Evidences of Reactive-Ion-Etching-Induced Damages to the Ferromagnet of Perpendicular Magnetic Tunnel Junctions

To minimize the R-H loop shift of a perpendicular magnetic tunnel junction (p-MTJ), a stop-on-tunnel-barrier etch is required to pattern the reference layer such that it is wider than the free layer. Our experiments show that reactive ion etching can induce penetrating damages to the ferromagnetic layers beyond the etched surface. Sufficient sacrificial layer atop the tunnel barrier must be kept to prevent both free and reference layers from damage, which forms a magnetic “step” in the reference layer and results in the R-H loop shift. The optimized p-MTJs revealed an average offset field of 1.4 Oe and also exhibited steady switching behaviors with one-sigma switching voltage distributions less than 6% for both resistance states. A low switching current density of 1.63 × 10⁶ A/cm² of an 80-nm p-MTJ was measured with a 10-μs pulse at zero external offset field.