Size Effect of the Dielectric Properties in Bismuth-Based Layer- Structured Ferroelectric Films

Bismuth-based-layer-structured ferroelectric films have been formed epitaxially on Nb-doped SrTiO3 substrates by pulsed laser deposition (PLD). These films show an atomically smooth surface with a wide terrace of 100 nm–200 nm, as observed by atomic force microscopy (AFM) which is ideal for measuring such properties. Crystal growth apparently changes from the step-flow mode to the island-state mode according to the number of perovskite layers sandwiched by bismuth oxide layers. Additionally, the dielectric constant of the three film types, that is Bi2VO5.5 (n=1), Bi3TiNbO9 (n=2), and Bi4Ti3O12 (n=3) decreases proportionally with decreasing film thickness. It is considered that the size effect plays an important role in determining dielectric properties. Bismuth-layered ferroelectric films, with their atomically flat surfaces and accurate electrical properties, are an ideal material for applications in semiconductor devices.