Elliptical planar Hall effect (PHE) sensors

An elongated ellipse of soft ferromagnetic films effectively behaves as a single magnetic domain with shape induced magnetic anisotropy

parallel to the long axis of the ellipse. The magnitude of the anisotropy field for a given film composition is proportional to the ratio

between the film thickness divided by the short axis of the ellipse (this is in case the ratio of the ellipse axes is sufficiently large- e.g. 6 or

more). Such patterned ellipses are the basis for magnetic sensors based on the planar Hall effect where current is driven along the axis a

and the voltage measured across b is proportional to the magnetic field applied in the b direction (the response is linear for magnetic field

much smaller than the anisotropy field. 

The elliptical planar Hall effect sensors combine:

Resolution in the pico-Tesla range

Simplicity in their fabrication (a single layer effect)

Magnetic stability due to the elliptical shape combined with magnetic film softness

Possibility of controlling the direction of the magnetic anisotropy and its strength by the dimensions and orientation of the ellipse

Possibility to measure the magnetic field at different locations in the same ellipse

High performance even when fabricated on flexible substrates

Possibility of using the sensors also as very sensitive strain gauge

The sensors have some unique features:

Gradiometers: The ability to measure the magnetic field at multiple points with a single sensor has advantages for simplicity in collecting

data from an array of sensors.

Flexible Sensors: Achieving pico Tesla for sensors on Kapton tape is advantageous for locating the senors. Furthermore, flexible sensors

can be designed for strain gauging.

Vector measurements: The possibility to control magnetic anisotropy with shape allows us to fabricate on the same chip sensors which

are sensitive to different field component. Furthermore, it allows us to fabricate on the same chip sensors with different field range.

Configurations and best magnetic resolutions:

PHE sensor with magnetic flux concentrators – 5 pT/√Hz @ 10 Hz

PHE sensor – 24 pT/√Hz @ 50 Hz

PHE sensor comprised of an array of 4 ellipses - 16 pT/√Hz @ 100 Hz

Gradiometer - 26 pT/mm/ √Hz @ 50 Hz

Flexible sensor – better than 200 pT/√Hz @ 10 Hz