Patterned magnetic tunnel junctions with Al conduction layers: Fabrication and reduction of pinhole effect

Magnetic tunnel junctions (MTJs), Ta(5 nm)/Al(20 nm)/Ni79Fe21 (5 nm)/Ir22Mn78 (10 nm)/Co75Fe25 (4 nm)/Al(x nm)-oxide/Co75Fe25 (4 nm)/Ni79Fe21 (20 nm)/Ta (5 nm) [x=0.8 and 0.9 nm], with 20 nm thick Al conduction layers were fabricated using magnetron sputtering deposition. Due to the surface roughness of the Al conduction layer, metallic pinholes could easily occur at the barrier layer. Remedies for such a pinhole issue can be solved by a critical underoxidation condition for the Al-oxide tunneling barriers and a postfabrication annealing process of the MTJs at 300 °C. A high magnetoresistance ratio of 45%, low resistance-area product of around 10 kΩ μm2, and sensing layer coercivity of approximately 20 Oe were obtained at room temperature for the annealed MTJs. The results suggest that pinhole defects could be eliminated or significantly reduced with a critical Al-oxide layer fabrication condition together with the annealing process. The MTJ structure after further structural and patterning modifications can be adopted as the cell elements for magnetoresistive random access memory based on the Al wring interconnection in semiconductor integrated circuit techniques.