Bias Voltage Dependence of Magnetic Tunnel Junctions Comprising Double Barriers and CoFe/NiFeSiB/CoFe Free Layer

Abstract

The typical double-barrier magnetic tunnel junction (DMTJ) structure examined in this paper consists of a Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlOx/free layer/AlOx/CoFe 7/IrMn 10/Ru 60 (nm). The free layer consists of an Ni16Fe62Si8 B14 7 nm, Co90Fe10 (fcc) 7 nm, or CoFe t1/NiFeSiB t2/CoFe t1 layer in which the thicknesses t1 and t2 are varied. The DMTJ with an NiFeSiB-free layer had a tunneling magnetoresistance (TMR) of 28%, an area-resistance product (RA) of 86 k Omega mum2, a coercivity (Hc) of 11 Oe, and an interlayer coupling field (Hi) of 20 Oe. To improve the TMR ratio and RA, a DMTJ comprising an amorphous NiFeSiB layer that could partially substitute for the CoFe free layer was investigated. This hybrid DMTJ had a TMR of 30%, an RA of 68 k Omegamu m2, and a Hc of 11 Oe, but an increased Hi of 37 Oe. We confirmed by atomic force microscopy and transmission electron microscopy that Hi increased as the thickness of NiFeSiB decreased. When the amorphous NiFeSiB layer was thick, it was effective in retarding the columnar growth which usually induces a wavy interface. However, if the NiFeSiB layer was thin, the roughness was increased and Hi became large because of the magnetostatic Neacuteel coupling