DC-voltage and cycling induced recovery of switched polarisation in fatigued ferroelectric thin films

We report results on electric DC-field induced and self induced recovery of the switched remanent polarisation (P-r(s)) in fatigued ferroelectric thin films. The field induced recovery is characterised by a strong asymmetry and depends on the ratio between the fatiguing and DC-field magnitudes. It is also dependent on the period of application of the DC-field. The self recovery effect occurs on further cycling beyond the fatigued state. It is dependent on the fatiguing field magnitude and also, if the cycling is performed with a square wave function, on the switching frequency. For both effects we propose a tentative explanation based on the pinning of ferroelectric domain walls by negatively charged defects close to the top electrode and on the annihilation of those defects by positively charged defects, the nature of which remains to be disclosed.