Epitaxial growth of non-c-axis-oriented ferroelectric rare-earth element-substituted bismuth titanate thin films on Si(100)

Abstract

Non-c-axis-oriented ferroelectric La-substituted Bi4Ti3O12 (BLT) and Nd-substituted Bi4Ti3O12 (BNT) epitaxial thin films of (104) orientation were grown on buffered Si(100) substrates by pulsed laser deposition. Electrically conducting (111)-oriented SrRrO3 layers on Pt(111)∕YSZ(100)∕Si(100) were used as an effective epitaxial template for the subsequent growth of the ferroelectric thin films. X-ray diffraction and transmission electron microscopy characterizations revealed that the SrRuO3 layers and the overlying ferroelectric thin films were multiply twinned due to the fourfold symmetry of YSZ(100) and the threefold symmetry of the Pt(111) plane. The BNT films showed ∼1.5 times higher remanent polarization (2Pr) of 38.7μC∕cm2 than the BLT films (2Pr=26.0μC∕cm2). The polarization enhancement for BNT films stems from an enhanced structural distortion of the TiO6 octahedra in the pseudoperovskite block by the Nd3+ ions (with a smaller ion radius than La3+) substituting for Bi3+. These (104)-oriented BLT and BNT films on buffered Si(100) exhibited a good fatigue endurance. No significant change in the shape of the hysteresis loops was observed even after 1×1011 switching cycles.