Characterisation of the fatigued state of ferroelectric PZT thin-film capacitors
In the present study, piezoelectric, conductivity and dielectric measurements have been performed on virgin and fatigued ferroelectric PZT thin films prepared by spin-on sol-gel deposition process on Si/SiO2/Ti/Pt substrates. By fatiguing, the polarisation shows a strong exponential degradation, the hysteresis loops of the piezoelectric coefficient d(33) become smaller and asymmetric and the polarisation-induced asymmetry of the conductivity at low voltage and the relative permittivity both decrease. The ensemble of these results shows that the fatigued state is produced by the freezing of ferroelectric domains with the preferential orientation from the top to the bottom electrode. However, since the magnitude of the total polarisation after poling in the same direction in the fatigued state is smaller than that observed in the virgin state, it is concluded that part of the frozen polarisation is oriented in the opposite direction.