Abstract
This paper presents a novel class of miniature fluxgate magnetometers fabricated on a print circuit board (PCB) substrate and electrically connected to each other similar to the current “flip chip” concept in semiconductor package. This sensor is soldered together by reversely flipping a 5 cm × 3 cm PCB substrate to the other identical one which includes dual magnetic cores, planar pick-up coils, and 3-D excitation coils constructed by planar Cu interconnections patterned on PCB substrates. Principles and analysis of the fluxgate sensor are introduced first, and followed by FEA electromagnetic modeling and simulation for the proposed sensor. Comprehensive characteristic experiments of the miniature fluxgate device exhibit favorable results in terms of sensitivity (or “responsivity” for magnetometers) and field noise spectrum. The sensor is driven and characterized by employing the improved second-harmonic detection technique that enables linear V-B correlation and responsivity verification. In addition, the double magnitude of responsivity measured under very low frequency (1 Hz) magnetic fields is experimentally demonstrated. As a result, the maximum responsivity of 593 V/T occurs at 50 kHz of excitation frequency with the second harmonic wave of excitation; however, the minimum magnetic field noise is found to be 0.05 nT/Hz1/2 at 1 Hz under the same excitation. In comparison with other miniature planar fluxgates published to date, the fluxgate magnetic sensor with flip chip configuration offers advances in both device functionality and fabrication simplicity. More importantly, the novel design can be further extended to a silicon-based micro-fluxgate chip manufactured by emerging CMOS-MEMS technologies, thus enriching its potential range of applications in modern engineering and the consumer electronics market.
Highlights
Fluxgate magnetometers are a class of sensitive sensors used to measure dc or low-frequency magnetic field vectors
To further develop the micro-fluxgate structure, we present a novel design of a Vacquier-Foerster type fluxgate magnetometer featuring 3D excitation coils and double layers of planar pick-up coils by using the “flip chip” concept, which is successfully employed in the current semiconductor packaging sector
A new design and manufacturing strategy for improving the device sensitivity and reducing the field noise of a miniature fluxgate magnetometer implemented by the “flip chip” concept is described for the first time
Summary
Fluxgate magnetometers are a class of sensitive sensors used to measure dc or low-frequency magnetic field vectors. Limitations are imposed by either weak excitation fields generated by the planar coils, or much more complicated MEMS fabrication processes, making it challenging to carry out further improvement of micro-fluxgate devices. To avoid such disadvantages, a CMOS dual-core micro-fluxgate featuring planar pick-up coils and 3D excitation coils, which are implemented by using standard CMOS process and connecting the interconnection metal with bonding wires, was previously proposed and characterized [21]. The proposed device results in the following two improvements: more protective solenoid-like excitation coils to provide sufficient magnetic flux, and double allocation of pick-up coils to enhance its sensitivity Both excitation and pick-up coils can be implemented by standard CMOS or print circuit board (PCB) fabrication processes. Comprehensive characterizations of the magnetic sensor’s features such as responsivity modulation, low-frequency field detection and noise spectra are analyzed and discussed
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