ECE PhD Proposal Review: Michele Pirro

PhD Proposal Review: Scandium-doped Aluminum Nitride for new MEMS technologies

Michele Pirro

Location: 432 ISEC

Zoom Link Meeting ID: 938 0086 0379 https://northeastern.zoom.us/u/abZS2SmtT1

Abstract: The increasing demand for data is pushing the MEMS industry to more performant and area-efficient systems to be used in IOT nodes as sensors and RF-components. In this market, AlN plays a pivotal role thanks to the piezoelectric properties accompanied with good stability over power and temperature in miniaturized devices. In fact, AlN is already present in different commercial MEM systems, such as duplexers, ultrasound generators, energy harvesters and so on, proving a mature mass-production process flow. The required more stringent specifications in terms of bandwidth, losses and efficiency are pushing towards piezoelectric materials with higher coupling coefficient, but still in a compatible post-CMOS process flow. Luckily, recent works showed how it is possible to enhance the piezoelectric effect by doping AlN with Scandium, allowing up to 400% increase in the d33 piezoelectric coefficient. The enhanced acoustic transduction along with the recent demonstration of ferroelectric switching and the post-IC compatibility, is making Sc-doped AlN a new material with the potential not only to replace AlN, but also to integrate different functionalities within the same component. Academy and industry all over the world are actively researching the actual potential of the material but there is still a lack of information on high-Sc concentration, which would allow lower-voltage switching along with higher d33. This work has the main objective to show Sc-concentration > 28% and their piezo/ferroelectric response for a new class of microelectromechanical devices.
The proposal will discuss the advance in the process flow of high Sc- concentrations, showing the impact of the deposition parameters on the material properties. Thin films with good crystallinity on IC-substrate and enhanced d33 are reported, along with first attempts to resonator-devices. An in-depth ferroelectric characterization will show how coercive field and leakage current are the main limiting factors the material is facing to integrate its memory effect. For this purpose, the work will present how tuning of Sc-concentration, substrate-rf and bulk stress can ease these limiting factor, opening to new acoustic devices with memory functionalities. The last part will focus on the co-integration of acoustic properties with ferroelectric switching for tunable filters and ultrasonic generators in post-IC compatible substrates.