【作者】 童建喜；

【导师】 杨辉；

【作者基本信息】 浙江大学 ， 材料学， 2006， 博士

【摘要】 现代移动通信、无线局域网、军事雷达等设备正趋向于小型、轻量、高频、多功能及低成本化方向发展，对以微波介质陶瓷为基础的微波元器件提出了更高的要求。为满足此要求，利用低温共烧陶瓷（Low Temperature Co-fired Ceramics，简称LTCC）技术设计制造片式多层微波器件已成为当今的研究热点。低温共烧技术的核心是研制能与高电导率Ag或Cu电极共烧的LTCC微波介质陶瓷。Ca[(Li_1／3Nb_2／3)，Ti]O_3-δ（CLNT）、MgTiO₃陶瓷具有介电常数适中、介电损耗低、频率温度系数可调等特点，如能降低烧结温度，并和LTCC技术制造工艺匹配，将是理想的LTCC介质材料。目前，已有部分低温烧结的研究报道，但存在以下问题：（1）液相烧结机制研究少，降温困难；（2）烧结温度可降至Ag电极熔点以下，但低烧陶瓷介电性能大幅度降低，如添加2wt％B₂O₃-6wt％Bi₂O₃复合助剂的CLNT陶瓷在920℃烧结致密，Q×f急剧恶化，仅为10600GHz；（3）材料研发与器件设计和制备工艺相脱节，材料的工艺匹配性较差。如由于B₂O₃易与粘合剂发生胶凝反应，添加B₂O₃助剂的陶瓷粉料经流延工艺不能获得高密度的生瓷带。本文从材料制备与器件设计、制造工艺相结合的角度出发，以CLNT和MgTiO₃陶瓷为研究对象，通过不同烧结助剂对陶瓷体系降温效果研究，揭示出低温烧结内在机制；系统研究了各种烧结助剂对微波介质陶瓷烧结特性、相组成、微观结构和介电性能的影响，阐明低温烧结陶瓷相组成、微观结构与介电性能之间的内在规律；研究了LTCC微波介质陶瓷CLNT和MgTiO₃工程化应用问题（料浆特性及其与Ag电极的共烧行为）；通过降温效果、介电性能、料浆特性以及与银电极共烧等方面协调优化，获得最佳烧结助剂及工艺条件。在此基础上，构建多层片式微波器件模型，通过器件仿真，利用LTCC技术制造工艺制备出满足性能要求的片式多层带通滤波器。（一）通过添加剂对CLNT和MgTiO₃陶瓷降温效果研究，结合陶瓷烧结特性、相组成和微观结构，揭示出低温烧结微波介质陶瓷液相烧结机制，为烧结助剂的选择提供依据。（1）烧结助剂与基体材料反应形成低温液相，可有效促进陶瓷的低温致密烧结。添加Bi₂O₃的CLNT陶瓷，在烧结过程中，Bi₂O₃与基体材料反应形成Li₂O-Bi₂O₃、Bi₂O₃-ZiO₂等低熔点液相；LiF可与CLNT反应生成CaF₂等第二相物质，LiF同CaF₂在766℃共熔成液相；Bi₂O₃和V₂O₅与MgTiO₃基体材料在低温下反应生成Bi₄V_1.5Ti_0.5O_10.85、BiVO₄等新相，在815～850℃，新相熔化成液相。（2）硼硅酸盐玻璃具有较低的软化温度，低温下可转变成低粘度的玻璃液相，有效降低陶瓷的烧结温度。ZnO-B₂O₃-SiO₂（ZBS）和Li₂O-B₂O₃-SiO₂（LBS）玻璃的软化温度分别为638℃和402℃，可分别降低CLNT和MgTiO₃陶瓷的烧结温度至930℃和890℃。（3）与单一助剂相比，复合烧结助剂有着更好的降温效果。Bi₂O₃、ZBS助剂可分别将CLNT陶瓷的烧结温度降至1020℃和930℃。复合添加Bi₂O₃和ZBS玻璃，形成低软化点的ZnO-Bi₂O₃-B₂O₃-SiO₂玻璃液相，促使CLNT陶瓷在900℃烧结致密。采用复合添加LiF和ZBS玻璃助剂，氟离子部分取代ZBS玻璃骨架中的桥氧，使玻璃负离子团解聚，导致玻璃熔体粘度降低，加速液相烧结进行。（二）揭示出低温烧结陶瓷相组成、微观结构与介电性能之间的内在规律。研究表明：（1）第二相物质（包括引入的烧结助剂以及反应生成的杂质相）对陶瓷介电性能产生重要影响。低介高损耗的ZBS和LBS玻璃可分别使CLNT和MgTiO₃陶瓷ε_r和Q×f值降低，τ_f向负值方向移动；复合添加Bi₂O₃和V₂O₅的MgTiO₃样品，当V₂O₅添加量为1～2mol％时，Bi₂O₃和V₂O₅与基体材料反应生成大量高介电损耗的Bi₂Ti₂O₇和Bi₄V_1.5Ti_0.5O_10.85相，造成陶瓷低的Q×f值。当V₂O₅添加量增加，此两相逐渐减少并消失，Q×f值急剧增加。（2）陶瓷体微观结构（如气孔、晶粒）也是影响介电性能的一个重要因素。Bi₂O₃等物质的挥发造成CLNT陶瓷气孔含量增加，体积密度ρ和ε_r减小，Q×f值下降；LiF等的挥发造成CLNT陶瓷的多孔结构，ρ和ε_r随LiF含量增加急剧下降；BiVO₄导致MgTiO₃晶粒的异常长大，造成结构不均匀性增加，Q×f急剧下降。（3）晶格缺陷对材料的介电性能产生较大影响。复合添加Bi₂O₃和ZBS玻璃的低烧CLNT陶瓷中，由于Bi³⁺在钙钛矿的A位对Ca²⁺的不等价置换，形成Ca²⁺空位，使晶格松弛，造成ε_r增大，Q×f显著下降，τ_f向负值方向移动；LiF和ZBS玻璃协同作用，引起Ca[(Li_1／3Nb_2／3)，Ti]O_3-δ相向化学计量Ca[(Li_1／4Nb_3／4)，Ti]O₃相转化，降低了陶瓷体中的氧空位，对提高Q×f值有利。（三）系统研究了LTCC微波介质陶瓷料浆特性、Ag电极共烧行为等工程化应用技术，为LTCC微波介质陶瓷产业化奠定基础。（1）V₂O₅易与PVB、PVA等粘合剂发生胶凝反应，导致添加Bi₂O₃-V₂O₅助剂的MgTiO₃陶瓷料浆粘度很大，不适宜流延，将Bi₂O₃-V₂O₅预反应形成BiVO₄可以克服MgTiO₃陶瓷因游离V₂O₅存在而难以流延的问题。（2）添加LiF的CLNT陶瓷与Ag电极共烧界面清晰，但由于两者收缩不匹配，造成分层现象，而且Ag电极有着不规整多孔结构，限制了该陶瓷材料的应用，而采用LiF-ZBS玻璃复合助剂，解决了单独添加LiF引起Ag电极多孔结构的问题。（3）添加Bi₂O₃-ZBS或LiF-ZBS的CLNT陶瓷和添加LBS玻璃的MgTiO₃-CaTiO₃陶瓷，避免了B₂O₃等助剂对陶瓷料浆特性的不利影响，流延得到的膜片表面光洁，陶瓷与Ag电极共烧界面结合状况良好，化学相容性好，无明显扩散反应现象。（四）通过降温效果、介电性能、料浆特性以及与银电极共烧等方面协调优化，获得两种介电性能优良的能产业化应用的配方及工艺。（1）选用LiF和ZBS玻璃协同降低CLNT陶瓷的烧结温度，制备出在900℃烧结致密的LTCC微波介质陶瓷，其介电性能为：ε_r=34.28，Q×f=17400GHz，τ_f=-4.6×10^-6／℃。与文献报道相比，低温共烧CLNT陶瓷Q×f值有大幅度的提高。（2）采用低软化点的自制LBS玻璃为烧结助剂，通过引入CaTiO₃组分协调MgTiO₃陶瓷的τ_f值，在890℃烧结，制备出介电性能为ε_r=16.38，Q×f=11640GHz，τ_f=-1.45ppm／℃的LTCC微波介质陶瓷。与文献报道相比，ε_r明显提高，Q×f值得到改善。（五）基于片式多层滤波器的结构和设计原理，采用宽边耦合带状线模型，借助Ansoft HFSS软件进行带通滤波器的结构构建和性能仿真。采用添加LiF-ZBS复合助剂的CLNT陶瓷为介质层，通过LTCC技术制造工艺，制备出外形尺寸为3.2mm×1.6mm×1.4mm，中心频率1.907GHz，带宽＞100MHz，插入损耗2.07dB，驻波比为17.9dB，f₀-0.450MHz处的阻带衰耗为53.2dB的片式多层带通滤波器。其性能指标达到日本Murata同类产品水平。更多还原

