Dark Count Rate Degradation in CMOS SPADs Exposed to X-Rays and Neutrons

Single-photon avalanche diode (SPAD) arrays fabricated in a 180-nm CMOS technology with a high-voltage option have been exposed to calibrated neutron and X-ray sources to evaluate their radiation tolerance. The technology is being investigated in view of the design of low material budget detectors for charged particle tracking based on the coincidence of the signals coming from two or more overlapping layers of SPAD sensors. Each element in the array is a monolithic detector including the processing electronics together with the diode in the same substrate. Different sensor dimensions and structures have been implemented in the test chip to thoroughly explore the technology features. This paper will present and discuss the results from the characterization, in terms of dark count rate, of SPAD arrays irradiated with X-ray doses reaching 1 Mrad(SiO ₂ ) and with neutron fluences up to $10^{11}~1$ -MeV neutron equivalent cm $^{-2}$ .