【作者】 梁军；

【导师】 吕文中；

【作者基本信息】 华中科技大学 ， 微电子学与固体电子学， 2010， 博士

【摘要】 在电子元器件日益趋向小型化、轻量化、集成化、多功能的今天,以低温共烧陶瓷(LTCC)技术制作的电子元器件及各种功能模块被广泛应用于现代通信、汽车电子、航空航天和计算机等方面,作为这些电子元器件关键材料的微波介质陶瓷正向低温共烧方向发展,新技术、新形势对微波介质陶瓷材料提出了更高的要求。本文在大量实验基础上,确定以Li2TiO3基陶瓷为研究对象,实现了Li2TiO3基陶瓷的低温烧结,通过改变配方、烧结工艺和成型工艺等改善了Li2TiO3基陶瓷的微波介电性能,研制出适于流延工艺的Li2TiO3基陶瓷配方,研究了Li2TiO3基陶瓷与Ag电极的共烧行为,证明了Li2TiO3基陶瓷是一种可能实用化的低温共烧微波介质陶瓷材料。本文首先研究了符合化学计量比的Li2TiO3陶瓷的烧结特性及微波介电性能。通过TG/DTA分析和XRD检测手段对Li2TiO3的预烧温度作了初步判定,在此基础上研究了烧结温度对Li2TiO3陶瓷的烧结特性和微波介电性能的影响。Li2TiO3的最佳预烧温度是820℃,最佳烧结温度是1200℃,在此条件下烧结的Li2TiO3陶瓷试样有最大的致密度和最好的微波介电性能,其微波介电性能为：εr=23.29, Q×f=15525 GHz,τf=35.78 ppm/℃.陶瓷体密度为ρ=3.30g/cm3,相对理论密度为96.75%。考虑到Li元素高温挥发的性质,研究了非化学计量比对Li2TiO3陶瓷的烧结特性及微波介电性能的影响。少量的Li过剩使在1200℃中温烧结的Li2Ti03陶瓷Q×f值明显升高,对其εr值及τf值影响不大。而少量Li过剩或Li缺乏均造成在900℃低温烧结的Li2Ti03陶瓷Q×f值下降,对陶瓷εr值及τf值影响不大。在满足低温共烧技术对陶瓷烧结温度要求的基础上,本文考察了不同种类的烧结助剂、烧结助剂的不同添加方式(复合氧化物和对应玻璃)、烧结助剂的配比和用量、预烧温度、烧结温度和不同成型工艺(等静压和单轴压)等因素对Li2Ti03陶瓷相组成、显微结构、烧结特性和微波介电性能的影响。添加H3BO3的Li2Ti03陶瓷晶粒较小而均匀,少量添加H3BO3促进了陶瓷的烧结,对Li2Ti03基陶瓷的微波介电性能有利,H3BO3添加量超过2.5 wt%时,Li2Ti03基陶瓷的烧结致密度下降,陶瓷的微波介电性能恶化。适当提高烧结温度促进了陶瓷晶粒生长,陶瓷的微波介电性能提高；添加ZnO-B2O3玻璃的Li2TiO3陶瓷晶粒生长较快,显微结构致密,Li2TiO3陶瓷晶粒尺寸随玻璃添加量增加而增大。添加2.5 wt%锌硼玻璃后在900℃烧结2小时的Li2TiO3基陶瓷具有最好微波介电性能为：εr=23.06, Q×f=32275 GHz,τf=35.79 ppm/℃,陶瓷的孔隙率为0.08%。在添加少量H3BO3或ZnO-B2O3玻璃的Li2TiO3基陶瓷中均只检测到唯一单斜Li2TiO3晶相；添加剂锌硼玻璃的ZnO/B2O3比例越高,则玻璃的软化点也高,玻璃的助烧能力降低,但玻璃对Li2TiO3基体的浸润性增加了,相应的Li2TiO3陶瓷的微波介电性能略有提高；添加锌硼玻璃比添加等量的复合氧化物更有利于提高Li2TiO3陶瓷的烧结特性和微波介电性能；用V2O5-ZnO-B2O3玻璃作烧结助剂的Li2Ti0O陶瓷可以用于流延,当添加1.5-3.0 wt%V2O5-ZnO-B2O3玻璃后,Li2TiO3陶瓷在920℃烧结,样品中均发现有少量的Li3VO4第二相存在。随着玻璃添加量增加,Li2TiO3陶瓷样品中的晶粒有逐渐长大的趋势,陶瓷的显微结构也变得更为致密。ZnO-B2O3-V2O5玻璃的添加量以3.0 wt%最为合适,此时样品烧结致密高,微波介电性能较好。在掺杂量一定时,提高烧结温度,样品的相对介电常数及Q×f值起初均有提高,达到饱和值后开始下降。饱和相对介电常数在样品达到饱和体密度时得到,而最大Q×f值在样品达到饱和体密度之后再略微提高烧结温度时得到。在880～960℃范围内,提高烧结温度对样品的谐振频率温度系数影响不大；等静压成型比单轴压成型更有利于提高Li2TiO3陶瓷的烧结特性和微波介电性能。实验中,采用等静压成型工艺可将低温烧结Li2TiO3基陶瓷的烧结温度降20～50℃。在研究Li2TiO3基陶瓷低温烧结的基础上,我们进一步用CeO2和MnCO3掺杂改善了Li2TiO3基陶瓷的Q×f值,用ZnNb2O6和Li2TiO3两相复合改善了Li2TiO3基陶瓷的τf值。CeO2掺杂有促进Li2TiO3基陶瓷烧结的作用,CeO2在Li2TiO3晶格中固溶度小,它在陶瓷中主要以第二相形式存在,适量CeO2掺杂明显提高了Li2TiO3基陶瓷的品质因子,0.9wt% CeO2掺杂的Li2TiO3基陶瓷(已含2wt%锌硼玻璃)在920℃烧结,其微波介电性能为：εr=22.97, Q×f=34881 GHz,τf=33.12 ppm/℃; MnCO3掺杂对促进Li2TiO3基陶瓷烧结作用明显,掺杂量大于0.3 wt%时,陶瓷中出现了不同程度的晶粒异常生长现象,显微结构开始恶化。在MnCO3掺杂的Li2TiO3基陶瓷中没有发现明显的第二相。适量MnCO3掺杂改善了920℃低温烧结Li2TiO3基陶瓷的微波介电性能；在ZnNb2O6和Li2TiO3复合陶瓷中,ZnNb2O6并不是独立存在的,而是和Li2TiO发生了复杂的化学反应,生成了Li2TiO3和LiNbO3等新相。ZnNb2O6因固相反应烧结机制促进了陶瓷的烧结,在ZnNb2O6的含量为8 wt%左右,复合陶瓷的谐振频率温度系数可以被调节至近0。用流延法制备了Li2TiO3基低温共烧微波介质陶瓷,研究了其烧结性能、显微结构及其与Ag电极的共烧行为。采用含有3 wt% V2O5-ZnO-B2O3玻璃的Li2TiO3基陶瓷粉料进行流延,流延膜片在920℃烧结1小时后陶瓷晶粒均匀,显微结构也较致密,其体密度为3.22 g/cm3,是其饱和密度的96.73%。Li2TiO3基陶瓷在与Ag电极共烧时界面清晰,接触较为紧密,二者没有发生化学反应,也没有Ag渗透现象。这些研究进一步证明,Li2TiO3基陶瓷可能是一种能够实用化的新型低温共烧微波介质陶瓷材料。更多还原

