Thin LGAD sensors for 4D tracking in high radiation environments: state of the art and perspectives

This contribution summarises the outcomes of the CSN5 eXFlu research project. In particular, it presents the first exploration of the performance of very thin Low-Gain Avalanche Diode (LGAD) sensors, with a bulk active thickness ranging from 45 µm down to 15 µm. Thin sensors have intrinsically good timing performances, as the non-uniformities of particle charge deposition, which contribute as one of the main components to the timing resolution, are minimised by the thin substrate. A timing resolution of 16.6 ps has been achieved with a 20 µm thick LGAD, which was further reduced to 12.2 ps by combining the timing information from two 20 µm thick sensors. Additionally, various designs of the gain implant, typical of LGAD devices, have been explored. In particular, the beneficial effect of Carbon atoms co-implanted with Boron has been enhanced by the simultaneous annealing of the two elements, resulting in the most radiation-hard LGADs produced by the FBK foundry. The eXFlu sensors have been operated efficiently with almost unchanged performance up to a fluence of 2.5 ✕ 10^15 1 MeV equivalent n/cm^2. Future developments of the LGAD sensor design to extend its operation to extreme fluences, above 1 ✕ 10^17 1 MeV equivalent n/cm^2, will be discussed.