Ion-Beam Etching on Nanostructured La2 Ti2 O7 Piezoelectric Thin Films

Abstract

The impact of generated Ga+ ion beams on the functional properties of crystallized lanthanum dititanate oxide (La2Ti2O7) ferroelectric thin films has been investigated at the nanometer scale by means of the scanning probe microscopy. Both the surface and the electrical response are shown to undergo sensitive modifications for areas exposed to ion irradiation. These are revealed through dynamic force mode, Kelvin force, and piezoresponse force (PFM) microscopies. Despite the nanometer film-dimensions, local piezoactivity is still detected, thus confirming the high resistance of the material to ion-beam exposures. In addition, crystallized La2Ti2O7 film, with a Pt electrode on top, is successfully patterned by focused ion beam (FIB) process. This allows the achieving of localized islands with lateral sizes ranging from 500 to 300 nm. Nanoscale electromechanical response is measured inside these nanostructures with the help of the PFM technique. In this case, the local piezosignal exhibits a level similar to the one obtained for the unetched film. The measures evidence no obvious sidewall effect in spite of not using the usual postannealing treatment that leads to functional properties recovery. This study demonstrates that the use of La2Ti2O7 materials combined with the FIB technique constitute a suitable and promising test-bench to pattern low-dimensional nanostructures. These investigations bear significant implications in view of the development of lead-free piezoelectric thin films for nanoelectromechanical systems applications.