Experimental realization of a resistive single flux quantum logic circuit

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 - Al <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> - Nb Josephson junctions with the critical current density ∼ 0.5 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . externally shunted by Mo resistors with R 1 Ohm. The shunting provided critical damping of the junctions ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\beta_{c}\lsim 1</tex> ) and reasonable ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sim 500 \mu</tex> V) I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> R product. The circuit operation has been tested by measurement of dc voltages <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\bar{V}_{i}</tex> 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.