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Parallel fabrication of magnetic tunnel junction nanopillars by nanosphere lithography.

Wang WG, Pearse A, Li M, Hageman S, Chen AX, Zhu FQ, Chien CL - Sci Rep (2013)

Bottom Line: We present a new method for fabricating magnetic tunnel junction nanopillars that uses polystyrene nanospheres as a lithographic template.Novel voltage induced switching has been observed in these structures.This method provides a cost-effective way of rapidly fabricating a large number of tunnel junction nanopillars in parallel.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA. wgwang@physics.arizona.edu

ABSTRACT
We present a new method for fabricating magnetic tunnel junction nanopillars that uses polystyrene nanospheres as a lithographic template. Unlike the common approaches, which depend on electron beam lithography to sequentially fabricate each nanopillar, this method is capable of patterning a large number of nanopillars simultaneously. Both random and ordered nanosphere patterns have been explored for fabricating high quality tunneling junctions with magnetoresistance in excess of 100%, employing ferromagnetic layers with both out-of-plane and in-plane easy axis. Novel voltage induced switching has been observed in these structures. This method provides a cost-effective way of rapidly fabricating a large number of tunnel junction nanopillars in parallel.

No MeSH data available.


(a) Distribution of resistance in 2 μm × 2 μm cells on a wafer with wedge shaped MgO barrier. The lines are guides for eyes only. (b) corresponding TMR ratios of the cells. (c) Histogram showing the counts of cells containing one, two or more nanopillars. (d) Representative TMR curve of a single-pillar cell. Inset shows the unipolar switching achieved with −0.76 V and −1.2 V pulses.
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f3: (a) Distribution of resistance in 2 μm × 2 μm cells on a wafer with wedge shaped MgO barrier. The lines are guides for eyes only. (b) corresponding TMR ratios of the cells. (c) Histogram showing the counts of cells containing one, two or more nanopillars. (d) Representative TMR curve of a single-pillar cell. Inset shows the unipolar switching achieved with −0.76 V and −1.2 V pulses.

Mentions: The intersection of the top Ta/Au electrode and the bottom mesa structure forms a 2 μm × 2 μm cell. Each cell has two top contact pads and two bottom contact pads (shared) for the 4-probe measurement. For a given distribution of nanospheres, there is a specific probability for having a certain number of nanopillar(s) present in a 2 μm × 2 μm cell. We have tested 200 such 2 μm × 2 μm cells patterned on a blanket film with a wedge-shaped MgO barrier (0.95 nm – 1.35 nm). About half of the 200 cells showed open-circuit (R > 107 Ω ), indicating no nanopillar in these cells. For the rest of cells, the resistance R is shown in Fig. 3a, where LogR increases linearly with the MgO thickness as expected for good MTJs. The tunneling magnetoresistance (TMR) of these MTJs are shown in Fig. 3b, where MTJs show TMR near 100% for this wafer after annealing for 10 min at 300°C, demonstrating that high quality MTJ structure has been achieved in majority of the nanopillars3234.


Parallel fabrication of magnetic tunnel junction nanopillars by nanosphere lithography.

Wang WG, Pearse A, Li M, Hageman S, Chen AX, Zhu FQ, Chien CL - Sci Rep (2013)

(a) Distribution of resistance in 2 μm × 2 μm cells on a wafer with wedge shaped MgO barrier. The lines are guides for eyes only. (b) corresponding TMR ratios of the cells. (c) Histogram showing the counts of cells containing one, two or more nanopillars. (d) Representative TMR curve of a single-pillar cell. Inset shows the unipolar switching achieved with −0.76 V and −1.2 V pulses.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3674430&req=5

f3: (a) Distribution of resistance in 2 μm × 2 μm cells on a wafer with wedge shaped MgO barrier. The lines are guides for eyes only. (b) corresponding TMR ratios of the cells. (c) Histogram showing the counts of cells containing one, two or more nanopillars. (d) Representative TMR curve of a single-pillar cell. Inset shows the unipolar switching achieved with −0.76 V and −1.2 V pulses.
Mentions: The intersection of the top Ta/Au electrode and the bottom mesa structure forms a 2 μm × 2 μm cell. Each cell has two top contact pads and two bottom contact pads (shared) for the 4-probe measurement. For a given distribution of nanospheres, there is a specific probability for having a certain number of nanopillar(s) present in a 2 μm × 2 μm cell. We have tested 200 such 2 μm × 2 μm cells patterned on a blanket film with a wedge-shaped MgO barrier (0.95 nm – 1.35 nm). About half of the 200 cells showed open-circuit (R > 107 Ω ), indicating no nanopillar in these cells. For the rest of cells, the resistance R is shown in Fig. 3a, where LogR increases linearly with the MgO thickness as expected for good MTJs. The tunneling magnetoresistance (TMR) of these MTJs are shown in Fig. 3b, where MTJs show TMR near 100% for this wafer after annealing for 10 min at 300°C, demonstrating that high quality MTJ structure has been achieved in majority of the nanopillars3234.

Bottom Line: We present a new method for fabricating magnetic tunnel junction nanopillars that uses polystyrene nanospheres as a lithographic template.Novel voltage induced switching has been observed in these structures.This method provides a cost-effective way of rapidly fabricating a large number of tunnel junction nanopillars in parallel.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, Maryland 21218, USA. wgwang@physics.arizona.edu

ABSTRACT
We present a new method for fabricating magnetic tunnel junction nanopillars that uses polystyrene nanospheres as a lithographic template. Unlike the common approaches, which depend on electron beam lithography to sequentially fabricate each nanopillar, this method is capable of patterning a large number of nanopillars simultaneously. Both random and ordered nanosphere patterns have been explored for fabricating high quality tunneling junctions with magnetoresistance in excess of 100%, employing ferromagnetic layers with both out-of-plane and in-plane easy axis. Novel voltage induced switching has been observed in these structures. This method provides a cost-effective way of rapidly fabricating a large number of tunnel junction nanopillars in parallel.

No MeSH data available.