Microfluxgate sensor with amorphous cobalt (Co–Nb–Zr) soft magnetic core for electronic compass

A silicon based microfluxgate sensor with a cobalt based amorphous soft magnetic core for electronic compass is presented in this paper. A sputtered Co₈₅Nb₁₂Zr₃ magnetic core having a rectangular ring shape is combined with microcopper solenoid coils for excitation and pickup, which were wound alternately around the core to increase the number of coil turns. The Co₈₅Nb₁₂Zr₃ as a core material is adopted for improving properties of the magnetic core and easy integration with micromachining processes to achieve a small size of the sensor. The sputtered Co₈₅Nb₁₂Zr₃ showed dc effective permeability of ∼10 000 and an extremely low coercivity of ∼0.03 Oe with the thickness of 1 μm. The Co₈₅Nb₁₂Zr₃ as a thin film core with high permeability and low coercivity was easily saturated by a low excitation magnetic field, enhancing the sensitivity and linearity of the microfluxgate sensor. Finally, the sensor showed excellent linearity response over the range of -300 to 300 μT with sensitivity of 60 V/T at the excitation condition of 3.0 V_p-p and 5.0 MHz square wave form. The sensor size excluding pad region is about 0.55×1.4 mm².