Piezoelectric micromachined ultrasonic transducers with increased coupling coefficient via series transduction

This work demonstrates a new electrode configuration for piezoelectric micromachined ultrasonic transducers (PMUTs) with increased electromechanical coupling coefficient (k_t²). The electrodes, a center electrode surrounded by a ring electrode, are identical to those used in differential PMUTs. Unlike a differential PMUT, where the two top electrodes (TEs) are referenced to a common ground electrode, here only the two TEs are used, effectively putting the two piezoelectric transducers in series. The benefit of series readout is that the transducer´s electrical capacitance is halved, doubling the receive sensitivity and electromechanical coupling coefficient k_t².