Towards radiation-hard Depleted Monolithic Active Pixel Sensors for High Energy Physics Experiments

Abstract

Particle track detection, reconstruction, and vertexing play a crucial role in high-energy physics experiments. Silicon strip detectors have conventionally been employed for spa- tial information near collision vertices. However, modern experiments increasingly utilize pixel detectors, which offer two-dimensional resolution, improving tracking and especially vertexing capabilities.Typically, such pixel detectors follow the hybrid approach with separate ASICs for sens- ing elements and readout electronics, requiring a bump bonding process. In contrast, mono- lithic devices, such as depleted monolithic active pixel sensors (DMAPS), integrate both functionalities into a single ASIC, eliminating the need for costly and error-prone bump bonding as well as reducing material budget and thereby reducing multiple Coulomb scat- tering in the detector material. DMAPS leverage technologies such as High-Voltage CMOS (HV-CMOS), which enable operation at high bias voltages, enhancing radiation tolerance and manufacturability. High-resistivity silicon substrates, as used in HV-CMOS sensors, further support this by enabling operation at high bias voltages, increasing radiation tol- erance. Moreover, HV-CMOS sensors are manufactured using industry-standard processes, facilitating cost-effective production.This Ph.D. thesis delves into the RD50-MPW series, a series of HV-CMOS DMAPS prototypes developed by the CERN RD50 collaboration, focusing on the latest prototypes, RD50-MPW3 and RD50-MPW4. The study includes comprehensive laboratory measure- ments as well as beam test evaluations at renowned accelerator facilities, including DESY, CERN, and MedAustron. Complementary Monte Carlo and TCAD semiconductor simula- tions, benchmarked by the experimental efforts, will be conducted, providing a tool-set for tuning and optimizing the state-of-the-art prototypes.The thesis further extends its scope to the OBELIX chip, which is being designed for integration into the tracking system of the BELLE II experiment. So far, the high energy physics community has designed DMAPS sensors using two main distinct design concepts. While the RD50-MPW series is designed in the so-called ”large collection electrode” de- sign, the OBELIX chip is fabricated in the ”small collection electrode” design. Therefore, both major approaches are studied, and the advantages/disadvantages of the two different architectures are showcased.The OBELIX chip will be studied in the laboratory and at beam facilities. The gathered results will be used to characterize the sensor itself and develop a so-called ”beam telescope”. A ”beam telescope” is built up by multiple sensor planes. By operating the planes simulta- neously and synchronizing them properly, such a telescope can be used for particle tracking by evaluating the position of hits at the various telescope planes. Therefore, the telescope can be used as a reference for other sensors and will enhance the performance of the cur- rent characterization and proton computer tomography (PCT) setup at MedAustron. The development and operation of the telescope will assess the sensor’s usability for the BELLE II experiment.Ongoing and future upgrades, such as the High-Luminosity LHC (HL-LHC) and the Future Circular Collider (FCC), demand high radiation tolerance levels, reaching up to 1016 neq/cm2. The HV-CMOS approach is a promising solution to meet these stringent requirements. The research conducted in this thesis spans non-irradiated samples as well as those exposed to fluences of up to 3 × 10^16 neq/cm2.