EFFECTS OF Mg CONTENTS ON ZnAl_2O_4 THIN FILMS BY SOL GEL METHOD AND ITS APPLICATION

摘要

The need for miniaturization and weight reduction of GPS patch antennas have forced scientists to search for new microwave dielectric materials. A sol-gel method was used to prepare Zn_(1-x)Mg_xAl_2O_4 (x = 0.00, 0.05, 0.10, 0.20 & 0.30) thin films based microwave dielectric ceramics and GPS patch antenna. The structural, optical, chemical property and dielectric properties of (Mg/Zn)Al_2O_4 - based microwave dielectric ceramics have been investigated. It is confirmed that ZnAl_2O_4 was succesfully formed with Mg by the X-ray diffraction (XRD) and Fourier Transform Infra-red (FTIR) patterns. The XRD patterns displayed the standard face-centered cubic of (Mg/Zn)Al_2O_4. The addition of Mg decreased the crystallite size (19.2 to 12.9 nm) and lattice parameter (8.082 to 8.048 A), whiles the apparent density increase linearly. The FTIR spectrum shows the bonding of (Mg/Zn)Al_2O_4 occurred at 666 cm~(-1). By using ultra-violet (UV-Vis) spectrophotometer, the band gap (Eg) energy of undoped was observed slightly lower than the Mg-doped. The Atomic Force Microscopy (AFM) data shows the Root Mean Square (RMS) roughness decreased due to Mg increases. The material with a higher density is associated with high dielectric constant (ε_r), which is suitable for GPS patch antenna application. The dielectric constant (ε_r) of the films was characterized at certain frequency using LCR spectrometer. It also observed there is a steady decrease in ε_r with applied frequency for each sample. The GPS patch antenna was fabricate using the Zn_(1-x)Mg_xAl_2O_4. Finally, the measured magnitude of return loss at 1.5754 GHz meets the requirements of GPS application.