High power studies of superconducting microstrip: The limitations of superconductors as low-loss interconnects and high Q filters

High power studies of superconducting microstrip transmission lines have been carried out, with a view toward using them as interconnects in future cryogenic computers and as elements in high power microwave filters. After a survey of the status of normal metal on-chip interconnects, this work evaluates the optimal size of on-chip superconducting interconnects, graphically shows their performance advantage over cooled normal metal interconnects and concludes that the required current densities will be high enough that superconducting breakdown will be an important consideration. The status of superconducting RF filters is then surveyed. Again, understanding and improving the high power limits of thin film superconductors will be critical.; Nonlinearities precede the onset of significant loss at breakdown in superconducting transmission lines. Pulse propagation simulations showed that the superconductor's intrinsic nonlinear inductance will not cause severe pulse distortion over the distance of a long on-chip interconnect and that no inductive nonlinearity will cause pulses to merge. Bounds are given for the magnitude of extrinsic nonlinearities which would cause significant distortion of digital signals.; Breakdown measurements on superconducting NbN, Nb and YBCO microstrip showed that the DC critical current consistently exceeds the RF critical current over a wide temperature range. A simple DC breakdown (critical current) measurement will therefore overestimate the RF current carrying capability of a superconducting transmission line or thin film resonator segment.; A model of breakdown and cross sectional current distribution was developed in order to try to quantitatively relate DC and RF critical currents. Its applicability to NbN, Nb and YBCO is discussed.; The high DC and low RF critical currents observed on YBCO microstrip suggest edge damage, for example, during patterning. The limited power handling of today's high T{dollar}sb{lcub}rm c{rcub}{dollar} superconducting RF filters may therefore not be intrinsic and might be improved by better control of edge quality.