Multilayer SAW device for flow rate sensing in a microfluidic channel

This paper presents a novel microfluidic flow rate sensor based on surface acoustic wave (SAW) principle and aluminum nitride (AlN) film on silicon substrate. The working principles of this proposed SAW device are velocity decay, delay time as well as insertion losses reported in cases of linear and exponential motion. It utilizes CMOS compatible materials, AlN film on Si substrate, being suitable for inexpensive and reliable systems. AlN thin film layer is deposited on the top of silicon substrate. The microfluidic channel is etched through wafer and perpendicular to the SAW propagation path between the transmitter IDT and receiver IDT. Electrical and mechanical characteristic analysis is performed to accurately determine the relation between flow motion and output signal. Velocity decay constant decreases and achieves the saturated state from -1 dB to -4.5 dB after 60 mm/s for the linear motion. Otherwise, velocity decay constant is inversely proportional to the exponential order of velocity due to the leaky acoustic wave in the microfluidic channel.