Empirical model for fatigue of PZT ferroelectric memories

Switched polarization fatigue was investigated for CVD PZT ferroelectric films of thickness <100 nm. The data shows that negligible switched polarization degradation occurs during an initial incubation period, CTF*, which can last up to ∼10⁸ polarization reversal cycles. This incubation period was found to be process dependent but nearly independent of cycling voltage and temperature. For cycles beyond CTF*, however, the data begins to show a strong exponential field dependence and a weak (∼0.1 eV) temperature dependence. An empirical model has been developed which describes the "Cycles to Failure" data quite well for these PZT thin films. Because of the large voltage-acceleration factor observed, the model can be used to demonstrate an equivalent fatigue lifetime at the expected operating voltage with relatively short test times.