Microstructural stability of Ag sinter joining in thermal cycling

As a heat-resistant die attach technology processed at low temperatures, three Ag filler-based sinter joining materials have been proposed. Among these, Ag flake pastes exhibited the greatest potential. Joining was carried out by sintering Ag nanoparticles/flakes in air at 200 °C for 60 min. All of the joined samples survived up to 1,000 thermal cycles in a temperature range from ?40 to 180/250 °C with a 30 min dwell time. In particular, the joining strengths with the Ag micron and, Ag nano-thick flake pastes maintained excellent strength. Neither thermal fatigue cracks nor large voids were observed in the Ag sintered layers. Thus, low-temperature and low-pressure sinter joining with Ag flakes is expected to have an application in high power semiconductor devices for ultra-high temperature operation.     

Quantitative Real-Time PCR Analysis of YKL-40 and Its Comparison with Mammalian Chitinase mRNAs in Normal Human Tissues Using a Single Standard DNA

YKL-40 (YKL for the first three N-terminal residues of a 40 kDa protein) belongs to a group of human chitinase-like proteins (CLPs), which are similar to chitinases but lack chitinolytic activity. YKL-40 mRNA and its protein levels have been reported elevated in multiple disorders including asthma, cystic fibrosis, rheumatoid arthritis and malignant tumors. Here, we quantified the YKL-40 mRNA levels and compared them with chitinases and housekeeping genes in normal human tissues. To establish the quantitative real-time PCR (qPCR) system for evaluation of relative YKL-40 mRNA levels, we constructed a human standard DNA molecule by ligating cDNAs of YKL-40, two mammalian chitinases and two housekeeping genes in a one-to-one ratio. We generated cDNAs from various normal human tissues and analyzed the YKL-40 mRNA expression levels using a qPCR system with the standard DNA. We found that YKL-40 mRNA is present widely in human tissues while its expression patterns exhibit clear tissue specificity. Highest YKL-40 mRNA levels were detected in the liver, followed by kidney, trachea and lung. The levels of YKL-40 mRNA in the kidney and liver were more than 100-times higher than those of chitotriosidase mRNA. Our study provides for the first time a comprehensive analysis of the relative expression levels of YKL-40 mRNA versus mammalian chitinases in normal human tissues.     

CT angiography in vascular intervention for steno-occlusive diseases: role of multiplanar reconstruction and source images

The aim of this study was to assess the efficacy of CT angiography for steno-occlusive diseases before and after interventional procedures, focusing on the role of multiplanar reconstruction (MPR) and source images. 17 patients with 20 steno-occlusive lesions underwent CT angiography before and after interventional procedures. For each lesion, the percentage stenosis obtained on CT angiography was compared with that on conventional angiography. In addition, MPR and source images were evaluated for the presence of wall thickening and calcification before interventional procedures, and the presence of dissection and luminal shape after interventional procedures. These findings were compared with those of conventional angiography. Although the percentage stenosis depicted on CT angiography correlated well with that on conventional angiography, MPR and source images clearly demonstrated the effect of intervention and the residual stenosis. MPR and source images clearly depicted wall thickening, wall calcification, the presence of dissection and the luminal shape. CT angiography provides useful information before intervention, while MPR and source images are of value in evaluating arterial wall abnormalities and morphological changes associated with interventional procedures.     

Characteristic Analysis of a Micro DC‐DC Converter for Portable Electronic Devices and an Improvement of Transient Response Characteristic

This paper describes the characteristic analysis of a micro DC‐DC converter which integrates inductor, controller and switching devices, and the improvement of the transient response characteristic. The steady‐state operation and the efficiency characteristics of the micro DC‐DC converter are presented as experimental data. The static characteristics are theoretically analyzed with consideration of the DC current characteristics of the inductor. The load transient response characteristics of the micro DC‐DC converter are also analyzed experimentally and theoretically. In addition, the factors responsible for the overshoot and undershoot of the output voltage when the load changes are discussed. Finally, a clamp circuit for reducing the overshoot and undershoot of the output voltage when the load changes is proposed. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 175(3): 56–64, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21081     

Numerical Analysis of Near-Field Magnetic Field for Automobile Electronic Key Systems

We propose a numerical method for analyzing near-field magnetic fields for automobile electronic key systems. The surface of an automobile body is divided into triangular patches and a modified inductance matrix formulation is employed. A large inductance matrix equation is solved using a block Gauss-Seidel method. A source magnetic field produced by a ferrite bar antenna is analyzed using a magnetic moment method to formulate a right-hand vector of the matrix equation. We have made a simplified automobile model and measured leakage of magnetic fields from windows of the model. Analyzed results agreed with the measured results with an error of 10%.     

10 Gbit/s series-connected voltage-balancing pulse driver with high-speed input buffer

A series-connected voltage-balancing pulse driver employing direct-coupled current switch architecture with a high-driving-capability input buffer and 0.1 /spl mu/m InP HEMTs is presented. By connecting two HEMTs in series the driver can output 3.6 V/sub pp/ voltage swing. With the input buffer, the -3 dB limiting bandwidth of the driver increases from 11 to 30 GHz, and the rise and fall times decrease from 33 to 16 and from 37 to 16 ps, respectively. These short rise and fall times enable the driver to output clear 10 Gbit/s eye opening.     

