SURFACE-ACOUSTIC-WAVE CHARACTERIZATION OF PECVD FILMS ON GALLIUM-ARSENIDE

Surface-acoustic-wave (SAW) measurement techniques can be effectively used to determine the acoustic properties of dielectric and piezoelect ric 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, sili con carbide, and TEOS glass, deposited by plasma-enhanced chemical-vap or-deposition (PECVD) on GaAs, have been characterized using linear ar rays of SAW interdigital electrodes operating in the harmonic mode ove r the frequency region from 30 MHz to above 1.0 GHz. The elastic const ants of these amorphous films have been determined by fitting theoreti cal dispersion curves to the measured SAW velocity characteristics. Fr equency-dependent SAW propagation-loss values have been determined fro m the observed linear change in loss as a function of transducer separ ation. Preliminary measurements of the temperature coefficient of freq uency (TCF) for SAW propagation of the films on GaAs are also given.