A Miniature Resonant and Torsional Magnetometer Based on Lorentz Force

Abstract

A microelectromechanical system (MEMS) torsional resonant magnetometer based on Lorentz force was investigated, consisting of torsional structures, torsional beams, metal plates, a coil, and a glass substrate. The Lorentz force, introduced by the interaction between the current in the MEMS coil and an external horizontal magnetic field, leads to displacement of the torsional structure. The strength of the magnetic field is proportional to this displacement, and can be detected with two sensing capacitors fabricated on the torsion structure and the substrate. To improve sensor sensitivity, a folded torsional beam and a double-layer excitation coil were introduced. The fabrication processes included lift-off, anodic bonding, chemical mechanical planarization, silicon nitride (SiNx) deposition, plasma-enhanced chemical vapor deposition, and inductively coupled plasma release. The prototype of the magnetometer was finished and packaged. The sensor performance, including its sensitivity and repeatability, was tested in a low-pressure environment. Additionally, the influences of structural parameters were analyzed, including the resistance of the excitation coil, the initial value of the capacitors, the elastic coefficient of the torsional beam, and the number of layers in the excitation coil. The test results demonstrated that this sensor could meet the requirements for attitude determination systems in low earth orbit satellites.

Design and fabrication of a microelectromechanical system resonator based on two orthogonal silicon beams with integrated mirror for monitoring in-plane magnetic field

“…For a magnetic field of 10,000 mT and I RMS = 30 mA, the mirror has a displacement of 395.8 nm, as shown in Figure 16. Based on the results of the FEM models and using three values I RMS (10,20, and 30 mA), the sensitivities of the sensor are 13.2, 26.4, and 39.6 mm T -1 , respectively. On the other hand, the sensor sensitivities Thus, the performance of the sensor will be safe for magnetic field less than 10,000 mT.…”

“…19,300 kg m -3 Thermal expansion coefficient 2.5 3 10 -6 K - 1 14.2 3 10 -6 K -1 FEM: finite element method. 17 Optical 2D sensing 13 mV mT -1 0.634 116 at P atm 3000 3 3000 Herrera-May et al 13 Piezoresistive 1D sensing 230 mV T -1 100.7 419.6 at P atm 472 3 300 Kumar et al 12 Piezoresistive 1D sensing 2.107 mV T -1 400 1.14 3 10 6 at P atm 800 3 800 Mehdizadeh et al 2 Piezoresistive 1D sensing 262 mV nT -1 2300 16,900 at P atm 100 3 100 Kyynäräinen et al 15 Capacitive 3D sensing b b 30,000 at 0.6 Pa 500 3 500 Li et al 14 Capacitive 3D sensing 9.28 pF T -1 49.1 12,700 at P atm 1800 3 1800 Said et al 10 Capacitive 1D sensing -46.6 fF T -1 mA 18.2 b 1969 3 62.5 Park et al 7 Capacitive 1D sensing 0.955 V mT -1 182 13,285 at 5.5 Pa 154 3 60 Li et al 4 Capacitive 1D sensing 6687 ppm mA -1 mT -1 21.9 540 at P atm 1200 3 680 Langfelder et al 3 Capacitive 1D sensing 0.8 aF mA -1 mT -1 28.3 327.9 at P atm 868 3 89 Wu et al 20 Capacitive 1D sensing 272 mV mT -1 1.38 2530.1 at 10 Pa 3000 3 2000 Liu et al 21 Electromagnetic induction 1D sensing 3.5 mV 20, and 30 mA), the sensor reached analytical sensitivities of 15.4, 30.7, and 46.1 mm T -1 , respectively. The sensor registered an experimental resonant frequency of 53 kHz.…”

“…Recently, some research groups have developed magnetic field sensors considering silicon resonators. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] These sensors are smaller than the conventional superconducting quantum interference devices, fluxgate sensors, and optical fiber sensors. Silicon resonators-based sensors can be fabricated using batch standard silicon micromachined fabrication processes, which decrease their cost and allow the integration with electronic circuits.…”

“…Also, these sensors can employ different sensing techniques, including the piezoresistive, capacitive, optical, or piezoelectric. [12][13][14][15][16][17][18][19][20][21] For instance, sensors with piezoresistive transduction have a simple operation principle and easy signal conditioning, but commonly they present offset voltages and their performance may be altered by temperature shifts. Instead, the magnetic field sensors with capacitive detection have less temperature dependence than those with piezoresistive sensing.…”

Stochastic Effects on the Dynamics of the Resonant Structure of a Lorentz Force MEMS Magnetometer

“…Indeed, sensitivity is not the only performance index to account for in the design, since power consumption is of paramount importance for mobile applications. In this regard, a so-called balanced optimization scheme was proposed in [6,7] to allow also for bandwidth and resolution of a capacitive, single-axis Lorentz force magnetometer similar to that here considered, see also [23][24][25].…”