AlOx barrier growth in magnetic tunnel junctions for sensor applications

• AlOx are a cost efficient alternative to MgO for sensing application.
• AlOx MTJs with RxA tunable over orders of magnitude by remote plasma oxidation.
• Better symmetry of double step barriers for AC biasing.

Magnetic tunnel junction (MTJ) research has been focused on MgO-based crystalline structures due to high tunnel magnetoresistance (TMR), despite requiring a more severe process control than previous generations of MTJ stacks based on amorphous barriers (e.g. AlOx). In this work, we study the electrical transport properties in AlOx barriers in MTJ sensors fabricated using Ion beam sputtering and remote plasma oxidation. Amorphous barriers were prepared from oxidation of thin Al films, deposited in single step barrier (SSB-Al 1 nm/oxidation) or double step barrier (DSB-Al 0.5  nm/oxidation/Al 0.5 nm/oxidation) structures. We show tunable resistance-area products (RxA) ranging from ≈10Ωμm2 (suited for nano devices) up to ≈100kΩμm2 (suited for large area sensors) with TMR above 30%. For all geometries studied, the structures have a coercivity free linear response and require none or one annealing step. This makes them very competitive for all industrial applications where the TMR level is not the dominant specification to meet.