Megapixel time-gated SPAD image sensor for 2D and 3D imaging applications

Abstract

We present the first 1Mpixel SPAD camera ever reported. The camera features 3.8ns time gating and 24kfps frame rate; it was fabricated in 180nm CIS technology. Two pixels have been designed with a pitch of 9.4µm in 7T and 5.75T configurations, respectively, achieving a maximum fill factor of 13.4%. The maximum PDP is 27%, median DCR 2.0cps, variation in gating length 120ps, position skew 410ps, and rise/fall time <550ps, all FWHM at 3.3V of excess bias. The sensor was used to capture 2D/3D scenes over 2m with an LSB of 5.4mm and a precision better than 7.8mm. Extended dynamic range is demonstrated in dual exposure operation mode. Spatially overlapped multi-object detection is experimentally demonstrated in single-photon time-gated ToF for the first time.

Wide-field Fluorescence Lifetime Imaging Microscopy with a High-Speed Mega-pixel SPAD Camera

“…Time-gated imaging. The imaging is based on a 1 megapixel SPAD image sensor [28]. The acquisition is performed by using half of the camera with 7% fill factor and 10% photon detection probability at 510 nm.…”

“…response of the SPAD array (see Fig. 5 in [28] for details) with a 'sliding thresholding' of the data, going from N tot = 1300 (right hand edge of the image) to N tot = 50 (left hand edge). We note that despite the 7% fill factor, the small pixel pitch of 9.4 µm (corresponding to a pixel active circular area of 6.18 µm 2 ) of the sensor provides sufficient sampling for microscopy at common magnification range.…”

“…We measured that the average 10% to 90% intensity rise time for the gate (evaluated over all the pixels) is (0.55 ± 0.08) ns [28]. The order N of the super-Gaussian is chosen such that it matches the actual measured profiles [28]. Namely, N = 6 in Eq.…”

“…SPAD array used in this work [28], a 512×512 SPAD array (SwissSPAD2 [29]) was the largest SPAD array available (recent developments in SPAD detectors are reviewed in [30]). In this work, we demonstrate 0.5 megapixel (500×1024 pixels) wide-field FLIM microscopy with a SPAD array, while protein fluorescent lifetimes are extracted directly from the data via a bespoke artificial neural network (ANN).…”

“…The SPAD array is described in detail in Ref. [28] and in the Methods. The camera operates in gated mode, i.e.…”