Silicon Photomultiplier technologies developed at FBK: roadmap towards 3D integrated devices

<!--HTML--><div>Thanks to the continuous improvement of their performance, Silicon Photomultiplier are now considered for the upgrades of several, big physics experiments, ranging from High-energy Physics to rare events physics, to astroparticle physics. Several sensor parameters contribute to the performance achieved in these applications. The latest iteration of the NUV-HD SiPM technology developed at FBK feature Photon Detection Efficiency (PDE) in excess of 60% at 410 nm, Dark Count Rate around 60 kHz/mm2&nbsp;and Single-photon Time resolution (SPTR) of 90 ps FWHM for a 4x4 mm2 device with 40&nbsp;μm cells, when coupled to a discrete, high-frequency readout. In addition, specific developments are required for different physics experiments, including increased radiation hardness for HEP, improved cryogenic operation for Time Projection Chambers employed for research on rare events, and reduction of optical crosstalk for experiments such as CTA. As an example, the use of metal-filled deep trench isolation allows reducing the optical crosstalk probability to 10% with a PDE of 60% (bare die). On the other hand, photon-starved applications, such as readout of Cherenkov light for RICH detectors, underline the importance of further improving the SiPM performance by increasing PDE, reducing noise, both primary and correlated, and improving the SPTR. Considering that the incremental improvements between subsequent generations of SiPMs are reaching saturation, a deeper redesign of the photon detector as a whole, including photosensor and readout electronics, is needed. In this context, FBK is working on the development of the next-generation of SiPMs, with a strong focus on 3D integration, such as SiPMs featuring medium-to-fine-pitch Through Silicon Vias (TSVs) and Backside-illuminated (BSI) devices. A fine segmentation of the sensitive area in separated mini-SiPMs, each one connected to a dedicated readout channel through a low-impedance interconnection, will reduce output capacitance and optimize signal integrity and timing. The use of TSVs will also enable advanced readout, triggering and local processing schemes in the readout ASICs, further improving system-level performance. Finally, BSI-SiPMs will potentially bring additional advantages, such as a PDE close to 100%, reduced output capacitance, enhanced radiation hardness, single-cell connection to the readout electronics and a uniform light entrance window, suitable for the most advanced optical stacks. In the presentation, FBK roadmap towards 3D integrated SiPMs and the preliminary results obtained so far will be discussed.</div>