| Ferroelectric material is an ideal candidate for memory cell fabrication because it exhibits a high dielectric constant {dollar}(varepsilonspprime){dollar} and charge retention ability when an applied electric field is reduced to zero. Among a variety of ferroelectric materials, PbTiO{dollar}sb3{dollar} (PT) and {dollar}rm Pb(Zrsb{lcub}x{rcub}Tisb{lcub}1-x{rcub})Osb3{dollar} (PZT) have been found to have unique properties and have been intensively studied. It is well known that properties of the deposited film are highly dependent on their microstructures. For example, PT has a tetragonal symmetry at room temperature and therefore its properties are anisotropic along different crystal orientation. In this study, the PT and PZT films were obtained by MOCVD on various substrates under different growth conditions. The substrate and growth parameter effects are found to be critical to the resulting film textures, domain structures, microstructures, and properties.; Substrates employed for PT and PZT film growth in this study can be categorized as the single crystalline substrates, polycrystalline substrates, and the amorphous substrates. The PT films grown on the single crystal oxide substrates (MgO(100) and LaAlO{dollar}sb3{dollar}(100)) are single crystalline and exhibit ferroelectric domain structures. The differential thermal stress and the transformation stress are important in determining the resulting domain structures. On the other hand, growth conditions and microstructures are different when PT and PZT films were deposited on polycrystalline or amorphous substrates (e.g. electrode-coated and bare Si with amorphous SiO{dollar}sb2{dollar} overlayer). The grown films are polycrystalline and are usually preferentially oriented. For films grown at a temperature higher than the PT transition temperature (i.e., grown in cubic phase), the film orientation is controlled by the anisotropic growth rates along different crystal directions, the epitaxial relationship and differential thermal stress between the film and substrate, as well as the transformation stress. On the other hand, textures of the films grown below the transition point are determined by the epitaxial relationship, the anisotropic growth rate, and the electrostatic effect. The purpose of this research is to develop a better understanding of formation mechanisms for PT and PZT thin films grown by MOCVD. |
