Direct current to 350 GHz operation of rapid-single-flux-quantum T-flipflop circuits in niobium technology

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Abstract
The operational functionality of rapid-single-flux-quantum (RSFQ) T-flipflop circuits has been experimentally investigated in the frequency range from dc up to nearly three times the characteristic frequency . The operational range found is divided into two domains different in nature. In the first domain, ranging up to frequencies of 120 GHz , correct digital operation of the device has been found. Beyond this range a second domain has been found, ranging from about 200 GHz to nearly 350 GHz, in which quasi-analogous operation of frequency dividing is suggested. Typical bias current margins are in the first domain and in the second. The circuits have been fabricated using - Al/Nb trilayer technology with externally shunted Josephson tunnel junctions of critical current densities of and smallest areas of about . The characteristic voltage is and the McCumber parameter .