Novel imaging method and optimized demodulation pixels for wide-field Fluorescence Lifetime Imaging Microscopy

A demodulation image sensor suitable for Fluorescence Lifetime Imaging Microcopy (FLIM) was developed in a standard CMOS process with a buried photodiode (BPD) option. Contrary to existing imagers with large demodulation pixels based on BPD, the pixel featuring a pitch of 6.3um was designed for high charge transfer speed by optimizing the transfer gate shape rather than the BPD shape. Demodulation up to 32MHz was achieved at low light level, corresponding to less than one photo-electron detected per pixel and demodulation cycle. A rapid lifetime determination algorithm is proposed for employing this type of pixels in a wide-field FLIM setup. The concept is finally validated by resolving the lifetime of a ruthenium complex.