Effect of magnetic flux modulation on noise characteristics of tunnel magnetoresistive sensors

摘要

Magnetic flux modulation technology aims to shift the low frequency or dc magnetic field to a higher frequency band and avoid the influence of 1/f noise in a magnetoresistance sensor. Despite decades of development, there are relatively few studies devoted to the impact of this technology on the noise characteristic of a magnetoresistance sensor. In this paper, we fabricated a tunnel magnetoresistance sensor integrated with a magnetic flux modulation structure and explored the noise characteristics under modulation. It was found that the noise at the modulation frequency will increase significantly when the external magnetic field is large, and this is caused by the ac magnetic field after modulation. The maximum value of noise at the modulation frequency is up to 12 μV/√Hz under modulation, which is 63 times higher than that without modulation. Obviously, this result indicates that magnetic flux modulation technology may be ineffective in reducing 1/f noise. Fortunately, it was also observed that when the external magnetic field is small, the noise increase is not obvious. Based on this, we proposed a magnetic field tracking compensation method to keep the measured magnetic field constantly close to zero and prevent the deterioration of noise, no matter how the external magnetic field changes. A compensating coil was designed and manufactured to generate the compensating magnetic field. The test results show that the increase in noise under modulation can be well suppressed with magnetic field tracking compensation.