Research On High Dielectric Tunability Of BST Ferroelectric Films

Barium strontium titanate（BST）is a common ferroelectric material,which has excellent dielectric,ferroelectric and piezoelectric properties,so it is widely used in filters,phase shifters and other fields.In recent years,electronic components are developing towards miniaturization and lightweight,so it is of great significance to study barium strontium titanate thin film materials.Ferroelectric-semiconductor heterostructures,as strong competitors of traditional Si based metal-ferroelectric-insulator-metal-semiconductor（MFMIS）structures,have been widely used in modern integrated ferroelectric appliances.In this paper,the design of the structure and the fabrication of the films were studied by software simulation and thin film preparation experiment.In the simulation parts,Materials Studio software is used to conduct first-principle analysis of BST ferroelectric Materials,including material properties and interlayer interface bonding.Six ordered Ba_（1-x）Sr _xTi O₃（x=0,0.2,0.4,0.6,0.8,1）have been studied in detail by first-principles method based on density functional theory,including lattice constant analysis,state density and energy band analysis and charge density analysis.Three kinds of BST/Si,BST/Li Nb O₃ and BST/Al₂O₃ heterojunction structures were constructed and their dynamics were analyzed.The electronic properties and interfacial bonding of these three models were studied to explain why Si was used as a BST substrate for the experiment.The dielectric properties of BST/Si,BST/LNO and BST/Al₂O₃ of the three heterojunction structures will also be verified by experimental measurements.At the same time,an electric field is applied to the BST/Si structure to analyze the internal law of the film under different electric field intensity.In the experiment parts,BST thin film,Si O₂ insulating layer and Ti/Pt metal layer were prepared by magnetron sputtering under different sputtering conditions.The fabrication process of BST thin film and high quality ferroelectric thin film were discussed in detail.The C-V properties of Si/Si O₂/Pt/BST/Pt structures were predicted by using the Hang-Ting Lue model,and the experimental results were compared with the theoretical model.Finally,the microstructure and dielectric properties of Si/Si O₂/Pt/BST/Pt（MFMIS）structures were tested.The crystal orientation,morphology and dielectric properties were characterized by X-ray diffractometer,scanning electron microscope and LCR measuring instrument.The structure orientation,surface morphology and dielectric properties of the films at different sintering temperatures,frequencies and different mismatched strains were studied and analyzed.