2025/02/12 by Seongjoo Jung, Jung, Seongjoo, Turan Birol +1 · 2 citations
Engineering · #Advancements in Semiconductor Devices and Circuit Design #FOS: Physical sciences #Ferroelectric and Negative Capacitance Devices #Materials Science (cond-mat.mtrl-sci) #Semiconductor materials and devices
paper · pdf · doi:10.48550/arxiv.2502.08633
openalex publication_date 2025/02/12 · openalex created_date 2025/02/15 · openalex updated_date 2026/07/29
Ferroelectric HfO2 has emerged as a highly promising material for high-density nonvolatile memory and nanoscale transistor applications. However, the uncertain origin of polarization in HfO2 limits our ability to fully understand and control its ferroelectricity. Ferroelectricity, the emergence of a spontaneous and switchable polarization in solids, is conventionally understood to be governed by unstable structural modes (phonons), arising either directly from an unstable polar phonon or indirectly through coupling of unstable nonpolar phonons with a polar mode. While these 'proper' and 'improper' mechanisms successfully explain ferroelectricity for most systems, they do not encompass all possible phenomena. Here, we present a novel mechanism of 'hybrid-triggered' ferroelectricity, where a polar order emerges through trilinear coupling without any structural instabilities. Our group theoretical analysis starting from a high-symmetry reference structure shows that this mechanism is realized in intensely-debated ferroelectric HfO2, along with quantitative confirmation from first-principles calculations. We also show that dynamical charges in this material are highly unconventional, and a significant contribution to the total polarization arises solely from high-order couplings of nonpolar phonons. These findings underline that even simple crystal structures can host surprisingly complicated interplay between different structural orders, elucidate the origin of ferroelectricity and antiferroelectricity in fluorite-related structures, and provide foundational understanding for designing superior ferroelectric materials.