Superconducting Kinetic-Inductance Microwave Filters

Several kinetic-inductance microstrip filters have been designed and tested. The microstrip consists of a superconducting niobium carbon nitride (NbCN) strip separated from a NbCN ground plane by an amorphous hydrogenated-silicon dielectric. The circuits investigated include an interferometer, a stepped-impedance, a low-frequency stub, and a high-frequency stub filter. Generally, for frequencies below 20 GHz, good transmission characteristics were measured for these structures. A simple physical model is used to determine the major features of the transmission characteristics over a wide temperature and frequency range. Other important issues such as the superconductor and dielectric losses, impedance matching, and film uniformity are addressed for these structures.