Submicron Nb Microwave Transmission Lines and Components for Single-Flux-Quantum and Analog Large-Scale Superconducting Integrated Circuits

We report results of measurements of Nb stripline resonators with linewidths ranging from 1.0 to 0.25 μ m, fabricated using an 8-Nb-layer process with planarized SiO2 dielectric developed at MIT Lincoln Laboratory for superconductor single-flux-quantum circuits. The fundamental resonant frequency f 0 was varied from 2.3 to 4.5 GHz. The results show that, at 4 K, the losses for the narrowest lines are dominated by losses in the dielectric. At high power, the nonlinear niobium losses dominate. Spiral inductors have also been used to design and fabricate multipole low-pass filters with three and five poles with cutoff at 1 GHz. The measured and simulated results for the filters agree very well and show almost ideal properties. The precision and high reproducibility of this fabrication process hold the promise of fabricating multipole filters without the need for tuning the individual poles.