RING-SHAPED PIEZOELECTRIC MICROMACHINED ULTRASONIC TRANSDUCERS (PMUT) WITH INCREASED PRESSURE GENERATION

As the application space of piezoelectric micromachined ultrasonic transducers (pMUT) expands and enters the industrial realm, it is necessary to continue improving the performance of individual devices, two of the most important metrics of which are generated acoustic pressure magnitude and directivity. Here, we present the first ring-shaped pMUT (r-pMUT), which have been fabricated using CMOS-compatible aluminum nitride (AlN) as both the transduction and elastic material. The r-pMUT exhibit newfound design freedom compared to standard circular pMUT (cpMUT), as their resonance frequency is found to be insensitive to mean radius r0. The frequency responses of fabricated devices were measured and shown to match well with finite element model (FEM) simulations. By comparing rand c-pMUT designed to operate at 1.5 MHz with the same film stack, we show that rpMUT are capable of generating over 11.8× the pressure and with over 9× the directionality of their circular counterpart. As such, this device architecture could allow for highly efficient pMUT in applications that benefit from high pressures and directionality, such as rangefinding, fingerprint scanning, and therapeutics.