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.