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

TL;DR

This paper evaluates the performance of novel thin planar pixel modules for the ATLAS detector upgrade, focusing on radiation hardness, charge collection, and efficiency at high irradiation levels and angles relevant to HL-LHC conditions.

Contribution

It presents a comprehensive characterization of 100-200 μm thick planar pixel sensors, including irradiation effects and high-angle incidence performance, for the HL-LHC upgrade.

Findings

Sensors maintain high charge collection after irradiation.

High hit efficiency achieved at high pseudo-rapidities.

Performance validated up to fluences of 5×10^{15} n_eq/cm².

Abstract

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 $1.4\times10^{16}\,$n$_\text{eq}$/cm$^{2}$. 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 $100-200\,\mu$m 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 $5\times 10^{15}\,$n$_\text{eq}$/cm$^{2}$ 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 $50$x$50\,\mu$m$^2$ pixels at high pseudo-rapidities, FE-I4 compatible planar pixel sensors are studied before and after irradiation in beam tests at high incidence angle ($80^\circ$) with respect to the short pixel direction. Results on cluster shape and hit efficiency will be shown.