Time-dependent dielectric breakdown (TDDB) distribution in n-MOSFET with HfSiON gate dielectrics under DC and AC stressing

This paper discusses time-dependent dielectric breakdown (TDDB) in n-FETs with HfSiON gate stacks under various stress conditions. It was found that the slope of Weibull distribution of T_bd, Weibull β, changes with stress conditions, namely, DC stress, unipolar AC stress and bipolar AC stresses. On the other hand, the time evolution component of stress-induced leakage current (SILC) was not changed by these stresses. These experimental results indicate that the modulation of electron trapping/de-trapping and hole trapping/de-trapping by stress condition changes the defect size in high-k gate dielectrics. Therefore, the control of injected carrier and the characteristics of trapping can provide the steep Weibull distribution of T_bd, leading to long-term reliability in scaled CMOS devices with high-k gate stacks.     

Synthesis of mesoporous MFI zeolite by dry gel conversion with ZnO particles and the catalytic activity on TMB cracking

A facile synthesis method for mesoporous MFI zeolite (MMZ) has been developed. MFI zeolite was synthesized by a dry gel conversion in the presence of ZnO nanoparticles with a size of 20 nm. The as-synthesized MFI zeolite included crystalline layered zinc silicate and already possessed 5–15 nm mesopores. After calcination, MMZ/zinc silicate composite was treated with hydrochloric acid to remove unreacted ZnO particles. The micropore (1–2 nm) volume was increased after the HCl treatment, suggesting that ZnO nanoparticles (1–2 nm) remained during crystallization as well as zinc silicate. The catalytic activity of MMZ on 1,3,5-trimethylbenzene (TMB) cracking was compared with that of conventional MFI nanocrystals with a size of 80–100 nm. The conversion of TMB on MMZ was much higher than that on the MFI nanocrystals even though crystal size of MMZ is larger than the conventional MFI zeolite. These results suggest that acid sites on the internal surface of mesopores of MMZ contribute to the high conversion of TMB.     

Development of SF6 Gas‐Insulated Disconnecting Switch with Spiral Electrodes Using Motor Operating Mechanism

Gas‐insulated switchgear (GIS) requires reliability and economic efficiency. Circuit breakers, disconnecting switches (DS), and earthing switches have been designed to be more compact. DS requires performance in terms of insulation and current interruption. The bus‐transfer current is the highest among all current interruption requirements for the DS. To develop an alternating current DS driven at a lower speed, it is necessary to reduce the electrode damage. This paper describes the fundamental characteristics of current interruption in a magnetically driven arc using a spiral electrode. Since the arc is rotated by magnetically driven force, the arcing time in the spiral electrode is shortened to about one‐third compared with that of a plain breaker electrode. The DS using a magnetically driven arc was confirmed to comply with the bus‐transfer current switching requirements in the JEC standard. Moreover, a physical model of the magnetic driven arc was constructed, and the behavior of the arc was evaluated quantitatively. As a result, performance of current interruption could be predicted. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(3): 31–39, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21147     

Suzuki segregation in Co–Ni-based superalloy at 973 K: An experimental and computational study by phase-field simulation

Suzuki segregation in Co–Ni-based superalloys is of longstanding interest. In this study, the development of widely extended stacking fault (SF) ribbons was confirmed in a Co–Ni-based superalloy aged at 973 K after deformation at room temperature, which supports the decrease in stacking fault energy (SFE) due to Suzuki segregation. In addition, the plastic deformation behaviors of Co–Ni-based superalloys with various Nb contents up to 3 wt.% were investigated focusing on the effect of Nb addition on dynamic strain-aging by Suzuki segregation. The negative strain-rate dependence of flow stress due to dynamic strain-aging became more significant with increasing Nb content; however, attempts to detect segregating elements by scanning transmission electron microscopy and energy-dispersive spectroscopy analysis were not successful. A phase-field simulation of Suzuki segregation suggested strong Ni depletion with segregation of Cr and Mo atoms at the SF, and the SFE can become negative as a consequence of the segregation. This agrees with the experimentally observed formation of wide SFs by the aging at 973 K after cold deformation. It is also suggested that Nb atoms are strongly depleted at SFs, and a small amount of Nb addition dramatically enhances Cr segregation, resulting in further decreases in the SFE, which is probably responsible for the observed enhancement of dynamic strain-aging by Nb addition. In addition, the local structural changes, such as short-range ordering and/or an in-plane ordering, accompanying the segregation were discussed as possible additional mechanisms for strain-aging enhancement.     

