PLD法制备BST铁电薄膜及其性质的研究

发布时间：2018-06-16 01:00

本文选题：钛酸锶钡 + 脉冲激光沉积　；参考：《华东师范大学》2010年硕士论文

【摘要】： 钛酸锶钡(简称BST)是一种铁电／介电性能十分优越的材料,因其具有低漏导电流密度、低介质损耗、低介电常数温度、高介电常数、热释电系数及其居里点温度可依据Ba/Sr比值可调等特点,广泛应用于微波可调谐器件、动态随机存储器、热释电红外探测器等方面。随着科技的发展,及大规模集成电路应用技术的发展和需要,BST铁电薄膜材料因具备优异的电学和光学性能,本应在应用领域中大展身手,却因为薄膜制备技术上仍然无法达到领域内所期望的高性能指标。这一定程度上阻碍了相关的科技的发展,因此,BST铁电材料的性能改善的研究工作有很高的研究价值和需要。为了解决上述问题,使得钛酸锶钡材料能够得到更加广泛的应用,本文主要研究了以下内容并将研究结果简单介绍如下： 1.采用脉冲激光沉积的方法,在不同的衬底上制备了BST薄膜样品,并通过改善工艺,如退火温度,衬底选择等,研究了这些工艺条件对薄膜的质量和性能包括物性和电学性质的影响。 2.XRD图谱表明衍射峰的相对强度随着沉积温度的增加而增加,随着沉积温度的上升,薄膜的生长质量和结晶状况得到改善。而在铂金衬底和镍酸镧衬底上制备的薄膜样品均良好结晶,呈现出不同的取向。在LNO衬底和Pt衬底上沉积的BST薄膜的晶粒尺寸分别为70nm和50nm。使用与钛酸锶钡材料晶格结构类似的镍酸镧薄膜作为衬底,薄膜的晶粒尺寸有明显的增加。结果也表明,衬底的选择的确对薄膜的取向和结晶性能有很显著的影响。 3.AFM的测试结果表明,在LNO和Pt衬底基片上生长的钛酸锶钡薄膜均结晶良好,表面光滑,无针洞裂纹。在LNO衬底上生长的薄膜样品,具备更平滑的表面形貌,更大的晶粒尺寸,以及更佳的结晶状况。在激光沉积法制备BST薄膜的过程中,BST的微晶成核和动态生长的过程明显对衬底的性质存在依赖。 4.XPS测试表明采用脉冲激光沉积工艺所制备的BST薄膜中Ba、Sr、Ti、O元素都以钙钛矿结构中各元素的相应的化学态而存在,而AES测试的结果表明样品出现了c元素的沾污,这是由于空气中的碳元素的污染造成的。 5.对所制备样品进行了电学特性分析,包括CF特性,介电损耗特性,CV特性,PE曲线特性等。分析表明,薄膜样品的介电特性受到频率的影响明显,尤其在高频区域。而不同衬底的选择,会对这一特性有明显的影响。这和薄膜的微结构,以及薄膜和电极间的过渡层的出现有关。 6.本文中着重研究了BST薄膜的介电特性的不对称性。结果表明,介电特性的不对称性是薄膜本身的性质造成,而非加诸的电压导致。而上下电极的不对称性,会加重其不对称性,为改善这一点,BST薄膜的上下电极均采用铂金电极后,显著改善了不对称性(薄膜的介电不对称率由50.38%减小至17.86%)。 7.BST薄膜材料在微波器件的研制领域有着广阔的前景。在本文的电学测试中,也着重研究了其介电可调谐性。结果表明,薄膜样品的可调谐度随着频率的上升而一定程度上出现下降趋势。且可调谐度受到底电极的影响较为明显。在LNO底电极上沉积的薄膜表现出更优良的可调谐度,在10kHz和100kHz下分别达到45.3％和39.5%,而沉积在Pt底电极上的薄膜的可调谐度均在30%左右,且随频率变化不大。薄膜样品的可调谐度随频率的变化与之前薄膜样品的C-F特性曲线相吻合。薄膜的微结构和介电性能,直接影响了其可调谐性能。要制备出可调谐性良好的薄膜材料,需要对薄膜的生长工艺和薄膜结构进行改进。 8.对于钛酸锶钡薄膜的铁电性也进行了测试和研究。在8V的测试电压下,电场强度约为400kv／cm,此时LNO上的样品的剩余极化强度Pr和矫顽电场Ec分别是0.409μC／cm2和22.04 kV／cm,而Pt上沉积的样品的对应的Pr和Ec分别为0.393μC／cm2和12.09 kV／cm。在Pt缓冲层上沉积的薄膜显示了更大和更明显的电滞回线,而在LNO缓冲层上沉积的薄膜的电滞回线沿着电场v=0轴线有一定程度的偏移,这一结果与CV测试结果相吻合这可能是由于薄膜的微畴结构上的差异造成的。结果表明,晶粒的大小和底电极的选择,对铁电性有明显的影响。
[Abstract]:Barium strontium titanate (BST) is an excellent ferroelectric / dielectric material. Because of its low leakage current density, low dielectric loss, low dielectric constant temperature, high permittivity, thermoluminescence coefficient and Curie point temperature can be adjusted according to the Ba/Sr ratio, it should be widely used in microwave tunable devices, dynamic random memory and heat. With the development of science and technology and the development of the application technology of large scale integrated circuits, the BST ferroelectric thin film materials have excellent electrical and optical properties. They should be in the field of application, but because the film preparation technology still fails to reach the expected high performance indicators in the field. To a certain extent, it hinders the development of related technology. Therefore, the research on the performance improvement of BST ferroelectric materials has high research value and needs.
In order to solve the above problems, barium strontium titanate materials can be more widely used. The following contents are mainly studied and the results are briefly introduced as follows:
1. the samples of BST films were prepared on different substrates by pulsed laser deposition, and the effects of these conditions on the quality and properties of the films, including physical properties and electrical properties, were investigated by improving the process, such as annealing temperature and substrate selection.
The 2.XRD map shows that the relative intensity of the diffraction peak increases with the increase of the deposition temperature. With the increase of the deposition temperature, the growth quality and crystallization of the film are improved. The films prepared on the platinum substrate and the lanthanum acid substrate are well crystallized, showing different orientation. The BST thin deposited on the LNO substrate and the Pt substrate. The grain size of the film is 70nm and 50nm., which is similar to the lattice structure of barium strontium titanate as the substrate, and the grain size of the film is obviously increased. The results also show that the selection of the substrate has a significant effect on the orientation and crystallization properties of the films.
