Sublayer thickness dependence of nanolaminated HfO2–Al2O3 films for ferroelectric phase stabilization

Abstract

In this study, to understand the effect of sublayer thickness of doped HfO2 films with limited dopant solubility on ferroelectric phase stabilization, nanolaminated HfO2–Al2O3 films with various sublayer thicknesses were prepared through atomic layer deposition (ALD), and the phase evolution behavior of these films with increasing post-metallization annealing (PMA) temperature was investigated. A narrow optimal range of the HfO2 sublayer thickness was required to achieve facile crystallization into a tetragonal phase, followed by orthorhombic phase transformation through sufficient Al diffusion. Because the Al2O3 sublayer cannot be completely dissolved, it should be as thin as possible so that it can easily agglomerate to provide an effective connection between the HfO2 sublayers during the PMA process. When stabilizing the ferroelectric phase of HfO2 films by mixing with dopants with limited solubility, the thicknesses of the HfO2 and Al2O3 sublayers in the nanolaminated form were revealed to be more critical than the nominal doping concentration inferred from their thickness ratios (ALD cycle ratios).

Combined effects of the deposition temperature and metal electrodes on ferroelectric properties of atomic-layer-deposited Hf0.5Zr0.5O2 films

“…When the o(111)/t(011) diffraction peaks are positioned in the higher and lower 2θ regions, the HZO films exhibit antiferroelectric-and ferroelectric-like polarization characteristics, respectively. Furthermore, the aspect ratios of the unit cells calculated using the measured positions of diffraction peaks [28,29] in figure S4 also reflect the possible phase change with increasing T dep . Therefore, the relative position of the o(111)/t(011) diffraction peak can be a good indicator for evaluating the predominant phase in the polycrystalline HZO films [30].…”

The Doping Effect on the Intrinsic Ferroelectricity in Hafnium Oxide-Based Nano-Ferroelectric Devices

“…However, they require capping layer stress to stabilize the o-phase, which leads to high manufacturing cost and complicated processes . In Al-doped HfO 2 (HfAlO) thin films, the small atomic radius of Al exerts mechanical stress in HfO 2 unit cells, which stabilizes the o-phase. , Lee et al demonstrated that the ferroelectric phase of HfO 2 films was stabilized by doping aluminum, which has limited solubility, and the aluminum doping concentration significantly influenced the ferroelectricity of the HfO 2 thin films . Celano et al.…”

“…11,12 Lee et al demonstrated that the ferroelectric phase of HfO 2 films was stabilized by doping aluminum, which has limited solubility, and the aluminum doping concentration significantly influenced the ferroelectricity of the HfO 2 thin films. 13 Celano et al used the flexoelectric effect in HfAlO for inducing polar rotations in HfO 2 thin films by applying an external stress. 14 Thus, it is crucial to investigate the influence of aluminum content on the ferroelectricity of HfO 2 devices.…”