A Micro-Fluxgate Magnetic Sensor Using Closely Coupled Excitation and Pick-Up Coils

Abstract

AbstractThis paper presents a micro-fluxgate magnetic sensor composed of a rectangular-ring shaped magnetic core and solenoid excitation and pick-up coils. In order to improve the sensitivity of sensing element, the excitation and pick-up Cu coils are formed as a closely coupled structure. This unique coil structure allows to excite the magnetic core in an optimal condition with reduced excitation current. The 11 μm thick excitation and pick-up Cu coils were electroplated using Cr (300 Å) / Au (1500 Å) seed layer. The 2.9 μm thick Ni0.8Fe0.2 (permalloy) magnetic core layer was also electroplated with photoresist frame using sputtered Ni0.8Fe0.2 seed layer. The rectangular-ring shaped core was covered by photoresist and wet etching using dilute sulfuric acid. The magnetic core has a DC permeability of ∼1100 and coercive field of 0.1 Oe. The magnetic core is easily saturated due to the low coercive field and closed magnetic path for the excitation field. The chip size of the fabricated sensing element is 1.3 × 1.0 mm2. Excellent linear response over the range of –100 μT to +100 μT is obtained with 14 V/T sensitivity at excitation sine wave of 3 VP-P and 150 kHz. This low magnetic field sensing element is very useful for various applications such as: portable navigation systems including north-up and map data scrolling, military research, medical research, and space research.