高濃度オゾン酸化法による金属Al膜の酸化過程とそれを用いて作製した強磁性トンネル接合膜の磁気抵抗効果

概要

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The ozone oxidization process of metal Al film for the formation of barriers in magnetic tunnel junctions (MTJs) is investigated. The ozone exposure method, in which atomic oxygen in the ground state is an oxidizing species, is expected to oxidize ultra-thin Al films more mildly than the plasma oxidization method, since the energy level of atomic oxygen is 〜2eV lower in the ozone method than in the plasma method. The main results were as follows: (1) In the case of ozone oxidation, the diffusion coefficient of oxygen in Al-O is much smaller than in the plasma oxidation case. (2) Ozone oxidation of Al films is spontaneously stopped at the interface to the bottom Co-Fe, regardless of the exposure amount. (3) In the case of plasma oxidation, the exposure condition in which the TMR ratio reaches its maximum shifts with increasing Al layer thickness. However, in the case of ozone oxidation, that exposure condition does not shift, regardless of the Al layer thickness. (4) In MTJs fabricated by ozone oxidation, a high TMR ratio is obtained without annealing. We conclude from all these findings that ozone oxidation of metal Al layers is a promising barrier formation process for realizing high-quality and very thin insulating layers.
社団法人日本磁気学会の論文
2005-08-01