Characterization of planar and 3D silicon pixel sensors for the high luminosity phase of the CMS experiment at LHC

The High Luminosity upgrade of the CERN Large Hadron Collider (HL--LHC) calls for an upgrade of the CMS tracker detector to cope with the increased radiation levels while maintaining the excellent performance of the existing detector. Specifically, new high--radiation tolerant solid--state pixel sensors, capable of surviving irradiation fluences up to $1.9 \times 10^{16} \: \rm{n_{eq}/cm^2}$ at 3 cm from the interaction point, need to be developed. For this purpose an R\&D program involving different vendors have been pursued, aiming at the development of thin n--in--p type pixel sensors. The R\&D covers both planar (manufactured by Fondazione Bruno Kessler, FBK; Hamamatsu Photonics, HPK and LFoundry) and single--sided 3D columnar (manufactured by FBK and Centro Nacional de Microelectronica, CNM) pixel devices. The target active thickness is 150 $\mu$m while two different pixel cell dimensions are currently investigated ($25 \times 100$ and $50 \times 50 \: \mu \rm{m^2}$). Sensors presented in this article have been bump--bonded to the RD53A readout chip (ROC), the first prototype towards the development of a ROC to be employed during HL--LHC operation. Test beam studies, both of thin planar and 3D devices, have been performed by the CMS collaboration at the CERN, DESY and Fermilab test beam facilities. Results of modules performance before and after irradiation (up to $2.4 \times 10^{16} \: \rm{n_{eq}/cm^2}$) are presented in this article.