CoFeB/MgO/CoFeB強磁性トンネル接合膜の積層界面制御による障壁膜配向制御とトンネル磁気抵抗効果

概要

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Crystallographic orientation of the MgO barrier in sputter-deposited CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) and its effect on tunnel magnetoresistance (TMR) were investigated. The degree of MgO(001) orientation was estimated with the integral intensity ratio (I(200)/I(220)) of diffraction lines from MgO(200) and MgO(220) planes obtained in grazing incident x-ray diffraction profiles. The main results are stated as follows. (1) I(200)/I(220)~4, meaning the (001) orientation of MgO, is realized when the underlaid CoFeB maintains amorphous structure, meanwhile MgO on bcc(110)-oriented CoFe shows (111) orientation (I(200)/I(220)=0). (2) The prevention of epitaxial growth on hcp(00.1)-oriented Ru layer is effective to maintain amorphous structure of CoFeB. (3) The achievable TMR ratio after high temperature (280°C-450°C) annealing is mainly dominated by the MgO orientation and giant TMR ratio exceeding 200% is only obtained with I(200)/I(220)≥3.4, while the resistance area product is independent of I(200)/I(220).
日本真空協会の論文
2008-09-20