PHOTOINDUCED CHANGES IN THE FATIGUE BEHAVIOR OF SRBI2TA2O9 AND PB(ZR,TI)O-3 THIN-FILMS

It is shown that SrBi2Ta2O9(SBT) thin films can be made to exhibit sig nificant polarization fatigue by electric-field cycling under broad-ba nd, optical illumination. Photoinduced fatigue is also observed for Pb (Zr,Ti)O-3 (PZT) thin-film capacitors with (La,Sr)CoO3 (LSCO) electrod es. These results demonstrate that both the Pt/SBT/Pt and the LSCO/PZT /LSCO systems are susceptible to fatigue effects, which are attributed primarily to pinning of domain walls due to charge trapping. Capacito rs that have been fatigued under illumination can be fully rejuvinated by applying a dc saturating bias with light or by electric-field cycl ing without light, which indicates an intrinsic, field-assisted recove ry mechanism. We suggest that fatigue is essentially a competition bet ween domain wall pinning and unpinning and that domain pinning is not necessarily absent in these nominally fatigue-free systems, but rather these systems are ones in which unpinning occurs at least as rapidly as any pinning. In both cases, the extent of photoinduced fatigue decr eases with increased cycling voltage, indicating the relative importan ce of field-assisted unpinning. Finally, the observation of photoinduc ed fatigue implies that increased injection rates, potentially due to oxygen vacancy accumulation, may account for the electrode dependence on fatigue in PZT thin films.