Yoshihisa Mizutani

Josephson characteristics in a‐axis oriented YBa2Cu3O7−δ/PrBa2Cu3O7−δ’/YBa2Cu3O7−δ junctions

A sandwich‐type all‐oxide Josephson junction consisting of an a‐axis oriented YBa2Cu3O7−δ/PrBa2Cu3O7−δ’/YBa2Cu3O7−δ structure has been realized and its Josephson characteristics experimentally investigated. Almost all the fabricated junctions showed the Josephson characteristics, including a resistively shunted junction (RSJ)‐like current‐voltage characteristic and a Fraunhofer‐like magnetic‐field dependence of the critical current. The obtained maximum values of the critical‐current density jc and the IcRn value were 110 A/cm2 and 80 μV, respectively, for a 50‐nm‐thick PBCO interlayer at 3 K. Besides, the temperature dependencies of the critical current and the normal resistance were measured. Ic was proportional to exp(− aT1/2), where a is a constant.

Characterization of Polycrystalline Silicon MOS Transistors and Its Film Properties. I

The characterization of polycrystalline silicon MOS transistors and its film properties are studied, with special emphasis on the relationship between crystalline defects and carrier transport phenomena. An increase in mobility with gate field in polycrystalline silicon MOS transistors and also with doping concentration in polycrystalline silicon films is observed. These phenomena are interpreted as space charge scattering effects caused by a high density of dislocations in the films. U-shaped drain current vs gate voltage curves are observed both in p-channel and n-channel polycrystalline silicon MOS transistors. The anomalous drain current in the accumulation region is interpreted as junction breakdown at the drain edge caused by crystalline imperfections in the films.

Effects of Oxygen Partial Pressure and Substrate Temperature on Crystalline Orientation in Y-Ba-Cu-O Films Prepared by Sputtering

The dependence of crystalline orientation in Y-Ba-Cu-O films on oxygen partial pressure and substrate temperature has been investigated for films prepared by magnetron sputtering on (100) SrTiO3 and (100) MgO substrates. The tendencies for preferential orientation were the same on both substrates. At low oxygen pressures, the c-axis was oriented perpendicularly to the film plane. In contrast, a/c-axis oriented films were formed at intermediate oxygen pressures, and the a-axis was oriented at high oxygen pressures. At higher temperatures, c-axis oriented films were formed, even at high oxygen pressures.

Josephson Effect in YBa2Cu3O7/Au-Ag/Pb Junctions

A comprehensive study was carried out on the Josephson effect in YBCO/Au-Ag/Pb SNS junctions prepared on YBCO thin films with various crystal orientations. Most of the fabricated junctions showed a dc Josephson current with a clear Fraunhofer pattern dependence on the applied magnetic field, which ensured the uniformity of the fabricated junction structure. Experimental results were quantitatively compared with the conventional junction theory based on the Usadel equation. The junction characteristics were confirmed to be reasonably explained by a junction model in which a thin insulating or highly resistive layer was assumed to exist at the YBCO-Au interface.

Structural Features and Superconducting Properties of As-Grown Y-Ba-Cu-O Films

The structural features of superconducting Y-Ba-Cu-O films prepared by reactive sputtering have been discussed in relation to the preparation conditions. Conductivity anisotropy and the anomalous diamagnetic response observed for the films have also been discussed.

High Speed MoSi2-Gate CMOS/SOS Devices

Characterization and optimization of CMOS/SOS devices with the effective channel length of 1.5 µm utilizing MoSi2-gate technology are investigated from the viewpoint of practical realization of CMOS/SOS VLSIs. Double ion implantation into the channel region was found to be effective for suppressing leakage currents in shorter channel CMOS/SOS devices. Floating substrate effect due to charge pumping was also studied. Using the MoSi2-gate CMOS/SOS technology, feasibility for a 4K (4K×1)-bit static RAM was verified.

Electric Properties of YBCO/PBCO/YBCO Junctions

A-axis oriented YBCO/PBCO/YBCO junctions have been fabricated and tested to investigate the possibilities of an all-oxide Josephson junction experimentally. Almost all the fabricated junctions exhibited not only an RSJ-like I-V characteristic but also a Fraunhofer-like magnetic field dependence of the critical current. The obtained maximum values of the critical current density and the I c R n -value were 110 A/cm2 and 80 μV, respectively, for 50 nm-thick PBCO interlayer at 3 K.