【作者】 宁平凡；

【导师】 郝虎在； 康爱国；

【作者基本信息】 太原理工大学 ， 物理电子学， 2009， 硕士

【摘要】 铁电薄膜存储器具有高存取速度、高密度、抗辐射和不挥发等特点,引起了人们广泛的研究兴趣。应用于非挥发性存储器的铁电薄膜必须满足极化反转多次(≥1012)而不发生存储单元失效的要求。铁电薄膜的极化疲劳是导致存储单元失效的最重要的因素之一,人们进行了大量的研究来探寻极化疲劳的机理,然而至今仍没有一个令人满意的物理模型。本论文的工作主要是通过总结分析铁电薄膜极化疲劳的典型实验现象和已有的各种解释,提炼出极化疲劳的微观物理图像,建立合理的极化疲劳模型。研究了PZT铁电薄膜的极化疲劳机制。铁电薄膜的极化疲劳是一个多种因素共同参与的复杂过程,而以往的模型大多只考虑一种因素主导而忽略了其他的因素。本文在综合考虑氧空位向界面层的跃迁汇聚、电子注入还原高价阳离子产生新的氧空位以及局部相分解(LPD,Local phase decomposition)三种因素的基础上得出了极化疲劳过程的基本物理图像,认为铁电薄膜与电极界面附近氧空位浓度的增加和LPD是相互促进的。将电荷注入以及LPD理论引入到Dawber-Scott模型中,建立了一个综合考虑多种因素的解析形式的PZT薄膜极化疲劳模型。结合新建立的综合模型讨论了低介电常数界面层在疲劳过程中的作用,认为界面层对疲劳的产生起关键作用。运用该模型分析了不同松弛时间、电压、频率以及温度下的疲劳特性。在与已报道的实验结果进行对比后发现,模型计算结果与实验数据具有很好的一致性。研究了铋层类钙钛矿结构铁电薄膜的极化疲劳问题。本文从两种材料晶体结构的差异出发,总结了Bi2O22+层影响疲劳特性的三个方面。将Bi2O22+的三种作用引入到PZT薄膜极化疲劳的模型中,将其扩展为适用于铋层类钙钛矿结构铁电薄膜的疲劳模型。利用扩展模型分析了电压、频率、温度以及材料的介电常数和畴结构等因素对疲劳特性的影响。将理论模拟结果与文献报道的实验现象进行对比,验证了引入铋氧层作用的合理性。更多还原

【Abstract】 Ferroelectric random access memories(FRAM) attract extensive interest due to high speed, low cost, low power, excellent radiation hardness and nonvolatile information storage. To FRAM, the ferroelectric thin films have to withstand up to 1012 switching cycles without cell failure. Polarization fatigue is one of the most central causes lead to device failure. Though extensive work has been performed to understand the mechanism of fatigue, there is not a full-accepted physical model.In this study, we attempt to abstract the microcosmic physical image and propose a model for fatigue in ferroelectric thin films by analyzing the classic experimental findings and all kinds of explanations.Fatigue mechanism of PZT thin films is investigated. Fatigue in ferroelectric thin films is a complex process caused by many kinds of factors. Previous models tend to include single major factor ignoring others. Based on the oxygen vacancies electro-migration to interfacial layer, generation of new vacancies due to deoxidization of high valence cations by injected charges and local phase decomposition(LPD) a physical image of polarization fatigue is derived. An analytical model is proposed by incorporating the switch-induced charge-injection mechanism and the local phase decomposition theory into the oxygen vacancy electro-migration model. The effects of the low permittivity interfacial layer on the fatigue property are analysed with this model. We conclude the interfacial layer is a crucial reason for polarization fatigue in ferroelectric thin films. The model can easily simulate the fatigue behavior of various ferroelectric thin films under different relaxation times, voltages, frequencies and temperatures.Fatigue problem of bismuth layered structure perovskite thin films(BLTF) is investigated. Bismuth layer is the most important difference between PZT and BLTF in crystal structure. Bismuth layer may improve fatigue property in three aspects. We extend the PZT thin film fatigue model to BLTF by introducing the effects of bismuth layer in it. The voltage, frequency, temperature and dielectric permittivity dependent fatigue properties of BLTF are calculated with the extend model. The results are compared with various experiments. As a whole, the calculations of our model are in agreement with the experiments.更多还原