Multi-Frequency Thin Film HBAR Microsensor for Acoustic Impedance Sensing Over the GHz Range

Here we present a longitudinal bulk-acoustic-wave microsensor using the pulse-echo mode of operation to identify presence of liquid in microchannels by its compressional properties, with the particularity of sub-I-volt and multi-frequency operation in the 1 - 10 GHz range. The effect produced by the configuration of layers and materials constituting these bulk acoustic transducers was studied analytically and by FEM simulations, finding multiple transduction peaks throughout the operating range of the 0.5 µm AlN film (fr = 10.9 GHz). The expected peaks for the 1 - 2 GHz range were verified experimentally by feeding the transducers with short RF pulses of 5 dBm, achieving SNR up to 27 dB. Since the detection surface lacks electronics or wires, this device can be used to detect both conductive and non-conductive liquid in real time applications.