Perpendicular spin transfer torque (STT) memory cell with double MgO interface and CoFeB layer for enhancement of perpendicular magnetic anisotropy

摘要

A perpendicular magnetization anisotropy (PMA) spin transfer torque (STT) magnetic tunnel junction (MTJ or TMR) forming a Magnetoresistive random access memory (MRAM) device. The STT-MTJ device has a CoFeB alloy free layer 104 located between the Magnesium Oxide MgO tunnel barrier layer 106 and a further upper MgO capping layer 130, and a CoFeB (Cobalt Iron Boron) alloy enhancement layer 140 between the MgO capping layer and a non-magnetic Tantalum (Ta) cap 150. The STT-MTJ device further comprises a ferromagnetic reference layer 102 (preferably comprising CoFeB), and an insulating tunnel oxide barrier layer 106 between the reference and free layers. The reference 102 and fixed free layers 104 have a fixed or programmable (switchable) perpendicular magnetization anisotropy PMA (respectively). The CoFeB alloy free layer has high Iron, Fe content (25% atomic concentration) to induce perpendicular magnetic anisotropy (PMA) at the interfaces with the MgO layers. To avoid creating unnecessary PMA in the enhancement layer due to its interface with the MgO capping layer, the enhancement layer has low Iron Fe content (4% atomic concentration). After all of the layers have been deposited on a substrate, the structure is annealed to crystallize the MgO. The CoFeB alloy enhancement layer inhibits diffusion of Ta from the Ta cap layer into the MgO capping layer and creates good crystallinity of the MgO by providing CoFeB at the MgO interface.