BCB-bridged distributed wideband SPST switch using 0.25-/spl mu/m In/sub 0.5/Al/sub 0.5/As--In/sub 0.5/Ga/sub 0.5/As metamorphic HEMTs

In/sub 0.5/Al/sub 0.5/As--In/sub 0.5/Ga/sub 0.5/As metamorphic high-electron mobility transistor (mHEMT) dc-30 GHz distributed single-pole-single through (SPST) switches were designed and fabricated using the low-/spl kappa/ benzocyclobutene (BCB) bridged technology. The current gain cutoff frequency, and the electron transit time of In/sub 0.5/Al/sub 0.5/As--In/sub 0.5/Ga/sub 0.5/As mHEMTs have been investigated. By analyzing the extrinsic total delay time, the effective velocity of electrons can be estimated, and the average velocity is 2.3/spl times/10/sup 7/cm/s. The dc-30 GHz distributed wideband SPST switch exhibits an insertion loss of less than 5.5 dB, and an isolation larger than 30 dB, which is the first demonstration of the high-isolation of InAlAs-InGaAs mHEMTs monolithic switch. As to the power performance, this switch can handle the power up to 12 dBm at 2.4 GHz. After over 250 h of 85-85 (temperature =85/spl deg/C, humidity =85%) environmental evaluation, this BCB passivated and bridged microwave and monolithic integrated circuit switch demonstrates reliable RF characteristics without any significant performance change, which proves that this process using the low-/spl kappa/ BCB layer is attractive for millimeter-wave circuit applications.     

Experimental study of forced convective boiling for non-azeotropic refrigerant mixtures R-22/R-124 in horizontal smooth tube

In this article, the experiment is carried out with four stages of test section and new experimental data of non-azeotropic refrigerant mixtures R-22/R-124 are presented. Existing correlations are analysed and new ones are proposed for pure refrigerants. The nucleate boiling correlation of the refrigerant mixtures is modified so as to obtain the evaporation heat transfer coefficient of the refrigerant mixtures in a smooth tube. The result shows that the majority of the predictions fall within ±30% of the experiments.     

On a transistor-type hydrogen gas sensor prepared by an electrophoretic deposition (EPD) approach

A Pd/GaN/AlGaN heterostructure field-effect transistor (HFET)-type hydrogen gas sensor, based on an electrophoretic deposition (EPD) approach, is fabricated and studied. Due to the formation of good Schottky gate contact by an EPD approach, the studied HFET shows improved DC performance including the suppressed gate current and better thermal stabilities on current–voltage (I–V) characteristics. This is mainly attributed to the reduction of interface trap density and improved Pd morphology. The EPD-based Pd morphologies are examined by X-ray diffraction, energy dispersive spectroscopy, Auger electron spectroscopy, scanning electron microscopy, and atomic force microscopy. For the used gate-dimension of 1 μm × 100 μm, an EPD-based HFET shows low gate current of 2.9 nA, maximum drain saturation current of 490 mA/mm, and maximum extrinsic transconductance of 78.9 mS/mm at room temperature. Also, solid thermal stabilities on maximum drain saturation current (−0.46 mA/mm K) and maximum extrinsic transconductance (−0.08 mS/mm K) are found as the temperature is increased from 300 to 600 K. For hydrogen gas sensing application, at 370 K, the maximum hydrogen sensitivity of 600.1 μA/mm ppm H₂/air under a 5 ppm H₂/air ambiance and fast response time (30 s) and recovery time (47 s) under a 10,000 ppm H₂/air ambiance are obtained. The EPD approach also demonstrates advantages of low cost, simple apparatus, easy process, little restriction on the shaped substrate, composited deposition, and adjustable alloy grain size. Therefore, the proposed EPD approach gives the promise for fabricating high-performance HFET devices and hydrogen gas sensors.     

Energy-Efficient Dual-Edge-Triggered Level Converting Flip Flops With Symmetry in Setup Times and Insensitivity to Output Parasitics

Level converting flip-flops (LCFFs) are crucial components for multisupply systems as interfaces between different voltage islands. The proposed energy-efficient LCFFs reduce the power consumption of clock networks with dual-edge triggering, support sleep mode of power management mechanisms with data retention, and have symmetry in setup times and insensitivity to output parasitics. With all these features, the proposed LCFFs have 19% and 38% lower power-delay product than the conventional LCFF, as demonstrated by postlayout simulation results.     

Comparison of potential water supply and demand in Taiwan

The authors estimated the potential water supply in Taiwan based on hydrologic and water resource data sets pertaining to 233 rainfall stations, 145 stage stations and 109 reservoirs. The comparison between potential water supply estimates and predicted water demand indicated a slight water shortage, even though Taiwan normally receives a large amount of rainfall. This predicted water shortage likely occurred due to the uneven distribution of rainfall in Taiwan. Taken together, the results of this study demonstrate the importance of conservation of forests and paddy fields for the maintenance of base flow and effective management of reservoirs in Taiwan.     

