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Background suppression plays a crucial role in particle physics experiments searching for rare events, such as neutrinoless double beta decay and dark matter interactions. Bolometers, that are among the most competitive devices in this field, would largely benefit from the development of ultrasensitive light detectors, as the combined readout of the bolometric and light signals enables the particle identification. The CALDER collaboration is developing superconducting light detectors that will match the requirements of next generation experiments: noise lower than 20 eV, large active area ($>$20 cm $^2$), wide temperature range of operation, high radiopurity, and ease in fabricating hundreds of channels. For this purpose, we are exploiting the excellent energy resolution and the natural multiplexed readout provided by kinetic inductance detectors (KIDs). KIDs have already demonstrated their potentiality as direct detectors of photons for different astrophysical applications. The aim of our project is to apply this technology in particle physics, using indirect detection. These devices can be operated in a phonon-mediated approach, in which KIDs are coupled to a large insulating substrates in order to increase the active surface from a few mm$^2$ to 25 cm $^2$. We have already demonstrated the feasibility of a phonon-mediated KIDs-based light detectors, using aluminium sensors. These device reached a baseline sensitivity of around 80 eV with an overall efficiency of about 20%. Currently, we are testing new materials (e.g., Ti-Al and nonstoichiometric TiN) to enhance the sensitivity and reach the goal of our project. We present our results and the physical interpretation of the device behavior. Finally, we also discuss the impact of this project on the most advanced bolometric experiments searching for neutrinoless double beta decay and dark matter. [ABSTRACT FROM PUBLISHER]

The main aim of the cryogenic wide-area light detectors with excellent resolution project is the development of cryogenic light detectors with large active area (∼50 mm × 50 mm) and noise energy resolution smaller than 20-eV RMS. Such detectors will be used to discriminate the background in next generation large-mass bolometric experiments, such as cryogenic underground observatory for rare events. In this paper, we present the fabrication process of the phonon-mediated kinetic inductance detectors (KIDs). In the first part of the project, Al KIDs have been developed. Thin film Al (40 nm) were evaporated on high quality, high resistivity (>10 kΩ·cm) Si(1 0 0) wafers using a high vacuum electron beam evaporator. Detectors were patterned by direct-write Electron Beam Lithography (EBL) using positive tone resist AR-P 669.06. To improve the energy resolution of our detector, superconductors with higher kinetic inductance, such as the substoichiometric titanium nitride (TiN x), were developed. TiNx is deposited with reactive dc magnetron sputtering. Thus, the fabrication process is subtractive and consists of EBL patterning through negative tone resist AR-N 7700 and SF6 etch using a Deep Reactive Ion Etching—Inductively Coupled Plasma. Critical temperature of TiNx samples was measured using the 4-point probe geometry. [ABSTRACT FROM AUTHOR]