Polarization fluctuation behavior of lanthanum substituted Bi₄Ti₃O₁₂ thin films

Polarization fluctuation behavior of lanthanum substituted Bi₄Ti₃O₁₂ (Bi_4-xLa_xTi₃O₁₂, BLT) ferroelectric thin films has been examined. Remnant polarization exhibits an initial increase (P_up, 1-10⁶ cycles) and a subsequent decrease (P_down, 10⁶-10⁹ cycles) with switching cycles, whereas the dielectric constant exhibits a continuous decrease. By careful investigations on the effect of switching frequency and annealing atmosphere on the polarization fluctuation characteristics, we propose that this polarization fluctuation characteristic of BLT films is attributed to the competition between domain pinning and passive layer growing effect, due to the redistribution of oxygen vacancy related defect under external applied field. P_up behavior is dominated by the unpinning of pinned domain, while P_down behavior is dominated by the reduction of applied field on BLT bulk layer, due to the growing of the passive layer between BLT and Pt electrode. By assuming the dielectric constant and initial thickness of passive layer, the passive layer was estimated to be about 2-5 times thicker than the initial state after 10⁹ cycling.