Micro Orthogonal Fluxgate Sensor Fabricated with Amorphous CoZrNb Film

We successfully fabricated micro orthogonal fluxgate sensors using amorphous CoZrNb films. The sensor, measuring 1.5 mm × 0.5 mm, consists of three main parts: the conductor for excitation current flow, the magnetic layer sensitive to an external magnetic field, and the detection coil for measuring output voltage dependent on an external magnetic field. The magnetic layer forms a magnetically closed-circuit in the cross-section, which reduces reluctance and power consumption. Key fabrication challenges, such as poor step coverage and delamination, were effectively addressed by adjusting the sputtering angle, rotating the substrate during deposition, incorporating a Ta adhesion layer, and applying O₂ plasma surface treatment. Optimal sensor performance was achieved by vacuum annealing the CoZrNb films at 300 °C under an applied magnetic field of 500 Oe. This process effectively enhanced magnetic softness and induced magnetic anisotropy, resulting in both very low coercivity (0.1 Oe) and a stable amorphous structure. The effects of operation frequency and the conductor width on the output characteristics of the fabricated sensors were quantitatively investigated. The sensor exhibited a maximum sensitivity of 0.98 mV/Oe (=9.8 V/T). Our results demonstrate that miniaturized orthogonal fluxgate sensors suitable for multi-chip packaging can be applied to measure the Earth's magnetic field.