Magnetic tunnel junctions with in situ naturally-oxidized tunnel barrier

${\mathrm{Al/Fe/Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{/CoFe/Al}$ junctions with dimensions of $\text{2×2–40×40\hspace{0.5em}}{\mathrm{\mu m}}^{\mathrm{2}}$ 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 ${\text{1.5×10}}^{\text{−5}}\mathrm{\hspace{0.5em}\Omega \hspace{0.17em}}{\mathrm{cm}}^{\mathrm{2}}$ 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 ${\text{1×10}}^3\hspace{0.5em}{\mathrm{A/cm}}^{\mathrm{2}}$ with increasing junction current density.