Critical current control and microwave-induced characteristics of (NbN/TiN/sub x/)/sub n//NbN stacked junction arrays

Stacked double and triple Josephson junctions with NbN electrodes and TiN/sub x/ barriers were fabricated for the nextgeneration 10 V programmable Josephson voltage standard. Because of difficulties in the growth of uniform junctions in a stack with a constant barrier thickness, a stack with carefully engineered thicknesses was grown that exhibited uniform junction properties. The junction arrays on these chips were biased with microwave power at 16 GHz resulting in constantvoltage steps consistent with the total number of junctions in the array, including the multiple junctions in the stacks. The steps had a current range greater than 1 mA at 4.2 K.