Fabrication and characterization of a new MEMS fluxgate sensor with nanocrystalline magnetic core

This paper presents a new MEMS fluxgate sensor with a Fe-based nanocrystalline ribbon magnetic core and 3D micro-solenoid coils. The excitation coils were placed vertically to the sensing coil on the chip plane. Second harmonic operation principle was adopted in this fluxgate sensor. The total size of the fluxgate sensor was 6.25 mm × 4.85 mm × 120 μm. A simple testing system was established to characterize the fabricated devices. A band pass filter was used to pick up the second harmonic signals in the sensing coils. When excitation rms current of 120 mA and the operational frequency of 200 kHz were selected for the testing of the fabricated devices, the sensitivity of the developed fluxgate sensor was 1005 V/T in the linear range of −500 μT to +500 μT. Due to the combination of the 3D structure coils with the nanocrystalline core, relatively low sensor noise was achieved. The noise power density was 544 pT/Hz0.5@1 Hz and the noise rms level was 9.68 nT in the frequency range of 25 mHz–10 Hz.

► 3D solenoid copper coils and Fe-based nanocrystalline core were combined.
► Gluing and wet etching were adopted in the fabrication of the fluxgate core.
► Polyimide was used as insulating and supporting material.
► The sensitivity and linear range of the sensor were improved notably.