Benchmarking flux trapping properties of superconducting films with patterned structures

Understanding and controlling vortex trapping in superconducting structures is crucial for advancing the performance of superconducting devices such as superconducting digital circuits (SDCs), high-Q resonators, and detectors. Patterned structures modify the density and locations of trapped vortices and provide an effective platform to study and benchmark flux trapping behavior in superconducting films. We use scanning superconducting quantum interference device (SQUID) microscopy to image vortex configurations in structures such as thin strips and films with artificial pinning sites or moats fabricated from NbTiN and Nb films, which are both relevant for realizing SDCs.

In this part of the talk, I will introduce our measurement and data analysis procedures. We primarily cool strips and moat structures that have various sizes and spacings through the critical temperature under different out-of-plane magnetic fields. From scanning SQUID images, we extract the temperature below which vortices are immobile, the percentage of vortices that are trapped in a moat, and other quantities. By characterizing the dependence of these quantities on measurement parameters (e.g., temperature, cooling rate) and film properties, we identify requirements for moat structures to successfully trap flux and build an understanding of the mechanisms that govern flux trapping in superconducting structures.