Minoru Aoyagi

Stress-induced migration model based on atomic migration

Stress-induced migration is one of the problems related to the reliability of metal interconnections in semiconductor devices. This phenomenon generates voids and disconnections in the metal interconnections. The purposes of this work are to establish the stress-induced model based on atomic migration and theoretically clarify the temperature characteristics of void formation and disconnection using the presented model. First, the stress-induced migration model based on atomic migration in which the driving force is the gradient of elastic potential is presented. Next, to clarify the temperature characteristics of stress-induced migration, the presented model is applied to the formation of voids and disconnections and the results of theoretical analyses are compared with experimental results. It was found that the temperature characteristics of the void formation show various patterns depending on the void interval, and the temperature characteristics of the disconnection show various patterns depending on the void interval and void radius. These theoretical results are in agreement with the experimental results.

Effects of Hydrogen Radical Treatment on Fabrication of Catalyst Nanoparticles from Metal Oxide Film at Low Temperature and Synthesis of Silicon Nanowires

Metal catalysts of indium nanoparticles were fabricated at a low temperature from an indium oxide film coated on a glass substrate under hydrogen radical treatment. It is found that by increasing the time of hydrogen radical treatment, the spherical surface of the catalysts is changed progressively. However, the quantities of nanoparticles remain constant. Subsequently, silicon nanowires were synthesized on the fabricated substrates at a temperature of 400 °C. Their quantity decreased with increasing hydrogen radical treatment time. On the basis of field-emission scanning electron microscopy, it is expected that the surface shape of catalysts fabricated at a low temperature directly affects the quantity of the silicon nanowires. Furthermore, a method of fabricating metal nanoparticles and a growth model of silicon nanowires based on hydrogen radical treatment are suggested.

Possibility of an embedded system for ultrasound-based measurement of the distances to two target objects

We developed an embedded system by which to simultaneously measure the distances to two target objects, such as an obstacle and a wall. The embedded system incorporates a set of ultrasound sensors, analog circuits, and a microcomputer to automatically measure the distances to the two targets, and displays the information on a liquid crystal display. For a single target, a large iron-plate wall, at a distance of from 0.5 to 2.75m, the percentage error in the detected distance was less than 5%. For two targets, such as an acrylic resin cylinder (object 1) in front of a wall (object 2), the percentage error in the detected distances was less than 5% in most cases. In some cases, however, there were significant measurement errors. Nevertheless, since the proposed measurement system revealed the exact distance in the majority of cases, this system could be applied to industrial and autonomous moving robots.

Fabrication of metal nanoparticles as catalyst at low temperature and growth of silicon nanostructures

We firstly investigated the effect of hydrogen radical treatment to fabricate metal nanoparticles as catalyst, which is used for synthesizing one dimensional nanostructure, from metal oxide film at low temperature as 200°C. The metal nanoparticles with spherical shape were successfully fabricated after hydrogen radical treatment. Their surface shapes were clearly changed with increasing the hydrogen radical treatment time at same temperature. In addition, silicon nanostructures after fabrication of metal nanoparticles were grown at varied temperatures. The ball- and wire-like silicon nanostructures at 200°C and 400°C were synthesized, respectively. Their structure depends strongly on the growth temperature.

Growth mechanisms for atypical forms of silicon nanowires

An investigation was carried out into the growth mechanisms for atypical forms of silicon nanowires (Si-NWs) synthesized using a vapor-liquid-solid growth process assisted by hydrogen radicals. Sn or Au nanoparticles, which act as catalysts during Si-NW growth, were produced by hydrogen radical treatment of Sn or Au thin films covering a silicon substrate. The Si-NWs were synthesized from silane gas excited by hydrogen radicals in the presence of these nanoparticle catalysts. In addition to normal Si-NW structures, atypical forms such as tapered, branched, bent, corrugated and block types, were synthesized. The growth of tapered, branched and bent-type Si-NWs was caused by contraction of the catalytic nanoparticles, adhesion of nanoparticles to the side wall of growing Si-NWs, and non-uniform supersaturation of the nanoparticles with Si, respectively. Growth of corrugated- and block-type Si-NWs was induced by an excess supply of Si atoms to the growing Si-NWs.

Automatic Detection System for Complete Connection of a Waterproof Soft-Shell Electronic Connector With a Sliding Locking Device

We developed a detection method for complete connection of a particular waterproof soft-shell electronic connector with a sliding locking device for automobiles and demonstrated a practical automatic detection system for complete connection. The proposed detection method is based on a click generated from the sliding-locking device at complete locking. However, the click generated by this type of connector is so quiet that it must be detected by a miniature microphone, amplified, and subjected to various electrical processes. Complete connection is then automatically determined from the signal level and the settling time and frequency components of the click. As a result of the demonstration of a practical automatic detection system, the detection system detected complete connection at a probability of 100% for 100 connectors and successfully rejected incomplete connections. There are limitations to the proposed detection method. The detection system did not prevent misdetection due to other types of connectors and noises that have sound components similar to those of the click for the waterproof soft-shell connector with a sliding-locking device. However, we do not consider these misdetections to be a serious problem, because sound components similar to the click for the waterproof soft-shell connector with a sliding-locking device are rare in the manufacturing environment.

Ultrasound Phantom Using Sodium Alginate as a Gelling Agent

For medical workers, ultrasound phantoms for human soft tissue are used not only for accuracy management of ultrasound diagnosis but also to aid ultrasound‐guided needle and blind catheter insertion training without risk to real patients. For the phantoms, ultrasound characteristics and a texture are required to mimic the human soft tissue. The proposed phantom was composed of sodium alginate, calcium sulfate dihydrate, trisodium phosphate 12‐hydrate, glycerol, and water. The propagation speed, attenuation coefficient, acoustic impedance, and texture of the proposed phantom were almost the same as those of human soft tissue. Expensive chemicals and special equipment are not required.