Neutron radiation hardness of single-photon avalanche diodes for future RICH detectors

The next generation of experiments in high energy particle physics will require a large increase in interaction density, which presents a challenge for particle detectors. Ring imaging Cherenkov detectors (RICH), planned for future upgrades of the LHCb, Belle II and ALICE 3 experiments, will have to operate at increased channel occupancy and background radiation, and currently no photodetector can fulfill all planned requirements. Analog silicon photomultipliers (SiPMs) would be an attractive photodetector candidate, if only their radiation hardness could be improved. To achieve the targeted radiation tolerance, as well as other RICH detector requirements, dedicated developments and a combination of radiation damage reduction and mitigation techniques are needed. We propose a dedicated digital analog SiPM design, achieving the required radiation hardness by using compensating electronics to adjust the sensor response, together with an optimized single-photon avalanche diode (SPAD) array architecture. In order to guide future SPAD designs, we studied the performance of 180 nm actively recharged CMOS SPADs irradiated with neutron fluxes up to 10
¹²
1-MeV neutron equivalent/cm
²
. We report on dark count rates and afterpulsing probability before and after irradiation, with results also for room temperature annealing and cooling down to -60°C.