Giant Conductivity Modulation of Aluminum Oxide Using Focused Ion Beam

Abstract

Precise control of the conductivity of semiconductors through doping has enabled the creation of advanced electronic devices, similarly, the ability to control the conductivity in oxides can enable novel advanced electronic and optoelectronic functionalities. While this was successfully shown for moderately insulating oxides, such as In 2 O 3 , a reliable method for increasing the conductivity of highly insulating, wide bandgap dielectrics, such as aluminum oxide (Al 2 O 3 ), has not been reported yet. Al 2 O 3 is a material of significant technological interest, permeating diverse fields of application, thanks to its exceptional mechanical strength and dielectric properties. Here we present a versatile method for precisely changing the conductivity of Al 2 O 3 . Our approach greatly exceeds the magnitude of the best previously reported change of conductivity in an oxide (In 2 O 3 ). With an increase in conductivity of about 14 orders of magnitude, our method presents about 10 orders of magnitude higher change in conductivity than the best previously reported result. Our method can use focused ion beam to produce conductive zones with nanoscale resolution within the insulating Al 2 O 3 matrix. We investigated the source of conductivity modulation and identified trap-assisted conduction in the ion damage-induced defects as the main charge transport mechanism. Temperature-dependency of the conductivity and optical characterization of the patterned areas offer further insight into the nature of the conduction mechanism. We also show that the process is extremely reproducible and robust against moderate annealing temperatures and chemical environment. The record conductivity modulation, combined with the nanoscale patterning precision allows the creation of conductive zones within a highly insulating, mechanically hard, chemically inert, and bio-compatible matrix, which could find broad applications in electronics, optoelectronics, and medical implants.Aluminum oxide (Al 2 O 3 ) is one of the most widely employed dielectric materials, thanks to its excellent insulating properties 1 , mechanical hardness and resistance 2 , and biocompatibility 2,3 , with applications ranging from device passivation 1,4-8 , MOSFET gate 9-13 , to biomedical implants and antifouling passivation 2,3,14,15 . Electrical functionalization of Al 2 O 3 via reliable and spatially-accurate control of its conductivity could enable novel sensing technologies encompassing electrical contacts embedded in a mechanically hard, chemically inert, and electrically insulating dielectric matrix. Examples of such technological applications include photon emission and detection 7,16-19 , low-energy in-terconnects 20-22 , energy conversion 1,23,24 , and implantable devices [25][26][27] . We here present an effective method for the non-subtractive nanopatterning of electrically conductive wires and other features embedded in a dielectric Al 2 O 3 substrate, using focused ion beam (FIB). While patterning of nanowires in transparent conductive In 2 O 3 has been ...