Mitigation of Magnetic Flux Trapping in Superconducting Electronics Using Moats

TL;DR

This study evaluates how moat designs in superconducting niobium films can reduce magnetic flux trapping, providing insights for improving superconducting circuit reliability.

Contribution

It systematically analyzes the effectiveness of various moat geometries in flux mitigation and offers design guidance for superconducting electronics.

Findings

Rectangular slit moats are most effective at flux sequestration.

Moats reduce flux trapping in magnetically shielded environments.

Material defects can still cause flux trapping despite moat design.

Abstract

Magnetic flux (vortex) trapping remains a major obstacle to very large scale integration in superconducting electronics. Moats -- etched regions in circuit layers placed in ground planes and around critical circuitry -- offer a simple passive approach to sequester flux. Here, we systematically examine the effectiveness of moat arrays in superconducting niobium films as a function of geometry (size, shape, and density) and background magnetic field. By measuring the vortex expulsion field, we estimate the flux saturation number and flux trapping temperature for a range of geometries. We find that many moat designs effectively sequester flux in magnetically shielded environments (< 1 $\mu$T), with high-aspect-ratio rectangular "slit" moats providing the strongest mitigation at minimal area cost. However, our measurements show that moats alone do not eliminate flux trapping in non-ideal films, as vortices can preferentially pin at material defects. These results provide design guidance for flux mitigation in superconducting integrated circuits and highlight the need for combined optimization of circuit geometries and materials.