Integrated acousto-NEMS on monolithic new-nitride thin films

Transition metal-doped aluminium nitride [(Al,TM)N] compounds combine exceptional mechanical and piezoelectric properties, offering enormous potential for a broad range of emerging technologies. Since the discovery of piezoelectrically enhanced (Al,Sc)N thin films in 2009, such materials have been intensely studied for applications including surface acoustic wave (SAW) devices, high-electron-mobility transistors (HEMTs), and ferroelectric layers. Despite significant progress, research on multifunctional, integrated acoustic systems that fully exploit enhanced piezoelectricity remains limited compared to traditional SAW devices. Moreover, while (Al,Sc)N has dominated the field, a broader class of transition metal dopants promises additional advantages and deserves focused investigation.

This interdisciplinary project aims to develop integrated acoustic nanoelectromechanical systems (acousto-NEMS) based on monolithic (Al,TM)N thin films. The goals are threefold:

1. Synthesis and characterization of new nitride compounds:
   The project will grow (Al,Hf)N and (Al,Zr)N layers on silicon (Si) and silicon carbide (SiC) substrates, combining expertise in molecular beam epitaxy (MBE) and reactive co-sputtering. Initial sputtered films will be used to determine fundamental physical properties, guiding subsequent MBE growth toward compositions optimized for GHz SAW generation. The team aims to demonstrate effective electromechanical coupling exceeding 5 % in the 4–8 GHz range and to identify the critical transition metal content related to wurtzite-to-cubic phase transitions.
2. Fabrication and phononic characterization of integrated acousto-NEMS:
   Building on the synthesized films, advanced nanofabrication and characterization will produce acousto-NEMS as phononic platforms with a focus on mechanical resonances at millikelvin temperatures. These studies will assess mechanical quality (Q) factors, which are critical for coupling to quantum systems and exceed targets by more than two orders of magnitude compared to traditional GaAs platforms. Gepris
3. Application-oriented transduction and sensing in harsh environments:
   Supported by the industrial partner Endress+Hauser, the project will investigate SAW-enabled wireless transduction mechanisms in (Al,TM)N-based devices, with an emphasis on force-based and high-temperature pressure sensing above 500 °C. Demonstration of robust performance under extreme conditions will advance sensor prototyping and broaden the impact of multifunctional materials.

The complementary expertise of the project partners ensures seamless integration of novel materials into functional devices. Outcomes will lay a solid foundation for coupling diverse quantum systems, expanding the utility of phononic platforms, and developing next-generation sensor technologies.

Funded within the framework of DFG Priority Programme SPP 2477 “Nitrides4Future – Novel Materials and Device Concepts”, with Project Number 563184308.