64 × 64-Pixel Current-Assisted Photonic Sampler Image Sensor and Camera System for Real-time Fluorescence Lifetime Imaging

A 64 × 64-pixel current-assisted photonic sampler (CAPS) image sensor is designed for real-time fluorescence lifetime (FLT) imaging. Current-assistance is used for swift detection and time-gating of the photogenerated carriers within the whole substrate. An additional bias node is used to decrease the dynamic power consumption and a photogate is applied to the sensor to reduce the carrier transfer time. The sensor is fabricated in a commercial 350 nm CMOS process on a 15 µm epi-layer, with 30 µm pixels and a 61 % fill factor. The pixel features gating widths below 1 ns subject to a 17 ps standard deviation on the gate width uniformity, and a 31 ps standard deviation on its temporal position. The pixel has a quantum efficiency (QE) above 40 % for near-infrared (NIR) wavelengths, whereas the peak QE is 61 % at 675 nm. The gate’s intrinsic decay is observed to be 320 ps, which allows for the FLT imaging of sub-nanosecond lifetime dyes. The real-time FLT imaging capabilities are demonstrated on commercial fluorescence phantoms and in a preclinical experiment.