| Ferroelectric thin films are under extensive investigation in developing nonvolatileinformation storage devices due to their ability to switch their polarization directionsbetween two spontaneous polarization states. To the FRAM device, the ferroelectricthin films have to withstand up to 1012 switching cycles without cell failure. However,continuous switching of the ferroelectric thin film can lead to the decrease of thepolarization values, which are referred to as fatigue in the literature, and lead to afailure of the memory cell. After the hysteresis shift along the voltage axis, thecoercive voltage shift might become so large that the programming voltage cannotswitch the ferroelectric capacitor. Meanwhile, the loss of the polarization is so seriousthat the sense amplifier cannot distinguish between the two logical states. Thoughextensive work has been performed to understand the physical origin of fatigue andimprint, there is not a full-accepted model for either of the two failure mechanisms.By the analysis of the ferroelectric fatigue possible mechanisms, both theintrinsic oxygen vacancy and the electron injection from the electrode shouldcontribute to ferroelectric fatigue. According to this inference, the model merelyconsidered the effect of the intrinsic oxygen vacancy was modified. The simulationresult of the modified model agrees with the experiment better than that of the originmodel. The impacts of the applied voltage, switching frequency, temperature andgrain size on fatigue property were also studied. The result shows fatigue tends to beserious with the increasing of applied voltage, temperature, grain size, and thedecrease of the switching frequency. And the simulation results accord theexperimental rule.For the imprint investigation, the impact of the film thickness and the annealingtemperature on the coercive voltage were studied. In view of these influences, thiswork considers that the different distribution of the oxygen vacancy in the interfaceinduce imprint action. By studying the imprinted samples, repetitious polarizationswitching can reduce imprint, the coercive voltage increases logarithmically with thetime increasing during the re-imprint process.By investigating the relation between grain size and the coercive voltage, a simple... |
