Beyond morphotropic phase boundaries: Atomic-scale mechanism unlocks thermal-stable high-κ performance in HfO2 via coherent interfaces

Abstract CMOS-compatible HfO₂-based high-κ dielectrics are pivotal for next-generation electronics in the post-Moore’s Law era. However, establishing coherent interfaces via morphotropic phase boundaries (MPBs) across the tetragonal (t) and orthorhombic (ferroelectric, o-FE or antiferroelectric, o-AFE) phases—a key strategy for enhancing dielectric properties—remains challenging due to unclear atomic-scale mechanisms and inherent thermal instability, which compromises long-term stability and reliability. To address this, we leverage metallurgical quenching principles to stabilize t/o-AFE MPBs in HfO₂-based (Lu:Hf0.6Zr0.4O₂) bulk crystals. Through precise composition tuning and growth optimization, we stabilize these metastable t/o-AFE MPBs at the t/t+o-AFE interface at room temperature, achieving a comparable κ-value (57) to actively studied t/o-FE MPBs. Microstructural characterization reveals how tensile strain within the t-phase drives dielectric enhancement through softening of the low-frequency Euphonon mode. Critically, the t/o-AFE MPB demonstrates a ~58% reduction in κ variation rate over 30–200°C relative to t/o-FE MPBs, signifying superior thermal stability. Our study establishes a generalizable design paradigm for developing high-κ dielectrics in fluorite-structured materials, advancing next-generation CMOS-integrated functional devices for data storage, energy harvesting, sensing, and integrated photonics.