Preparation of Ferroelectric Superlattice Using Phot-excited Process and Their applications to Functional Deviccs

点击翻译按钮获取中文摘要

PbTiO_3, Pb (Zr, Ti) O_3 (PZT) and (Pb, La) (Zr, Ti) O_3 (PLZT) thin films were prepared by MOCVD in order to realize the Pb-based ferroelectric superlattice structure. For the evaluation of the crystallinity and epitaxial relationship of the ultrathin films, the energy dispersive typed total reflection X-ray diffraction (TRXD) method was used for the first time. The growth mechanism of pbTiO_3 and PZT thin films at the initial growth stage was also investigated using an atomic force microscope (AFM).Using TRXD,in-plane orientation, epitaxial relationship and lattice spacing of PbTiO_3 and PZT thin films (3 nm - 100 nm in thickness) grown on Pt/MgO were evaluated. From these measurements, it was found that the in-plane orinetations of PbTiO_3 and PZT were strongly dependent on that of Pt on MgO.Lattice spacing of PZT (100) in in-plane at an azimutal angle of 0ﾟ was 0.399nm. It was also found that PZT on Pt/MgO was compressed in the in-plane and tensed in the vertical direction by the internal stress derived from the inner strains such as lattice mismatch, differnce in the thermal expansion coefficient and the volume change with the ferroelectric phase transition. AFM observations of initial growth stage of PbTiO_3 showed that the islands grew gradually in a lateral dimension until finally they covered the entire substrate surface. From AFM observatins, it was found that the main growth mechanism initial growth stages (-100 nm in thickness) was two-dimensional growth.From our experiments, it was found that the TRXD method and AFM are very useful to evaluate the structural nature of ultrathin ferroelectric films. In particular, the energy dipersive type TRXD method is very promising to evaluate ferroelectric superlattice structure because highly precise in-situ measurement with high reliability can be carried out.