Magnetic tunnel junctions with in situ naturally-oxidized tunnel barrier

Al/Fe/Al 2 O 3 /CoFe/Al junctions with dimensions of 2×2–40×40 μm2 were prepared on a 2 in. Si wafer using conventional photolithography and ion-beam etching. The junction trilayers were deposited sequentially without breaking vacuum and a tunnel barrier was in situ naturally oxidized. The resultant junction resistance scaled linearly with the junction area over all dimensions used. Normalized resistance of less than 1.5×10−5 Ω cm2 was obtained in maintaining a magnetoresistance (MR) ratio of about 5%. The resistance values are much smaller than ever reported and close to those required for an MR head device. The MR ratio exhibited no significant change up to at least 1×103 A/cm2 with increasing junction current density.