A 0.2-μm 180-GHz-fmax 6.7-ps-ECL SOI/HRS self-alignedSEG SiGe HBT/CMOS technology for microwave and high-speed digitalapplications

A technology for combining 0.2-μm self-aligned selective-epitaxial-growth (SEG) SiGe heterojunction bipolar transistors (HBTs) with CMOS transistors and high-quality passive elements has been developed for use in microwave wireless and optical communication systems. The technology has been applied to fabricate devices on a 200-mm SOI wafer based on a high-resistivity substrate (SOI/HRS). The fabrication process is almost completely compatible with the existing 0.2-μm bipolar-CMOS process because of the essential similarity of the two processes. SiGe HBTs with shallow-trench isolations (STIs) and deep-trench isolations (DTIs) and Ti-salicide electrodes exhibited high-frequency and high-speed capabilities with an f_max of 180 GHz and an ECL-gate delay of 6.7 ps, along with good controllability and reliability and high yield. A high-breakdown-voltage HBT that could produce large output swings for the interface circuit was successfully added. CMOS devices (with gate lengths of 0.25 μm for nMOS and 0.3 μm for pMOS) exhibited excellent subthreshold slopes. Poly-Si resistors with a quasi-layer-by-layer structure had a low temperature coefficient. Varactors were constructed from the collector-base junctions of the SiGe HBTs. MIM capacitors were formed between the first and second metal layers by using plasma SiO₂ as an insulator. High-Q octagonal spiral inductors were fabricated by using a 3-μm thick fourth metal layer     

Simultaneous impurity doping with Zn and Se in AlGaInP by MOVPE

We studied the simultaneous doping with zinc and selenium in AlGaInP by metalorganic vapor phase epitaxy. We measured the dependence of zinc and selenium incorporation on substrate orientation from (100) to (311)A faces, showing that the simultaneously doped layer becomes n-type on the (100) face and p-type on the (311)A face. The simultaneously doped layer was examined by photoluminescence, capacitance-voltage, Hall, and secondary ion mass spectrometry analysis. We showed that the simultaneously doped layers have good electrical conduction characteristics and optical qualities for cladding layers in optical devices. We also demonstrated a lateral p-n junction on a patterned substrate.     

Crown structure of the maxillary molars in the Japanese shrew mole, Urotrichus talpoides (Insectivora, Talpidae)

The maxillary first and second molars (M1 and M2) in the Japanese shrew mole, Urotrichus talpoides, were investigated using an odontometrical approach. The mesiodistal crown diameter was larger in M1 than in M2, while the buccolingual diameter of M1 was nearly equal to that of M2. M2 was more compressed mesiodistally than M1. M1 had a large distal triangle on the stylar shelf. The mesial triangle of M2 was slightly larger than the distal triangle. Despite being smaller than M1, M2 was less variable than M1 in terms of size. The distal triangle of M1 and the mesial triangle of M2 were well developed, and thus this area, which corresponds to the inflection point of the maxillary dental arch, was most likely the center of an occlusal function.     

Effects of mouth cleansing on the levels of exhaled nitrous oxide in young and older adults

Nitrous oxide (N2O) is produced by denitrification, i.e. by microbial reduction of nitrate (NO3-). Our previous studies have established an analytical method for demonstrating the existence of N2O in exhaled air, and we showed that levels of N2O in exhaled air increase with age after puberty. However, the source of this change and its biological significance are still unclear. The purpose of this study was to examine whether the oral microorganisms are the main source of N2O. We measured exhaled N2O in 35 young adults (aged 19-29 years) and 34 older adults (aged 61-79 years) before and after mouth cleansing. N2O was measured using an infrared-photoacoustic analyzer equipped with an optical filter (UA0985, 2215 cm-1). Participants were classified as producers and non-producers according to the levels of exhaled N2O relative to the level in the atmosphere. N2O production differed significantly between the young adult producers and the older adult producers. Mouth cleansing resulted in an immediate reduction in exhaled N2O in both groups. We only found seven (20.0%) producers in the young, and 32 (94.1%) producers in the older after mouth washing. The differences before and after mouth cleansing were significant in both groups (P < 0.01 in the young and P < 0.05 in the older). The oral cavity is a major source of N2O. However, since approximately half-levels of N2O were still observed in exhaled air after mouth, cleansing, there may exist another N2O source in the human body.     