【Abstract】 With the rapid progress in mobile telecommunication, wireless local area network （LAN） and military radar technologies, it has been strongly required that the related components become small-sized, light-weighted, multifunctional, low-cost, and usable at higher frequency range. In order to fulfill these requirements, design and fabrication of multilayer chip microwave components using low temperature co-fired ceramics （LTCC） technology has become a research hotspot nowadays.The key technology of LTCC is preparation of microwave dielectric ceramics which can co-fired with low cost and high conductivity inner electrode such as Ag and Cu.Ca[(Li_1/3Nb_2/3),Ti]O_3-δ （CLNT） and Magnesium titanate （MgTiO₃） ceramics exhibit moderate dielectric constant, low dissipation factor and adjustable temperature coefficients of resonant frequency. These two material systems could be promising LTCC materials if they can be sintered at low temperature and compatible with LTCC technics. Recently, some research work on low temperature sintering ceramic based on these two material systems have been reported, but there still exist many problems as follows: （1） It’s difficult to decrease the sintering temperature and the study on liquid phase sintering mechanism is limited. （2） Though the sintering temperature of dielectrics was decreased lower than the melting point of Ag electrode, dielectric properties critically deteriorated. For example, CLNT ceramic with 2wt%B₂O₃-6wt%Bi₂O₃ compound additives can be densified at 920℃, whereas the quality factor values （Q×f） rapidly decreased to 10600GHz. （3） Research and development of new materials disjoint with design and preparation process of components. Many materials have bad adaptability with the fabrication process. For example, it’s difficult to get dense green tape by tape casting process use ceramic powder with B₂O₃ additive, because B₂O₃ is easy to react with binder such as PVB.From the view points of combination of material properties, components design and preparation technics, ceramic systems of CLNT and MgTiO₃ were selected as the research objects in this dissertation. Based on the effect of different sintering aids to reduce the sintering temperature of microwave ceramic systems, the low temperature sintering mechanisms were revealed. The effects of different sintering aids on sintering characteristics, phase compositions, microstructures and dielectric properties of microwave ceramics were studied systematically. The relation among phase compositions, microstructures and dielectric properties of low temperature sintered ceramics was explained. The sintering aids and preparation processes were optimized. Engineering practice problems of LTCC materials （CLNT and MgTiO₃） including slurry character and co-firing behavior between ceramic and silver electrode were also studied. Based on above researches, a multilayer component model was built. By component simulation and LTCC technics,a kind of multilayer band-pass filter with demand property was prepared.1. Based on the effect of different sintering aids to reduce the sintering temperature of microwave ceramic systems, combined with sinterability, phase compositions and microstructures, the liquid-phase sintering mechanisms of LTCC ceramics were revealed. It can provide references for choosing sintering additives. （1） The reaction between sintering addition and host material can increase the substance activity, liquid phase formed simultaneously, so