Fatigued state of the Pt-PZT-Pt system

The fatigued state of Pt-PZT-Pt ferroelectric capacitors (FECAP) was investigated by means of piezoelectric coefficient, polarisation charge and permittivity measurements. The suppression of switching polarisation P_r^s appears to be the result of freezing of ferroelectric domains without affecting the lattice dielectric properties. The frozen polarised domains show a preferential orientation which is related to the electrode interface asymmetry. The fatigue mechanism in thin films is not assisted by a growing passive layer and is characterised by a substantial reversible character and adaptation to the used fatiguing field (field self-adjusting). With consideration of the frozen asymmetry and of the newly discovered slow cycling fatiguing effect in thicker samples, the fatigue mechanism was interpreted as inhibition of the nucleation at the top electrode interface. Since it is unlikely that the domain walls (DW) cross the grain boundaries, it is suggested that the effective suppression of P_r^s occurs grain by grain and corresponds to the creation of "ferroelectrically dead areas".