Stable orthorhombic ferroelectric Hf_0.5Zr_0.5O₂ films with platinum seed electrodes grown by sputtering

High quality ferroelectric Hf_0.5Zr_0.5O₂ films are crucial for next generation nanoelectronics. However, the growth of large-sized stable ferroelectric Hf_0.5Zr_0.5O₂ films is challenging. Here, we demonstrate the synthesis of large-sized stable orthorhombic ferroelectric Hf_0.5Zr_0.5O₂ thin films through the use of a (111)-oriented platinum electrode acting as a seed template. Pt(111) is chosen as a seed layer to grow HfO₂ and Hf_0.5Zr_0.5O₂ layers on top of it using physical vapor deposition. High-quality monoclinic HfO₂ is obtained and verified by X-ray diffraction (XRD) and transmission electron microscopy (TEM). We further obtained orthorhombic phase Hf_0.5Zr_0.5O₂ on MgO and sapphire substrates with Pt seed layers, characterized by XRD, scanning TEM, and selective area diffraction. The Hf_0.5Zr_0.5O₂ thin films show robust and switchable ferroelectric polarization. Thermodynamic analyses reveal the role of nucleation and surface energy in stabilizing the polar orthorhombic phase and the non-polar-monoclinic phase along different directions. The strain due to the lattice and thermal expansion coefficient mismatch is crucial for stabilizing the stable orthorhombic ferroelectric Hf_0.5Zr_0.5O₂ films.