Daisuke Miyauchi

Design and analysis of micromechanical tunable interferometers for WDM free-space optical interconnection

This paper proposes a new concept of high density chip-to-chip optical interconnection based on wavelength division multiplexing (WDM), which can be realized as a microelectromechanical system (MEMS) device. The output signals from a preprocessing integrated circuit (IC) chip (N channels) are converted to optical signals of different wavelengths by using wavelength tunable laser diodes and projected onto an array of wavelength-selective photodiodes. Channel connection is made by wavelength matching between the light sources and detectors, by using micromechanical Fabry-Perot interferometers. In this scheme arbitrary 1 to 1 connection as well as 1 to N or N to 1 connection is available. Since the input/output connections are made in an optical manner, the switching state can be reconfigured and the whole switching system can be integrated in a compact space. We have investigated design principle of the micromechanical Fabry-Perot interferometers for tunable photodiodes to maximize the switching contrast and channel density in a given wavelength range. The preliminary interferometer arrays are implemented by silicon-based surface micromachining.

An out-of-plane polysilicon actuator with a smooth vertical mirror for optical fiber switch application

Micromachined optical switches are under intensive study for optical communication networks. Some of them require special high aspect-ratio technologies such as LIGA and deep RIE. Some are a few millimeters in size. We have designed a 2/spl times/2 micro optical switch which is micro-meters in size, fully micromachined except for one step, and has a simple mechanism because of electrostatic actuation.

Transport and Magnetic Properties of CPP-GMR Sensor With CoMnSi Heusler Alloy

We investigated structural and magnetic properties of CoMnSi (CMS) Heusler alloy films and giant magneto-resistance (GMR) ratio of current-perpendicular-to-plane (CPP) GMR sensor elements. The films were deposited with magnetron sputtering method and annealed at 673 K and 773 K. The CMS films were identified as B2 structure by using X-ray diffraction and the magnetization of the films were evaluated as 0.95 T. We fabricated the CPP-GMR sensors varying the composition of the CMS films, Co48 Mn21 Si31 (at. %) as Si-rich CMS and Co51Mn25Si24 (at. %) as CMS-ref, having a FeCo layer between the CMS and Cu spacer. It was found that the element with Si-rich CMS exhibited higher GMR ratio of 9.0% than that with CMS-ref. Our calculations indicate that larger spin polarization of contact region between the CMS film and the FeCo film relates to larger GMR ratio.

Linearity and hysteresis in the magnetoresistive response of (NiFe,NiFeCo)/Cu and Co/Cu/NiFe multilayers in patterned stripes

The linearity and hysteresis in the magnetoresistive (MR) response of NiFe/Cu and NiFeCo/Cu multilayers prepared by ion beam sputtering, and Cu/Co/Cu/NiFe multilayers prepared by MBE are investigated. These characteristics in the linear regions for the second peak of antiferromagnetically coupled NiFe/Cu multilayers are almost the same as those of NiFeCo/Cu ones at 50‐Hz ac applied fields. The MR amplitude at the first peak is inferior to that at the second one, whereas, the linearity and hysteresis are superior. In weakly coupled Cu/Co/Cu/NiFe multilayers, a nonhysteretic MR response is obtained at a NiFe layer thickness of 10 A. The linearity and symmetry around the zero magnetic field of the MR curve depend on the Cu layer thickness. When the thicknesses of the NiFe and Cu layers are 10 and 45 A, respectively, good linearity and no hysteresis are observed without biasing techniques. The output levels in the linear regions of three different multilayers are 1.5–2.5 times as large as that of the conventi...

Cluster Size and Shape Effects on Giant Magnetoresistance of Evaporated Co-Ag Alloy Films

Magnetoresistive (MR) and magnetic properties of Co-Ag alloy films evaporated in ultrahigh vacuum were studied. The measured MR ratios were 24.7% at room temperature (RT) for Co40Ag60 (at%) alloy film and 48.6% at 77 K for Co32Ag68 alloy film. In addition, the MR profile shows an anistropy between two applied field directions, transverse and normal to the current in plane. This anisotropy is caused by the pancake-shaped Co clusters.

Magnetoresistance properties of Cu/Co/Cu/NiFe multilayers with a few stacking numbers

[Cu/Co/Cu/NiFe]N multilayers were prepared using electron-beam evaporation in an ultrahigh vacuum and their magnetoresistive (MR) properties with a few stacking numbers (N) were studied. The N dependence of the MR property was affected by the magnetic layer thickness. In the range of N2, a thick magnetic layer was required to obtain a large MR ratio. In the multilayer of Cr(50 A)/NiFe(50 A)/Cu(50 A)/Co(50 A)/Cu(50 A)/NiFe(50 A) (N=1.5), the MR ratio of 5.6% and the MR slope of 0.5%/Oe were obtained.

Micromechanical fiber optic switches based on electromagnetic torsion mirrors

Summary form only given. Micromachined optical switches are under intensive study for data communication networks and measurement instruments. We have demonstrated electrostatic micro torsion mirrors for fiber optic switches. However, the electrostatic operation required large operation voltage. On the other hand the magnetic operation is expected to realize self-latching optical switches, which hold on/off-state without power consumption. We study the magnetic operation of NiFeCo sputterd torsion mirrors.

Thermal Stabilities of Cu/Co/Cu/NiFe Multilayers

Cu/Co/Cu/NiFe multilayer films prepared by evaporation deposition in an ultrahigh vacuum were heat-treated in air and in ultrahigh vacuum. Heat treatment in ultra-high vacuum brought about no changes in the MR ratio or MR slope for annealing temperatures less than 400C. The thermal stability in air was limited by gradual oxidation from the surface, and thermal stability up to 250°C was verified. Improved thermal stability was achieved by the use of thicker NiFe layers.

Giant magnetoresistance in induced ferrimagnetic multilayers grown by MBE

Induced ferrimagnetic Cu/(Co,CoNi,CoFe)/Cu/NiFe multilayers were prepared by E-beam evaporation in molecular beam epitaxy system and showed giant magnetoresistance. It is confirmed that weak interlayer magnetic interacuon works between soft and hard magnetic layers. The output voltage was roughly estimated as twice and a half as that of conventional NiFe element in an ac magnetic field of 50 Hz. Thermal stabilities were verified for the Cu/Co/Cu/NiFe multilayers for more than 400 in heat treatment in vacuum and 250°C in air.