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Spin tunnel junctions with tunneling magnetoresistance of 36.5%±0.5%, resistance-area product of 35±6 kΩ×μm2, and junction area between 6 and 75 μm2 were fabricated. The barrier height is 2.5±0.3 eV and the barrier thickness is 7.7±0.3 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 21%±1.7%, and an as-deposited resistance-area product of 25±6 kΩ×μm2. 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.

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The temperature and annealing effects on junctions with high (10–13 MΩ μm2) and low (25–30 kΩ μm2) resistance-area products were studied. Junction tunneling magnetoresistance (TMR) is almost unchanged and above 20% up to 200 °C. A sharp and reversible TMR decrease is observed between 200 and 220 °C and is due to the exchange loss in the pinning layer. Junction TMR increases from 22% to 26% in high resistance-area product samples (resistance decreases a factor of 2), and from 22% to 37% (resistance increases 30%) in low resistance-area product samples, upon anneal up to 200–230 °C. Rutherford backscattering (RBS) analysis of the oxygen distribution in as-deposited samples indicates oxygen asymmetry in the barrier. This asymmetry and asymmetry in barrier parameters, found in as-deposited samples, disappear after anneal at 200 °C. Two regimes for the TMR dependence on anneal are proposed. The first up to 200 °C, where TMR increases, as barrier is homogenized and polarization near the top electrode increases. The second, above 200 °C in low-resistance junctions, where TMR increase is related with barrier height increase.

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.