Design, Fabrication, and Characterization of a 3-D CMOS Fluxgate Magnetometer

A dual-core 3-D microfluxgate magnetometer fabricated by a simple and inexpensive fabrication process is described in this paper. The microfluxgate is able to operate along a nearly linear V-B relationship at the second harmonic frequency and features good characteristics of high sensitivity and low noise response. These characteristic results indicate a field-to-voltage transfer coefficient of 11 V/T measured at the second harmonic frequency, power consumption of 67.3 mW, and a field noise response less than 12 nT/√ Hz at 1 Hz. In brief, our proposed device not only enhances responsivity capability and linear V-B characteristics, but also is CMOS process compatible, which is considered both function-efficient and cost-effective.

I. Introduction

Among classes of magnetic sensors for the detection of low magnetic fields, fluxgate magnetometers mainly benefit from room temperature operation, tiny zero-point drift, and significant linearity, and allow detection of dc magnetic fields down to 0.1 nT [1], [2]. Recently, interesting applications using fluxgate sensors have been electronic compasses, current inspectors, bioimaging systems, space exploration, and even consumer electronics [3]. However, the large volume and high power consumption of the traditional fluxgates have imposed some limitations on their applications. To meet the requirements for emerging miniature systems, microfluxgate sensors have been recently developed and fabricated via CMOS and MEMS technologies [4]–[7], [11]. This class of magnetic sensors features miniature structure, planar or 3-D design, and more importantly, consumes lower electric power than traditional devices. However, by shrinking the sensor size, the tradeoff is the enhanced field noise level. Among the reported miniature fluxgates, it was shown that the dual-core (Vacquier-type) microfluxgates could achieve a relatively low noise level down to 5 nT/ Hz at 10 Hz [6].