【作者】 王焕平；

【导师】 杨辉；

【作者基本信息】 浙江大学 ， 材料学， 2007， 博士

【摘要】 随着信息技术的高速发展，电子元器件正向高频化、微型化、集成化、模块化、多功能化以及低成本化等方向发展，特别是高频化与微型化已经成为目前先进电子元器件的基本特征。为满足片式多层元器件向高频化、微型化发展的需要，研制出能与Ag、Cu等贱金属电极共烧，并满足微型片式多层元器件制备工艺要求的纳米级微波介质陶瓷粉体具有重要意义。目前，纳米级微波介质陶瓷粉体已经得到广泛研究，但其研究主要集中在提高材料组分纯度以及优化介电性能等方面，而在纳米微波介质陶瓷粉体的降温烧结与器件制备等方面的研究较为缺乏，特别是对低温共烧纳米微波介质陶瓷粉体的研制报道极少，究其原因主要是存在以下难点：（1）微波介质陶瓷组分复杂，低温共烧陶瓷还包含各种微量助剂，致使纳米粉体的物相及组分均匀性难以控制；（2）纳米粉体在烧结后难以获得优良的介电性能；（3）不能满足片式器件的制备工艺要求，如不能配制成稳定的陶瓷料浆，或材料与金属电极反应等；（4）烧结后不易获得细小晶粒，难以满足微型超薄介质器件的制备要求。本文利用溶胶-凝胶法，通过在溶胶中引入低温烧结助剂先驱体，克服低温共烧纳米微波介质陶瓷粉体的制备难点，获得组分均匀、物相可控、烧结温度低于900℃的（Ca，Mg）SiO₃-CaTiO₃系纳米微波介质陶瓷粉体；优化凝胶煅烧工艺条件，控制粉体物相与粒径来提高陶瓷的介电性能；通过凝胶包裹、稀土元素掺杂、物相调整，以及烧结工艺优化等手段来细化烧结后的陶瓷晶粒。在此基础上，对低温共烧纳米微波陶瓷粉体的应用技术展开研究，研制出厚度小于10μm、能与银电极共烧的超薄流延陶瓷膜片，为微型片式多层微波元器件的产业化奠定基础。本文主要研究成果如下：（一）首次研究了（Ca，Mg）SiO₃与CaTiO₃系的溶胶-凝胶工艺条件，揭示了溶胶系统的凝胶化机理，建立了干凝胶在煅烧过程中的晶相形成与晶粒长大模型。通过系统研究溶胶-凝胶工艺中各因素对煅烧后粉体形貌的影响，获得具有良好分散性纳米粉体的临界工艺条件，系统研究了纳米粉体的烧结特性及介电性能。（1）（Ca，Mg）SiO₃溶胶系统和CaTiO₃溶胶系统的凝胶化过程分别通过正硅酸乙酯与钛酸丁酯的水解聚合完成，钙、镁等离子未参与凝胶网络的形成，而是被均匀“冻结”在凝胶网络中。（2）（Ca，Mg）SiO₃成胶的最佳条件：先驱体浓度0.8mol／l，pH值4.5，[H₂O]／[Si]比4／1，反应温度60℃，2wt％油酸作为分散剂。CaTiO₃成胶的最佳条件：先驱体浓度0.8mol／1，pH值2，反应温度60℃，2wt％的PEG400作为分散剂。（3）（Ca，Mg）SiO₃凝胶在煅烧过程中的晶相形成与晶粒长大机制为：煅烧温度低于800℃时，主要发生硅氧硅键的断裂，晶相形成量少，粉体粒径随着温度的升高而减小；煅烧温度超过900℃后，晶相大量形成，粉体粒径随着温度的升高而逐渐增大。（4）Mg²⁺在CaSiO₃中的固溶极限不超过0.2，随着Mg²⁺取代量的增加，陶瓷主晶相由CaSiO₃相向CaMgSi₂O₆相转变；Mg²⁺取代量为0.3时，烧结后形成CaSiO₃与CaMgSi₂O₆的混合相，混合相的存在克服了单相陶瓷易成片长大的缺点，明显改善了陶瓷的烧结特性与介电性能，在1320℃烧结后获得介电性能：ε_r=6.62，Q×f=36962GHz。（5）800℃煅烧凝胶可获得窄分布、粒径60～70nm的单相CaTiO₃粉体，在1250℃即可实现致密烧结，烧结温度比微米级粉体降低约100℃，且Q×f值有大幅度提高。1250℃烧结后陶瓷的介电性能为：ε_r=171，Q×f=4239GHz，τ_f=+768ppm／℃。（二）（Ca，Mg）SiO₃溶胶中引入锂钒烧结助剂先驱体，实现助剂先驱体与基体材料先驱体的分子级混合，制得具有良好烧结特性与介电性能的低温烧结纳米微波介质陶瓷粉体，探索出一条制备低温共烧纳米介质陶瓷粉体的技术路线。（1）(Ca_0.7Mg_0.3)SiO₃溶胶中引入锂钒低温烧结助剂先驱体，凝胶在700℃煅烧后即可获得粒径60～80nm，相组成为CaSiO₃、CaMgSi₂O₆、Ca₂MgSi₂O₇的陶瓷粉体，晶相合成温度降低了300℃以上，解决了钙镁硅晶相需要经高温煅烧才能合成的难题。将上述合成的粉体简记为低温烧结(Ca_0.7Mg_0.3)SiO₃粉体。（2）通过对不同温度煅烧后低温烧结(Ca_0.7Mg_0.3)SiO₃陶瓷粉体烧结行为的研究发现，采用常规烧结法时，粒径过小或过大的粉体均不利于陶瓷的致密烧结，适宜的粒径为80～100nm，在890℃能实现致密烧结，其介电性能为：ε_r=6.96，Q×f=23645GHz，τ_f=-75.10ppm／℃。（3）溶胶中引入锂钒助剂先驱体的(Ca_0.7Mg_0.3)SiO₃粉体在烧结过程中，助剂与基体材料发生反应生成了微量的Ca₃LiMgV₃O₁₂与Li₂SiO₃新相，致使烧结助剂对基体材料发挥了最佳的润湿效果，起到了良好的降温烧结作用。（4）CaTiO₃陶瓷能有效调节低温烧结(Ca_0.7Mg_0.3)SiO₃纳米微波介质陶瓷的频率温度系数，添加12wt％的纳米CaTiO₃粉体，890℃烧结后获得优良的介电性能：ε_r=9.42，Q×f=15767GHz，τ_f=+2.3ppm／℃。（三）揭示了溶胶包裹、稀土元素掺杂、物相调整，以及烧结工艺优化等对低温烧结（Ca，Mg）SiO₃-CaTiO₃纳米粉体在烧结后晶粒大小的影响规律，解决了（Ca，Mg）SiO₃-CaTiO₃陶瓷晶粒难以细化的难题，为低温共烧微波介质陶瓷的晶粒细化提供了新的思路和途径。（1）利用CaTiO₃凝胶对低温烧结(Ca_0.7Mg_0.3)SiO₃粉体进行包裹，阻隔粗大晶粒CaSiO₃相粉体颗粒间的接触，虽然能有效提高陶瓷的体积密度及介电性能，但对细化陶瓷晶粒效果不甚理想。（2）稀土元素的掺杂，恶化了陶瓷的介电性能，对细化（Ca，Mg）SiO₃-CaTiO₃陶瓷晶粒的作用有限。（3）通过调整物相组分，避免烧结后陶瓷中粗大晶粒CaSiO₃相的生成，达到有效细化陶瓷晶粒的目的。当调节基体材料组分为(Ca_0.5Mg_0.5)SiO₃-12wt％CaTiO₃时，在890℃烧结后获得良好的介电性能：ε_r=9.74，Q×f=16433GHz，τ_f=-2.78ppm／℃；陶瓷主晶相为CaMgSi₂O₆与CaTiO₃相，平均粒径为0.6μm。（4）低温烧结纳米(Ca_0.5Mg_0.5)SiO₃-CaTiO₃粉体在890℃烧结0.5h，再在850℃长时间保温，能在有效阻止陶瓷晶粒长大的基础上提高其介电性能。（四）通过对纳米粉体分散行为、陶瓷流延料浆配制、陶瓷膜片与银电极共烧等的研究，研制出厚度小于10μm的流延陶瓷膜片，适用于微型片式多层微波元器件的产业化生产，对促进片式多层微波元器件的微型化具有重要意义。（1）非离子型分散剂与有机酸阴离子型分散剂对低温共烧（Ca，Mg）SiO₃-CaTiO₃纳米粉体的分散作用有限，AB001离子型分散剂由于对纳米粉体有着良好的空间位阻与静电排斥作用，当添加量为0.5wt％时即能有效分散低温共烧（Ca，Mg）SiO₃-CaTiO₃纳米粉体。（2）利用正交实验，优化低温共烧（Ca，Mg）SiO₃-CaTiO₃陶瓷流延料浆配方。当分散剂、溶剂、粘合剂、增塑剂等含量分别按陶瓷粉体的1.5wt％、70wt％、65wt％、4wt％添加时，陶瓷料浆具有良好的成膜性能，经过流延后获得厚度为9.8μm的超薄陶瓷膜片。（3）低温共烧（Ca，Mg）SiO₃-CaTiO₃陶瓷膜片与内电极银浆在890℃共烧研究表明：陶瓷与银电极结合紧密，界面无分层现象，陶瓷膜片与内电极银浆具有良好的工艺匹配性，适用于微型片式多层微波元器件的制备。更多还原

