High-frequency performance of RSFQ circuits realized in SINIS technology

The paper presents the determination of the high-frequency performance of Rapid Single Flux Quantum (RSFQ) circuits fabricated in superconductor-insulator-normal metal-insulator-superconductor (SINIS) technology. Circuits of different designs have been realized and were experimentally investigated, including specially designed T flip-flop (TFF) structures and circuits consisting of a switch terminated in Josephson transmission lines. For TFF circuits, the operational functionality was investigated in the frequency range from dc up to nearly 200 GHz. Two frequency domains were found. In the first domain, ranging up to frequencies of 80 GHz (f_C≅Y_C/Φ₀), correct digital operation of the device was ascertained. Beyond this range a second domain was found, ranging to nearly 200 GHz, for which quasi-analog frequency dividing is assumed. The bias current margins are ±30% at 40 GHz and ±15% between 130 GHz and 200 GHz. For circuits consisting of a switch, the operational functionality was proved in the frequency range from dc up to 50 GHz, with bias current margins of more than ±20%. The critical current density of the circuits is j_C≅750 A/cm². The smallest junction area is about A=12 μm², and the characteristic voltage is V_C =170 μV