Comparison of the pulsed field gel electrophoresis patterns and virulence profiles of the multidrug resistant strains of Salmonella enterica serovar Schwarzengrund isolated from chicken meat and humans in Taiwan

Salmonella Schwarzengrund is one of the frequent serovars isolated from chicken meat in Taiwan. This organism is also one of the invasive Salmonella serovars which may cause human salmonellosis and animal infections. In this study, a total of 466 strains of S. Schwarzengrund including 232 retail chicken meat isolates and 234 human isolates in Taiwan were analyzed for their antibiotic resistance and pulsed field gel electrophoresis (PFGE) patterns. For XbaI-digested DNA, a total of 110 PFGE patterns were obtained. When patterns from both origins were analyzed, of these patterns, 21 were shared by isolates from chicken meat samples and humans. In these 21 patterns, 153 (32.8%) isolates from both origins shared the top five patterns. Since ACSSXTT R-type strains are the major concern worldwide and they accounted for 74.5% of total strains used in this study, such R-type strains in the top five XbaI-digested patterns were then further analyzed with AvrII digestion followed by PFGE and PCR assay targeted to 10 Salmonella virulence genes, i.e., avrA, ssaQ, mgtC, siiD, sopB, gipA, sodC1, sopE1, spvC, and bcfC. When PFGE patterns and virulence gene profiles were combined for the analysis of ACSSXTT R-type strains of S. Schwarzengrund, 29 strains from both origins showed the same pattern combinations. Such results suggested the possible transmission of S. Schwarzengrund from chicken meat to humans.     

A full code-patterns coverage high-speed embedded ROM using dynamic virtual guardian technique

Crosstalk between bitlines induces read failure and limits the coverage of applicable code-patterns for high-speed contact/via-programming read-only memories (ROMs) in SoC. Owing to the variation in bitline loading across code-patterns, the amount of coupled noise on an accessed bitline is code-pattern-dependent. This crosstalk effect worsens, with larger coupling capacitance and smaller intrinsic loading, as the technology node shrinks. This study proposes dynamic virtual guardian (DVG) techniques for contact/via-programming ROM macros and compilers to eliminate the crosstalk-induced read failure and increase the code-patterns coverage. Compared with conventional ROMs, DVG techniques achieve higher speed, lower power consumption and better design for manufacturing (DFM) capability with full code-patterns coverage. Experiments on fabricated designs, a conventional ROM and two 256 Kb DVG ROMs, using 0.18 /spl mu/m 1P5M CMOS technology have demonstrated that DVG techniques achieve 100% code-pattern coverage under a small sensing margin.     

Evaluation of current techniques for isolation of chars as natural adsorbents

Chars in soils or sediments may potentially influence the soil/sediment sorption behavior. Current techniques for the isolation of black carbon including chars rely often on acid demineralization, base extraction, and chemical oxidation to remove salts and minerals, humic acid, and refractory kerogen, respectively. Little is known about the potential effects of these chemical processes on the char surface and adsorptive properties. This study examined the effects of acid demineralization, base extraction, and acidic Cr2O7 2- oxidation on the surface areas, surface acidity, and benzene adsorption characteristics of laboratory-produced pinewood and wheat-residue chars, pure or mixed with soils, and a commercial activated carbon. Demineralization resulted in a small reduction in the char surface area, whereas base extraction showed no obvious effect. Neither demineralization nor base extraction caused an appreciable variation in benzene adsorption and presumably the char surface properties. By contrast, the Cr2O7 2- oxidation caused a >31% reduction in char surface area. The Boehm titration, supplemented by FTIR spectra, indicated that the surface acidity of oxidized chars increased by a factor between 2.3 and 12 compared to non-oxidized chars. Benzene adsorption with the oxidized chars was lower than that with the non-oxidized chars by a factor of >8.9; both the decrease in char surface area and the increase in char surface acidity contributed to the reduction in char adsorptive power. Although the Cr2O7 2-oxidation effectively removes resistant kerogen, it is not well suited for the isolation of chars as contaminant adsorbents because of its destructive nature. Alternative nondestructive techniques that preserve the char surface properties and effectively remove kerogen must be sought.     

Miscibility of SAN with polyacrylates and polymethacrylates

Styrene-acrylonitrile copolymers, SAN, are known to be miscible with poly(methyl methacrylate). Based on the presence of a single composition dependent glass transition and lower critical solution temperature behaviour, it is shown that SAN is also miscible with poly(ethyl methacrylate). However, the SAN does not appear to be miscible with other polymethacrylates or polyacrylates.