Planar Hall Effect Sensors With Subnanotesla Resolution

We report the fabrication of elliptical planar Hall effect sensors made of Permalloy with response determined by shape-induced uniaxial anisotropy. By using ac excitation and by optimizing the sensor thickness and the amplitude of the excitation current, we have obtained a magnetic field resolution which is better than 600 pT/ √Hz at 1 Hz and close to 1 nT/ √Hz at 0.1 Hz. We discuss possible routes for further improvement of the obtained resolution.