Spin transfer torque switching in double magnetic tunnel junctions based on dual MgO layers

Abstract

We report fabrication and characterization of double magnetic tunnel junction (DMTJ) magneto-resistive random access memory cells that exhibit characteristic about 2X reduction of switching current compared to single reference layer junctions, but maintain high tunneling magnetoresistance ratio exceeding 120 %, high coercive fields of the free layer of more than 2 kOe for 65 nm cells, and magnetically stable reference layers with pinning fields above 6 kOe. Switching analysis performed for two different relative magnetization orientations of the reference layers shows that the net switching current is the result of combined spin transfer torque effects of the individual reference layers, with tunneling and spin-valve-like contributions adding constructively. Our work shows that efficient reduction of switching current can be achieved in double magnetic tunnel junctions with dual MgO layers where one of the layers has significantly lower resistance-area product to enable high magnetoresistance ratio.