Yasuhiro Tosaka

Magnetooptical Kerr Spectrometer for 1.2-5.9 eV Region and its Application to FePt/Pt Multilayers

The apparatus for measurement of magnetooptical spectra using a polarization modulation technique has been improved to extend the short-wavelength limit to about 200 nm in the ultraviolet range. Short-wavelength characteristics of the light source, the focusing system including mirrors and lenses, the monochromator, the polarizer and the analyzer were improved. The techniques of calibration for Kerr rotation and ellipticity were also refined. With the use of the newly designed system, the magnetooptical Kerr rotation and Kerr ellipticity of FePt/Pt multilayers, as well as of FePt alloys of different compositions were evaluated for photon energies between 1.2 and 5.9 eV.

Fundamental studies and application of short-wavelength magneto-optical effect in Pt-based multilayers

Abstract Recent trends in the research and development to realize higher recording densities in magneto-optical (MO) disk systems are briefly reviewed, with particular emphasis on the importance of developing the short-wavelength media. A brief review of Pt-based multilayers for MO recording is given, and fundamental MO properties in Pt/Fe, Pt-Co and Pt/NiCo multilayers are discussed in detail based on our studies of MO spectra for the wide-wavelength region.

Magnetic polarization of interfacial Pt in FePt/Pt multilayers witnessed by magneto-optical spectra

Magneto-optical spectra in FePt(x A)/Pt(50 A) multilayers prepared by the ion-beam sputtering technique were measured between 1 and 6 eV. Simulation by the virtual optical constant method, assuming the existence of a magnetic Pt layer at the interface, provided a fairly good explanation of the x-dependence of the magneto-optical spectra. The magnetic coupling between FePt and Pt was found to be antiparallel for x ≥ 50 and parallel for x < 50.

Magneto-optical spectra in Co-based multilayers

Abstract Magneto-optical spectra of Pd/Co multilayers were measured between 1.2 and 5.9 eV, from which the off-diagonal elements of the conductivity tensor were deduced and were compared with those of Pt/Co multilayers.

Silicon Nitride Final Passivation for GaAs Metal Semi-Conductor Field Effect Transistors (MESFETs) Packaged in Plastic Mold

A highly reliable SiNx final passivation film for GaAs metal semi-conductor field effect transistor (MESFETs) packaged in plastic mold has been developed. The addition of He to N2 for the carrier gas in plasma enhanced chemical vapor deposition (PE-CVD) has been found effective to reduce both stress and pinholes and to significantly improve the resistance to moisture of the SiNx film. Rutherford back scattering (RBS), hydrogen forward scattering (HFS) and FT-IR analyses demonstrated that the SiNx with less pinhole has fewer hydrogen atoms in the film. Regarding the FETs housed in the SOT-89 mold package, no failure was observed up to 1000 h in the 85°C–85% relative humidity (RH) reverse bias test.

Magnetooptical Spectra in Pt-Ni Alloys and Multilayers

Pt-Fe, Pt-Co and Pt-NiCo alloys and multilayer films were prepared on a SiO2 substrate by the dc magnetron sputtering technique. The reflectivity spectra and magnetooptical Kerr spectra of these specimens were measured, and the diagonal and off-diagonal elements of the conductivity tensor were deduced. The results of this work are as follows: (1) The peak energy position of the magnetooptical Kerr rotation spectra showed a systematic shift to lower energies as the transition metal was changed from Fe to Ni, both in multilayer and alloy samples. (2) Simulation using the above-determined conductivity tensor for alloys revealed that alloy layers exist at the interfaces between Pt and the transition metal in all the Pt-based multilayer films investigated. (3) Obvious effects of plasma enhancement were confirmed in the short-wavelength magnetooptical Kerr spectra of the Pt-based alloys.

Highly-reliable and reproducible InGaAs/InP double heterojunction bipolar transistor utilizing all-wet etching process for triple mesa formation

The authors have succeeded in making a robust fabrication process applied to InP-based double heterojunction bipolar transistors. The process, featuring all-wet etching method for formation of triple-mesa structure, has shown markedly high reproducibility and reliability. The variation of the current gain has been 4.6% through 130 wafers, and the mean time to failure at the junction temperature of 100°C has been longer than 4 × 106 hours, whose criterion is a 5% change in current gain. These excellent results show that our structure of DHBT, which has an InP passivation layer on the surface of the base layer, and our all-wet mesa formation process, are sufficient to be applied to the manufacturing of integrated circuits.