Enhanced athermal phonon responsivity in a kinetic inductance detector with integrated phonon collectors

Cryogenic phonon detectors are adopted in light dark matter searches and coherent elastic neutrino-nucleus scattering experiments as they can achieve low energy thresholds. The phonon-mediated sensing of silicon particle absorbers has already been proved with kinetic inductance detectors (KIDs), acting both as sensors and athermal phonon absorbers. In this work, we present the design and the performance of an improved detector design. In this architecture, the KID acts only as a sensor and is coupled to dedicated phonon collectors. When a signal is coming from the substrate, the presence of a separated collector allows to detect a higher increase in quasi-particle density, thereby enhancing its responsivity. The meander of the KID is composed of a 77 nm trilayer wire of aluminum–titanium–aluminum, while the phonon collectors are made of a 100 nm aluminum layer and act as quasi-particle funnels. Inside the collectors, the absorbed athermal phonons generate quasi-particles, which, after diffusion, are trapped in the lower-gap superconducting trilayer. The performance of this setup is compared to that of a standard phonon-mediated KID, showing an increased phonon collection efficiency by a factor of around 7.