【作者】 邹佳丽；

【导师】 杨辉；

【作者基本信息】 浙江大学 ， 材料学， 2007， 博士

【摘要】 随着通信事业的迅速发展，各类移动通讯设备对小型化、高性能化的微波器件的需求量日益增加，微波介质陶瓷的研究与实用化也取得了长足的进步。为了满足移动通讯终端设备的小型化要求，利用低温共烧陶瓷（简称LTCC）技术和多层结构复合技术开发片式多层微波器件成为目前的研究热点。在中高介电常数微波陶瓷领域，掺杂改性和低温共烧方面的研究取得快速进展，并进入实用化阶段。同时，随着移动通信、无线局域网、军事通信等通讯设备日益向高频方向发展，具有低介电常数和高频特性的微波陶瓷具有了越来越广阔的市场应用前景。近年来，国内外科研工作者对低介电常数微波介质陶瓷都有浓厚的兴趣，新种类的低介陶瓷不断被开发出来，但它们也存在着各种各样的问题和缺点，如：（1）烧结温度过高，难以实现低温烧结；（2）频率温度系数较大或品质因数较低，不能满足微波电子元器件的要求；（3）与Ag或Cu电极共烧情况报道较少。因此，开发能满足LTCC技术要求的新型低介高频微波陶瓷具有重要的意义。作者通过对ZnO-SiO₂陶瓷系统的研究发现：该陶瓷体系具有较小的介电常数（ε_r-6）和优异的介电性能，且原料价格低廉，来源丰富。但也存在烧结温度高，烧结温区窄、频率温度系数较大的缺点。本文侧重通过复合取代，有效改善了陶瓷的高温烧结特性，将频率温度系数调节至零，并通过添加复合助剂实现了陶瓷体系在900℃下低温烧结。低烧陶瓷材料能够配制成稳定的料浆，并与Ag电极具有良好的共烧兼容性，是一种非常有潜力的可应用在高频领域的低介电微波陶瓷材料。在上述基础上，采用溶胶-凝胶法制备出分散性好、具有优良微波介电性能的纳米级ZnO-SiO₂陶瓷粉体，为小型片式多层微波器件的制备奠定基础。本文的主要研究成果如下：（一）首次系统研究了新型ZnO-SiO₂体系的烧结特性和微波性能，通过MgO、TiO₂复合添加，协同改善陶瓷系统的烧结特性和微波性能，获得了一种具有宽烧结温区、介电常数8左右、品质因数较高和温度系数接近于零的低介高频微波陶瓷，为高频微波电子元器件的制备提供了一种新的材料选择。（1）ZnO-ySiO₂陶瓷系统在高温下难以获得致密的结构，烧结温区较窄，当烧结温度高于1440℃会发生熔化现象；SiO₂过量可细化晶粒，阻止晶粒异常长大；y=0.6时可获得最佳性能为：ε_r=6.23，Q×f=52500GHz，τ_f=-55.2ppm／℃。（2）Al₂O₃添加能够促进主晶相的形成，展宽烧结温区，降低烧结温度至1300℃；1wt％Al₂O₃添加的ZnO-0.5SiO₂陶瓷可获得较佳性能：ε_r=6.43，Q×f=43500GHz，τ_f=-48.4ppm／℃。（3）Mg²⁺能够在一定范围内（＜50mol％）取代Zn²⁺与陶瓷系统形成固溶体，促进陶瓷的烧结，烧结温区＞75℃；Zn_0.8Mg_0.2O-0.5SiO₂在1275℃烧结获得的最佳性能为：ε_r=6.19，Q×f=49000GHz，τ_f=-54.1ppm／℃。（4）TiO₂不与ZnO-SiO₂陶瓷发生反应，以单质金红石相存在，可有效调节陶瓷的频率温度系数，但缺点是烧结温区窄；（5）复合添加MgO、TiO₂后，ZnO-0.5SiO₂陶瓷具有了更宽的烧结温区，能够在1250-1325℃内良好烧结，10wt％TiO₂添加获得的最佳性能为：ε_r=8.16，Q×f=43200GHz，τ_f=-13.7ppm／℃。（二）通过复合添加低熔点烧结助剂，分别实现了ZnO-SiO₂陶瓷、复合添加MgO和TiO₂的ZnO-SiO₂陶瓷（以下简称ZMST陶瓷）在900℃左右的低温烧结，低烧陶瓷能够配制成稳定料浆，流延膜片能与Ag电极的良好共烧，获得了一种具有良好微波介电性能，并适应LTCC技术要求的低介高频微波陶瓷，为新型LTCC毫米波电子元器件的研制奠定了材料基础。（1）Li₂CO₃-Bi₂O₃助剂分别在598℃和720℃形成液相，并在烧结过程中与陶瓷反应形成低熔点Bi₄Si₃O₁₂相，在多重液相作用下，将ZnO-ySiO₂陶瓷的烧结温度从1400℃降至910℃。Bi₂O₃-SiO₂助剂预合成的Bi₄Si₃O₁₂相则在833℃左右形成液相，在单一液相作用下将ZnO-0.6SiO₂陶瓷的烧结温度降至960℃-990℃，降温效果不如Li₂CO₃-Bi₂O₃助剂显著。（2）低烧ZnO-ySiO₂陶瓷的体积密度和介电常数随着SiO₂含量的增加而下降，陶瓷的Q×f值与相组成和微观形貌密切相关。5wt％Li₂CO₃-4wt％Bi₂O₃添加的ZnO-0.6SiO₂陶瓷获得最佳性能：ε_r=6.65，Q×f=33000GHz，τ_f=-70ppm／℃；（3）随着Bi₂O₃-SiO₂助剂添加量的增加，ZnO-0.6SiO₂陶瓷的体积密度增大，介电常数有所提高，Q×f值略有下降，3wt％添加可获得性能为：ε_r=6.19，Q×f=41800GHz，τ_f=-52.9ppm／℃。（4）Li₂O-B₂O₃-SiO₂玻璃助剂具有较低的软化点（在402℃左右），Li₂CO₃-B₂O₃复合助剂在600℃热处理后的产物在660℃左右形成液相，两种助剂均能在烧结过程中与ZMST陶瓷中的TiO₂反应形成高活性未知相，从而降低陶瓷烧结温度至840-900℃。（5）低烧ZMST陶瓷介电性能同时受相组成和微观结构影响变化较为复杂，3wt％Li₂CO₃-B₂O₃复合助剂添加获得的最佳性能为：ε_r=8.84，Q×f=15500GHz，τ_f=+17.8ppm／℃。（6）低烧ZMST陶瓷材料能够配制成稳定、分散良好的料浆，流延膜片表面平整光洁，颗粒无团聚现象。低烧ZMST陶瓷材料不与Ag电极发生发应，且与Ag电极具有良好共烧界面，是一种极具潜力的LTCC低介高频陶瓷材料，具有广阔的应用前景。（三）采用溶胶-凝胶法低温合成出100-200nm、分散性好的混合纳米粉体，纳米粉体具有较高烧结活性，可在1250℃烧结，并获得比固相法更加优异的介电性能，为此陶瓷体系在超薄流延介质层中的应用奠定基础。（1）以Zn（NO₃）₂·6H₂O、正硅酸乙酯为前驱体，乙醇作为溶剂，通过控制工艺条件，能够获得透明、均一、稳定的ZnO-SiO₂凝胶。系统的溶胶凝胶过程主要是正硅酸乙酯的水解和聚合，Zn²⁺离子则均匀镶嵌在凝胶网络中。（2）不同工艺条件对ZnO-SiO₂系统的凝胶时间和干凝胶热处理后的粉体有较大影响，当前驱体浓度为0.5-1mol／l、[H₂O]／[Si]比为0-8／1、pH值控制在1.5-3之间、静置温度为10-40℃时，ZnO-SiO₂系统可在合适的时间内获得透明凝胶，干凝胶热处理后，能够获得粒径范围在100-200nm，分散性较好的纳米级粉体。（3）采用溶胶凝胶法制备的ZnO-SiO₂纳米粉体具有更高的烧结活性，与固相法相比，降低陶瓷烧结温度150℃以上，并将陶瓷Q×f值从52500提高至67500GHz。更多还原

