The Fatigue Property Of Ferroelectric Thin Films Under Thermal And Electrical Loads

Ferroelectric materials, with the ferroelectric and piezoelectric characteristics, can be widely applied in many fields, such as information memory, communication, navigation, accurate measurement and machinery et al. With the development of microelectronic technology and high degree integration, people need ferroelectric films with more excellent properties. Therefore, the preparation and the properties study on the ferroelectric film have become research subjects that have highly been paid attention to in the world. However, this kind of film would be inevitably influenced by the environment and self-working conditions, and in this case, the properties will be changed after the repetition of outside temperature and consecutive polarization reverse. In the master thesis, the fatigue characteristics of the ferroelectric films under thermal load and electrical load were investigated. The thermal load was induced by a pulse laser beam of Nd:YAG and the electrical load was made by RT6000S ferroelectric tester to act on the films respectively. The effect of thermal or electric loads on the films properties was discussed.In the introduction of this thesis, the application, good properties, preparation methods of the films as well as the key projects for the research on the films are reviewed firstly. According to this, the research of the fatigue properties of the ferroelectric films was proposed. The lead zirconate titanate (PZT) film was prepared by a metal-organic decomposition method. The films' physical properties were analysed by X-ray diffraction (XRD), scanning electron microscopy(SEM) and hysteresis loops. Furthermore, in order to study the thermal fatigue of the films, the PZT films were heated by a laser beam, it was found that in the films the remnant polarization value decreased, the coercive voltage was basically constant, and the fatigue property of the films became more stabilized. It was due to that the laser heating on the films would result in the movement of the polarized molecules and the defectswith charge in the films. The surface of the films was observed for the films heated with many times by laser beam, it was found that PZT films' interfacial crack appeared. The experimental result was the same with the result predicted by Xuejun Zheng. The PZT ferroelectric films' fatigue characteristics were studied, and here the electrical load was produced by RT6000S; it was known that with the voltage increasing or frequency reducing, the degree of ferroelectric fatigue decay would increase. The space-charge theory of Dawber and Scott was modified, and here in the modified model, the depletion width was not a constant. Meanwhile, it was found that there was a relationship between the depletion width and the number of cycles[N(50%)] which the polarization degraded 50% in the experiment. With this relationship, we can predict the ferroelectric films' service life.