Epitaxial ferroelectric aurivillius-type phases on metallic oxides by pulsed laser deposition

摘要

Bi-based layered perovskites, also called Aurivillius-type phases, are superior to simple perovskite material with regard to their ferroelectric long-term stability. Another way to alleviate fatigue and aging problems in metal-ferroelectric-metal (MFM) heterostructures is to replace the bottom metallic electrode with a conductive oxide electrode. An attempt to combine the two approaches has bene made to investigate whether a further improvement in stability can be achieved. the promote an oriented growth of the ferroelectric films, epitaxial buffer layers (YSZ, CeO_2) and epitaxial electrodes of (La_0.5Sr_0.5) CoO_3 (LSC) have been consecutively deposited onto Si (100). Finally a ferroelectric thin film of the layered perovskite Bi_4Ti_3O_12 (BiT) has been grown. Rocking curve measurements demonstrate good epitaxial growth of both the buffer and the electrode layers. The ferroelectric thin films show a preferred c-axis orientation. Cross-section TEM images reveal a twinned superstructure in the LSC layer with a triplingof the lattice parameter. EDX line-scans show that a Co-enriched and Bi-depleted layer had formed at the BiT/LSC interface. After depositon of Au electrodes on both the BiT and the LSC layer, a hysteretic behavior could be detected and the ferroelectric properties of the c-oriented BiT film be confirmed.