Mitigation of the Magnetic Field Susceptibility of Transition Edge Sensors using a Superconducting Groundplane

TL;DR

This paper introduces a superconducting groundplane as an effective local magnetic shielding method for transition edge sensors, significantly reducing magnetic interference and preserving detector performance in compact applications.

Contribution

The study presents a novel superconducting groundplane technique that enhances magnetic shielding for TES detectors, addressing limitations of external shields and mitigating internal magnetic fields.

Findings

Shielding factor of at least ~75 against external magnetic fields.

High resilience of detectors to magnetic fields up to several microTesla.

No degradation in energy resolution or calibration shifts under magnetic interference.

Abstract

Transition edge sensor (TES) microcalorimeters and bolometers are used for a variety of applications. The sensors are based on the steep temperature-dependent resistance of the normal-to-superconducting transition, and are thus intrinsically sensitive to magnetic fields. Conventionally the detectors are shielded from stray magnetic fields using external magnetic shields. However, in particular for applications with strict limits on the available space and mass of an instrument, external magnetic shields might not be enough to obtain the required shielding factors or field homogeneity. Additionally, these shields are only effective for magnetic fields generated external to the TES array, and are ineffective to mitigate the impact of internally generated magnetic fields. Here we present an alternative shielding method based on a superconducting groundplane deposited directly on the backside of the silicon nitride membrane on which the TESs are located. We demonstrate that this local shielding for external magnetic fields has a shielding factor of at the least ~ 75, and is also effective at reducing internal self-induced magnetic fields, as demonstrated by measurements and simulation of the eddy current losses in our AC biased detectors. Measurements of 5.9 keV X-ray photons show that our shielded detectors have a high resilience to external magnetic fields, showing no degradation of the energy resolution or shifts of the energy scale calibration for fields of several microTesla, values higher than expected in typical real-world applications.