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环境友好型Ba-Ca-Zr-Ti-O基铁电薄膜的制备及性能研究
杨世华
学位类型硕士
导师徐金宝
2012-05
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业微电子学与固体电子学
关键词薄膜 铁电相变 晶粒取向 氧空位 空间电荷极化
摘要铁电材料由于具有铁电特性和压电特性而在信息储存、通信、导航、精密测量、机械等众多领域得到广泛的应用。但当前高性能的铁电材料主要是铅基材料,其在生产、使用和废弃处理过程中都给人类健康和生态环境造成严重的损害。近年来,随着人们环保意识的增强,新型环境友好的无铅铁电材料已经成为研究领域的一个热点。本文对环境友好型Ba-Ca-Zr-Ti-O基铁电薄膜材料的制备工艺、介电、漏电流特性以及相关机理进行了系统的研究。重点探讨了薄膜的晶粒取向和电性能的相互关系。主要的研究内容如下: (1) 利用溶胶-凝胶工艺在Pt/Ti/SiO2/Si衬底上成功合成了晶粒自由取向的Ba-Ca-Zr-Ti-O系薄膜。讨论了薄膜材料的制备工艺,分析了薄膜的铁电相变过程和漏电流特性。Ba-Ca-Zr-Ti-O系薄膜的居里温度比其陶瓷的居里温度下降了25-75 ºC,而且其陶瓷的Zr含量对铁电相变的调制规律不再适用于薄膜材料。这表明薄膜的铁电相变受到了晶粒尺寸(~20 nm)效应的影响。漏电流特性分析表明Ba0.85Ca0.15Zr0.1Ti0.9O3薄膜的漏电流密度最小而且欧姆电导区间最宽,反映出薄膜的缺陷态主要位于浅能级而且其态密度最小。 (2)在(100)LaNiO3/Si衬底上制备了(100)取向和随机取向Ba0.85Ca0.15Zr0.1Ti0.9O3薄膜。研究了不同晶粒取向薄膜的制备工艺、介电频谱和介电非线性。(100)取向薄膜比随机取向薄膜表现出更大的介电常数(在10 kHz分别为320和145)和介电调制率(在250 kV/cm电场下分别为27%和12%)。但是(100)取向薄膜的介电弛豫频率(400 kHz)远小于随机取向薄膜的介电弛豫频率(>2MHz)。我们进一步分析了晶粒取向与薄膜介电属性的关联性:晶粒的取向生长导致了偶极子的定向排布,这使得(100)取向薄膜具备了有序无序型铁电体的性质。 (3) 对不同温度(60-210 ºC)条件下的(100)取向Ba0.85Ca0.15Zr0.1Ti0.9O3薄膜进行复阻抗分析。薄膜的晶界效应随着温度的升高表现得越来越明显。晶粒电阻和晶界电阻的对数随绝对温度的倒数均呈线性关系(其斜率对应的激活能分别为0.37 eV和0.27 eV)。晶粒和晶界的电导激活能与氧空位的一级电离能相一致表明这一现象的本质是氧空位的存在。薄膜的漏电流密度与电场的变化受到空间电荷限制电流机制的作用,表明薄膜的缺陷态位于浅能级。 (4) 在(100)LaNiO3/Si衬底上制备了Ba0.85Ca0.15Zr0.1Ti0.9O3-xKNbO3薄膜。讨论了KNbO3掺杂对薄膜介电属性的影响。KNbO3掺杂使薄膜的介电弛豫频率从400 kHz减小到2 kHz以下,而且使其C-V曲线表现出明显的回线特征。薄膜中K+、Nb5+离子分别取代了Ba2+、Ca2+和Zr4+、Ti4+离子,导致了被占据晶格呈现出电荷性,这些电荷被外电场极化从而产生了空间电荷极化,使薄膜表现出赝铁电性。 关键词:薄膜;铁电相变;晶粒取向;氧空位;空间电荷极化
其他摘要The ferroelectric materials are widely used in the information storage, communication, navigation, precision measurement and machinery etc. due to their ferroelectricity and piezoelectricity. However, the current ferroelectrics with high-performance are mainly lead-based materials, which are seriously harmful to human health and environment during the manufacturing, usage and waste treatment. In the recent years, with the increasing environmental awareness, the study of new environmentally friendly lead-free ferroelectric materials has been a hotspot. This paper has systematically studied the preparation technology, dielectric properties, leakage current characteristics and correlative mechanism of Ba-Ca-Zr-Ti-O based ferroelectric thin films. The main research contents are following: (1) By the sol-gel process, the Ba-Ca-Zr-Ti-O based thin films with random orientation grains are successfully prepared on Pt/Ti/SiO2/Si substrates. The preparation process, ferroelectric phase transitions and leakage current characteristics of the films are discussed in details. The Curie temperature of the Ba-Ca-Zr-Ti-O based thin films is 25-75 ºC lower than that of the corresponding ceramics and the influence of zirconium content is also significantly weakened on the ferroelectric phase transition for the films. This means that the size effect (~20 nm) takes part in the ferroelectric phase transition of the films. Compared with the other films, the