Observation of boron diffusion in an annealed Ta/CoFeB/MgO magnetic tunnel junction with standing-wave hard x-ray photoemission

Abstract

The CoFeB/MgO system shows promise as a magnetic tunnel junction with perpendicular magnetization and low critical current densities for spin-torque driven magnetization switching. The distribution of B after annealing is believed to be critical to performance. We have studied the distribution of B in a Ta/Co0.2Fe0.6B0.2/MgO sample annealed at 300 °C for 1 h with standing-wave hard x-ray photoemission spectroscopy (SW-HXPS). Comparing experimental rocking curve data to x-ray optical calculations indicates diffusion of 19.5% of the B uniformly into the MgO and of 23.5% into a thin TaB interface layer. SW-HXPS is effective for probing depth distributions in such spintronic structures.

Spin–Orbit Effects in CoFeB/MgO Heterostructures with Heavy Metal Underlayers

“…This is consistent with earlier studies in which Ta is found to absorb boron from CoFeB. [64][65][66][67] There is also a possibility that the CoFeB layer intermixes with the neighboring HM layer, which will likely result in degradation of M S . However, for most cases, M S does not fall below that of bulk CoFeB, indicating that the degree of intermixing is not large.…”

“…As the thickness of the dead layer is less than half a nanometer in most cases, it is di±-cult to identify the constituting elements. Recent studies 66 have shown that a thin TaB layer forms at the interface between Ta and CoFeB. It is yet to be con¯rmed whether the di®usion of boron is responsible for the formation of the dead layer for¯lms with other HM underlayers.…”

Concentration and chemical-state profiles at heterogeneous interfaces with sub-nm accuracy from standing-wave ambient-pressure photoemission

“…Tailoring the exciting X-ray wave field into a standing wave is a method for achieving greater depth sensitivity in photoemission, and it has been applied to a number of solid/solid interfaces [13][14][15][16][17] . In fact this method has also been applied previously in X-ray reflectivity and emission measurements on multilayer systems and at the solid-liquid interface 2,18 , but photoemission has the significant advantages of being more interface sensitive due to the shorter escape depths of electrons and of providing more direct chemical-state information from chemical shifts in core-level binding energies.…”

Asymmetric angular dependence of spin-transfer torques in CoFe/Mg-B-O/CoFe magnetic tunnel junctions

“…[15][16][17][18] Meanwhile, the B atoms are pushed out of the CoFeB electrodes and then diffused into the MgO layers forming Mg-B-O spacer. [19][20][21][22][23] around (001) axis and compressing lattice slightly.…”