the sintering process gets accelerated. During the sintering process, Bi₂O₃ reacted with CLNTto form liquid phase of Li₂O-Bi₂O₃、 Bi₂O₃-TiO₂ at low temperature; LiF reacted with CLNT with the production of CaF₂, LiF and CaF₂ transferred into liquid phase at the eutectic point of 766℃; Bi₂O₃ and V₂O₅ reacted with MgTiO₃ host material at low temperature to form new phases like Bi₄V_1.5Ti_0.5O_10.85 and BiVO₄. The new phases melted into liquid phase at 815～850℃. （2） Borosilicate glass exhibits low softening temperature. At low temperature, it formed into molten glass with low viscosity, so can effectively decrease the sintering temperature of ceramics. The softening temperature of ZnO-B₂O₃-SiO₂ （ZBS） and Li₂O-B₂O₃-SiO₂ （LBS） glass are 638℃ and 402℃ respectively, with which the sintering temperature of CLNT and MgTiO₃ ceramics can be decreased to 930℃ and 900℃, respectively. （3） The combined additives are more effective to decrease the sintering temperature of microwave ceramics than single additive. Bi₂O₃ and ZBS can decrease the sintering temperature of CLNT to 1020℃ and 930℃ independently. CLNT ceramic with Bi₂O₃-ZBS compound additive can densified at 900 ℃ by the effect of ZnO-Bi₂O₃-B₂O₃-SiO₂ molten glass with low viscosity. As for LiF-ZBS compound additive, the replacement of the bridging oxygen of ZBS glass network by F^- can disaggregate the anion conglomeration, which can decrease the viscosity of molten glass and accelerate the liquid-phase sintering process.2. The relationship among phase composition, microstructure and dielectric properties of low temperature sintered ceramic was disclosed. （1） Second phases, including additives introduced and impurity formed during reaction, affect dielectric properties of ceramic greatly. When ZBS and LBS, which all have low dielectric constant and high dissipation factor, added into CLNT and MgTiO₃ ceramic respectively. ε_r and Q×f value of ceramic decreased, τ_f shift to negative value; As for MgTiO₃ specimen with Bi₂O₃-V₂O₅ combined additives, when V₂O₅ content was 1～2mol%, Bi₂O₃ and V₂O₅ could react with host material to generate lots of Bi₂Ti₂O₇ and Bi₄V_1.5Ti_0.5O_10.85 phases with high dissipation factor, which caused the low Q×f value of ceramic. When the V₂O₅ content increased, these phases decreased gradually and then disappeared, the Q×f value increases sharply. （2） Microstructure, such as pore and crystalline size, is also important factor that can affect dielectric properties. The volatilization of Bi₂O₃ led to the increasing of pores in CLNT ceramic, which caused the decrease of bulk density （ρ）, ε_r and Q×f value; The volatilization of LiF result in the porous structure of CLNT ceramic, ρ and ε_r decreased quickly with the increase of LiF content; BiVO₄ induced the abnormal grain growth of MgTiO₃, which caused the inhomogeneity of microstructure and led to the great decrease of Q×f value. （3） Lattice defect affect greatly on dielectric properties. For CLNT ceramic with Bi₂O₃-ZBS combined additives, Bi³⁺ ions substituted Ca²⁺ ions in the A-site of perovskite structure that resulted in formation of calcium vacancy and relaxation of crystalline lattice. As a result, ε_r increased and Q×f value greatly decreased, τ_f shift to negative value; LiF and ZBS glass could coordinated and accelerated the phase