VORTEX TRANSITIONAL NONDESTRUCTIVE READ-OUT JOSEPHSON MEMORY CELL

A vortex transitional Non Destructive Read-Out (NDRO) Josephson memory cell was proposed, fabricated and successfully tested. The memory cel l consists of two superconducting loops in which a single flux quantum is stored, and a two-junction interferometer gate as a sense gate. Th e memory cell employs vortex transitions in the superconducting loops for writing and reading data. The vortex transitional memory operation of the cell contributes to improving its sense discrimination and ope rating margin. The memory cell is activated by two control signals wit hout timing control signals. Memory cell chips have been fabricated wi th Nb/AlO(x)/Nb junctions, three Nb wirings, SiO2 insulators and Mo re sistors. It has also been miniaturized by developing a vertically inte grated device structure and refining small junction technology. The ce ll size is 22 mum x 22 mum. The memory cells functioned properly, with a large operating margin of +/-20%. The single flux quantum operation s of this memory cell makes it an attractive basic element for a high- speed cache memory.