INFN-FBK developments of 3D sensors for High-Luminosity LHC

3D type of pixel sensors is a promising option for the innermost pixel layer at the High-Luminosity LHC. However, the required very high hit-rate capabilities, finer pixel granularity, extreme radiation hardness and reduced material budget call for a downscale of the pixel size as compared to existing 3D sensors, involving smaller pitch (e.g. 50 × 50 or $25\times 100\mu m^2$), shorter inter-electrode spacing ($\sim 30\mu m$), narrower electrodes ($\sim 6\mu m$ diameter), and reduced active thickness ($\sim 100$–$150\mu m$). Within a joint R&D effort with INFN, FBK has produced a new generation of 3D pixel sensors with these challenging features. In this talk preliminary results from the electrical and functional characterisation of the first prototypes are reported, included their behaviour after large radiation fluence, close to the ones expected in the High Luminosity LHC environment. Prospects for the next prototypes are also presented.