Improvement in Power-Handling Capability of Superconducting Filters Using Multi-Layered Microstrip Line Resonators

We investigated the power-handling capability of superconducting filters using multi-layered microstrip line resonators (MSLRs). A multi-layered MSLR consists of superconducting/insulating/superconducting multi-layered film to improve the power-handling capability of the superconducting filter. The current flowing along the bottom edges of the multi-layered MSLR was less concentrated than that in the conventional MSLR. A 3-pole filter using a straight-type MSLR was designed based on the Chebyshev function to have a center frequency of 5 GHz and a bandwidth of 100 MHz. The single-layered and multi-layered MSLR filters were fabricated with the simulated filter design using NbN single-sided 600-nm thick film and NbN/AlN/NbN single-sided 300/20/300-nm multi-layered film on MgO substrates. Both filters showed good frequency responses at 6.8 K. The input-output relations of both filters at 6.8 K were measured. The power-handling capability of the multi-layered MSLR filter was 1.9 dB larger than that of the single-layered MSLR filter. Thus, the multi-layered MSLR helped to improve the power-handling capability of superconducting filters.