Regulating crystal structure and ferroelectricity in Sr doped HfO2 thin films fabricated by metallo-organic decomposition

Abstract

HfO2 based binary ferroelectric oxides are promising candidate for nonvolatile memory devices due to their compatibility with the current Si-based technology. In this work, Sr doped HfO2 (Sr:HfO2) ferroelectric thin films with Sr concentration from 0% to 10 mol% were prepared on the platinum electrodes by metallo-organic decomposition (MOD). It was demonstrated that uniform Sr:HfO2 thin films with extremely low roughness can be achieved and crystallized by MOD under a 700 °C annealing process. A wake-up stage was believed more essential for the ferroelectricity of the MOD derived Sr:HfO2 thin film, since the remnant polarization of 13.3 µC/cm2 and high dielectric constant of 30 were obtained after 105 cycling tests. The transformation from monoclinic phase to cubic phase was observed with increasing the Sr concentration and the thickness of the films. X-ray photoelectron spectroscopy analysis confirmed the bonding type of O-Hf-O and O-Sr-O bonds in the film. The microscopic crystal structure of ferroelectric orthorhombic phase was observed by high resolution transmission electronic microscope. The intrinsic ferroelectricity of Sr:HfO2 film was demonstrated by the hysteresis polarization-voltage loops and distinct current peaks in the current-voltage curve. Stable domain structure and its switching dynamics were monitored by piezoresponse force microscopy, indicating the native polarization of Sr:HfO2. This work will provide a controllable routine to fabricate ferroelectric HfO2 based thin films using MOD method.