<i>In-situ</i> characterization of rapid crystallization of amorphous CoFeB electrodes in CoFeB/MgO/CoFeB junctions during thermal annealing

Wang, W. G.; Jordan-Sweet, Jean; Miao, Guo‐Xing; Ni, Chaoying; Rumaiz, Abdul K.; Shah, Lubna; Fan, Xin; Parsons, Paul; Stearrett, Ryan; Nowak, E. R.; Moodera, J. S.; Xiao, John Q.

doi:10.1063/1.3273397

Cited by 51 publications

(33 citation statements)

References 27 publications

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“…The same behavior has been reported by Wang et al before [17]. In a subsequent paper [18], these authors studied the kinetics of crystallization processes by x-ray diffraction and electron microscopy and identified the crystallization of CoFeB in an inhomogeneous solid-state epitaxy mode. By combining the time evolution of CoFeB crystallization with spin-dependent coherent tunneling, which is strongly affected by the defect density in the MgO barrier, they later attempted to quantitatively separate the contributions of structural changes in the barrier and the electrodes during annealing [19].…”

Section: Resultssupporting

confidence: 58%

“…Specific useful information has been obtained from the time evolution of the TMR ratio during annealing. In particular, it was shown by in situ synchrotron-based x-ray diffraction that for annealing at 420 • C the gradual increase of the TMR ratio is primarily related to a progressive crystallization of the CoFeB electrodes [18]. However, in these studies the effect of annealing on the I -V characteristics was not considered.…”

Section: Introductionmentioning

confidence: 99%

“…The kinetics of the processes occurring during annealing have been studied in detail [17][18][19]. Specific useful information has been obtained from the time evolution of the TMR ratio during annealing.…”

Section: Introductionmentioning

confidence: 99%

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Conductance anomalies of CoFeB/MgO/CoFeB magnetic tunnel junctions

et al. 2014

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The I -V characteristics of CoFeB/MgO/CoFeB magnetic tunnel junctions show pronounced nonlinearities which are relevant both for sensor applications and for the basic understanding of spin-dependent tunneling. To study the relation between the tunnel characteristics and the tunnel magnetoresistance (TMR) ratio, a series of CoFeB/MgO/CoFeB junctions was annealed with stepwise increasing annealing time at different temperatures. The related TMR ratio and the I -V characteristics were measured in the temperature range between 15 K and 300 K. This allowed the comparison of I -V characteristics of the same junction for TMR ratios between 25% and 150% at 300 K thus eliminating the influence of variations in the preparation process of separate individual samples. In addition to a zero bias anomaly observed in particular at low temperatures and for large TMR ratios, a conductance anomaly in the I -V curves was observed around a bias voltage of 350 mV. A general correlation between the deviation from Ohmic I -V characteristics and the TMR ratio was found both for parallel and antiparallel magnetizations of both ferromagnetic layers. This means that the shape of the I -V curves directly scales with the spin polarization of the tunneling current and the proportion of coherent electron tunneling. Both the 350 mV conductance anomaly and the correlation between non-Ohmic characteristics and the TMR ratio can be explained by considering the contributions of the relevant majority and minority spin bands of the ferromagnetic contacts.

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Section: Resultssupporting

confidence: 58%

Section: Introductionmentioning

confidence: 99%

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Conductance anomalies of CoFeB/MgO/CoFeB magnetic tunnel junctions

et al. 2014

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“…Presently, sensors used in modern disk drives rely on tunnel magnetoresistance (TMR) in trilayer CoFeB/MgO/CoFeB structures, which succeeds earlier generation devices based on CoFe [4,7]. While device fabrication has been empirically refined to meet strict quality demands, the fundamental understanding of the modifications in the TMR structure introduced by various optimization processes, e.g., postannealing [8][9][10][11][12][13][14][15][16], resulting in a different magnitude of the TMR [10,11], is still missing. In particular, the behavior of boron, apparently playing a crucial role for high magnetoresistance, has remained controversial in spite of extensive investigations [12,13,[15][16][17][18][19][20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Role of boron diffusion in CoFeB/MgO magnetic tunnel junctions

et al. 2015

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Several scientific issues concerning the latest generation read heads for magnetic storage devices, based on CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) are known to be controversial, including such fundamental questions as to the behavior and the role of B in optimizing the physical properties of these devices. Quantitatively establishing the internal structures of several such devices with different annealing conditions using hard x-ray photoelectron spectroscopy, we resolve these controversies and establish that the B diffusion is controlled by the capping Ta layer, though Ta is physically separated from the layer with B by several nanometers. While explaining this unusual phenomenon, we also provide insight into why the tunneling magnetoresistance (TMR) is optimized at an intermediate annealing temperature, relating it to B diffusion, coupled with our studies based on x-ray diffraction and magnetic studies.

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“…5 Therefore, the annealing effect on the magnetic anisotropy of CoFeB thin films is a crucial process and has been widely discussed. 4,[6][7][8] In this work, the annealing effect on perpendicular magnetic anisotropy (PMA) of a CoFeB/MgO ultra thin film is investigated with ferromagnetic resonance (FMR) technique. FMR is well known to provide high sensitivity on magnetic anisotropy and dynamic properties.…”

Section: Introductionmentioning

confidence: 99%

Ferromagnetic resonance probed annealing effects on magnetic anisotropy of perpendicular CoFeB/MgO bilayer

Chen

Cheng

Chern

et al. 2012

Journal of Applied Physics

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The annealing effects of perpendicular MgO/CoFeB/Ta structure are investigated with ferromagnetic resonance technique. The data of angular dependent resonance field, linewidth, and intensity are obtained for both as-grown and annealed samples. An increment of magnetic out-of-plane anisotropy field from 1800 to 3300 Oe with annealing is observed, which should be related to the improvement of crystalline at the interface. Ferromagnetic resonance linewidth significantly broadens after annealing, and this broadening is attributed to the enhancement of inhomogeneity of the internal field.

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In-situ characterization of rapid crystallization of amorphous CoFeB electrodes in CoFeB/MgO/CoFeB junctions during thermal annealing

Cited by 51 publications

References 27 publications

Conductance anomalies of CoFeB/MgO/CoFeB magnetic tunnel junctions

Conductance anomalies of CoFeB/MgO/CoFeB magnetic tunnel junctions

Role of boron diffusion in CoFeB/MgO magnetic tunnel junctions

Ferromagnetic resonance probed annealing effects on magnetic anisotropy of perpendicular CoFeB/MgO bilayer

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