Magnetostatic detection using magnetoresistive sensors with vertical motion flux modulation

Abstract

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.

Novel Magnetic Field Modulation Concept Using Multiferroic Heterostructure for Magnetoresistive Sensors

“…The FMF is located above the air gap of the FC. Different to the VMFM structure prepared in MEMS actuators [7,10,20], the FMF in this new scheme is prepared in a FE substrate, which constructs an artificial FE/FM multiferroic heterostructure. Due to the magnetoelectric coupling, the permeability of the FMF can be regulated when the electric field is applied to the FE substrate [19,21,22].…”

“…Up to now, several schemes have been proposed to reduce the MR 1/f noise via modulating the detected low frequency magnetic field to a high frequency output signal, including magnetic flux modulation, chopping technology, etc [5,6]. Among them, magnetic flux modulation has attracted the most interest and was successively put forward by many groups [6][7][8] for its advantage of effective suppression for both electric 1/f noise and magnetic 1/f noise. For example, Edelstein et al proposed a magnetic flux modulation adopting the mechanical resonance with MEMS technology [9], in which a pair of flux concentrators integrated into MEMS driven by an electrostatic comb modulated the detected magnetic field to a higher frequency (tens of kHz).…”

Hybrid Integration of Magnetoresistive Sensors with MEMS as a Strategy to Detect Ultra-Low Magnetic Fields

“…Microelectromechanical flux concentrator, where MFCs are defined on MEMS flaps can then be integrated with MR sensors. The novelty of this device relies on the mechanical modulation of (quasi-)DC fields at the sensor position achieved by the MFCs oscillation at a frequency corresponding to the MEMS resonance, allowing a shift in the operating point to the high-frequency range [ 40 , 41 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ]. A schematic is shown in Figure 3 .…”

“…This modulates the field in the sensing area shifting the sensor operation point to high frequencies. Recently, a distinct MEMS drive method using piezoelectric materials was introduced [ 56 , 58 , 59 , 60 ]. The output voltage of the MR sensor induced by the resonator with incorporated MFCs has a magnetic contribution arising from the modulated field.…”

Remedying magnetic hysteresis and 1/f noise for magnetoresistive sensors

“…As a result, the low-frequency external magnetic field is transferred to a higher frequency where 1/f resistance noise is tens or hundreds of times lower. [12][13][14] In our prototype sensor, as shown in Fig. 3, an AA002 MR die (Nonvolatile Electronics Corp.) was adopted for magnetic sensing.…”