Guided SH-SAW sensors for liquid-phase detection

The design and performance of guided shear horizontal surface acoustic wave (guided SH-SAW) devices on LiTaO₃ substrates are investigated for high sensitivity biochemical sensor in liquids. The device sensitivity to mass and viscoelastic loading is increased using a thin guiding layer of (cross-linked or cured) poly(methyl methacrylate) (PMMA) or cyanoethylcellulose (CEC) on the device surface. The devices have been tested in biosensing and chemical sensing experiments. Suitable design principles for these applications are discussed with regard to wave guidance, electrical passivation of the interdigital transducers (IDT) from the liquid environments, acoustic loss and sensor signal distortion. In biosensing experiments, using optimal PMMA thickness of approximately 2 μm, mass sensitivity greater than 1500 Hz/(ng/mm²) is demonstrated, resulting in a minimum detection limit less than 20 pg/mm². For chemical sensor experiments, it is found that optimal waveguide thickness must be modified to account for the chemically sensitive layer