Reversible linear transfer curves of MTJ-based magnetic sensor with AC/DC longitudinal biasing

Magnetoresistance (MR) devices are helpful for various magnetic sensor applications, especially for ultra-sensitive magnetic field detection. In this study, we report on tunnel magnetoresistance sensors with two CoFeB ferro- magnetic electrodes on both sides of a MgO tunnel barrier, with a higher MR ratio of ≈ 180%. The transfer curve of the sensors with push-pull Wheatstone bridge configuration reported a bipolar transfer curve with a sensitivity of 180±10 mV/V/Oe and hysteresis of 8 Oe. However, with the application of longitudinal biasing (LB) under an externally applied AC/DC biasing field, the reversible transfer curves were observed above a critical LB field. The critical LB field for AC was around 23 G, and the measured sensitivity was 47 mV/V/Oe with field detectivity of approximately ±400 nT @ 1 Hz, whereas for the DC case, these values were 35 G, 25 mV/V/Oe, and ± 25 nT @ 1 Hz, respectively.