Effect of Zn Site for Ca Substitution on Optical and Microwave Dielectric Properties of ZnAl2O4 Thin Films by Sol Gel Method

CaxZn( 1-x)Al2O4(x-0.00, 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30) thin films were prepared by a sol gel method. The XRD patterns displayed the characteristic peaks of (Ca/Zn)Al2O4 with the standard pattern of face-centred cubic (fcc). The addition of Ca decreased the lattice constant from 14.6 nm to 23.2 nm. The optical bandgap of undoped thin film was found to be at 3.84 eV while for doped Ca was observed at 3.50 to 3.73eV. The substitution of Zn2+ by Ca2+ in ZnAl2O4 thin films was found to increase the crystallite size, grain size, and surface morphology which evidently affect the density and dielectric constant. The CaxZn( 1-x)Al2O4 thin films were characterized at 20 to 1MHZ frequency to determine the dielectric constant (epsilon(gamma)) and unloaded quality factor (Q(u)) using LCR spectrometer. It can be observed that specimen using Ca0.25Zn0.75Al2O4 possesses epsilon(gamma) similar to 10.41 and Q(u) similar to 5770 which is suggested as a candidate material for millimetre-wave applications. Therefore, this ceramic is suggested as a candidate material for GPS patch antennas.