Fatigue, rejuvenation and self-restoring in ferroelectric thin films

Abstract

Abstract 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 contribution to the switching parameters has been isolated from the leakage current contribution, thus allowing the identification of several salient features of the above phenomena. Incorporating our present results with already established properties of PZT thin films, a set of characteristic features of switching, fatigue and rejuvenation is formulated. 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 electric field exists in virgin films due to contact phenomena. (ii) Extra near-electrode space-charge layers are created during polarization reversal and destroyed by d.c. rejuvenating fields or by the field of fatiguing pulses. (iii) The built-in electric field is affected by these space-charge layers and then, in its turn, governs the evolution of the switching parameters (remanent-polarization, coercive field) of the film 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 properties of the film. This approach explains the thickness dependence of the coercive field, the variation of remanent polarization and coercive field with the number of switching cycles, and the rejuvenation phenomena including self-restoring.