Study On Epitaxial Y-doped HfO₂ Ferroelectric Thin Films

Hafnium oxide（HfO₂）is a gate oxide material in CMOS processes.In 2011,researchers observed ferroelectricity in Si-doped HfO₂ thin films for the first time,which triggered an upsurge of research on Hf-based ferroelectric thin films.Compared with traditional ferroelectric materials,HfO₂ ferroelectric thin films have several advantages:the material system is compatible with CMOS technology,and can realize large-scale integration;thin thickness,low driving voltage,and outstanding miniaturization ability;high remnant polarization.The above advantages make this material a good prospect in application scenarios such as microelectromechanical systems,ferroelectric memories,and energy storage systems.However,the research on the structure-property relationship of HfO₂ thin films has not been developed so far.One of the outstanding problems is that most of the HfO₂ thin films reported in the current literature have a polycrystalline structure.The random orientation of the crystals and the parasitic secondary phase hinder the further characterization of the thin films and the understanding of the relationship between structure and performance.Therefore,it is necessary to study the growth of epitaxial HfO₂ferroelectric thin films.method to study the relationship between the structure of the material and the ferroelectric properties.In view of the above problems,this thesis carried out the epitaxial Y-doped HfO₂（YHO）ferroelectric thin film research.Using the pulsed laser deposition method,the YHO ferroelectric film growth method with lanthanum strontium manganese oxide(La_0.7Sr_0.3Mn O₃,LSMO)as the buffer layer was developed,and the epitaxial YHO film on the strontium titanate（Sr Ti O₃,STO）substrate was developed;The effects of epitaxial YHO ferroelectric film growth process on its crystal structure,orientation and ferroelectricity were characterized.It provides a material basis for the development of ferroelectric devices based on epitaxial YHO thin films.The third chapter mainly introduces the influence of laser energy and growth oxygen pressure on the structure and properties of the buffer layer LSMO,and clarifies the growth oxygen pressure on the conductivity of the buffer layer LSMO and the influence of laser energy on its surface roughness.Increasing the conductivity of LSMO helps to improve the surface roughness of the film.It is found that when the laser energy is 55 m J and the growth oxygen pressure is 30 Pa,LSMO with excellent crystal quality and good conductivity can be obtained.film.The fourth chapter mainly introduces the influence of the growth process on the structure and ferroelectric properties of the epitaxial YHO ferroelectric film,and analyzes the effects of laser energy,Y doping concentration,growth temperature and growth oxygen pressure on the film in detail,and analyzes the orthorhombic（111）orientation and orthorhombic（111）/（002）double orientation epitaxial YHO ferroelectric thin film epitaxy relationship and ferroelectric properties,It is found that increasing the oxygen pressure during cooling can effectively enhance the ferroelectricity of the film.When the oxygen pressure during cooling is increased to 1.6x10⁴ Pa,2P_r is close to 45μC/cm².