Temperature stable low loss ceramic dielectrics in (1-x)ZnAl $\mathsf{_{2}}$ O $\mathsf{_{4}}$ -xTiO $\mathsf{_{2}}$ system for microwave substrate applications

Abstract

The microwave dielectric properties of ZnAl2O4 spinels were investigated and their properties were tailored by adding different mole fractions of TiO2. The samples were synthesized using the mixed oxide route. The phase purity and crystal structure were identified using X-ray diffraction technique. The sintered specimens were characterized in the microwave frequency range (3-13 GHz). The ZnAl2O4 ceramics exhibited interesting dielectric properties (dielectric constant ( $\varepsilon_{r}) = 8.5$ , unloaded quality factor (Q u ) = 4590 at 12.27 GHz and temperature coefficient of resonant frequency ( $\tau_{f}) = -79$ ppm/ $^{\circ}$ C). Addition of TiO2 into the spinel improved its properties and the $\tau_{f}$ approached zero for 0.83ZnAl2O4-0.17TiO2. This temperature compensated composition has excellent microwave dielectric properties ( $\varepsilon _{r} = 12.67$ , Q u = 9950 at 10.075 GHz) which can be exploited for microwave substrate applications.