Ferroelectric and Leakage Properties of CaBi4Ti4O15/Bi4Ti3O12 and Bi4Ti3O12/CaBi4Ti4O15 Double-layered Thin Films

Double-layered ferroelectric thin films consisting of CaBi4Ti4O15 (CBT) and Bi4Ti3O12 (BTO) layers have been fabricated on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method. The crystal structures and the surface morphologies of CBT/BTO and BTO/CBT double-layered thin films are investigated by using X-ray diffraction and scanning electron microscope, respectively. Their ferroelectric and leakage properties significantly depend on the stacking sequence of the layers. CBT/BTO thin films exhibited enhanced ferroelectric properties, such as a remanent polarization (2P(r)) of 49 mu C/cm(2) and a coercive electric field (2E(c)) of 169 kV/cm at an applied electric field of 300 kV/cm, compared to BTO/CBT thin films with 8 mu C/cm(2) and 236 kV/cm, respectively. The leakage current density of CBT/BTO thin films measured at room temperature was 4.9 x 10(-7) A/cm(2), which is an order of magnitude lower than the 6.6 x 10(-6) A/cm(2) of BTO/CBT thin films. Different conduction behaviors at high electric field were observed between the two thin films. Furthermore, the values of the pulse polarizations [i.e., +(P*-P boolean AND) or -(P*-P boolean AND)) of CBT/BTO and BTO/CBT double-layered thin films were reasonably unchanged up to 1.4 x 10(10) switching cycles.