Characterization of Random Telegraph Signal in Neutron-Irradiated 150-nm CMOS SPADs

This article investigates the neutron irradiation effects on the random telegraph signal (RTS) observed in the dark count rate (DCR) of single-photon avalanche diodes (SPADs) fab ricated in a 150-nm complementary metal–oxide–semiconductor (CMOS) technology. Two similar chips, F2 and S2, were exposed to neutron fluences of 4.15 × 1010 and 3.90 × 109 1 MeV neutron equivalent cm−2, respectively. Time-resolved DCR mea surements were acquired both before and after irradiation. RTS detection and characterization techniques are discussed, revealing that although the weighted-time-lag plot (W-TLP) is effective in accurately detecting RTS levels, it presents chal lenges in extracting other RTS characteristics. The primary effect observed in the irradiated samples is an increase in the number of pixels exhibiting RTS post-irradiation, along with more complex RTS behavior, attributed to multi-stable RTS defects in neutron-induced clusters. To further understand these defects, temperature- and voltage-dependent measurements were conducted.