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

Spin-dependent tunnel junctions with resistance-area products (RJ×A) down to 1.8 kΩ×μm2 and tunneling magnetoresistance (TMR)⩾15% were fabricated. Junction areas vary from 6 to 45 μm2. A systematic study of junction resistance and TMR versus deposited Al thickness (tAl=7, 9, 11, and 13 Å), and oxidation time (from 4 to 90 s) is presented. The TMR is maximum (25% to 27%) for tAl=11 Å, with 6 s oxidation time (RJ×A=10 to 20 kΩ×μm2). At 6–10 s oxidation time, reducing the Al thickness from 11 to 7 Å reduces the resistance-area products from 10–20 kΩ×μm2 to 1–3 kΩ×μm2, while TMR decreases from 22%–27% to 13%–17%. Excess oxidation or incomplete oxidation of the Al layer leads to current–voltage curve asymmetry.