Limits of the time resolution and avalanche build-up analysis of FBK NUV-HD-MT SiPMs

Silicon Photomultipliers (SiPMs) timing performance, in particular the Coincidence Time Resolution (CTR), is of paramount importance in applications like Time-of-Flight Positron Emission Tomography (ToF-PET). In turns, the CTR strongly depends on the Single Photon Time Resolution (SPTR) defined as the time jitter when a single photon is detected by the SiPM. In this study, we performed a characterization of the recently introduced FBK Near Ultra Violet-High Density with Metal-filled Trenches (NUV-HD-MT) technology in terms of its timing performance by measuring the SPTR of single Single Photon Avalanche Diodes (SPADs) with different cell sizes. We used a femto-second laser with a wavelength of 390nm and a custom-made high frequency amplifier. The single SPADs show an excellent SPTR of (17.63 ± 0.04) ps, (22.5 ± 0.1) ps, (24.4 ± 0.1) ps FWHM for the 30μm, 40μm, 50μm microcell respectively. We performed a signal shape analysis to study the influence of the avalanche point injection in the microcell active area on the SPTR. Furthermore, in order to investigate the effect of a peculiar metal-layer layout, involving the metal masking of the border regions of the SPAD, we compared SPADs with 40μm cell size and two different masking versions having 0μm overlap with the nominal active area (M0) and 3μm overlap (M3). We found a SPTR of (18.4±0.1)ps, (16.1±0.1)ps FWHM for the two SPADs respectively, showing that the SPTR is strongly improved by the metal masking in the microcell layout due to the better capacitive coupling. Additional SPTR measurements performed on SiPMs with different active areas show that the masking is more effective on larger sensors. Thus, additional studies with a collimated-light femtosecond-laser setup are ongoing to further investigate this effect and to deeply study the avalanche build-up jitter in different injection positions inside the microcell and of the SiPM.