外延钛酸锶薄膜及介电调谐性能研究
发布时间：2019-03-20 19:14
【摘要】：钛酸锶(STO)薄膜在液氮温区具有非常好的非线性介电性质,这种介电常数随着外加电场变化的特性,使得它在电可调谐微波集成器件上有着广阔的应用前景。虽然介电材料已经得到了广泛的研究,但如何在实现高调谐率的同时依然保持较低的介电损耗仍然是研究的难点。近年来,研究发现多层外延薄膜可以实现这种协调。镍酸镧(LNO)薄膜与STO同属钙钛矿结构,具有良好的导电性且与STO晶格匹配性好,因而可以成为外延STO薄膜优异的电极材料。本文从STO薄膜的热处理温度和上电极材料两方面对其介电调谐性能的影响进行了研究,取得以下研究成果:(1)采用溶胶-凝胶法在(00l)LAO基板上制备了以LNO为底电极的外延STO薄膜,研究了异质同构薄膜取向特性的检测方法,发现采用高指数晶面可以分析外延薄膜的面内取向。进一步研究了热处理温度对STO/LNO复合薄膜介电调谐性能的影响,发现随着热处理温度的提高,Pt/STO/LNO结构的介电调谐率增加,介电损耗降低,最佳热处理温度下制备的Pt/STO/LNO复合结构的调谐率为49.8%,介电损耗为0.0115,优值因子为43.3。(2)采用感光溶胶-凝胶法制备出了具有良好导电性的LNO图形化薄膜,将其应用于STO/LNO复合薄膜上电极的制备,形成上下电极对称的LNO/STO/LNO电容结构,介电性能分析表明LNO/STO/LNO结构比Pt/STO/LNO结构介电性能更加优异,其优值因子可达到82.4。(3)通过J-V特性分析了 Pt、LNO上电极材料对STO/LNO结构中STO介电性能的影响机理。研究发现,随着温度的降低(80～300 K温度范围内),Pt/STO/LNO和LNO/STO/LNO两种异质结构中的漏电流密度均减小,进一步分析发现Pt/STO/LNO结构中Pt/STO界面存在肖特基势垒,LNO/STO/LNO结构中并没有观察到明显的势垒,肖特基势垒的存在影响了 STO的极化过程,导致Pt/STO/LNO异质结构中更高的介电损耗。
[Abstract]:Strontium titanate (STO) thin films have very good nonlinear dielectric properties in the liquid nitrogen temperature region. This dielectric constant changes with the applied electric field, which makes it have a broad application prospect in electrically tunable microwave integrated devices. Although dielectric materials have been extensively studied, how to achieve high tunability while maintaining low dielectric loss is still a difficult problem. In recent years, it has been found that multilayer epitaxial films can achieve this coordination. Lanthanum nickel (LNO) films belong to perovskite structure as well as STO, and have good electrical conductivity and good lattice matching with STO. Therefore, lanthanum nickel thin films can be used as excellent electrode materials for epitaxial STO films. In this paper, the effects of heat treatment temperature and upper electrode material on the dielectric tuning properties of STO thin films have been studied. The research results are as follows: (1) the epitaxial STO thin films with LNO as the base electrode were prepared by sol-gel method on (00l) LAO substrate, and the methods of measuring the orientation characteristics of heterogeneous and isomorphic thin films were studied. It is found that the in-plane orientation of epitaxial films can be analyzed by using high index crystal plane. The effect of heat treatment temperature on the dielectric tuning properties of STO/LNO composite films was further studied. It is found that the dielectric tunability of Pt/STO/LNO structure increases and the dielectric loss decreases with the increase of heat treatment temperature. The tunability and dielectric loss of the Pt/STO/LNO composite structure prepared at the optimum heat treatment temperature are 49.8% and 0.0115, respectively. The excellent value factor was 43. 3. (2) LNO patterned thin films with good conductivity were prepared by photosensitive sol-gel method and applied to the preparation of electrodes on STO/LNO composite films. The structure of LNO/STO/LNO capacitor with symmetrical upper and lower electrodes is formed. The dielectric properties of LNO/STO/LNO structure are better than that of Pt/STO/LNO structure, and the dielectric properties are better than that of Pt/STO/LNO structure. The excellent value factor can reach 82.4. (3) the mechanism of the effect of the electrode material on Pt,LNO on the dielectric properties of STO in STO/LNO structure is analyzed by J _ (?) V characteristics. It is found that the leakage current density in both Pt/STO/LNO and LNO/STO/LNO heterostructures decreases with the decrease of temperature (in the temperature range of 80? 300K). Further analysis shows that there is Schottky barrier at the interface of Pt/STO in Pt/STO/LNO structure, but no obvious barrier is observed in LNO/STO/LNO structure. The existence of Schottky barrier affects the polarization process of STO. It leads to higher dielectric loss in Pt/STO/LNO heterostructure.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.2
本文编号：2444539
[Abstract]:Strontium titanate (STO) thin films have very good nonlinear dielectric properties in the liquid nitrogen temperature region. This dielectric constant changes with the applied electric field, which makes it have a broad application prospect in electrically tunable microwave integrated devices. Although dielectric materials have been extensively studied, how to achieve high tunability while maintaining low dielectric loss is still a difficult problem. In recent years, it has been found that multilayer epitaxial films can achieve this coordination. Lanthanum nickel (LNO) films belong to perovskite structure as well as STO, and have good electrical conductivity and good lattice matching with STO. Therefore, lanthanum nickel thin films can be used as excellent electrode materials for epitaxial STO films. In this paper, the effects of heat treatment temperature and upper electrode material on the dielectric tuning properties of STO thin films have been studied. The research results are as follows: (1) the epitaxial STO thin films with LNO as the base electrode were prepared by sol-gel method on (00l) LAO substrate, and the methods of measuring the orientation characteristics of heterogeneous and isomorphic thin films were studied. It is found that the in-plane orientation of epitaxial films can be analyzed by using high index crystal plane. The effect of heat treatment temperature on the dielectric tuning properties of STO/LNO composite films was further studied. It is found that the dielectric tunability of Pt/STO/LNO structure increases and the dielectric loss decreases with the increase of heat treatment temperature. The tunability and dielectric loss of the Pt/STO/LNO composite structure prepared at the optimum heat treatment temperature are 49.8% and 0.0115, respectively. The excellent value factor was 43. 3. (2) LNO patterned thin films with good conductivity were prepared by photosensitive sol-gel method and applied to the preparation of electrodes on STO/LNO composite films. The structure of LNO/STO/LNO capacitor with symmetrical upper and lower electrodes is formed. The dielectric properties of LNO/STO/LNO structure are better than that of Pt/STO/LNO structure, and the dielectric properties are better than that of Pt/STO/LNO structure. The excellent value factor can reach 82.4. (3) the mechanism of the effect of the electrode material on Pt,LNO on the dielectric properties of STO in STO/LNO structure is analyzed by J _ (?) V characteristics. It is found that the leakage current density in both Pt/STO/LNO and LNO/STO/LNO heterostructures decreases with the decrease of temperature (in the temperature range of 80? 300K). Further analysis shows that there is Schottky barrier at the interface of Pt/STO in Pt/STO/LNO structure, but no obvious barrier is observed in LNO/STO/LNO structure. The existence of Schottky barrier affects the polarization process of STO. It leads to higher dielectric loss in Pt/STO/LNO heterostructure.
【学位授予单位】：西安理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB383.2
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