Oxide Dielectric Multilayer Film Growth And Electrical Properties

For the excellent electrical properties of LaAlO3 and BaTiO3, we have prepared LaAlO3/BaTiO3 (LAO/BTO) superlattices by laser molecular beam epitaxy (L-MBE), and found that LAO/BTO superlattices had better electrical properties than SrTiO3/BaTiO3 superlattices, such as the remnant polarization of 25 μc/cm2. It had been found that the properties of ferroelectric superlattices strongly depended on the growth and structure of LAO/BTO superlattice, so the growth and structure were investigated by X-ray diffraction (XRD) and reflective high-energy electron diffraction (RHEED) technologies. The clear and bright streak lines in RHEED patterns proved the epitaxial growth of LAO/BTO superlattices, and a series of satellite peaks in XRD patterns showed the formation of multilayer structure. The different interface roughness obtained by the small-angle X-ray diffraction (SAXRD) and the change of diffraction streaks observed in RHEED illustrated the different growth mode for BaTiO3 and LaAlO3 layers in the superlattice. This was attributed to the lattice mismatch in the superlattice. On the basis of the eptaxial growth of LAO/BTO superlattice, the relation between ferroelectric properties and superlattice structures had been researched. First, the use of LAO cap layer enhanced the ferroelectric properties due to the restricted strain effect. Second, the relation of the ferroelectric properties to the strain was studied with the different stacking periodicity at a fixed periodic number. The results showed that the strains play an important role on remnant polarization. The maximum remnant polarization was obtained at the highest c-axis strain stacking periodicity of 4/4. Last, we found that the ferroelectric properties were enhanced as the thickness of LAO layers increased at fixed thickness of BTO layers for unsymmetrical LAO/BTO superlattices, which proved the key role of strain on the ferroelectric properties in LAO/BTO superlattices.