Low-resistance spin-dependent tunnel junctions with HfAlOx barriers for high-density recording-head application

Spin-dependent tunnel junctions with the structure (Ta 70 Å/NiFe 70 Å/MnIr 80 Å/CoFe 35 Å/HfAlO_x/CoFe 35 Å/NiFe 40 Å/TiW(N) 150 Å) were fabricated on top of 600-Å-thick ion-beam-smoothed low-resistance Al electrodes. HfAlO_x barriers were formed by natural oxidation (5 min at 1 torr in pure O₂) of 5-Å-thick (2-Å Hf+3-Å Al) films or 6-Å-thick (2-Å Hf+4-Å Al) films. Resistance×area (R×A) products of 0.65 Ω×μ² and 2.1 Ω×μm² were achieved with 9.5% and 13.5% tunnel magnetoresistance signal (TMR), respectively. Current inhomogeneity effects on the measured (R×A) products and TMR values were calculated in particular for junctions with resistance below 1 Ω×μm². Transmission electron microscopy indicates that HfAlO_x forms a continuous amorphous barrier that follows conformally the topography of the bottom electrode. X-ray photoelectron spectroscopy analysis indicates that 2.5% metallic Hf is left inside the barrier closer to the bottom electrode. These low-resistance tunnel junctions are attractive for read-head applications at recording densities above 100 Gbit/in².