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Thick CoFeB with perpendicular magnetic anisotropy in CoFeB-MgO based magnetic tunnel junction
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Figures

Image of FIG. 1.

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FIG. 1.

(a) Schematic diagrams of the stack structures of baseline and Ta inserted CoFeB stacks. (b) and (c) M-H loops for baseline and Ta inserted CoFeB stacks for T a = 250 °C. (d) The critical thickness (t c ) of CoFeB needed to sustain PMA as a function of Ta thickness.

Image of FIG. 2.

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FIG. 2.

CoFeB thickness dependence of (a) saturation magnetization (M S ) and (b) the product of effective magnetic anisotropy constant (K eff ) and thickness of CoFeB i.e., K eff .t for different Ta thickness for T a = 250 °C. The inset shows the same for fixed CoFeB thickness of 1.65 nm with Ta thickness variation.

Image of FIG. 3.

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FIG. 3.

CoFeB thickness dependence of (a) surface anisotropy constant (K S ) and (b) anisotropic field (H K ) for different Ta thickness for T a = 250 °C. The inset shows the same for fixed CoFeB thickness of 1.6 nm with Ta thickness variation.

Image of FIG. 4.

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FIG. 4.

The out-of-plane M-H loops for baseline and Ta inserted CoFeB stacks annealed at two selected temperatures, T a = 250 °C and 300 °C for 1 hour.

Image of FIG. 5.

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FIG. 5.

Tunnel magnetoresistance (TMR) and resistance-area product (RA) as a function of CoFeB thickness for both baseline and Ta inserted CoFeB magnetic tunnel junctions annealed at three selected temperatures, T a = 240 °C, 270 °C and 300 °C for 1 hour.

Image of FIG. 6.

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FIG. 6.

Thermal stability factor (Δ = K effV/k BT) for of baseline and Ta inserted CoFeB free layers with T a = 250 °C as a function of STT-MRAM device size.

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/content/aip/journal/adva/2/4/10.1063/1.4771996
2012-12-12
2014-04-24

Abstract

We have investigated the effect of an ultra-thin Ta insertion in the CoFeB (CoFeB/Ta/CoFeB) free layer (FL) on magnetic and tunneling magnetoresistance (TMR) properties of a CoFeB-MgO system with perpendicular magnetic anisotropy (PMA). It is found that the critical thickness (t c ) to sustain PMA is doubled (t c = 2.6 nm) in Ta-inserted CoFeB FL as compared to single CoFeB layer (t c = 1.3 nm). While the effective magnetic anisotropy is found to increase with Ta insertion, the saturation magnetization showed a slight reduction. As the CoFeB thickness increasing, the thermal stability of Ta inserted structure is significantly increased by a factor of 2.5 for total CoFeB thickness less than 2 nm. We have observed a reasonable value of TMR for a much thicker CoFeB FL (thickness = 2-2.6 nm) with Ta insertion, and without significant increment in resistance-area product. Our results reveal that an ultra-thin Ta insertion in CoFeB might pay the way towards developing the high-density memory devices with enhanced thermal stability.

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Scitation: Thick CoFeB with perpendicular magnetic anisotropy in CoFeB-MgO based magnetic tunnel junction
http://aip.metastore.ingenta.com/content/aip/journal/adva/2/4/10.1063/1.4771996
10.1063/1.4771996
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