FBK VUV-sensitive Silicon Photomultipliers for cryogenic temperatures

Fondazione Bruno Kessler (FBK) has been continuously developing and improving silicon photomultiplier technologies, for example with peak efficiency in the blue (near-ultra-violet, NUV), or in the green (red-green-blue, RGB) region of the spectrum. Over the last years there has been a growing interest in silicon photomultipliers (SiPMs) applications at cryogenic temperatures (e.g.: for the readout of the scintillation light from liquefied noble gases in rare-events experiments). One example is the DarkSide-20k experiment, in which LAr scintillation light is detected after wavelength-shifting to match the SiPMs' spectral response. A dedicated silicon photomultiplier technology has been developed in FBK: the NUV-HD-Cryo. SiPMs made in such technology reach primary dark count rates of about 2 mHz/mm(2) and an after-pulsing probability of about 12% when biased at 4 V above breakdown in liquid nitrogen (LN). In other experiments, like for example the nEXO experiment, direct detection of vacuum ultra-violet (VUV) light in cryogenic conditions is required. In this case, the sensitivity in VUV has to be combined with the advantages of the Cryo'' technology. In this contribution, the latest results from the cryogenic characterization of FBK VUV-HD technology for cryogenic temperatures will be presented. Among the produced devices, one promising split has been identified with reduced after-pulsing probability at 100 K, less than ``standard'' VUV-HD device.