Design and characterization of superlattice infrared photodetectoroperating at low bias voltage

In this paper, we investigate the performance and characterization of a 15-period superlattice embedded between two thick AlGaAs barriers. The structure can operate at low bias voltage with less power consumption for 8-10 μm long-wavelength infrared detection. In our design, one barrier is used to reduce the dark current and the other one is designed to enhance the collection efficiency of photoelectrons at the collector contact. The fabricated detector can be operated at a bias voltage lower than 0.1 V and exhibits a pronounced photovoltaic response. The spectral response shows voltage dependence around 0 V. At high bias voltage (>25 mV) the spectral lineshape is independent of bias and is around 8-10 μm with peak wavelength at 9.3 μm. At lower bias voltage the response is shifted toward shorter wavelength range. The peak responsivity was found to be 12 mA/W at λ_p =8.7 μm and zero bias and 85 mA/W at λ_p=9.3 μm and 0.1 V. Background limitation can be achieved up to 65 K with bias voltage less than 0.1 V. The measured noise power spectral density of the dark current at 77 K shows the characteristics of full shot noise rather than generation-recombination noise. The peak detectivity is determined to be D^*=3.5×10⁹ cm√(Hz)/W at 77 K and 0.1 V. In comparison with a conventional 30-period QWIP, our detector has the advantages of better performance at low bias voltages with lower power consumption and a tunable feature of spectral range     

Temperature and current-density distributions in flip-chip solder joints with Cu traces

Three-dimensional simulation was performed to investigate the temperature and current density distribution in flip-chip solder joints with Cu traces during current stressing. It was found that the Cu traces can reduce the Joule heating effect significantly at high stressing currents. When the solder joints were stressed by 0.6 A, the average temperature increases in solder bumps with the Al traces was 26.7°C, and it was deceased to 18.7°C for the solder joint with the Cu traces. Hot spots exist in the solder near the entrance points of the Al or Cu traces. The temperature increases in the hot spot were 29.3°C and 20.6°C, for solder joints with the Al traces and Cu traces, respectively. As for current density distribution, the maximum current density inside the solder decreased slightly from 1.66×10⁵ A/cm² to 1.46×10⁵ A/cm² when the Al traces were replaced by the Cu traces. The solder joints with the Cu traces exhibited lower Joule heating and current crowding effects than those with the Al traces, which was mainly attributed to the lower electrical conductivity of the Cu traces. Therefore, the solder joints with the Cu traces are expected to have better electromigration resistance.     

Design of self-bias tail transistor technique for low phase noise CMOS VCO with harmonic suppression using capacitance ground

This paper presents a low phase noise wideband CMOS VCO based on the self-bias tail transistor technique and harmonic suppression using a capacitance ground. This VCO utilizes switching capacitor arrays in which four channels are able to be selected for multi-band application. Moreover, the design of CMOS VCO makes good use of the self-bias tail transistor and capacitance ground filter technique to reduce the phase noise. The MOS varactors are used as fine tuning for wideband operating application. The fully integrated VCO provides excellent performance with high FOM −193 dBc/Hz. The bandwidth of the frequency is 1.1 GHz and the tuning range is 13.8%. The power dissipation of the core circuit is 8.28 mW under a 1.8 V supply and phase noise is measured as low as −123.6 dBc/Hz at 1 MHz offset under 8.5 GHz oscillation frequencies. This VCO was made by the TSMC 0.18 μm 1P6M CMOS standard process and the chip area is 0.75×0.69 (mm²).     

Polarity Effect in a Sn3Ag0.5Cu/Bismuth Telluride Thermoelectric System

This study investigates electromigration in Bi₂Te₃ thermoelectric (TE) material systems and the effectiveness of the diffusion barrier under current. The Peltier effect on the interfacial reaction was decoupled from the effect of electromigration. After connecting p- and n-type Bi₂Te₃ to Sn3Ag0.5Cu (SAC305) solders, different current densities were applied at varying temperatures. The Bi₂Te₃ samples were fabricated by the spark plasma sintering technique, and an electroless nickel-phosphorous (Ni-P) layer was deposited at the solder/TE interfaces. The experimental results confirm the importance of the Ni diffusion barrier in joint reliability. Intermetallic compound layers (Cu,Ni)₆Sn₅ and NiTe formed at the solder/Ni-P and Ni-P/substrate interfaces, respectively. The experimental results indicate that the mechanism of NiTe and (Cu,Ni)₆Sn₅ compound growth was dominated by the Peltier effect at high current density. When the current density was low, the growth of NiTe was affected by electromigration but the changes of thickness for (Cu,Ni)₆Sn₅ were not obvious.     

Structure and mechanical properties of Ti–5Cr based alloy with Mo addition

The effects of molybdenum (Mo) on the structure and mechanical properties of a Ti–5Cr-based alloy were studied with an emphasis on improving its strength/modulus ratio. Commercially pure titanium (c.p. Ti) was used as a control. As-cast Ti–5Cr and a series of Ti–5Cr–xMo (x = 1, 3, 5, 7, 9 and 11 wt.%) alloys were prepared by using a commercial arc-melting vacuum-pressure casting system, and investigated with X-ray diffraction (XRD) for phase analysis. Three-point bending tests were performed to evaluate the mechanical properties of all specimens and their fractured surfaces were observed by using scanning electron microscopy (SEM). The experimental results indicated that Ti–5Cr–7Mo, Ti–5Cr–9Mo and Ti–5Cr–11Mo alloys exhibited ductile properties, and the β-phase Ti–5Cr–9Mo alloy exhibited the lowest bending modulus. However, the Ti–5Cr–3Mo and Ti–5Cr–5Mo alloys had much higher bending moduli due to the formation of the ω phase during quenching. It is noteworthy that the Ti–5Cr–9Mo alloy exhibited the highest bending strength/modulus ratios at 26.0, which is significantly higher than those of c.p. Ti (8.5) and Ti–5Cr (13.3). Furthermore, the elastically recoverable angle of the Ti–5Cr–9Mo alloy (30°) was greater than that of c.p. Ti (2.7°). The reasonably high strength (or high strength/modulus ratio) β-phase Ti–5Cr–9Mo alloy exhibited a low modulus, ductile property, and excellent elastic recovery capability, which qualifies it as a novel implant materials.     

