The Upgrade of the CMS Inner Tracker for HL-LHC

During the Long Shutdown (LS) from 2024 to 2026 the Large Hadron Collider (LHC) will be upgraded in order to provide a ten-fold increase of the data rate to the experiments. This will enhance the sensitivity of the experiments to possible unexplored rare processes and to allow for precision measurements of known processes, in particular of the properties of the Higgs Boson which was discovered in 2012. This accelerator upgrade project is called High-Luminosity LHC (HL-LHC). The entire silicon tracker of the Compact Muon Solenoid (CMS) experiment will be replaced for the HL-LHC with a new detector featuring increased radiation hardness during the collection of above 3000\,fb$^{-1}$ of integrated luminosity and capability to handle the higher data rate at an instantaneous luminosity of $10^{35}$cm$^{-2}$s$^{-1}$ and longer trigger latency of 12.5\,$\mu$s. The Inner Tracker will be exposed to radiation levels up to a non ionizing energy loss equivalent to \mbox{$2.3 \times 10^{16}$\, n$_{\text{eq}}$/cm$^2$} and an accumulated ionizing dose of 1.2\,Grad, requiring advanced technologies and novel solutions among others for the readout and powering electronics. The new detector will also feature extended pseudo-rapidity $\eta$ coverage with a tracking volume up to $\eta = 4$. The High-Luminosity upgrade of the CMS silicon pixel detector is reviewed in this paper. The novel features of the detector layout and electronics system are discussed, and the expected performance is summarized.