(1-x)MgAl2O4-xTiO2 dielectrics for microwave and millimeter wave applications

The MgAl2O4 ceramics were prepared by the conventional solid-state ceramic route and the dielectric properties studied in the microwave frequency region (3–13 GHz). The phase purity and crystal structure were identified using the X-ray diffraction technique. The MgAl2O4 spinel ceramics show interesting microwave dielectric properties (εr=8.75, Quxf=68900 GHz (loss tangent = 0.00017 at 12.3 GHz), τf=-75 ppm/°C). The MgAl2O4 has high negative τf, which precludes its immediate use in practical applications. Hence the microwave dielectric properties of MgAl2O4 spinels were tailored by adding different mole fractions of TiO2. The εr and Q factor of the mixed phases were increased with the molar addition of TiO2 into the spinel to form mixtures based on (1-x)MgAl2O4-xTiO2 (x=0.0-1.0). For x=0.25 in (1-x)MgAl2O4-xTiO2, the microwave quality factor reaches a maximum value of Quxf=105400 GHz (loss tangent = 0.00007 at 7.5 GHz) where εr and τf are 11.035 and -12 ppm/°C, respectively. The microwave dielectric properties of the newly developed 0.75MgAl2O4-0.25TiO2 dielectric is superior to several commercially available low loss dielectric substrates.