【Abstract】 Nowadays electronic components and devices tend to be miniature, light, integrative, and multifunctional, some electronic components and devices based on LTCC technologies were widely used in fields such as telecommunication, car industry, navigate, and computer. Microwave dielectric ceramics are the key materials to fabricate these electronic components, their sintering temperatures (Ts) need to be decreased below 950℃and they should be compatible with electrode Ag during sintering in air for the request of LTCC technologies. Li2TiO3 was choose as the matrix based on results of some experiments, its sintering temperature was decreased, the microwave dielectric properties of Li2TiO3-based ceramics were improved by adjusting the composition, sintering process, and molding process. The Li2TiO3-based compound suitable for the process of tape-casting was obtained and its sintering behavior when co-fired with electrode Ag was investigated. It was proved that the Li2TiO3-based ceramics may be promising candidates for LTCC applications.Firstly the sintering behavior and microwave dielectric properties of stoichiometric Li2TiO3 ceramics were investigated. The calcination temperature (Tc) of Li2TiO3 ceramics was determined by means of TG/DTA and XRD. The best microwave dielectric properties ofεr=23.29, Q×f=15525 GHz,τf=35.78 ppm/℃were obtained for the sample sintered at 1200℃for 3 hours, its density was 3.30 g/cm3,96.75% of the theoretic density.Then effects of non-stoichiometry on the sintering behavior and microwave dielectric properties of the Li2TiO3-based ceramics were studied. A little additional Li obviously improved the Q×f value of the Li2TiO3-based ceramics sintered at 1200℃, while it had no effect on theεr value andτf value of the samples. Non-stoichiometry decreased the Q×f value of the Li2TiO3-based ceramics sintered at low temperatures and it had little effect on theεr andτf value of the samples.Further studies were carried out about the effects of sintering aids, the means of adding sintering aids into the matrix, the content of sintering aids, Tc, Ts, and the process of molding on the crystal phase, microstructure, sintering behavior, and microwave dielectric properties of the Li2TiO3-based ceramics. Only monoclinic Li2TiO3 was found in the H3BO3-doped Li2TiO3 ceramics. The grain size was small and the microstructure was uniform. About 1.0 wt% H3BO3 addition aided the sintering of Li2TiO3 ceramics effectively while excessive H3BO3 (≥2.5 wt%) was not favorable. A higher Ts accelerated the growth of grain in the ceramic and improved the Q×f value of the samples; Less ZnO-B2O3 frit added into Li2TiO3 compound decreased the Ts of ceramics to 900℃accelerating the grain growth, meanwhile the ZnO-B2O3 frit doped Li2TiO3 ceramics maintained good microwave dielectric properties. When the ZnO-B2O3 frit content was 2.5 wt%, the best microwave dielectric properties ofεr=23.06, Q×f=32275 GHz,τf=35.79 ppm/℃were obtained. The porosity of the sample was 0.08%; The addition of ZnO-B2O3 frit into