Ultrahigh-speed HEMT LSI technology for supercomputer

The current status of high electron mobility transistor (HEMT) technology at Fujitsu for high-performance VLSI is presented, focusing on device performance in the submicrometer dimensional range and the HEMT LSIs implemented in supercomputer systems. The HEMT is a very promising device for ultrahigh-speed LSI/VLSI applications because of the high-mobility GaAs/AlGaAs heterojunction structure. A 1.1 K-gate bus-driver logic LSI has been developed to demonstrate the high-speed data transfer in a high-speed parallel processing system at room temperature, operating at 10.92 GFLOPS. A cryogenic 3.3 K-gate random number generator logic LSI with maximum clock frequency of 1.6 GHz has also been developed to demonstrate the high-clock-rate system operations at liquid-nitrogen temperature. For VLSI level complexity, a HEMT 64-kb static RAM with 1.2-ns access operation and a 45 K-gate gate array with 35-ps logic delay have been developed operating at room temperature, demonstrating the high performance required for future high-speed computer systems     

Relationship between thermal treatment conditions and minority carrier lifetimes in p-type, FZ Si wafers

Minority-carrier lifetimes in FZ-p Si wafers were evaluated at various thermal treatments to investigate the effect of the recombination centers. Bulk lifetimes became longer in the case of annealing in O₂ ambient at around 1000°C, while it decreased drastically in N₂ and Ar ambients. Both N₂ annealing sample and oxidation sample after N₂ annealing were measured using deep level transient spectroscopy. Deep levels related to nitrogen defect were observed for the N₂ annealing sample. However, no deep level was observed for the oxidation samples. These results suggest that recombination of minority carriers in the bulk occurred at deep levels related to the nitrogen-vacancy complex.     

Decomposition Characteristics of an Artificial Biogas in a Low‐Pressure DC Glow Discharge

The decomposition characteristics of an artificial biogas, which is a mixture of CH ₄, CO ₂, and H ₂ S, using a low‐pressure DC glow discharge have been investigated. It is found that H ₂, CO, C ₂ H ₂, H ₂ O, CS ₂, and COS are produced from the artificial biogas in the glow discharge. About 65% of the hydrogen atoms in CH ₄ are converted into H ₂ at an input energy of 800 J, at which CH ₄ is completely decomposed, and the decomposition characteristics of the artificial biogas are minimally dependent on the H ₂ S additive. Further, H ₂ S has a tendency to be decomposed earlier than the other components of the artificial biogas. When the glow discharge is generated in the artificial biogas with H ₂ S, some of the carbon atoms are found to deposit on the electrodes and the wall of the discharge chamber. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(1): 26–33, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22304     

Optimum design of integrated tandem-type a-Si solar cell submodule

A new optimum design, in which the actual daily spectral data under outdoor conditions over a year were considered, was developed for the integrated tandem-type a-Si solar cell submodule with a structure of glass/TCO/a-Si: H(pinpin)/metal. It was found by this design that the optimum cell number connected in series, at which maximum total annual output power was obtained, was small compared with that obtained by the conventional optimum design under standard conditions (AM1.5, 100 mW cm⁻²). It was also found that when light-induced degradation was considered, the thickness of the i-layer for the second pin cell was thinner than that by the conventional optimum design.     

Characteristics of a-Si solar cells prepared by the super chamber at a high substrate temperature

A new approach to high-performance a-Si solar cells was studied. a-Si films prepared at a high substrate temperature (> 250°C) have a higher absorption coefficient and a low Si H₂ bond density. the effect of deposition temperature on the open-circuit voltage (V_oc) has been investigated systematically for glass/SnO2 Ipin/metal and glass/metal/nip/indium tin oxide (ITO) structure a-Si solar cells. The V_oc is found to depend strongly on the thermal history of the p/i interface. A short-circuit current of 19.5 mA/cm⁻⁻² was achieved for an a-Si solar cell using an a-Si i-layer with a thickness of 4000 Å, which was prepared at a substrate temperature of 270°C.     

