Kazuyuki Ozaki

Planar patterned media fabricated by ion irradiation into CrPt3 ordered alloy films

Planar patterned media using CrPt3 ordered alloy films were fabricated by Ar+ or Kr+ ion irradiation through nanoimprinted or electron beam lithography made masks. CrPt3 ordered alloy film on fused quartz substrate exhibits a large perpendicular anisotropy of 5×106 erg/cc and a large coercivity of 12 kOe, and we found that its magnetic order (magnetization) was completely suppressed by a quite low Ar+ or Kr+ ion dose of about 1–2×1014 ions/cm2. Magnetic force microscope image of the ion-beam patterned CrPt3 with a bit size of 90×90 nm showed clear magnetic contrast in nonirradiated regions, while no magnetic contrast in irradiated regions. The read-back waveform taken from an ion-beam patterned CrPt3 disk with 600 nm patterning pitch showed sharp signal transition between irradiated and nonirradiated regions, which indicates the possibility of high-density planar patterned media using CrPt3 ordered alloy.

Fluctuation field and time dependence of magnetization in TbFeCo amorphous rare earth-transition metal thin films for perpendicular magnetic recording

In this work we report on the experimental analysis of the time decay of magnetization in the films of amorphous TbFeCo alloys for perpendicular magnetic recording. It is shown that the experimental results can be explained on the basis of the thermally activated incoherent subnetwork magnetization reversal model. Thermally activated reversal of the transition metal subnetwork and associated reversal of the antiferromagnetically coupled rare-earth subnetwork may result in effective stabilization of the net film magnetization. Experimentally obtained activation diameter value Da∼5–6 nm corresponds to the exchange length or the domain wall width in the films under study. The small activation diameter value combined with high stability factor k∼250 mean that the TbFeCo amorphous film should be capable of supporting a thermally stable perpendicular recording at over 100 Gbit/in2 recording density.

Novel optical probing system with submicron spatial resolution for internal diagnosis of VLSI circuits

In this paper, we introduce a novel optical probing system for the internal diagnosis of VLSI circuits. Based on an electro-optic sampling technique, this probing system achieved a sub-/spl mu/m spatial resolution by utilizing the scanning force microscopy technique. The optical sampling pulse width was 30 ps, and the minimum detectable voltage was as small as 10 mV. In an atmospheric environment this system can measure internal signal waveforms of VLSI circuits much faster than electron-beam testers.

Phase and intensity control of multiple coil currents in resonant magnetic coupling

We studied the effects of the phase and intensity of multiple coil currents in a wireless power transfer system using resonant magnetic coupling. Resonant magnetic coupling is regarded as one of the most promising methods for mid-range wireless charging systems. For mid-range charging, the charging device can assume various positions and postures, and some of the conditions make wireless charging difficult. To solve this problem, we propose a method to control the phase and intensity of multiple coil currents. By performing numerical simulations using an equivalent circuit model and electromagnetic analysis, we confirmed that it had the desired effect.

Epitaxial growth of HgCdTe on sapphire for photoconductive detectors

Abstract We used a combination of isothermal vapor phase epitaxy (ISOVPE) and liquid phase epitaxy (LPE) to grow HgCdTe on a CdTe/sapphire substrate by metal organic chemical vapor deposition (MOCVD). ISOVPE was used to convert a CdTe layer to Hg 0.8 Cd 0.2 Te. The ISOVPE and LPE processes were consecutive and performed in a closed tube. Using the conversion process, the lattice mismatch between CdTe and HgCdTe decreases. The conversion also reduces the compositional gradient caused by interdiffusion between the CdTe substrate and the epitaxial layer. After annealing the wafer in a Hg atmosphere, performance as a photoconductive detector was used to examine the wafer quality. The results are comparable to the performance of conventional detectors made of LPE-grown HgCdTe on CdZnTe.

Millimeter-wave beam multiplexing method using hybrid beamforming

A millimeter-wave beam multiplexing method using a hybrid beamforming is proposed. We theoretically show that inter-subarray coding at the subarray type interleaved configuration can reduce interference and multiple beams of the same high gain as the full connection type. The condition that a hybrid beamforming of the subarray type can create the multiple high gain beams is clarified. For the case of beam multiplexing, the interleaved configuration with inter-subarray coding is confirmed to be robust for interference increasing by errors of beam direction estimation. Therefore, we think that the interleaved configuration is suitable for millimeter-wave beam multiplexing.

Magnetic Recording on Magneto-Optical Media Using Merge Type Giant Magneto-Resistive Head.

TbFeCo media for perpendicular magnetic recording were developed by employing a NiP underlayer that controls the magnetic properties of a TbFeCo magnetic layer. Dynamic write-read characteristics were examined using a conventional merge-type giant magneto-resistive (GMR) head originally designed for longitudinal magnetic recording. A clear magnetic transition of 450 kFCI (kilo Flux Change per Inch), a high media signal-to-noise ratio (SNR), and acceptable overwrite properties were obtained by optimizing the magnetic properties of TbFeCo films. The thermal stability of a written bit in TbFeCo film is sufficient for practical application.

System validation of millimeter-wave beam multiplexing with interleaved hybrid beam-forming antennas

This paper describes beam division multiplexing at millimeter wave band using interleaved hybrid beam-forming (BF) antennas. The antenna elements are located alternately to make narrow beam-width of about 5 degrees, and the user multiplexing calculation on the digital signal processing part can suppress the undesired grating-lobe. The authors manufacture the interleaved hybrid beamforming antennas at 60GHz, and conduct antenna beam pattern measurements and transmission experiments. The measurement results show the desired-undesired ratio of 18dB after the suppression of the grating lobe by digital weight multiplication, and show good communication performance from the results of received constellation patterns of OFDM 16QAM modulation scheme.

Zone division model for capacity analysis in multi-hop data acquisition systems with hidden nodes

Data acquisition systems play an important role in several industries. Because highly scalable ad-hoc networks with multi-hop transmissions can be easily constructed at low cost, such networks are considered suitable for data acquisition systems. However, a lack of centralized control makes it difficult to respond to congestion when system capacity is exceeded. Therefore, the estimation of system capacity is a critical issue for system design. In this paper, we propose a novel zone division model to analyze the capacity of multi-hop data acquisition systems using Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocols. We divide the one-hop area to a gateway (GW) into two zones: (1) an outer zone where an access node (AN) can relay packets from multi-hop ANs; and (2) an inner zone where ANs cannot relay packets. Using this approach, we calculate packet loss for each zone, considering the difference in the communication range of the GW and ANs, as well as the collision with hidden nodes. Simulation results show that our model achieves higher estimation accuracy than conventional methods, indicating that we have successfully modeled phenomena of the real system more accurately.

Electron Beam (EB) delay tester

Abstract We have developed an EB delay tester for high-speed, high-accuracy measurement of the delay time between I/O pins of LSIs. In order to replace the measured LSI in the air, the LSI is placed on a multilayer board and measurement terminals on the back of the board are put in vacuum. For high-speed and high-accuracy measurement, we made an EB column with a large EB current of 100 nA and designed measuring technique based on binary search and feedback. The parameters of all measurement terminals are registered in advance to compensate position-dependence of the s-curve. Because these parameters are affected by EB current and vary over time, they are calibrated just before the edge timing measurement. Its measuring time is 168 ms and measurement accuracy is 56 ps when specified time resolution is 50 ps and repetition rate is 2.5 MHz.