Abstract
Ferromagnetic tunnel junctions of Ta/Al/Ta/Ni80Fe20/IrMn/Co/Al-oxide/Co/Ni80Fe20/Ta/Cu with various Al-oxide thicknesses were fabricated by rf magnetron sputtering and ICP oxidization. The thickness of Al was varied from 6 Å to 13 Å. With decreasing thickness, the tunnel resistance decreased from 3 x 105 Ω·μm2 to 1.2 x 102Ω·μm2. At Al thicknesses of 13 and 10 Å, the MR ratio was 22%-20%, and increased to 35%-30% after annealing. In other junctions, the MR ratios were small and increased only slightly after annealing, the I-V curves of all junctions were asymmetric before annealing. The curves were analyzed by taking account of both barrier heights φ1 and φ2 (upper and lower interfaces). The difference between φ1 and φ2 was reduced by annealing, and the MR ratio became large at φ1 = φ2.
