  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.
