Abstract
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 fres = 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.
Highlights
T HE measurement of the electrical activity of the skeletal muscles, that is the electromyography (EMG) technique, is an established method in research and diagnosis of medicalManuscript received March 15, 2020; revised May 4, 2020; accepted May 20, 2020
We developed a high-performance Hall sensor integrated with its readout circuit in CMOS technology previously [25]
The device wafer and the cap wafer are brought into contact and bonded using Au/Sn transient liquid phase bonding process [69]
Summary
T HE measurement of the electrical activity of the skeletal muscles, that is the electromyography (EMG) technique, is an established method in research and diagnosis of medical. The current standard method performing the MMG measurement is the SQUID, which has a limit-of-detection about sub-fT/ÝHz range It is bulky, expensive, energy consumptive because of the required cooling and large shielding environment. Spintronic sensors [27], our previous design of tunnel magnetoresistance (TMR) sensors [28], offer high sensitivity and small size for biosensing applications Both a single TMR sensor and a sensor array (Wheatstone bridge structure) are active, requiring stable power supply and suffering higher 1/f noise, while the ME sensor is driven with a magnetic bias and generates electric charge by itself, indicating that it is a passive two-terminal element, which can minimize the size of a ME measurement system without external batteries and achieve a low-power consumption. An active geomagnetic field cancellation system is developed to test fabricated ME sensors with its readout circuitry to achieve on-chip signal processing and noise cancellation [29]
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