Quantum computing, space and coolCMOS applications drive the demand for reliable embedded non-volatile memories. Here, we demonstrate reliable ferroelectric FETs with 2.3 V memory window based on hafnium oxide at cryogenic temperatures (2.5K to 77K). Defect characterization and device simulations allow to explain the observed behavior and provide insights into the defect dynamics in FeFET devices as well as a fast measurement methodology to estimate retention behavior.