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

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 280 Mev/c, protons of 25 Mev/c and reactor neutrons resulting in a combined fluence of up to 3×1015 1 MeV 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 3000 fb−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 40 MHz. 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. -- Highlights: •Charge collection measurements of n-in-p strip detectors irradiated up to 3E15 neq/cm2. •Signal reduced from 25 k electrons before irradiation to 9–11 k electrons at 600 V bias. •Signal-to-noise ratio measured above 10 at 600 V after irradiation with pions, protons and neutrons. •N-in-p strip detectors functional for doses in inner strip layers of ATLAS in the HL-LHC. •Results agreeing to results after single particle irradiation