Backside illuminated wafer-to-wafer bonding single photon avalanche diode array

We present an innovative sensor chip, exploiting backside illumination of a silicon-on-insulator (SOI) wafer integrating custom single photon avalanche diodes (SPADs), flipped and wafer-bonded on a standard CMOS wafer integrating the analog front-end circuit, in-pixel digital processing and readout electronics. Two major improvements are achieved: higher pixel density and fill-factor, since these detectors are placed on the top of the corresponding smart-pixel electronics, instead of being placed side-by-side (as in planar structures); enhanced spectral sensitivity in the near-infrared, up to 1 μm wavelength, thanks to thicker active volume within the SOI detector wafer and to the backside illumination of the active area.