Polymer Assisted Deposition On Nickel Substrate Study Of Barium Titanate Thin Film Growth

BaTiO₃（BTO）is a typical perovskites ferroelectric oxide with good dielectric,ferroelectric and piezoelectric properties. BTO thin films deposited on polycrystallinebase-metallic foils, such as nickel and copper foils, are interesting and have potentialapplications in structural health monitoring systems, embedded capacitors andMicro-Electro-Mechanical Systems （MEMS）, etc. However, it is still of great challengeto grow high quality ferroelectric oxide thin films on polycrystalline base-metallicsubstrates, due to the difficulties in controlling the interface. In this thesis, polymerassisted deposition （PAD） technique was employed to fabricate ferroelectric BTO thinfilms directly on polycrystalline nickel foils. It is found that pretreatment of nickel foilswith hydrogen peroxide （H₂O₂） solution to form thin nickel oxide layers on the surfacesis critical for the growth of BTO films. The growth dynamics was systematically studiedto optimize the single phase BTO films with good dielectric properties. In details, wemainly investigated the following topics:1. The effect from annealing ambience and temperatures were investigated. Thethermodynamics of the BTO thin films growth were carefully discussed. The growthprocess was carefully optimized. The BTO thin films grown in the optimal conditionexhibit good crystalline structures and dielectric properties （εr⁴00, tanδ <0.025）.2. Nickel oxide buffer layers were fabricated on Ni substrates through thepretreatment of the substrates in hydrogen peroxide （H₂O₂） solution. The crystallinestructures and dielectric properties of the BTO thin films with various pretreatmentconditions were investigated. It is found that the thickness of the nickel oxide bufferlayer strongly affects the electric properties of the BTO thin film.3. Water vapor was added to the annealing ambience of BTO thin films and the impacts on dielectric properties of those films were investigated. It is found thatannealing BTO thin films in the ambience containing water vapor is helpful toimprove the dielectric properties of the films, especially the dielectric tunability.4. Magnetoelectric effect （ME） of Ni/BTO heterostructures was investigated. Ahigh magnetoelectric coefficient of αME=89.58m V/cm-Oe was obtained in the BTOthin films with the optimal growth condition. The good magnetoelectric properties ofthe BTO thin films were attributed to the well controlled Ni/BTO interface. TheMagnetoelectric effect of the BTO thin films with nickel oxide buffer layer of variousthickness were investigated and compared. It is demonstrated that the buffer layerstrongly affects the ME properties of the BTO/Ni heterostructures.