Design of ST-cut quartz surface acoustic wave chemical sensors

Abstract

This research investigates the design rules polymer-based ST-cut quartz surface acoustic wave (SAW) sensors used in detecting organophosphorous compounds. A complex shear modulus is used to represent express different types of polymer (glassy, glassy–rubbery, and rubbery). Different propagation directions lead to different wave propagation properties in SAW devices, such as attenuation and velocity. Hence, the choice of polymer type and wave propagation direction is a very important aspect of sensor design. Calculations indicate that the glassy–rubbery and rubbery film coated on SAW sensors very sensitively detect organophosphorous vapor. However, the glassy–rubbery film is most suitable in sensing applications, because it makes signal attenuation significantly. Although sensitivity is high when an acoustic wave propagates in the Y-direction, the X-direction is preferred at the optimum path on account of the excellent temperature stability in the X-propagation direction. Therefore, SAW vapor sensors with an appropriate chemical interface and wave propagation direction are designed to yield superior performance.