Demonstration of chip-to-chip propagation of single flux quantum pulses

We report experimental results on chip-to-chip transfer of single-flux-quantum (SFQ) pulses using an active multichip module (MCM). Josephson transmitters and receivers are integrated on both a chip and an MCM substrate. An MCM consisting of a 4.8-mm chip and an 8.2-mm MCM substrate was fabricated using a 1.6-kA/cm² Nb-trilayer process and a solder-bumped flip-chip bonding technology. The correct operation of the circuit was confirmed by low-speed testing. Bit-error rate (BER) of the circuit was measured down to 10^-5, and extrapolation of the error-function fits suggested a very small BER, lower than 10^-200, at the optimum bias point. Experimental margins on the bias voltage were as large as ±34%