【Abstract】 With the rapid progress in information technology, it has been strongly required that the related electronic components become small-sized, light-weighted, integrated, multifunctional, low-cost, and usable at high frequency range. Especially, small-size and using at high frequency have become the basic character of advanced electronic components. In order to meet the requirement of small-size and high frequency, it is important to prepare nanopowder that should have the following characters: could be co-fired with low cost and high conductivity inner electrode such as Ag and Cu, have good microwave dielectric properties in high frequency after sintered, and should be sufficiently to meet the requirement for preparation technology of multilayer components.Nanopowder with good microwave dielectric properties after sintered has been investigated for a long time, and the study mainly focuses on improving the pure of materials and dielectric properties of ceramic. However, little investigation was carried on the preparation of nanopowder which could be sintered at low temperature, and so did the preparation of subminiature component with these nanopowders. So far, the preparation of nanopowder which could be co-fired with Ag or Cu used at microwave frequency range has not been investigated yet. There are many problems as follows: （1） It’s difficult to control the component and phase of nanopowder because the composition is complex, especially when a small amount of sintering aids were added in. （2） Dielectric properties critically deteriorated though the sintering temperature of nanopowder was below the melting point of Ag electrode. （3） Many materials have bad adaptability to the fabrication process of components. For example, it’s difficult to get dense green tape by tape casting process use nanopowder, and there may be reaction between ceramic and electrode. （4） It’s difficult to control the grain size of ceramic. If the grain grows larger, there will be only two or three grains between the two electrode layers, which deteriorate the dielectric properties.In order to overcome the above problems and prepare dielectric nanopowder used at microwave frequency which could be co-fired with Ag, the low temperature co-fired （Ca, Mg）SiO₃-CaTiO₃ nanopowder was investigated in this work by sol-gel method. Dissolving the precursor of sintering aids into host materials sol, the nanopowder was prepared with uniform component, controllable phase and particle size, and the sintering temperature was below 900℃. The dielectric properties of ceramic were optimized through controlling the phase and particle size of nanopowder. The grain size of ceramic was minimized through enwrapping with gel, doping with rare earth elements, adjusting the phase composition and sintering process. Based on above researches, the applied technology