Could We Efficiently Operate 3D Silicon Pixel-Based Tracking Detectors Irradiated with Neutron Fluences up to 1x10^18 1 MeV neq cm^-2 ?

Future new high luminosity colliders will require exceptionally radiation tolerant detectors, in particular those that will be closer to the interaction regions, i.e. tracking and vertexing detectors. 3D trench pixel sensors developed by the TimeSPOT R&D project have shown an incredible time resolution of about 10 ps and radiation hardness up to 1 ⋅ 1017 1MeVneq cm−2. To push these limits further, a new irradiation campaign has recently been completed at the TRIGA Mark II Reactor at the Jožef Stefan Institute, reaching extreme fluences of 1 ⋅ 1018 1MeVneq cm−2. To evaluate the post-irradiation performance, a dedicated Transient Current Technique (TCT) setup has been developed at the INFN Cagliari laboratories, employing a laser system for controlled energy deposition with a micro-metric spatial accuracy, within the sensors. The TCT characterizations show a complete recovery for the charge collection efficiency (CCE) for the 1 ⋅ 1017 1MeVneq cm−2 which is compatible to what was measured on a recently conducted beam test by using minimum ionizing particles. However, sensors irradiated to the highest fluences exhibit an incomplete recovery of CCE at the tested bias (up to 400 V) suggesting that even higher bias voltages will be necessary to optimize charge collection and detection efficiency under such extreme condition.