Spin-dependent tunnel junctions with AlOx barriers were fabricated by in situ natural oxidation of a 7 Å thick Al film. Oxygen pressure was varied from 0.5 to 100 Torr, and oxidation time ranged from 5 min to 2 h. Junction resistances as low as 10 to 12 Ω μm2 were obtained with corresponding tunnelling magnetoresistance values (TMR) ranging from 14% to 17%, for the junctions oxidized at the lower pressure (0.5 Torr). Rutherford backscattering analysis (RBS) indicates an O/Al ratio of 1.29±0.34 denoting incomplete oxidation of the Al. Junctions oxidized at higher pressures (⩾10 Torr) can reach 25% to 30% TMR, with resistances ranging from 30 to 70 Ω μm2. RBS shows near-stoichiometric Al2O3 oxide composition (O/Al=1.51±0.43) in these barriers.
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Zhang et al. (2001) studied this question.
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