Study On The Temperature Stable Molybdenum-based Microwave Dielectric Ceramics With Low Sintering Temperatures

In recent years, with the rapid development of mobile communication and satellite communication industry, low temperature co-firing ceramic(LTCC) technology palys a more and more important role in the microwave dielectric ceramics research field. In order to meet the miniaturization, integration, high reliability and low cost demand for LTCC applications, dielectric ceramics need to fulfill the requirement of a low sintering temperature(below melting points of Ag, Al, Cu, Au. etc), a range of high dielectric permittivities(εr), a high quality factor(Q×f)(f = resonant frequency, Q = 1/dielectric loss at f), a near-zero temperature coefficient of resonant frequency(τf ≈ 0 ppm/oC), chemical compatibility with inner metal electrodes.The sintering temperature, crystal structure and microwave dielectric propreties were investigated from the phase diagram of the Pb O-Mo O3 binary system. A series of promising candidates for LTCC were expolored in the Pb O-Mo O3 binary system: the Pb2 Mo O5 ceramic sintered at 610 °C with εr of 19.1, Qf value of 21960 GHz, TCF value of-60ppm/°C; the Pb Mo O4 ceramic sintered at 650°C with εr of 26.7, Qf value of 42830 GHz, TCF value of +6.2ppm°C. and chemical compatibility with silver and aluminum for Pb2 Mo O5 and Pb Mo O4 ceramics.Based on the Ca Mo O4 ceramic with excellent microwave dielectric properties, the sintering temperature was lowered by the(Li0.5Sm0.5)2+ or(Li0.5Nd0.5)2+ substitution for Ca2+ in Ca Mo O4 ceramic. A series of promising candidates for LTCC were explored in [(Li0.5Ln0.5)1-xCax]Mo O4 system: the [(Li0.5Sm0.5)0.20Ca0.80]Mo O4 ceramic sintered at 875°C with εr of 10.6, Qf value of 18405 GHz, TCF value of +6.9ppm/°C, chemical compatibility with silver; the [(Li0.5Sm0.5)0.15Ca0.85]Mo O4 ceramic sintered at 900°C with εr of 11.0, Qf value of 23590 GHz, TCF value of-5.2ppm/°C; [(Li0.5Nd0.5)0.20Ca0.80]Mo O4 ceramic sintered at 800°C with εr of 11.0, Qf value of 18695 GHz, TCF value of +4.3ppm/°C and chemical compatibility with silver; the [(Li0.5Nd0.5)0.15Ca0.85]Mo O4 ceramic sintered at 825°C with εr of 10.8, Qf value of 24070 GHz, TCF value of-7.4ppm/°C. The phase composition of the ceramic samples were analyzed by Raman spactra and infrared spectra. It is that different vibration mode contribution to the dielectric polarization are studied.The sintering temperature, crystal structure and microwave dielectric propreties and chemical compatibility with silive electrodes were investigated on a series of compounds in the(Na0.5Ln0.5)Mo O4(Ln= La, Nd and Ce) system. The compounds in(Na0.5Ln0.5)Mo O4 system was prepared by solid state reaction method with excellent microwave dielectric properties: the(Na0.5La0.5)Mo O4 ceramic sintered at 740°C with εr of 10.9, Qf value of 25105 GHz, TCF value of-59.3ppm/°C, and chemical compatibility with silver; the(Na0.5Nd0.5)Mo O4 ceramic sintered at 760°C with εr of 10.5, Qf value of 19605 GHz, TCF value of-48.5ppm/°C and chemical compatibility with silver; the(Na0.5Ce0.5)Mo O4 ceramic sintered at 780°C with εr of 11.2, Qf value of 19365 GHz, TCF value of-44.2ppm/°C, and reacted with silver.