Micro fluxgate sensor using solenoid driving and sensing coils

This paper describes a MEMS-based micro-fluxgate magnetic sensor composed of solenoid driving coil, sensing coil and rectangular-ring shaped magnetic core. Solenoid coils and magnetic core were separated by benzocyclobutene (BCB) having high resistivity and good planarization characteristics. To take advantage of low cost, small size and low power consumption, MEMS technology was used to fabricate micro fluxgate sensor. Copper coil with 20 μm width and 3.5μm thickness was electroplated on Cr (300Å)/Au (1500Å) films for driving and sensing coils. We designed the magnetic core into a rectangular-ring shape to reduce the magnetic flux leakage. Permalloy (NiO_0.8Fe_0.2) film with the thickness of 2 μm was electroplated under 2000 gauss to induce magnetic anisotropy. The magnetic core had the high DC effective permeability of ∼1,100 and coercivity of ∼0.1 Oe. The fabricated fluxgate sensor had the sensitivity of ∼650 V/T and power consumption of 40 mW at the driving frequency of 2 MHz and the driving voltage of 5 Vp-p.