Design of SNS Josephson Arrays for High Voltage Applications

The voltage from a single, microwave-biased Josephson junction is a small quantity; thus useful voltages are generated only through series arrays of many thousands of junctions. Arrays of superconductor-normal metal-superconductor junctions have been fabricated and tested with as many as 16,500 junctions per array. The arrays are optimized for the highest voltage operation with the largest operating margins for the current bias. Measurements show that these arrays, driven with 20 GHz microwaves, generate a dc voltage greater than 680 mV per array with a dc bias margin over 1 mA. To increase the microwave uniformity across the array, the transmission line impedance has been tapered. By use of this technique, ac Josephson voltages over 110 mV_rms per array have been generated, also with over 1 mA dc bias margin.