S. Ohnuma

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.

Magnetic Properties of Amorphous CoNbZr/AlN Multilayered Films

The dependence of the magnetic properties of multilayer CoNbZr/AlN films on the conditions of film preparation was investigated. AlN films were prepared by N2 reactive sputtering deposition on CoNbZr films. The soft magnetic properties of the as-deposited films were found to be strongly related to the rf input power during AlN deposition. The anisotropy field decreases drastically at an input power of greater than 2 W/cm2, and a high permeability of around 10,000 (at 5 MHz) was obtained for as-deposited films prepared at an rf input power during A1N deposition of 4.4 W/cm2. SEM observations revealed that CoNbZr films in as-deposited multilayer form have nearly the same morphology as amorphous alloy films annealed at the optimum temperature for reduction of the anisotropy field. The annealing process during film preparation (self-annealing effect) is attributed to the heat generated during AlN deposition, originating mainly in the heat of formation in AlN reactive sputtering.

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.

Soft Magnetic Properties of FeSiN/Ceramics Multi-Layers

Magnetic and structural properties of multilayer FeSiN/ceramic films produced by dual-type sputtering were investigated. Laminating of FeSiN with ceramic layers enhanced not only the frequency response of the permeability ¿, but also the value of ¿. These soft magnetic properties of as-deposited films were found to be strongly related to the substrate temperature Tsub, but were independent of the kind of ceramic used. Multilayered FeSiN/AIN films deposited at Tsub=300°C exhibited a large ¿ (at 5 MHz) of about 5,000 and a saturation induction Bs of more than 17 kG. SEM observation suggested that the soft magnetic properties of FeSiN-base multilayers arise from the decrease in magnetic anisotropy of the assembly of magnetically interacting small grains, and also from the (111) plane orientation of the grains. Most multilayered films exhibited greater thermal resistance to aging up to 600°C, because the ceramic layers prevent the growth of ¿-Fe grains.