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Reliability characteristics of ferroelectric thin films (10 nm) based on Si-doped HfO2 have been investigated with focus on potential memory applications. Extensive retention, imprint, and endurance data for this new type of ferroelectric material are presented for the first time. The variability of reliability characteristics in terms of capacitor annealing temperatures as well as excitation amplitude effects is analyzed. Stable ferroelectric switching behavior can be observed in a wide temperature range from 80 K up to 470 K. Bake tests at 125 °C show almost no retention loss for saturated polarization states up to cumulative testing times of 1000 h. In addition to the same-state retention, opposite-state retention was observed to be equally stable. Traditional imprint behavior of the programmed state occurs after a few hours of baking time, and stable behavior could be verified until the end of the 1000-h retention test. Endurance characteristics of the ferroelectric thin films are shown to depend significantly on the annealing temperature of the capacitors and on the cycling voltage during testing. In thin films which had been annealed at 1000 °C, breakdown at 2 MV/cm limits endurance after 108 cycles. A lower annealing temperature of 650 °C could improve the breakdown-limited endurance to 1010 cycles.