Development of dicing technique for thin semiconductor substrate using temporally shaped femtosecond laser

Recently, semiconductor substrates for integrated circuits (ICs) have been required to be as thin as 50 µm, because many electronic devices must be miniaturized and light in weight. Machining of such thin substrates with conventional dicing techniques is very difficult. Therefore, we have proposed processing them using femtosecond laser ablation. In this work, we investigate the influence of conditions of a double pulsed laser such as the delay time and fluence on the depth and diameter in order to develop a new dicing technique for very thin ICs. A double pulsed laser (λ = 780 nm, τ = 150 fs, f = 10 Hz, Δt = 0 to 100 ps, E₁ + E₂ = 100 µJ) was focused on the Si substrate with a plano‐convex lens having a nominal focal length of 100 mm. At a delay time of 10 ps, singularly shallow and flat‐bottomed holes were obtained. When the substrates were diced under these conditions, the bottom of the processing groove was flat and very smooth, whereas many microcracks starting from the bottom of the groove formed by the conventional method have been observed. From these results, we were able to identify femtosecond laser processing conditions that were applicable to dicing of thin Si substrates. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 149(3): 43–48, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20028     

Investigation of uncovered-bundle heat transfer under high-pressure boil-off conditions

Uncovered-bundle heat transfer tests under high-pressure boil-off conditions were conducted in ranges of pressure from 3 to 12 MPa, heat flux from 3.3 to 18 W/cm² and vapor Reynolds number from 10000 to 62000. There existed two boil-off patterns depending on bundle power, low-power boil-off and high-power boil-off. Though existing steam cooling heat transfer correlations fitted approximately the low-power boil-off test data, they underpredicted considerably the high-power boil-off test data. Intermittent droplet cooling effect in the froth region was fairly larger in high-power boil-off than in low-power boil-off. The FLECHT correlation was modified to account for the intermittent droplet cooling effect in the froth region by using the test data. The modified correlation was in approximate agreement with the high-power boil-off test data as well as the lower-power boil-off test data.     

Iconic memory-based omnidirectional route panorama navigation

A route navigation method for a mobile robot with an omnidirectional image sensor is described. The route is memorized from a series of consecutive omnidirectional images of the horizon when the robot moves to its goal. While the robot is navigating to the goal point, input is matched against the memorized spatio-temporal route pattern by using dual active contour models and the exact robot position and orientation is estimated from the converged shape of the active contour models.     

A novel method to prevent secondary exposure of medical and rescue personnel to toxic materials under biochemical hazard conditions using microwave radar and infrared thermography

In order to prevent secondary exposure of medical personnel to toxic materials under biochemical hazard conditions, we performed a noncontact determination of exposure to toxic conditions via 1215-MHz microwave radar and thermography. A toxic condition was induced by intravenous administration of lipopolysaccharide (LPS) in rabbits. The exposure to LPS was determined by linear discriminant analysis using non-contact derived variables.     

Effects of Elemental Additives on Electrical Resistivity of Silicon Carbide Ceramics

Effects of various elemental additives on the electrical resistivity of hot-pressed SiC ceramics were studied. The electrical resistivity at room temperature of dense SiC ceramics varied greatly depending on the additives used. SiC ceramics with added Be had an extremely high electrical resistivity of 3 × 10¹²°.cm. On the other hand, SiC ceramics with added B and Al had electrical resistivities of 2 × 10 and 0.8 °cm, respectively. The differences in the electrical resistivity of the dense SiC ceramics were considered to be due to different solubilities of the additives in SiC grains. SiC ceramics with added Be had a low level of impurities in the SiC grains as a result of the low solubility of Be in these grains.     

Subacute systemic toxicity assessment of β-tricalcium phosphate/carboxymethyl-chitin composite implanted in rat femur

The efficacy of a composite of β-tricalcium phosphate particles and carboxymethyl-chitin (β-TCP/CM-chitin) for bone repair has already been established in animal experiments. In the present study, subacute systemic toxicity was evaluated to further assess the biological safety of the implanted composite. β-TCP/CM-chitin (approximately 4 mg/kg and 7 mg/kg in male and female rats, respectively) was implanted for 28 days into penetrating defects (2 mm diameter) made artificially in the shaft of the right femur of rats. Sham operation groups with the defect only were prepared as controls. Haematology, blood chemistry, urinalysis, and the histopathology of 44 organs and tissues were investigated. Body weight measurements and clinical observations were performed daily throughout the study. No subacute systemic toxicity possibly caused by the implantation of β-TCP/CM-chitin was detected. These findings indicate that β-TCP/CM-chitin composite is a highly biocompatible bone substitute, at least with an implantation dosage of < 4–7 mg/kg.     

