Characterization of Novel Thin N-in-P Planar Pixel Modules for the ATLAS Inner Tracker Upgrade

The ATLAS experiment will undergo a major upgrade of the tracker system in view of the high luminosity phase of the LHC (HL-LHC) to start operation in 2026. The most severe challenges are to be faced by the innermost layers of the pixel detector which will have to withstand a radiation fluence of up to 1.4×10¹⁶ n_eq/cm². Thin planar pixel modules are promising candidates to instrument these layers, thanks to the small material budget and their high charge collection efficiency after irradiation. Sensors of 100-200 μm thickness, interconnected to FE-I4 read-out chips, are characterized with radioactive sources as well as testbeams at the CERN-SPS and DESY. The performance of sensors irradiated up to a fluence of 5 × 10¹⁵ n_eq/cm² is compared in terms of charge collection and hit efficiency. Highly segmented sensors are a challenge for the tracking in the forward region of the pixel system at the HL-LHC. To reproduce the performance of 50×50 μm² pixels at high pseudo-rapidities, FE-I4 compatible planar pixel sensors are studied before and after irradiation in beam tests at high incidence angle (80^°) with respect to the short pixel direction. Results on cluster shape and hit efficiency will be shown.