Large tunneling magnetoresistance enhancement by thermal anneal

Spin tunnel junctions with tunneling magnetoresistance of $\text{36.5\%±0.5\%,}$ resistance-area product of $\text{35±6\hspace{0.17em}}{\mathrm{k\Omega \times \mu m}}^{\mathrm{2}},$ and junction area between 6 and $\text{75\hspace{0.5em}}{\mathrm{\mu m}}^2$ were fabricated. The barrier height is $\text{2.5±0.3\hspace{0.17em}}\mathrm{eV}$ and the barrier thickness is $\text{7.7±0.3\hspace{0.17em}Å.}$ Large tunneling magnetoresistance (TMR) values are obtained by vacuum anneal (at temperatures from 100 to 240 °C for over 5 h) of junctions prepared with as-deposited TMR of $\text{21\%±1.7\%,}$ and an as-deposited resistance-area product of $\text{25±6\hspace{0.17em}}{\mathrm{k\Omega \times \mu m}}^{\mathrm{2}}.$ Two regimes occur during anneal. The first one occurs for anneals up to 200 °C where TMR and junction resistance increase, but the barrier parameters are unaltered. The second occurs above 200 °C, where TMR increases faster, together with an increase in barrier height. At 240 °C, TMR starts to decrease. Rutherford backscattering analysis indicates an asymmetry in the oxygen distribution in the as-deposited barrier. The oxygen distribution becomes homogeneous for anneals above 150 °C.