A High Dynamic Range 128 × 120 3-D Stacked CMOS SPAD Image Sensor SoC for Fluorescence Microendoscopy

A miniaturized 1.4 mm $\times \,\, 1.4$ mm, $128\times120$ single-photon avalanche diode (SPAD) image sensor with a five-wire interface is designed for time-resolved fluorescence microendoscopy. This is the first endoscopic chip-on-tip sensor capable of fluorescence lifetime imaging microscopy (FLIM). The sensor provides a novel, compact means to extend the photon counting dynamic range (DR) by partitioning the required bit depth between in-pixel counters and off-pixel noiseless frame summation. The sensor is implemented in STMicroelectronics 40-/90-nm 3-D-stacked backside-illuminated (BSI) CMOS process with 8- $\mu \text{m}$ pixels and 45% fill factor. The sensor capabilities are demonstrated through FLIM examples, including ex vivo human lung tissue, obtained at video rate.