Preliminary design and noise considerations for an ultrasensitive magnetic field sensor

In this paper, we discuss the structural design including the materials, junction areas, and magnetic layers thicknesses, and various noise sources including Johnson noise, shot noise, 1/f noise, and thermal magnetic noise, that must be considered when building a magnetic tunnel junction (MTJ) magnetic field sensor with the goal of SQUID-like sensitivity. Analytical derivations of the sensor sensitivity and different noise sources are provided. A highly-portable software design tool is developed to optimize the various parameters of the sensor design, while also predicting the expected sensitivity, operating frequency range, operating current and power of the finished sensor. The functions and operations of this design tool are described. The relationships between the sensor detectivity and some critical design parameters are studied with this design tool. A possible design for the construction of an ultrasensitive magnetic field sensor is proposed.