of nanopowder was studied and green tape with a thickness of thinner than 10μm was prepared, which can be co-fired with Ag electrode and was adaptive to fabricate subminiature multilayer ceramic components.1. The sol-gel process of （Ca, Mg）SiO₃ and CaTiO₃ was studied, respectively. The mechanism of gelatin was discussed. Based on phase composition, micro-morphology and calcination temperature, the model of （Ca, Mg）SiO₃ phase formation and grain growth was founded. The nanopowder with excellent dispersion was prepared, and then the sintering process and dielectric properties of nanopowder were investigated. （1） In the sol of （Ca, Mg）SiO₃ and CaTiO₃, the network of gel was formed through the hydrolysis and aggregation of Si（OC₂H₅）₄ and Ti（OC₄H₉）₄, respectively, and the ions of Ca²⁺ and Mg²⁺ were embedded in the gel network. （2） Controlling the factors of （Ca, Mg）SiO₃ （CaTiO₃） sol under the condition of c（precursors） = 0.8mol/l, T（bath temperature） = 60℃, pH = 4.5 （2）, [H₂O]/[Si] = 4/1 （none）, and added with 2wt% oil acid （PEG400） as dispersant, the gel process was appropriate and the nanoparticles with excellent dispersion were obtained by calcining gel. （3） The model of （Ca, Mg）SiO₃ phase formation and grain growth was founded. When the calcination temperature of the gel was below 800℃, a small amount of crystal phases were formed, and the grain size reduced gradually with increasing the calcination temperature due to the break of Si-O-Si bond in the network. When the calcination temperature was over 900℃, a large amount of crystal phases were emerged and the grains grew with increasing the calcination temperature. （4） The soluble limitation of Mg²⁺ in CaSiO₃ was below 0.2 and CaSiO₃ phase was transformed into CaMgSi₂O₆ phase with the substitution of Ca²⁺ by Mg²⁺. When x is 0.3, the growth of grains was restrained and pores decreased due to the coexistence of CaSiO₃ and CaMgSi₂O₆, and then the density of ceramic was enhanced. The dielectric constant and quality factor of (Ca_0.7Mg_0.3)SiO₃ ceramic sintered at 1320℃ is 6.62 and 36962 GHz, respectively. （5） CaTiO₃ nanoparticles with an average grain size of 60-70nm were obtained by calcining the CaTiO₃ gel at 800℃. CaTiO₃ ceramic sintered at 1250℃ prepared from nanopowders had good dielectric properties: ε_r= 171, Q×f = 4239 GHz, τ_f= +768 ppm/℃.2. Through mingling LiNO₃-NH₄VO₃ liquid phase sintering aids and precursors of （Ca, Mg）SiO₃ in sol, the （Ca, Mg）SiO₃-LiV nanopowder with lower sintering temperature and good dielectric properties was prepared, which initiated a novel route to prepare nanopowder could be sintered at low temperature. （1） The crystallization temperature decreased enormously （>300℃） by mingling precursors of Li-V liquid phase sintering aids and precursors of （Ca, Mg）SiO₃ in sol. Calcining the （Ca, Mg）SiO₃-LiV gel at 700℃, the nanopowder with grain size of 60⁸0nm and phases of CaSiO₃ CaMgSi₂O₆ Ca₂MgSi₂O₇ was obtained. （2） The sintering properties of （Ca, Mg）SiO₃-LiV powder deteriorated if the grain size was smaller or larger than one dimension. Using