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Description
This work introduces a miniaturized fluxgate sensor integrated on a chip fabricated using CMOS technology. The sensor uses a "acetrack" shape of the core, laser-cut out of a 25 $\mu$m thick sheet of VITROVAC 6025F amorphous metal. The structure is Vacquier type, with solenoid excitation and sensing coils. The coils are fabricated using chip’s metal layer and bonding wires. The sensing coil winding has 60 turns, and the excitation coils have 40 turns in total. TSMC D35 technology was used for fabrication. Dimensions of the chip are 8 mm $\times$ 2.7 mm (21.6 mm$^{2}$).
In open-loop operation, the linear range of the sensor is $\pm200\,\mu \mathrm{T}$. Maximum sensitivity of around 5000 V/T is reached at an excitation frequency of 1.5 MHz. The current required to fully saturate the core is around 110 $\mathrm{mA_{RMS}}$ when using sinewave excitation, resulting in 300 mW power dissipation on the excitation coil. Core loss is 100 mW at 1 MHz excitation. Noise at 1 Hz may be as low as 2 $\mathrm{nT}/\sqrt{Hz}$ depending on excitation signal parameters. Typical offset is in order of 100 nT. Possible applications of this sensor include electronic compass, contactless current measurement, and measuring position relative to permanent magnet.
Fig. 1 a) Microscope photo of the micro-fluxgate. b) Measured characteristics of the micro-fluxgate.
Acknowledgements
The chips were fabricated in cooperation with Taiwan Semiconductor Research Institute (TSRI).
