Ultralow Loss CaMgGeO4 Microwave Dielectric Ceramic and Its Chemical Compatibility with Silver Electrodes for Low-Temperature Cofired Ceramic Applications

A new ultralow dielectric loss cofired CaMgGeO 4 dielectric material with olivine structure was fabricated by the solid-state route. The X-ray patterns, Rietveld refinement, and microstructure revealed the characteristics of the synthesized material. CaMgGeO 4 ceramic belongs to the orthorhombic system with a Pbmn space group. Sintered at 1300 °C for 6 h, the ceramic exhibited a densification of 96.5%, an ultrahigh quality factor ( Q × f ) of 124 900 GHz (tan δ = 1.24 × 10 –4 ) at a frequency of 15.5 GHz, a permittivity (ε r ) of 6.71, and a temperature coefficient of resonant frequency (τ f ) of −73.7 ppm/°C, and the average coefficient of thermal expansion of CaMgGeO 4 was 12.4 ppm/°C. The sintering temperature of the CaMgGeO 4 ceramic was reduced from 1300 to 940 °C with the addition of 5 wt % B 2 O 3 . The CaMgGeO 4 + 5 wt % B 2 O 3 ceramics exhibited favorable microwave dielectric performances: Q × f = 102 000 GHz (at 16.4 GHz), ε r = 5.80, and τ f = −64.7 ppm/°C, respectively. In addition, the CaMgGeO 4 ceramic did not react with Ag electrodes, which could be advantageous in low-temperature cofired ceramic multilayer microwave devices.