Compact eight channel SPAD module for photon timing applications

Multi-dimensional Time Correlated Single Photon Counting has nowadays reached a prominent position among analytical techniques employed in the medical and biological fields. The development of instruments able to perform simultaneously temporal and spectral fluorescence analysis (sFLIM) is limited by the performances of single-photon detectors; in fact currently available arrays cannot satisfy simultaneously all the requirements. To face this rising quest, a fully-parallel eight channel module, based on a monolithic Single Photon Avalanche Diode (SPAD) array with great temporal resolution, high Photon Detection Efficiency (PDE) and low Dark Counting Rate (DCR), has been designed and fabricated. The system relies on a novel architecture of the single pixel, based on the integration of the timing pick-up circuit next to the photodetector, making the negative effects of electrical and optical crosstalk on photon timing performance negligible. To this aim, the custom technological process used to fabricate the SPAD has been modified, allowing the integration of MOS transistors without impairing the structure and the performance of the detector. The single channel is complemented by an external Active Quenching Circuit, fabricated in a standard CMOS technology, that ensures high maximum counting rate (> 5MHz) and low afterpulsing (< 2%). Finally, the output timing signals are read and conditioned by a proper CMOS electronics. The complete pixel shows a very good temporal resolution of about 45 ps (FWHM).