Fabrication of Ferromagnetic Tunnel Junctions with ICP Oxidized Tunnel Barriers.

Ferromagnetic tunnel junctions with a spin-valve-like structure of NiFe/Co/Al-O/Co/IrMn were fabricated by inductively coupled plasma-assisted magnetron sputtering using metal masks. The tunnel barriers were formed by oxidization of an Al layer using an inductively coupled oxygen-argon mixed plasma. The dependence of the saturated resistance (Rs), magnetoresistance (MR) ratio, barrier height (φ), and width (d) on the oxidization time and Al thickness were investigated Rs increased linearly and the MR ratio increased rapidly with increasing oxidization time. The MR ratio saturated when the oxidization time exceeded 120 sec. When the Al thickness was decreased from 1 to 0.5 nm, the MR ratio and φ decreased, while d increased Below 1 nm, the Al layer was not continuous, but an island-like structure.