Wurtzite Solid Solutions as a New Material Class for Ferroelectric Microelectronics

• Applicants: Dr. 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

Since their discovery 100 years ago, ferroelectric materials are a center of scientific attention. The ability to switch their spontaneous polarization between several states using external electric fields makes them highly attractive for applications such as information storage, e.g. in the context of neuromorphic computing. Approaches that are based on ferroelectrics can surpass alternative technologies for instance due to their superior energy efficiency. In 2011, scientist at NaMLab could report on ferroelectricity in doped HfO2 for the first time, thereby reinvigorating the research field of ferroelectric materials. This development was spurred by several properties of HfO2 that could not be reached with previously available materials. For the same reason, the discovery of the first wurtzite ferroelectric AlScN at Kiel University promises to further accelerate the development of ferroelectric microelectronics. In this project, Kiel University and NaMLab now want to combine their internationally recognized competence in the field of emerging ferroelectric thin films.The core aim of this cooperation consists of advancing the fundamental and application driven research on ferroelectric wurtzites. Due to their potentially great impact on society and economy, memristors for neuromorphic computing are selected as the application goal. For this goal, AlScN could possess decisive advantages over other materials, due to properties like phase-purity and polarization stability.As a preparation towards the integration of AlScN into microelectronic devices, we aim to start this project by investigating its scaling behavior down to switching voltages of significantly below 10 V – by reducing the film thickness to less than 20 nm. To this end, we investigate atomic layer deposition as a particularly suitable technique for this thickness range. AlScN capacitors with compatibility to the major semiconductor technology platforms are subsequently investigated. The so developed thin films and capacitors will form the basis for further research towards ferroelectric transistor based memories and tunnel-barriers for neuromorphic electronics. To establish wurtzite ferroelectrics as an independent material class with the added benefit of developing a particularly suitable growth template for AlScN, we will research GaScN as a potential second wurtzite ferroelectric. In addition, further investigations that deal with fundamental aspects that are essential to the understanding of these new functional materials will be conducted. Among these aspects is the long term stability of their polarization alignment (retention), switching kinetics (i.e. domain nucleation and growth) as well as charge injection and their endurance with respect to the number of switching cycles. This project can significantly advance the development of ferroelectric microelectronics by researching a promising group of emerging ferroelectric materials.

• DFG Programme: Research Grants