CMOS pixel sensor development for the ATLAS experiment at the High Luminosity-LHC

The current ATLAS Inner Detector will be replaced with a fully silicon based detector called Inner Tracker (ITk) before the start of the High Luminosity-LHC project (HL-LHC) in 2026. To cope with the harsh environment expected at the HL-LHC, new approaches are being developed for pixel detectors based on CMOS technology. Such detectors can provide charge collection, analog amplification and digital processing in the same silicon wafer. The radiation hardness is improved thanks to multiple nested wells which give the embedded CMOS electronics sufficient shielding. The goal of this programme is to demonstrate that depleted CMOS pixels are suitable for high rate, fast timing and high radiation operation at the LHC . A number of alternative solutions have been explored and characterised. In this document, test results of the sensors fabricated in different CMOS processes are reported.