Small pitch pixel sensors for the CMS Phase II upgrade

The CMS experiment intends to exchange the pixel detector for the high luminosity phase of the Large IIadron Collider (HL-LHC). Therefore, a large R&D effort has been started in order to develop sensors capable of withstanding the expected extremely high radiation damage. The targeted integrated luminosity of 3000 fb(-1), estimated for 10 years of operation at the design center-of-mass energy of 14 TeV, translates into an equivalent NIEL (Non-Ionizing Energy Loss) of 2x10(16) neq cm(-2) and an IEL (Ionizing Energy Loss) dose in the SiO2 of 5 MGy at the expected position of the innermost pixel detector layer. The CMS collaboration has undertaken two sensor R&D programs on thin n-in-p planar and 3D silicon sensor technologies. To cope with the increase in instantaneous luminosity, the pixel area has to be reduced to approximately 2500 mu m(2) to keep the occupancy at the percent level. Suggested pixel cell geometries to match this requirement are 50 x 50 mu m(2) or 25 x 100 mu m(2), leaving little space for design choices and a possible biasing scheme. Monte Carlo studies comparing the hit resolution for these two scenarios are presented. CMS has initiated the production of test-sensors with the envisaged pixel geometries. Status, progress, and prospects of this effort are discussed.