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

This paper investigates the neutron irradiation effects on Random Telegraph Signal (RTS) observed in the Dark Count Rate (DCR) of Single-photon Avalanche Diodes (SPADs) fabricated in a 150 nm CMOS technology. Two similar chips, F2 and S2, were exposed to neutron fluences of 4.15 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sup> and 3.90 × 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> 1 MeV neutron equivalent cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup>, respectively. Time-resolved DCR measurements 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 challenges in extracting other RTS characteristics. The primary effect observed in the irradiated samples is an increase in 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.