| With the rapid development of science and technology,electronic devices have gradually developed in the direction of miniaturization,integration and multi-function.Ferroelectric thin films have become a research hotspot of functional materials due to their excellent dielectric,piezoelectric,ferroelectric,and pyroelectric properties.The epitaxial film induced on the single crystal substrate not only has higher performance than the polycrystalline film,but also helps to study the basic characteristics of the material.Therefore,the preparation and research of the epitaxial ferroelectric film has received extensive attention.Bismuth sodium titanate(Bi0.5Na0.5TiO3,BNT)is widely used in the fields of mechanical and electronic precision control due to its strong ferroelectricity,high Curie temperature,low dielectric constant,and large piezoelectric coefficient.Lanthanum nickelate（LaNiO3,LNO）is a conductive metal oxide with a pseudo-cubic perovskite structure.It is used as an electrode material in the field of ferroelectric film capacitors due to its excellent conductivity and lattice constant that match ferroelectric materials.And the oriented growth of LNO can induce the oriented growth of ferroelectric films.The use of radio frequency magnetron sputtering（MS）,pulsed laser deposition（PLD）and other physical methods can easily obtain epitaxial films,but expensive equipment and complex processes limit its further development.The chemical method has the advantages of low cost,simple process equipment,uniform and easy control of chemical composition,and large-area preparation,which has become another choice for the preparation of oriented films.In this work,BNT is selected as the ferroelectric layer and LNO is selected as the electrode layer.A series of research work has been carried out on the preparation of BNT/LNO epitaxial films by chemical solution deposition.The LNO epitaxial conductive film was prepared by two different chemical methods,and its structure,morphology and electrical properties were studied.Then the LNO epitaxial conductive film was used as the bottom electrode.The BNT epitaxial film was prepared on the LNO,and the ferroelectric and dielectric properties of the BNT film under different orientations were explored.The main research content and research results are as follows:（1）Preparation of LNO epitaxial film by chemical solution deposition（CSD）:Selecting lanthanum nitrate,nickel acetate and 2-methoxyethanol as solute and solvent system,rapid heat treatment process of 150℃drying,450℃pyrolysis and700℃annealing were carried out to deposite LNO film.Then the LNO epitaxial films with different orientations were successfully prepared and the FWHM values of the rocking curve are 1.1°,0.42°and 0.57°respectively.The resistivity at room temperature is 0.64×10-3Ω·cm,0.63×10-3Ω·cm,0.58×10-3Ω·cm respectively,indicating that the LNO epitaxial film prepared by CSD has good crystallinity and conductivity.（2）Preparation of LNO epitaxial films by polymer assisted deposition（PAD）:The FWHM values of the rocking curve of LNO epitaxial films with different orientations are 0.38°,0.37°and 0.64°respectively.The resistivity at room temperature is 0.16×10-3Ω·cm,0.25×10-3Ω·cm,0.25×10-3Ω·cm respectively,indicating that the LNO epitaxial film prepared by PAD has good crystallinity and conductivity,which broadens the chemical preparation of LNO epitaxial film.（3）Preparation of BNT/LNO epitaxial films by chemical solution deposition（CSD）:The FWHM values of the rocking curve of BNT films with different orientations are 0.282°,0.435°and 0.395°respectively,indicating that it has high out-of-plane orientation.The surface roughness（1μm×1μm）of BNT films with different orientations are 0.267 nm,0.236 nm and 0.363 nm respectively,indicating that it has smooth surface.Compared with the other two orientations,the（001）oriented BNT/LNO film has the best ferroelectricity,and it has the largest polarization(Pmax=41.9μC/cm2@600 kV/cm),the largest remanent polarization（2Pr=25.92μC/cm2@600 kV/cm）and minimum coercive electric field（Ec=115 kV/cm@600kV/cm）.And it has the best room temperature dielectric performance.When the test frequency is 100 Hz,the dielectric constant is 570 and the dielectric loss is 0.022.The leakage current density of BNT films with different orientations is on the order of 10-5A/cm2（@215 kV/cm）. |
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