Improvement of Thermal Tolerance of CoFeB-MgO Perpendicular-Anisotropy Magnetic Tunnel Junctions by Controlling Boron Composition

• Published in: IEEE transactions on magnetics 2016-07, Vol.52 (7), p.1-4
• Main Authors: Honjo, H., Ikeda, S., Sato, H., Sato, S., Watanabe, T., Miura, S., Nasuno, T., Noguchi, Y., Yasuhira, M., Tanigawa, T., Koike, H., Muraguchi, M., Niwa, M., Ito, K., Ohno, H., Endoh, T.
• Format: Article
• Language: English
• Subjects: Anisotropic magnetoresistance; Anisotropy; Annealing; Boron; CoFeB-MgO; Cross sections; Magnesium oxide; Magnetic properties; magnetic tunnel junction; Magnetic tunneling; Magnetism; Periodic structures; Saturation (magnetic); STT-MRAM; Tunnel junctions; Tunneling magnetoresistance
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/TMAG.2016.2518203

We investigated annealing temperature T a dependence of tunnel magnetoresistance (TMR) ratio and magnetic properties for perpendicular-anisotropy (CoFe) 100-X B X /MgO magnetic tunnel junctions (MTJs) with single (CoFe) 100-X B X /MgO interface (s-MTJ) and double CoFeB-MgO interface (d-MTJ) structures with various boron compositions X. High TMR ratio over 100% was observed in the s-MTJ with X= 35 at.% after annealing at 360°C-400°C, whereas the s-MTJ with X = 30 at.% showed the degradation of TMR ratio with the increase of T a above 360°C, resulting from the decrease of perpendicular anisotropy. The d-MTJ with X = 25 at.% maintained high TMR ratio up to T a = 400°C owing to its higher perpendicular anisotropy compared with the s-MTJ. The difference of perpendicular anisotropy between the s-MTJ and the d-MTJ can be attributed to higher interfacial anisotropy together with lower saturation magnetization of the d-MTJs. The lower saturation magnetization is attributable to two MgO layers that suppress boron diffusion from CoFeB layers, which was verified by cross-sectional line analysis using electron energy-loss spectroscopy.