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

CMOS-compatible HfO ₂ -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 HfO ₂ -based (Lu:Hf _0.6 Zr _0.4 O ₂ ) 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 E _{u phonon 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.}