Surface acoustic wave characterization of PECVD films on galliumarsenide

Surface-acoustic-wave (SAW) measurement techniques can be effectively used to determine the acoustic properties of dielectric and piezoelectric films. Such films can be used for the development of semiconductor-integrated microwave-frequency surface and bulk acoustic wave devices. The acoustic properties of silicon nitride, silicon oxynitride, silicon carbide, and TEOS glass, deposited by plasma-enhanced chemical-vapor-deposition (PECVD) on GaAs, have been characterized using linear arrays of SAW interdigital electrodes operating in the harmonic mode over the frequency region from 30 MHz to above 1.0 GHz. The elastic constants of these amorphous films have been determined by fitting theoretical dispersion curves to the measured SAW velocity characteristics. Frequency-dependent SAW propagation-loss values have been determined from the observed linear change in loss as a function of transducer separation. Preliminary measurements of the temperature coefficient of frequency (TCF) for SAW propagation of the films on GaAs are also given