Epitaxial bismuth-layer-structured perovskite ferroelectric thin films grown by pulsed laser deposition

Thin films of bismuth-layer-structured perovskites such as SrBi2Ta2O9 (SBT) and BaBi4Ti4O15 (BBiT) with preferred orientations have been grown by pulsed laser deposition (PLD) on epitaxial conducting LaNiO3 (LNO) electrodes on single crystalline (100) SrTiO3 (STO) or on top of epitaxial buffer layers on (100) silicon. X-ray diffraction (XRD) analysis and cross-section electron microscopy reveal that the films consist of c-axis oriented regions and mixed a-axis and c-axis oriented regions. The regions with mixed a-axis and c-axis orientation show high surface roughness due to the rectangular crystallites protruding out of the surface, whereas the c-axis oriented regions show a smooth surface morphology. In the mixed a-axis and c-axis oriented regions, the SET and BBiT films exhibit saturated ferroelectric hysteresis loops with a remnant polarization P-r of about 2 mu C/cm(2) and coercive fields E-c of about 20 kV/cm for SET and 60 kV/cm for BBiT. No polarization fatigue was observed up to 10(8) cycles neither for SET nor for BBiT films. The regions having c-axis orientation with a smooth surface morphology in contrast exhibit a linear P-E curve. The results show that the ferroelectric properties of a planar capacitor consisting of ferroelectric Bi-layer-structured perovskites depend on the crystalline orientation of the film.