FATIGUE, REJUVENATION AND SELF-RESTORING IN FERROELECTRIC THIN-FILMS

The switching, fatigue and rejuvenation phenomena of ferroelectric PZT thin films with differently processed electrode-PZT interfaces and of different thicknesses have been investigated. The ferroelectric contr ibution to the switching parameters has been isolated from the leakage current contribution, thus allowing the identification of several sal ient features of the above phenomena. Incorporating our present result s with already established properties of PZT thin films, a set of char acteristic features of switching, fatigue and rejuvenation is formulat ed. This set is interpreted using a framework which takes into account the ferroelectric and semiconductor properties of the system. The key issues of the framework are: (i) Strong inhomogeneous built-in electr ic field exists in virgin films due to contact phenomena. (ii) Extra n ear-electrode space-charge layers are created during polarization reve rsal and destroyed by d.c. rejuvenating fields or by the field of fati guing pulses. (iii) The built-in electric field is affected by these s pace-charge layers and then, in its turn, governs the evolution of the switching parameters (remanent polarization, coercive field) of the f ilm during fatigue and rejuvenation. (iv) Near-electrode nucleation of opposite domains is believed to create the extra near-electrode space -charge layers. Therefore, this nucleation seems to be responsible for the fatigue and for the sensitivity of fatigue to the surfacial prope rties of the film. This approach explains the thickness dependence of the coercive field, the variation of remanent polarization and coerciv e field with the number of switching cycles, and the rejuvenation phen omena including self-restoring.