128  ×  128-Pixel Current-Assisted Photonic Sampler Image Sensor and Camera System for Macroscale Fluorescence Lifetime Imaging With Multiexposure for Extended Dynamic Range

A 128 × 128-pixel current-assisted photonic sampler (CAPS) image sensor is designed for macroscale fluorescence lifetime imaging (MFLI). Current assistance is used for swift detection and time gating of the photogenerated carriers within the whole substrate. The sensor is fabricated in a commercial 350nm CMOS process on a 15μm epi-layer, with 19μm pixels and a 62% fill factor. The pixel features gating widths below 1 ns subject to a 42 ps standard deviation on the gate width uniformity, and a 27 ps standard deviation on its temporal position. The pixel has a quantum efficiency (QE) above 40% for near-infrared wavelengths, whereas the peak QE is 60% at 675 nm. The gate’s intrinsic decay is observed to be 280 ps, which allows for the MFLI of sub-nanosecond lifetime dyes. A multi-exposure method has been implemented, where the pixel is non-destructively read-out multiple times - with different exposure times - after each reset. This allows for imaging with an extended dynamic range, and is validated on commercial fluorescence phantoms. The MFLI capabilities are further demonstrated in a preclinical experiment.