In-Liquid LSAW Resonant Sensors with Enhanced Sensitivity

Here we propose and demonstrate a one-port resonant in-liquid gravimetric SAW sensor suitable for integration with microfluidic systems. In this concept, a 100nm thick Au layer is simultaneously employed as sensing surface and waveguiding layer that promotes a significant enhancement of the mass sensitivity. The Au sensing layer is electrically decoupled from the interdigital transducer (IDT) by means of 0.188λ thick SiO2 layer sandwiched between the Au layer and the IDT, thus effectively screening the sensor from liquid conductivity and permittivity, while retaining the device electromechanical coupling. We designed, prototyped and tested a one-port 225MHz SAW resonator integrated with simple microfluidic system with projected mass sensitivity of 400 cm²/g. The device operates in liquid with retained Q factor of 170 and electromechanical coupling of 3.5%. Initial in-liqud sensitivity tests are further shown and discussed.