Ferroelectric Bi_3.25La_0.75Ti₃o₁₂ films of uniform a-axis orientation on silicon substrates

The use of bismuth-layered perovskite films for planar-type nonvolatile ferroelectric random-access memories requires films with spontaneous polarization normal to the plane of growth. Epitaxially twinned a axis-oriented La-substituted Bi₄Ti₃O₁₂ (BLT) thin films whose spontaneous polarization is entirely along the film normal were grown by pulsed laser deposition on yttria-stabilized zirconia-buffered Si(100) substrates using SrRuO₃ as bottom electrodes. Even though the (118) orientation competes with the (100) orientation, epitaxial films with almost pure (100) orientation were grown using very thin, strained SrRuO₃ electrode layers and kinetic growth conditions, including high growth rates and high oxygen background pressures to facilitate oxygen incorporation into the growing film. Films with the a-axis orientation and having their polarization entirely along the direction normal to the film plane can achieve a remanent polarization of 32 microcoulombs per square centimeter.