Novel Stack Structure of Magnetic Tunnel Junction with MgO Tunnel Barrier Prepared by Oxidation Methods: Preferred Grain Growth Promotion Seed Layers and Bi-layered Pinned Layer

Abstract

Despite superior compatibility to mass-production, magnetic tunnel junction (MTJ) with MgO barrier prepared by oxidation process (MgOx) has shown unacceptable magnetotransport properties for proper operation of spintronics devices because poor crystalline MgOx cannot properly provide a template for crystallization of amorphous CoFeB layers, thus lack of pseudo-epitaxy in overall. We report novel stack structure for MgOx-based MTJ to assure acceptable magnetotransport properties: insertion of preferred-grain-growth-promotion (PGGP) seed layer and bi-layered ferromagnetic pinned layer (bi-PL) to induce preferred grain growth in MgOx and crystallization of CoFeB layers at higher temperature annealing. Microstructure analysis confirms highly crystalline MgOx in pseudo-epitaxy with fully crystallized CoFeB via PGGP by high temperature annealing, attributed to enhanced thermal stability of bi-PL. Tunneling magnetoresistance (TMR) 132.6% at resistance-area product (RA) 1.2 Ω µm2 and 253% at 5.9 Ω µm2 from novel MTJ stack successfully satisfy specifications for spintronics devices.