Binary-divided arrays with intrisically overdamped Nb/Al-AlOx/Nb (SNIS) junctions driven at 70 GHz

Binary-divided IV arrays with 8192 overdamped Nb/Al-AlOx/Nb Josephson junctions, fabricated within a joint cooperation between INRIM and PTB, have been tested at 4.2 K and in a temperature range from 6 to 7 K. We measured the microwave-induced step amplitude and checked the uniformity of junction parameters and microwave response on the whole array and sub-segments. The characteristic voltage Vc of the fabricated junctions varies from 0.25 to 0.6 mV. For the lower limit of Vc we could demonstrate at 4.2 K proper operation of the 1 V circuits with current margins larger than 1 mA for all array segments. In the case of larger values for Vc the arrays can be operated at the second and third Shapiro step, when radiated with microwaves from 69 to 74 GHz. Unsloped 3rd harmonic steps whose width ranged from 0.3 mA up to and above 1 mA have been measured on all subsegments providing voltages up to 3.73 V at 73.7 GHz across the whole array. Devices with high values of Vc (at 4.2 K) have been also successfully operated at 6-7 K, by optimizing the first Shapiro step. Quantized voltages up to 1.24 V with current margins between 0.5 and 0.8 mA have been observed.