transformation from Ca[(Li_1/3Nb（2/3）),Ti]O_3-δ phase to stoichiometric Ca[(Li_1/4Nb_3/4),Ti]O₃ phase. Oxygen vacancy in the ceramic body decreased during the transformation, which was helpful to keep the high Q×f value.3. In order to lay the foundation for the industrialization of LTCC materials, engineering techniques including slurry character and co-firing behavior of ceramic and silver electrode were studied systematically. （1） Gelation between V₂O₅ and binder such as PVB or PVA could greatly increase the viscosity of MgTiO₃ slurry system with Bi₂O₃-V₂O₅ combined additives. The obtained slurry with high viscosity is unsuitable for tape casting. Preliminary reaction of Bi₂O₃ with V₂O₅ to form BiVO₄ could resolve the tape casting problem of the systemwith free V₂O₅. （2） The co-fired interface between CLNT ceramic with LiF addition and Ag electrode is distinct. The delamination phenomenon was observed for the nonmatched shrinkage of ceramic and Ag. The Ag electrode also had anomalous porous structure. All these problems limited the application of CLNT ceramic with LiF addition. The substitution of LiF-ZBS combined addition for LiF can resolve these problems. （3） CLNT ceramic with Bi₂O₃-ZBS or LiF-ZBS and MgTiO₃-CaTiO₃ ceramic with LBS glass can avoid the disadvantageous effect of free B₂O₃ on slurry character. Green tapes with glabrous surface were gained by the tape casting process. It has a good conjoint status and chemical compatibility between ceramic and Ag electrode. No evident diffusion was happened.4. On the premise of harmonization and optimization of cooling effect, dielectric properties, slurry character and co-firing behavior of ceramic and silver electrode, two kinds of low temperature firing microwave dielectric ceramics which had excellent properties and application values were acquired. （1） Low temperature sintering ceramic CLNT was prepared with LiF-ZBS compound additives. It acquired microwave dielectric properties of ε_r=34.28, Q×f=17400GHz, τ_f= - 4.6×10^-6/℃ sintered at 900℃. The Q×f value of low temperature sintered CLNT ceramic increased greatly than reported before. （2） CaTiO₃ was used to adjust τ_f of MgTiO₃, home-made LBS glass with low softening temperature was adopted as the sintering additive, low temperature sintering microwave dielectric ceramic with dielectric properties of ε_r= 16.38. Q×f=11640GHz, τ_f=-1.45ppm/℃ was acquired when sintered at 890℃. Compared with dielectric properties of low temperature sintered MgTiO₃ ceramic reported before, dielectric constant increased evidently and Q×f also got improved.5. According to the structure and design principle of multilayer filter, a multilayer laminated bandpass filter model was constructed based on broadside coupled strip line. Ansoft HFSS software was adopted for electric properties simulation. Low temperature sintering ceramic CLNT with LiF-ZBS addition was used as the dielectric layer. By using LTCC fabrication technics, a mulilayer laminated bandpass filter with dimension of 3.2mm×1.6mm ×1.4mm was acquired. The electric properties were as following: center frequency is 1.907GHz, bandwidth >100MHz, VSWR is 17.9dB, insertion loss is 2.07dB, stopband loss at f₀-450MHz is 53.2dB. Its synthesized performance reached the similar level of the same kind of products of Murata company.更多还原