Conceptual material design for magnetic tunneling junction cap layer for high magnetoresistance ratio

Journal Article · Sat Apr 15 00:00:00 EDT 2006 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.2173637· OSTI ID:20788137

Nagamine, M; Nagase, T; Nishiyama, K; Yoshikawa, M; Amano, M; Asao, Y; Ikegawa, S; Yoda, H; Honjo, H; Mori, K; Ishiwata, N; Tahara, S ^[1]

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1. Corporate Research and Development Center, Toshiba Corporation, c/o MRAM TG, System Devices Research Laboratories, NEC Corporation, 1120 Shimokuzawa, Sagamihara, Kanagawa 229-1198 (Japan)

A conceptual material design for magnetic tunneling junction cap layer realizing a steep NiFe/AlOx interface is proposed. Tunnel magneto resistance stack of cap/NiFe/AlOx/CoFe/Ru/CoFe/PtMn/Ta//sub was prepared. Maximum magnetoresistance (MR) ratios of nonmagnetic-NiFeZr, Zr, Ta, Ru, and Rh caps at 0 V were 55%, 28%, 50%, 43%, and 42%, respectively. The decrease of MR ratio and the increase of resistance area product RA with Ru cap compared to Ta cap correlate with the partial oxidation of the NiFe/AlOx interface occurring in additional postannealing, which was confirmed by focused-ion-beam-transmission-electron-microscope-energy-dispersive- x-ray-fluorescence observation. Since standard electrode potential is Ta<Fe<Ni<Ru, it is supposed that NiFe with Ru cap is positively charged, the NiFe/AlOx interface is easily oxidized during annealing by negatively charged oxidizing species, and increase of RA and decrease of MR ratio occur. RA with Rh cap was even higher than that with Ru cap, consistent with the higher electrode potential of Rh than that of Ru. On the other hand, as the electrode potential of Ta is lower than NiFe, we think that NiFe with Ta cap is negatively charged, the oxidation of the NiFe/AlOx interface is suppressed, and the lower RA and higher MR ratio than those with Ru cap are obtained. Since the electrode potential of Zr is still lower than Ta, we expected an even higher MR ratio with Zr cap. However, magnetism and magnetostriction of Zr/NiFe/AlOx//sub sample changed significantly at first and saturated rapidly in sequential postannealing processes, indicating that the diffusion of Zr to NiFe proceeds at the beginning and saturates promptly. Therefore, we introduced nonmagnetic-NiFeZr alloy cap and the highest MR ratio of 55% was realized, without suffering from the diffusion of Zr. The highest MR ratio with nonmagnetic-NiFeZr cap is consistent with the lowest electrode potential of Zr, and we believe that nonmagnetic-NiFeZr cap realizes a steep NiFe/AlOx interface without the oxidation of NiFe.

• OSTI ID: 20788137
• Journal Information: Journal of Applied Physics, Vol. 99, Issue 8; Other Information: DOI: 10.1063/1.2173637; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM COMPOUNDS
ANNEALING
COBALT ALLOYS
ELECTRODES
FLUORESCENCE
IRON ALLOYS
MAGNETISM
MAGNETORESISTANCE
MAGNETOSTRICTION
MANGANESE ALLOYS
NICKEL ALLOYS
OXIDATION
PLATINUM ALLOYS
RUTHENIUM
TANTALUM
TRANSMISSION ELECTRON MICROSCOPY
TUNNEL EFFECT
X-RAY FLUORESCENCE ANALYSIS
ZIRCONIUM
ZIRCONIUM ALLOYS