MagnetoMyoGraphy (MMG) with superconducting quantum interference devices (SQUIDs) enabled the measurement of very weak magnetic fields (femto to pico Tesla) generated from the human skeletal muscles during contraction. However, SQUIDs are bulky, costly and require working in a temperature-controlled environment, limiting wide-spread clinical use. We introduce a low-profile magnetoelectric (ME) sensor with analog frontend circuitry that has sensitivity to measure pico-Tesla MMG signals at room temperature. It comprises magnetostrictive and piezoelectric materials, FeCoSiB/AlN. Accurate device modelling and simulation are presented to predict device fabrication process comprehensively using the finite element method (FEM) in COMSOL Multiphysics®. The fabricated ME chip with its readout circuit was characterized under a dynamic geomagnetic field cancellation technique. The ME sensor experiment validate a very linear response with high sensitivities of up to 378 V/T driven at a resonance frequency of ${f_{res}}$ = 7.76 kHz. Measurements show the sensor limit of detections of down to 175 pT/Hz at resonance, which is in the range of MMG signals. Such a small-scale sensor has the potential to monitor chronic movement disorders and improve the end-user acceptance of human-machine interfaces.

MEMS sensors based on magnetoelectric composites have attracted great interest due to their capability to detect weak magnetic fields, showing high potential in applications like biomagnetic field detection and magnetic particle imaging. This paper reports on a scandium aluminum nitride thin film-based MEMS magnetoelectric sensor. The sensor consists of a polycrystalline silicon cantilever with a size of 1000 μm × 200 μm covered by a piezoelectric Al_0.73Sc_0.27N and a magnetostrictive (Fe₉₀Co₁₀)₇₈Si₁₂B₁₀ thin film. The performance of the presented sensor is investigated based on the magnetoelectric (ME) voltage coefficient, voltage noise density, and limit of detection and compared to the characteristics of the aluminum nitride thin film-based ME sensor with the same layout and fabrication technology. By using an Al_0.73Sc_0.27N thin film with a higher piezoelectric activity instead of AlN in MEMS ME sensors, the ME voltage coefficient of (1334 ± 84) V/cm Oe in resonance is almost double, thereby lowering the requirements for the electronic system. The limit of detection of (60 ± 2) pT/Hz^0.5 remains unchanged due to the dominant thermomechanical noise in resonance.

In this work, we present a method for growing highly c-axis oriented aluminum scandium nitride (AlScN) thin films on (100) silicon (Si), silicon dioxide (SiO₂) and epitaxial polysilicon (poly-Si) substrates using a substrate independent approach. The presented method offers great advantages in applications such as piezoelectric thin-film-based surface acoustic wave devices where a metallic seed layer cannot be used. The approach relies on a thin AlN layer to establish a wurtzite nucleation layer for the growth of w-AlScN films. Both AlScN thin film and seed layer AlN are prepared by DC reactive magnetron sputtering process where a Sc concentration of 27% is used throughout this study. The crystal quality of (0002) orientation of Al_0.73Sc_0.27N films on all three substrates is significantly improved by introducing a 20 nm AlN seed layer. Although AlN has a smaller capacitance than AlScN, limiting the charge stored on the electrode plates, the combined piezoelectric coefficient d_33,f with 500 nm AlScN is only slightly reduced by about 4.5% in the presence of the seed layer.

In this work, the first surface acoustic-wave-based magnetic field sensor using thin-film AlScN as piezoelectric material deposited on a silicon substrate is presented. The fabrication is based on standard semiconductor technology. The acoustically active area consists of an AlScN layer that can be excited with interdigital transducers, a smoothing SiO₂ layer, and a magnetostrictive FeCoSiB film. The detection limit of this sensor is 2.4 nT/$\sqrt{\mathrm{Hz}}$ at 10 Hz and 72 pT/$\sqrt{\mathrm{Hz}}$ at 10 kHz at an input power of 20 dBm. The dynamic range was found to span from about $\pm$1.7 mT to the corresponding limit of detection, leading to an interval of about 8 orders of magnitude. Fabrication, achieved sensitivity, and noise floor of the sensors are presented.

Magnetoelectric thin-film sensors based on the delta-E effect have widely been reported for the detection of low frequency and small amplitude magnetic fields. Such sensors are usually fabricated with microelectromechanical system technology, where aluminum nitride (AlN) is the established piezoelectric material. Here, we present aluminum scandium nitride (AlScN) for delta-E effect sensors instead and compare it with AlN using two sensors of identical design. The sensors are experimentally and theoretically analyzed regarding sensitivity, noise, limit of detection (LOD), and resonator linearity. We identify the influence of the dominating piezoelectric coefficients d_ij and other material parameters. Simulations and measurements demonstrate that, in contrast to the conventional direct operation of magnetoelectric sensors, a sensitivity increase ∝d_ij² and a LOD improvement ∝d_ij⁻¹ can be achieved if thermal–mechanical noise is dominant. In the present case, an 8× improved sensitivity and LOD are measured with AlScN at small excitation amplitudes. This factor decreases with increasing amplitude and resonator nonlinearities. The overall minimum LOD does not change due to an earlier onset of magnetic noise in the AlScN sensor. All in all, this study reveals the influence of the piezoelectric material on the signal and noise of delta-E effect sensors and the potential of AlScN to significantly improve sensitivity.

This paper reports on frequency tunable MEMS magnetoelectric (ME) sensors. Different designs are studied in respect to ME voltage coefficient and frequency tunability. Compared to state-of-the-art ME sensors, the presented ME resonators display a highly reversible and linear frequency tuning, enabled by applying a DC voltage to piezoelectric actuators. A frequency shift of up to 0.2 Hz V⁻¹ is demonstrated for a sensor with a limit of detection of 128 pT/Hz^0.5 at resonance frequency of 13 kHz. This sensor type is of particular interest for vector field sensors and sensor arrays in bio-magnetic applications, where sensors with either identical resonance frequencies or precisely defined frequency spacing are required.