Epitaxial Cuprate Superconductor/Ferroelectric Heterostructures

Thin-film heterostructures of Bi 4 Ti 3 O 12/ Bi 2 Sr 2 CuO 6+ x have been grown on single crystals of SrTiO 3 , LaAlO 3 , and MgAl 2 O 4 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 YBa 2 Cu 3 O 7- x and Bi 2 Sr 2 CaCu 2 O 8+ x , and single-crystal Bi 2 Sr 2 CuO 6+ x as the bottom electrodes. These films look promising for use as novel, lattice-matched, epitaxial ferroelectric film/electrode heterostructures in nonvolatile memory applications.