LARGE TUNNELING MAGNETORESISTANCE ENHANCEMENT BY THERMAL ANNEAL

Spin tunnel junctions with tunneling magnetoresistance of 36.5% +/- 0. 5%, resistance-area product of 35 +/- 6 k Ohm x mu m(2), and junction area between 6 and 75 mu m(2) were fabricated. The barrier height is 2 .5 +/- 0.3 eV and the barrier thickness is 7.7 +/- 0.3 Angstrom. Large tunneling magnetoresistance (TMR) values are obtained by vacuum annea l (at temperatures from 100 to 240 degrees C for over 5 h) of junction s prepared with as-deposited TMR of 21% +/- 1.7%, and an as-deposited resistance- area product of 25 +/- 6 k Ohm x mu m(2). Two regimes occu r during anneal. The first one occurs for anneals up to 200 degrees C where TMR and junction resistance increase, but the barrier parameters are unaltered. The second occurs above 200 degrees C, where TMR incre ases faster, together with an increase in barrier height. At 240 degre es C, TMR starts to decrease. Rutherford backscattering analysis indic ates an asymmetry in the oxygen distribution in the as-deposited barri er. The oxygen distribution becomes homogeneous for anneals above 150 degrees C. (C ) 1998 American Institute of Physics. [S0003-6951(98)027 48- X].