Magnetic Tunnel Junction Sensors With Conetic Alloy

Al₂O₃ magnetic tunneling junction (MTJ) sensors were fabricated with Conetic alloy Ni₇₇Fe₁₄Cu₅Mo₄ deposited as the free layer and pinned layer for its soft magnetic properties. It was observed that the Al₂O₃ MTJ sensors with Conetic exhibited relatively small easy-axis coercivity. Tunneling magnetoresistance (TMR) and noise measurements were carried out to characterize the sensors. TMR of 9.5% and Hooge parameter of 3.825 × 10^-7 μm² were achieved without any hard-axis field. Hard-axis bias field was applied to eliminate the hysteresis and improve the linear field response of the MTJ sensor. The hysteresis was removed by applying an external magnetic field along the hard axis at 8 Oe and the sensor sensitivity was 0.4 %/Oe within a linear region at room temperature. The relationship between the Hooge parameter and hard-axis field was also investigated and the result demonstrated that the 1/f noise can be suppressed by an optimized hard-axis bias field. This work shows that it is feasible to use Conetic alloy as the soft magnetic layers in MTJ sensors for its small coercivity, and a hard-axis bias field can be used to linearize the sensor response and suppress the 1/f noise.