Vibration measurements of radio frequency micro-scale acoustic devices

Abstract

Current micromachining and IC manufacturing technology has enabled the development of a wide range of acoustic sensors and devices operating at frequencies up to several GHz. Accurate measurements of the vibrational behavior of these devices is often complicated by their small size, intricate geometry and high operating frequencies. To address these issues a measurement system based on a fiber delivered heterodyne laser interferometer has been developed to perform spatially dense measurements of the surface displacement at high frequencies. With this system, noncontact displacement measurements can be made with sub-angstrom sensitivity for a spot several micrometers in diameter. Evaluation of the system is made with 2-D scans of the normal surface displacement of a 110-MHz delay line surface acoustic wave (SAW) chemical vapor sensor. Measured displacement levels of the uncoated quartz substrate for this device are typically less than 1 nm for acoustic wavelengths of 29 mum. Limitations of this method are discussed, including the effect of spatial filtering brought about by the finite optical spot size. [Work sponsored by the Office of Naval Research.] a)National Research Council-NRL Research Associate. b)Also with SFA, Inc., Landover, MD 20785.