Radiation resistant innovative 3D pixel sensors for the CMS upgrade at the High Luminosity LHC

An extensive R\&D program aiming at radiation hard, small pitch, 3D pixel sensors has been put in place % in CMS between Istituto Nazionale di Fisica Nucleare (INFN, Italy) and FBK Foundry (Trento, Italy). The CMS experiment is supporting % profiting of these developments the R\&D in the scope of the Inner Tracker upgrade for the High Luminosity phase of the CERN Large Hadron Collider (HL-LHC). In the HL-LHC the Inner Tracker will have to withstand an integrated fluence up to $2.3 \times 10^{16} \, \mathrm{n_{eq}/cm^2}$. % (1 MeV equivalent neutrons). A small number of 3D sensors were interconnected with the RD53A readout chip, which is the first prototype of 65 nm CMOS pixel readout chip designed for the HL-LHC pixel trackers. In this paper results obtained in beam tests before and after irradiation are reported. Irradiation of a single chip %interconnected module was performed up to a maximum equivalent fluence of about $1 \times 10^{16} \, \mathrm{n_{eq}/cm^2}$. Analysis of the collected data shows excellent performance: spatial resolution in not irradiated (fresh) sensors is about 3 to 5 $\mathrm{ \mu }$m depending on the pixel pitch. Hit detection efficiencies are close to 99\% measured both before and after the above mentioned irradiation fluence.