the powder with grain size of 80-100nm as raw material, the ceramic sintered at 890℃ possessed excellent dielectric properties: ε_r = 6.96, Q×f= 23645GHz, τ_f=-75.10ppm/¤. （3） Ca₃LiMgV₃O₁₂ and Li₂SiO₃ were obtained due to the reaction between sintering additions and host materials, which increased the substance activity and resulted in the acceleration of the sintering process. （4） The τ_f value was adjusted by the addition of CaTiO₃ nanopowder into （Ca, Mg）SiO₃-LiV nanopowder. Doping 12wt% CaTiO₃ nanopowder into （Ca,Mg）SiO₃-LiV nanopowder, the ceramic sintered at 890℃ had good dielectric properties: ε_r = 9.42, Q×f= 15767GHz, T_f=+2.3ppm/℃.3. The factors influenced the grain size were investigated, which including the means of （Ca, Mg）SiO₃-LiV nanopowders enwrapped with CaTiO₃ gel, the addition of rare earth elements, and the adjustment of component and sintering process. The average grain size of low temperature co-fired （Ca, Mg）SiO₃-CaTiO₃ ceramic was refined to 0.6μm, which offered new approaches to refine the grain size of ceramic. （1） It’s hard to play a role in refining the grain size of （Ca, Mg）SiO₃ through enwrapping with CaTiO₃ gel, though the dielectric properties were improved. （2） The dielectric properties deteriorated enormously with doping rare earth elements, which had a little effects on refining the grain size of （Ca, Mg）SiO₃-CaTiO₃ ceramic. （3） The grain size of low temperature co-fired （Ca, Mg）SiO₃-CaTiO₃ ceramic was refined by adjusting component. Adjusting the component of (Ca_0.7Mg_0.3SiO₃ to (Ca_0.5Mg_0.5)SiO₃, the average grain size of (Ca_0.5Mg_0.5)SiO₃-LiV-12wt%CaTiO₃ ceramic sintered at 890℃ was refined to 0.6μm with the main phases of CaMgSi₂O₆ and CaTiO₃, which had good dielectric properties: ε_r = 9.74, Q×f= 16433GHz, τ_f = -2.78ppm/℃. （4） It was effective to refine the grain size and improve the dielectric properties of （Ca, Mg）SiO₃-CaTiO₃ ceramic with appropriate sintering process （first sintered for 0.5h at 890℃, and then sintered at 850℃ for a long time）.4. Based on the study about dispersion of nanopowders, preparation of slurry, co-firing of ceramic and Ag electrode, the green tape with the thickness of 9.8μm was gained by the tape casting process, which was appropriate to prepare subminiature multilayer component. （1） It was limited to disperse low temperature co-fired （Ca, Mg）SiO₃-CaTiO₃ nanopowders by adding non-ionic surfactant or anionic organic acid. Owing to steric hindrance and electrostatic rejection, the agglomeration of nanopowders could be reduced effectively and a homogeneous mixture suspension could be obtained with the ionic surfactant AB001 added in. （2） Green tape with glabrous surface was gained by the tape casting process with the content ratio of M_nanopowder : M_dispersant:M_solvent:M_bond:M_plasticizer = 100:1.5: 70: 65: 4. （3） When co-firing the green tape and Ag slurry, there was a good conjoint status and chemical compatibility between ceramic and Ag electrode, which indicated that the nanopowder is appropriate to prepare subminiature multilayer component.更多还原