Performance of LGAD sensors for the ATLAS High-Granularity Timing Detector HGTD

The High Granularity Timing Detector (HGTD) will be installed in the ATLAS detector to mitigate pile-up effects during the high luminosity (HL) upgrade of the LHC at CERN. The HGTD is based on the use of 50 µm-thick Low Gain Avalanche Detectors (LGADs) that provide precise time measurements. LGAD technology has been chosen as it provides an internal gain good enough to reach large signal over noise ratio needed for excellent time resolution. The HGTD will improve the particle-vertex assignment by measuring track times with a resolution ranging from approximately 30 ps at the beginning of the HL-LHC operations to 50 ps at the end. A set of un-irradiated and neutron and proton irradiated LGAD samples from different vendors have been tested in several test beam campaigns during the years 2018 and 2019 at CERN SPS and DESY. Single pads and 2×2 arrays with a pad size of 1×1 mm2 are compared for their performances based on the collected charge, timing performance, post-irradiation efficiency and uniformity at fluences up to 2.5e15 neq/cm2. A time resolution of < 50 ps is observed in most cases.