Development of a MAGLEV superconducting magnet for the Yamanashitest line in Japan: vibration characteristics and analysis for design

A high-performance and high-reliability magnetically levitated (MAGLEV) superconducting magnet (SCM) was developed. Its heat generation per unit time by the electromagnetic forces due to the spatially fifth ripple magnetic fields from levitation coils is under 2 W at the frequency range in which vehicles are levitated. The vibration mode of inner vessels that makes the largest contribution to heat generation in SCMs is clarified, the torsion mode. A modeling method to analyze SCM vibration, which considers the effect of the bogie frames of a vehicle, is examined, and heat generation in SCMs is calculated from the vibration of the inner vessel. Using the numerical analysis method, new SCMs combined with new bogie frames for the Yamanashi Test Line are designed. Good performance in vibration and heat generation of these SCMs is predicted by numerical analysis     

A 1.9-GHz Si-bipolar variable attenuator for PHS transmitter

A 4-dB step 28-dB variable attenuator for 1.9 GHz personal handy-phone system (PHS) transmitter was fabricated using silicon bipolar technology with f_T of 15 GHz. Step accuracy within 1.2 dB and total vector modulation error of less than 4% are realized for -15 dBm output. The attenuator consumes 21 mA with 2.7-V power supply and occupies 1.1 mm×0.5 mm     

High-reliability and low-dark-current 10-Gb/s planar superlatticeavalanche photodiodes

For compact and high-sensitivity 10 Gb/s optical receiver applications, we have developed low-dark-current planar-structure InAlGaAs-InAlAs superlattice avalanche photodiodes with a Ti-implanted guard-ring. The APDs exhibited dark current as low as 0.36 μA at a gain of 10. The temperature dependence of the dark current was confirmed to be in a sufficient level for practical 10-Gb/s applications. The APDs also exhibited a quantum efficiency of 67%, a gain-bandwidth-product of 110 GHz, a top 3-dB bandwidth of 15.2 GHz, and a minimum gain for 10-GHz bandwidth of 1.6. Preliminary aging test also showed a stable dark current operation after aging of over 2200 h at 200°C. These high-reliability, low-dark-current, high-speed, and wide-dynamic-range characteristics are promising for 10-Gb/s high-sensitivity optical receiver use     

The growth of (InGa)As quantum wells on GaAs(111)A, (211)A and (311)A substrates

The ability to grow high quality (InGa)As on the (111)A surface is essential for the production of a wide range of optoelectronic devices, but the topic has so far received little attention. What work there has been shows it to be highly problematic, reflected in the very broad photoluminescence (PL) peaks observed for GaAs:(InGa)As multiple quantum well structures. The origin of this broadening is unclear but is certainly related to the difficulty in choosing appropriate conditions for the growth of III-Vs on the (111)A surface. We have undertaken a study of the growth of (InGa)As on the GaAs(111)A, (211)A and (311)A surfaces with the goal of achieving high quality quantum well structures, the test being the ability to obtain narrow PL line widths. We have demonstrated that 80 Å 15% InGaAs(111)A single quantum wells with 12K PL peak widths of less than 8 meV can be obtained by growth at 400°C under a V:III ratio of 5:1.     

Numerical Analysis of the Boundary Scattering Effect on Transport Properties in Bi-Sb Nanowires

In this study, we have numerically analyzed the transport properties of Bi-Sb nanowires, taking into account wire boundary scattering. Wire boundary scattering slightly decreased the Seebeck coefficient of Bi-Sb nanowires. This effect is due to the observation that boundary scattering and the mobility ratio of L-point electrons to T-point holes in the nanowires are smaller than those in bulk Bi-Sb because the wire boundary scattering suppresses the mobilities of L-point electrons and heavy holes. The largest Seebeck coefficient for all wire diameters was obtained when the Sb concentration was 5 at.%. The effective mass approached zero near 5 at.% Sb, and the small effective mass led to a large subband shift in each band. Thus, a small effective mass enhances the quantum effect at a fixed wire diameter, even if wire boundary scattering is taken into account.     

