Development of microwave superconducting microresonators for neutrino mass measurement in the HOLMES framework

TL;DR

This paper reports on developing superconducting microwave microresonators, specifically Ti/TiN multilayers, for neutrino mass measurement in the HOLMES project, aiming for high energy resolution and scalability.

Contribution

It introduces Ti/TiN multilayer microresonators with tunable critical temperatures for MKID applications in neutrino mass experiments, including design, fabrication, and characterization.

Findings

Ti/TiN multilayer microresonators achieved T_c from 70 mK to 4.5 K.

Microresonators showed low loss and uniformity.

Suitable for large-scale X-ray calorimetric spectroscopy.

Abstract

The European Research Council has recently funded HOLMES, a project with the aim of performing a calorimetric measurement of the electron neutrino mass measuring the energy released in the electron capture decay of 163Ho. The baseline for HOLMES are microcalorimeters coupled to Transition Edge Sensors (TESs) read out with rf-SQUIDs, for microwave multiplexing purposes. A promising alternative solution is based on superconducting microwave resonators, that have undergone rapid development in the last decade. These detectors, called Microwave Kinetic Inductance Detectors (MKIDs), are inherently multiplexed in the frequency domain and suitable for even larger-scale pixel arrays, with theoretical high energy resolution and fast response. The aim of our activity is to develop arrays of microresonator detectors for X-ray spectroscopy and suitable for the calorimetric measurement of the energy spectra of 163Ho. Superconductive multilayer films composed by a sequence of pure Titanium and stoichiometric TiN layers show many ideal properties for MKIDs, such as low loss, large sheet resistance, large kinetic inductance, and tunable critical temperature $T_c$. We developed Ti/TiN multilayer microresonators with $T_c$ within the range from 70 mK to 4.5 K and with good uniformity. In this contribution we present the design solutions adopted, the fabrication processes and the characterization results.