Design and Characterization of Near-Infrared Sensitivity-Enhanced Three-Tap Fully Depleted Image Sensor for Fluorescence Lifetime Imaging

A backside illumination (BSI) silicon-based CMOS image sensor (CIS) with three transfer gates is designed and optimized for near-infrared (NIR) fluorescence lifetime imaging microscopy (FLIM) applications. A three-tap design is considered for a more efficient fluorescence acquisition, avoiding sample damage and photobleaching. A thick silicon substrate and a p-well funnel are applied to obtain better external quantum efficiency (EQE) and lower parasitic light sensitivity (PLS) in the NIR range. In addition, the photocharge collection speed of the pixel is investigated and optimized. This three-tap image sensor performs a high EQE of 42.6% and a low PLS of −60 dB at 940 nm and a pixel response of 7.41 ns. Fluorescence lifetime imaging with a developed image sensor is demonstrated with accuracy as an example with the 705-nm peak emission.