MECHANISM OF FATIGUE IN FERROELECTRIC THIN-FILMS

A quantitative fatigue model is proposed for ferroelectric thin films on the basis of effective one-directional movement of defects due to asymmetric polarization under alternating pulses, defect entrapment at electrode-ferroelectric interface (and/or at grain and domain boundaries), and the resultant polarization loss at these surfaces due to structural damage. A fatigue equation is derived in accordance with this model and three fatigue parameters such as initial saturation polarization, piling constant, and decay constant are defined. The predicted values from the model show very good agreement with experimental data. Temperature and voltage dependence of fatigue parameters are studied on the basis of the fatigue model. The jump distance of defects is calculated from the voltage dependence of the decay constant which turns out essentially to be the same as the lattice parameter. Based on the fatigue model, an improved method to overcome fatigue property is also presented.