Voltage offsets and imprint mechanism in SrBi₂Ta₂O₉ thin films

It is shown that voltage shifts in the hysteresis response of SrBi₂Ta₂O₉ (SBT) thin-film capacitors can be induced using both thermal and optical methods. These voltage shifts are important since they can lead to imprint failure in ferroelectric memory devices. It is suggested that the voltage shifts in the hysteresis curve of SBT are caused by trapping of electronic charge carriers near the film/electrode interfaces, as has been previously reported for the Pb(Zr,Ti)O₃ (PZT) system. In addition, a direct correlation is established between the magnitude and sign of remanent polarization (P_r) and the thermally induced voltage shifts (V_i), where V_i = αP_r + β. It is also found that, unlike the PZT system, the thermally induced voltage shifts in SBT are smaller than those optically induced. One possible implication of this result is that the contribution of defect-dipole complexes to the voltage shirts in SBT is negligible. We suggest that the smaller contribution of defect-dipole complexes to the voltage shifts in SBT may be related to a smaller oxygen vacancy concentration in the perovskite sublattice of SBT as compared to that of PZT.