Ferroelectricity in Single-Crystalline BaTiO3 Nanodisks on Silicon

Abstract

The miniaturization of ferroelectrics with lateral size reduction is crucial for technological advancement but requires an understanding of the fundamental behavior of ferroelectrics at the nanoscale. While much attention has been focused on vertical scaling of perovskite ferroelectrics with thickness reduction, lateral scaling remains less explored. In this study, ferroelectricity is investigated in 20 nm thick single-crystalline BaTiO3 nanodisks with a diameter ranging from ≈ 400 down to 100 nm. They are fabricated by Ne ion milling of a 20 nm BaTiO3 film epitaxially grown on SrTiO3-buffered silicon. The nanodisks are ferroelectric with a Curie temperature in the range 230–270 °C as determined by temperature-dependent piezoresponse force microscopy. In 100 nm-diameter nanodisks, the vertical polarization component adopts three distinct patterns in the pristine state, aligning with theoretical predictions. The most prevalent pattern features a uniformly up-oriented vertical component. The rotational invariance of these domain patterns in the plane suggests a combination of center-type and flux-closure domains. Additionally, the up polarization can be switched progressively to down polarization upon application of a pulsed bias of increasing time width. The control of the polarization in nanostructures and of their progressive switching is of particular interest for memory applications.