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

Atlas is a 128 x 128 pixel array, consisting of 512 x 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 demonstrate the potential use of the Atlas sensor in time-gated Raman spectroscopy. We achieve a mean full width at half-maximum of 1.44 ns, and median timing offset of ~ 153 ps. Testing the system on both fluorescent standards and diamond, we find that the Atlas sensor achieves a 10.8× 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 maintained with microsecond exposures. This demonstrates the significant advantage of the BSI 3D-stacked technology for spectroscopy applications.