We present a CMOS imager consisting of 32×32 smart pixels, each one able to detect single photons in the 300-900 nm wavelength range and to perform both photon-counting and photon-timing operations on very fast optical events with faint intensities. In photon-counting mode, the imager provides photon-number (i.e, intensity) resolved movies of the scene under observation, up to 100 000 frames/s. In photon-timing, the imager provides photon arrival times with 312 ps resolution. The result are videos with either time-resolved (e.g., fluorescence) maps of a sample, or 3-D depth-resolved maps of a target scene. The imager is fabricated in a cost-effective 0.35-μm CMOS technology, automotive certified. Each pixel consists of a single-photon avalanche diode with 30 μm photoactive diameter, coupled to an in-pixel 10-bit time-to-digital converter with 320-ns full-scale range, an INL of 10% LSB and a DNL of 2% LSB. The chip operates in global shutter mode, with full frame times down to 10 μs and just 1-ns conversion time. The reconfigurable imager design enables a broad set of applications, like time-resolved spectroscopy, fluorescence lifetime imaging, diffusive optical tomography, molecular imaging, time-of-flight 3-D ranging and atmospheric layer sensing through LIDAR

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This paper reports the design and the characterization of Single-Photon Avalanche Diodes (SPADs) fabricated in a standard 0.35 um CMOS technology aimed at very low noise and sharp timing response. We present the investigation on the breakdown voltage, photon detection efficiency (PDE), dark count rate (DCR) and timing response on devices with different dimensions and shapes of the active area. Results show uniform breakdown voltage among different structures, PDE above 50% at 420 nm, DCR below 50 cps at room temperature and timing response with no exponential tail and typical full-width at half-maximum of 77 ps and 120 ps for 10 um and 30 um active areas, respectively. The fabricated devices enable the fabrication of imagers with CMOS SPAD arrays suitable for advanced applications demanding extremely low noise and picosecond timing accuracy