Performance optimization of surface acoustic wave chemical sensors

Acoustic wave devices coated with a thin layer of chemoselective material provide highly sensitive chemical sensors for the detection and monitoring of vapors and gases. In this work, a variety of coating materials and coating deposition techniques have been evaluated on surface acoustic wave (SAW) devices. A novel thin film deposition technique, matrix assisted pulsed laser evaporation (MAPLE), is utilized to coat high quality polymer films on SAW devices, and conventional pulsed laser deposition is used to deposit a passivation layer of diamond-like-carbon on a SAW device surface to prevent water adsorption. In addition, chemoselective coatings are formed by covalent attachment of functionalized species to the silica surface of SAW devices. The self-assembled monolayer or near monolayer structures are designed to populate the SAW device surface with the desirable hexafluoroisopropanol moeity. The 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 deposition, growth, and vapor testing, the electrical characteristics of the SAW sensor have been characterized. The quality factor and residual phase noise of polymer coated SAW devices are examined, and a prediction of the theoretical limit of the phase noise performance of the loop oscillator is made.