Magnetic tunnel junctions using reactively sputtered Al2O3 barriers

Magnetic tunnel junction (MTJ) films were deposited using reactively sputtered AlOx barriers. In contrast to earlier attempts we show that sizable tunnel magnetoresistance (TMR) can be achieved at moderate resistance area (RA) products using this method. For instance, 45% at 580 Ωμm² is obtained using Co₇₀Fe₃₀ electrodes. The barrier formation can be understood by monitoring the oxidation state of the target in the presence of oxygen flow. Target oxidation plays a very important role in determining the final thickness and stoichiometry of the barrier, and is easily monitored by target voltage measurements. In addition to complete MTJ films, isolated barriers were also deposited. X-ray fluorescence (XRF) was used to determine their thickness and oxygen content.