【Abstract】 With the rapid development of communication businesses, the demands for miniature and functional microwave components used in mobile communication devices have been greatly increased. At the same time, the research and utilization of microwave dielectric ceramics have also achieved remarkable progresses. In order to meet with the requirement for the miniaturization of mobile communication terminal devices, Low Temperature Co-fired Ceramics （LTCC for short） technology and multilayer microwave components have been the research focus. In the middle & High dielectric constant ceramic field, the research on additives and LTCC materials have been developed rapidly and furthermore, have been put into application. Simultaneously, with the communication devices of mobile communication, wireless LAN and military communication developing to higher frequencies, a large market demand emerged for low dielectric constant high frequency microwave ceramics.Recent years, low dielectric constant microwave ceramics have received much interests. New kinds of low dielectric constant microwave ceramics were developed continuously. However, these materials have some problems and disadvantages, such as （1） difficult to sintered at lower temperature; （2） large τ_f or low Q×f values; （3）the research on cofiring with Ag or Cu was limited. Therefore, it is of much importance to develop new kind of low dielectric constant microwave ceramics used in LTCC technology.The research by author on ZnO-SiO₂ ceramic system shows: ZnO-SiO₂ ceramic have low dielectric constant of 6 and excellent dielectric properties with lower expenses. But this ceramic system have some disadvantages such as high sintering temperature, narrow sintering range and large negative τ_f. In this study, the sintering characteristics and dielectric properties of ZnO-SiO2 ceramics were improved by adding additives. The sintering temperature was decreased to 900°C with composite sintering aids. The low-fired ceramics can prepare stable slurry and have good compatibility with Ag electrode. Thus, it can be a promising low dielectric constant microwave ceramics working at higher frequency. Based on these results, nano ZnO-SiO₂ ceramic powders with excellent dispersity and properties were obtained by sol-gel method. This study established foundation to prepare miniature multilayer components. The main research results are as follows:1. The sintering characteristics and microwave dielectric properties