An 80MHz frame-rate 17.4% fill-factor 16×16 SPAD image array with event-based multiplexing for super-resolution microscopy

We present a 16×16 single-photon avalanche diode (SPAD) image array prototype for super-resolution imaging under photon-starved environments. To take advantage of photon sparsity, we introduce a 16-to-1 multiplexing scheme at the column level which shares the same quenching circuitry among 16 SPAD pixels. This includes column-level address encoding to support super-resolution microscopy (SRM) despite multiplexing. The quenching circuit uses a 16 input pseudo-NMOS OR gate to decrease SPAD recovery time and circuitry area. The imager array was implemented in a 180nm high-voltage CMOS process and consists of SPADs with a pixel pitch of 21.3 µm and a fill factor of 17.4 % to provide high system detection efficiency. The total die area is 1.5×2.5 mm2 with a photosensitive SPAD array area of 340×340 µm2. At an excess bias of 3.6 V, we measured a photon detection probability up to 22 % at a wavelength of 520 nm. The mean dark count rate of the arrayed detectors is approximately 20 Hz/µm2. We measured a detector dead time of 4ns, which enables lifetime measurement at our target laser repetition rate of 80MHz. To demonstrate SRM with our multiplexing scheme, we localized gold nanoparticle displacement at 40nm, which is 3.7 times smaller than our pixel pitch.