Zhou Songsong, Rappe Andrew M
Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104-6323.
Proc Natl Acad Sci U S A. 2025 Jan 7;122(1):e2406316122. doi: 10.1073/pnas.2406316122. Epub 2024 Dec 31.
Ferroelectric hafnia exhibits promising robust polarization and silicon compatibility for ferroelectric devices. Unfortunately, it suffers from difficult polarization switching. Methods to enable easier polarization switching are needed, and the underlying reason for this switching difficulty is not understood. Here, we investigated the 180 domain walls of hafnia and their motion through nucleation. We found that the domains of multiple-order parameter hafnia possess complicated three-dimensional dipole patterns and lead to domain walls of different symmetry. The most common domain wall type is a complex domain wall involving reversal of both polarization and tetragonality order parameters. This domain wall symmetry ensures a good matching of the dipoles perpendicular to the domain wall, which leads to low domain wall energy. However, this ensures a sharp, high-energy, charged domain wall on the edges of nuclei that results in difficult nucleation. Thus, this domain wall is too stable to move, which explains the switching difficulty of hafnia. By contrast, another simple domain wall, involving only polarization reversal, has a poor matching of dipoles perpendicular to the domain wall. This leads to higher domain wall energy and ensures a diffusive and low-energy charged domain wall that enables easier nucleation. This simple domain wall is thus not too stable and easier to move. Our theory advances domain wall nucleation theory from the field of conventional single-order parameter to multiple-order parameters. We propose controlling the populations of different domain wall types in hafnia as a way to enable fast polarization switching and lower coercive fields.
铁电氧化铪在铁电器件方面展现出了有前景的稳健极化特性和与硅的兼容性。不幸的是，它存在极化切换困难的问题。需要找到能使极化切换更容易的方法，而这种切换困难的根本原因尚不清楚。在此，我们研究了氧化铪的180°畴壁及其通过成核的运动。我们发现，多序参量氧化铪的畴具有复杂的三维偶极模式，并导致不同对称性的畴壁。最常见的畴壁类型是一种涉及极化和四方度序参量反转的复杂畴壁。这种畴壁对称性确保了垂直于畴壁的偶极良好匹配，从而导致畴壁能量较低。然而，这也确保了在核边缘存在尖锐、高能且带电的畴壁，导致成核困难。因此，这种畴壁过于稳定而难以移动，这就解释了氧化铪的切换困难。相比之下，另一种仅涉及极化反转的简单畴壁，其垂直于畴壁的偶极匹配较差。这导致更高的畴壁能量，并确保了一种扩散性且低能量带电的畴壁，使得成核更容易。因此，这种简单畴壁不太稳定且更容易移动。我们的理论将畴壁成核理论从传统的单序参量领域推进到了多序参量领域。我们提出控制氧化铪中不同畴壁类型的数量，以此作为实现快速极化切换和降低矫顽场的一种方法。
