Series Arrays of NbSi Barrier Junctions with RF Power Dividers for AC Josephson Voltage Standards

Overdamped Josephson junctions for AC voltage standards are realized with Nb
_x
Si
_1-x
barrier junctions at PTB. The characteristic parameters of the junctions can be tuned over a wide range by adjusting the Nb content and the thickness of the barrier. For the pulse-driven Josephson Arbitrary Waveform Synthesizer (JAWS), series arrays of up to 15,000 Josephson junctions have been fabricated using junction stacks containing five Josephson junctions. In addition, two types of on-chip power dividers have been investigated at PTB, namely Wilkinson and serial-parallel power dividers, respectively. These developments aim for further increasing the number of Josephson junctions on a single chip and thus for increasing the output voltage.