Development of monolithic active pixel sensors for radiation imaging

The development of Fully Depleted Monolithic Active Pixel Sensors (FD-MAPS) represents nowadays a hot-topic in the radiation detector community. The advantages in terms of production costs and easiness of manufacturing in comparison to the state-of-the-art hybrid detectors boost the research effort in the direction of developing new CMOS compatible detector technologies. To this end, the INFN ARCADIA project targeted the design of a sensor platform for the production of FD-MAPS to be employed in different scientific, medical and space applications. The sensor technology has been developed in collaboration with LFoundry on the basis of a standard 110nm CMOS production process with some modifications needed to meet the project requirements. High resistivity n-type silicon substrates have been chosen for the sensor active volume and a n-type epitaxial layer has been included at the sensor frontside to delay the onset of the punch-through current flowing between the frontside and backside p-type implants. The sensor n-type collection electrodes are surrounded by pwells, which can host the embedded analog and digital frontend electronics, and deep pwells have been included below the pwells to shield them from the sensor substrate. Three engineering runs have been submitted and the produced wafers have been delivered in 2021, 2022 and 2023, respectively. An additional p-type implant has been added in the third production run to create an embedded gain layer below the n-type collection electrodes, to enhance the signal through avalanche multiplication. A selection of the main results obtained from the TCAD simulations and of the most relevant measurements performed on the designed MAPS passive test structures will be presented and discussed in chapter 4. In an analogous way, the experimental results obtained from the characterization of an active sensor designed for brachytherapy, called COBRA, are reported in chapter 5. The calibration of the capacitance included in the internal charge injection circuit of two TJ-Monopix2 MAPS having different substrate types is reported in chapter 6. These sensors represent examples of fully functional and full scale monolithic prototypes realized in a 180nm Tower-Jazz CMOS process, that have been characterized using X-rays fluorescence techniques at the SiLab of the University of Bonn. Finally, in the Conclusions section the main results of the research activity are summarized and the possible future spin-offs of the project are presented.