Bipolar and unipolar electrical fatigue in ferroelectric lead zirconate titanate thin films: An experimental comparison study

摘要

By performing standard positive-up-negative-down, hysteresis-loop and dielectric measurements on the ferroelectric lead zirconate titanate thin-film capacitors subject to bipolar/unipolar electrical cycling, we show that unipolar fatigue is evident though still less severe than bipolar fatigue conducted at the same voltage. That has been attributed to a series of periodic events of polarization backswitching (driven by the residual depolarization field) and switching (driven by the residual applied field) during unipolar electrical cycling, and explained using the LPD-SICI model (LPD-SICI stands for local phase decomposition caused by switching-induced charge injection). The dielectric results have been used to estimate the effective thickness d, of the fatigue-induced degraded (pyrochlorelike) interfacial layer after bipolar/unipolar fatigue, which has not been done so far to our best knowledge. The fact that d_i is still much less than the film thickness even after the most severe bipolar fatigue strongly suggests that polarization fatigue in ferroelectrics is an interface effect, not a bulk one.