钙钛矿型氧化物薄膜的性能与微观结构研究

发布时间：2018-05-08 08:57

本文选题：钙钛矿氧化物薄膜 + 微波介电可调性　；参考：《湖南大学》2016年博士论文

【摘要】：B位离子为过渡金属阳离子的钙钛矿型复合氧化物显示出大量有趣的电学和磁学性能,在微波可调器件、存储器、固体燃料电池、催化等领域具有广阔的应用前景。以它们为基础的薄膜器件,部分已开发为产品并广泛应用,但大多数仍处于试验阶段。(Ba_xSr_(1-x))TiO_3是微波可调器件的研究与开发中的重要材料体系。然而,尺寸效应等使得(Ba_xSr_(1-x))TiO_3薄膜的介电特性远差于(Ba_xSr_(1-x))TiO_3陶瓷和单晶材料。过去二十多年的研究发现,BaTiO_3/SrTiO_3多层薄膜内的界面调制作用可以明显改善薄膜材料在低频区域的介电性能,然而对于它们在Ghz频段的微波介电性能的报道却很少。本文以脉冲激光沉积制备的Ba TiO_3/SrTiO_3多层薄膜为研究对象,利用共面波导结构对它进行微波介电性能测试,然后运用X射线衍射、透射电子显微镜等结构表征技术,结合O点阵理论、弹性理论,说明了影响薄膜介电性能的微观结构原因,并且提出了多层薄膜的生长过程和应力弛豫机制。以材料电阻开关效应为基础形成的新型非易失性存储器——电阻式存储器,因设备结构简单、存储性能优越成为当下的研究热点。然而开关机制的不明确性却限制了它的发展。虽然目前研究人员普遍认同氧空位在电阻开关效应中起了重要作用,但它所扮演的角色还需进一步研究确认。本文以脉冲激光沉积制备的BaZrO_3薄膜为研究对象,通过对它进行电学性能测试,然后运用透射电子显微术,结合绝缘体电流传导机制,尝试理解氧空位和晶界等缺陷在电阻开关效应中所起的作用,以及沉积氧压对BaZrO_3薄膜微观结构和电性能的影响。总的来说,本文的研究目的是通过探究薄膜材料的结构和性能之间的联系,阐明影响薄膜的具体性能的微观结构根源,为理解薄膜中的各种性能和现象提供思路。得到的主要结论如下:(1)薄膜晶体的畸变程度以及缺陷密度的改变是导致[(BaTiO_3)0.5/(SrTiO_3)_(0.5)]_(16)和[(BaTiO_3)_(0.4)/(SrTiO_3)_(0.6)]_(30)两者介电性能差异的原因。(2)虽然包含32层亚层薄膜,[(BaTiO_3)_(0.5)/(SrTiO_3)_(0.5)]_(16)多层薄膜却显示出具有不同形貌的双层结构——即底层薄膜和顶层薄膜。底层薄膜和MgO基体保持外延关系,且层内的应变能通过形成失配位错、反相畴界、层错等晶体缺陷得到释放。而顶层薄膜则形成具有择优取向的多晶柱状薄膜。在整个生长过程中,BaTiO_3和SrTiO_3之间显示出了非常一致的生长行为。(3)在以BaZrO_3薄膜为阻变层的Ag/BaZrO_3/SrRuO_3结构中发现了可转向的二极管效应,并从机理上证实了界面处氧空位对载流子的捕获/释放是形成该效应的原因。此外,和常见非铁电钙钛矿材料相比,BaZrO_3薄膜数据保持能力的改善源于BaZrO_3/SrRuO_3界面处晶界的存在,但是氧空位的积累导致Ag/Ba ZrO_3/SrRuO_3在长期使用后电阻退化。(4)在Ag/BaZrO_3/SrRuO_3结构中,当BaZrO_3采用的的氧压小于2′10-4 Pa时,SrRuO_3薄膜会发生热分解,形成Ru颗粒以及非晶SrO。BaZrO_3薄膜为多晶薄膜,存在不少孪晶,并且能够检测到Sr元素的存在。而当BaZrO_3采用的沉积氧压为1.33 Pa时,SrRuO_3为外延薄膜,BaZrO_3出现双层结构,其中底层为单晶薄膜,顶层为多晶薄膜。结构以及成分的差异,使得这两种Ag/BaZrO_3/SrRuO_3结构出现电行为的差异。另外,SrRuO_3外延薄膜在电子束辐照的作用下会发生辐照分解,形成SrO以及晶格缺陷。
[Abstract]:The perovskite type oxides with B position ions as transition metal ions show a lot of interesting electrical and magnetic properties. They have broad applications in the fields of microwave tunable devices, memory, solid fuel cells, catalysis and other fields. Some of them have been developed as products and widely used, but most of them are still in the field. The experimental stage. (Ba_xSr_ (1-x)) TiO_3 is an important material system in the research and development of microwave tunable devices. However, the dielectric properties of (Ba_xSr_ (1-x)) TiO_3 thin films are much worse than (Ba_xSr_ (1-x)) TiO_3 ceramics and single crystal materials. In the past more than 20 years, the interfacial modulation in BaTiO_3/SrTiO_3 multilayer films has been found. The dielectric properties of the thin film materials in the low frequency region can be obviously improved. However, there are few reports on their microwave dielectric properties at the Ghz band. In this paper, the Ba TiO_3/SrTiO_3 multilayer films prepared by pulsed laser deposition are used as the research object. The dielectric properties are tested by the coplanar waveguide structure, and then X ray diffraction is used. The structure characterization technology such as transmission electron microscope, combined with the theory of O lattice and elastic theory, illustrates the microstructural reasons that affect the dielectric properties of the film, and puts forward the growth process and the stress relaxation mechanism of the multilayer thin films. However, the uncertainty of the switching mechanism has limited its