Time-gated Raman spectroscopy using a 3D-stacked back-side illuminated CMOS SPAD array

Atlas is a 128 × 128-pixel array, consisting of 512 × 512 back-side illuminated (BSI) single photon avalanche diodes (SPADs) in 3D-stacked 65/40 nm CMOS technology. On-pixel auto-correlator and single photon counting capabilities have been previously described, but the chip also has time-resolved sensing capabilities. In this work, we characterize the temporal response of the sensor and, to the best of our knowledge, present the first demonstration of a back-side illuminated SPAD array used for time-resolved Raman spectroscopy. We achieve a mean full width at half-maximum (FWHM) time resolution of 1.44 ns, and a mean timing offset of ~153 ps. Testing the system on both fluorescent standards and diamond, we find that the Atlas sensor achieves a 10.7× improvement in count rate versus the RaII (a front-side illuminated SPAD array previously developed by this group for fluorescence lifetime applications). We observe Raman spectral peaks with microsecond exposures. This demonstrates the significant advantage of the BSI 3D-stacked technology for spectroscopy applications.