TY - JOUR
T1 - Influence of Hard Mask Materials on the Magnetic Properties of Perpendicular MTJs with Double CoFeB/MgO Interface
AU - Honjo, H.
AU - Niwa, Masaaki
AU - Nishioka, K.
AU - Nguyen, T. V.A.
AU - Naganuma, H.
AU - Endo, Y.
AU - Yasuhira, M.
AU - Ikeda, S.
AU - Endoh, T.
N1 - Funding Information:
ACKNOWLEDGMENT This work was supported in part by the CIES’s Industrial Affiliation on STT MRAM Program, in part by the CIES Consortium, in part by the JST-OPERA Program under Grant JPMJOP1611, and in part by Cabinet Office, Government of Japan, Cross-ministerial Strategic Innovation Promotion Program (SIP).
Publisher Copyright:
© 1965-2012 IEEE.
PY - 2020/8
Y1 - 2020/8
N2 - We investigated the influence of hard mask (HM) materials on tunnel magnetoresistance (TMR) properties and magnetic properties for the magnetic tunnel junctions with pependicular easy axis (p-MTJs) with double CoFeB/MgO interface annealed at 400 °C for 0.5-10 h. After annealing at 400 °C for 5 h, the TMR ratio of the MTJ with TiN HM was significantly decreased, whereas the TMR ratio of the MTJ with Ta-HM was maintained at a value of more than 120%. The analysis results by secondary-ion mass spectrometry (SIMS) and energy-dispersive X-ray spectroscopy (EDX) revealed that Ru in Ru-cap for the MTJ with TiN-HM diffused into the free layer through the MgO-cap layer, resulting in the degradation of the magnetic and TMR properties of the MTJ with TiN-HM. In contrast, Ru did not diffuse into the free layer for the MTJ with Ta-HM, which results from suppression of Ru diffusion into the free layer due to the formation of Ta-Ru alloy. Furthermore, in both the MTJs with TiN-HM and Ta-HM annealed at 400 °C for 10 h, EDX analysis revealed Pt diffusion into the CoFeB reference layer, which could degrade the magnetic properties of the reference layer, resulting in the degradation of TMR properties. To obtain a double CoFeB/MgO interface p-MTJ with higher thermal tolerance, it is necessary to design an HM material that suppresses the diffusion of the cap material into the free layer in addition to suppressing the Pt diffusion of the reference layer.
AB - We investigated the influence of hard mask (HM) materials on tunnel magnetoresistance (TMR) properties and magnetic properties for the magnetic tunnel junctions with pependicular easy axis (p-MTJs) with double CoFeB/MgO interface annealed at 400 °C for 0.5-10 h. After annealing at 400 °C for 5 h, the TMR ratio of the MTJ with TiN HM was significantly decreased, whereas the TMR ratio of the MTJ with Ta-HM was maintained at a value of more than 120%. The analysis results by secondary-ion mass spectrometry (SIMS) and energy-dispersive X-ray spectroscopy (EDX) revealed that Ru in Ru-cap for the MTJ with TiN-HM diffused into the free layer through the MgO-cap layer, resulting in the degradation of the magnetic and TMR properties of the MTJ with TiN-HM. In contrast, Ru did not diffuse into the free layer for the MTJ with Ta-HM, which results from suppression of Ru diffusion into the free layer due to the formation of Ta-Ru alloy. Furthermore, in both the MTJs with TiN-HM and Ta-HM annealed at 400 °C for 10 h, EDX analysis revealed Pt diffusion into the CoFeB reference layer, which could degrade the magnetic properties of the reference layer, resulting in the degradation of TMR properties. To obtain a double CoFeB/MgO interface p-MTJ with higher thermal tolerance, it is necessary to design an HM material that suppresses the diffusion of the cap material into the free layer in addition to suppressing the Pt diffusion of the reference layer.
KW - Diffusion
KW - hard mask (HM)
KW - magnetic tunnel junction
KW - perpendicular anisotropy
KW - spin-transfer-torque magnetoresistive random access memories (STT-MRAM)
KW - thermal tolerance
UR - http://www.scopus.com/inward/record.url?scp=85090296951&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85090296951&partnerID=8YFLogxK
U2 - 10.1109/TMAG.2020.3004576
DO - 10.1109/TMAG.2020.3004576
M3 - Article
AN - SCOPUS:85090296951
SN - 0018-9464
VL - 56
JO - IEEE Transactions on Magnetics
JF - IEEE Transactions on Magnetics
IS - 8
M1 - 9123981
ER -