Influence of thermal annealing on oxidation states of Al-oxide in spin tunneling junctions

Abstract The dielectric constant in annealing coercive differential spin tunneling junctions Co/Al-oxide/Co has been investigated in order to clear the influence of thermal annealing on oxidation states. Al oxidized naturally in pure O 2 shows the relative dielectric constant of 10–40 before annealing. It indicates that Al oxidized in pure O 2 can be AlO 2 because the dielectric constant of AlO 2 is approximately 22.7. This dielectric measurement result is in good agreement with XPS analysis results that O/Al ratio is 1.9–2.0. After annealing at temperature ranging from room temperature up to 250 °C, the relative dielectric constant approaches approximately 8.0, which is equal to that of Al 2 O 3 . This indicates that the phase of Al-oxide is changing from AlO 2 to Al 2 O 3 by annealing. This dielectric measurement will help investigate the oxidation state, such as chemical composition for junctions themselves.

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