A multipurpose monolithic array of 2×2 multi-channel digital silicon photomultipliers (MD-SiPMs) fabricated in 40nm CMOS technology is presented. Each MD-SiPM comprises 64×64 smart pixels connected to 128 low-power 45ps sliding-scale time-to-digital converters (TDCs). The MD-SiPMs are designed to indirectly capture gamma events in positron emission tomography (PET). The sensor can operate in frame-based and event-driven mode; the latter best suited to capture gamma events. The digital read-out is fully embedded in the sensor and it is reconfigurable by way of serial communication. Data packets are sent following a simple protocol compatible with an external FIFO, therefore eliminating the need of an FPGA. A dedicated input can be used to operate synchronously with an event generator, such as a pulsed laser, useful in other applications, like LiDAR. The system is inherently compatible with 3D-stacking technology; thus serving as a front end for different SPAD technologies, suitable for a variety of applications.@en

We present a complete pixel based on a singlephoton avalanche diode (SPAD) fabricated in a backsideilluminated (BSI) 3D IC technology. The chip stack comprises an image sensing tier produced in a 65 nm image sensor technology and a data processing tier in 40 nm CMOS. Using a simple, CMOS-compatible technique, the pixel is capable of passive quenching and active recharge at voltages well above those imposed by a single transistor whilst ensuring that the reliability limits across the gate-source (VGS), gate-drain (VGD) and drain-source (VDS) are not exceeded for any device. For a given technology, the circuit extends the maximum excess bias that SPADs can be operated at when using transistors as quenching elements, thus improving the SPAD sensitivity, timing performance and photon detection probability (PDP) uniformity. Implemented with 2.5 V thick oxide transistors and operated at 4.4 V excess bias, the design achieves a timing jitter of 95 ps FWHM, maximum photon detection efficiency (PDE) of 21.9% at 660 nm and 0.08% afterpulsing probability with a dead time of 8 ns. This is both the lowest afterpulsing probability at 8 ns dead time and the highest peak PDE for a BSI SPAD in a 3D IC technology to date.

@en