CoFeBMgO

CoFeBMgO refers to a ferromagnetic heterostructure that combines a cobalt-iron-boron alloy (CoFeB) with a magnesium oxide (MgO) layer. It is most notably used as part of magnetic tunnel junctions in spintronic devices such as magnetoresistive random-access memory (MRAM) and magnetic sensors.

Composition and structure: CoFeB is typically an amorphous alloy whose exact composition varies, commonly in the vicinity of 40–60% cobalt and iron and 10–20% boron. The MgO layer acts as a crystalline tunnel barrier. During post-deposition annealing, boron diffuses out of the CoFeB layer and the adjacent regions crystallize at the MgO interfaces, enabling more efficient coherent tunneling of electrons across the barrier.

Properties: The MgO-based MTJs with CoFeB electrodes exhibit high tunneling magnetoresistance due to symmetry filtering, particularly for electrons with Δ1 symmetry. This arrangement can support perpendicular magnetic anisotropy in thin CoFeB layers, aiding scaling for memory applications. CoFeB also offers relatively low magnetic damping, which benefits switching dynamics in MRAM and related devices.

Fabrication and applications: CoFeB and MgO stacks are typically deposited by magnetron sputtering and then subjected to annealing at moderate temperatures to crystallize the interfaces. The resulting structures are central to STT-MRAM and other spintronic devices, including read heads and sensors, where high TMR and low switching energy are desirable.

Variants and challenges: Variations in CoFeB composition, annealing conditions, and layer thickness affect TMR, PMA strength, and thermal stability. Boron diffusion and interfacial intermixing must be controlled to maintain performance over time and temperature, posing ongoing materials engineering challenges.