Development of micro-fluxgate sensors with electroplated magnetic cores for electronic compass

Abstract

Micromachined electronic compass integrating two-axis micro-fluxgate sensors was investigated. These sensors were perpendicularly aligned to measure the magnitude of X- and Y-axis magnetic fields, respectively and each of them was composed of rectangular-ring shaped magnetic core, solenoid excitation (49 turns), and pick-up (46 turns) coils. Excitation and pick-up coil patterns, which were formed opposite to each other, wound the magnetic core alternately to improve the sensitivity. In order to induce magnetic anisotropy, the magnetic core(Ni 0.81Fe 0.19 permalloy) was electroplated under the external magnetic field of 2000 G The fabricated core has dc effective permeability of ∼1250 and has the characteristics to be easily saturated due to the low coercive field of ∼0.1 Oe and closed magnetic path for the excitation field. The size of each micro-fluxgate sensor excluding pad region was about 2.6 mm×1.7 mm. The fabricated two-axis micro-fluxgate sensors have excellent linear response over the range of −100 to +100 μT with 210 V/T sensitivity at the excitation condition of 2.8 V P–P and 1.2 MHz square wave. The power consumption was estimated to be ∼8.5 mW and perming effect was suppressed below 1.7 μT for the magnetic field shock of 60 G.