Rapid single-flux quantum logic using π-shifters

We have found that the size of some rapid single-flux quantum (RSFQ) logic cells based on conventional 0-type Josephson junctions can be significantly reduced by using a pi-type junction as a phase shifter in passive (nonswitching) mode. In comparison with the recently suggested active (switching) pi-junctions mode, the passive mode offers much greater operation margins for their critical current I-c(pi). This gives pi-junctions a chance to be implemented in RSFQ designs in the near future. As an example, we have simulated the operation of a toggle flip flop with zero-geometrical inductance of the fluxon storage loop. Simulations show that the parametric inductance of the pi-junction and its normal resistance R-n form a low-pass filter, which sets the low limit for pi-junctions (IcRn)-R-pi product, but offers a wide range of variations of the other parameters. The possible reduction of RSFQ cell size by using pi-junctions opens the way to scale superconducting logic circuits down to the submicron dimensions. (C) 2003 American Institute of Physics.