of ZnO-SiO₂ ceramics were investigated systematically at the first time. The sintering characteristics and microwave dielectric properties of ZnO-SiO₂ ceramics were improved effectively by MgO and TiO₂ addition. A low dielectric constant microwave ceramics with wide sintering rangeand excellent dielectric properties especially near zero τ_f- was obtained. This results provide a potential material for microwave electronic components working at higher frequency. （1） Itis difficult for ZnO-ySiO₂ to obtain a dense structure at high temperature. When the sintering temperature was higher than 1440℃, the ceramic began to melt. Excess SiO₂ content can reduce the grain size and inhibit abnormal grain growth. The ceramics with y=0.6 obtained best dielectric properties of ε_r = 6.23, Q×f= 52500GHz, τ_f= -55.2ppm/℃. （2） Al₂O₃ can improve the sintering process by improving the formation of main phase. The sintering temperature was decreased to 1300℃ and the ZnO-0.5SiO₂ ceramic with 1wt% Al₂O₃ addition obtained properties of ε_r=6.43, Q×f =43500GHz , τ_f = -48.4ppm/℃. （3） Mg²⁺ can substitute Zn²⁺（<50mol%） and form a solid solution in Zn₂SiO₄ crystalline and thus improved the sintering process, the sintering range is more than 75℃. Zn_0.8Mg_0.2O-0.5SiO₂ ceramic sintered at 1275℃ obtained dielectric properties of ε_r=6.19, Q×f=49000 GHz , τ_f= -54.1ppm/℃. （4） TiO₂ did not react with host material, thus it can adjust the τ_f of host material. However, the ceramics had narrow sintering range with TiO₂ addition. （5） When MgO and TiO₂ were added, ZnO-0.5SiO₂ ceramics can be sintered from 1250 to 1325℃. With 10wt% TiO₂ addition, Zn_0.8Mg_0.2O-0.5SiO₂ ceramics had an excellent dielectric properties of ε_r= 8.16, Q×f=43200GHz, τ_f= -13.7ppm/℃.2. The sintering temperature of ZnO-SiO₂ and ZnO-SiO₂ ceramics with TiO₂&MgO addition （ZMST for short） were decreased to 900℃ by adding composite sintering aids. The low-fired ceramics can prepare stable slurry and have good compatibility with Ag electrode. The low-fired ceramics with low dielectric constant was suitable for LTCC technology and was promising to prepare LTCC microwave components working at millimeter wave. （1） Li₂CO₃-Bi₂O₃ can form liquid phases at 598℃ and 720℃. During the sintering process, it can react with host material to form low-melting-point phase Bi₄Si₃O₁₂. Multiple liquid phases can effectively reduce the sintering temperature of ZnO-ySiO₂ from 1400 to 910℃. Bi₂O₃-SiO₂ aids was calcined to form Bi₄Si₃O₁₂ phase, which can melt at 833℃. The single liquid phase can reduce the sintering temperature of ZnO-0.6SiO₂ ceramics form 1380 to 960-990℃. （2） The densities and ε_r of ZnO-ySiO₂ decreased as y increased. Q × f values were closely related with phase composition and microstructure. ZnO-0.6SiO₂ ceramics with 5wt°/oLi₂CO₃-4wt%Bi₂O₃ obtained properties of ε_r = 6.65, Q×f= 33000 GHz, τ_f= -70ppm/℃. （3） As Bi₂O₃-SiO₂ addition increased, densities and ε_r increased and Q×f decreased slightly. With 3wt% Bi₂O₃-SiO₂ addition, the ZnO-0.6SiO₂ ceramics have properties of ε_r=6.19, Q×f=41800GHz, τ_f=-52.9ppm/℃. （4） Li₂O-B₂O₃-SiO₂ glass have a low soften point（402℃）. The mixture from Li₂CO₃-B₂O₃ calcined at 600℃ can form a liquid phase at 660℃. Both additives can form a high activity unknown phase with TiO₂. These results can decreased the sintering temperature of ZMST to 840-900℃. （5） Thedielectric properties of low-fired ZMST ceramics show a complex variety influenced by phase composition and microstructure. With 3wt% Li₂CO₃-B₂O₃ addition, ZMST ceramics obtained optimum properties of ε_r = 8.84, Q×f = 15500GHz, τ_f = +17.8ppm/℃. （5）Stable and well dispersive slurry of the low-fired ceramics can be prepared and the green tapes have a glabrous surface. There were no aggregations of the particles. The low-fired ceramics also have good compatibility with Ag electrode. It can be a promising low dielectric constant microwave ceramics for LTCC technology.3. The ZnO-SiO₂ nanopowders with particle size of 100-200nm and well dispersity were prepared by sol-gel method at a relatively low temperature. Compared to solid reaction method, the nanopowders prepared by sol-gel method have higher sintering activity, and can be sintered well at 1250℃ and excellent dielectric properties were obtained. These results were useful to further application in thinner dielectric layers.（1） Using Zn（NO₃）₂·6H₂O and Si（OC₂H₅）₄ as precursors, ethanol as solvent, transparent and homogeneous ZnO-SiO₂ gel was prepared by controlling gelation process. The gel of ZnO-SiO₂ system was formed though the hydrolysis and polymerization of Si（OC₂H₅）₄, and the Zn²⁺ ion were embedded in the gel network. （2） The gelation of ZnO-SiO₂ system and the characteristics of powders calcined from dried gel were influenced by process parameters. The transparent gel and suitable gelation time were obtained under the condition of c（precursors） = 0.5-1mol/l, T（gelation temperature） = 10-40℃, pH = 1.5-3, [H₂O]/[Si]=0-8/1. At the same process condition, the nanopowders with particle size of 100-200nm and well dispersity were obtained when the Si（OC₂H₅）₄ were hydrolyzed and polymerized completely. （3）The ZnO-SiO₂ nanopowders prepared by sol-gel method have higher sintering activity, and compared to solid reaction method, it decreased the sintering temperature more than 150℃ and increased the Q×f values from 52500 to 67500GHz.更多还原