Thermal annealing of junctions with amorphous and polycrystalline ferromagnetic electrodes

Dimopoulos, Théodoros; Gieres, G.; Wecker, J.; Wiese, N.; Sacher, Marc

doi:10.1063/1.1808899

Cited by 28 publications

(18 citation statements)

References 13 publications

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“…The temperature at which the x-ray scattering indicates sharpening of the Co 60 Fe 20 B 20 / AlO x interface corresponds directly to the temperature at which the maximum TMR occurs. 7 This sharpening takes place in the amorphous phase of Co 60 Fe 20 B 20 , well below the crystallization temperature determined by high-angle x-ray diffraction, and provides direct evidence of the importance of interface structure in determining the magnitude of the TMR in MTJ devices. …”

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Interface sharpening in CoFeB magnetic tunnel junctions

Pym

Lamperti

Tanner

et al. 2006

Applied Physics Letters

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We report grazing incidence x-ray scattering evidence for sharpening of the interface between amorphous Co60Fe20B20 and AlOx during in situ annealing below the Co60Fe20B20 crystallization temperature. Enhancement of the interference fringe amplitude in the specular scatter and the absence of changes in the diffuse scatter indicate that the sharpening is not a reduction in topological roughness but a reduction in the width of the chemical composition profile across the interface. The temperature at which the sharpening occurs corresponds to that at which a maximum is found in the tunneling magnetoresistance of magnetic tunnel junctions.

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Interface sharpening in CoFeB magnetic tunnel junctions

Pym

Lamperti

Tanner

et al. 2006

Applied Physics Letters

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“…There is a small increase in alumina barrier thickness at the higher annealing temperatures which may be responsible for the increase in resistance-area product observed above about 300°C. 6 The reduction in alumina barrier density may be associated both with a change in stochiometry, from the reduction in interface width, and the conservation of material necessary upon increase in the barrier thickness. Increase in density of the Co 0.6 Fe 0.2 B 0.2 layers is consistent with conservation of material upon decrease in Co 0.6 Fe 0.2 B 0.2 layer thickness.…”

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“…6,15 Calculation of the spindependent tunneling in epitaxial MgO/Fe junctions 20 reveals that interface disorder significantly reduces the TMR and by implication, reduction in interface intermixing width should also enhance the spin coherence in the amorphous system. However, associated with the increased TMR on annealing is also a rise in the resistance-area product.…”

Section: -3mentioning

confidence: 99%

“…5 We have previously reported experiments showing that in the annealing process, used to maximize the TMR without pushing the resistance-area product unacceptably high, 6 the interface between the alumina barrier and bottom CoFeB electrode reduces in width, there being no change in topological roughness. 7 As the grazing incidence x-ray scattering experiments were conducted on partial device structures, this conclusion of chemical sharpening arose from detailed modeling of complex reflectivity profiles.…”

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Layer and interface structural changes in Co0.6Fe0.2B0.2/AlOx multilayers on annealing

Pym

Rührig

Tanner

2010

Journal of Applied Physics

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Sputtered multilayers of Co 0.6 Fe 0.2 B 0.2 and AlO x have been measured using grazing incidence x-ray scattering to determine the changes in layer and interface structure during in situ annealing. We confirm our earlier deduction of a sharpening of the interfaces on annealing up to 400°C. This sharpening arises from reduction in chemical intermixing, not from change in topological roughness and provides an explanation for the enhanced tunneling magnetoresistance. The annealing is shown to result in a decrease in Co 0.6 Fe 0.2 B 0.2 mean layer thickness and increase in the layer density. There is a commensurate increase in AlO x mean layer thickness while at the same time there is a reduction in the layer density. The increase in thickness could explain the corresponding increase observed in the resistance-area product.

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“…[6][7][8][9]11 Despite a great deal of work relating Mn diffusion to annealing temperature T a ͑Refs. 12-14͒ and to oxygen diffusion, 9 and the speculation 14 that at moderate T a amorphous CoFeB can block Mn diffusion more effectively than polycrystalline CoFe, there is not a clear physical picture of Mn-diffusion mechanism and what roles individual microstructures play.…”

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Temperature-dependent Mn-diffusion modes in CoFeB- and CoFe-based magnetic tunnel junctions: Electron-microscopy studies

et al. 2007

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We show that Mn atoms diffuse with two different mechanisms at high and low temperatures in CoFeB-and CoFe-based magnetic tunnel junctions. By combining high resolution and scanning transmission electron microscopy, we reveal that below 300°C, the amorphous CoFeB and the textured CoFe are equally effective in blocking the diffusion of Mn, contradicting the conventional wisdom that the diffusion occurs primarily along grain boundaries. Below 300°C, Mn diffusion in crystalline CoFe occurs through the bulk and is assisted by oxygen atoms which only diffuse parallel to the bcc close-packed ͑110͒ plane. Above 300°C, Mn diffuses through vacancies along the grain boundaries of CoFe and in the bulk of amorphous CoFeB. A universal diffusion temperature is proposed based on an isokinetic relation. The physics of spintronics devices 1-5 is studied in terms of their electronic, magnetic, and structural properties. These properties are intimately connected. The first two have been reasonably understood. The much less understood structural property of magnetic tunnel junctions ͑MTJs͒ includes the critical question of their thermal stability. It is known that Mn atoms diffuse into the barrier layer and act as magnetic impurity, which can greatly reduce the tunneling magnetoresistance ͑TMR͒ of MTJs in a manner similar to spin valves. [6][7][8][9]11 Despite a great deal of work relating Mn diffusion to annealing temperature T a ͑Refs. 12-14͒ and to oxygen diffusion, 9 and the speculation 14 that at moderate T a amorphous CoFeB can block Mn diffusion more effectively than polycrystalline CoFe, there is not a clear physical picture of Mn-diffusion mechanism and what roles individual microstructures play.It was shown that the measured diffusivity of Mn in Co cannot account for the observed Mn profile in annealed MTJs, and oxygen-assisted diffusion was proposed 9 as the most likely Mn-diffusion mechanism. Usually, diffusion along grain boundaries is much faster than in the bulk.10 This is the assumed reason for why amorphous CoFeB can block Mn ͑or oxygen͒ diffusion. This assumption implies that diffusion mechanisms in crystalline CoFe and amorphous CoFeB are different. Then, is it a coincidence that the TMRs for both types of MTJs peak at the same annealing temperature of just below 300°C?In this paper, we first present observations from CoFeBand CoFe-based MTJs using high resolution transmission electron microscopy ͑HRTEM͒ and high angle annular dark field ͑HAADF͒ image with line scan energy dispersive spectrum ͑EDS͒ in scanning transmission electron microscopy ͑STEM͒ mode. We show that both amorphous CoFeB and textured polycrystalline CoFe can effectively block Mn diffusion at low temperature, while nontextured polycrystalline CoFe cannot. Based on this observation, we propose that two different diffusion mechanisms are at play. At low temperature, the dominant mechanism is oxygen-assisted Mn diffusion. Such diffusion occurs more easily through the bulk of the crystalline CoFe but only parallel to the close-packed ͑110͒ plane, whi...

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Thermal annealing of junctions with amorphous and polycrystalline ferromagnetic electrodes

Cited by 28 publications

References 13 publications

Interface sharpening in CoFeB magnetic tunnel junctions

Interface sharpening in CoFeB magnetic tunnel junctions

Layer and interface structural changes in Co0.6Fe0.2B0.2/AlOx multilayers on annealing

Temperature-dependent Mn-diffusion modes in CoFeB- and CoFe-based magnetic tunnel junctions: Electron-microscopy studies

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