Activation of Mast-Cell-Derived Chymase in the Lacrimal Glands of Patients with IgG4-Related Ophthalmic Disease

The purpose of this present study was to investigate the distribution and expression of chymase in the lacrimal glands (LGs) of patients afflicted with IgG4-related ophthalmic disease (IgG4-ROD). LGs from patients with severe canalicular obstruction were considered the control group. Toluidine blue staining confirmed a significant increase in the number of mast cells in the LGs obtained from the IgG4-ROD patients. In addition, immunostaining of serial sections from the LGs showed a significant increase in the number of chymase-positive cells and tryptase-positive cells in the IgG4-ROD LGs compared to the normal control LGs. The mRNA expression of chymase, tryptase, TGF-β1, and collagen-I tended to increase in the IgG4-ROD LGs. Immunostaining of vimentin and α-smooth muscle actin (α-SMA) showed that myofibroblasts were the main cellular components in severely fibrotic regions of LGs in patients with IgG4-ROD. Linear regression analyses on the number of mast cells, chymase-positive cells, and tryptase-positive cells revealed significant positive correlations between those respective cells. Our findings suggest that chymase may play a role in the fibrotic disorder of IgG4-ROD LGs through the regulation of TGF-β1 activation and collagen-I deposition, and that it may be a therapeutic target for patients afflicted with IgG4-ROD.     

Neuroelectric Mechanisms of Delayed Cerebral Ischemia after Aneurysmal Subarachnoid Hemorrhage

Delayed cerebral ischemia (DCI) remains a challenging but very important condition, because DCI is preventable and treatable for improving functional outcomes after aneurysmal subarachnoid hemorrhage (SAH). The pathologies underlying DCI are multifactorial. Classical approaches to DCI focus exclusively on preventing and treating the reduction of blood flow supply. However, recently, glutamate-mediated neuroelectric disruptions, such as excitotoxicity, cortical spreading depolarization and seizures, and epileptiform discharges, have been reported to occur in high frequencies in association with DCI development after SAH. Each of the neuroelectric disruptions can trigger the other, which augments metabolic demand. If increased metabolic demand exceeds the impaired blood supply, the mismatch leads to relative ischemia, resulting in DCI. The neuroelectric disruption also induces inverted vasoconstrictive neurovascular coupling in compromised brain tissues after SAH, causing DCI. Although glutamates and the receptors may play central roles in the development of excitotoxicity, cortical spreading ischemia and epileptic activity-related events, more studies are needed to clarify the pathophysiology and to develop novel therapeutic strategies for preventing or treating neuroelectric disruption-related DCI after SAH. This article reviews the recent advancement in research on neuroelectric disruption after SAH.     

Design and performance evaluation of a haptic interface based on MR fluids for endovascular tele-surgery

Microsystem Technologies - In this paper, a magnetorheological (MR) fluids based haptic interface has been developed in master site to provide the haptic sensation to the interventionalist during...     

Two-dimensional multiarray formation of hepatocyte spheroids on a microfabricated PEG-brush surface

A two-dimensional microarray of ten thousand (100 x 100) hepatocyte heterospheroids, underlaid with endothelial cells, was successfully constructed with 100 microm spacing in an active area of 20 x 20 mm on microfabricated glass substrates that were coated with poly(ethylene glycol) brushes. Cocultivation of hepatocytes with endothelial cells was essential to stabilize hepatocyte viability and liver-specific functions, allowing us to obtain hepatocyte spheroids with a diameter of 100 microm, functioning as a miniaturized liver to secret albumin for at least one month. The most important feature of this study is that these substrates are defined to provide an unprecedented control of substrate properties for modulating cell behavior, employing both surface engineering and synthetic polymer chemistry. The spheroid array constructed here is highly useful as a platform of tissue and cell-based biosensors and detects a wide variety of clinically, pharmacologically, and toxicologically active compounds through a cellular physiological response.