High-K Ferroelectric Films And Multilayers Fabricated By Pulsed Laser Deposition

This thesis introduces in detail the future application of high-K ferroelectric films, the main problem of the materials and the method to solve these problems. In the thesis, uniform Pb_0.72La_0.28TiO₃ (PLT28) and polycrystalline BaTiO₃/SrTiO₃(BT/ST) multilayered films have been investigated, respectively. For PLT28, study indicated that oxygen deposition pressure exerts a strong impact on the microstructure and the dielectric properties of the films, and we found a proper deposition condition to prepare PLT28 films with high K and low loss. On the other hand, through controlling oxygen pressure during the time interval in between two adjacent depositions, the dielectric enhancement was obtained in BT/ST multilayers. The dielectric constant is about two times that of uniform Ba_0.5Sr_0.5TiO₃ films. PLT28 thin films have been prepared on Pt/Ti/SiO₂/Si substrates by Pulsed Laser Deposition (PLD) under various oxygen pressures. Study indicated that oxygen deposition pressure exerts a strong impact on the microstructure and the dielectric properties of the films. The PLT28 film deposited under 2Pa oxygen pressure had larger dielectric constant while the dielectric loss kept low. At 10 kHz frequency, the dielectric constant was approximately 852 and dielectric loss was 0.0110. Meanwhile, we find that other La modified PbTiO3 films have the same dielectric constant-pressure relation. An explanation has been given in the text. On the other hand, pulsed-laser-deposited polycrystalline BaTiO3/SrTiO3 multilayered films on Pt/Ti/SiO2/Si substrates have been fabricated with interfacial modification through lowering the oxygen pressure during the time interval in between two adjacent depositions. It is found that the formation of the heterolayered structure is essential to get the dielectric enhancement. Such heterolayered films have large dielectric constant of 1201 with a loss tangent below 0.1 at 10 KHz. This is about two times that of the identically prepared Ba0.5Sr0.5TiO3/Ba0.5Sr0.5TiO3 homolayered and uniform Ba0.5Sr0.5TiO3 films. The enhancement of dielectric properties is attributed to the presence of the interfacial regions with low and controllable resistivity due to the formation of oxygen vacancies at lower oxygen pressure. In conclusion, our research shows that controlling oxygen pressure is an effective method to enhance the dielectric constant of ferroelectric uniform film and mutilayered film.