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

Abstract

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 SBT and BBiT films exhibit saturated ferroelectric hysteresis loops with a remnant polarization P_r of about 2 μC/cm² and coercive fields E_c of about 20 kV/cm for SBT and 60 kV/cm for BBiT. No polarization fatigue was observed up to 10⁸ cycles neither for SBT 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.

Key Words:

• Pulsed laser deposition
• Bi-layer-structured perovskites
• epitaxial ferroelectric films