A MODEL FOR OPTICAL AND ELECTRICAL-POLARIZATION FATIGUE IN SRBI2TA2O9AND PB(ZR,TI)O-3

We find that significant polarization fatigue (> 90%) can be induced i n SrBi2Ta2O9 (SBT) thin films using (a) broad-band optical illuminatio n combined with a bias neat the switching threshold and (b) electric f ield 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 de bias with Light or by el ectric field cycling without light, which suggests a field-assisted re covery mechanism. A similar behavior was observed in Pb(Zr,Ti)O-3 (PZT ) films with LSCO electrodes. Based on these results, we suggest that polarization fatigue in ferroelectrics is essentially a dynamic compet ition between domain wall pinning due to electronic charge trapping, a nd field-assisted unpinning of the domain walls. Thus, domain wall pin ning is not necessarily absent in nominally fatigue-free systems. Inst ead, these systems are ones in which domain wall unpinning occurs at l east as rapidly as any pinning. Factors which may affect the pinning a nd unpinning rates will be discussed.