Transmission electron microscopy study on the effect of various capping layers on CoFeB/MgO/CoFeB pseudo spin valves annealed at different temperatures

S. V. Karthik, Y. K. Takahashi, T. Ohkubo, K. Hono, H. D. Gan, S. Ikeda, H. Ohno

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45 Citations (Scopus)

Abstract

The microstructure of pseudo spin-valve magnetic tunnel junctions (MTJs) comprising a stacking structure of Ta/Ru/Ta/CoFeB/MgO/CoFeB/ with and without X Pd, Ti, Ta fabricated on thermally oxidized Si wafer with different annealing temperatures, T a 250°C, 300°C, 400°C, and 500°C, has been investigated. The as-deposited MTJs exhibit an amorphous CoFeB structure that crystallizes into bcc Fe-Co (001) from the MgO (001) interface upon annealing at T a≥250°C. A bcc Fe-Co (110) crystallizes from the fcc Pd (111) interface. The Fe-Co layer is alloyed with Pd layer at T a 500°C to form an (Fe, Co)-Pd alloy layer, which causes a drastic reduction in the tunneling magnetoresistance (TMR) from 171 to -2.7. In the Ti capped MTJs, bcc Fe-Co (001) crystallizes from the hcp (001) Ti interface at T a 300°C. Upon further annealing to T a 400°C, the Ti oxidizes to form amorphous Ti-O x. The rejected B diffuses back to the CoFe layer at T a=500°C that degrades the TMR. On the other hand, the Ta capped MTJs annealed at 300≤T a≤500°C show a perfect grain-to-grain epitaxy with an orientation relationship of (001)110 MgO (001)100 CoFe without interdiffusion or oxidation, resulting in the highest TMR value among all the MTJs with various capping layers.

Original languageEnglish
Article number083922
JournalJournal of Applied Physics
Volume111
Issue number8
DOIs
Publication statusPublished - 2012 Apr 15
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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