Characterisation of HV-CMOS silicon pixel sensors with a transient current technique before and after proton irradiation

For operation at the High Luminosity LHC, the ATLAS detector will need to be upgraded. Its Inner Detector will be replaced by an all-silicon tracking system called the Inner Tracker (ITk). The ITk will cope with harsher radiation conditions and a higher number of simultaneous collisions with respect to the current LHC environment. The ATLAS Collaboration is currently developing a new monolithic radiation hard sensor for the outer ITk pixel detector layers. This new sensor technology is based on the High Voltage CMOS (HV-CMOS) process, which makes the integration of CMOS electronics on a high voltage biased substrate possible. This enables such sensors to operate in a high radiation environment, the material budget can be reduced and the production can be simplified. A study of the radiation hardness of prototype HV-CMOS sensors is presented in this thesis. In particular, a characterisation of the depletion depth with the transient current technique was performed. To calculate the depletion depth, a dedicated analysis was developed. The study covers the performance before and after proton irradiation with fluences up to $1.5 \cdot 10^{15}\ 1\ \text{MeV}\ \text{n}_\text{eq}/\text{cm}^2$. Two proton beams with different energies were exploited for the study. The irradiation with protons of 24 GeV was performed at CERN's Proton Synchrotron, while an irradiation with 16.7 MeV protons was conducted at the Bern Cyclotron. For the latter, an irradiation setup measuring the proton flux was developed. The acceptor removal seen in neutron irradiation of HV-CMOS sensors is also observed in the proton irradiations, but to a much larger extent. This increases the depletion depth after proton irradiation to more than 100 $\mu \text{m}$.