Logic Operation of SFQ Circuit Elements Made of YBCO Junctions

YBa2Cu3O7-x(YBCO) ramp-edge junction technologies have been developed for fabricating high-operating-temperature SFQ(Single Flux Quantum) circuits. The Ic(critical current) spread that is the key parameter for integrating junctions could be decreased to 8% for a 1000-junction array that was formed on a groundplane. The background technologies that enabled this uniform junction characteristic are precise control of the counter-electrode deposition-conditions and deposition of the extremely smooth multiplayer that showed the roughness as small as 2 nm. Based upon these ramp-edge junction technologies, oxide SFQ-circuit-elements were fabricated and their logic operations were investigated. SFQ circuit elements such as a confluence buffer, a set-reset flipflop, and a toggle flipflop have been fabricated and their logic operations were measured by using an SFQ-dc converter. Both toggle flipflops that have one output and two outputs have been fabricated. These circuits could be operated up to the temperature of near 60 K under finite operating margins. These experimental results enable us to further develop fuctional and much more integrated SFQ circuits.