TY - JOUR
T1 - Transmission electron microscopy study on the effect of various capping layers on CoFeB/MgO/CoFeB pseudo spin valves annealed at different temperatures
AU - Karthik, S. V.
AU - Takahashi, Y. K.
AU - Ohkubo, T.
AU - Hono, K.
AU - Gan, H. D.
AU - Ikeda, S.
AU - Ohno, H.
N1 - Funding Information:
S.V.K. acknowledges the International Center for Materials Nanoarchitronics (MANA) for providing the MANA post doctorate fellowship. This work was in part supported by a Grant-in-Aid for Scientific Research in Priority Area “Creation and Control of Spin Current,” the World Premier Research Center Initiative (WPI Initative) on Materials Nanoarchitectronics, MEXT, Japan, and the “Funding Program for World-Leading Innovative R & D on Science and Technology (FIRST Program)” of JSPS.
PY - 2012/4/15
Y1 - 2012/4/15
N2 - 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.
AB - 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.
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U2 - 10.1063/1.4707964
DO - 10.1063/1.4707964
M3 - Article
AN - SCOPUS:84860534199
SN - 0021-8979
VL - 111
JO - Journal of Applied Physics
JF - Journal of Applied Physics
IS - 8
M1 - 083922
ER -