1.9 Magnetoelectronic Components

The interaction of the magnetic field and moving charge carriers i.e., electric current carriers is known for centuries now. The most impressive experience in that was probably the one of Ohm when experimenting with wires carrying current. Namely, at the time there were no quality constant voltage sources and proper ampere meters. He was forced to measure the force exercising the wires one to another in order to deduce the values of the current in a very indirect manner. We, of course, nowadays appreciate his fantastic intuition to discover one of the most important laws in nature. It was Lorenz, however, the one who quantified the force imposed by a magnetic field on a charge carrier and to open the era of another kind of electromagnetic sensor. Namely, one may now control the movement of the carriers in a semiconductor being non-magnetic material and so create proper transducersTransducer. The interaction of the magnetic field and the charge carriers in the semiconductor is far from being simple despite the validity of the Lorenz forceLorenz force expression. Namely, due to mutual interaction of the carriers, the scattering on the atoms of the crystal lattice, recombination and generation, and even the surface effects in semiconductors, additional effects should be considered in order to fully characterize the ongoing events in a semiconductor exposed to a magnetic field. To get a general picture, on earth at the equator an average induction of about 0.035 mT may be measured. However, if the distance to earth is large or if variations in the earth's magnetic field are to be detected, a resolution of 0.5 gamma (1 gamma = 1 nT) would be required. On the other side magnetic induction in motors reaches several tens of Tesla so one may imagine the range of sensitivitySensitivity that is expected from this kind of sensors. Note also that the earth field is omnipresent and has to be compensated in cases when fable magnetic fields of artificial origin are to be measured. Finally, if integrated, the magnetic sensor would normally be encapsulated in plastic or ceramic housing. If so, however, the rest of the integrated circuit would become exposed to the same magnetic field and its functionality would be damaged. In such cases, a special ferromagneticFerromagnetic (iron) covering is used to protect the rest of the IC. In this chapter, we will briefly describe semiconductor components acting as magnetic sensors where one out of four effects dominates. These are Hall effectHall effect, magnetoresistivityMagnetoresistivity, magnetoconcentrationMagnetoconcentration, and the effect of bending the current lines. Proper components and their characteristics will be described including the main parameters governing their properties. A very rudimentary example will be given for the implementation of one of them.