DCR Performance in Neutron-Irradiated CMOS SPADs From 150- to 180-nm Technologies

Single-photon avalanche diodes (SPADs) fabricated using two different CMOS technologies were exposed to a neutron source up to a maximum fluence of 3 × 10
¹¹
1-MeV neutron equivalent cm
^-2
. Significant changes in the dark count rate (DCR), with a strong dependence on the fluence and the device active area, were detected after irradiation. A model for the probability of DCR degradation, accounting for the source spectrum and the geometry of the device under test (DUT), was proposed and proved to be in good agreement with experimental data. The model may be helpful in performing worst-case analysis of SPAD-based detection systems under neutron irradiation.