A High-Resolution Planar Hall Effect Magnetometer for Ultra-Low Frequencies

Recent reports have demonstrated field resolutions of planar Hall effect magnetometers in the picotesla range. Here, we report a significant improvement in the field resolution of these sensors by decreasing their preamplifier white noise and the sensing element 1/ f noise. We design, build, and test a miniature transformer-matched amplifier with a record noise level of 200 pV/root Hz and improve the fabrication process of the sensing element to increase its volume and reduce its associated 1/ f noise. The magnetometer exhibits a magnetic resolution of similar to 200 pT/root Hz at 1 Hz and similar to 600 pT/root Hz at 0.1 Hz. These values are threefold better than previously reported results. The obtained resolution may enable applications for which high-end magnetometers, such as fluxgates, are currently used. We discuss routes for the further improvement of the magnetic field resolution.