Fundamental operation of single-flux-quantum circuits using coplanar-type high-T-c SQUIDs

We have fabricated coplanar type dc SQUIDs using NdBa2Cu3Oy superconducting thin films and operated fundamental single-flux-quantum (SFQ) circuits. The Josephson junctions were made by the narrow-focused ion beam irradiation technique. For a 145 mu m wide and 10 mu m long logic SQUID having a critical current of 105 mu A and an inductive parameter (beta(L)) of 28, a store and a restore of the flux quantum have been demonstrated at temperatures of 4.2-30 K. These operations were performed with an input pulsewidth of 5 ns (5 ns was the shortest input pulse width available from our function generating equipment). These results show experimentally the possibility of high speed operation in all high-T-c superconducting digital circuit. (C) 1996 American Institute of Physics.