A Quaternary van der Waals Ferromagnetic Semiconductor AgVP2Se6

The recent realization of 2D magnetism in van der Waals (vdWs) magnets holds promise for future information technology. However, the vdWs semiconducting ferromagnets, which remain rare, are especially important in developing 2D magnetic devices with new functionalities due to the possibility of simultaneous control of the carrier charge and spin. Metal thiophosphate (MTP), a multifunctional vdWs material system that combines the sought‐after properties of complex oxides, is a promising vdWs magnet system. Here, single crystals of a novel vdWs ferromagnetic semiconductor MTP AgVP₂Se₆ with a room‐temperature resistivity of 1 Ω m are successfully synthesized. Due to the nature of vdWs bonding along the c‐axis, the magnetic properties of the few‐layer AgVP₂Se₆ with different thicknesses are characterized on the exfoliated samples. The AgVP₂Se₆ flakes exhibit significant thickness‐dependent magnetic properties, and a rectangular hysteresis loop with a large coercive field of 750 Oe at 2 K and an undiminished Curie temperature of 19 K are observed in the 6.7 nm AgVP₂Se₆ flake. The discovered vdWs ferromagnet AgVP₂Se₆ with semiconducting behavior will provide alternative platforms for exploring 2D magnetism and potential applications in spintronic devices.     

Stoichiometry Control for the Tuning of Grain Passivation and Domain Distribution in Green Quasi‐2D Metal Halide Perovskite Films and Light‐Emitting Diodes

Quasi‐2D metal halide perovskite films are promising for efficient light‐emitting diodes (LEDs), because of their efficient radiative recombination and suppressed trap‐assisted quenching compared with pure 3D perovskites. However, because of the multidomain polycrystalline nature of solution‐processed quasi‐2D perovskite films, the composition engineering always impacts the emitting properties with complicated mechanisms. Here, defect passivation and domain distribution of quasi‐2D perovskite films prepared with various precursor compositions are systematically studied. As a result, in perovskite films prepared from stoichiometric quasi‐2D precursor compositions, large organic ammonium cations function well as passivators. In comparison, precursor compositions of simply adding large organic halide salt into a 3D perovskite precursor ensure not only the defect passivation but also the effective formation of quasi‐2D perovskite domains, avoiding unfavorable appearance of low‐order domains. Quasi‐2D perovskite films fabricated with a well‐designed precursor composition achieve a high photoluminescence quantum yield of 95.3% and an external quantum efficiency of 14.7% in LEDs.     

Comparisons of computed mobile phone induced SAR in the SAM phantom to that in anatomically correct models of the human head

The specific absorption rates (SAR) determined computationally in the specific anthropomorphic mannequin (SAM) and anatomically correct models of the human head when exposed to a mobile phone model are compared as part of a study organized by IEEE Standards Coordinating Committee 34, Sub-Committee 2, and Working Group 2, and carried out by an international task force comprising 14 government, academic, and industrial research institutions. The detailed study protocol defined the computational head and mobile phone models. The participants used different finite-difference time-domain software and independently positioned the mobile phone and head models in accordance with the protocol. The results show that when the pinna SAR is calculated separately from the head SAR, SAM produced a higher SAR in the head than the anatomically correct head models. Also the larger (adult) head produced a statistically significant higher peak SAR for both the 1- and 10-g averages than did the smaller (child) head for all conditions of frequency and position.     

A 1.5-V full-swing BiCMOS logic circuit

A BiCMOS logic circuit applicable to sub-2-V digital circuits has been developed. A transiently saturated full-swing BiCMOS (TS-FS-BiCMOS) logic circuit operates twice as fast as CMOS at 1.5-V supply. A newly developed transient-saturation technique, with which bipolar transistors saturate only during switching periods, is the key to sub-2-V operation because a high-speed full-swing operation is achieved to remove the voltage loss due to the base-emitter turn-on voltage. Both small load dependence and small fan-in dependence of gate delay time are attained with this technique. A two-input gate fabricated with 0.3-μm BiCMOS technology verifies the performance advantage of TS-FS-BiCMOS over other BiCMOS circuits and CMOS at sub 2-V supply