+. Department of Chemistty
David s.Ballantine,
NorUmrn Illinois University
DeKalb. IL 60115
Hank Wohltm
MiCroSensor Systems, Inc. P.O. Box 90 Fairfax. VA 22030
Interest in chemical microsensor research has increased substantially during the last decade, as indicated by the number of recent publications and presentations at professional meetings and symposia dealing with the subject (1-5). This interest has heen spurred by the microsensors' small size, ruggedness, sensitivity, and low power consumption. When used in applications such as procesa control, clinical diagnostics, or environmental monitoring, these characteristics translate into the availability of abundant and inexpensive chemical information, with profound implications for maintaining and improving quality control in manufacturing and for improving our qualit y of life. Surface acoustic wave (SAW) devices are transducers based on highfrequency mechanical oscillators. They offer a simple, direct, and sensitive method for probing the chemical and physical properties of materials. SAW devices are unique in that the acoustic wave energy is constrained to the surface region of the substrate, a feature that also accounts for their versatility as chemical and physical sensors. This REPORT will introduce SAW device 704A
technology through a brief explanation of operational principles, discusa some of the factors to he considered in the design of a SAW chemical sensor, and present an overview of the use of SAW devices both as chemical sensors and as basic research tools. POSsibkapplications SAW device technology was born with the development of the interdigital transducer (IDT) by White and Volltmer in 1965 (6). Deposition of IDTs on the surface of piezoelectric suhatrates made it possible to excite a variety of elastic waves, including Rayleigh surface waves, in these materials. When first introduced, SAW devices were primarily used in rf signal processing, where they offered unique ca-
REPORT1 pahilities for the generation, L---
