Magnetic Tunnel Junctions with Low Resistance-area Product of 0.5 Ωμm2

裕二, 上原; 篤史, 古屋; 和晋, 須永; 豊生, 宮島; 均, 金井

doi:10.3379/msjmag.1003r027

Cited by 14 publications

(17 citation statements)

References 13 publications

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“…This value exceeded that of hexagonal ZnO films grown by sputtering technique and used as tunnel barrier in ZnO-MTJs previously reported. 6 The use of O 2 flow of 2.0 SCCM enhanced the epitaxial growth of ZnO films on Co 3 Pt buffer layers and prevented the massive oxidation of the latter ones surfaces. …”

Section: Discussionmentioning

confidence: 99%

“…4 Also, many groups have reported their research results on ZnO-based MTJs and detected a positive MR ratio in fully epitaxial oxide-stacks 5 or with rock-salt type ZnO (001)-based MTJs. 6 All these MTJs structures were deposited by sputtering techniques. Nevertheless, the combination of ferromagnetic (FM) metals with high quality hexagonal ZnO films in MTJs has not been revealed yet.…”

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confidence: 99%

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Investigation of ZnO thin films deposited on ferromagnetic metallic buffer layer by molecular beam epitaxy toward realization of ZnO-based magnetic tunneling junctions

Belmoubarik

Nozaki

Endo

et al. 2013

Journal of Applied Physics

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Section: Discussionmentioning

confidence: 99%

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confidence: 99%

Investigation of ZnO thin films deposited on ferromagnetic metallic buffer layer by molecular beam epitaxy toward realization of ZnO-based magnetic tunneling junctions

Belmoubarik

Nozaki

Endo

et al. 2013

Journal of Applied Physics

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“…Thanks to the coherent spin-polarized tunneling, the observed MR ratio is several times higher than those reported in MTJs consisting of polycrystalline FM electrodes with an amorphous GaO x barrier (at most ~22% at RT) [22,23,24]. This is the highest value among the reported MTJs with a SC barrier at RT [14,15,22,23,24,25,26,27,28,29,30,31]. It was found in the fully epitaxial MTJs that the growth of a few monoatomic (ML; 1 ML = 0.21 nm) MgO(001) underlying layers on the Fe(001) bottom electrode are indispensable to realize a high MR ratio and that a tunneling MR (TMR) effect cannot be observed without the MgO underlying layer.…”

Section: Introductionmentioning

confidence: 90%

“…Semiconductors (SC) have great potential as the tunnel-barrier of MTJ for a low resistance-area product [14,15] because of its rather narrow band-gap, compared with insulators. Also, fully single-crystalline FM/SC/FM structure is one of the important building blocks of a vertical-type spin field-effect-transistor having nonvolatile memory functionality [16,17,18,19].…”

Section: Introductionmentioning

confidence: 99%

Effect of MgO Underlying Layer on the Growth of GaOx Tunnel Barrier in Epitaxial Fe/GaOx/(MgO)/Fe Magnetic Tunnel Junction Structure

Narayananellore

Doko

Matsuo

et al. 2017

Sensors

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We investigated the effect of a thin MgO underlying layer (~3 monoatomic layers) on the growth of GaOx tunnel barrier in Fe/GaOx/(MgO)/Fe(001) magnetic tunnel junctions. To obtain a single-crystalline barrier, an in situ annealing was conducted with the temperature being raised up to 500 °C under an O2 atmosphere. This annealing was performed after the deposition of the GaOx on the Fe(001) bottom electrode with or without the MgO(001) underlying layer. Reflection high-energy electron diffraction patterns after the annealing indicated the formation of a single-crystalline layer regardless of with or without the MgO layer. Ex situ structural studies such as transmission electron microscopy revealed that the GaOx grown on the MgO underlying layer has a cubic MgAl2O4-type spinel structure with a (001) orientation. When without MgO layer, however, a Ga-Fe-O ternary compound having the same crystal structure and orientation as the crystalline GaOx was observed. The results indicate that the MgO underlying layer effectively prevents the Fe bottom electrode from oxidation during the annealing process. Tunneling magneto-resistance effect was observed only for the sample with the MgO underlying layer, suggesting that Ga-Fe-O layer is not an effective tunnel-barrier.

