Improved Electromechanical Transduction for PiezoMUMPS HBAR Impedance Sensors

This study discloses how the distribution of the effective electromechanical coupling in the modes of our HBAR ultrasonic sensors at GHz range is significantly affected by the configuration of layers and materials used for its manufacture. Using analytical models from the literature supported by FEM simulations, frequency bands with greater coupling were found due to the effect of extra materials on the stack. S11 measurement of the devices proved this effect. The foregoing is a glance of how to increase the effective coupling in HBAR modes far distant from the resonance frequency of the piezoelectric element while preserving the high bandwidth and low input impedance inherent to the thin piezoelectric layer, in contrast to the relatively low coupling that can be expected with a similar HBAR of negligible electrodes at such frequencies.