Speaker
Description
The IBIS and IBIS_NEXT projects, a joint effort between INFN and Fondazione Bruno Kessler (FBK), aim to develop an innovative generation of Silicon Photomultipliers based on a Back-Side Illuminated (BSI) architecture. In this approach, photon absorption occurs through a dedicated backside entrance window, while metallisation layers, quenching resistors, and electrical contacts are relocated to the opposite side of the device. This design introduces a clear separation between the charge collection and avalanche multiplication regions, enabling charge focusing and offering several key advantages over conventional front-illuminated SiPMs. These include an almost 100% geometrical fill factor even for small microcell sizes, enhanced sensitivity extending down to vacuum ultraviolet (VUV) wavelengths through optimised surface treatments, improved radiation tolerance due to a reduced high-field volume, and simplified hybrid integration with readout electronics via bump bonding.
BSI-SiPMs developed within the IBIS programme are particularly well suited for demanding applications in particle and nuclear physics, such as Cherenkov-based detectors for ePIC at the Electron–Ion Collider and future upgrades of ALICE3 and LHCb, as well as noble-liquid experiments like DUNE. Beyond fundamental research, the architecture also opens new opportunities for high-resolution SiPM-based imaging in other scientific and technological domains.
This contribution presents the first experimental characterisation of prototype BSI-SiPMs fabricated by FBK in the initial production cycle of the project (IBIS Run 1). The devices, with SPAD pitches ranging from 15 μm to 35 μm and an active area of 1$\times$1 mm$^2$, already implement the backside illumination concept, although substrate thinning is not yet applied. Electrical and noise performance has been investigated through current–voltage measurements, dark count rate and optical cross-talk studies, as well as preliminary timing measurements. Characterisation was performed under dark conditions, in a temperature-controlled climatic chamber over a wide temperature range, and at cryogenic temperature (77 K), providing a first assessment of the potential and limitations of this new SiPM architecture.