The test results of 3.AFM show that barium strontium titanate thin films on the substrate of LNO and Pt have good crystallization, smooth surface and no needle hole cracks. The thin film samples on the LNO substrate have more smooth surface morphology, larger grain size, and better crystallization condition. In the process of preparing BST thin films by laser deposition, BST micro The process of nucleation and dynamic growth obviously depends on the properties of the substrate.
The 4.XPS test showed that the Ba, Sr, Ti and O elements in the BST films prepared by pulsed laser deposition were all in the chemical state of the elements in the perovskite structure, and the results of AES test showed that the samples were contaminated by the C elements, which was caused by the pollution of the carbon elements in the air.
5. the electrical characteristics of the prepared samples were analyzed, including CF characteristics, dielectric loss characteristics, CV characteristics, and PE curve characteristics. The analysis showed that the dielectric properties of the films were affected by frequency, especially at high frequency regions. The selection of different substrates would have a significant effect on this specificity. This and the microstructure of the film, and film It is related to the appearance of the transition layer between the electrodes.
6. in this paper, the asymmetry of dielectric properties of BST films is emphatically studied. The results show that the asymmetry of dielectric properties is caused by the properties of the film itself, not the voltage added, and the asymmetry of the upper and lower electrodes will aggravate its asymmetry. In order to improve this point, the upper and lower electrodes of the BST film are changed to a platinum electrode. The asymmetry of the dielectric asymmetry is reduced from 50.38% to 17.86%.
7.BST thin film materials have a broad prospect in the development of microwave devices. In the electrical test, the dielectric tunability is also studied. The results show that the tunability of the thin film samples decreases with the increase of frequency. And the tunability is influenced by the electrode. At the bottom of the LNO, the tunability is more obvious. The deposited film shows a better tunability at 45.3% and 39.5% under 10kHz and 100kHz respectively, while the tunability of the films deposited on the Pt substrate is about 30%, and the frequency varies little with the frequency. The tunability of the film samples coincides with the C-F characteristic curve of the thin film samples. The microstructure and dielectric properties directly affect its tunable properties. To prepare thin film materials with good tunability, it is necessary to improve the film growth process and thin film structure.
8. the ferroelectric properties of barium strontium titanate thin film are also tested and studied. Under the test voltage of 8V, the electric field strength is about 400kV / cm. At this time, the residual polarization strength of the samples on LNO and the coercive electric field Ec are 0.409 C / cm2 and 22.04 kV / cm respectively, while the corresponding Pr and 12.09 samples are 0.393 Mu and 12.09 respectively. The film deposited on the Pt buffer layer of cm. shows a larger and more obvious hysteresis loop, and the hysteresis loop of the film deposited on the LNO buffer layer is offset to a certain extent along the v=0 axis of the electric field. This result is in agreement with the CV test results, which may be due to the difference on the microdomain structure of the film. The result shows that the grain size is large. The choice of small and bottom electrodes has a significant effect on ferroelectricity.
【学位授予单位】：华东师范大学
【学位级别】：硕士
【学位授予年份】：2010
【分类号】：TM221

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