Synthesis and Surface Acoustic Wave Properties of AlN Thin Films Fabricated on (001) and (110) Sapphire Substrates Using Chemical Vapor Deposition of AlCl₃–NH₃ System

Thin films of AlN were prepared on sapphire C- and A-plane by chemical vapor deposition. Crystal orientations, oxygen impurity contents and surface acoustic wave properties (SAW) of the films were investigated. Under optimized conditions, epitaxial AlN films were deposited and the crystal orientation relationships were (001)[110]AlN//(001)[110]Al 2 O 3 and (001)[110]AlN//(110)[110]Al 2 O 3 . The crystal orientation of the AlN films decreased as the thickness of the films increased slightly, and the oxygen impurity content was less than 1 atm% for both systems. The dependences of SAW velocity ( V s ) and the temperature coefficient of the center frequency (τ f ) on the film thickness were measured, and τ f was found to increase as the film thickness increased for all measurment directions; however, zero-temperature coefficient was not achieved.