Synthesis of epitaxial ferroelectric (Hf,Zr)O2 thin films with ultra-smooth surface

Abstract

In many years of research on hafnium dioxide (HfO2), stabilization of its ferroelectric phase was such a challenging issue in field of the thin film physics. HfO2 is often believed that it could be the candidate of unconventional ferroelectricity; which is frequently referred as “improper ferroelectricity”. It still maintains polarization with the thickness-free property in contrast to conventional ferroelectric materials; such as BaTiO3, PbTiO3. Because the downsizing of the circuit system is important topic for application, thickness-free property is quite fascinate and prospect. By fabricating ferroelectric hafnia sample at proper conditions and with impurity dopants (Zr; zirconium), ferroelectricity can be revealed by orthorhombic distortion (structural transition). However, improper ferroelectricity of hafnia was mostly dealt with theoretical calculations. Against to those prospect anticipations, there were no evident experimental proof for improper ferroelectricity though the ferroelectricity phase has been repeatedly observed. Mainly on recent experimental papers, I concluded that there were no accuracy for thickness measurement. In this thesis, the step-terrace formed surface image would convince accuracy for the thickness of hafnia sample, which can precisely count the definite number of layer. Controlling the layer of deposited hafnia thin film may close to the verification for improper ferroelectric. Furthermore, this verification could front for future applications for ferroelectric devices.