Signal and charge collection efficiency of n-in-p strip detectors after mixed irradiation to HL-LHC fluences

Abstract

For the year 2020, an upgrade of the LHC with a factor ten increase in luminosity is planned. The resulting severe radiation doses for the ATLAS tracker demand extremely radiation tolerant detectors. In this study six planar n-in-p strip sensors produced by Hamamatsu Photonics were irradiated in consecutive irradiation steps with pions of 280Mev/c, protons of 25Mev/c and reactor neutrons resulting in a combined fluence of up to 3×1015 1MeV neutron equivalent particles per square centimeter (neq/cm2). This particle composition and fluence corresponds to the qualification limit specified by the ATLAS experiment for the outer pixel layers (assuming an integrated luminosity of 3000fb−1). The 320μm thick devices are investigated using electrons from a 90Sr source. After each irradiation step both charge collection efficiency and noise measurements have been performed using the ALIBAVA readout system, which is based on analogue Beetle ASICs clocked at 40MHz.Measurements of the signal and signal-to-noise ratio of detectors will be given after the sensors were exposed to radiation that both in fluence and composition are corresponding to the expectations for the HL-LHC trackers. Conclusions will be drawn on their operation in the ATLAS inner detector upgrade.