Characterization of 3D pixel sensors for the CMS upgrade at the High Luminosity 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 fluence, $1.9\times10^{16}$~n$_{eq}$/cm$^2$ (1~MeV equivalent neutrons) for the innermost layer, while maintaining the excellent performance of the existing detector. An extensive R\ and D program, aiming at using 3D silicon pixel sensors, has been put in place by CMS in collaboration with FBK (Trento, Italy) and CNM (Barcelona, Spain) foundries. The basic 3D pixel cell sizes is $25\times100$~$\mu$m$^2$, with one central readout electrode to be connected to the readout chip. In this presentation results obtained in beam test experiments before and after irradiations, up to $\sim2.6\times10^{16}$~n$_{eq}$/cm$^2$, will be reported. The sensors were read out by the RD53A chip, a prototype version of the 65~nm CMOS technology pixel readout chip which will be adopted to read out the CMS pixel detector at HL-LHC.