MEMS‐based Air Turbine with Radial‐inflow Type Journal Bearing

A microelectromechanical‐systems (MEMS)‐based air turbine with a new bearing system was designed, fabricated, and evaluated. The bearing system uses a radial‐inflow type journal bearing and a single‐sided hydroinertia thrust bearing. To fabricate the radial‐inflow type journal bearing, cavity‐through deep reactive ion etching (DRIE) in conjunction with silicon‐to‐silicon direct bonding was used. Two etched silicon substrates were directly bonded, and then the bonded silicon substrates were etched by DRIE through the inside cavities. A maximum rotation speed of 95 000 rpm was achieved. The measured and calculated frequency responses of the rotor‐bearing system suggest that the maximum rotation speed was probably limited by the pitching mode resonance. © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Collapse of dilute suspension in different circulating fluidized bed risers with respect to different particles

The collapse of dilute suspension was studied in three different circulating fluidized bed (CFB) risers with two types of particles. The risers had the same height of 3.0 m but different inner diameters of 66 mm, 97 mm and 150 mm, respectively. FCC particles (Geldart A) and silica sand particles (Geldart B) were used. It was found that the collapse of dilute suspension is characterized by rapid accumulation of particles at the riser bottom, independent of the riser diameter and the types of particles. In accordance with the observation, an approach was developed to determine the collapsing point from experimental measurements. Then, the dilute suspension collapse was found to be dominated by an identical differential pressure drop at the riser bottom. This critical pressure drop is independent of gas velocity and riser diameter, whereas varies with the properties of particles. Riser diameter has different influences for FCC and silica sand particles upon the saturation carrying capacity, the solids circulation rate at the dilute suspension collapse. Under a given gas velocity, the collapse in a larger riser is observed to take place at a larger solids circulation rate for FCC, but at a smaller solids circulation rate for silica sand. This diversified dependence on riser diameter of the saturation carrying capacity was identified as a result of the different influences of the riser diameter on the bed density for those two types of particles.     

Interfacial interaction between poly(p-phenylene terephthalamide) filament and nylon 6 matrix crystallized from the melt

Nylon 6 was isothermally crystallized at 483 K for 45 in the presence of poly(p-phenylene terephthalamide) (PPTA) filament. Two kinds of traqnscrystalline zones were observed around the surface of PPTA filament by polarized optical microscopy. The two are designated as the interfacial and the intermediate zones from the surface of PPTA filament. The aggregation state of molecular chains in these zones was characterized by means of microbeam x-ray diffraction and birefringence. The a*-and the a-axes of nylon 6 oriented perpendicularly to the filament surface, aligning along the radial direction in the interfacial and intermediate zones, respectively. The b- and c-axes rotate around these a*-and a-axes. The DSC measurement revealed that nylon 6 molecules in the interfacial zone crystallized and also melted at a higher temperature, compared with those in the intermediate zone or with the usual three-dimensional spherulite. Viscoelastic measurement clarified the fact that the interfacial zone had a restraining effect on the molecular motion of nylon 6 in the compostes with PPTA fiber. The interfacial zone is preferable for reinforcing the composite with respect to modulus.     

Quantitative Evaluation of Oxidative Stability of Biomembrane Lipids in the Presence of Vitamin E

In this report, the oxidation of biomembrane lipids, phospholipid and cholesterol (ChH), was examined experimentally in the presence of vitamin E (V_EH) by using a liposome system, which is widely used as a biomembrane model. A kinetic model was constructed by taking into account mechanisms of antioxidation and pro-oxidation by V_EH and the co-oxidation mechanisms of biomembrane lipids reported previously. The model quantitatively described oxidation behavior in the liposome system under various V_EH addition conditions. The model also predicted oxidation behavior in vivo under various oral ingestion conditions of V_EH. The results suggest that ChH oxidation, which causes various diseases, can be suppressed effectively by taking a certain amount of V_EH once a day to avoid a reduction in the V_EH concentration present in the biomembrane. The proposed kinetic approach should be a useful tool for quantitatively characterizing complicated reaction systems, such as biomembrane oxidation.