Experimental investigation of local timing parameter variations in RSFQ circuits

Circuit parameter variations resulting from the fabrication process affect the timing parameters of rapid single flux quantum (RSFQ) digital circuits. This determines the maximum clock rate and the yield of the circuit. It is generally believed that the global parameter variations (target-to-wafer) are much more significant in this regard than the local parameter variations (on-chip), but there has been little experimental evidence for this. This experiment measures the distribution of local parameter variations of the timing parameter of RSFQ circuits. The experiment consists of a 10 by 10 matrix of nominally identical RSF~ "clock rings" covering an integrated circuit area, a total of 3500 Josephson junctions. Each ring is activated individually, and its frequency is measured with accuracy better than 1%.