Low-temperature Sintering And Microwave Dielectric Properties Of Mg₃B₂O₆-Glass Composites

As the development of information technology requires high-speed datatransmission and high current density transport, the demands for miniaturization,integration, high frequency and modularity of microelectronics and informationtechnology are getting more and more urgent. Low temperature co-fired ceramics （LTCC）is regarded as a promising future technology for the integration of components andsubstrates that are compact, light, and offers high-speed and functionality for portableelectronic devices for high frequency applications.The microwave ceramic materials prepared by LTCC technology is widely used inpassive components and modules such as resonators, filters, diplexers, bluetooth, antennaswitch and RF front-end for its low sintering temperature, low dielectric loss, lowfrequency-temperature coefficient, and low dielectric constant.In this paper, we studied the effects of LBS （Li₂O-B₂O₃-SiO₂） glass, LMABS（Li₂O-MgO-Al₂O₃-B₂O₃-SiO₂） glass and LMZBS （Li₂O-MgO-ZnO-B₂O₃-SiO₂） glass onthe densification, phase development, microstructure and microwave dielectric propertiesof the Mg₃B₂O₆ceramics. Finally, we got three kinds of LTCC substrate composites.LBS glass with the content of5wt%can lower the sintering temperature ofMg₃B₂O₆ceramics from1300°C to950°C. But the Q×f value was significantlydeteriorated. Though CuO and B₂O₃were added to replace LBS glass, the effect onimproving the Q×f value was not obvious.The Mg₃B₂O₆-LMABS composites had an optimum sintering temperature （975°C）.By increasing addition of LMABS glass, Mg₃B₂O₆ceramic reacted with glass and thephases of Mg₂B₂O₅and Mg2SiO4generated. It is found that the35wt%LMABS-addedcomposite sintered at975°C for3h had excellent microwave dielectric properties: εr=6.6, Q×f=20,990GHz, and τf=-46ppm/°C at6.41GHz.The addition of LMZBS glass improved the densification and lowered the sintering temperature of Mg₃B₂O₆ceramics to950°C. Mg₃B₂O₆transformed into Mg₂B₂O₅and anew phase, Li₂ZnSiO4, crystallized from the glass phase. Because of the high dielectricperformance of these phases, Mg₃B₂O₆mixed with55wt%LMZBS sintered at950°Cfor3h had εr=6.8, Q×f=50,000GHz, and τf=-64ppm/°C at7.28GHz. Co-fired thecomposites with Ag, we found that Ag did not react with these phases and this systemexhibited chemical compatibility with Ag electrodes which also indicated thatMg₃B₂O₆-LMZBS composites were promising materials for LTCC applications.