Relative stabilities and physical parameters of rhombohedral distorted HfO 2 crystalline phases
Journal
Journal of Physics D: Applied Physics
Journal Volume
59
Journal Issue
2
Start Page
025117
ISSN
0022-3727
1361-6463
Date Issued
2026-01-16
Author(s)
Chen, Yun-Wen
Abstract
The discovery of wake-up-free phenomena in metal-ferroelectric-metal devices with (111)-oriented hafnium oxide (HfO2)-based ferroelectric thin films has prompted extensive investigations in recent years. The crystalline HfO2-based thin films were found to grow epitaxially and commonly suggested to be rhombohedral phases (R3m or R3). Several strategies were proposed to stabilize (111)-oriented HfO2-based thin films, including the use of hexagonal/trigonal substrates. Via theoretical modeling with density functional theory calculations, we study the in-plane strain effects on rhombohedral distorted HfO2 phases. The analysis of phase stabilities, polarizations, and lattice parameters strongly suggests that the rhombohedral distorted orthorhombic phase should be the origin of ferroelectricity in (111)-oriented HfO2-based thin films instead of the rhombohedral phases. Small compressive in-plane strain could enhance the ferroelectricity; however, both high compressive and tensile strain will result in zero remanent polarization because of the instability of the orthorhombic phase under high rhombohedral distortion. The window for the hexagonal/trigonal in-plane lattice constant for fabricating ferroelectric (111)-oriented HfO2-based thin films ranges from 7.06 to 7.51 Å. In further comparison with experimental observations on strained (111)-oriented hafnium zirconium oxide films, our results agree well with the trends in orthorhombic phase content and d111 with respect to the in-plane lattice constant.
Subjects
density functional theory
ferroelectricity
hafnium oxide
phase stability
strain effect
Publisher
IOP Publishing
Type
journal article