Difference between chemical structures of the interface at the Al-oxide tunneling barrier prepared by plasma or by radical oxidation

Jongill Hong, Donkoun Lee, Yoonsung Han, Kyenam Lee, Inwoo Jang, Youngjin Park, Min Kyu Lee, Ha Jin Song, Hyun Joon Shin, Koji Tsunekawa, Naoki Watanabe

Research output: Contribution to journalArticle

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Abstract

We have studied chemical structures of the interface between the Al-oxide tunneling barrier and the underlying Co90Fe10 layer in magnetic tunnel junctions when a 1-nm thick metallic Al barrier was oxidized by two different methods: plasma oxidation and radical oxidation. Our chemical analyses confirmed that the underlying CoFe layer was unavoidably attacked by oxygen during the oxidation and that this left different oxide states at the AlOx/CoFe interface, depending on the oxidation method. The radical oxidation required long oxidation time for optimizing tunneling performance and resulted in a large amount of oxygen at the interface, which, in turn, resulted in the formation of mostly α-Fe2O3 and Al2O3. Conversely, the plasma oxidation required a relatively short oxidation time for optimization and left FeO as a dominant phase at the interface. Our results also show that the thermal treatment helped AlOx, an oxygen-deficient phase, to be re-oxidized and transformed into Al2O3, the thermodynamically stable stoichiometric phase. The oxygen that diffused from the reduced CoFe layer into the barrier is likely responsible for this oxygen enrichment. We show that such differences in the chemical structure of the interface are critical clues to understanding what causes the change in tunneling properties of magnetic tunnel junctions.

Original languageEnglish
Pages (from-to)7632-7638
Number of pages7
JournalApplied Surface Science
Volume253
Issue number18
DOIs
Publication statusPublished - 2007 Jul 15

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Oxides
Plasmas
Oxidation
Oxygen
Tunnel junctions
Heat treatment

All Science Journal Classification (ASJC) codes

  • Surfaces, Coatings and Films

Cite this

Hong, Jongill ; Lee, Donkoun ; Han, Yoonsung ; Lee, Kyenam ; Jang, Inwoo ; Park, Youngjin ; Lee, Min Kyu ; Song, Ha Jin ; Shin, Hyun Joon ; Tsunekawa, Koji ; Watanabe, Naoki. / Difference between chemical structures of the interface at the Al-oxide tunneling barrier prepared by plasma or by radical oxidation. In: Applied Surface Science. 2007 ; Vol. 253, No. 18. pp. 7632-7638.
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title = "Difference between chemical structures of the interface at the Al-oxide tunneling barrier prepared by plasma or by radical oxidation",
abstract = "We have studied chemical structures of the interface between the Al-oxide tunneling barrier and the underlying Co90Fe10 layer in magnetic tunnel junctions when a 1-nm thick metallic Al barrier was oxidized by two different methods: plasma oxidation and radical oxidation. Our chemical analyses confirmed that the underlying CoFe layer was unavoidably attacked by oxygen during the oxidation and that this left different oxide states at the AlOx/CoFe interface, depending on the oxidation method. The radical oxidation required long oxidation time for optimizing tunneling performance and resulted in a large amount of oxygen at the interface, which, in turn, resulted in the formation of mostly α-Fe2O3 and Al2O3. Conversely, the plasma oxidation required a relatively short oxidation time for optimization and left FeO as a dominant phase at the interface. Our results also show that the thermal treatment helped AlOx, an oxygen-deficient phase, to be re-oxidized and transformed into Al2O3, the thermodynamically stable stoichiometric phase. The oxygen that diffused from the reduced CoFe layer into the barrier is likely responsible for this oxygen enrichment. We show that such differences in the chemical structure of the interface are critical clues to understanding what causes the change in tunneling properties of magnetic tunnel junctions.",
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Hong, J, Lee, D, Han, Y, Lee, K, Jang, I, Park, Y, Lee, MK, Song, HJ, Shin, HJ, Tsunekawa, K & Watanabe, N 2007, 'Difference between chemical structures of the interface at the Al-oxide tunneling barrier prepared by plasma or by radical oxidation', Applied Surface Science, vol. 253, no. 18, pp. 7632-7638. https://doi.org/10.1016/j.apsusc.2007.03.072

Difference between chemical structures of the interface at the Al-oxide tunneling barrier prepared by plasma or by radical oxidation. / Hong, Jongill; Lee, Donkoun; Han, Yoonsung; Lee, Kyenam; Jang, Inwoo; Park, Youngjin; Lee, Min Kyu; Song, Ha Jin; Shin, Hyun Joon; Tsunekawa, Koji; Watanabe, Naoki.

In: Applied Surface Science, Vol. 253, No. 18, 15.07.2007, p. 7632-7638.

Research output: Contribution to journalArticle

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T1 - Difference between chemical structures of the interface at the Al-oxide tunneling barrier prepared by plasma or by radical oxidation

AU - Hong, Jongill

AU - Lee, Donkoun

AU - Han, Yoonsung

AU - Lee, Kyenam

AU - Jang, Inwoo

AU - Park, Youngjin

AU - Lee, Min Kyu

AU - Song, Ha Jin

AU - Shin, Hyun Joon

AU - Tsunekawa, Koji

AU - Watanabe, Naoki

PY - 2007/7/15

Y1 - 2007/7/15

N2 - We have studied chemical structures of the interface between the Al-oxide tunneling barrier and the underlying Co90Fe10 layer in magnetic tunnel junctions when a 1-nm thick metallic Al barrier was oxidized by two different methods: plasma oxidation and radical oxidation. Our chemical analyses confirmed that the underlying CoFe layer was unavoidably attacked by oxygen during the oxidation and that this left different oxide states at the AlOx/CoFe interface, depending on the oxidation method. The radical oxidation required long oxidation time for optimizing tunneling performance and resulted in a large amount of oxygen at the interface, which, in turn, resulted in the formation of mostly α-Fe2O3 and Al2O3. Conversely, the plasma oxidation required a relatively short oxidation time for optimization and left FeO as a dominant phase at the interface. Our results also show that the thermal treatment helped AlOx, an oxygen-deficient phase, to be re-oxidized and transformed into Al2O3, the thermodynamically stable stoichiometric phase. The oxygen that diffused from the reduced CoFe layer into the barrier is likely responsible for this oxygen enrichment. We show that such differences in the chemical structure of the interface are critical clues to understanding what causes the change in tunneling properties of magnetic tunnel junctions.

AB - We have studied chemical structures of the interface between the Al-oxide tunneling barrier and the underlying Co90Fe10 layer in magnetic tunnel junctions when a 1-nm thick metallic Al barrier was oxidized by two different methods: plasma oxidation and radical oxidation. Our chemical analyses confirmed that the underlying CoFe layer was unavoidably attacked by oxygen during the oxidation and that this left different oxide states at the AlOx/CoFe interface, depending on the oxidation method. The radical oxidation required long oxidation time for optimizing tunneling performance and resulted in a large amount of oxygen at the interface, which, in turn, resulted in the formation of mostly α-Fe2O3 and Al2O3. Conversely, the plasma oxidation required a relatively short oxidation time for optimization and left FeO as a dominant phase at the interface. Our results also show that the thermal treatment helped AlOx, an oxygen-deficient phase, to be re-oxidized and transformed into Al2O3, the thermodynamically stable stoichiometric phase. The oxygen that diffused from the reduced CoFe layer into the barrier is likely responsible for this oxygen enrichment. We show that such differences in the chemical structure of the interface are critical clues to understanding what causes the change in tunneling properties of magnetic tunnel junctions.

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