Bernard Herrera-Soukup PhD Dissertation Defense

“Ferroelectric Micro-machined Ultrasonic Transducers for Biomedical and Processing In-Sensor Applications”

Abstract:

Piezoelectric Micromachined Ultrasonic Transducers (PMUTs) are Micro Electro-Mechanical Systems (MEMS) devices that have become an established technology in applications such as range-finding, fingerprint sensing and imaging due to their capability of ultrasonic transduction in a miniaturized footprint, easily amenable to create large arrays. However, their application space still remains quite open. PMUTs are well fitted to applications in liquid media, such as implantable and underwater devices, due to their inherent acoustic matching and wide bandwidth. Thus, in the first part of the dissertationl, we explore novel applications such as PMUT-based intra-body and underwater networking, power transfer, source localization, wide-band matching and duplexing.

Aluminum Nitride (AlN) has been the material of choice for our PMUTs due to its biocompatibility and possibility of single-chip integration with supporting CMOS circuitry. Scandium doping of AlN thin films has recently been demonstrated to increase piezoelectric coupling coefficients while introducing ferroelectric properties in the material. However, a simultaneous use of both capabilities has not been demonstrated in the state-of-the-art. The ability of having distinct ferroelectric states, that alter the mechanical performance of the devices, allows for Processing-In-Sensor features and provides the building blocks for neuromorphic signal processing capabilities. The second part of the dissertation explores the AlScN material integration into novel Ferroelectric Micromachined Ultrasonic Transducers (FMUTs) and their emerging application space.

Committee:

Prof. Matteo Rinaldi (Advisor)
Prof. Tommaso Melodia
Prof. Cristian Cassella