Performance of highly irradiated FBK 3D and planar pixel detectors

The High Luminosity upgrade of the CERN Large Hadron Collider (HL-LHC) requires new radiation tolerant silicon pixel sensors. In the case of the CMS experiment, the first layer of pixel detectors will be installed at about 3 cm from the beam line, where an integrated fluence of about $2\times10^{16} \mathrm{n_{eq}cm^{-2}}$ (1 MeV equivalent neutrons) is expected (HL-LHC Runs 4 and 5). The first tracker layer will be substituted before the start of HL-LHC Run 6. The 3D concept for silicon pixel sensors presents several advantages with respect to traditional (planar) sensors. Thanks to short anode-to-cathode distances, 3D sensors are much more resistant to radiation damage, making them suitable for use in the inner layer of the future tracker. This paper describes results from beam tests with highly irradiated planar and 3D sensor and RD53A readout chip combinations. RD53A is the first prototype in 65 nm technology developed by the RD53 collaboration for use in HL-LHC pixel detectors. The sensors were made in FBK foundry in Trento, Italy, and their development was done in collaboration with INFN (Istituto Nazionale di Fisica Nucleare, Italy). Both planar and 3D sensors feature a pixel area of $2500$ $\mu\mathrm{m^2}$ and an active thickness of 150 $\mu$m. The pixel detectors, irradiated to fluences up to $2.4\times10^{16} \mathrm{n_{eq}cm^{-2}}$, were tested in the DESY test beam facility and the analysis of the data shows excellent performances even for the highest irradiation fluences. All results are obtained in the framework of the CMS R\&D activities.