Investigation of a Novel MEMS Orthogonal Fluxgate Sensor Fabricated with Electroplated Cu/FeNi Composite Core

Orthogonal fluxgate sensors can measure static and low-frequency magnetic fields at room temperature and are valuable for geomagnetic exploration, navigation and positioning, and target recognition. In response to the sensitivity degradation and noise increase associated with device miniaturization, this paper presents a micro-orthogonal fluxgate sensor fabricated via MEMS technology, comprising a meander-shaped Cu/FeNi composite core and a three-dimensional solenoidal sensing coil. The performance of four sensors—Sensor A (4 core strips and 4.5 mm long, with a 40-turn sensing coil), Sensor B (4 core strips and 8.5 mm long, with an 80-turn sensing coil), Sensor C (10 core strips and 4.5 mm long, with a 40-turn sensing coil), and Sensor D (10 core strips and 8.5 mm long, with an 80-turn sensing coil)—was compared in fundamental mode. Under the optimized test conditions, Sensor D exhibited the best overall performance, with a sensitivity of 133.8 V/T and an equivalent magnetic-field noise spectral density of 0.67 nT/√Hz @ 1 Hz. During a 1 h test, its average zero offset was approximately 125 nT, with a maximum peak-to-peak variation of approximately 10 nT. Comparison of the four structures indicates that, within the tested designs, increasing the number of core strips and combining longer strips with more sensing-coil turns can help achieve high sensitivity and low noise in micro-orthogonal fluxgate sensors.