Papers by Author: Satoru Kishida

Abstract: Which parameter dominantly decides the value of time required to reset ReRAM (t_reset) among possible parameters, the value of a low resistance (R_L), voltage to induce reset (V_reset), and temperature to induce reset (T_reset) Although to answer this question is important to achieve faster resistive switching, detailed correlations between the parameters are still unclear. In this paper, we extracted t_reset, V_reset, R_L and T_reset at the same time by combining two electrical measurements. As a result, we found a clear correlation between V_reset, R_L, and T_reset, meaning that each parameter can not be controlled independently. T_reset increases not only with increasing V_reset but also with increasing R_L, which suggests the necessity of introducing ununiformly-shaped filamens and resistive switching takes place at the narrowing part of the filament.

Abstract: We synthesized Ca-rich Bi-based superconducting whiskers by an Al2O3-seeded glassy quenched platelet method. The grown whiskers were precisely characterized by synchrotron radiation X-ray photoemission spectroscopy and high-resolution transmission electron microscopy. The Ca-rich Bi-based superconducting whiskers show a high critical current density of 2×105A/cm2 at 40K in self-field. We found that excess Ca2+ ions substitute for the Sr2+ sites and cause nano crystalline domains with shorter-period modulation embedded in the base crystalline. The embedded nano crystalline domains can result in structural distorted defects which work as strong pinning center.

Abstract: Both a low and a high resistance stateｓ which were written by the voltage application in a local region of NiO/Pt films by using conducting atomic force microscopy (C-AFM) were observed by using scanning electron microscope (SEM) and electron probe micro analysis (EPMA). The writing regions are distinguishable as dark areas in a secondary electron image and thus can be specified without using complicated sample fabrication process to narrow down the writing regions such as the photolithography technique. In addition, the writing regions were analyzed by using energy dispersive X-ray spectroscopy (EDS) mapping. No difference between the inside and outside of the writing regions is observed for all the mapped elements including C and Rh. Here, C and Rh are the most probable candidates for contamination which affect the secondary electron image. Therefore, our results suggested that the observed change in the contrast of the secondary electron image is related to the intrinsic change in the electronic state of the NiO film and a secondary electron yield is correlated to the physical properties of the film.

Abstract: We prepared SmBa2Cu3Oy (SmBCO) superconducting bulks by partial melting growth with a top seed. From the results, we found that the SmBCO bulks prepared by melting process showed good superconductivity, where the critical temperature Tc and the temperature transition width ΔT of the bulk were 94K and about 1K, respectively. The as-prepared bulks required annealing at 500°C for 24h to improve the superconductivity. However, the characteristics of the bulks may be improved by more detailed study, for example optimum preparation and annealing conditions.

Abstract: We deposited Bi2Sr2Ca1Cu2Oy (Bi-2212) superconducting thin films on MgO substrates with or without Al2O3 particles by the rf magnetron sputtering method. From the results, we found that optimum target-substrate distance, rf powers and substrate temperature for obtaining the Bi-2212 films on the MgO substrates were 5mm, 150W and 830°C, respectively. The Bi-2212 films were Bi-2212 single-phase and had the Tc of about 54K . The particle size and the distribution density of Al2O3 were controlled by annealing temperature. The Bi-2212/Al2O3/MgO film showed Bi-2212 single-phase, whereas did not show zero-resistance.