PERFORMANCE OPTIMIZATION OF SURFACE-ACOUSTIC-WAVE CHEMICAL SENSORS

Acoustic wave devices coated with a thin layer of chemoselective mater ial provide highly sensitive chemical sensors for the detection and mo nitoring of vapors and gases. In this work, a variety of coating mater ials and coating deposition techniques have been evaluated on surface acoustic wave (SAW) devices. A novel thin film deposition technique, m atrix assisted pulsed laser evaporation (MAPLE), is utilized to coat h igh quality polymer films on SAW devices, and conventional pulsed lase r deposition is used to deposit a passivation layer of diamond-like-ca rbon on a SAW device surface to prevent water adsorption. In addition, chemoselective coatings are formed by covalent attachment of function alized species to the silica surface of SAW devices. The self-assemble d monolayer or near monolayer structures are designed to populate the SAW device surface with the desirable hexafluoroisopropanol moeity. Th e rapid kinetic signals achievable with the various coated SAW sensors during vapor tests are examined as a function of the coating material and the quality of the thin films. In parallel to the thin film depos ition, growth, and vapor testing, the electrical characteristics of th e SAW sensor have been characterized. The quality factor and residual phase noise of polymer coated SAW devices are examined, and a predicti on of the theoretical limit of the phase noise performance of the loop oscillator is made.