Radiation hard sensor materials for the CMS Tracker Phase II Upgrade - Charge collection of different bulk polarities

Abstract

The upgrade of the LHC machine to deliver a significantly higher luminosity of about 5×1034cm−2s−1 is planned to be operational after 2022. This will simultaneously increase the radiation dose for the inner detector systems, requiring new radiation hard sensor materials for the CMS Tracker. To identify the appropriate materials which are able to withstand the radiation environment in the middle to outer layers of the CMS Tracker during the full lifetime of the high luminosity LHC, a large irradiation and measurement campaign has been conducted. Several test structures and sensors have been designed and manufactured on 18 different combinations of wafer materials, thicknesses and production technologies. The structures have been electrically characterised before and after irradiation with different fluences of neutrons and protons.This paper reports the final results on strip sensor performance considering the comparison of p-in-n technology with n-in-p type. Outcomes from signal and noise measurements before and after annealing depending on the radiation dose are discussed and the final recommendation of the CMS Tracker Collaboration for the strip sensor polarity for the Phase II Upgrade is presented.