Status of the CMS Phase 1 Pixel Upgrade

The silicon pixel detector is the innermost component of the CMS tracking system, providing high precision space point measurements of charged particle trajectories. Before 2018 the instantaneous luminosity of the LHC is expected to reach 2\,$\times 10^{34}\,{\rm cm^{-2}s^{-1}}$, which will significantly increase the number of interactions per bunch crossing. The current pixel detector of CMS was not designed to work efficiently in such a high occupancy environment and will be degraded by substantial data-loss introduced by buffer filling in the analog Read-Out Chip (ROC) and effects of radiation damage in the sensors, built up over the operational period. To maintain a high tracking efficiency, CMS has planned to replace the current pixel system during ``Phase 1'' (2016/17) by a new lightweight detector, equipped with an additional 4th layer in the barrel, and one additional forward/backward disk. A new digital ROC has been designed, with increased buffers to minimize data-loss, and a digital read-out protocol to increase the read-out speed. Prototypes of digital single-chip modules have been characterized in a testbeam at DESY, before and after irradiation. Furthermore, energy calibrations using monochromatic X-rays were performed, and their dependence on irradiation and temperature were studied. This document will give an overview of the upgraded detector and will give a description of the module production of the 4th layer, which is being assembled and pre-tested by german institutes.