A high current gain gate-controlled lateral bipolar junction transistor with 90 nm CMOS technology for future RF SoC applications

A CMOS-compatible gate-controlled lateral BJT (GC-LBJT) was prepared with a conventional 90 nm CMOS technology for radio frequency system-on-chip (RF SoC) applications. The emitter injection efficiency and the doping profile in P-well were optimized by properly controlling source, drain, and well implants. Consequently, the GC-LBJT with a gate length of 0.15 μm can achieve a current gain over 2000 and 17/19 GHz for the f_T/f_max, respectively, which are 1000%, 200%, and 60% improvements in current gain, f_T and f_max, respectively as compared to the LBJT reported previously.     

Dynamic hard-real-time scheduling using genetic algorithm for multiprocessor task with resource and timing constraints

Most publications in shop scheduling area focus on the static scheduling problems and seldom take into account the dynamic disturbances such as machine breakdown or new job arrivals. Motivated by the computational complexity of the scheduling problems, genetic algorithms (GAs) have been applied to improve both the efficiency and the effectiveness for NP-hard optimization problems. However, a pure GA-based approach tends to generate illegal schedules due to the crossover and the mutation operators. It is often the case that the gene expression or the genetic operators need to be specially tailored to fit the problem domain or some other schemes may be combined to solve the scheduling problems. This study presents a GA-based approach combined with a feasible energy function for multiprocessor scheduling problems with resource and timing constraints in dynamic real-time scheduling. Moreover, an easy-understood genotype is designed to generate legal schedules. The results of the experiments demonstrate that the proposed approach performs rapid convergence to address its applicability and generate good-quality schedules.     

InGaN/GaN multiple quantum wells grown on nonpolar facets of vertical GaN nanorod arrays

Uniform GaN nanorod arrays are grown vertically by selective area growth on (left angle bracket 0001 right angle bracket) substrates. The GaN nanorods present six nonpolar {1?100} facets, which serve as growth surfaces for InGaN-based light-emitting diode quantum well active regions. Compared to growth on the polar {0001} plane, the piezoelectric fields in the multiple quantum wells (MQWs) can be eliminated when they are grown on nonpolar planes. The capability of growing ordered GaN nanorod arrays with different rod densities is demonstrated. Light emission from InGaN/GaN MQWs grown on the nonpolar facets is investigated by photoluminescence. Local emission from MQWs grown on different regions of GaN nanorods is studied by cathodoluminescence (CL). The core-shell structure of MQWs grown on GaN nanorods is investigated by cross-sectional transmission electron microscopy in both axial and radial directions. The results show that the active MQWs are predominantly grown on nonpolar planes of GaN nanorods, consistent with the observations from CL. The results suggest that GaN nanorod arrays are suitable growth templates for efficient light-emitting diodes.     

Dynamic question generation system for web-based testing using particle swarm optimization

One aim of testing is to identify weaknesses in students’ knowledge. Computerized tests are now one of the most important ways to judge learning, and, selecting tailored questions for each learner is a significant part of such tests. Therefore, one current trend is that computerized adaptive tests (CATs) not only assist teachers in estimating the learning performance of students, but also facilitate understanding of problems in their learning process. These tests, must effectively and efficiently select questions from a large-scale item bank, and to cope with this problem we propose a dynamic question generation system for web-based tests using the novel approach of particle swarm optimization (PSO). The dynamic question generation system is built to select tailored questions for each learner from the item bank to satisfy multiple assessment requirements. Furthermore, the proposed approach is able to efficiently generate near-optimal questions that satisfy multiple assessment criteria. With a series of experiments, we compare the efficiency and efficacy of the PSO approach with other approaches. The experimental results show that the PSO approach is suitable for the selection of near-optimal questions from large-scale item banks.     

Synthesis, phase transformation and dielectric properties of sol–gel derived Bi2Ti2O7 ceramics

Sol–gel derived Bi₂Ti₂O₇ ceramic powders have been prepared from methoxyethoxides of bismuth and titanium (molar ratio of Ti/Bi = 1.23 and water/alkoxides = 1.31). The Bi₂Ti₂O₇ phase was stable at a low temperature (700 °C), but it then transformed into mixed phases of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ at 850–1150 °C. The single phase of Bi₂Ti₂O₇ reoccurred at 1200 °C. Dielectric properties and ferroelectric behavior of samples sintered at 1150 and 1200 °C were examined. Under frequency of 1 MHz, samples sintered at 1150 and 1200 °C had a dielectric constant of 101.3 and 104.2, and a loss tangent of 0.0193 and 0.0145, respectively. Only the sample sintered at 1150 °C showed ferroelectric behavior, where remanent polarization is 3.77 μC cm⁻² and coercive field is 24 kV cm⁻¹. Thus, the Bi₂Ti₂O₇ did not exhibit ferroelectricity, but the mixed phase of Bi₄Ti₃O₁₂ and Bi₂Ti₄O₁₁ did.     

