Low Tc Hafnium Kinetic Inductance Device with High Internal Quality Factor

TL;DR

This paper demonstrates that Hafnium-based kinetic inductance detectors (KIDs) with very low critical temperature and high internal quality factors are promising for sensitive detection applications, with tunable properties via annealing.

Contribution

It introduces Hafnium as a superconducting material for KIDs with low T_c and high Q_i, and shows how post-fabrication annealing enhances their performance.

Findings

Hafnium KIDs have T_c below 249 mK and Q_i exceeding 10^5.

Annealing reduces T_c and disorder parameter without compromising Q_i.

Performance aligns with the generalized Mattis-Bardeen model.

Abstract

Kinetic inductance devices (KIDs) are superconducting resonators with high kinetic inductance sensitive to external energy perturbations. KIDs made with superconductors having $T_c$ far below one Kelvin are of particular interest for sensing minuscule signals, such as light dark matter detection and millimeter wave telescopes for astronomy and cosmology. In this work, we report the promising performance of KIDs fabricated with Hafnium from heated sputter depositions. The KIDs have $T_c$ lower than 249$\pm$2 mK, the internal quality factor ($Q_i$) of the resonators exceeds $10^5$ and the temperature dependence of the resonances can be described by the generalized Mattis-Bardeen model with a disorder parameter $\Gamma=4\times10^{-3}\Delta_0$. Post-fabrication annealing at temperatures above the deposition temperature can further reduce the $T_c$ and $\Gamma$ without reducing $Q_i$, leading to improvements in energy resolution.