EPITAXIAL CUPRATE SUPERCONDUCTOR FERROELECTRIC HETEROSTRUCTURES

Thin-film heterostructures of Bi4Ti3O12/Bi2Sr2CuO6+x have been grown on single crystals of SrTiO3, LaAlO3, and MgAl2O4 by pulsed laser deposition. X-ray diffraction studies show the presence of c-axis orientation only; Rutherford backscattering experiments show the composition to be close to the nominal stoichiometry. The films are ferroelectric and exhibit a symmetric hysteresis loop. The remanent polarization was 1.0 microcoulomb per square centimeter, and the coercive field was 2.0 X 10(5) volts per centimeter. Similar results were obtained with YBa2Cu3O7-x and Bi2Sr2CaCu2O8+x and single-crystal Bi2Sr2CuO6+x as the bottom electrodes. These films look promising for use as novel, lattice-matched, epitaxial ferroelectic film/electrode heterostructures in nonvolatile memory applications.