On the frequency dependent drain conductance of ion-implanted GaAs MESFETs

The effect of MESFET structure on the frequency dispersion of drain conductance (g/sub d/) was examined, It was found that a shorter gate length, lower buried p-layer concentration, lower sheet resistance of n/sup +/ layer, and thinner active layer thickness are effective in suppressing the frequency dependent g/sub d/. These phenomena are explained by the presence of deep traps in the depletion layer between the semi-insulating substate and active layer. We also show that the cross-point change of eye-pattern for density of input signal in logic ICs is due to frequency dependent g/sub d/ The cross-point change between mark ratio of 1/8 and 7/8 shows a linear relationship with gd/sub RF//gd/sub dc/ (the ratio of the drain conductance at RF and dc input), These results indicate that an optimized device structure with g/sub d/ small frequency dispersion can be used to realize high-speed and high quality logic ICs.     

Effect of Coarse-Powder Portion on Abnormal Grain Growth during Hot Pressing of Commercial-Purity Alumina Powder

By classification, two powder portions, one consisting of coarse particles and the other consisting of fine particles, were separated from a MgO-doped (1000 ppm) commercial-purity Al₂O₃ powder. Examinations of microstructure evolution during hot pressing showed that extensive abnormal grain growth occurred for the coarse portion. For the fine portion, although there was an indication that grain-size distribution deviated from normal distribution on prolonged hot pressing, such extensive abnormal grain growth did not occur. Extensive abnormal grain growth also occurred when the coarse portion was mixed into a high-purity powder that exhibited no abnormal grain growth alone. Chemical analyses revealed that the coarse portion contained the higher concentration of impurities but lower concentration of magnesium than the fine portion. It was discussed that particle aggregates in the coarse portion might have been responsible for the higher concentration of impurities but lower concentration of magnesium and, thus, for the extensive abnormal grain growth.     

Biliary bile acids in the gall-bladder and the common bile duct of patients with anomalous pancreaticobiliary ductal junction

The high incidence of biliary tract carcinoma in patients with anomalous pancreaticobiliary ductal junction (APBDJ) with or without choledochal cyst (CC) has been well documented. Twenty-two patients with APBDJ were divided into three groups: Group A, four patients not associated with CC and biliary tract carcinoma; Group B, 13 patients with CC but without biliary tract carcinoma; and Group C, five patients with biliary tract carcinoma (four with and one without CC). Profiles of bile acids in the gall-bladder and/or common bile duct were analysed in these patients and compared with those in the control patients with cholecystlithiasis to examine the hypothesis that the levels of deoxycholic acid (DCA) and lithocholic acid (LCA) are elevated in patients with APBDJ because these secondary bile acids are mutagenic. Bile acids were quantified by gas-liquid chromatography. Total bile acid concentration in the gall-bladder bile was significantly lower in any group with APBDJ than that of controls. In the gall-bladder, increased proportion of chenodeoxycholic acid (CDCA) in Group A and B, decreased proportion of DCA in Group B and increased proportion of cholic acid (CA) in Group C were found in bile. In the bile duct, total bile acid concentration and proportion of DCA were significantly low in bile from Group C and decreased proportion of DCA and increased proportion of CDCA were found in bile from Group B. In both the gall-bladder and hepatic bile, proportion of LCA was not significantly different between any intergroups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Multiple pulmonary nodules in association with pyoderma gangrenosum

This report describes a patient with extensive pyoderma gangrenosum in whom there were co-existent lung abnormalities. The patient's X-ray showed peripherally sited multiple pulmonary lesions bilaterally. A lung biopsy showed chronic non-specific inflammatory changes with neutrophil and lymphocyte infiltration which were similar to the skin lesions. This case was diagnosed as multiple aseptic nodules in pyoderma gangrenosum. The pulmonary infiltrative shadows were controlled only with prednisolone treatment. Steroid therapy is considered to be the first choice to control pulmonary lesions of this disease.     

Comparison between tensile-strained AlGaInP SQW and MQW LDsemitting at 615 nm

The optimum design for tensile-strained quantum-well structures, and the laser characteristics of AlGaInP LDs emitting at 615-635 nm are investigated. MQW structures are effective in reducing threshold currents at wavelengths shorter than 620 nm. The lowest threshold current of 95 mA at 20°C is attained in a quaternary MQW LD emitting at 615 nm     

Superconducting magnet system containing Bi-2212/Ag Coil Generates 21.8 T at 1.8K

We fabricated a Bi-2212/Ag double stacked pancake coil of 13 mmØ) in inner bore and of 46.5 mmØ in outer diameter, by using Bi-2212/Ag tapes prepared by the combination of continuous dip-coating process and melt-solidification technique. This small superconducting magnet was used as an insert magnet of a conventional superconducting magnet system and tested at saturated superfluid helium temperature (～ 1.8K) in various bias fields. The generated field of Bi2212/Ag coil was 0.9 T, with I_c of 310 A(criterion 10^-13Ω·m), in the bias field of 20.9 T. Thus, this superconducting magnet system achieved generation of magnetic field of 21.8 T in the full superconducting state.     

A robust all-wet-etching process for mesa formation of InGaAs-InP HBT featuring high uniformity and high reproducibility

A simple InP-based heterojunction bipolar transistors (HBT) fabrication process featuring high uniformity and high reproducibility is introduced. No dry etching method was utilized for triple-mesa formation to avoid plasma damage to the device surface. An all-wet etching method was specially developed. This process is relatively simple compared to the conventional HBT fabrication process with respect to the emitter mesa formation by one-step selective etching. Uniformity of the current gain over a 3-in diameter wafer was approximately 2.9%, and the variation of the current gain of 17 wafers was 2.9 (max.-min.). The current gain cutoff frequency and the maximum oscillation frequency were 145 and 174 GHz, respectively. The mean time to failure was over 5 /spl times/ 10/sup 6/ h at 150/spl deg/ C whose criterion was over 3% changes in the current gain. This process is suitable for mass production of ultrahigh speed ICs in high yield.