Magnetic Tunnel Junctions Fabricated Using Ion Neutralization Energy As A Tool

The neutralization energy of highly charged ions (HCIs) is used during the fabrication of magnetic tunnel junctions (MTJs) to modify their electrical properties, providing additional flexibility in the devices' properties. While most ion species used in electronic fabrication (e. g., implantation or plasma cleaning/oxidation) have charge q approximate to 1 and negligible neutralization energies, the HCIs utilized in this work are up to q=44 and carry as much as 52 keV per HCI of neutralization energy, ample to modify the chemical and electrical properties of the tunnel barriers at the impact site. Hundreds of MTJ devices have been fabricated, revealing some general characteristics of the HCI modified tunnel junctions: the electrical conductance increases linearly with the number of HCIs used; the conductance added per HCI depends on the initial tunnel barrier thickness and the barrier stoichiometry; the transport is usually tunneling (not Ohmic); and the conductance added by the HCI process can substantially increase the magneto-conductance. Recent experiments (not shown) have also revealed an enormous dependence on the charge state of the HCI used in tunnel barrier irradiation.