Investigation of an electroplated NixFey film for magnetometer applications

Abstract

This paper has investigated the development of a Microelectromechanical System (MEMS)-based magnetometer utilizing the Ultraviolet-Lithographie, Galvanoformung, Abformung (UV-LIGA) technique, with a structural layer composed of nickel-iron (Ni_xFe_y) alloy. Earlier implementations of MEMS magnetometers using pure nickel as a structural material encountered challenges due to high residual stress, leading to performance degradation and mechanical instability. To address this, an optimized composition of Ni (87%) and Fe (13%) is employed to minimize residual stress and enhance the structural integrity of the device. The proposed magnetometer is fabricated on a boro-float glass substrate, chosen for its low parasitic capacitance and reduced requirement for passivation layers. The design incorporates a novel resonant structure with support arms positioned at the extreme ends of the beam, maximizing the overlap area between movable and fixed electrodes for improved sensitivity. The device operates based on Lorentz force transduction, where an excitation current applied at the resonant frequency interacts with an external magnetic field, inducing vibrations. Extensive experimental investigations were conducted to optimize the electroplating process and reduce stress. Elemental analysis of the NiFe film was performed using energy dispersive spectroscopy (EDS) to verify the composition, The mechanical sensitivity of the device was measured as 237 pm/Gauss at atmospheric pressure using a Laser Doppler Vibrometer (LDV), demonstrating its high-performance capabilities. This work reports a novel MEMS-based Lorentz force magnetometer with Ni₈₇Fe₁₃ as the structural layer, fabricated using the UV-LIGA process. The study establishes a reliable methodology for the development of stress-free, high-sensitivity magnetic sensors, contributing to advancements in miniaturized sensing technologies for applications in navigation and industrial automation.