Preparation and characterization of ferroelectric Hf_0.5Zr_0.5O₂ thin films grown by reactive sputtering

HfO₂-ZrO₂ solid-solution films were prepared by radio frequency sputtering, and the subsequent annealing process was optimized to render enhanced ferroelectric behavior. The target power, working pressure and O₂ partial pressure ratios were varied, along with the annealing gas, time and temperature. Then, the film's structural and electrical properties were carefully scrutinized. Oxygen-deficient conditions were necessary during the sputter deposition to suppress grain growth, while annealing by O₂ gas was critical to avoid defects and leakage problems. It is expected that the grain size difference under various deposition conditions combined with the degree of TiN top and bottom electrode oxidation by O₂ gas will result in different ferroelectric behaviors. As a result, Hf_0.5Zr_0.5O₂ prepared by radio frequency sputtering showed optimized ferroelectricity at 0% of O₂ reactive gas, with a doubled remnant polarization value of ∼20 μC cm^-2 at a thickness of 11 nm. Film growth conditions with a high growth rate (4-5 nm min^-1) were favorable for achieving the ferroelectric phase film, which feasibly suppressed both the grain growth and accompanying monoclinic phase formation.