Evaluation of novel KEK/HPK n-in-p pixel sensors for ATLAS upgrade with testbeam

摘要

A new type of n-in-p planar pixel sensors have been developed at KEK/HPK in order to cope with the maximum particle fluence of 1-3 × 10~(16) 1 MeV equivalent neutrons per square centimeter (n_(eq)/cm~2) in the upcoming LHC upgrades. Four n-in-p devices were connected by bump-bonding to the new ATLAS Pixel front-end chip (FE-I4A) and characterized before and after the irradiation to 2 × 10~(15) n_(eq)/cm~2. These planar sensors are 150 μm thick, using biasing structures made out of polysilicon or punch through dot and isolation structures of common or individual p-stop. Results of measurements with radioactive ~(90)Sr source and with a 120 GeV/c momentum pion beam at the CERN Super Proton Synchrotron (SPS) are presented. The common p-stop isolation structure shows a better performance than the individual p-stop design, after the irradiation. The flat distribution of the collected charge in the depth direction after the irradiation implies that the effect of charge trapping is small, at the fluence, with the bias voltage well above the full depletion voltage.