Dielectric Properties And Relaxor Behavior Of Pulsed-laser-deposited Pb_0.5Sr_0.5TiO₃ Films And (Pb,Sr)TiO₃/(Pb,La)TiO₃ Multilayers

Ferroelectric thin films have attracted much attention in recent years for dynamic random access memory (DRAM) devices, but each of the promising candidates has its own drawbacks for practical applications. Recently, Sr-modified lead titanate (Pb_1-xSr_x)TiO₃ solid solution has received considerable attention for its interesting dielectric, ferroelectric, pyroelectric, piezoelectric, and nonlinear electro-optic properties. Researchers recently proposed that it might serve as an alternative material to PLZT films in the DRAM applications. Additionally, relaxor behavior is always a key subject in the field of ferroelectric material. However, the relaxor characteristics of PST materials have only been reported for bulk PST and there are few published data on the relaxor behavior of PST thin films. In this paper, we developed an optimized method of deposition to prepare (Pb_0.5Sr_0.5)TiO₃ (PST) thin films by pulsed laser deposition. The dielectric, ferroelectric and leakage characteristics were compared in PST, Ba_0.5Sr_0.5TiO₃ and Pb_0.5Ba_0.5TiO₃ thin films. From the research, PST showed higher dielectric constant, higher tenability and lower leakage current. Based on recent published research, we studied the relaxor behavior of PST films. By fitting the experiment data, the relaxor character of PST films was found that it was ascribed to both the true relaxor property of the PST film and the interface of the film-electrode interface. The dielectric properties of PST/Pb_0.8La_0.2TiO₃(PLT) multiplayer films were also studied in this thesis. Significant enhancement of dielectric constant has been observed for both the multilayers with respect to identically prepared single-component PST and PLT films. Larger frequency dispersion of dielectric property has also been obtained in the multilayers. After analyzing the result of the multilayer's structure, we found the effect is ascribed to the compositional fluctuation revealed by the atomic interdiffusion and additional Pb-deficient in the interface regions of the multilayers. Furthermore, thermally and electric-field driven space charges at relative low temperature and low electric field were found in the PLT/PST/PLT and PLT films, which is attributed to the substitution of La3+ nonisovalent for Pb2+ in these films.