title: Evaluation of fine-pitch hybrid silicon pixel detector prototypes for the CLIC vertex detector in laboratory and test-beam measurements
Creators: name: Williams, Morag Jean
Publisher: name: University of Glasgow
Year: 2021

description: The Compact Linear Collider (CLIC) is a concept for a high-energy, high-luminosity e+ e− linear collider for precision measurements of Standard Model processes and to search for new phenomena, proposed to be built after the lifetime of the upgraded Large Hadron Collider. The beam conditions expected at CLIC impose strict requirements on the CLIC detector design in order for the physics programme to be achieved. In the vertex detector subsystem, the pixelated detectors are required to achieve a spatial resolution of approximately 3μm, a hit detection efficiency ≥99.7%, a timing resolution of ≤5ns, and a material budget per layer of 0.2% of a radiation length. Currently, no pixel detector technology can achieve these requirements simultaneously, therefore prototype pixel detectors with novel designs are being developed and tested within the CLIC detector and physics collaboration. The CLICpix2 hybrid readout ASIC aims to fulfil the CLIC vertex detector requirements. It has been designed using a 65nm CMOS process with a fine pixel pitch of 25×25μm^2, simultaneous per-pixel charge and time measurements, and power-pulsing capabilities. Within this thesis, the performance of CLICpix2 ASICs bump-bonded to active-edge planar silicon sensors is evaluated using laboratory and test-beam measurements. The detectors were hybridised using a novel single-chip bonding process, and the interconnect quality is quantified using a data-driven pixel categorisation scheme. High interconnect qualities are achieved for a small number of assemblies, with yields up to 99.6%. The formulated categorisation method successfully identifies unexpected behaviour of the devices, which were used as feedback to the manufacturer to optimise the solder bump-bonding process. Calibration measurements are also performed to convert the threshold and charge measurements of the assemblies into physical units. The performance of the two highest quality assemblies is evaluated and compared to the CLIC vertex detector requirements. Test-beam data recorded at the CERN and DESY test-beam facilities with CLICpix2 planar sensor assemblies is reconstructed using the Corryvreckan software framework, significantly contributed to as part of this study. Similar results are recorded for both assemblies, despite the large differences in test-beam telescope set-ups and data reconstruction processes used for each. The intrinsic spatial resolution of CLICpix2 assemblies with 130 μm planar sensors is determined to be &lt;3μm. CLICpix2 planar sensor assemblies are calculated to have hit detection efficiencies of above 99.95% at the optimal operating conditions, and an intrinsic timing resolution of ≤5 ns is achieved after a time-walk correction is applied to the pixel data. The CLICpix2 detectors meet the hit detection efficiency, spatial resolution, and timing resolution requirements of the CLIC vertex detector with planar silicon sensors of thickness 130μm. To achieve these requirements with the target sensor thickness of 50μm, a silicon sensor with enhanced charge sharing or a smaller pixel pitch would be required.