High-speed gated CMOS detector for fluorescence lifetime microscopy extending to near-infrared wavelengths

A current-assisted photonic sampler (CAPS) is presented, building on the principles of the current-assisted photonic demodulator (CAPD), but modified for high-speed gating applications such as time-resolved fluorescence-lifetime microscopy. This detector uses an internally applied electric field to move photo-generated electrons by fast drift to selected detection junctions to achieve nanosecond lifetime measurements for incident visible and near-infrared (NIR) light. The fast drift overcomes the shortcomings of conventional gated CMOS detectors based on the slow diffusion processes involved when using charge transfer gates. Furthermore, the applied fields reach deep into the substrate collecting photoelectrons with high efficiency, even for near-infrared (NIR) wavelengths with a high contrast ratio (> 1000). The new detector is fabricated in an X-Fab 0.35 μm process and is tested and characterized as a single pixel but is ready for implementation in an imaging array. The lifetimes of two nanosecond fluorescent dyes in the visible spectrum and one in the NIR are measured.