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 next-generation 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 constant-voltage 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.