Evidence for boron diffusion into sub-stoichiometric MgO (001) barriers in CoFeB/MgO-based magnetic tunnel junctions

Journal Article · Sun Apr 28 04:00:00 EDT 2013 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4802692· OSTI ID:22102364

Harnchana, V. ^[1]; Hindmarch, A. T.; Marrows, C. H. ^[2]; Sarahan, M. C. ^[3]; Brown, A. P.; Brydson, R. M. D. ^[1]

---

1. Institute for Materials Research, School of Process, Environmental and Materials Engineering, University of Leeds, Leeds LS2 9JT (United Kingdom)
2. School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom)
3. EPSRC UK National SuperSTEM Facility for Aberration-corrected STEM, Daresbury Laboratories, Warrington WA4 4AD (United Kingdom)

Evidence of boron diffusion into the MgO barrier of a CoFeB/MgO based magnetic tunnel junction has been identified using analytical scanning transmission electron microscopy (STEM) and X-ray photoelectron spectroscopy. Structures were deposited by DC/RF-magnetron sputtering, where defective, sub-stoichiometric MgO barriers degrading device performance have been previously mitigated against by deposition of thin Mg layers prior to MgO deposition. We show that despite the protection offered by the Mg layer, disorder in the MgO barrier is still evident by STEM analysis and is a consequence of the oxidation of the Co{sub 40}Fe{sub 40}B{sub 20} surface during MgO deposition. Evidence of boron diffusion from CoFeB into the MgO barrier in the as-deposited and annealed structure is also presented, which in the as-deposited case we suggest results from the defective structures at the barrier interfaces. Annealing at 375 Degree-Sign C results in the presence of B in the trigonal coordination of [BO{sub 3}]{sup 3-} in the MgO barrier and partial crystallization of the top electrode (we presume there is also some boron diffusion into the Ta capping layer). The bottom electrode, however, fails to crystallize and much of the boron is retained in this thicker electrode. A higher annealing temperature or lower initial boron content is required to crystallize the bottom electrode.

• OSTI ID: 22102364
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 16 Vol. 113; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANNEALING
BORON
BORON COMPOUNDS
COBALT COMPOUNDS
CRYSTALLIZATION
DEPOSITION
DIFFUSION
INTERFACES
IRON COMPOUNDS
LAYERS
MAGNESIUM OXIDES
MAGNETORESISTANCE
SCANNING ELECTRON MICROSCOPY
STOICHIOMETRY
SUPERCONDUCTING JUNCTIONS
TERNARY ALLOY SYSTEMS
TRANSMISSION ELECTRON MICROSCOPY
TUNNEL EFFECT
X-RAY PHOTOELECTRON SPECTROSCOPY