Akio Tago

A new planar microtransformer for use in micro-switching converters

A planar microtransformer for use in microswitching converters of portable equipment is described. This microtransformer, consisting of planar coils and CoZrRe amorphous magnetic layers on a Si substrate, is fabricated by a dry process. It is about 0.3-mm thick, and 3*4 mm/sup 2/. Its coils provide a relatively high inductance of 33 nH/mm/sup 2/. This microtransformer is implemented in a forward converter, which operates well at 32 MHz. >

Planar microtransformer with monolithically-integrated rectifier diodes for micro-switching converters

A microtransformer that is monolithically integrated with rectifier diodes is developed as the first step towards developing a monolithic microswitching converter that can be integrated with semiconductor devices and magnetic components. This microtransformer consists of planar coils and CoZrRe amorphous magnetic layers on Si substrate. Two Schottky barrier diodes are formed on the Si substrate and directly connected to the secondary coil. This microtransformer chip is shown to perform both conversion and rectifying functions.

A compact buck-converter using a thin-film inductor

We have developed a compact buck-converter using a thin-film inductor that is suitable for portable electronic equipment. The inductor consists of planar Cu coils and CoZrTa magnetic layers on a Si substrate; it is fabricated by a dry process. The converter is 3 mm thick and 10/spl times/6 mm in area; it operates at 1.6 MHz and has an efficiency of up to 85%.

Well-defined uniaxial anisotropy in iron film formed by ion beam sputtering

This paper reports on the results of an experimental investigation into the magnetic properties of iron films formed by ion beam sputtering. Through the iron film formation at various nitrogen partial pressures and substrate angles, nitrogen ion bombardment is found to reduce the coercive force of the magnetic hard axis in addition to inducing uniaxial anisotropy. The decrease in the coercive force corresponds well to the increase in the nitrogen concentration and the anisotropy constant of the α‐Fe‐composed films. The uniaxial anisotropy is confirmed to mainly result from directional ordering rather than crystalline anisotropy. The magnetic properties of the film having well‐defined uniaxial anisotropy are a coercive force of 0.3 Oe, a saturation magnetization of 2.2 T, an anisotropy field of 3.5 Oe, and a permeability of 5000.

Magnetic properties of ion beam sputtered Co-Zr and Co-Zr-Re amorphous films

In this paper, the optimum deposition conditions of amorphous Co-Zr films fabricated by ion beam sputtering and their magnetic properties are investigated. The amorphous state is achieved at a low Zr content ( near 5 - 10 at% ) and is dependent on the substrate temperature. Co-Zr alloy films with a Zr content of 4.5 at% become amorphous on a -130 °C substrate, whereas a Zr content of more than 6 at% is necessary to obtain amorphous films on a 40 °C substrate. The resistivity of the films increases monotonically with Zr content or as the substrate temperature decreases from +300 °C to -130 °C. It is shown that the addition of a small amount of Re to the films decreases magnetostriction, although it lowers saturation magnetization slightly. A magnetostriction value of less than 10-7is obtained when 2 to 3 at%Re is added to the Co-Zr films with a 6 to 8 at%Zr. Ion beam sputtered Co-6 at %Zr-2at% Re in 1 to 3 μm thick amorphous films exhibits the following excellent properties: a saturation magnetization of more than 13 kG, a permeability at 10 MHz of more than 5000, and a Vickers hardness of over 700.

Ion bombardment effect on preferred orientation in Ni–Fe film formed by ion beam sputtering

This paper reports on the results of experimental investigation into the preferred orientation of Ni–Fe film formed by ion beam sputtering. Through experiments concerning ion bombardment and substrate temperature, argon ion bombardment is found to increase the amount of the (111) crystal texture in addition to contributing to the texture orientation itself. In terms of film morphology, the fracture cross section indicates a more obvious columnar structure with the film surface becoming slightly rougher as the amount of argon ion bombardment increases. Conversely, nitrogen and oxygen‐mixed ion bombardment weakens the (111) preferred orientation, and the effect becomes more notable when the ion has a higher energy. On the other hand, although the substrate temperature increase makes the (111) texture better oriented, the amount of the crystal texture becomes smaller due to this temperature increase. Additionally, the observed lattice distortion corresponds well to that estimated by the internal stress.

Characterization of hydrogen and oxygen atoms in SiN films produced by plasma‐enhanced reactive sputtering

Silicon nitride films are prepared by helium‐excited magnetron radio‐frequency sputtering. Excitation energy transfer from He to N2 and existence of hydrogenation and oxidation source (O+ and OH⋅) in the plasmas are confirmed by optical emission spectroscopy. The structure and characteristics of the resultant films depend on the gas pressure during sputtering: Films produced at pressures above 5 Pa are etched rapidly in a buffered hydrogen fluoride solution and have low refractive indices because their structure is coarse and rich in oxygen and hydrogen or both.

CoZrRe amorphous film heads for high-density magnetic recording

CoZrRe amorphous film heads with superior performance have been developed for use in high-density magnetic recording. These films produce near-zero magnetostriction of less than +2.5*10/sup -7/ and saturation magnetization of 1.2 T. It is found that the addition of a small amount of Re to CoZr markedly improves the stability of magnetic properties during head fabrication. However, the process temperature must be less than 200 degrees C. To realize the required temperature, a dry process is developed, using sputtered SiO/sub 2/ films for insulation instead of conventional hard-cured photoresist. A maximum process temperature of about 150 degrees C is obtained As a result, a high linear density of more than 2100 fr/mm (53 kfci) at a spacing of 0.1 mu m is achieved using CoZrRe film heads and metal-sputtered media with a coercivity of 1300 Oe. >

Magnetic properties of CoZr amorphous films prepared by low energy ion beam sputtering

In this paper, magnetic properties of CoZr amorphous films prepared using low-energy ion-beam sputtering are investigated by varying the accelerator voltage and beam current of a single-grid ion-beam sputtering system. It is shown that CoZr films become amorphous with a lower Zr content when the films are prepared with lower accelerator voltage or lower ion-beam current. It is also clarified that the saturation magnetostriction constant of amorphous CoZr film becomes smaller as the Zr content becomes smaller ; a film with a Zr content of approximately 3.3at% has a magnetostriction constant of zero without adding a third element such as Nb, Ta or Re. CoZr amorphous films with a saturation magnetization of more than 1.5T, a coercive force of less than 0.2Oe and a magnetostriction constant of zero could be obtained using low-energy ion-beam sputtering with an accelerator voltage of less than 300V.

Thin‐film formation using single‐grid ion‐beam sputtering

This paper discusses fundamental characteristics of a single‐grid ion‐beam sputtering system as well as indicating the optimum aperture dimensions and transparency of a grid. With an optimum thickness and aperture size, a high deposition rate of over 90 nm/min and a grid lifetime of over 10 h were obtained at an accelerator voltage of <600 V. The effect of the accelerator voltage or the beam current on the thin‐film properties were investigated and it was clarified that films prepared with a lower accelerator voltage or lower beam current are likely to become amorphous.