Experimental realization of a resistive single flux quantum logic circuit

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Abstract
An integrated circuit including all basic components of the recently suggested Resistive Single Flux Quantum (RSFQ) logic family has been designed, fabricated and tested successfully. The circuit includes a generator of periodic SFQ pulses, four buffer/amplifier stages for splitting, channeling and regeneration of the pulses, a detector/load stage, and universal RSFQ logic gate (here performing the NOT function). The 10μm design rule circuit employs 13 active Nb - Al2O3- Nb Josephson junctions with the critical current density ∼ 0.5 kA/cm2. externally shunted by Mo resistors with R 1 Ohm. The shunting provided critical damping of the junctions (\beta_{c}\lsim 1) and reasonable (\sim 500 \muV) IcR product. The circuit operation has been tested by measurement of dc voltages\bar{V}_{i}across various Josephson junctions as functions of the dc current through the pulse generator. Correct and stable operation of the circuit for the clock frequencies from 0 to ∼30 GHz has been demonstrated.

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