Increase in switching charge of ferroelectric SrBi2Ta2O9 thin films with polarization reversal

The increase in switching charge of as-grown SrBi2Ta2O9 (SBT) capacitors with polarization reversal was investigated. We call this phenomenon wake-up. The switching charge was increased and the rectangularity of the D-E hysteresis loops was improved with polarization reversal. The switching pulse with larger amplitude, longer width and shorter period generated a larger increase in the switching charge with polarization reversal. At the same time, the capacitors came to exhibit a rapid increase in leakage current at a certain applied field after the switching. Furthermore, the D-E hysteresis loop of the capacitors with wake-up shifted toward the positive- or negative-bias field according to the sweeping direction of the applied voltage. We have concluded that some spontaneous polarizations locked by localized space charges at the interface layer in the wake-up-exhibiting SET capacitors were freed by the application of numerous switching pulses, and trap levels generated in the interface layer by the switching rendered the rapid increase in leakage current and the voltage shift of D-E hysteresis easy.