Energy Harvesting for a Microscale Biosensing Device via Piezoelectric Micromachined Ultrasonic Transducers

Microdevices with dimensions comparable to a blood cell, i.e., tens of micrometers, show great potential for use in the human body. They can be adopted to identify the source of diseases, track their evolution and enhance the effectiveness of therapies, significantly improving patients’ quality of life. A key challenge is how to power the devices, which should ideally be performed wirelessly from a remote source. Piezoelectric micromachined ultrasonic transducers (pMUTs) offer a solution thanks to their ability to generate and collect energy via acoustic waves. In this work, numerical simulations of transmitter pMUT arrays are performed with the aim of generating an acoustic wave synchronized with a single pMUT or pMUT array receiver. The latter is intended for insertion in the human body. The characteristics required to switch on and power nano-electronics, in terms of generated voltage and electrical power at the receiver, are studied in ballistic gel, a material that mimics human organs. The focus is on a bio-compatible material for the piezoelectric layer, i.e., aluminum nitride enriched with scandium. Coupled electromechanical and acoustic simulations show that, of the considered pMUT devices, an 8 × 8 transmitter array combined with a single-device receiver (with a 50 µm pitch) or a 2 × 2 receiver array provide alternative options, with each offering advantages in terms of voltage amplitude or power at a steady state. The overall dimensions of the receiver, at a maximum of only 100 × 100 µm2, is compatible with a future proof-of-concept biosensing platform test chip.