Stable orthorhombic ferroelectric Hf0.5Zr0.5O2 films with platinum seed electrodes grown by sputtering

High quality ferroelectric Hf0.5Zr0.5O2 films are crucial for next generation nanoelectronics. However, the growth of large-sized stable ferroelectric Hf0.5Zr0.5O2 films is challenging. Here, we demonstrate the synthesis of large-sized stable orthorhombic ferroelectric Hf0.5Zr0.5O2 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 Hf0.5Zr0.5O2 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 Hf0.5Zr0.5O2 on MgO and sapphire substrates with Pt seed layers, characterized by XRD, scanning TEM, and selective area diffraction. The Hf0.5Zr0.5O2 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 Hf0.5Zr0.5O2 films.