Fe–Al2O3–CoFe mesa junctions with micron scale areas have been fabricated from dc sputtered whole wafer heterostructures by standard photolithographic processing. The junctions showed magnetoresistances (JMRs) of 6.2% at room temperature and 9.2% at 77 K. Resistance-area (RA) products as small as 9.6×10−10 Ω m2, suitable for device applications, were obtained. A JMR/RA ratio of 6.5×109% Ω−1m−2 was also achieved. The fabrication processes we used provide a useful basis for manufacturing ferromagnetic tunnel devices for MR sensor applications.

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