Performance evaluation of pre-production pixel modules of ATLAS ITk after full characterisation process

The ATLAS inner detector will be completely replaced with a new all-silicon tracking detector (ITk) in 2026–28 to cope with the challenging conditions of the High Luminosity LHC. The pixel detector will be located in the innermost part of the ITk detector. It will be instrumented with 3D sensor technology in the innermost layer (L0), where a fluence up to 2 × 10 16 n eq /cm 2 is expected, and with n-in-p planar hybrid modules 150 µm and 100 µm thick in the three outer layers (L2-L4) and in the first layer (L1), respectively. Before starting production of final modules, following the ITk Pixel QC programme, 16 pre-production quad modules were assembled with ITkPixV1.1 chips and 150 µm thick planar sensors at the University of Glasgow as part of the United Kingdom contribution to the production, among which 10 are reported here. These modules underwent a series of characterisation processes to evaluate electrical performance before and after parylene coating at both +20°C and -15°C temperatures. Mechanical durability of the bump bonding was also tested by thermally cycling between high (+45°C) and low (-45°C and -55°C) temperatures, and stability of the module was tested by running the module for 48 hours. All the processes were run under constant monitoring of temperature, humidity, low voltage, and high voltage; an interlock system also operated to ensure the safety of the module. This study reports on the performance of a significant fraction of modules that participated in evaluating pre-production site capability and deciding the production procedure in different stages of characterisation.