Fabrication of bismuth nanowire devices using focused ion beam milling

In this work, a focused ion beam (FIB) milling process has been developed to fabricate 50nm Bi nanowire and transistor structures using FEI-200 dual beam FIB system. For the fabrication, 50nm bismuth film was thermally evaporated through EBL patterned PMMA windows onto SiO₂ substrates with pre-defined contact pads. Bi nanowire widths ranging from 30nm to 100nm have been successfully fabricated by milling out unwanted areas using 30KeV Ga+ ion beam. A single-pixel-line ion beam blanking technique has been utilised to fabricate Bi nanowire as small as 30nm in diameter and few micrometers long. In order to form good ohmic contacts for sub 50nm bismuth nanowires, a drilland- fill process has been developed using FIB to sputter away the surface oxide of bismuth after the in-situ platinum nanowire contacts deposition. To our knowledge, this is the first time a focused ion beam process has been used to fabricate bismuth nanowire. The fabricated Bi nanowires were electrically characterised using a semiconductor analyzer that showed good ohmic contact to the electrodes. In this paper, the fabrication experiments and the characterization results for Bi nanowires as small as 50nm in diameter are presented. Several FIB issues involved in Bi device making and ohmic contacts to Bi nanowires will also be discussed.