Reduction of Low-Frequency Noise in Tunneling-Magnetoresistance Sensors With a Modulated Magnetic Shielding

The high-noise level at low frequency in magnetic tunnel junction (MTJ) sensors is the key problem for their applications in measuring the low values of static magnetic field. In this paper, we investigated a shielding-type flux chopper to resolve the 1/ f noise issue. By the using a cylindrical chopper with its axis perpendicular to the sensing direction of MTJ sensor, the noise at 1 Hz was reduced from 4 to 0.3 nT/ √ Hz by chopping the magnetic flux at 5 kHz. The reduction in noise can be qualitatively explained by the 1/ f behavior and the chopping efficiency. The proposed method is promising in enhancing the detectivity of MTJ sensor for sensing the static geomagnetic field.