【作者】 秦文峰；

【导师】 李言荣；

【作者基本信息】 电子科技大学 ， 材料物理与化学， 2008， 博士

【摘要】 BaTiO₃（BTO）基薄膜是目前电子功能材料领域倍受关注的一类新材料。其中，Ba_1-xS_rxTiO₃（BST）薄膜具有介电非线性效应，即材料的介电常数随着外加电场变化的非线性特性。这种特点使其在电压可调微波器件上具有广阔的应用前景，成为近年国际上的一个热点，而提高其介电可调率和降低损耗一直是BST薄膜材料研究的重点。本论文首先开展了BST薄膜脉冲激光沉积技术（PLD）的生长研究，探索了主要工艺参数（沉积温度、氧分压，激光能量）对BST微观结构影响的机制，优化了BST薄膜生长工艺，制备出了高质量的BST薄膜。在半导体集成研究中，BST薄膜通常是生长在Pt-Si基底材料上，形成MIM结构，电极材料和薄膜间界面处过多的缺陷会导致BST薄膜介电性能的下降，限制了集成铁电学器件发展。由于金属氧化物镧锶钴氧（LSCO）电极和BST薄膜的晶体结构相似，利用LSCO与金属Pt形成多层电极，可以有效改善BST薄膜的结构和性能。研究表明LSCO电极可以诱导BST薄膜沿（001）择优生长，改善薄膜和电极材料间的界面处组分和结构的不均匀性，有效提高薄膜的介电常数和调谐率，其可调率从36．17％上升到78．89％。由于底电极晶格常数的差异，生长在不同电极上的BST薄膜所受的界面应力大小不一样，从而薄膜的微结构、晶粒大小以及介电性能也存在差别。本论文利用不同氧化物电极形成不同界面结构，研究其对BST薄膜微观结构与介电性质的影响，并讨论电极对BST薄膜非线性介电性质的调控机制。研究结果发现：BST薄膜的电学性能和电极密切相关。由于晶格常数的差异，在LaSrCoO₃（LSCO）电极上生长的BST薄膜受的压应力大于在SrRuO₃（SRO）电极生长的压应力，导致BST／LSCO介电可调率（79．58％）大于BST／SRO的介电可调率（68．26％）。这些研究结果为优化BST薄膜非线性介电性质提供了必要的依据。杂质的加入会导致BST薄膜介电性能的改变。为此，本论文深入研究了稀土Y掺杂对BST薄膜介电性质的影响。研究表明：杂质浓度对BST介电有性能较大影响。掺杂浓度为3．0％的Y-BST薄膜其非线性介电性能反而低于1．5％的Y-BST薄膜。深入研究发现低掺杂浓度下（1．5％），Y取代BST的A位，而在较高的掺杂浓度下（3．0％），Y取代BST的B位。Y掺杂可有效地调整BST薄膜的介电性能，以满足微波调谐器件应用的要求。多层薄膜由于具有一些特殊性能一直倍受青睐。论文开展了BST／BZT／BST多层薄膜与单层薄膜（BST，BZT）的对比研究。通过原位高能电子衍射RHEED发现BST／BZT／BST多层薄膜中BST、BZT都是二维层状生长。与单层BST和BZT薄膜相比较，多层薄膜具有更加优良的介电性能，其优值因子达到42．07。论文中采用Maxwell-Magner模型分析了多层薄膜介电常数增强效应机理。多层薄膜的研究为BST铁电材料的非线性应用寻找到了新的途径。更多还原

【Abstract】 As a sort of valuable ferroelectric materials, barium titanate BaTiO₃ （BST） thin films have recently been of immense scientific and technological interests in the world. Because of the excellent non-linear dielectric properties that are the dielectric constant change with applied electric filed, thin films of Ba_1-xSr_xTiO₃ （BST） are being developed for tunable microwave device applications. However, the work to improve the dielectric tunability and decrease the dielelctric loss is very important.The BST thin films were prepared by pulsed laser deposition （PLD） method, the effect of growth parameters （the substrate temperature , the oxygen pressure and laser energy） on the microstructure of BST thin films were systematically studied in the dissertation and high quality dielectric BST thin films were obtained under optimum conditions.To integrate with semiconductivty, the BST thin films usually are gown on Pt-Si substrate to form MIM constructure. For electrical measurements, electrodes were also deposited on annealed BST films. Therefore, interface between films and substrates or electrodes will play an important role for characteristics of BST films. For released the influence of interfaces, La_0.5Sr_0.5CoO₃ （LSCO） electrode was investigated. Highly （001） oriented BST/LSCO films have smaller grain size and larger dielectric constant and dielectric tunability （78.89%） compared to un-oriented BST/Pt films （36.17%） .The relationship between the microstructure and the dielectric properties of BST thin films, which were grown on different lattice constant oxide bottom electrodes, was studied and the effect of bottom electrode on non-linear dielectric properties of BST thin films was discussed in the dissertation. The results indicated the tunability of Ba_0.6Sr_0.4TiO₃/ LaSrCoO₃ （BST/LSCO） （79.58%） is larger than that（68.26%） of BST as the compressive stress of BST on LSCO is larger that of BST on SRO. The experimental results are benefit for the optimization of the non-linear dielectric properties of BST thin films.It is important to improve the dielectric properties of the BST thin films to add the impurity into the BST. As is well known, the properties will vary with the added element. The effect of Y doped BST thin film on dielectric character has been studied in this dissertation. With the increase of Y content, the electric properties vary significantly. When the suitable Y content is 1.5%,the dielelctric nonlinear charactertic is best, but when the Y content increase（3.0%）, the the dielelctric nonlinear charactertic become worse. The reason is that the Y elements can subitite the different sit of the BST thin films. The BST film, which was doped with Y, shows better dielectric properties, so it was more favorable for micro tunable microwave applications.As is well-known, a multilayer approach, in which the film is composed of alternating layers of different compositions or even different materials, appears to be very promising in optimizing the properties of materials. A comparative study between heterolayered ferroelectric thin films （BST/BZT/BST） and homospheric （BST and BZT） thin films was carried out. The surface information has been in-situ monitored by reflection high-energy electron diffraction （RHEED）.It was found that the BST and BZT thin films grow by layer-by-layer mode.Compared with homospheric （BST and BZT） thin films, BST/BZT/BST poess the better dielectric charatertic.Our results indicated that the multilayer structure was beneficial to enhancing the figure of merit （42.07）.更多还原