Microwaves Effect on Structural Properties of Aluminum Nitride at High Temperatures

Aluminum nitride (AlN) is selected for microwave dielectric measurements in frequency ranges, 615 MHz, 1412 MHz, 2214 MHz, 3017 MHz, and 3820 MHz at temperatures ranging from 25℃ to 2000℃. The structural characterizations of this sample before and after the microwave measurements are determined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The goal of this work is to compare the microwave measurements of the dielectric properties of AlN ceramic to the structural measurements. The results show that AlN has stability below 1400℃, which is the best range for microwave processing and applications of this material. AlN starts to absorb more microwaves above 1400℃ due to the hydrolysis to aluminum hydroxide (Al(OH)_3).