Ion-beam deposited low resistance magnetic tunnel junctions prepared by a two-step oxidation process

Spin tunnel junctions with ultrathin (<1 nm) AlOx tunnel barriers were fabricated by ion-beam deposition. The tunnel barrier was formed by natural oxidation of an ultrathin Al layer (4-8.5 angstrom thick) by either a single-step or a two-step oxidation process. The magnetic and transport properties of these tunnel junctions indicate the barrier to be pinhole free for t(Al)>= 6.5 angstrom. The minimum Al thickness at which pinholes form depends on ion acceleration voltage used for Al deposition. Single-step oxidation of an 8 angstrom Al layer leads to a magnetic tunnel junction with a 25% tunnel magnetoresistance (TMR) and RxA of 14 Omega mu m(2). The two-step oxidation procedure was used for thinner Al layers. TMR ranges from 18%-23% at 8-10 Omega mu m(2) resistance values, for a total Al thickness of 6.5 angstrom. Junction resistance has been further decreased down to 4.35 Omega mu m(2) with a TMR of 10.6% by two-step oxidizing a 6 angstrom Al layer. (C) 2003 American Institute of Physics.