Low resistance spin-dependent tunnel junctions deposited with a vacuum break and radio frequency plasma oxidized

Spin-dependent tunnel junctions with resistance-area products (R-J x A) down to 1.8 k Omega x mu m(2). and tunneling magnetoresistance (TMR)greater than or equal to 15% were fabricated. Junction areas vary from 6 to 45 mu m(2). A systematic study of junction resistance and TMR versus deposited Al thickness (t(Al) = 7,9,11, and 13 Angstrom), and oxidation time (from 4 to 90 s) is presented. The TMR is maximum (25% to 27%) for t(Al) = 11 Angstrom,with 6 s oxidation time (R-J x A = 10 to 20 k Omega x mu m(2)). At 6-10 s oxidation time, reducing the Al thickness from 11 to 7 Angstrom reduces the resistance-area products from 10-20 k Omega x mu m(2) to 1-3 k Omega x mu m(2), while TMR decreases from 22%- 27% to 13%- 17%. Excess oxidation or incomplete oxidation of the Al layer leads to current-voltage curve asymmetry. (C) 1999 American Institute of Physics. [S0003-6951(99)01203-6].