本文以超薄层高可靠贱金属内电极多层片式陶瓷电容器（BME-MLCC）用纳米晶介质材料与器件为研究对象，通过选用小尺寸的BaTiO3原料、优化掺杂剂的组成，制备了高可靠性MLCC用纳米晶BaTiO3基陶瓷材料。通过对MLCC器件排胶工艺与烧结工艺进行优化，研究了电极质量、电极与介质的共烧匹配对器件介电性能及可靠性的影响规律，为下一代超薄层高可靠MLCC器件的设计与制备提供了理论指导。以平均粒径100~200nm，c/a约1.0096的BaTiO3粉体为原料，使用化学包覆的方法引入合适的掺杂元素，制备了晶粒尺寸为120nm~210nm的BaTiO3陶瓷，研究了晶粒尺寸对陶瓷介电性能与可靠性的影响规律。小粒径粉体致密化所需烧结温度低，烧成后陶瓷的介电性能对晶粒尺寸高度敏感，细晶化虽然会使介电常数降低，但在绝缘电阻、温度稳定性、直流偏压特性和绝缘电阻劣化特性上均有显著改善。结合微观形貌与高温阻抗谱分析，阐明了细晶化提升材料可靠性的机理。研究了两性稀土元素Dy掺杂以及Dy-Ho共掺杂对BaTiO3基陶瓷性能的影响，发现掺杂元素含量影响其在BaTiO3基体中的占位及陶瓷的“芯-壳”结构与介电性能，结合高温阻抗谱与热激励去极化电流测试结果，说明了掺杂离子通过形成氧空位迁移活化能高的壳部，改善了陶瓷的可靠性。通过加入SiO2有效降低了纳米晶陶瓷的烧结温度，适量的SiO2有助于元素扩散形成均匀的“芯-壳”结构，从而阻碍氧空位的迁移，改善了陶瓷的可靠性与偏压特性。针对厚介质层（10μm）与薄介质层（1.4μm）MLCC生坯样品分别进行了排胶工艺的优化研究，结合有机物的热解动力学，分析了排胶条件对有机物残余量的影响，并建立其与内电极质量和电学性能的关联。同时探究了烧结升温速率对电极介质共烧匹配的作用，结合TEM与高温阻抗谱说明了抑制电极-介质界面处元素扩散和提高电极连续性是改善器件可靠性的重要手段，为高可靠超薄层MLCC制备工艺优化提供了思路。本文研制的纳米晶BaTiO3基介质粉体材料已用于制备介质层厚度0.9~1.4μm的MLCC，烧成后器件的介质材料表现出优异的电学性能，为国产高端超薄层BME-MLCC的开发提供了关键材料与技术指导。
In this dissertation, base metal electrode ultra-thin layered multilayer ceramic capacitors (BME-MLCC) and BaTiO3-based dielectric materials were studied. Highly reliable nano crystalline ceramics were prepared by using BaTiO3 powders with small particle size and optimizing the composition. Through the adjustment of binder removal process and sintering process, the effects of electrode quality and the co-firing of electrode and dielectric on device performance were investigated. This study provided guidance for the design and preparation of dielectric materials and devices for next-generation ultra-thin layer highly reliable MLCCs. BaTiO3 powders with an average particle size of 100-200 nm, whose c/a ratio were about 1.0096, were used as raw materials. Doping elements were introduced by a chemical coating method and ceramics with an average grain size of 120~210 nm were prepared. Fine-grained ceramics could be sintered at lower temperature and the dielectric properties of the ceramics were highly sensitive to the grain size. Although fine-grained ceramics had a decrease on dielectric constant, other properties such as insulation resistance, temperature stability, DC bias stability and the insulation resistance degradation characteristics were improved. The mechanism of reliability improvement was clarified by microscopic morphology and impedance spectroscopy analysis.The effects of Dy doping and Dy-Ho co-doping on the properties of BaTiO3-based ceramics were investigated. The results of impedance analysis and TSDC confirmed that the “core-shell” structure formed by rare earth elements doping hindered the migration of oxygen vacancies, and thus improve the reliability and DC bias stability. The sintering temperature of nanocrystalline ceramics was effectively reduced by doping with SiO2, and it was found that the appropriate amount of SiO2 helped the element diffusion to form a "core-shell" structure, which is preferable for the synthesis of highly reliable ceramics.The binder removal process and sintering process for MLCCs with 10μm and 1.4μm dielectric layers were studied separately. The residual binder was found to be strongly related to the quality of electrode and thus influenced the dielectric properties. Sintering process with rapid heating rate was efficient in improving electrode continuity and reducing the elements diffusion between Ni electrode and BaTiO3 ceramic, which was clarified by TEM and high temperature impedance analysis. High heating rate resulted in better reliability especially for thin layered MLCCs and the mechanism was useful for designing of sintering process. BaTiO3-based dielectric ceramics fabricated in this work were used to prepare MLCCs with dielectric layer thicknesses of 0.9-1.4μm, and the dielectric materials exhibited promising properties, providing a reference for the development of domestic ultra-thin layered BME-MLCCs.
