A HIGH-TC SUPERCONDUCTOR JOSEPHSON SAMPLER

This is a review of our high-Tc superconductor (HTS) sampler developme nt. The design and experimental demonstration of a Josephson sampler c ircuit based on YBa2 Cu3Ox(YBCO)/PrBa2Cu3Ox/YBCO ramp-edge junctions i s described. The sampler circuit contains five edge junctions with a s lacked YBCO groundplane and is based on single-flux quantum (SFQ) oper ations. Computer simulation results show that the time resolution of t he sampler circuit depends strongly on the IcRn product of the junctio n and can be reduced to a few picoseconds with realistic parameter val ues. The edge junctions were fabricated using an in-situ process in wh ich a barrier and a counter-electrode layer are deposited immediately after the edge etching without breaking the vacuum. The in-situ proces s improved the critical current uniformity of the junctions to 1 sigma =20% in twelve 4-mu m-width junctions. An YBCO groundplane was placed on the junctions in a multilayer structure we call the HUG (HTS circui t with an upper-layer groundplane) structure. The inductance of YBCO l ines was reduced to 1 pH per square without junction-quality degradati on in the HUG structure. SFQ current-pulse generation, SFQ storage, an d SFQ readout in the circuit have been confirmed by function tests usi ng 3-kHz pulse currents. The successful operation of the sampler circu it has been demonstrated by measuring a signal-current waveform at 50 K.