Relaxation of remanent polarization in Pb(ZrTi)O3 thin film capacitors

The retained charge (memory window) of a ferroelectric capacitor measured by the pulse method is smaller than that measured by the continuous wave method. This is attributed to the relaxation phenomenon which represents the fast loss of the remanent polarization after removal of the applied voltage. The relaxation phenomenon is induced by the depolarization field which is affected by various parameters such as the ferroelectric properties and thickness of the ferroelectric film, measurement temperature, electrode material and the formation of an interfacial layer between the ferroelectric film and the electrodes. In this study, the effects of each parameter and the causes of the relaxation phenomenon were investigated. The magnitude of polarization loss increases with that of the initial remanent polarization. The increased polarization loss with increasing measurement temperature is attributed to the reduced coercive field with temperature. The fatigue stressing and the use of a RuO2 top electrode cause the formation of a nonswitching interfacial layer between the ferroelectric film and the electrodes, resulting in the large relaxation and thus large polarization loss. The reduction in the thickness of the ferroelectric film also results in the increasing polarization loss by increasing the magnitude of the depolarization field.