PTB´s status of AC voltage metrolgy by microwave- and pulsetrain-driven josephson junction arrays

The report describes the most recent PTB developments and applications of large Josephson arrays for the generation of very precise sine waves and arbitrary waveforms. By means of large70 GHz sine-wave-driven binary arrays, AC voltages with frequencies up to 1 kHz and amplitudes of more than 10 V were generated with an uncertainty of better than 1μV/V. For the fabrication of this array type with up to 70000 junctions in series connection, an SNS junction technology with Nb_xSi_x-1 barriers is now completely installed and permanently in use. With pulse-driven arrays of Josephson junctions, arbitrary waveforms were generated with a level of higher harmonics smaller than -120 dBc for frequencies from 150 Hz to 100 kHz at rms voltages less than 100 mV. These results were achieved with extended arrays of up to 4795 very small SNS junctions with Hf_0.5Ti_0.5 barriers. Also the NbSi-technology technology has successfully been applied for the fabrication of pulse-driven Josephson arrays. As it seems to be difficult to considerably increase the wave amplitude by enhancing the junction number of the arrays, experiments were performed to combine a binary array system with a pulse-driven system with the goal to make use of the high amplitude of stepwise generated waves without losing the low noise and precision of quantum based rf waveforms generated by pulse trains at a clock frequency of 15 GHz.