Uncovering Atomic Migrations Behind Magnetic Tunnel Junction Breakdown.

As advances in computing technology increase demand for efficient data storage solutions, spintronic magnetic tunnel junction (MTJ)-based magnetic random-access memory (MRAM) devices emerge as promising alternatives to traditional charge-based memory devices. Successful applications of such spintronic devices necessitate understanding not only their ideal working principles but also their breakdown mechanisms. Employing an in situ electrical biasing system, atomic-resolution scanning transmission electron microscopy (STEM) reveals two distinct breakdown mechanisms. Soft breakdown occurs at relatively low electric currents due to electromigration, wherein restructuring of MTJ core layers forms ultrathin regions in the dielectric MgO layer and edge conducting paths, reducing device resistance. Complete breakdown occurs at relatively high electric currents due to a combination of joule heating and electromigration, melting MTJ component layers at temperatures below their bulk melting points. Time-resolved, atomic-scale STEM studies of functional devices provide insight into the evolution of structure and composition during device operation, serving as an innovative experimental approach for a wide variety of electronic devices.