Ferroelectric multilayer composite films based on the solid solution (Bi1/2Na1/2)TiO3-BaTiO3

The integration of ferroelectric oxides in microelectronic devices is usually hampered by the degradation of their properties in thin film form. For example, films based on solid solutions with excellent piezoelectric properties around their Morphotropic Phase Boundaries, such as Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMNT) or the lead free (Bi1/2Na1/2)TiO3-BaTiO3 (BNBT), show a drastic decrease of the remnant polarization respect to their bulk counterparts. The decrease of the grain size associated to the reduced thickness has been reported as the main cause of this effect in polycrystalline films. The stabilization of relaxor-like domains in submicrometric grains reported in ceramics makes that, as it happens in relaxor ferroelectrics, the removal of the electric field results in the disappearance of the polarization, which reduces drastically all remnant properties. A solution is the combination of the low remnant film with hard ferroelectric layers in multilayer composite films. The hard ferroelectric layers, when poled, induce an internal bias in the low remnant film, which therefore maintains the good properties of this film when the electric field is removed. In this work a study of the properties of BNBT and BiFeO3 (BFO) multilayer composite films is shown. Not only it allows taking advantage of the excellent properties of BNBT, but also solves part of the problem of the large leakage currents of multiferroic BFO, which supports a possible magneto-electric functionality.