采用旋涂法制备了厚度为140 nm的聚(偏氟乙烯-三氟乙烯)[P(VDF-TrFE)]纳米薄膜，研究了不同退火温度以及环境相对湿度对薄膜的极化反转和疲劳性能的影响。运用X射线衍射仪、扫描电子显微镜和傅里叶变换红外光谱仪等测试技术对薄膜的微结构进行了表征。实验结果表明，通过不同温度的退火处理， P(VDF-TrFE)铁电薄膜的结晶度随着退火温度的升高而不断提高，并且一定的温度范围内的退火处理可以提高薄膜的极化性能；此外， P(VDF-TrFE)铁电薄膜性能还表现出一定的环境湿度的敏感特性，这与薄膜的物理性能和结构特点密切相关；P(VDF-TrFE)铁电薄膜在不同的环境湿度条件下表现出较好的电学特性，其漏电流均保持在10−7 A/cm2的较低水平。本工作揭示了再退火过程对薄膜的极化反转速度和疲劳恢复特性的影响，并结合薄膜二次疲劳结果，探讨了薄膜可逆的内部疲劳恢复特性机理。%The nano-films of poly (vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer, with mole ratio of VDF-TrFE 70/30, are deposited on titanium-metallized silicon wafer by spin coating technique. Annealing temperature and humidity dependence of polarization switching and fatigue babivors in ferroelectric P(VDF-TrFE) copolymer thin film capacitors have been investigated. Firstly, the effect of different annealing temperature on polarization behavior is revealed. It is found that the polarization of the film is improved by increasing annealing temperatures. When the annealing temperature is higher than 100 ◦C, with increasing switching cycles, the ferroelectric polarization characteristics exhibit a trend of increasing firstly and then decreasing, a top value appears at the number of cycles near 104. A more appropriate heat treatment temperature is 130 ◦C. Further analyses on the crystalline structures with X-ray diffraction show that the degree of crystallinity of the films is strongly dependent on the annealing temperature. It can be seen that the diffraction peak of the ferroelectric phase (β phase) becomes very strong and sharp with increasing annealing temperatre. It is demonstrated that the effect of annealing temperature on ferroelectric properties could be explained by the changes of the degree of crystallinity in these films from the results of X-ray and the polarization behaviors. Meanwhile, the microstructure of the 140 nm film annealed at 130 ◦C is obtained by using scanning electron microscope, which shows that the film exhibits a worm-like, dense, well-crystallized microstructure. Secondly, for the capacitor P(VDF-TrFE) films with a thickness of 140 nm, the ferroelectric polarization hysteresis loops as functions of electric field for the films at different relative humidities are achieved. It is obvious that the polarization properties depend on the relative humidity during the film preparation process, the polarizaiton fatigue can be further enhanced through a higher relative humidity during the sample preparation. In addition, one of the most important features for ferroelectric material to be used as an alternative FeRAM is the low leakage current density. Therefore, the descriptions of the leakage current density versus different relative humidities are given. It is observed that the voltage behavior of the leakage current has a minor dependence on relative humidity. In a word, these results illustrate that the polarization properties are strongly dependent not only on the annealing temperature, but also the relative humidity in a process for the preparation of the nano-films. Furthermore, according to a re-annealing treatment to improve the crystalline degree of the ferroelectric phase, the influence of the re-annealing process on the fatigue properties of the films is also studied. The polarization fatigue can be improved obviously by a re-annealing process, and the possible origins have been discussed. To further understand the variation of crystallization properties of the samples before and after re-annealing, the crystallinity of the film are studied by the technique of Fourier transform infrared spectroscopy. It is indicated that the crystallinity of the films can partly be recovered through re-annealing treatment. These results are very helpful and provide an available way to improve the ferroelectric polarization and fatigue properties of the ferroelectric nano-films.
展开▼
