(471a) Simulation and Experimental Investigation of a SAW Sensor With Delay Path Modifications

We developed a surface acoustic wave (SAW) device that includes an array of cavities having square cross-sectional areas (microcavities). It is common when dealing with SAW sensors to have high insertion losses.  Several approaches have been utilized which includes the incorporation of reflective gratings, grooves and corrugated surfaces, and the application of a waveguide material to remedy this problem. Decreasing the amount of power consumed will limit the amount of heat generated that can adversely affect protein activity and increasing sensitivity will allow the detection of antigens at clinically relevant concentrations. Two different substrates commonly used in biosensors were studied, ST-Quartz and 36° YX -LiTaO_3. From simulations, we find that microcavities optimized for a particular substrate and wave mode scatter the incident wave causing constructive interference while acting as a waveguide limiting its penetration into the bulk. Using results from the simulations as a basis we fabricated devices on both substrates that support shear-horizontally polarized waves.   A standard SAW delay-line and a SAW device containing microcavities were compared by measuring insertion loss and determining the sensitivity to changing glycerol concentrations.  Our experimental results agree well with simulations and we conclude that a delay path modification in the form of microcavities is an effective way to improve SAW sensing performance.