Low-Noise Single Photon Avalanche Diodes in a 110nm CIS Technology

The increasing performance requirements on the development of single-photon image sensors has led to a tendency towards smaller technological nodes which allow to get higher levels of integration. This makes necessary the successful implementation of Single Photon Avalanche Diodes (SPAD) on deep sub-micron processes. This work presents the design and characterization of SPADs fabricated in a 110nm CMOS Image Sensor technology. These devices are characterized by a remarkably low dark count rate varying linearly with the SPAD active area, with median values per unit area as low as 0.06 to 1.15Hz/um2 when they are biased 1 to 6V above their breakdown voltage, respectively. A Photon Detection Efficiency larger than 50% (at 455nm) has been obtained biasing the device 6V over the breakdown voltage. The timing resolution does not exhibit any diffusion tail, and the FWHM values that have been measured at 4V excess bias are 86.5 (468-nm laser) and 69ps (831-nm laser).