Highly radiation tolerant pixelated sensors for the high luminosity upgrade of the CMS detector of the Large Hadron Collider

Due to its large instantaneous luminosity, the future upgrade of the largest particle accelerator of the world, the Large Hadron Collider (LHC), is going to set strong requirements on the radiation hardness of all the technology involved in its accelerating system, but also in its particle detection machines. One of the big detectors recording the energetic proton collisions is the Compact Muon Solenoid (CMS). The sensors comprising its inner tracker (IT) will have to face an unprecedented rate of collisions, ten times higher than the current detector. The silicon 3D pixel technology, with its superior radiation hardness and lower operation voltage and power dissipation, is being considered in CMS as a valid option for the inner most layers in order to cope with these extremely high radiation tolerance requirements. After contextualizing the current CMS situation, as well as stating the future upgrade conditions, a study of the Physics behind the detection processes and the state-of-the-art is carried out. This will bring us to the presentation of the technology I have tested - the 3D sensors - together with the characterisation techniques and analysis processes employed. A full study and characterisation of pixelated 3D silicon sensors fabricated by Centro Nacional de Microelectronica (CNM, Spain) and Fondazione Bruno Kessler (FBK, Italy) is performed. The sensors were bump-bonded to ROC4SENS and RD53A readout chips. They were measured, both fresh and after proton irradiation, at several test beams in the LHC Super Proton Synchrotron (SPS), and in the German Electron Synchrotron (DESY). Chapter 1 introduces the current LHC and its high luminosity upgrade future necessities. The requirements 3D sensors must fulfill to be successfully operated inside the upgraded CMS IT are explained. Chapter 2 gives a comprehensive overview of the physical processes and working principles behind silicon sensors, as well as how they are structured and fabricated. Chapter 3 introduces the devices under test, their irradiation process and testing setups, as well as the data reconstruction algorithm and parameters of interest. Chapter 4 constitutes the summary of the results obtained from the full characterisation. Results on hit efficiency, charge collection, cluster size and hit resolution, for fresh and irradiated samples, are presented. Response as a function of bias voltage, particle beam incidence angle and temperature is considered. This thesis aims to demonstrate that the 3D technology is highly suitable for the CMS inner most tracking layers.