Random Telegraph Signal in Proton Irradiated Single-Photon Avalanche Diodes

Single-Photon Avalanche Diodes in CMOS technology are very attractive solution for photon detection due to the excellent timing resolution achievable. Unfortunately, such devices suffer from large values of the dark count pedestals. In this work we analyzed a test chip containing SPADs with different layouts, implemented in 150-nm CMOS technology. The behaviour of such devices has been investigated after proton irradiation. It is observed that, after irradiation, the Dark Count Rate switches between two or more discrete levels, phenomenon known as Random Telegraph Signal (RTS). The effect is related to the density and distribution of defects in the semiconductor lattice. RTS characteristics have been studied as function of both temperature and bias voltage. Discussion of results and main hypotheses on defect types responsible for RTS are reported.