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存储器用铁电薄膜及电极材料的研究

Ferroelectric thin films and electrodes for random access memories

  • 摘要: 铁电体独特的自发电极化双稳性质和非线性光学性质使其在光电子器件中得到广泛应用.为了实现器件的小型化和与微电子、光电子工艺兼容,铁电薄膜已成为一个研究热点.自发电极化的大小和取向以及外电场、缺陷和铁电薄膜/电极界面与自发电极化的交互作用决定了铁电薄膜的性质和服役行为.文章以铁电存储器和光电子器件应用为背景,选择了具有重大应用前景的Bi4-xLaxTi3O12(BLT)、SrBi2Ta2O9(SBT)、PbZrxTi1-xO3(PZT)和LiNbO3(LN)铁电薄膜以及相关的 La(Sr,Co)O3 (LSCO) 和LaNiO3(LNO)等电极材料为研究对象,研究了缺陷电荷和电畴的交互作用和它们在交变外电场中的动力学行为,探明了铁电薄膜疲劳现象的物理本质;从晶格结构与缺陷的观察研究入手,探索了材料铁电性质的起源和优化材料铁电性质的途径;从铁电薄膜/电极界面结构与性质的研究入手,寻找更有效、更稳定的电极材料与结构,从而为器件应用打下了基础;在研究外电场对铁电薄膜生长机制影响的基础上,找到了利用外电场调控铁电薄膜结构的新途径,发展了新的、与半导体器件和光电子器件工艺兼容的制膜方法.

     

    Abstract: Ferroelectrics possess spontaneous polarization which can be switched by applying an electric field; this property can be used to produce random access memories. Some ferroelectrics have large nonlinear optical coefficients and strong electro-optical effects, which may be exploited in opto-electronic and optical communication devices. In this work ferroelectric Bi4-xLaxTi3O12, SrBi2Ta2O9, PbZrxTi1-xO3 and LiNbO3( films of the perovskite structure as well as related perovskite La(Sr,Co)O3 and LaNiO3 electrode films were studied, and the interaction between defect charges and domain walls and their dynamic behavior in an ac electric field investigated to elucidate the mechanism of the fatigue phenomenon. Studies on the lattice structures and defects of the films by high resolution transmission electron microscopy and Raman scattering measurements were made to find a way to optimize the electrical properties. The microstructure and properties of film/electrode interfaces were also studied, from which the optimal film/electrode combinations for memory applications were proposed. The growth mechanism of ferroelectric thin films in an electric field was investigated both experimentally and theoretically, and a technique to control the growth texture by using an electrical field was developed.

     

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