A novel 3D CMOS micro-fluxgate magnetic sensor for low magnetic field detection

A novel dual-core 3D CMOS fluxgate magnetic sensor, including device design, manufacturing process, frequency characterizations and measurement of earth magnetic field, is reported in this article. Our design concept that differs from recently developed planar CMOS fluxgate sensors realizes the implementation of conventional wire-winded fluxgate sensors on a silicon wafer and features miniature dimensions and simple post-CMOS process. The fabricated 3D fluxgate is implemented in a 2.5 mm × 2.5 mm chip and comprises two excitation solenoids enclosing the ferromagnetic cores by using wire-bonding technique, which enables a sufficient excitation field to saturate the magnetic cores. Experimental results revealed that the novel device is able to output a linear B-V diagram in the neighborhood of zero-magnetism point regardless of in- or quadrature-phases while operated at 5 V of excitation voltage and 25 kHz of excitation frequency. In addition, the noise analysis indicated the micro-fluxgate has low noise decreasing with the increasing excitation frequency, e.g., 17.03 nT/√Hz at 1 Hz and 1.92 nT/√Hz at 10 kHz. In conclusions, our proposed device not only has enhanced field-to-voltage transfer coefficient (4.7 V/T) and excellent linear B-V characterization, but also is volume-miniature and CMOS-compatible when compared with conventional fluxgate and planar fluxgate sensors.