Thickness dependence of elliptical planar Hall effect magnetometers

We fabricate elliptical planar Hall effect magnetometers with Permalloy thickness ranging between 25 and 200 nm. We study the thickness dependence of their equivalent magnetic noise by examining the effect of the layer thickness on the signal and noise including Joule heating contributions. Sensors with a thickness of 50 nm achieve equivalent magnetic noise as low as ∼24 pT/ √ Hz at 50 Hz and ∼36 pT/ √ Hz at 10 Hz, which are the best reported values for any type of magnetic sensor of similar or smaller size. These results are achieved without the use of magnetic flux concentrators, which helps to reduce the sensor volume while improving its spatial resolution and reducing the complexity and time of its production and, hence, its potential cost. We discuss different routes for further resolution improvements.