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| Magnetotransport Properties of Co-Fe/Al-O/Co-Fe Tunnel Junctions Oxidized with Microwave Excited Plasma |
| Journal of Magnetics, Volume 7, Number 3, 30 Sep 2002, Pages 63-71 |
Kazuhiro Nishikawa*  (New Industry Creation Hatchery Center, Tohoku University, Production Technology Development Center, SHARP Corporation), Satoshi Ogata(Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Vaccum Engineering Division, Tsukishima Kikai Co. Ltd.), Toshihiro Shoyama(Department of Electronic Engineering, Graduate School of Engineering, Tohoku University), Wan-Sick Cho(Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Research Center for Advanced Magnetic Materials, Chungnam National University), Tae-Sick Yoon(Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Research Center for Advanced Magnetic Materials, Chungnam National University), Masakiyo Tsunoda(Department of Electronic Engineering, Graduate School of Engineering, Tohoku University), Migaku Takahashi* (New Industry Creation Hatchery Center, Tohoku University, Department of Electronic Engineering, Graduate School of Engineering, Tohoku University) |
| Abstract |
| Three fabrication techniques for forming thin barrier layer with uniform thickness and large barrier height in magnetic tunnel junction (MTJ) are discussed. First, the effect of immiscible element addition to Cu layer, a high conducting layer generally placed under the MTJ, is investigated in order to reduce the surface roughness of the bottom ferromagnetic layer, on which the barrier is formed. The Ag addition to the Cu layer successfully realizes the smooth surface of the ferromagnetic layer because of the suppression of the grain growth of Cu. Second, a new plasma source, characterized as low electron energy of 1 eV and high density of 1012 cm-3, is introduced to the Al oxidation process in MTJ fabrication in order to reduce damages to the barrier layer by the ion-bombardment. The magnetotransport properties of the MTJs are investigated as a function of the annealing temperature. As a peculiar feature, the monotonous decrease of resistance area product (RA) is observed with increasing the annealing temperature. The decrease of the RA is due to the decrease of the effective barrier width. Third, the influence of the mixed inert gas species for plasma oxidization process of metallic Al layer on the tunnel magnetoresistance (TMR) was investigated. By the use of Kr-O2 plasma for Al oxidation process, a 58.8 % of MR ratio was obtained at room temperature after annealing the junction at 300℃, while the achieved TMR ratio of the MTJ fabricated with usual Ar-O2 plasma remained 48.4%. A faster oxidization rate of the Al layer by using Kr-O2 plasma is a possible cause to prevent the over oxidization of Al layer and to realize a large magnetoresistance. |
| Keywords: Annealing temperature dependence; Electrode material; Inert gas; Magnetic tunnel junction; Plasma source. |
| DOI: |
| Full Text: PDF |
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