Qualitative model for the fatigue-free behavior of SrBi2Ta2O9

Abstract

SrBi2Ta2O9 (SBT) thin films are known to exhibit no polarization fatigue with electric field cycling. However, we have discovered that optical illumination combined with a bias voltage near the switching threshold can result in significant (≳90%) suppression of the switchable polarization of SBT thin film capacitors. A similar effect has also been reported for Pb(ZrxTi1−x)O3 (PZT) capacitors. However, it is found that electric field cycling of the optically fatigued SBT capacitors results in near-complete recovery of the suppressed polarization. In contrast, electric field cycling of optically fatigued PZT capacitors does not result in any polarization recovery. These results suggest that optical fatigue in both SBT and PZT capacitors results from pinning of domain walls due to trapping of the photogenerated carriers at domain boundaries, whereas the recovery exhibited by SBT thin films indicates that the domain walls are more weakly pinned in SBT than in PZT thin films. Consequently, the fatigue-free behavior of SBT thin films during electric field cycling can be viewed as a competition between domain wall pinning due to charge trapping and domain wall unpinning by the cycling field; the latter process occurring at least as rapidly as the former.