F. Matsumoto

System for Measuring Thin-Film Permeability by Using a Parallel Line

A method of measuring the permeability of soft magnetic films at high frequencies was investigated. The main components of this system are a network anlyzer and a parallel line. We attempted to discover why the value of the permeability given by the parallel line method is smaller than that given by the coil impedance method. We found that the leakage of field energy outside the line must be considered in evaluating the permeability correctly. The parameter ¿ was introduced to describe the leakage of field energy. We then measured the value of the permeability by the parallel line method (10 MHz to 500 MHz), and the value obtained agreed well with measurements using a figure-8 type permeameter (1 MHz to 100 MHz). The parallel line was 15 mm long, 11.3 mm wide and 1.5 mm deep.

Magnetic Properties of Amorphous Co-Base Films with Dispersed Fine Nitride

In efforts to obtain excellent-quality magnetic thin films for use in micro-inductance cores, amorphous Co-base films containing fine dispersed nitride particles were investigated. Sputter-deposited films were confirmed to have an amorphous structure, near-zero magnetostriction (¿) and high electrical resistivity. TEM observations clarified that films were composed of two kinds of amorphous phase. The soft magnetic properties of films were found to be related to the film thickness: at thicknesses below 0.1 ¿m, films became magnetically soft. Based on this relation, we attempted to prepare multilayered films consisting of thin Co-base layers and thin BN ceramic layers, and obtained excellent properties as a result, with a high ¿ (≫300 ¿¿-cm), low ¿ (1×10-6) and high ¿ (≫1000) at high frequencies near 100 MHz.

Soft Magnetic Properties of Highly Resistive Co-Al-N Alloy Films

The effects of the Al and N content on the structure and properties of Co.95Fe.05-Al-N films prepared by rf reactive magnetron sputtering using (N2+Ar) gas were studied. TEM observations revealed that nitrided films are composed of heterogeneous phases with a very fine network structure. It was found that the properties of films are determined mainly by the combination of the Al and N concentrations. The coercivity of films containing more than 10 at% Al decreases with increasing N content, even when the film thickness is more than 2 ¿m. A steep increase in the electrical resistivity and a slight decrease in the magnetization of films containing more than 15 at% Al were observed during the initial increase in the N concentration, and both electrical resistivity and magnetization decreased rapidly when the N concentration was the same as that of Al. These anomalies are attributed to intergranular materials, indicating the presence in these films of a phase rich in Al and N.

Soft Magnetic Properties of Nanocrystalline Fe-Ceramic Films

Fe-M-(O,F) (M=Si, Mg, Y, Zr, Ca, Al) films were prepared by co-sputtering of Fe and ceramic targets. These films have a network-like structure consisting of fine metallic grains of diameter 50 to 100 Å and ceramic-like boundaries. Those films that consist of bec Fe grains have soft magnetic properties and low magnetostriction in the as-deposited state. Their permeability has good frequency response, which seems to be attributable to the reduction of eddy current losses by the highly resistive boundaries.

Relationship between Deposition Conditions and the Magnetic Properties of Highly Resistive Fe-BN Films

In an effort to obtain a high-quality magnetic thin film for use in micro-inductors, the magnetic and structural properties of highly resistive Fe-BN films were studied. In the case of films deposited on substrates electrically isolated from ground, the Bs value, resistivity, and Hc all varied as functions of the sputtering gas pressure (Ps). The structures of as-deposited films were amorphous, and on annealing they crystallized into an ¿-Fe single phase. On the other hand, the above parameters were independent of Ps for films deposited with a negative bias voltage applied to the substrate. These films were also amorphous in the as-deposited state, and crystallized into Fe3B and ¿-Fe on annealing. XPS analyses revealed that application of a negative bias voltage decreased the N and O contents, and especially the concentration of BN, in these films. This finding is attributed to the enhancement of Ar+ ion bombardment at the time of deposition.

The Size Effects on High Frequency Magnetic Properties of Amorphous Wires

The frequency dependence of the permeability, jU^, in amorphous Co-Fe- Si-B wires was investigated as a function of the wire diameter, annealing temperature, tensile stress and drawing parameters. Results show that the level of ¿i and the critical frequency for holding ¿i constant depend mainly on the wire diameter, suggesting that eddy currents affect ¿i at high frequencies. It was also found that two-stage annealing, in which drawing followed by annealing was performed twice, results in an improved frequency characteristic of ¿i

Magnetic Properties of Ring-Shaped Composite Anisotropy Multilayers

We have investigated eight-layered and twelve-layered composite anisotropic films to obtain advanced properties for practical use, and to understand the relation between the magnetic layers. Calculations of the permeability based on the Landau-Lifshitz relation predict that the dipole-dipole coupling between the magnetic layers works in favor of the Ku (in-plane uniaxial anisotropy) in each magnetic layer. When the gap between the magnetic layers is varied using ceramic layers, the dipole moment of the metal layers is influenced by the magnetic interaction of a ripple stray field in a 45° direction across intervening ceramic layers. In order to clarify the mechanism governing the isotropic permeabilities of these multilayer films, we extended our study to include ring-shaped as well as disk-shaped samples. In comparison with a uniaxial multilayer film, a ring-shaped composite anisotropy multilayer film has a closed magnetic circuit and hence a large inductance. Composite anisotropy effects are discussed.

Soft Magnetic Properties of High-Resistive CoBN/AIN Multilayers

The magnetic and structural properties of multilayered CoBN/AIN films prepared by sputtering were investigated with the intention of creating film suitable for application in micromagnetic devices operating at high frequencies. A CoBN single-layer film has a resistivity ¿ of about 340 ¿¿-cm, a Bs of about 10.3 kG, and perpendicular magnetic anisotropy. CoBN/AIN multilayer films, even when the AIN layer thickness is about 3Å, exhibit soft magnetic properties (Hc≪1 Oe and ¿≫500) for a variety of layer thickness combinations. SEM observations suggest that the soft magnetic properties of the multilayer films originate in their in-plane uniaxial anisotropy and in the fine grains in the CoBN layers. The magnetostriction of multilayer films ranged between ±1×10-6, and the anisotropy field was over 15 Oe. Although film thicknesses exceeded 2 ¿m, a high permeability ¿ was maintained, even at frequencies close to 300 MHz.