Preparation And Study Of Perovskite Structure Thin Films

Perovskite oxide thin films have attracted great interest for their potential and wide applications in microelectronic, optoelectronic and semiconductor devices. In this dissertation, preparation and electrical properties of ferroelectric thin films and heterostructures of ferroelectric/conducting oxide films have been investigated. Investigations on optical properties of pure and doped perovskite thin films have also been carried out. The research work and experimental results are as follows:1. Effect of heat treatment on structures of LaNiO3 (LNO) thin films grown on Si(100) substrates derived from Solution Chemistry Decomposition (SCD) process has been investigated. The LNO thin films annealed at lower temperature have (110) preferred orientation, while the films annealed at higher temperature have (100) preferred orientation. This can be explained by considering lattice mismatch and thermal stress between LNO thin films and Si substrates.2. Effect of annealing atmosphere on LNO thin films has been studied. The results indicate that the resistivity of LNO thin films annealed in oxygen is only half of the resistivity of samples annealed in air, which can be explained by the influence of oxygen vanancy on the energy structure of LNO thin films.3. Pb(Zr,Ti)O3 (PZT) thin films are prepared on LNO/Si substrates by sol-gel route. Effect of Zr/Ti ratio on PZT has been analyzed. The results show that the main reason leading to the change of lattice constant in PZT thin films is not the ion radius effect but the charge effect between the cations and anions. Influence of annealing on PZT thin films has been studied. The results display that the ferroelectric and dielectric characters of PZT thin films can be improved by increasing annealing temperature.Effect of bottom electrode fabricated by LNO thin films derived in different4. atmosphere on properties of Pt/PZT/LNO heterostructures has been investigated. The results show that the LNO thin films annealed in oxygen can improve the ferroelectric property of heterostructures. Post-annealing can improve the interface of Pt and PZT thin films, which can enhance the ferroelectric properties of the heterostructures.5. BaTiO3 thin films are prepared on different substrates using sol-gel route and the growth mechanism of thin films is discussed. During crystallization, the homogeneous nucleation and the heterogeneous nucleation happen simultaneously in BaTiO3 thin films.6. The photo-voltage property of the BaTiO3 thin films grown on Si(111) substrate is studied by surface photovoltaic spectroscopy (SPS). The results show that the signal intensity for the heterostructures is far stronger than that for the Si under irradiation of visible light, which can be explained by disassociation of photo-induced carrier at the interface between BaTiO3 thin films and Si substrate.7. The optical properties of BaTiO3 thin films are studied by using spectroscopic ellipsometry. The dispersion properties of refractive index and extinction coefficient are elucidated according to Cauchy formula and Urbach relationship, respectively. 8. BaTiO3 thin films are doped with Mn, Co, Ni and Cu in small doping concentrations. It is found that the doping concentration has effect on the energy gap of the films. The linear change of energy gap with M-doped (M=Mn, Co, Ni) concentration can be explained using the energy band model of mix-crystalline semiconductor. As to the Cu doping, the change of energy gap results from the change of cation vanancy concentration induced by the replacement with Ti4+.