| 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.
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