Ba0.85Ca0.15Zr0.1Ti0.9O3 film has the lowest leakage current density and widest ohmic conductivity region, indicating that the defect states of the film mainly lie in the shallow energy levels and the defect state densities of the film are the smallest in all the samples. (2) The (100)-oriented and random orientation Ba0.85Ca0.15Zr0.1Ti0.9O3 films are successfully fabricated on the (100) LaNiO3/Si substrates. The preparation process, dielectric spectrum and dielectric nonlinearity of the thin films are compared and discussed in details. The (100)-oriented film has higher dielectric constant (320 and 145 at the frequency of 1 kHz, respectively) and dielectric nonlinearity (27% and 12% at the electric field of 250 kV/cm, respectively). We furthermore analyze the relevance uniform dipole alignment, which makes the (100)-oriented film with the character of order-disorder ferroelectric.between grain orientation and the dielectric properties: the oriented growth of the crystalline grains leads to the (3) The complex impedance spectrum analysis is used to study the electrical properties of the (100)-oriented Ba0.85Ca0.15Zr0.1Ti0.9O3 film at different temperatures (60-210 ºC). With the increasing of temperature, the grain boundary effect is more and more significant. Both the logarithms of dc conductivities of grains and grain boundaries have the linear relationships with the reciprocal absolute temperature (the corresponding activation energies of slopes are 0.37 eV and 0.27 eV, respectively). It suggests that the nature of the phenomenon is the existence of oxygen vacancies that activation energies of dc conductivities of grains and grain boundaries are consistent with the first ionization energies of the oxygen vacancies. The leakage current characteristic of the film is in the space charge limited current mechanism, indicating that the defect states of the film lie in the shallow energy levels. (4) The Ba0.85Ca0.15Zr0.1Ti0.9O3-xKNbO3 thin films are successfully fabricated on the (100) LaNiO3/Si substrates. The preparation process and influence on the dielectric properties of KNbO3 doping are discussed in details. The KNbO3 doping reduces the dielectric relaxation frequencies of films largely from 400 kHz to the below 2 kHz and make the C-V curves of films featured hysteresis. The respective substitution of K+ and Nb5+ for Ba2+or Ca2+ and Zr4+ or Ti4+ lead to the space charge of the occupied lattice which can be polarized by the electric filed to result in the space charge polarization, leading to the pseudo ferroelectricity of the films. Key words: thin films; ferroelectric phase transition; grain orientation; oxygen vacancies; space charge polarization
文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4375
专题材料物理与化学研究室
作者单位中国科学院新疆理化技术研究所
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杨世华. 环境友好型Ba-Ca-Zr-Ti-O基铁电薄膜的制备及性能研究[D]. 北京. 中国科学院研究生院,2012.
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