Pb-based ferroelectric thin films prepared by MOCVD

This Chapter focuses on the preparation and ferroelectric properties of Pb-based thin films and nanostructures. First, the growth behavior of MOCVD-deposited PbTiO3 and PbZrxTi1-xO3 (PZT) thin films on various substrates, such as polycrystalline Pt(111)/SiO2/Si(100), SrTiO3(100) single crystals and epitaxial SrRuO3(100)/SrTiO3(100), has been investigated. SEM, AFM and TEM observations revealed that PbTiO3 and PZT showed the V-W (Volmer-Weber) growth mode when they were grown on polycrystalline Pt-covered Si substrates. From AFM observations, it was found that PZT grown on etched SrTiO3(100) with a surface terminated by TiO2 and on the TiO2 planes of annealed SrTiO3 (100) showed the SK (Stranski-Krastanov) growth mode. The V-W growth mode was also observed for PZT on the SrO planes of annealed SrTiO3(100). When PZT was grown on epitaxial SrRuO3(100)/SrTiO3(100), the S-K growth mode was observed. Epitaxial PZT ultrathin films 20 nm thick were successfully grown on SrRuO3(100)/SrTiO3(100) with a terrace and step structure. Only when PZT films were grown on SrRuO3 with a terrace and step structure did they exhibit good ferroelectric hysteresis loops, with remanent polarizations (P-r) of 29 mu C/cm(2) to 33 mu C/cm(2) and coercive fields (E-c) of 340 kV/cm to 370 kV/cm. A 15 nm-thick PZT film showing an unsaturated hysteresis loop was also studied. The ferroelectricity and local current flow of PZT ultrathin films with thicknesses smaller than 10 run were investigated by SPM techniques. V-W growth was observed for PbTiO3 and PZT on epitaxial Pt/SrTiO3 and Pt/MgO substrates. Pyramidal-shaped, triangular-prism-shaped and squareshaped PbTiO3 and PZT self-assembled nanostructures were successfully prepared on epitaxial Pt/SrTiO3(111), (110) and (100) substrates, respectively, demonstrating structural control. Piezoresponse measurements using SPM proved that PbTiO3 and PZT nanoislands prepared on various substrates had ferroelectricity even before they became films. The minimum volume of a PbTiO3 nanostructure was 1.9 x 10(3) nm(3) (38 nm width x 1.7 nm height). This result has led us to a new study and development, of self-assembled and self-organized ferroelectric nanostructure technology.