5ZnO·2B₂O₃ Ceramics With Near-zero Temperature Coefficient Of Resonant Frequency For Substrates

With the growth of mobile and wireless telecommunication system, the low temperature cofired ceramic(LTCC) technology is playing an important role in the development of various electronic modules. By the LTCC technology, ceramic dielectric substrates and metallic conductors are stacked and cofired in multilayers in special patterns to fulfill different electrical functions. Generally ceramic substrates are required to have a low relative permittivity(?r < 10), a high quality factor(Q×f > 10,000 GHz), and a near-zero temperature coefficient of resonant frequency(?f = ~ 0 ppm/°C). In addition, substrates must have a sintering temperature lower than the melting point of the conductor such as Ag(961 °C) and be chemically compatible with the conductor during cofiring. 5Zn O·2B2O3 ceramics sintered at 955 °C exhibited excellent microwave dielectric properties: ?r = 6.9, Q×f = 20,647 GHz, ?f =-80 ppm/°C. The ceramics need to be tailored its ?f and lowered its sintering temperature without degrading its microwave dielectric properties.The effects of(Li0.5Bi0.5)Mo O4 addition were studied on the densification and microwave dielectric properties of 5Zn O·2B2O3 ceramics. It was found that(Li0.5Bi0.5)Mo O4 addition to 5Zn O·2B2O3 ceramics lowered its sintering temperature to 900 °C without degrading its microwave dielectric properties. 5Zn O·2B2O3 ceramics sintered at 900-920 °C with 4-6 mol%(Li0.5Bi0.5)Mo O4 additions exhibited excellent microwave dielectric properties: ?r = 6.7-6.9, Q×f = 17,200-30,300 GHz, and-57 ppm/°C ? ?f ?-44 ppm/°C. Due to the reaction between(Li0.5Bi0.5)Mo O4 and 5Zn O·2B2O3 ceramics, the value of ?f was not tailored. The sintering temperature was lowered because of the addition of Li and Bi.The effects of Pb1.5Nb2O6.5 addition were investigated on the phase evolution, microstructure, densification, and microwave dielectric properties of 5Zn O·2B2O3 ceramics. It was shown that a 5.5 mol% addition of Pb1.5Nb2O6.5 to 5Zn O·2B2O3 ceramics successfully tailored its ?f to ~ 0 ppm/°C and lowered its sintering temperature to 890 °C without degrading its microwave dielectric properties. 5Zn O·2B2O3 ceramics sintered at 890-910 °C with 5.0-6.0 mol% Pb1.5Nb2O6.5 additions exhibited excellent microwave dielectric properties: ?r = 7.8-8.3, Q×f = 11,500-15,200 GHz, and-9.2 ppm/°C ? ?f ? +6.6 ppm/°C. The ceramics showed cofiring compatibility with Ag. The value of ?f was tailored thanks to the fact that Pb1.5Nb2O6.5 phase still existed. The formed Zn O-Pb O-B2O3 liquid promoted the densification of ceramics.