Bias voltage dependence of magnetic tunnel junctions comprising double barriers and amorphous NiFeSiB layers

A double-barrier magnetic tunnel junction (DMTJ) comprising an amorphous ferromagnetic NiFeSiB was investigated to reduce bias voltage dependence of tunneling magnetoresistance (TMR) ratio. The typical DMTJ structures were Ta 45Ru 9.5IrMn 10CoFe 7 AlOx free layer 7 AlOx CoFe 7IrMn 10Ru 60 (in nanometers). Various free layers such as CoFe 7, NiFeSiB 7, CoFe 3.5NiFeSiB 3.5, and NiFeSiB 3.5CoFe 3.5 were prepared and compared. The NiFeSiB-used DMTJ shows a low root-mean-square surface roughness of 0.17 nm, a resistance of about 860 , a Vh (voltage where the TMR ratio becomes half of its nonbiased value) of 1.1 V, and a high junction breakdown voltage of 2.0 V. The DMTJ with an amorphous NiFeSiB free layer offers smooth surface roughness resulting in reduced interlayer coupling field and bias voltage dependence.