Optimizing Perpendicular Magnetic Anisotropy in MgO/CoFeB Structures Through Ultrathin CoFeB-Enhanced Ta Capping Layers

Abstract

This study presents an innovative approach to optimizing perpendicular magnetic anisotropy (PMA) in CoFeB/MgO structures through the strategic insertion of an ultrathin CoFeB layer between the top capping layer (Ta or Mo) and the CoFeB/MgO stack. Adding a 0.43 nm CoFeB insertion layer significantly enhances PMA by improving Fe-O hybridization, suppressing interfacial diffusion, and stabilizing MgO crystallinity. Postannealing at 400 °C, the CoFeB (free)/MgO (capping)/CoFeB (0.43 nm insertion layer)/Ta (top capping) configuration demonstrates superior performance, achieving an interfacial anisotropy constant (K_i ) of 3.8 erg/cm², the highest reported for similar structures under these conditions. Advanced analyses using high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy reveal that the ultrathin CoFeB insertion effectively mitigates diffusion from the top capping layer, maintaining optimal oxidation and structural integrity at the interface. These findings not only deepen the understanding of PMA enhancement mechanisms but also provide a thermally stable, high-performance solution compatible with CMOS back-end-of-line processing. This work underscores the potential of interfacial engineering for advancing next-generation spintronic technologies.