Biaxial Planar Hall Effect Sensors with Sub-Nanotesla Resolution

The planar Hall effect (PHE) magnetic sensors are attractive for various applications, where the field resolution is required in the range of sub-nanotesla or in picotesla. Here, we present a detailed noise study of PHE sensors consisting of two or three intersecting ellipses. It can be used to measure two components of the magnetic field vector in the sensor plane in particular along the two perpendicular easy axes in the overlapping region for two intersecting ellipses and three easy axes at an angle of 60° for three crossing ellipses. Thus, for each remanent magnetic state in the overlap area, the sensor can measure the vector component of the magnetic field perpendicular to the direction of the remanent magnetization. The two field components are measured with a field resolution ≤ 200 pT/√Hz at 10 Hz and 350 pT/√Hz at 1 Hz in the same region, while maintaining a similar size and noise level of a single-axis sensor. Furthermore, we discuss here the possible route for future improvement of the field resolution.