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. 2023 Oct 21;23(20):8626.
doi: 10.3390/s23208626.

High Isolation, Double-Clamped, Magnetoelectric Microelectromechanical Resonator Magnetometer

Thomas Mion  1 , Michael J D'Agati  2 , Sydney Sofronici  2 , Konrad Bussmann  3 , Margo Staruch  3 , Jason L Kost  4 , Kevin Co  5 , Roy H Olsson 3rd  2 , Peter Finkel  3
Affiliations

High Isolation, Double-Clamped, Magnetoelectric Microelectromechanical Resonator Magnetometer

Thomas Mion et al. Sensors (Basel). .

Abstract

Magnetoelectric (ME)-based magnetometers have garnered much attention as they boast ultra-low-power systems with a small form factor and limit of detection in the tens of picotesla. The highly sensitive and low-power electric readout from the ME sensor makes them attractive for near DC and low-frequency AC magnetic fields as platforms for continuous magnetic signature monitoring. Among multiple configurations of the current ME magnetic sensors, most rely on exploiting the mechanically resonant characteristics of a released ME microelectromechanical system (MEMS) in a heterostructure device. Through optimizing the resonant device configuration, we design and fabricate a fixed-fixed resonant beam structure with high isolation compared to previous designs operating at ~800 nW of power comprised of piezoelectric aluminum nitride (AlN) and magnetostrictive (Co1-xFex)-based thin films that are less susceptible to vibration while providing similar characteristics to ME-MEMS cantilever devices. In this new design of double-clamped magnetoelectric MEMS resonators, we have also utilized thin films of a new iron-cobalt-hafnium alloy (Fe0.5Co0.5)0.92Hf0.08 that provides a low-stress, high magnetostrictive material with an amorphous crystalline structure and ultra-low magnetocrystalline anisotropy. Together, the improvements of this sensor design yield a magnetic field sensitivity of 125 Hz/mT when released in a compressive state. The overall detection limit of these sensors using an electric field drive and readout are presented, and noise sources are discussed. Based on these results, design parameters for future ME MEMS field sensors are discussed.

Keywords: aluminum nitride; iron cobalt hafnium; magnetoelectric; magnetometer; magnetostriction; mems.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
COMSOL model of (a) the fundamental mode (44.2 kHz) and (b) piezoelectric polarization generated when subjected to an external magnetic field. (c) Top-down view and (d) side view cross-section (film stack) of the suspended resonator.
Figure 2
Figure 2
(a) Single 10 mm × 10 mm chip layout with multiple beam lengths and designs fabricated (b) tilted SEM image of four 1 mm long beams after XeF2 release step that were examined in this study (c) top-down SEM image of the beam anchor point where the lighter grey sections with red arrows show the XeF2 etch area and the width of the beam (d) high angle tilt SEM image of released beams showing the fully released suspended beams above the release pit.
Figure 3
Figure 3
The functionality of the magnetoelectric resonator when (a) driven by a voltage source with no magnetic field present and (b) the shifting resonance frequency (phase) as a magnetic field approaches the beam (colors of phase peak plotted are not representative of field strength, only meant to signify frequency shift due to influence of a magnetic field).
Figure 4
Figure 4
(a) Circuit diagram and image of charge amplifier board with sensor chip mounted. (b) Image of the charge amplifier placed in a vacuum chamber between coils used for applying bias magnetic field. (c) Admittance profile of a beam under atmosphere (770 Torr) and under vacuum (17 mTorr) plotted with the same axis scale for comparison.
Figure 5
Figure 5
Measurements of the 2nd harmonic using (a) lock-in amplifier measured directly from the beam contact pads on the chip with the linear portion of the slope fitting noted by dashed lines, and (b) vector network analyzer after chip was mounted on the charge amplifier board, both phase plots offset to 0 for clarity.
Figure 6
Figure 6
(a) Magnetization and (b) magnetostriction measurement of (Fe0.5Co0.5)0.92Hf0.08 film.
Figure 7
Figure 7
Sensor characteristics operating on the 2nd harmonic resonant frequency (a) magnetic bias field dependence (HDC) with 50 mV excitation (b) FFT of the modulated spectrum with HAC = 11.8 μTRMS and fm = 200 Hz (c) HDC dependence of the sidepeak amplitudes shown in (b) with blue arrow indicating sweep direction (d) Transfer function for 50, 80 and 100 mV excitation voltages with HDC = −20 Oe.
Figure 8
Figure 8
(a) Sensor response with HDC = −20 Oe resulting in detection limit of ~460 nTRMS (b) Bias voltage dependence of the fundamental resonance frequency.
See this image and copyright information in PMC

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