Vertex Detectors for the Future Circular Collider: Characterising Monolithic Active Pixel Sensors

The Standard Model (SM) of particle physics is one of the most successful theories of nature, unifying the strong, weak, and electromagnetic forces, however, it still leaves fundamental questions unanswered, many related to the Higgs boson. The Future Circular Collider (FCC), comprising a lepton collider (FCC-ee) and a consecutive hadron collider (FCC-hh), aims to explore these open questions with unprecedented precision. This thesis investigates the feasibility of Monolithic Active Pixel Sensors (MAPS) for the vertex detector of the FCC-ee by characterising the Analogue Pixel Test Structure (APTS), designed for the Inner Tracking System upgrade (ITS3) of the ALICE experiment, which shares similar requirements. APTS variants were evaluated through lab measurements at the University of Zurich and test beams at CERN's Proton Synchrotron and Super Proton Synchrotron. The measurements focussed on characterising the charge collection properties, spatial resolution, and detection efficiency under various conditions, including different pixel pitches, bias voltages, irradiation levels and pixel geometry. The results indicated that all APTS versions efficiently collected all generated charge, with the \textit{larger n-well collection electrode} pixel geometry showing greater susceptibility to noise. All variants achieved 99~\% detection efficiency and the 10~\textmu m pitch sensors met the spatial resolution requirement of less than 3~\textmu m, crucial for the FCC-ee vertex detectors. Furthermore, APTS was shown to maintain a detection efficiency of over 99~\% up to an irradiation of 10$^\text{14}$~1~MeV~n$_\text{eq}$~cm$^\text{-2}$, reaching the radiation hardness requirements of the FCC-ee. The findings support the feasibility of MAPS for future high-precision collider experiments, providing a promising foundation for the vertex detector development of the FCC-ee.