Excitonic photoluminescence in CuAlS2 powders

Copper aluminum disulfide (CuAlS₂) powders were synthesized in the evacuated ampoule. The luminescence properties of obtained powders were evaluated by photoluminescence (PL) at various temperatures. The visible emission peaks at 2.16 and 1.90 eV, and weak ultraviolet emission peak at 3.47 eV were obtained in the room temperature PL. The temperature dependence of the PL revealed that the ultraviolet emission at room temperature was considered to be free-exciton. Several emission peaks related to free-exciton, bound-exciton and phonons were observed in the high-resolution PL at 12 K, reflecting that the obtained powders had high crystallinity. Emission peaks at 3.459 and 3.300 eV for CuAlS₂ were observed for the first time. The former emission might be originated from the bound exciton and the latter from the donor–acceptor pair recombination.     

Route-Enabling Graph Orientation Problems

Given an undirected and edge-weighted graph G together with a set of ordered vertex-pairs, called st-pairs, we consider two problems of finding an orientation of all edges in G: min-sum orientation is to minimize the sum of the shortest directed distances between all st-pairs; and min-max orientation is to minimize the maximum shortest directed distance among all st-pairs. Note that these shortest directed paths for st-pairs are not necessarily edge-disjoint. In this paper, we first show that both problems are strongly NP-hard for planar graphs even if all edge-weights are identical, and that both problems can be solved in polynomial time for cycles. We then consider the problems restricted to cacti, which form a graph class that contains trees and cycles but is a subclass of planar graphs. Then, min-sum orientation is solvable in polynomial time, whereas min-max orientation remains NP-hard even for two st-pairs. However, based on LP-relaxation, we present a polynomial-time 2-approximation algorithm for min-max orientation. Finally, we give a fully polynomial-time approximation scheme (FPTAS) for min-max orientation on cacti if the number of st-pairs is a fixed constant.     

Effect of self-representation of interaction history by the robot on perceptions of mind and positive relationship: a case study on a home-use robot

A question in research is concerning the most important factors for increasing the motivation of a human to continue interacting with an interactional robot. Previous studies have argued that the perceptions of mind and interactability of the robot by the interacting human are essential factors. However, ways of improving such perceptions have not sufficiently investigated. In this study, we focused on the case of a home-use interactional robot and investigated ways to improve such perceptions. We proposed the perceived interaction history of the robot to be another essential factor and hypothesized that adding this factor can promote the perceptions of mind and positive relationship. We conducted a human–robot interaction experiment with 32 human subjects, and the experimental results verified our hypothesis.     

A bilevel decomposition algorithm for simultaneous production scheduling and conflict-free routing for automated guided vehicles

We address a bilevel decomposition algorithm for solving the simultaneous scheduling and conflict-free routing problems for automated guided vehicles. The overall objective is to minimize the total weighted tardiness of the set of jobs related to these tasks. A mixed integer formulation is decomposed into two levels: the upper level master problem of task assignment and scheduling; and the lower level routing subproblem. The master problem is solved by using Lagrangian relaxation and a lower bound is obtained. Either the solution turns out to be feasible for the lower level or a feasible solution for the problem is constructed, and an upper bound is obtained. If the convergence is not satisfied, cuts are generated to exclude previous feasible solutions before solving the master problem again. Two types of cuts are proposed to reduce the duality gap. The effectiveness of the proposed method is investigated from computational experiments.