| As a most important kind of ferroelectric materials in the filed of electric functional ceramics, perovskite (ABO3) ferroelectric thin films have excellent nonvolatile storage ferroelectric and some other important sensing properties: insulation dielectric, piezoelectric, pyroelectric, electro-optic, etc. It can achieve the conversion between electrical energy and electrical energy, mechanical energy and electrical energy, thermal energy and electrical energy, or light energy and electrical energy, creating conditions for miniaturization and integration of various electronic components. It has important application prospect in the areas of energy, national defense, automotive, automation, etc.It is worth noting that, the ferroelectric thin films used in electronic devices are usual single component with polycrystalline structure, their residual polarization is small and electrical performance is poor. At the same time, the effect of interface tailoring in heterostructures become very weak, as well as for the film compositions. This has limited the investigations on perovskite ferroelectric films in both properties research and efficient applications. Therefore, it has important theoretical significance and application value for the research on orientation growth and performance tailoring in ABO3-type ferroelectric thin films.In the part of experimental research, based on BTO materials, oriented BTO-base films heterostructures were prepared by using multiple target radio frequency magnetron sputtering (RFMS), then, the rules of orientation growth were investigated, as well as the taioring effect of interface and orientation on the microstructures and properties of ferroelectric films in the heterostructure of "top electrode-ferroelectric thin film-bottom electrode-substrate". In the part of theoretical research, the piezoelectric properties of PZT ferroelectric film heterostructures were investigated. The main research contents are summarized as follows:(1) BTO ferroelectric thin films were deposited on single crystal substrates of STO and MgO with LSCO as bottom electrode in different RFMS parameters. The influences of the radio frequency power, sputtering pressure, deposition atmosphere and cooling rate on crystal orientation, microstructure and domain structure of BTO films were investigated. After the process conditions were optimized, the influences of film thickness on the electrical performance were further studied, and provide experimental foundation for the following researches.(2) BTO films were deposited on (100) MgO substrates, noble metal Pt and oxide LSCO were used as bottom electrode, respectively. The results showed that BTO film on Pt/MgO was polycrystalline structure, and (001) epitaxial on LSCO/MgO. It has poor dielectric properties in the orientation of (001), so the former one, which contains other orientations, exhibited better dielectric properties. In addition, the crystalline structure of BTO films can be controlled effectively by controlling the texture orientation of Pt layer, which was strongly depending on its growth temperature,(111) highly preferred orientation in low temperature(200℃), and gradually transferred to (200) with increasing growth temperature.(3) Different conductive oxides LSCO, LNO and SRO were used as bottom electrode, and the BTO/OBE/STO epitaxial heterostructures were obtained. All BTO films had good ferroelectric and high breakdown voltage characteristics. Comparative analysis found that the greater interfacial compressive stress, the higher dielectric constant and tunability of BTO film; the bigger bottom electrode work function, the greater leakage current of BTO film. Heterointerface space charge states were investigated by using metal-semiconductor contact theory, and the interface barrier height (0.79-0.88eV), space charge density (5.14x1019-1.51x1020cm-3), free carrier concentration (3.7x1018-1.1x1019cm-3), the thicknesses of depletion layer and interface layer(δ(V)) were calculated, then the influence of these parameters on related electrical properties of BTO films were analyzed. The interface transmission mechanism was schottky, Ionic and Pool-Frenkel emission from low voltage range to high voltage range, respectively.(4) Different single crystal substrates with different orientations were used to deposited BTO films, and BTO/SRO/Sub(hkl) heterostructures were formed. According to the degree of lattice matching, the oriented growth mechanism and its influence on the electrical performances of BTO film were investigated. The results showed that the crystal structure of BTO film was influenced by the lattice parameters and the orientation of substrate. The electric properties of BTO films exhibited a strong anisotropy, the best dielectric performance for (111)-BTO film, the best ferroelectric performance for (001)-BTO film. In addition, BTO/LSCO/Sub heterostructures were prepared as piezoelectric cantilever beams, the piezoelectric coefficient e31,f can be tailored by using different substrate materials.(5) Highly (001) preferred orientation BTO-STO superlattice nano-composite films were deposition on (100)-STO substrate by RFMS. Because of the effect of the superlattice interface strain, the low frequency dielectric constant of BTO-STO superlattices were3.6-4.5times lager than BTO films in the same conditions, and increased with decreasing of the single layer thickness for symmetry superlattice.(6) The thickness ratio dependence of the piezoelectric coefficient of "epitaxial PZT ferroelectric thin film-elastic substrate" elastic couples were calculated by using the continuum mechanics, along with the change of heterostructure coefficient of thought with the representation method, it showed that the piezoelectric coefficient of PZT films closely related to the characterization methods, elastic properties of substrates, crystal structure and electromechanical properties of films, and the orientation of heterostructures.This work was supported by National Natural Science Foundation of China (Nos.51002088and91122024), Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry (ROCS, SEM). Shandong Province Outstanding Young Scientist Research Fund (No. BS2010CL029), and Open Fund of State Key Laboratory of New Ceramic and Fine Processing of Ministry of Education in Tsinghua University. |
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