Glass-free SiPMs with Through Silicon Vias for VUV/NUV light detection

Glass-free Silicon Photomultipliers (SiPMs) optimized for Vacuum Ultraviolet (VUV) light detection have been developed and characterized at FBK, including Through Silicon Vias (TSVs) that bring the top contact to the backside of the device tier to be able to perform 3D integration with the readout electronics. R&D activity was carried out on SiPMs on Vacuum Ultraviolet-High Density (VUV-HD) SiPMs with a 1x1 cm 2 active area and a Photon Detection Efficiency of about 23% at 175 nm. Two different TSV fabrication strategies have been developed: "Via-Mid", in which the TSV is formed during the processing of the frontside of the wafer, and "Via-Last", in which the TSV is fabricated with backside-only processing. Both approaches provided functional TSVs, showing good characteristics, such as high connection yield, good insulation from the substrate and no modification of the SiPM characteristics for the "Via-Last" approach. A notable feature of the TSVs fabricated at FBK and customized for the VUV-HD SiPMs is the absence of the glass support wafer, which allows preserving sensitivity to VUV light as well as a reduction of the external component of the optical crosstalk. In this work, we discuss the different microfabrication strategies and report on the detailed electro-optical characterization of 1x1 cm 2 VUV-HD SiPMs with "Via-Last" TSVs.