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 at the same time. In this work we present the design and the performance of an improved detector, where the KID acts only as sensor and is coupled to dedicated phonon collectors. The separation between the detector and the collectors increases the variation of the quasi-particle density within the device, thereby enhancing its responsivity. The meander of the KID is composed of a 77nm trilayer wire of Aluminum-Titanium-Aluminum, while the phonon collectors are made of a 100nm Aluminum layer and act as quasi-particles 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 increase in responsivity by around a factor of five.