Influence of Pb excess on the properties of lead lanthanum titanate ferroelectric thin films on Pt and LaNiO₃ electrodes

The influence of Pb excess on the properties of lead lanthanum titanate (PLT) ferroelectric thin films on Pt and LaNiO₃ electrodes is studied in this paper. Electron probe analysis results show that there is still quite an amount of excess Pb in PLT films after annealing at 550 °C for one hour. The distribution of excess Pb in the films is investigated by an Auger electron spectroscopy (AES) depth profile. It is found that the bottom electrodes have significant effects on both the content and the distribution of excess Pb in the PLT films. Meanwhile, the bottom electrodes have great effects on the size of the grains and also on the distribution of the excess Pb. The excess Pb and its appearance at grain boundaries and accumulation at the interface between the film and bottom electrodes may act as pinning centres and have a pinning effect on domains, which can be observed by abnormal P-E hysteresis loops and abnormal C-V curves. The excess Pb content in the films and Pb accumulation at the interface is high in the PLT films deposited on Pt/Ti/SiO₂/Si; their pinning is severe. This is one of the primary reasons why the films have a high fatigue rate. While LaNiO₃ has absorbed most of the excess Pb in PLT films, the content of excess Pb in the films deposited on LaNiO₃/SiO₂/Si is very low: the pinning effect is hardly observed. This is one of the primary reasons that the films have good fatigue properties.