Conversion of a Precursor Derived from Cage-Type and Cyclic Molecular Building Blocks into Al-Si-N-C Ceramic Composites

A precursor derived from (HAlN ⁱ Pr) _m and [MeSi(H)NH] _n , which mainly consisted of cage-type compounds and cyclic compounds, respectively, was converted into Al-Si-N-C ceramic composites via pyrolysis. A dehydrocoupling reaction between AlH groups and NH groups occurred at low temperatures (≤∼250°C), which mainly accounts for its high ceramic yield (69% up to 900°C). At high temperatures (≥∼250°C), the organic groups were decomposed. The product pyrolyzed at 1350° and 1500°C under Ar contained a 2H wurtzite-type compound and a β-Si₃N₄-type compound, while β-SiC was clearly detected in addition to these compounds in the product pyrolyzed at 1600°C under Ar. On the other hand, the product pyrolyzed at 800°C under NH₃ and subsequently at 1350°C under N₂ consisted of AlN and β-Sialon.     

Correlation of MR imaging-determined cerebral blood volume maps with histologic and angiographic determination of vascularity of gliomas

OBJECTIVE: Our purpose was to evaluate the relationships between the ratio of maximum relative cerebral blood volume (rCBV) (rCBV ratio = rCBV[tumor]/rCBV[contralateral white matter]) and histologic and angiographic vascularities of gliomas using the gradient-echo echoplanar MR imaging technique. We also evaluated the usefulness of rCBV maps for grading gliomas. SUBJECTS AND METHODS: We examined 30 patients with histologically verified gliomas. Gliomas were classified as glioblastoma, anaplastic glioma with enhancement, anaplastic glioma without enhancement, and low-grade glioma. The maximum rCBV ratio of each glioma was compared with both histologic and angiographic vascularities, and the relationship between the maximum rCBV ratios and each type of glioma was established. RESULTS: The maximum rCBV ratios of the gliomas significantly correlated with both histologic and angiographic vascularities (p < .001). Mean values and SDs of maximum rCBV ratios of each type of tumor were 7.32+/-4.39 for glioblastomas, 5.84+/-1.82 for anaplastic gliomas with enhancement, 1.53+/-0.75 for anaplastic gliomas without enhancement, and 1.26+/-0.55 for low-grade gliomas. The maximum rCBV ratios of the glioblastomas were significantly higher than those of the anaplastic gliomas without enhancement (p = .002) and the low-grade gliomas (p < .001). The maximum rCBV ratios of the anaplastic gliomas with enhancement were higher than those of the anaplastic gliomas without enhancement and the low-grade gliomas, but the differences were not statistically significant (p = .08 and p = .03, respectively). CONCLUSION: The results of perfusion-sensitive MR imaging with gradient-echo echoplanar technique correlated with both histologic and angiographic vascularities.     

Low haze transparent electrodes and highly conducting air dried films with ultra-long silver nanowires synthesized by one-step polyol method

Transparent electrodes made of silver nanowires （AgNWs） exhibit higher flexibility when compared to those made of tin doped indium oxide （ITO） and are expected to be applied in plastic electronics. However, these transparent electrodes composed of AgNWs show high haze because the wires cause strong light scattering in the visible range. Reduction of the wire diameter has been proposed as a way to weaken light scattering, although there have seldom been any studies focusing on the haze because of the difficulty involved in controlling the wire diameter. In this report, we show that the haze can be easily reduced by increasing the length of AgNWs with a large diameter. Ultra-long （u-long） AgNWs with lengths in the range of 20-100 μm and a maximum length of 230 μm have been successfully synthesized by adjusting the reaction temperature and the stirring speed of a one-step polyol process. Compared to typical AgNWs （with diameter and length of 70 nm and 10 μm, respectively） and ITO, a transparent electrode consisting of u-long AgNWs 91 nm in diameter demonstrated a low haze of 3.4%-1.6% and a low sheet resistance of 24-109 Ω/sq. at a transmittance of 94%-97%. Even when fabricated at room temperature without any post-treatment, the electrodes composed of u-long AgNWs achieved a sheet resistance of 19 Ω/sq, at a transmittance of 80%, which is six orders of magnitude lower than that of typical AgNWs.     

Refinement of the Microstructure of Sn-Ag-Bi-In Solder,by Addition of SiC Nanoparticles,to Reduce Electromigration Damage Under High Electric Current

The trends of miniaturization, multi-functionality, and high performance in advanced electronic devices require higher densities of I/O gates and reduced area of soldering of interconnections. This increases the electric current density flowing through the interconnections, increasing the risk of interconnection failure caused by electromigration (EM). Accelerated directional atomic diffusion in solder materials under high current induces substantial growth of intermetallic compounds (IMCs) at the anode, and also void and crack formation at the cathode. In the work discussed in this paper, addition of SiC nanoparticles to Sn-Ag-Bi-In (SABI) lead-free solder refined its microstructure and improved its EM reliability under high current stress. Electron backscattering diffraction analysis revealed that the added SiC nanoparticles refined solder grain size after typical reflow. Under current stress, SABI joints with added nano-SiC had lifetimes almost twice as long as those without. Comparison of results from high-temperature aging revealed direct current affected evolution of the microstructure. Observations of IMC growth indicated that diffusion of Cu in the SiC composite solder may not have been reduced. During current flow, however, only narrow voids were formed in solder containing SiC, thus preventing the current crowding caused by bulky voids in the solder without SiC.