Electron-phonon coupling in Ti/TiN MKIDs multilayer microresonator

TL;DR

This paper investigates the electron-phonon coupling in Ti/TiN multilayer microresonators used for thermal detection, highlighting the trade-offs between critical temperature, power handling, and signal-to-noise ratio.

Contribution

It provides new measurements of electron-phonon coupling in Ti/TiN multilayer resonators, informing optimal design for thermal particle detection.

Findings

Lowering critical temperature weakens electron-phonon coupling.

Optimal thermal response requires balancing critical temperature and power handling.

Measured electron-phonon coupling parameters for Ti/TiN multilayers.

Abstract

Over the last few years there has been a growing interest toward the use of superconducting microwave microresonators operated in quasi-thermal equilibrium mode, especially applied to single particle detection. Indeed, previous devices designed and tested by our group with X-ray sources in the keV range evidenced that several issues arise from the attempt of detection through athermal quasiparticles produced within direct strikes of X-rays in the superconductor material of the resonator. In order to prevent issues related to quasiparticles self-recombination and to avoid exchange of athermal phonons with the substrate, our group focused on the development of thermal superconducting microresonators. In this configuration resonators composed of multilayer films of Ti/TiN sense the temperature of an absorbing material. To maximize the thermal response, low critical temperature films are preferable. By lowering the critical temperature, though, the maximum probing power bearable by the resonators decrease abruptly because of the weakening of the electron-phonon coupling. A proper compromise has to be found in order to avoid signal to noise ratio degradation. In this contribution we report the latest measurement of the electron-phonon coupling.