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

Abstract

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 Å 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 tAl⩾6.5 Å. The minimum Al thickness at which pinholes form depends on ion acceleration voltage used for Al deposition. Single-step oxidation of an 8 Å Al layer leads to a magnetic tunnel junction with a 25% tunnel magnetoresistance (TMR) and R×A of 14 Ω μm2. The two-step oxidation procedure was used for thinner Al layers. TMR ranges from 18%–23% at 8–10 Ω μm2 resistance values, for a total Al thickness of 6.5 Å. Junction resistance has been further decreased down to 4.35 Ω μm2 with a TMR of 10.6% by two-step oxidizing a 6 Å Al layer.