Strain Engineering Boosts Piezo-/Ferroelectricity in AlScN Alloy: Insights from First-Principles Calculations

AlScN is a highly promising novel ferroelectric material featuring excellent high-temperature stability and CMOS compatibility, making it a potential candidate for 5G RF front-end filters, next-generation power devices, memories, and emerging in-memory computing devices. However, the rather mediocre piezoelectric coefficient and relatively large coercive field remain critical bottlenecks for its widespread adoption in applications. To provide theoretical guidance and effective strategies for optimizing the AlScN performance, we propose a synergistic regulation strategy based on alloying and strain engineering and conduct first-principles calculations using density functional theory to investigate the effects of Sc concentration and epitaxial tensile strain on the properties of AlScN. The proposed strategy is found to effectively enhance the piezoelectric strain coefficient (d33 > 300 pC·N–1) and electromechanical coupling coefficient (k332 ∼ 55%) of AlScN, and reduce its coercive field (EC), while maintaining a large polarization (Psp > 68 μC·cm–2). The substantial increase in d33 and k332 is highly beneficial for optimizing the performance of bulk acoustic wave resonators for signal processing in RF applications. Meanwhile, the reduction in EC provides new opportunities for low-power ferroelectric memory devices, such as ferroelectric random-access memory and in-memory computing synaptic devices. The weakened bond strength and enhanced Born effective charge are found to be crucial in these performance optimizations. Furthermore, we examine the high-temperature stability of strain-engineered AlN-based piezo-/ferroelectric materials through ab initio molecular dynamics simulations. This work not only provides an effective strategy and valuable insights for physical property optimization in AlScN from the theoretical point of view but also clarifies the mechanisms of enhanced piezo-/ferroelectricity in wurtzite alloy systems by application of epitaxial strain and chemical modification.