Growth optimization and characterization of ferroelectric properties of Aurivillius thin film

Abstract

Ferroelectric thin film is applied to many aspects of electromagnetic devices, especially to non-volatile memory, because of there spontaneous electric polarization. For more denser memory, the thinner film with strong ferroelectricity is needed. However, this challenge is facing difficulty by the depolarizing filed which hinders c-axis ferroelectric polarization more as a film is getting thinner. To overcome this problem, a material with pure a-axis or b-axis ferroelectricity is needed. Bi2WO6 (BWO) is the simplest member of the Aurivillius family, with one WO6 octahedron sandwiched between two Bi2O2 layers. BWO has a high Curie temperature around 950 °C and exhibits a large, spontaneous, pure in-plane polarization of about 50 μC/cm2 at room temperature. The robust ferroelectricity combined with the in-plane polarization, thereby makes BWO an attractive candidate for non-volatile memory devices that could overcome the size-effect problem by depolarizing field of canonical ferroelectrics like BaTiO3 or PbTiO3. Despite this advantage, most of the study about BWO is focusing on the photocatalyst effect and a systematic study focusing on the growth optimization, structural, and ferroelectric characterization of BWO thin films is not done yet. Using the pulsed laser deposition (PLD) technique, we have grown epitaxial BWO thin films on (001)-oriented SrTiO3 substrates and optimized growth conditions based on the X-ray diffraction (XRD) and atomic force microscopy (AFM) data. In this paper, the best growth condition of BWO films grown by PLD method will be presented. Also, the ferroelectric property of the optimized BWO film probed by the piezoresponse force microscopy (PFM) technique and scanning transmission electron microscopy (STEM) will be presented.