News: Microelectronics
21 October 2025
University of Michigan develops first PEALD-grown ScAlN thin film layers on 3D surfaces
The first demonstration of scandium aluminium nitride (ScAlN) thin films grown by plasma-enhanced atomic layer deposition PEALD expands application to complex 3D structures, according to a University of Michigan study published in Applied Physics Letters and funded partly by the Army Research Office (W911NF-24-2-0210).
Conventional methods — such as sputtering and epitaxy — can only layer ScAlN on flat surfaces, limiting application as most devices have complex geometries. The new method allows precise control over ScAlN thickness, scandium content and uniformity at lower processing temperatures.
“This approach makes high-performance ScAlN more accessible to research labs and paves the way for integrating it into advanced devices that were previously out of reach,” says Md Mehedi Hasan Tanim, a doctoral student of electrical and computer engineering and lead author of the study.
Picture: Zetian Mi (left), the Pallab K. Bhattacharya Collegiate Professor of Engineering at U-M, and Md. Mehedi Hasan Tanim (right), a doctoral student of electrical and computer engineering. (Photo courtesy of Jero Lopera, Michigan Engineering).
ScAlN’s piezoelectric ability to generate electricity when mechanically stressed has been investigated for use in wearable energy harvesters capable of converting mechanical motion, such as walking or body movement, into usable electrical power.
As an ultrawide-bandgap material, ScAlN can also improve high-power devices like electric vehicle EV power converters, as it can handle high voltages without breaking down. High-frequency devices, like filters or amplifiers for future 5G or 6G cell phones, can also leverage ScAlN’s superior piezoelectric and acoustic properties — as well as high current handling capability, which allows better signal quality and higher data rates.
But, despite the worldwide interest in ScAlN, it has remained unknown if it can be grown or synthesized using plasma-enhanced atomic layer deposition.
To create ScAlN thin films, researchers use a supercycle growth approach — fine tuning the timing and ratio of aluminium nitride (AlN) and scandium nitride (ScN) layers — within a temperature range of 225–250°C.
“Each pass lays down an ultrathin, self-limiting coat and, by repeating the process, we achieve a precise, uniform film,” says the study’s corresponding author Zetian Mi, the Pallab K. Bhattacharya Collegiate Professor of Engineering at the University of Michigan, who is also a professor of electrical & computer engineering and materials science & engineering at U-M.
Thin films were grown on a gallium nitride/sapphire substrate — well-suited for high-power, high-frequency or piezoelectric devices. Electron microscopy confirmed that the new method allows precise control of scandium composition (0–25%) while maintaining atomically smooth surfaces.
Further, each element was evenly mixed rather than clumped, and there were few defects at the boundary between the thin film and substrate. Both properties ensure the ease of integration into existing gallium nitride devices.
Piezoelectric strength in ScAlN grown with PEALD matched those produced with conventional sputtering or epitaxy, proving that piezoelectric properties persist even when layered in different geometries.
“Going forward, we plan to explore integrating ALD-grown ScAlN into device prototypes to leverage its unique material properties and scalable processing,” says Mi.
The technique was developed in the Lurie Nanofabrication Facility and studied at the Michigan Center for Materials Characterization, both of which are operated and maintained with support from indirect cost allocations in federal grants.
DARPA awards University of Michigan’s Zetian Mi $3m to scale III–V materials on silicon