Fabrication of barium titanate nanopillars by neon ion milling
Résumé
Functional nanostructures can exhibit tunable physical properties and hold great promise for future application in nanoelectronics. These properties are largely governed by their size, surface, and geometry; hence accurate and damage-free fabrication techniques are key to reliable device functionalities. In contrast to other nanofabrication methods, focused ion beam (FIB) milling has proven to be a powerful machining method, offering the advantage of precision, rapid prototyping, and an operational capability on many materials. Light ion sources with helium (He) and neon
(Ne) yield low ablation rates and less milling damage near the surface. A low surface damage is of particular interest for the fabrication of ferroelectric nanostructures, in which polarization patterns are largely governed by the boundary conditions.
Here, we investigate Ne ion milling (NIM) of BaTiO3 single crystals and epitaxial thin films on Si substrate. A Zeiss Orion NanoFab microscope was used. BaTiO3 nanopillars and nanodisks of ~sub-500 nm dimensions were fabricated. The pillars were characterized by Raman spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Different processing conditions were investigated for neon ion milling on (001) BaTiO3 single crystals. We will first examine the effect of ion beam energy (in the range 15-30 keV) and fluence on the sputter rate and on the damaged depth in BaTiO3. Then, we will discuss the evolution of the pillar geometry and damage of the single crystalline structure with different milling conditions based on the Raman, TEM and SEM analyses. The effects of the milling sequence (in-out, out-in or alternating), beam spacing, beam dwell time and number of repetitions were investigated. Finally, we will consider the case of BaTiO3 nanopillars fabricated in BaTiO3 epitaxial thin films (20 nm)
on SrTiO3-buffered silicon with different aspect ratios