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 CaMg-GeO4 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. CaMgGeO4 ceramic belongs to the orthorhombic system with a Pbmn space group. Sintered at 1300 degrees C for 6 h, the ceramic exhibited a densification of 96.5%, an ultrahigh quality factor (Q x f) of 124 900 GHz (tan delta = 1.24 X 10(-4)) at a frequency of 15.5 GHz, a permittivity (epsilon(r)) of 6.71, and a temperature coefficient of resonant frequency (tau(f)) of -73.7 ppm/degrees C, and the average coefficient of thermal expansion of CaMgGeO4 was 12.4 ppm/degrees C. The sintering temperature of the CaMgGeO4 ceramic was reduced from 1300 to 940 degrees C with the addition of 5 wt % B2O3. The CaMgGeO4 + 5 wt % B2O3 ceramics exhibited favorable microwave dielectric performances: Q x f = 102 000 GHz (at 16.4 GHz), epsilon(r) = 5.80, and tau(f) = -64.7 ppm/degrees C, respectively. In addition, the CaMgGeO4 ceramic did not react with Ag electrodes, which could be advantageous in low-temperature cofired ceramic multilayer microwave devices.