development. Although the researchers generally agree that the oxygen vacancy plays an important role in the resistance switching effect, the role it plays needs further research and confirmation. The BaZ prepared in this paper is based on pulsed laser deposition. RO_3 film is the research object. By electrical properties testing, transmission electron microscopy and insulator current conduction mechanism are used to try to understand the effect of oxygen vacancy and grain boundary defects on the resistance switching effect, as well as the influence of oxygen pressure on the microstructure and electrical properties of BaZrO_3 films. The purpose of this study is to investigate the relationship between the structure and properties of the thin film materials, to clarify the microstructural causes affecting the specific properties of the film, and to provide ideas for understanding the various properties and phenomena in the film. The main conclusions are as follows: (1) the distortion of the film and the change of the density of the defects lead to [(BaTiO_3) 0.5/ (SrTi) O_3) causes (16) and [(BaTiO_3)] (0.4) / (SrTiO_3) (0.6)] (30) the difference in dielectric properties. (2) although there are 32 layers of thin film, [(BaTiO_3)] (0.5) / (0.5)] (16) multilayer thin films show a double layer structure with different morphologies, that is, the bottom film and the top film. The bottom film and the MgO matrix maintain the epitaxial relationship. In addition, the strain energy in the layer can be released by forming mismatched dislocations, reverse domain boundaries, and stacking faults, while the top layer films form a polycrystalline columnar film with preferred orientation. During the whole growth process, BaTiO_3 and SrTiO_3 show a very consistent growth behavior. (3) Ag/BaZrO_3/SrRuO_ with BaZrO_3 film as the resistive layer. The 3 structure has found a steerable diode effect, and it has been proved by the mechanism that the oxygen vacancy at the interface is responsible for the formation of the carrier. In addition, the improvement of the BaZrO_3 film data retention capacity is due to the existence of the grain boundary at the BaZrO_3/ SrRuO_3 interface, but the product of the oxygen vacancy. The resistance causes the Ag/Ba ZrO_3/SrRuO_3 to degenerate after long term use. (4) in the Ag/BaZrO_3/SrRuO_3 structure, when the oxygen pressure of BaZrO_3 is less than 2 '10-4 Pa, the SrRuO_3 film will have thermal decomposition, forming Ru particles and amorphous SrO.BaZrO_3 thin films as polycrystalline thin films, there are few twins and can detect the existence of Sr elements. And Ba When the oxygen pressure of ZrO_3 is 1.33 Pa, SrRuO_3 is epitaxial film, and BaZrO_3 appears double layer structure, in which the bottom is single crystal film and the top layer is polycrystalline thin film. The difference of structure and composition makes the two kinds of Ag/BaZrO_3/SrRuO_3 structure appear electrical behavior difference. In addition, SrRuO_3 epitaxial film will be irradiated by electron beam irradiation. According to decomposition, SrO and lattice defects are formed.

【学位授予单位】：湖南大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TB383.2

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