【作者】 王新儒；

【导师】 吴顺华；

【作者基本信息】 天津大学 ， 微电子学与固体电子学， 2010， 硕士

【摘要】 随着电子信息终端设备在高温极端环境下的应用,能适应于高温条件下工作的MLCC成为迫切需要。BaTiO₃是一种性能优良的陶瓷介电材料,宽温型BaTiO₃基介质陶瓷电容器是当前陶瓷电容的研究方向之一。钛酸钡是一种重要的铁电相晶体材料,但纯BaTiO₃在130℃附近存在着介电常数异常的居里峰,使得介电性能急剧恶化,制约着其在高温介质陶瓷中的应用。通过适当的掺杂及控制工艺条件可以获得介电性能优良的BaTiO₃基介电材料,本文重点讨论了掺杂介质粉体初始粒度及烧结制度对BaTiO₃基陶瓷介电性能的影响。根据所制备的介质陶瓷样片的T-C曲线及SEM形貌图,深入分析了粉体粒度和烧结制度对BaTiO3基介质陶瓷介电性能的影响,并制备出了符合EIA X9R标准的介质陶瓷。介质粉体的初始粒度对介质陶瓷的介电性能有着重要影响,论文中通过采用不同粒径的球磨介质和球磨不同的时间,制备出了不同粒度的初始粉体。实验表明,初始粉体粒度对系统最终的介电性能有着重要影响。当粉体粒度减小,将具有更大的比表面积,表面原子数急剧增多,这些表面原子由于原子配位不足和高表面能而具有高活性。在同样的烧结温度下,粉体粒度更小和比表面积更大,能更有效地抑制BaTiO₃晶粒生长并产生细晶效应。掺杂元素对BaTiO₃颗粒进行均匀的包裹形成更多的壳-芯晶粒,即铁电相BaTiO3晶核的比例减小,而顺电相晶壳的体积比增大,使得居里峰压平展宽,介电常数变化率趋于平缓,提高掺杂BaTiO₃陶瓷的介电-温度性能。同时,BaTiO₃粒度的减小导致晶粒中壳/芯体积比增大,壳芯之间失配产生的内应力随之增加,BaTiO₃陶瓷由四方相转变为赝立方相,使居里点Tc提高。烧结制度对电子陶瓷的物理和电学特性有着重要的影响,烧结温度对晶粒的生长、空洞的密度、杂质离子的扩散分布、晶相的组成等有着重要的作用,并对介质陶瓷最终的介电性能产生重要影响。通过控制烧结温度和保温时间,文中制备了符合EIA X9R标准的介质陶瓷,主要性能指标:室温介电常数ε25oC>1820,tanδ≈1.6%,在-55℃～200℃最大介电常数变化率不超过±15%。更多还原

【Abstract】 As electronic information terminal equipments are applied into the high temperature environment of extreme heat, MLCCs adapting to the hash working condition, become urgent need now. BaTiO₃ has an excellent performance of dielectric properties, and BaTiO3-based dielectric ceramic capacitors with wide-raged working temperature, is the research direction of the ceramic capacitors. Barium titanate is a kind of important ferroelectric phase crystal materials, however purifed-BaTiO₃ has abnormal dielectric constants at Curie peak around 130℃, which makes dielectric properties worse sharply and restricts the application in the high temperature.Through proper-doping and control of preparing technology, BaTiO3-based dielectric material can be obtained with a fine dielectric properties. The effect of initial size of medium and sintering-temperature to BaTiO3-based dielectric ceramics is discussed especially in the paper. According to the T-C curve and SEM morphology of dielectric ceramic sample, the role of powder size and sintering steps to BaTiO3-based dielectric ceramic is analysed deeply, and a kind of dielectric ceramic meeting the specification of EIA X9R is prepared.The dielectric property of ceramic is greatly influenced by the initial size of medium size, and different particle sizes of powder is prepared by different milling-balls and variant milling time in the paper. In the experiments, it is showed that the dielectric properties of the system is greatly influenced by the initial powder size . With the decrease of powder size, the surface energy of particle is enhanced and the amount of surface atoms will also be increased, which will be active due to inadequate atom and high surface energy.Under the condition of invariable sintering temperature,the growth of BaTiO₃ grain can be more effectively restricted with smaller specific surface area and smaller powder size ,and fine-grain effect can be produced.More shell-core grain can be formed with the doping elements distributing into BaTiO₃ particles greatly, and the volume of ferroelectric phase core is increased while the volume of shell decreased. The dielectric property of doping BaTiO₃ is enhanced with the Curie peak flat and a slowing rate of dielectric constant. At the same time, the ratio of core to shell is increased with the decrease of BaTiO₃ grain size, and the crystal phase of BaTiO3 is changed from tetragonal phase to the artifact cubic. Because the increase of inner-stress mismatch between the shell and core, the Curie Point is shifted to higher temperature.The physical and electrical properties of ceramics are greatly influenced by sintering process, and the growth of grain、density of holes、the distribution of doping elements and the crystal phase are affected by the sintering temperature, which also determine the final dielectric properties. The dielectric ceramic meeting EIA X9R specification, were made through the controlling of sintering temperature and keeping time. The main performance indexes are as follows:ε25oC>1820、tanδ≈1.6%、△ε\ε≤±15% （-55℃～200℃）.更多还原