The planar Hall sensor is a type of magnetic sensor based on the planar

Hall effect The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor that is transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was dis ...

of ferromagnetic materials. It measures the change in anisotropic

magnetoresistance Magnetoresistance is the tendency of a material (often ferromagnetic) to change the value of its electrical resistance in an externally-applied magnetic field. There are a variety of effects that can be called magnetoresistance. Some occur in b ...

caused by an external magnetic field in the Hall geometry. As opposed to an ordinary Hall sensor, which measures field components perpendicular to the sensor plane, the planar Hall sensor responds to magnetic field components in the sensor plane. Generally speaking, for ferromagnetic materials, the resistance is larger when the current flows along the direction of magnetization than when it flows perpendicular to the magnetization vector. This creates an asymmetric electric field perpendicular to the current, which depends on the magnetization state of the sensor. Exactly controlling the magnetization state is the key to the operation of the planar Hall sensor. From fabrication the magnetization is confined to one certain direction in zero applied field, and the application of a field perpendicular to this direction changes the magnetization state in such a way that the electronic readout is linear with respect to the magnitude of the applied field. This is true for applied fields smaller than a fourth of the intrinsic effective anisotropy field (see ref. 1 for details on the working principle). The planar Hall sensor has been demonstrated as a magnetic bead detector and to measure the Earth's field with

nanotesla The tesla (symbol: T) is the unit of magnetic flux density (also called magnetic B-field strength) in the International System of Units (SI). One tesla is equal to one weber per square metre. The unit was announced during the General Conferenc ...

precision As a magnetic bead sensor, the planar Hall sensor can be used as sensing principle in a magnetic bioassay. In ref. 5 detection of influenza virusses was demonstrated using an immunoassay imitating a sandwich ELISA based on monoclonal antibodies.

References

{{Reflist Electrical components Electric and magnetic fields in matter Hall effect Spintronics