SPP 2477 - Subproject: Integrated acousto-NEMS on monolithic new-nitride thin films

Basic data for this project

Description

Aluminium transition metal nitride [(Al,TM)N] compounds pose enormous potential for a broad range of future technologies. Since its discovery in 2009, piezoelectrically enhanced (Al,Sc)N thin films have been intensively explored as new materials for surface-acoustic-wave (SAW) devices, high-electron-mobility transistors, and as ferroelectric layers. Despite considerable advances in the study of (Al,Sc)N and related SAW devices for application in 6G networks, multi-functional, integrated systems that can benefit from the enhanced piezoelectricity have been only scarcely explored compared to traditional SAW devices. Moreover, (Al,Sc)N remains dominant, while a broader range of uncharted (Al,TM)N offers potential advantages and deserves directed focus. Motivated by the unique combination of mechanical and piezoelectric properties in this class of materials, we propose a collaboration aimed at developing an integrated acousto-NEMS (nanoelectromechanical system) based on monolithic (Al,TM)N thin films. The objectives are: 1. Synthesis of new nitride compounds on Si and SiC substrates, elucidating composition-structure-property relationships in (Al,Hf)N and (Al,Zr)N predicted to have better wurtzite (piezoelectric) phase stability than (Al,Sc)N, and their utilization for GHz SAW generation. We combine expertise for thin film synthesis using both molecular beam epitaxy (MBE) and reactive co-sputtering. We will use sputtering to grow (Al,Hf/Zr)N and to determine the basic physical properties. This information will then inform MBE growth efforts, targeting specific composition spaces offering best properties for SAW. We aim to demonstrate effective electromechanical coupling exceeding 5% at 4-8 GHz for SAW and determine the critical TM content correlated to wurtzte-cubic transition. Established MBE growth of(Al,Sc)N will provide a materials basis and head-start for the following device-oriented goals. 2. Fabrication and characterization of integrated acousto-NEMS as phononic platforms focusing on mechanical resonances in the mK temperature regime, towards application as quantum links. The access to both sputtered and MBE films enables us to directly compare the mechanical Q-factors, generally linked to defect-mediated tunneling in two-level systems. Q-factors 100 times better than monolithic GaAs (Q<1000) platform is the target. 3. Investigation of transduction in (Al,TM)N-based acousto-NEMS devices, focusing on force-based sensing in harsh environments, supported by close interactions with our industrial partner Endress+Hauser. Wireless operation enabled by GHz-SAW excitation will also be tested. Here, our key target is to demonstrate pressure sensing above 500°C. The results will lay a solid foundations for broader impact, paving the path towards multifunctional materials, the coupling to other quantum systems, and sensor prototyping. The complementary expertise of the partners ensures a smooth integration of new material to functional devices.