Michele Pirro’s PhD Dissertation Defense

“AlScN material characterization for MEMS applications”

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. 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.
I will discuss the advance in the process flow of high Sc-concentrations, showing the impact of the deposition parameters on the material properties with focus on the ferroelectric behavior. Effect of RF powers on the substrate and on the target are also analyzed, demonstrating the possibility to properly optimize the AlScN deposition. Last, I will present MEM devices which exploit the enhanced piezoelectric activity (high frequency resonators and pmut) and the ferroelectric properties (impedance with memory), confirming the potential of the material for new multi-functionalities MEMS.

Committee:

Prof. Matteo Rinaldi (Advisor)

Prof. Cristian Cassella

Prof. Siddhartha Ghosh