The dependence of the threshold current of a double-contact low-inductance interferometer on the capacitance of a Josephson contact and geometric inductance was found.
Threshold curves for multijunction superconducting interferometers have been calculated previously, showing general agreement with observed features, especially in symmetric cases. We here add some more details to the analysis, paying particular attention to the effects of asymmetries in coupling, inductance, or critical currents. Feed-loop inductance and flux quantization in the feed loop can be important. A changing lobe pattern over many periods, asymmetries within a period, shifting patterns between runs spanning a warm-up, and sudden changes in pattern because of noise in the environment are all quantitatively explainable on the basis of this model. By use of a single ’’calibration curve’’, the inductance for symmetric two- or three-junction interferometers can be obtained immediately.
We have investigated various geometrical design dependencies for rapid single-flux-quantum (RSFQ) circuits in high-Tcsuperconductors (HTS) technology, including the characteristics of the intermediate inductances. Structural- and temporal-dependent combinations of Cn-Rn(capacitance and normal resistance of the Josephson junctions, JJs) in the HTS technology are also investigated. Relatively favorable combinations of normal resistance and low capacitance of the JJs needed in the HTS technology for RSFQ circuits have been made possible by recent fabrication methods of high-quality YBCO films. Obtaining these devices is made achievable by using the grain boundary structures and high critical current density (JC) of the HTS JJs. Mutual interactions of the intermediate inductances with other parts of the whole circuit are examined and optimized for the best operation situation. Here in particular, the operation of the HTS Josephson transmission-line (JTL) cells utilizing the grain boundary Josephson junctions, including various structural inductances, is studied based on the reported parameters of the developed devices and thoroughly analyzed by simulation results.