A fully-coupled fluid-structure interaction simulation of cerebral aneurysms

This paper presents a computational vascular fluid-structure interaction (FSI) methodology and its application to patient-specific aneurysm models of the middle cerebral artery bifurcation. A fully coupled fluid-structural simulation approach is reviewed, and main aspects of mesh generation in support of patient-specific vascular FSI analyses are presented. Quantities of hemodynamic interest such as wall shear stress and wall tension are studied to examine the relevance of FSI modeling as compared to the rigid arterial wall assumption. We demonstrate the importance of including the flexible wall modeling in vascular blood flow simulations by performing a comparison study that involves four patient-specific models of cerebral aneurysms varying in shape and size.     

Grape wine lees improves the rheological and adds antioxidant properties to ice cream

The effect of adding grape wine lees (GWL) (50, 100 and 150 g kg⁻¹, wet weight basis) on the rheological and antioxidant properties of ice cream was evaluated to determine the potential of using GWL as a value-added ingredient in ice cream. Black queen grape was selected because it was the only species for red winemaking in Taiwan. The addition of GWL decreased the specific gravity, pH, melting rate, firmness, lightness and the amount of freezable water in ice cream, but increased the viscosity, yellowness and fat destabilization in a dose dependent circumstance. However, the ice cream with high GWL contents (100 and 150 g kg⁻¹) also showed unpleasant effects, such as the decrease of overrun and the increase of particle size of fat globule. The level of 50 g kg⁻¹ was applicable because it improved the functionality without the disadvantages in the overrun and particle size. Furthermore, GWL significantly increased the DPPH radical scavenging activity and reducing power of ice cream, and also its inhibitory effect toward the oxidation of human erythrocyte membrane. It appeared that the antioxidants in GWL were quite stable to the process of ice cream making.     

Effect of different acids on the extraction of pepsin-solubilised collagen containing melanin from silky fowl feet

Four acid treatments: acetic acid (FA), citric acid (FC), hydrochloric acid (FH) and lactic acid (FL) were used in this study to extract the pepsin-solubilised collagen (PSC) containing melanin from silky fowl feet. The collagen content, melanin content, electrophoresis and ultraviolet (UV) absorption spectra (200–400 nm) were determined in order to develop a collagen with UV protection. Among four acid extractions, the acetic acid treatment had both the highest extracting yield (7.3%) and collagen content (516.6 mg/g). PSCs obtained from silky fowl feet using four acid extractions exhibited melanin content; whereas no similar observations were found in that of broiler feet by acetic acid extraction (FB). Moreover, the PSC via acetic acid extraction resulted in the significantly highest melanin content (210 mg/g) (P < 0.05), which contributed to UV absorption. In electrophoresis, three subunits were found in PSCs from silky fowl feet using the four acid extractions, which were different from typical type I collagen and assumed that the PSCs obtained from silky fowl feet consisted of more than two types of collagens.     

Biotransformation of ginsenoside Rd in the ginseng extraction residue by fermentation with lingzhi (Ganoderma lucidum)

Ginseng and lingzhi (Ganoderma lucidum) both are valuable traditional Chinese medicines and have been extensively utilised in functional foods and traditional medicines in many Asian countries. However, massive quantity of ginseng residue is produced after extraction of ginseng which still contains a lot of bioactive compounds such as ginsenosides. The goal of this study was to reuse the American ginseng extraction residue as the fermentation medium of G. lucidum to produce bioactive ginsenoside enriched biotransformation products. The changes of ginsenosides in the fermentation products were analysed during fermentation. Our results showed that after 30 days of fermentation, ginsenoside Rg1, Rd, and compound K (CK) significantly increased, especially Rd, while other ginsenosides (Re, Rb1 and Rc) decreased during fermentation. Ginsenoside Rd is the major ginsenoside in the final fermentation product. Furthermore, the biotransformation of ginsenosides was the major reaction in this fermentation process.     

Production of beta-galactosidase by Bifidobacteria as influenced by various culture conditions

Beta-Galactosidase production by Bifidobacterium longum CCRC 15708, Bifidobacterium longum B6 and Bifidobacterium infantis CCRC 14633 was first examined with B. longum CCRC 15708 showing the highest production of beta-galactosidase and the highest specific activity. Further study with B. longum CCRC 15708 revealed that the highest level of beta-galactosidase was produced with lactose and yeast extract as carbon and nitrogen sources, respectively. Optimal enzyme production occurred at an initial pH of 6.5 and at 37 degrees C. Under these optimum culture conditions, a maximumbeta-galactosidase activity of 18.6 U/ml could be obtained after 16 h of fermentation in a medium contain 4% lactose, 3.5% yeast extract, 0.3% K2HPO4, 0.1% KH2PO4, 0.05% MgSO4.7H2O and 0.03% L-cysteine. The highest transgalactosylation activity was also detected in this culture after 14-16 h of fermentation.