Micro Fluxgate Magnetic Sensors Using Planar Coils Wrapped around a Film Core

Abstract

This paper presents highly-sensitive fluxgate magnetic sensors based on silicon microtechnology and electrodeposited magnetic thin films. To achieve high sensitivity, we propose a coil structure that both the excitation and the pickup coils are wrapped around a thin-film core. The optimal coupling structure between excitation and pickup coils is investigated. The closely-coupled coil structure that a one turn of excitation coil and a few turns of pick-up coil are wound alternatively around the magnetic core is effective to achieve high sensitivity. In general, the magnetic performance of the core prepared by electrodeposition is degraded due to the thermal treatment process during the fabrication. The addition of indium in the plating bath of permalloy greatly reduces the degradation of magnetic core due to the thermal treatment process. An improved basic micro fluxgate sensing element chip employing new-type coil structures and the indium-added permalloy prepared by electrodeposition is fabricated. The maximum sensitivity of the fabricated sensor is measured to be 2700V/T at the excitation frequency of 3MHz. The noise spectral density is measured to be 0.6nT/√Hz at 10Hz.