Insertion Trade-off Effects on the Spin-Transfer Torque Memory Explored by In Situ X-ray

Abstract

Magnetoresistive random-access memory (MRAM) relies on magnetic tunnel junctions (MTJs) comprising heterostructures of CoFeB/MgO/CoFeB. Nonetheless, the dielectric breakdown of MgO limits the lifespan of MRAM devices. In the current study, we terminated MgO with a Mg surface facing the CoFeB free layer to reduce the mismatch in band alignment across the barrier. The Mg-modified interface was shown to enhance the breakdown voltage while reducing the switching current and asymmetric switching behavior, with a moderate sacrifice of perpendicular magnetic anisotropy, tunneling magnetoresistance, and resistance–area product. This performance trade-off was observed in all MTJs, regardless of cell size (180, 130, and 80 nm; each size has been tested with at least 20 cells). Visualization of the proposed junction via in situ X-ray absorption spectroscopy proved effective in elucidating the reconstruction of the interface within the context of energy barrier height, asymmetric switching behavior, and the voltage-driven movement of oxygen ions. A spin-dependent band diagram was constructed to correlate the tunneling/switching properties of the MTJ with such a trade-off scenario. The atomistic simulation of the magnetic properties revealed that Mg termination lowered the switching energy barrier with an effective domain wall motion within the CoFeB free layer.