Novel tunable laser sources with 1.5-μm and 1.57-μm cascaded DFB reflectors for in situ gas monitoring applications

Novel tunable lasers based on 1.5-μm and 1.57-μm cascaded distributed-feedback reflectors are realized for real-time monitoring of H₂O and CO gas mixtures immediately in multi-gas sensor systems. With simple fabrication procedures, the new design allows the realization of a widely tunable laser source that can cover the H₂O and CO absorption wavelength bands. With the temperature tuning of 0.1 nm/°C and current tuning of 0.014 nm/mA, the laser can be tuned to cover over 3 nm wavelength range in each wavelength band. Experiments verify that the lasers can have more than 38 dB SMSR over the tuning range. The characteristics of high power, excellent spectral purity, and simple wavelength switching control can simplify the analysis procedures of gas sensing and thus reduce the cost. By direct absorption method, the tunable laser has been successfully adopted in a diode laser sensor system for monitoring of water vapor concentration near 1.5 μm and carbon monoxide near 1.57 μm. Less than 15% error in the line strength is observed between the measured data and HITRAN database.     

Water adsorption on silica and calcium-boroaluminosilicate glass surfaces—Thickness and hydrogen bonding of water layer

Adsorption isotherm of water on silica (modeled with fused quartz) and calcium-boroaluminosilicate (Ca-BAS) glass surfaces as a function of relative humidity (RH) was studied using Fourier transform infrared (FTIR) spectroscopy. The effective thickness of the adsorbed water layer and the distribution of hydrogen bonding interactions of water molecules in the adsorbed layer were determined by comparing the transmission FTIR spectra collected at the Brewster incidence angle with the theoretically calculated spectra. In the sub-monolayer regime (<30% RH), differences between the water spectra on fused quartz and Ca-BAS glass could be related to the areal density of hydroxyl groups as well as the elemental composition of the surface determined with x-ray photoelectron spectroscopy. In the transition regime (30%–60% RH), multilayers start growing and the difference between the fused quartz and Ca-BAS surfaces diminishes as the humidity increases. In the multilayer regime (>60% RH), the total amount as well as the hydrogen bonding interactions of adsorbed water layers become insensitive to the surface chemistry and are governed mostly by the phase transition (vapor condensation) behavior. Overall, this study reveals how the water layer thickness and structure on the multicomponent silicate glass surface in ambient conditions are different from those on the pure silica surface.     

Polybenzimidazole/poly(tetrafluoro ethylene) composite membranes for high temperature proton exchange membrane fuel cells

A porous poly(tetrafluoro ethylene) (PTFE) thin film (thickness 16 ± 2 μm) is used as a supporting material for polybenzimidazole (PBI) to prepare the PBI/PTFE composite membrane (thickness 38 ± 2 μm). The perfluorosulfonic acid resin (Nafion) is used as a coupling agent at the interface between PTFE and PBI to improve the bonding between PBI and PTFE. The composite membrane, after doping with phosphoric acid, is used to prepare membrane electrode assemblies (MEAs). A 450 h continuous fuel cell life test at 160 °C with a fixed current density i = 200 mA cm⁻² and a 20 cycles cell on/off test, in which the fuel cell is operated at 160 °C with i = 200 mA cm⁻² for 12 h and then switched off at room temperature in an ambient environment for 12 h per cycle, are performed. Both tests show good fuel cell performances.     

An intelligent view box system for cephalometry

In the routine analysis of cephalometry, the orthodontist usually needs to manually draw the tracing paper with the help of the view box, and then some cephalometric measurements are performed to evaluate growth aspects of the skull and the effects of treatment. Due to the varied display quality and clinical training, many orthodontists rely heavily on the view box rather than the computer monitor for cephalometry. Without the appropriate and affordable digital imaging devices, the computerized analysis for cephalometry is hard to apply in practice. In this paper, a novel design of an intelligent view box that combines an X-ray film view box, a touch panel, and analysis software is proposed. It is designed for acquiring both the landmarks and feature curves of the cephalogram for the automated cephalometric system use. There are two merits of the proposed system. One is that the relationship between the label and position for manually defined landmarks may be automatically corrected, and the other is that the manual drawing process may be automatically followed and guided based on the cephalogram. In addition, the proposed system also includes an image manipulation system. Thus, both the landmarks and feature curves may be automatically and correctly overlaid on the cephalogram for further assessment. From the experimental results, the repeated repositioning of the pen in ten times only produces a standard deviation not more than 0.5 mm in x and y directions. The spatial resolution for the proposed intelligent view box system is about 164 pixels/inch. It is demonstrated to be very useful in the clinics for the automated cephalometric analysis.     

Improvement of TDDB reliability, characteristics of HfO2 high-k/metal gate MOSFET device with oxygen post deposition annealing

In this work, influences of oxygen effect on an Hf-based high-k gate dielectric were investigated. A post deposition annealing (PDA) including oxygen ion after high-k dielectric deposition was used to improve reliability of the Hf-based high-k/metal gate device. The basic electrical characteristics of devices were compared with and without the PDA process. Experiment results show that the oxygen PDA did not degrade the drive current and effective oxide thickness of the Hf-based gate devices. In addition, reliability issues such as positive bias instability, negative bias instability and TDDB were also improved by the oxygen PDA significantly. During the TDDB test, the charge trapping was characterized by an in situ charge pumping system, which could make us to understand the variations of interface trap during the reliability stress easily.