Properties Of Perovskites Oxide Ferroelectric Thin Films Fabricated By Pulsed Laser Deposition

BaTiO3(BTO) and BiFeO3(BFO) are ferroelectric materials with perovskite structure and they are attracting more and more attentions for their excellent properties. We grew thin films of these two kinds of materials by pulsed laser deposition (PLD) method. Crystal structures, surface topography, ferroelectric polarization, dielectric properties and leakage current of each sample are measured in this work in order to investigate the following three problems:Fist, the influence of oxygen pressure environment on the microstructure and physical properties of BTO thin films; second, growing process of ultra-thin BFO films on SrTiO3(STO) substrates with primitive cell stepped surface; third, effects of different buffer layers on the structure and properties of BFO thin film. To study the influence of oxygen pressure on properties of BTO thin films, we have grown BTO thin films of same thickness with identical other growing conditions except different oxygen pressure. By X-ray diffraction and electric measurements, we get the relationship between oxygen pressure and lattice constants as well as electric properties. As usual, oxygen pressure affects the quantity of oxygen vacancies in the film. As we expected, the experiments’ results reveal the dependents of lattice constant and leakage current to oxygen vacancies.In order to explore the effects of the substrate surface morphology to the BFO film growth process, we successfully obtained surface atomically flat STO substrate with steps primitive cell by chemistry method. Then BFO/SRO epitaxy films with different thickness are deposited on these STO substrates. Using atomic force microscope (AFM) to research the changes of surface morphology of samples with different thickness, we have observed that the BFO films first grow along the stepped direction as strips and then transform to layered growth mode.In addition, we have grown BFO films with BTO and STO buffer layers respectively, on one hand, to change the strain state of the BFO film by buffer layers; on the other hand to study the impact of different characteristics of buffer layers to the properties of BFO films. We have successfully prepared BFO/BTO/SRO/STO and BFO/STO/SRO/STO two kinds of multilayer structure epitaxial thin films. Using XRD to determine the effects on lattice constant of the BFO layer and achieved the adjustment of BFO film strain through the buffer layer. Moreover, dielectric, ferroelectric and leakage characteristics test results show that the buffer layer has a significant impact on the characteristics of the BFO thin film dielectric constant, remanent polarization, coercive field and leakage current.