Biofilm Spreading by the Adhesin-Dependent Gliding Motility of Flavobacterium johnsoniae: 2. Role of Filamentous Extracellular Network and Cell-to-Cell Connections at the Biofilm Surface

Flavobacterium johnsoniae forms a thin spreading colony on nutrient-poor agar using gliding motility. As reported in the first paper, WT cells in the colony were sparsely embedded in self-produced extracellular polymeric matrix (EPM), while sprB cells were densely packed in immature biofilm with less matrix. The colony surface is critical for antibiotic resistance and cell survival. We have now developed the Grid Stamp-Peel method whereby the colony surface is attached to a TEM grid for negative-staining microscopy. The images showed that the top of the spreading convex WT colonies was covered by EPM with few interspersed cells. Cells exposed near the colony edge made head-to-tail and/or side-to-side contact and sometimes connected via thin filaments. Nonspreading sprB and gldG and gldK colonies had a more uniform upper surface covered by different EPMs including vesicles and filaments. The EPM of sprB, gldG, and WT colonies contained filaments ~2 nm and ~5 nm in diameter; gldK colonies did not include the latter. Every cell near the edge of WT colonies had one or two dark spots, while cells inside WT colonies and cells in SprB-, GldG-, or GldK-deficient colonies did not. Together, our results suggest that the colony surface structure depends on the capability to expand biofilm.     

Thermochemical liquefaction of Indonesian biomass residues

Eighteen kinds of biomass residues in Indonesia were liquefied to heavy oil in hot-compressed water with sodium carbonate as the catalyst at 300°C and around 10 MPa. The oil was obtained in the range of the yields between 21-36 wt% on an organic basis. Typically the oils had almost the same properties; carbon, around 70 wt%, hydrogen, 7 wt%, nitrogen, < 1 wt%, calorific value, around 30 kJ/g, and viscosity, > 10⁵ mPa.s. The result of the simple energy balance estimation shows that this liquefaction process might become a net energy producer.     

A high efficiency thin film silicon solar cell and module

A photoelectric conversion efficiency of over 10% has been achieved in thin-film microcrystalline silicon solar cells which consist of a 2 μm thick layer of polycrystalline silicon. It was found that an adequate current can be extracted even from a thin film due to the very effective light trapping effect of silicon with a low absorption coefficient. As a result, this technology may eventually lead to the development of low-cost solar cells. Also, an initial aperture efficiency as high as 13.5% has been achieved with a large area (91 cm × 45 cm) tandem solar cell module of microcrystalline silicon and amorphous silicon (thin film Si hybrid solar cell). An even greater initial efficiency of 14.7% has been achieved in devices with a small size (area of 1 cm²), and further increases of efficiency can be expected.     

N2 post-deposition treatment on silicon thin films with a hot-wire chemical vapor method at a low wire temperature

For nitride layer formation on a hydrogenated microcrystalline silicon film surface, post-deposition treatments were carried out using a tungsten wire heated to 1700 °C in N₂ (12 Torr) or N₂/H₂ (4 Torr) atmospheres. The nitride layers were investigated with an X-ray photoelectron spectroscopy. The intense peaks due to the Si-N bonds were observed. Those in N₂ treatment were larger with increasing the treating time and decreased with depth direction, while those in N₂/H₂ treatment were virtually unchanged with the treating time and the depth up to about 20 nm. These findings indicate that even at a low wire temperature of 1700 °C, N₂ molecules decompose sufficiently and nitride layers can be formed when high gas pressures are used.     

On the temperature dependence of flammability limits of gases

Flammability limits of several combustible gases were measured at temperatures from 5 to 100 °C in a 12-l spherical flask basically following ASHRAE method. The measurements were done for methane, propane, isobutane, ethylene, propylene, dimethyl ether, methyl formate, 1,1-difluoroethane, ammonia, and carbon monoxide. As the temperature rises, the lower flammability limits are gradually shifted down and the upper limits are shifted up. Both the limits shift almost linearly to temperature within the range examined. The linear temperature dependence of the lower flammability limits is explained well using a limiting flame temperature concept at the lower concentration limit (LFL)--'White's rule'. The geometric mean of the flammability limits has been found to be relatively constant for many compounds over the temperature range studied (5-100 °C). Based on this fact, the temperature dependence of the upper flammability limit (UFL) can be predicted reasonably using the temperature coefficient calculated for the LFL. However, some compounds such as ethylene and dimethyl ether, in particular, have a more complex temperature dependence.     

Preparation of novel transparent glass–ceramics containing fluoride crystals

Transparent glass–ceramics containing YLiF₄ nano-crystals were synthesized by controlled heat-treatments of LiFYF₃Al₂O₃SiO₂ glass. The crystallite size estimated to be about 8 nm was much less than the wavelength of the visible light. The transmittance of the glass–ceramic with a thickness of 2 mm was more than 85% at 400 nm and as high as 95% in the infrared region. The fluorescence centered around 1000 nm was hardly observed from Er³⁺-doped precursor glass under 800 nm excitation, while the emission with the Stark spitting was clearly observed for the Er³⁺-doped glass–ceramic. The phonon sideband of the ⁷F₀ → ⁵D₂ excitation spectra of Eu³⁺ reveals that Eu³⁺ doped in precursor glass is in silicate network while Eu³⁺ doped in the glass–ceramic is in not only silicate framework but also fluoride framework. These results indicate that rare-earth ions such as Er³⁺ and Eu³⁺ could be successfully incorporated into YLiF₄ nano-crystals in the glass–ceramics.