The 1/f resistance noise is one of the main noise sources of giant magnetoresistive sensors, which will cause intrinsic detection limit at low frequency. To suppress this noise, a vertical motion flux modulation (VMFM) scheme with high efficiency and simple structures is proposed. And the electrical coupling effect is investigated with an equivalent circuit model. We found that the electrical coupling disturbance can be suppressed by improving the symmetry of VMFM sensors. The modulation efficiency of VMFM sensors has reached 18.8%, which is higher than most prototype sensors with other flux modulation schemes.
1/f noise is the dominant detection limit of magnetoresistive (MR) sensors at low frequency. The vertical motion flux modulation (VMFM) integrating with microelectromechanical systems (MEMS) can reduce 1/f noise by tens or hundreds of times, although thermal-mechanical noise possibly has strong impact on the detection ability of VMFM sensors like common MEMS sensors. Surprisingly, the voltage noise originated from thermal-mechanical noise is actually far less than the noise base of MR sensors, which indicates a great perspective for the integration of MEMS and MR sensors.
Recently, the flux modulation has been presented to deal with the 1/f noise of magnetoresistive (MR) sensors. However, the efficiency of most flux modulation schemes with simple micro- electromechanical-system (MEMS) actuators is not satisfying yet. In this paper, the vertical motion flux modulation (VMFM) is proposed to improve the modulation efficiency. In VMFM, the soft magnetic film driven by a MEMS actuator vibrates vertically above the MR sensors with a pair of flux concentrators. Consequently, the detected magnetostatic field is modulated to the higher frequency where the 1/f noise is much lower. A VMFM prototype based on AA002 (multi-layered giant magnetoresistive sensors) was fabricated and its flux modulation efficiency can reach 18.7%, which exceeds most achieved efficiency with other schemes. Also, the magnetostatic detection ability is improved to 530 pT/√Hz.
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