A model for optical and electrical polarization fatigue in SrBi{sub 2}Ta{sub 2}O{sub 9} and Pb(Zr,Ti)O{sub 3}

Polarization fatigue, the decrease in switchable polarization with electric field cycling, has received considerable attention lately because ferroelectric thin films are being evaluated for use in nonvolatile memory applications. Here, the authors find that significant polarization fatigue (> 90%) can be induced in SrBi{sub 2}Ta{sub 2}O{sub 9} (SBT) thin films using (a) broad-band optical illumination combined with a bias near the switching threshold and (b) electric field cycling under broadband optical illumination. In the latter case, the extent of polarization fatigue increases with decreasing cycling voltage. In either case, the optically fatigued SBT capacitors can be fully rejuvenated by applying a saturating dc bias with light or by electric field cycling without light, which suggests a field-assisted recovery mechanism. A similar behavior was observed in Pb(Zr,Ti)O{sub 3} (PZT) films with LSCO electrodes. Based on these results, they suggest that polarization fatigue in ferroelectrics is essentially a dynamic competition between domain wall pinning due to electronic charge trapping, and field-assisted unpinning of the domain walls. Thus, domain wall pinning is not necessarily absent in nominally fatigue-free systems. Instead, these systems are ones in which domain wall unpinning occurs at least as rapidly as any pinning. Factors which may affect the pinning and unpinning rates will be discussed