Li2TiO3 ceramics was more favorable for the microwave dielectric properties of the samples compared with the addition of the same amount of ZnO and B2O3 powders; The V2O5-ZnO-B2O3 frit was a sintering aids developed for the process of tape-casting. When the content of V2O5-ZnO-B2O3 frit was in the range of 1.5～3.0 wt%, the second phase Li3VO4 was formed in the Li2TiO3 ceramics sintered at 920℃. The best microwave dielectric properties were obtained for the sample with 3.0 wt% V2O5-ZnO-B2O3 frit. Theεr value and Q×f value increased initially and then decreased, the saturatedεr value occurred together with the saturated density of the samples. The best microwave dielectric properties occurred right after the saturated density of the sample was obtained. The increase of Ts in the range of 880-960℃had little effect on theτf value of the samples. The samples pressed isotropic statically had higher densities and better microwave dielectric properties than the samples pressed uniaxially, the Ts of the Li2TiO3 ceramics with V2O5-ZnO-B2O3 frit was decreased about 20-50℃when the new process was introduced.The Q×f value of the Li2TiO3-based ceramics sintered at 920℃was increased by the addition of CeO2 and MnCO3, the if value of the Li2TiO3-based ceramics sintered at 920℃was improved by the addition of ZnNb2O6. A right amount of CeO2 or MnC03 would improve the microwave dielectric properties of the Li2TiO3-based ceramics. CeO2 existed as the other crystal phase in the samples for its low solubility in Li2TiO3 matrix and it aided the sintering of the Li2TiO3-based ceramics. No other crystal phase was found in the samples of Li2TiO3-based ceramics doped with MnC03. The addition of MnCO3 accelerated the grain growth and excessive grain growth appeared in most samples. The 0.9 wt% CeO2-doped Li2TiO3-based ceramics had the microwave dielectric properties ofεr=22.97, Q×f=34881 GHz,τf=33.12 ppm/℃; ZnNb2O6 did not exit as a independent phase, it reacted with Li2TiO3 and the new phases of ZnTiO3, Zn2TiO4, and LiNbO4 were formed. ZnNb2O6 aided the sintering of the composite ceramics as a result of solid state reaction. When the content of ZnNb2O6 was 8 wt%, the composite ceramics dad aτf value near zero.Li2TiO3-based ceramics doped with 3 wt% V2O5-ZnO-B2O3 frit were also obtained by the process of tape-casting. The tape sheet was sintered at 920℃for 1 hour. The sintering behavior, microstructure of the ceramic, and its compatibility with electrode Ag during sintering were investigated. The ceramic developed a dense and uniform microstructure, its density was 3.22 g/cm3. The image of SEM/EDS shows that Li2TiO3 did not reacted with electrode Ag and the interface of Li2TiO3 ceramic and electrode Ag was clear. These studies paved the way for the application of the Li2TiO3-based microwave dielectric ceramics in LTCC technologies.更多还原