Amplitude modulated Lorentz force MEMS magnetometer with picotesla sensitivity

Abstract

This paper demonstrates ultra-high sensitivities for a Lorentz force resonant MEMS magnetometer enabled by internal-thermal piezoresistive vibration amplification. A detailed model of the magneto-thermo-electro-mechanical internal amplification is described and is in good agreement with the experimental results. Internal amplification factors up to ~1620 times have been demonstrated by artificially boosting the effective quality factor of the resonator from 680 to 1.14 × 10 6 by tuning the bias current. The increase in the resonator bias current in addition to the improvement in the quality factor of the device led to a sensitivity enhancement by ~2400 times. For a bias current of 7.245 mA, where the effective quality factor of the device and consequently the sensitivity is maximum (2.107 mV nT −1 ), the noise floor is measured to be as low as 2.8 pT (√Hz) −1 . This is by far the most sensitive Lorentz force MEMS magnetometer demonstrated to date.

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

“…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.…”

100 pT/cm single-point MEMS magnetic gradiometer from a commercial accelerometer

“…The existing magnetic sensing technology is listed in Fig. 1a, where uniform field sensors are converted to gradient fields, to compare it to this work 1,2,[4][5][6][7][8][9][11][12][13][14][15][16][17][18][19] . A gradient configuration is commonly, used where two magnetometers (sensitive to uniform magnetic fields) are arranged such that the two sensors are spaced some distance apart, as shown in Fig.…”

Frequency Modulated Magnetometer Using a Double-Ended Tuning Fork Resonator

“…Along the years, magnetic sensors have been widely used in numerous fields and several applications are reported, such as, magnetic resonance imaging (MRI) and magnetoencephalography [1]. In the literature, several technologies (magnetic tunnel junction, Hall-effect, anisotropic magnetoresistance, among others) have been presented, but their incompatibility with microelectromechanical systems (MEMS) fabrication processes have been an important downside [2].…”