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We focused on a focused ion beam (FIB) technology, called nitrogen gas field ion source FIB (N2 GFIS-FIB), which can etch directly at the 10 nm level or finer. We performed single line etching of Nb thin film microbridges deposited by N2 GFIS-FIB and fabricated Josephson junction (JJ) devices. The microbridge area was separated into two parts by the processing line, whose width was around 20 nm. We performed electrical characterizations of the devices at low temperature and observed typical behaviors of JJ devices, such as a superconducting current region and current jumping to the normal current region in some of the deeply etched devices. We also observed an AC resistance oscillation in some of the shallowly etched devices. The oscillation may be due to a sub-harmonic gap structure that originates from Andreev reflection. These results indicate that simple single line etching of Nb by N2 GFIS-FIB can form JJ devices.

We demonstrated epitaxial growth of magnesium oxide (MgO) on silicon (Si) substrate with cubic on cubic structure [MgO(001) // Si(001) and MgO(100) // Si(100)]. Epitaxial films were prepared by using pulsed laser deposition method, and with dependent on deposition conditions of oxygen partial pressure and substrate temperature, the lattice constants of MgO decreased along both surface normal and in-plane directions. To support the facts of (1) constriction of lattice constants and (2) cubic on cubic growth, we show (1) optimal lattice constants with defects in crystal structure, (2) domain mismatch between MgO and Si instead of lattice mismatch, and (3) stability of MgO crystal on the surface of Si substrate.

Field-plate trench MOSFETs (FP-MOSFETs), with the features of ultralow on-resistance and very low gate–drain charge, are currently the mainstream of high-performance applications and their advancement is continuing as low-voltage silicon power devices. However, owing to their structure, their output capacitance (Coss), which leads to main power loss, remains to be a problem, especially in megahertz switching. In this study, we propose a structure-based capacitance model of FP-MOSFETs for calculating power loss easily under various conditions. Appropriate equations were modeled for Coss curves as three divided components. Output charge (Qoss) and stored energy (Eoss) that were calculated using the model corresponded well to technology computer-aided design (TCAD) simulation, and we validated the accuracy of the model quantitatively. In the power loss analysis of FP-MOSFETs, turn-off loss was sufficiently suppressed, however, mainly Qoss loss increased depending on switching frequency. This analysis reveals that Qoss may become a significant issue in next-generation high-efficiency FP-MOSFETs.

Simultaneous switching noise and electromagnetic radiation in electronic systems are becoming serious problems with the increase in operating speed of digital circuits. Recently, it was recognized that LSI chips are primary sources of electromagnetic radiation. This paper presents experimental results using two types of test chips, one with and one without an on-chip decoupling capacitor. The effects of the on-chip decoupling capacitor on radiated emission and simultaneous switching noise were characterized by activating I/O circuits or core logic circuits. More than 5 dB of electromagnetic radiation were reduced with the implementation of the on-chip decoupling capacitor for core logic operation.

The possibility has been indicated that polymers with helical chirality, such as poly-L-lactic acid (PLLA), show a large optical rotatory power ρ (about 9600 deg/mm: J. Kobayashi et al., J. Appl. Phys. 77 (1995) 2957) or piezoelectric constant in their fiber axial direction (helical chain direction). To attempt the realization of a new optical or piezoelectric active polymer device, we fabricated the PLLA on a basal plate using end-grafted polymer technology. The structure of PLLA on a basal plate was observed by atomic force microscopy. As a result, we found that the PLLA on a basal plate with annealing grows into have a needle-like structure. The roughness of the aggregate PLLA on a basal plate is 12.5 nm. ρ of the PLLA on a basal plate is about 80 deg/mm. This ρ value is larger than that of the quartz crystal which is a very well-known crystal with high optical activity. We speculated, on the basis of Kobayashi et al.'s report, that the helical chain direction of the PLLA on a basal plate obtained in this study is not perpendicular to but has a fixed angle to the surface of the basal plate.

We developed a testing method to determine the influence of dust adhesion on digital versatile disk (DVD). First, the dust testing system was developed. This system can control the dust density with an accuracy of ±20%. Second, the dust testing method was investigated. Reflectivity and jitter deteriorated gradually, making it easy to estimate the readability and lifetime of DVD. The system, testing procedure, and estimation indexes are adequate for the DVD dust test. Dust adhesion was observed. Dust particles adhere along the airflow direction and accumulate to 100 µm thickness. Third, in order to discuss the difference in readability between disks of 0.6 mm and 1.2 mm substrate thicknesses, the dust test was performed for DVD and compact disk (CD). It was found that the normalized reflectivity of DVD is 7% smaller than that of CD after 100 h exposure.

