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AlN-based HBAR ultrasonic sensor for fluid detection in microchannels with multi-frequency operation capability over the GHz range

Current bulk acoustic microresonators offer improved resolution respect to Quartz Crystal Microbalance and Surface Acoustic Wave devices, but tend to be brittle during operation as sensors or requires multiple precisely controlled deposition steps. Here we present an acoustic microsensor to identify presence of liquid in microchannels, which is mechanically robust and simpler to manufacture. Its electrical response was studied analytically and by FEM simulations, finding multi-frequency operating capabilities in the 1–10 GHz range. The detection principle was experimentally verified by S11 measurements. Results are consistent against theoretical and numerical predictions. Since the detection surface lacks electronics or wires, this resonator can be used to detect both conductive and non-conductive liquid samples in real time applications.