Performance Before and After Irradiation of Pixelated 3D Silicon Sensors for the HL-HLC CMS Tracker

Silicon pixel detectors located in the inner tracker of the Compact Muon Solenoid (CMS) general-purpose experiment at the Large Hadron Collider (LHC) at the European Center for Nuclear Research (CERN) require replacement for the High Luminosity LHC (HL-LHC) upgrade, planned to begin in 2026. Existing silicon pixel detectors will be unusable due to sustained radiation damage, and will be replaced with sensors designed for increased precision and radiation hardness, in order to enable HL-LHC study of known mechanisms in greater detail and detection of increasingly rare particles. In testing one prototype 3D silicon pixel detector created by Centro National de Microelectronica (CNM) before and after irradiation at Fermi National Laboratory (FNAL) at fluences similar to those which will be observed at the HL-LHC, sensor efficiency was found to decrease by 0.1-1% after irradiation, depending on beam incident angle, though efficiency values remained high, with plateaus above 99.5% efficiency. Sensor resolution (RMS average residual width, telescope resolution subtracted) was not significantly impacted post-irradiation. After irradiation, charge deposited on the sensor was found to increase with applied bias voltage suggesting increased depletion zone width; peak deposited charge was around 7000 electrons post-irradiation and 14000 electrons pre-irradiation suggesting post-irradiation results were taken without full sensor depletion. Post-irradiation results showed smaller pixel cluster sizes, with average cluster size decreasing by up to 20%, with the largest differences seen at acute beam incidence angles.