Silicon Photomultipliers technologies for 3D integration

Progress in 3D interconnecting technologies paved the way to a new generation of Silicon Photomultipliers (SiPM) by combining the integrated functionalities of the digital SiPM with the high performance, in terms of noise and efficiency, of the analog SiPM. Recently, FBK has been developing new 3D integration technologies, specifically designed for SiPMs, to improve performances and functionalities by using backside-illuminated (BSI) devices and Through Silicon Vias (TSV) interconnections. Two different technology platforms have been identified: a BSI design for NIR and TSV interconnections for NUV/VUV SiPMs. Two R&D batches are under development to demonstrate the feasibility as well as robustness and reliability of both the technologies. For NIR applications, electrical characterization of ultra-thin SiPM wafers with a metal reflector on the front side has shown an improved photon detection efficiency when operated in BSI configuration compared with thinned front-side illuminated (FSI) devices, allowing at the same time high-segmentation access to the SiPM output from the front-side. Instead, for NUV/VUV applications, a FSI stacked approach is more suitable since the junction depth needs to be shallower to absorb short wavelengths. In this case, TSV interconnections have been implemented allowing to place the contacts on the backside of the wafer.