Experimental and theoretical investigations on short-channel effects in 4H-SiC MOSFETs

In this paper, a fundamental investigation on short-channel effects (SCEs) in 4H-SiC MOSFETs is given. Planar MOSFETs with various channel lengths have been fabricated on p-type 4H-SiC (0001), (0001) and (1120) faces. In the fabricated MOSFETs, SCEs such as punchthrough behavior, decrease of threshold voltage, deterioration of subthreshold characteristics, and saturation of transconductance occur by reducing channel length. The critical channel lengths below which SCEs occur are analyzed as a function of p-body doping and oxide thickness by using device simulation. The critical channel lengths obtained from the device simulation is in good agreement with the empirical relationship for Si MOSFETs. The critical channel lengths in the fabricated SiC MOSFETs are slightly longer than simulation results. The dependence of crystal face orientations on SCEs is hardly observed. Impacts of interface charge on the appearance of SCEs are discussed.     

A new solid model HSM and its application to interference detection between moving objects

In order to realize collision-free coordination of multiple robots, it is crucial to model the robots in a computer adequately and to detect existence or nonexistence of an interference between them on the basis of data structure of the robot models. Motivated by this observation, this article proposes a new solid model named “Hierarchical Sphere Model” (HSM) for modeling moving objects (robots) and presents a feasible algorithm for checking an interference between them on the basis of HSM. HSM arranges region informations in a hierarchical tree structure whose nodes correspond to spherical regions. On the basis of hierarchy of HSM, the algorithm checks only intersections between HSMs' nodes which are close to each other, and hence it works efficiently even if the objects have complicated shape. Furthermore, because a node of HSM represents a spherical region, intersection between, two nodes can be easily found just by calculating the distance between two spheres corresponding to them no matter how the objects move. Finally, the efficiency of the algorithm is demonstrated by several experiments.     

Vacuum sieve tray for tritium extraction from liquid Pb–17Li

Formation of droplet of liquid Li–17Pb released from a nozzle into vacuum was studied for the evaluation of the feasibility as a tritium extraction process. Size of droplets formed from the nozzles was estimated by theoretical and experimental methods. For the theoretical estimation, the non-dimensional comparison of the physical bulk property of liquid Pb–17Li with water (H₂O) at ambient temperature was applied. It was found to be reasonable to apply the Plateau-Rayleigh-Instability theory for the droplet size formula of the fluid Pb–17Li for the nozzle diameter 0.4 mm–1.0 mm, temperature 400 °C–500 °C, at initial velocity of 3 m/s. The experimental results of the droplet size showed good agreement with the theory. This device was used for the parametric study of extraction of deuterium during their free fall in vacuum. The scaling of the device suggests the engineering feasibility of the process.