Doppler particle sizing by self-mixing laser was demonstrated by using a laser-diode-pumped thin-slice Nd:GdVO4 laser with extreme optical sensitivity. A substantial improvement of optical frequency shifters led to quick and accurate sizing of Brownian particles with concentration as low as 50 parts per billion (ppb) for 262-nm polystyren latex spheres in water. A successful real-time measurement of sub-nanometer vibrations was also demonstrated with the present self-mixing laser.

We developed a micro-area X-ray diffraction system using a sub-µm X-ray beam of 10 keV energy that was produced by a phase zone plate made of tantalum. Using this system, we were able to measure the lattice strain distribution in InGaAsP metalorganic vapor phase epitaxial layers selectively grown on InP stripe regions a few µm in width between a pair of SiO2 mask stripes, with strain sensitivity of about 1×10-4. We found that the strain distribution in a 3-µm-wide stripe layer is almost completely uniform, while that in a 4-µm-wide layer is not.

Electron doping into Cd3TeO6 with a 1:1 ordered perovskite-type structure was carried out by two methods: the introduction of oxygen vacancies, and the atomic substitution of In for Cd. Both methods turned polycrystalline samples into metallic conductors while single crystals with metallic conductivity were obtained by the second method. The resistivity and thermoelectric power of the single-crystal indium-substituted sample were 0.6 mΩcm and -50 µVK-1, respectively, giving a power factor of 4×10-4 WK-2m-1, which is the highest among nontransition metal oxides.

Crystal growth of radial p–i–n InP nanowires (NWs) with InAsP quantum well (QW) layers by metalorganic vapor-phase epitaxy was studied, and vertical NW light-emitting devices were fabricated. Radial p–i–n NWs were formed using position-controlled n-type InP NW cores. By optimizing the flow rates of the Zn source, Zn-doped p-type InP shells were grown on the sidewall of the radial QW structures while maintaining the photoluminescence intensity of the QWs. The fabricated devices showed current rectification originating from the p–i–n diode structures. Electroluminescence from the radial QWs was clearly observed in the 1.5-µm-wavelength region at room temperature for the first time.

Diamond-like carbon (DLC) has been applied as a coating material to improve the basic properties of strength, chemical stability, and biocompatibility. In this study, a DLC film was prepared on a titanium (Ti) coating film with tetramethylsilane (TMS) buffer for application in vivo. Although the surface roughness of the Ti film increased with increasing Ti thickness, both TMS and DLC coatings deposited on Ti films resulted in the formation of a flat surface. Observation of the initial growth of the TMS layer indicated that a TMS buffer of more than 50 nm thickness was required for DLC coating even on the flat surface of the Ti thin film.

The internal quantum efficiency (IQE) of three types of InGaN-based near-UV light-emitting diodes (LEDs) grown on different substrates was studied by excitation-power-density-dependent and temperature-dependent photoluminescence (PL) spectroscopy. IQE was evaluated under both the band-to-band excitation of GaN cladding layers and the selective excitation of InGaN active layers. A correlation between IQE and threading dislocation density was clearly observed under both excitation conditions. In addition, the dynamics of radiative and nonradiative recombinations was studied by time-resolved PL spectroscopy. The rate of nonradiative recombination was evaluated by measuring temperature-dependent nonradiative recombination lifetime. The validity of our method for estimating IQE is discussed on the basis of the correlation between IQE and nonradiative recombination rate for three LEDs with different threading dislocation densities.

A low operation voltage of only 1 V at 10 mW was achieved for 1.5 µm wavelength active multi-mode-interferometer laser diodes (MMI-LDs) due to a significant reduction in resistance of 60% compared with that of conventional LDs. We also investigated the dynamic characteristics of the MMI-LDs. Although there was concern that current modulation might cause changes in refractive index, thus, deteriorating self-imaging properties, stable 1 Gbps operation without jitter and improved roll-off frequency due to the low resistance were confirmed experimentally.

We have studied impurity-free disordering of InGaAs/InGaAlAs quantum wells on InP, induced by three different dielectric cap films, namely, SiO2, SiNx and SrF2. The difference in photoluminescence characteristics of these materials after heat treatment has been discussed. Furthermore, the in-plane spatial resolution of the disordering process has been investigated for the first time.