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“…This means the necessity of alternative barriers having a low barrier height. Doping other elements into MgO has been known to reduce the MgO barrier height; e.g., Zn 6,7 and Ti 8 dopings were reported to provide lower RA values although such dopings are likely to cause reduction of TMR ratios.…”

mentioning

confidence: 99%

MgGa2O4 spinel barrier for magnetic tunnel junctions: Coherent tunneling and low barrier height

Sukegawa

Kato

Belmoubarik

et al. 2017

Applied Physics Letters

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Epitaxial Fe/magnesium gallium spinel oxide (MgGa2O4)/Fe(001) magnetic tunnel junctions (MTJs) were fabricated by magnetron sputtering. Tunnel magnetoresistance (TMR) ratio up to 121% at room temperature (196% at 4 K) was observed, suggesting a TMR enhancement by the coherent tunneling effect in the MgGa2O4 barrier. The MgGa2O4 layer had a spinel structure and it showed good lattice matching with the Fe layers owing to slight tetragonal lattice distortion of MgGa2O4. Barrier thickness dependence of the tunneling resistance and current-voltage characteristics revealed that the barrier height of the MgGa2O4 barrier is much lower than that in an MgAl2O4 barrier. This study demonstrates the potential of Ga-based spinel oxides for MTJ barriers having a large TMR ratio at a low resistance area product. * Electronic mail: sukegawa.hiroaki@nims.go.jp 2 Magnetic tunnel junctions (MTJs) have played a central role in spintronic devices such as read heads of hard disk drives and non-volatile magnetoresistive random access memories (MRAMs) for the last two decades, and many efforts have been made to improve their performance. 1 One of the most prominent achievements which accelerated the practical applications was the realization of giant tunnel magnetoresistance (TMR) ratios by using rock-salt type MgO crystalline barrier. [2][3][4][5] The giant TMR effect is attributed to the spin-dependent coherent tunneling through the 1 Bloch state in MgO(001). Toward ultra-high density spin transfer torque (STT)-MRAM applications, MTJs with low resistance area (RA) product of around 1 m 2 are needed as well as high TMR ratios. In MgO-based MTJs, the thickness of the MgO barrier must be reduced to a few monoatomic layers for achieving such a low RA, which causes substantial reduction of TMR ratios. This means the necessity of alternative barriers having a low barrier height. Doping other elements into MgO has been known to reduce the MgO barrier height; e.g., Zn 6,7 and Ti 8 dopings were reported to provide lower RA values although such dopings are likely to cause reduction of TMR ratios.Spinel oxide MgAl2O4(001) barrier also exhibits the coherent tunneling effect, 9,10 and over 300% TMR ratios at room temperature (RT) were reported in MgAl2O4-based MTJs. 11,12 Very recently, a TMR ratio at RT of 92% in an MgO/spinel-type -Ga2O3(001) bilayer barrier MTJ 13 and that of 120% in a Li-Mg-Al-O quaternary spinel-based barrier MTJ were reported, 14 showing the capability of the spinel based barriers for MTJs. The lattice spacing of MgAl2O4 is 4% smaller than that of MgO. In 3 addition, the lattice spacing can further be tuned by the Mg/Al composition, leading to the highly lattice-matched interfaces with various ferromagnetic materials. 9,12 On the other hand, the experimental band gap of MgAl2O4 is reported to be 7.8 eV, 15 which is similar to that of MgO (7.587.8 eV); 15 therefore, no reduction in RA values using an MgAl2O4 barrier was observed. 16 Some of spinel oxides other than MgAl2O4, such as ZnAl2O4, SiMg2O4 and SiZ...

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Magnetic Tunnel Junctions with Low Resistance-area Product of 0.5 Ωμm2

Cited by 14 publications

References 13 publications

Investigation of ZnO thin films deposited on ferromagnetic metallic buffer layer by molecular beam epitaxy toward realization of ZnO-based magnetic tunneling junctions

Investigation of ZnO thin films deposited on ferromagnetic metallic buffer layer by molecular beam epitaxy toward realization of ZnO-based magnetic tunneling junctions

Effect of MgO Underlying Layer on the Growth of GaOx Tunnel Barrier in Epitaxial Fe/GaOx/(MgO)/Fe Magnetic Tunnel Junction Structure

MgGa2O4 spinel barrier for magnetic tunnel junctions: Coherent tunneling and low barrier height

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