No-heating deposition of ferroelectric epitaxial Hf0.5Zr0.5O2 films using a sputtering method with precise RF power density and thickness control

The no-heating deposition of (111)-oriented epitaxial (Hf0.5Zr0.5)O2 films was successfully achieved on (111) indium tin oxide//(111) yttria-stabilized zirconia substrates using a radio-frequency (RF) magnetron sputtering method. As the RF power density was increased, the crystal phase changed sequentially from the tetragonal, the orthorhombic, and then to the monoclinic phase. A similar trend in the crystal phase was also observed with increasing film thickness. The (Hf0.5Zr0.5)O2 film exhibited ferroelectric properties comparable to the (Y0.07Hf0.93)O2 film previously produced via non-heating film deposition. Upon heat treatment at 1000 °C, the crystal phase of the film transitioned from the orthorhombic phase to the monoclinic phase, indicating that the stability of the orthorhombic phase is low compared with (Y0.07Hf0.93)O2. Therefore, precise control of the RF power density and film thickness is essential for preparing ferroelectric (Hf0.5Zr0.5)O2 films without heating.