The punchthrough characteristics of Josephson logic circuits

This paper reports the first experimental results on the punchthrough probabilities of Josephson logic circuits. High performance Josephson latching logic circuits are driven by an ac power supply which allows the circuits to reset when the power supply reverses polarity, and also acts as the system clock. A circuit is said to punchthrough when it carries its logic "1" state from one cycle of the power supply onto the next without resetting. Punchthrough probabilities of 2.5 µm Current Injection Logic (CIL) 2-input AND and 4-input AND circuits were measured as a function of the power supply frequency for two different values of load resistors. The probability for punchthrough was found to decrease exponentially with increasing transition time. For a particular value of power supply frequency, the punchthrough probability was higher for the 4-input AND than for the 2-input AND. It was also found to be higher for the higher value of load resistor. These dependencies have the same functional form as predicted by theoretical models for the punchthrough characteristics of point junctions.