Tuning ferroelectricity in HfO₂/CeO₂ heterostructures via epitaxy

Hf_0.5Zr_0.5O₂ (HZO) thin films have been shown to exhibit robust ferroelectricity when their thickness is reduced to the nanometer scale (1). The metastable ferroelectric orthorhombic phase of HZO can be stabilised by engineering epitaxial strain and tuning the concentration of oxygen vacancies within the film. Oxygen vacancies have therefore been shown to play a major role in the ferroelectric behaviour of HZO by linking oxygen exchange with ferroelectric switching (2). The exchange of oxygen vacancies can occur via an interface with another material, such as the common fluorite-structure oxygen-conductor Gd-doped CeO₂ (CGO). The use of a CeO₂ layer has been shown to improve the ferroelectric performance of HfO₂-based films (3).

In this work, we use pulsed laser deposition to deposit epitaxial CGO/HZO heterostructures on a single crystalline substrate. The heterostructures consist of highly coherent CGO and HZO layers with epitaxial lattice strain effects imposed at the interface. A study of the stabilization of orthorhombic HZO on CGO was conducted. The role of oxygen stoichiometry in the overall electromechanical properties of the heterostructure was also investigated. This result establishes the baseline for tuning the ferroelectric properties of HZO via oxygen defectivity interplay with CGO.

References

1. Müller, J. et al. Ferroelectricity in simple binary ZrO2 and HfO2. Nano Lett. 12, 4318–4323 (2012).

2. Nukala, P. et al. Reversible oxygen migration and phase transitions in hafnia-based ferroelectric devices. Science 372, 630–635 (2021).

3. Mizutani, K. et al. Cerium oxide capping on Y-doped HfO2 films for ferroelectric phase stabilisation with endurance improvement. Jpn. J. Appl. Phys. 61, 021006 (2022).