SPAD Microcells with 12.1 ps SPTR for SiPMs in TOF-PET Applications

In this work, we present a single-photon avalanche diode (SPAD) microcell, at the core of each silicon photomultiplier, capable of delivering single-photon time resolution (SPTR) of 12.1 ps FWHM. The device, fabricated in 180 nm CMOS technology, measures 25, 50, and 100 µm and can be scaled to large arrays. The microcell features a localized quenching and active recharge circuitry and it achieves peak photon detection probability (PDP) of 55% at 480 nm and 6 V excess bias with a large sensitivity spectrum covering NUV, VIS, and NIR. The normalized dark count rate (DCR) is 0.2 cps/μm ² at the same excess bias. The SPAD microcell embeds active recharge circuitry capable of reducing the dead time to 3 ns. At this level, the measured afterpulsing probability is as low as 0.1% at the same excess bias.