Observation of the barrier structure in magnetic tunnel junctions using high-resolution electron microscopy and electron holography

Shen, Fang; Zhu, Tao; Xiang, X. H.; Xiao, John Q.; Voelkl, E.; Zhang, Z.

doi:10.1063/1.1637129

Cited by 14 publications

(10 citation statements)

References 13 publications

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“…Since the conventional TEM and HRTEM are difficult to resolve due to the delocalization effects, 11 EH has been applied to study the shape of barrier in single barrier MTJs by several researchers. [10][11][12] However, the shape of barrier in their reconstructed phase profile is found to be inconsistent. The AlO x layer in phase profile shows a "potential well" in Ref.…”

Section: Resultsmentioning

confidence: 99%

“…In some previous reports, electron holography ͑EH͒ has been used to study the structure and barrier shape of single barrier MTJs in which the AlO x barrier layers are relatively broad ͑Ͼ2 nm͒. [10][11][12] Since DBMTJs are complicated and more interfaces are involved, EH is considered to be very useful for the investigation of the microstructures of DBMTJs. On the other hand, two barriers in the DBMTJs are not similar to that in the single barrier MTJs and also different from each other in the same DBMTJ due to the specific deposition sequence; thus the double barriers with equal height are hard to be obtained.…”

Section: Introductionmentioning

confidence: 99%

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Microstructure investigation on barrier shapes of double barrier magnetic tunnel junctions

Wang

Zeng

Sharif

et al. 2006

Journal of Applied Physics

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Barrier shapes and its detailed microstructures in the double barrier magnetic tunnel junctions were intensively investigated by both high resolution transmission electron microscopy and electron holography. Two broad (>2nm) potential wells (i.e., shapes of AlOx layers) with slanted interfaces were observed in the electron hologram of the as-deposited samples. However, in the hologram of the annealed samples, two narrowed (down to 1.18nm) and almost equal (height) potential wells with sharp and steep interfaces were acquired. This indicates that the value of tunnel magnetoresistance can be increased from 12.8% to 29.4% at room temperature by annealing treatment where the sharpness and height of the barriers played a critical role.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Microstructure investigation on barrier shapes of double barrier magnetic tunnel junctions

Wang

Zeng

Sharif

et al. 2006

Journal of Applied Physics

Self Cite

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“…Hence, the top electrode was oxidized little for these two conflicting reasons and the top interface of the barrier is thus less sharp. Along the wedge direction of the Al layer, the sharpness of the bottom interface can change corresponding to the over-and under-oxidation in the barrier [14]. On the other hand, along the whole wedge, the top interfaces always have similar slopes, independent of the oxidation condition of the barrier.…”

Section: Structure Analysismentioning

confidence: 97%

Recent developments in magnetic tunnel junctions

et al. 2003

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The authors present various new phenomena in magnetic tunneling junction (MTJ). Since the interface and barrier structure play a significant role in determining the physical phenomena, they have employed various techniques to characterize this structure. For obtaining the barrier information, they have performed electron holography studies which directly show the energy profile with atomic resolution. The interdiffusion between different layers has been studied using high-resolution transmission electron microscopy, elemental mapping, and time-of-flight secondary ion mass spectrometry. With this structural information, the authors showed the existence of bulklike contribution in MTJ and determined the characteristic length. In addition, they also observed a conductance minimum anomaly which is much different from the normally observed zero bias anomaly. Large inversed TMR has also been observed at bias as high as 0.4 V in MTJs with an Al 2 O 3 -ZrO barrier. The authors have modified the Brinkman model by incorporating the voltage dependent density of states of the ferromagnetic electrodes, which sucessfully explains the bias dependence of the tunneling magnetoresistance (TMR), conductance minimum anomaly, and inversed TMR.Index Terms-Electron holography, magnetic tunneling junction (MTJ), tunneling magnetoresistance (TMR) bias dependence.

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“…25 On the other hand, there are also reports that the resistance-area product does not change during post-deposition annealing 26 or increases with annealing temperature. 27 The asymmetry in the shape of the barrier potential has been probed by using photoconductance 10 and off-axis electron holography 23,28 which allowed the asymmetric voltage dependence of the electron transport behavior to be observed. Transmission electron microscopy (TEM) is a powerful tool in the study of the microstructure and chemical distribution of materials at the sub-nanometer scale, and has proven to be particularly useful in the study of MTJs.…”

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confidence: 99%

Effect of annealing and applied bias on barrier shape in CoFe/MgO/CoFe tunnel junctions

et al. 2011

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Energy-filtered transmission electron microscopy and electron holography were used to study changes in the MgO tunnel barrier of CoFe/MgO/CoFe magnetic tunnel junctions as a function of annealing and in-situ applied electrical bias. Annealing was found to increase the homogeneity and crystallinity of the MgO tunnel barrier. Cobalt, oxygen and trace amounts of iron diffused into the MgO upon annealing. Annealing also resulted in a reduction of the tunneling barrier height, and decreased the resistance of the annealed MTJ relative to that of the asgrown sample. In-situ off-axis electron holography was employed to image the barrier potential profile of an MTJ directly, with the specimen under electrical bias. Varying the bias voltage from −1.5 V to +1.5 V was found to change the asymmetry of the barrier potential and decrease the effective barrier width as a result of charge accumulation at the MgO-CoFe interface. Introduction Metal-oxide interfaces are the subject of extensive experimental and theoretical research for next generation nano-scale spintronic devices that exploit spin as a degree of freedom for charged electrons. 1 They play a key role in metal-oxide based science and engineering, with applications including magnetic tunnel junctions (MTJs) 2 and other heterogeneous structures such as resistance switching oxides 3 with uses or potentials uses in low-power non-volatile memories. In its simplest form, the MTJ is a trilayer structure consisting of two ferromagnetic (FM) electrode layers separated by an ultra-thin dielectric layer. The electrical resistance across the insulating tunnel barrier is dependent upon the relative orientation of the magnetizations of the two ferromagnetic electrodes. In most cases, the electrical resistance is lower when the magnetization of the two ferromagnetic layers is

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Observation of the barrier structure in magnetic tunnel junctions using high-resolution electron microscopy and electron holography

Cited by 14 publications

References 13 publications

Microstructure investigation on barrier shapes of double barrier magnetic tunnel junctions

Microstructure investigation on barrier shapes of double barrier magnetic tunnel junctions

Recent developments in magnetic tunnel junctions

Effect of annealing and applied bias on barrier shape in CoFe/MgO/CoFe tunnel junctions

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