Wurtzite Solid Solutions as a New Material Class for Ferroelectric Microelectronics 2 (WUMM 2)

• Applicants: Dr.-Ing. Simon Fichtner; Professor Dr.-Ing. Thomas Mikolajick
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 458372836

The stability of the ferroelectric properties beyond 1000°C in wurtzite-structured aluminum scandium nitride (Al1-xScxN), combined with the intrinsic radiation hardness of the ferroelectric switching process, places novel nitride ferroelectrics at the forefront for developing the next generation of non-volatile memory technologies operating in the harshest environments. Integrating Al1-xScxN with the promising properties of GaN, such as wide band gap and strong Ga-N bonds, leads to the vision of an all-nitride semiconductor memory platform that can overcome the intrinsic limits of Si-based technologies for high-temperature and radiation-tolerant applications. Therefore, the joint project WUMM2 between Christian-Albrechts-Universität zu Kiel (CAU) and NaMLab gGmbH (NaMLab) aims to harness the natural chemical and structural compatibility of Al1-xScxN with GaN for developing fully nitride-based non-volatile memories that operate in extreme environments. Two integration approaches will be evaluated and compared during the project. CAU will lead the optimization of metal/Al1-xScxN/GaN heterostructures aiming for good epitaxial quality. NaMLab will lead the development of metal/Al1-xScxN/metal/GaN heterostructures, which benefit from more flexible electrical boundary conditions. Three optimization phases are planned within the project to identify the optimal Sc-content and thickness of the ferroelectric film, electrode material, and interface layer properties for operating in harsh environments. Each optimization phase will involve fabricating micrometer and sub-micrometer laterally scaled devices and their structural and electrical characterization performed in state-of-the-art cleanrooms and research facilities. In particular, a comprehensive set of experimental techniques, from impedance spectroscopy to scanning transmission electron microscopy, will be used to investigate possible environment- and operation-induced degradations, such as those caused by exposure to high temperatures and field- and radiation-induced charging effects. In-depth scientific understanding will be correlated with the electrical performance of the devices to demonstrate the feasibility of all-nitride ferroelectric memories with unprecedented long-term data retention in harsh environments. Combining the complementary expertise of CAU and NaMLab on nitride ferroelectrics as well as on ferroelectrics and memory devices in general, the WUMM2 project thus aims to demonstrate one of the most promising emerging applications for Al1-xScxN while simultaneously promoting knowledge transfer among young researchers in the field of materials science, electrical engineering, and nanoelectronics.

• DFG Programme: Research Grants
• Co-Investigator: Dr. Uwe Schröder