Akira Fujimaki

Vortex Transitional Memory Developed with Nb 4-Layer, 10-kA/cm² Fabrication Process

We report random access memories (RAMs) based on vortex transitional (VT) memory cell developed with the newly developed AIST 10-kA/cm2, Nb 4-layer fabrication process, called High-Speed Standard Process (HSTP). We obtained more effective mutual coupling structure by fully use of all the wiring layer, and successfully reduced the cell size to 25 μm square, which indicated roughly 50% increase in density compared to the previous design. We reduced the critical currents of Josephson junctions and load resistance to be matched with driving circuitry. We tested the miniaturized VT memory cell, and obtained a sufficient margin width of ~15%, and also confirmed correct operations of the other components, including a latching driver and address decoder.

Microwave Properties of Bi 2 Sr 2 CaCu 2 O x Films Fabricated by Multitarget Sputtering

We investigated the surface resistance of Bi2Sr2CaCu2Ox films by the dielectric resonator method. The surface resistance of the films fabricated by the multitarget sputtering method is the order of 10−3Ω at about 20 GHz at 30 K, while that of the ones annealed at 820°C for 2 hours in O2 is about 10−4 Ω. These values are as low as those of Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O or lower, while it is also necessary to confirm the accuracy of the surface resistance measurement.