Microwave Dielectric Properties of LiF- and CaTiO3-Added MgO with Low Dielectric Loss and Near-Zero Temperature Coefficient of Resonant Frequency for Low-Temperature Cofired-Ceramic

Abstract

The influences of LiF and CaTiO3 addition on the microwave dielectric properties of MgO ceramics were investigated in this study. The LiF was effective in reducing the sintering temperature of MgO without a detrimental effect on the quality factor (Q·f). The 0.05 mol LiF-added MgO ceramics were sintered at a temperature of 950 °C which resulted in dielectric constant (εr) and Q·f values of 9.6 and 215,000 GHz, respectively, though the temperature coefficient of resonant frequency (TCf) had a large negative value of -63.5 ppm/°C. In order to achieve near-zero TCf values, (0.95-x)MgO–xCaTiO3–0.05LiF ceramics were also investigated and the formation of a secondary phase in MgO–CaTiO3–LiF ceramics was not observed in the X-ray powder diffraction profiles. Although the Q·f values of the ceramics were lowered by CaTiO3 addition, a near-zero TCf was obtained at x = 0.05 (TCf= -3.2 ppm/°C). The εr and Q·f values of the 0.90MgO–0.05CaTiO3–0.05LiF (x = 0.05) ceramic were 12.7 and 93,500 GHz, respectively. From these results, it is considered that CaTiO3-added (0.95-x)MgO–xCaTiO3–0.05LiF ceramics are appropriate candidates as high-Q low-temperature cofired-ceramics (LTCCs).