RSFQ Logic/Memory Family: A New Josephson-Junction Technology for Sub-Terahertz-Clock-Frequency Digital Systems

Recent developments of the rapid single-flux-quantum (RSFQ) circuit family are reviewed. Elementary cells of the family can generate, pass, memorize, and reproduce picosecond voltage pulses V(t) with nominally quantized area integral V(t)dt = Phi(0), corresponding to transfer of a single magnetic flux quantum Phi(0) = h/2e across a Josephson junction. Functionally, each cell can be viewed as a combination of a logic gate and an output latch (register) controlled by clock pulses, which are physically similar to the signal pulses. Hand-shaking style of local exchange by the clock pulses enables one to increase complexity of the LSI RSFQ systems without loss of operating speed. The simplest components of the RSFQ circuitry have been experimentally tested at clock frequencies exceeding 100 GHz, and an increase of the speed beyond 300 GHz is expected as a result of using an up-to-date fabrication technology. The review includes a discussion of possible future developments and applications of this novel, ultrafast digital technology.