Analysis and test of a novel photodetector device.

This thesis presents the test of an innovative 3D-stacked front-side illuminated(FSI) multi-channel digital silicon photomultiplier (MD-SiPM) fabricated in0.18μmCMOS technology for time-of-flight positron emission tomography (TOF-PET).During the master project, carried out at AQUA laboratory at EPFL, a completetesting system for the chip was designed and implemented. This work focuses onthe implementation of the necessary firmware to interface with the unit under test,and the related software. The former is designed on a Opal Kelly XEM 7630 board,integrating a Kintex 7 FPGA from Xilinx. This board is fully supported by theFrontPanel SDK, a C++ class library to interface a software with the board. Thisis exploited to program a custom graphical user interface (GUI) to perform testsin a semi-automatic way. Its main purpose is to transfer data between PC andFPGA, so to provide an effective controllability and observability of the design.On the FPGA side of the interface, some FrontPanel’s HDL modules work just asexternal pins, enabling the communication with the PC. The designed system wasalso employed to perform a preliminary characterisation of the chip, with the aimof verifying its basic functionalities and the successful outcome of this innovative,3D-integrated design. On-chip time-to-digital converters’ (TDCs) characterisation,dark count rate (DCR), photon counts and preliminary photon detection efficiency(PDE) measurements are presented. Some corruption of the TDCs’ output bits willneed further testing to be resolved, but, in general, they look active and working.The noise level results particularly higher than usual values and some artifactsmight also be present in the counting system. The PDE, although preliminary andnot complete, shows, instead, a very promising result, following the expected trend.A calibration with a photodiode will be necessary, to get a precise estimation.The chip seems to work correctly overall, apart from some minor issues. The3D integration process looks successful and can be exploited for future designs.Nevertheless, a more detailed characterisation of the system is still ongoing andmore accurate results will be available in the future.