Precision timing detectors for the upgrade of the LHC experiments

For the HL-LHC, the CMS and ATLAS collaborations have defined the detector geometry of their respective timing layers. Even though both collaborations have selected UFSD in their baseline design, the requirements for the two experiments differ in key aspects such as with pixel size, radiation hardness, number of layers. In this contribution we review the requirements and challenges in the design and production of the sensors for CMS and ATLAS, outlining similarities and differences.