Evaluation of Planar Silicon Pixel Sensors with the RD53A Readout Chip for the Phase-2 Upgrade of the CMS Inner Tracker

TL;DR

This paper evaluates planar silicon pixel sensors with the RD53A readout chip for the CMS Inner Tracker upgrade, demonstrating high spatial resolution and efficiency after irradiation to meet HL-LHC requirements.

Contribution

It presents the characterization of prototype pixel sensors with different geometries and their performance post-irradiation for the CMS HL-LHC upgrade.

Findings

Achieved ~3.4μm spatial resolution before irradiation.

Maintained >99% hit efficiency after high-fluence irradiation.

Demonstrated sensor performance at high bias voltages post-irradiation.

Abstract

The Large Hadron Collider (LHC) at CERN will undergo an upgrade in order to increase its luminosity to $7.5 \times 10^{34}$ cm$^{-2}$s$^{-1}$. The increased luminosity during this High-Luminosity running phase (HL-LHC), starting around 2029, means a higher rate of proton-proton interactions, hence a larger ionizing dose and particle fluence for the detectors. The current tracking system of the CMS experiment will be fully replaced in order to cope with the new operating conditions. Prototype planar pixel sensors for the CMS Inner Tracker with square $50 \mu $m $ \times \; 50 \mu$m and rectangular $100 \mu $m $ \times \; 25 \mu$m pixels read out by the RD53A chip were characterized in the lab and at the DESY-II testbeam facility in order to identify designs that meet the requirements of CMS at the HL-LHC. A spatial resolution of approximately 3.4$\mu$m (2$\mu$m) is obtained using the modules with $50 \mu $m $ \times \; 50 \mu$m ($100 \mu $m $ \times \; 25 \mu$m) pixels at the optimal angle of incidence before irradiation. After irradiation to a 1 MeV neutron equivalent fluence of $\Phi_{\rm eq} = 5.3 \times 10^{15}$ cm$^{-2}$, a resolution of 9.4$\mu$m is achieved at a bias voltage of 800 V using a module with $50 \mu $m $ \times \; 50 \mu$m pixel size. All modules retain a hit efficiency in excess of 99\% after irradiation to fluences up to $2.1 \times 10^{16}$ cm$^{-2}$. Further studies of the electrical properties of the modules, especially crosstalk, are also presented in this paper.