Layered Surface Acoustic Wave Chemical and Bio-Sensors

Surface acoustic wave (SAW) sensors are currently being investigated in a wide range in fields including physical, chemical and bio-sensing. The basic principle in a SAW sensor is the detection of changes in the propagation characteristics of the surface acoustic waves which are caused by perturbations on the active surface of the device. The most common situation is measuring the change in propagation velocity of the surface wave as a change in resonant frequency. This chapter is a review of layered SAW devices for sensing applications. A conventional SAW device consists of a piezoelectric substrate with the inter-digital transducer (IDT) patterned on the surface. The layered devices are fabricated by depositing a thin film onto the conventional SAW substrate. Almost any SAW chemical sensor will employ a sensitive layer which interacts with the analyte. However, in this chapter we are concerned with devices where an intermediate layer has been added between the substrate and sensitive layer for its acoustic, dielectric or protective properties. Layered SAW sensors offer a number of advantages over conventional SAW devices without layers: