The CMS Pixel Detector Upgrade and R&D for the High Luminosity LHC

The High Luminosity Large Hadron Collider (HL-LHC) at CERN is expected to collide protons at a centre-of-mass energy of 14 TeV and to reach an unprecedented peak instantaneous luminosity of $5 \times 10^{34}\,{\rm cm}^{-2} {\rm s}^{-1}$ with an average number of pileup events of 140. This will allow the ATLAS and CMS experiments to collect integrated luminosities of up to $3000\,{\rm fb}^{-1}$ during the project lifetime. To cope with this extreme scenario the CMS detector will be substantially upgraded before starting the HL-LHC, a plan known as CMS Phase-2 Upgrade. In the upgrade the entire CMS silicon pixel detector will be replaced and the new detector will feature increased radiation hardness, higher granularity and capability to handle higher data rate and longer trigger latency. In this report the Phase-2 Upgrade of the CMS silicon pixel detector will be reviewed, focusing on the features of the detector layout and on the development of new pixel devices.