Epitaxial Ferroelectric Nanostructures Fabricated by FIB Milling

Abstract

In this chapter we explore the possibilities offered by focused ion beam milling to fabricate epitaxial islands out of bismuth ferrite thin films. Three processes are described: first one consisting of high-energy direct milling of a film followed by annealing procedures, a second one of high-energy milling of a film coated with a sacrificial layer which is removed successively, and a third one of lowenergy milling of a film previously structured with sacrificial layer islands. Ferroelectric properties of the obtained structures have been investigated at a nanoscale level by piezoresponse force microscopy, in order to evaluate the impact of fabrication-induced damages on the functional properties. Structures produced by direct milling display ferroelectricity only after a post-fabrication annealing procedure, exhibiting polarization pinning only for structures with lateral sizes <500 nm. Detailed investigations have revealed occurrence of pinning and/or high imprint in an area within 100 nm distance from the structure edges, independently of the structure size. On the contrary, 250 nm large islands produced by milling through a sacrificial layer and over the structured sacrificial layer display ferroelectricity, without diminution of functional properties. Hence we conclude that focused ion beam milling is a viable technique for fabrication of ferroelectric structures, in particular bismuth ferrite nanoislands.

Deterministic Switching in Bismuth Ferrite Nanoislands

“…Details on film growth are described elsewhere 24 . Fabrication of the islands from the BFO parent film was performed by a mask-assisted Focused Ion Beam (FIB) milling procedure 25 , which has been demonstrated to produce islands which retain their ferroelectric properties with minimal fabrication-induced damage 26 . The milling procedure yielded a milled square area (5x5um 2 ) containing a number of BFO islands about 400nm in diameter and 25nm in height ( Figure 1).…”