Final Steps Towards Production of the ITk Pixel Detector for the ATLAS High Luminosity Upgrade

The Large Hadron Collider (LHC) upgrade to the High-Luminosity LHC (HL-LHC) will bring an unprecedentedly challenging environment to the detectors, with an instantaneous luminosity of $5\times10^{34}\,\rm cm^{-2}s^{-1}$, which corresponds to approximately 140 inelastic proton-proton collisions per bunch crossing. Therefore, in the ATLAS detector upgrade for the HL-LHC, the current Inner Detector will be replaced with an all-silicon Inner Tracker (ITk), to operate under the higher occupancy and radiation damage. The ITk pixel detector is the innermost part of the ITk. It will be equipped with pixel modules consisting of pixel sensors and front-end chips implemented in 65$\,$nm CMOS technology. The ITk project is currently in the pre-production stage. To ensure that the quality of the production components will meet the ITk specifications, practise the production workflow, and provide modules for larger scale tests, various steps are exercised in the module pre-production process. Sensors and test structures from different vendors were sent to ITk collaborating institutes for quality assurance (QA), irradiation, and follow-up testing. Test-beam campaigns were conducted to evaluate the performance of sensors in fully-assembled modules in particle beam. To guarantee smooth and uniform production of modules, all ITk institutes are required to demonstrate their ability of fulfilling their responsibilities by going through a Site Qualification. For module assembly, the ITk Pixel Quad Assembly Tooling V2 was developed, reviewed and produced. Module production involves module assembly, parylene coating for high voltage protection, mechanical wire-bond protection, as well as full electrical quality control (QC) tests. This thesis presents the characterisation of the pre-production planar sensors for the ITk pixel detector. The results are within specifications, except for the leakage current stability from one vendor. In test-beam studies, hit detection efficiency of un-irradiated planar sensors in quad modules was measured. The Site Qualification procedure and requirements are introduced. For module assembly, the performance of the tooling was demonstrated, and 16 modules were assembled. QC tests were performed on three assembled modules. In addition to the work related to the ITk pixel detector, a small project on flavour tagging within the scope of this thesis is introduced.