, the salt is in a concentration of 1/3-2 mol/1. The divalent iron ion may be any of iron sulfate, iron chloride, iron sulfamate, iron nitrate, etc., or a mixture of these salts. The concentration is 0.01-0.2 mol/
1 is good, but in order to precipitate the desired alloy composition, the concentration ratio of cobalt ions and iron ions should be adjusted. Phosphorous acid and/or phosphite which is a phosphorus source is 0601-5.0
Formation of an amorphous alloy foil is possible at mol/1. Here, in order to obtain an amorphous alloy thin film with good film formability, it is necessary to add at least one kind of reducing agent or complexing agent,
Hydroquinone, hydrazine, dimethylamine borane, sodium hydride, etc. are used as the reducing agent, and citric acid, hydroxycarboxylic acid, EDTA, gluconic acid, etc. are used as the complexing agent. The above plating bath has a pH of 1.0 to 2.
．． 0, and electrolytic plating is performed at a temperature of 40°C or higher, preferably 60°C or higher. Current density is usually 0.005~
1.0 A/ca is good. Particularly when it is desired to increase the amount of metalloid elements in the alloy, the concentration of phosphorous acid and/or phosphite, which is a phosphorus source, is increased and at the same time the current density is lowered. The current density is preferably 0.05 A/Cl11 or less, preferably 0.02 A/Cl11 or less. To extract the amorphous alloy thin film, a working electrode whose surface is polished to a surface roughness of 0.1 s or less is used.

The present invention will be explained in more detail below using examples.

〔Example〕

<Example> Iron chloride (II) 11.9 g/j as a color stopper for caged polygonal tumors! , cobalt sulfate (II)
) 264.3 g/l, phosphorous acid 164 g/f
(2 mol/l), an aqueous solution containing 6.2 g/l of halonic acid and 0.2 g/l of hydroquinone (reducing agent) was adjusted to pH 1.3, and the current density was 0.05 A/cffl.
Electrodeposition was performed at The electrodeposition time was 50 seconds and the thickness was 1 μm. When this was peeled off from the electrode, a highly flexible foil with no pinholes was obtained. The electrode used at this time was a stainless steel plate polished to a surface roughness of 0.1 μm. X
Line diffraction results revealed that the crystals had no diffraction peaks and were amorphous. In addition, ICP emission spectrometer (
As a result of quantitative analysis using ICMP-575MK (manufactured by Nippon Shisharel Ash), the atomic ratio was Fe: Co.
: P=5 Near 5:20 (at%) result was obtained.

At this time, the atomic ratio of iron and cobalt is approximately 6:94.
Met.

The surface roughness of this sample measured by the stylus method is shown in FIG. 2(b). It is much smoother than in FIG. 2(a).

<Comparative example> A comparison was made between the present invention and an amorphous alloy produced by a rapid cooling method.

Comparative sample B: METGLAS@2 manufactured by Nippon Amorphous Alloy ■
605CO comparative sample C: METG made by Japan Amorphous Alloy ■
LAS" 2714A (thickness is 25mm in both cases) Disc transparent Keizaaki constant magnetic thin film A and comparative samples B and C magnetic thin films with a width of 5Inf
It was cut into a tape shape of fl and coated with alumina powder (1-particle size) dispersed in an organic solvent on one side. The magnetic thin film
It was wound around a quartz tube with an outer diameter of 15 mm, a length of 5 m+n, and a thickness of II]III+, and annealed at 300''C in a nitrogen atmosphere.

An enameled wire of 0.511 Imφ was wound around this quartz tube for 20 turns. Made by Yokogawa Heuret Bara Card ■ 4
Inductance and resistance were measured using a 275A multi-frequency LCR meter, and initial permeability and tan δ were determined using the following formula. However, the frequency is l0K)
At Iz -10MHz, the excitation current is 0.75mA (4w
OE conversion).

L-fi・109 Here, L is the inductance (H), ω is 2πf (f: frequency), l is the average magnetic path length (cm), n is the number of windings, S is the total cross-sectional area of the magnetic film (c+fl), R is the measured effective resistance (Ω) and Ro is the resistance of the winding (Ω).

The results are shown in Fig. 3 and the frequency dependence of the initial permeability, and Fig. 4 shows the ta
It is shown as frequency dependence of nδ. Comparative samples B and C show a decrease in initial magnetic permeability starting from low frequencies, but no decrease is observed in the magnetic thin film according to the present invention.

Further, it can be seen that the magnetic thin film of the present invention has a small value of tan δ and has little magnetic loss.

Electrical resistivity was measured with four terminals using MCP-TESTEREP model manufactured by Ai Satomi and Hoshinobu Mitsubishi Yuka. For comparison, a copper foil with a thickness of 20 μΦ was also measured. The results are shown in the table below. The magnetic thin film of the present invention has an electrical resistivity nearly two orders of magnitude higher than that of copper foil, and can sufficiently reduce eddy currents at high frequencies.

(Table) [Effects of the Invention] According to the present invention, a magnetic material is provided that has high magnetic permeability at high frequencies, high electrical resistivity, and low eddy current loss.

[Brief explanation of drawings]

Figure 1 is a graph showing the frequency dependence of relative magnetic permeability of commercially available magnetic materials, Figure 2 (a) is the surface roughness of the rapid cooling method (comparative sample B), and Figure 2 (b) is the magnetic thin film A. 3 is a graph showing the frequency dependence of initial magnetic permeability, and FIG. 4 is a graph showing the frequency dependence of tan δ.

Claims (1)

[Claims] 1. An amorphous alloy whose main components are iron and cobalt,
The electrical resistivity at room temperature is 50 μΩ·cm or more,
A magnetic thin film having good high frequency magnetic properties, characterized in that there exists a high μ between the initial magnetic permeability μ and the excitation frequency f (Hz) that satisfies the following formula. log_1_0μ>8.9-0.9log_1_0f