Single-structure 3-axis Lorentz force magnetometer based on an AlN-on-Si MEMS resonator

Area of Science:

• Microelectromechanical Systems (MEMS)
• Sensor Technology
• Solid-State Physics

Background:

• Conventional Lorentz force magnetometers (LFMs) often rely on capacitive sensing, which can be limited by parasitic effects and operating conditions.
• Achieving multi-axis magnetic field sensing in a single, compact device presents significant engineering challenges.

Purpose of the Study:

• To develop and characterize a single-structure, 3-axis Lorentz force magnetometer (LFM) utilizing a piezoelectric AlN-on-Si MEMS resonator.
• To demonstrate the capability of measuring magnetic fields along three orthogonal axes using distinct mechanical vibration modes within a single device.
• To present a novel equivalent circuit model for accurate analysis and separation of Lorentz force effects.

Main Methods:

• Fabrication of a single-structure AlN-on-Si MEMS resonator.
• Excitation of an out-of-plane drum-like mode (277 kHz) for x- and y-axis magnetic field measurement.
• Excitation of an in-plane square-extensional mode (5.4 MHz) for z-axis magnetic field measurement.
• Application of precisely controlled excitation currents for mode actuation and cross-interference suppression.
• Development and application of a novel equivalent circuit model to distinguish Lorentz force signals from capacitive feedthrough.

Main Results:

• The piezoelectric LFM successfully measured magnetic fields along x, y, and z axes using dual mechanical modes.
• Achieved magnetic responsivities of 1.74 ppm/mT (x-axis), 1.83 ppm/mT (y-axis), and 6.75 ppm/mT (z-axis).
• Demonstrated high sensitivity and good cross-interference immunity among axes, comparable to capacitive LFMs.
• The equivalent circuit model effectively separated Lorentz force effects from capacitive feedthrough.

Conclusions:

• The presented piezoelectric AlN-on-Si MEMS LFM offers a viable, high-sensitivity solution for 3-axis magnetic field sensing.
• The dual-mode operation within a single structure simplifies device design and enhances performance.
• This technology holds promise for applications requiring compact, sensitive magnetic field measurement at ambient conditions.