【作者】 符春林；

【导师】 杨传仁；

【作者基本信息】 电子科技大学 ， 材料学， 2005， 博士

【摘要】 钛酸锶钡(Ba_xSr_1-xTiO₃,简称BST)薄膜具有非线性强、漏电流小、居里温度可调等特点,因而在介质移相器、压控滤波器等方面有着广泛的应用前景。本文对Ba_xSr_1-xTiO₃（x=0.45～0.9）系列陶瓷的晶体结构和介电性能、膜厚均匀性控制、BST薄膜的微结构（包括组成、晶体结构、电畴等）和电压非线性尺度效应、铁电薄膜电压非线性模型、薄膜型介质移相器的设计和制作等重要问题进行了研究,取得了以下研究结果: 通过研究靶基中心不重合的磁控溅射系统,建立了平面磁控溅射膜厚分布的数学模型,提出了采用T=integral from n=L to （d（x,y）ds）=integral from n=O to (d（ξ（t）,ψ（t））·(ξ^’2（t）+ψ^’2（t）·dt)^1/2)来描述靶基中心不重合的平面磁控溅射的膜厚分布情况。在靶基距为72mm、公自转转速比为5.3的条件下,采用自行设计的射频磁控溅射设备和φ120mm靶材制备的BST薄膜膜厚均匀性偏差为2.8%。 采用压电力显微镜（PFM）研究了BST薄膜中电畴的类型和尺寸。不仅证实BST薄膜中存在90°铁电畴,而且确定了BST薄膜由多畴转变为单畴结构的晶粒临界尺寸（单畴临界尺寸）为31nm左右。 通过研究BST薄膜的电压非线性尺度效应,我们发现晶粒尺寸和膜厚对薄膜的电压非线性具有重要的作用。随着晶粒尺寸和膜厚的增加,BST薄膜的介电系数、介电系数变化率都逐渐增大。晶粒尺寸对单畴态薄膜的介电系数电压变化率和矫顽场强影响特别显著,而对多畴态薄膜的介电系数电压变化率和矫顽场强影响不明显。 在上述实验研究的基础上,对铁电材料的电压非线性机理进行了研究。首先,从简单、实用的角度出发写出表征P（E）和ε（E）非线性的数学多项式,根据介电偏压特性曲线和电滞回线的特征值和连续性原理,给出边界条件和初始条件,解出表达式中的各项系数,从而建立了铁电晶体的电压非线性模型。然后,采用理想的晶粒-晶界几何模型,画出铁电陶瓷材料的等效电路,引入晶粒和晶界的大小,从而建立了铁电陶瓷的电压非线性模型。再采用理想二极管等效界面势垒,得到薄膜型平板电容器等效电路,引入膜厚和界面厚度两个尺度变量,更多还原

【Abstract】 Barium strontium titanate (BaxSr1-xTiO3, short for BST) thin films are potential materials for the applications of microwave devices such as dielectric phase shifters and tunable filters due to their high dielectric nonlinearity, low leakage current and adjusting Curie temperature. The microstructures and dielectric properties of BaxSr1-xTiO3 (x=0.45~0.9) ceramics, film thickness uniformity, microstructures and size effect on dielectric nonlinearities of BST films, model for dielectric nonlinearity of ferroelectric films, design and fabrication of phase shifters were investigated. Moreover, there are a series of results as follows:On condition that the center of the substrate is not coincident with that of the target, the magnetron sputtering system was studied. Under the conditions of planetary movement of a substrate underneath a magnetron sputter cathode, a model on the relation between the film thickness and the parameters, such as rotation speed, revolution speed and the distance from target to substrate, was obtained. The relative film thickness distribution can be expressed by T= . It is found that the relative deviation of film thickness distribution is 2.8% within a diameter of φ 100 mm when the ratio of the rotation speed to revolution speed and the distance from target to substrate are 5.3 and 72 mm, respectively.The species and sizes of domains in BST thin films were investigated by piezoresponse force microscopy (PFM). The results show that there are 90° domains. It is found that the critical grain size from a multi-domain to a single-domain is about 31nm.The size effects on nonlinearity of BST thin films were investigated and the results show that the grain size and film thickness play an important role on nonlinearity of ferroelectric films. The dielectric constant and the tunability of BST thin films increase as the grain size and/or film thickness increase. The tunability and the coercive electric field of BST films with mono-domain configuration are更多还原