Magnetic noise in a low-power picotesla magnetoresistive sensor

We present a design of a low power, compact, magnetoresistive sensor. The key features of the design are (1) decreasing the noise by the use of a 64 element magnetic tunnel junction (MTJ) bridge, (2) reducing the magnetic noise by annealing of the MTJ sensors in high magnetic field and a hydrogen environment, and (3) increasing the signal by the use of external low-noise magnetic flux concentrators. The field noise of our prototype magnetic sensor is approximately 4.5 pT/Hz^1/2 at 1 kHz, and 222 pT/Hz^1/2 at 1 Hz at room temperature. The magnetic sensor dissipates about 2 mW of power while operating at an applied voltage of 2 V.