The Hall effect is a fundamental method for studying the properties of semiconductor materials. The Hall coefficient, measured through Hall effect experiments, can be used to determine important parameters of semiconductor materials, such as conductivity type, carrier concentration, and carrier mobility.
Hall effect principle
According to the principle of the Hall effect, the magnitude of the Hall potential depends on: Rh, which is the Hall constant and is related to the semiconductor material; I, which is the bias current of the Hall element; B, which is the magnetic field strength; and d, which is the thickness of the semiconductor material.
For a given Hall device, when the bias current I is fixed, UH will depend entirely on the measured magnetic field strength B.
A Hall element typically has four terminals: two are the input terminals for the bias current I, and the other two are the output terminals for the Hall voltage. If the two output terminals form an external circuit, a Hall current will be generated. Generally, the bias current is set by an external reference voltage source; if high accuracy is required, a constant current source is used instead. To achieve high sensitivity, some Hall elements have a high-permeability alloy coating on their sensing surface; these sensors have a relatively large Hall potential, but saturate around 0.05T, making them suitable only for low-range, small-scale applications.
When a control current I is passed through both ends of a semiconductor wafer, and a uniform magnetic field with magnetic induction intensity B is applied in the direction perpendicular to the wafer, a Hall voltage with a potential difference of UH will be generated in the direction perpendicular to the current and the magnetic field.
Hall sensor working principle
A Hall semiconductor plate is placed in a magnetic field, and a constant current I flows through the plate from A to B. Under the influence of the Lorentz force, the electron flow of I is deflected to one side when passing through the Hall semiconductor, causing a potential difference in the CD direction on the plate, which is known as the Hall voltage.
The Hall voltage changes with the strength of the magnetic field; the stronger the magnetic field, the higher the voltage, and the weaker the magnetic field, the lower the voltage. The Hall voltage value is very small, usually only a few millivolts, but it can be amplified by an amplifier in an integrated circuit to a level sufficient to output a strong signal. To enable the Hall integrated circuit to function as a sensor, a mechanical method is needed to change the magnetic flux density.
A rotating impeller acts as a switch to control magnetic flux. When the impeller blades are in the air gap between the magnet and the Hall effect integrated circuit, the magnetic field deviates from the integrated circuit, and the Hall voltage disappears. Thus, the change in the output voltage of the Hall effect integrated circuit indicates a specific position of the impeller drive shaft. Using this working principle, the Hall effect integrated circuit can be used in ignition timing sensors. Hall effect sensors are passive sensors; they require an external power supply to operate, a characteristic that allows them to detect low-speed operation.
