Bipolar magnetic sensors

Abstract

Lateral bipolar magnetic sensors have been developed whose output signal is measured as a differential voltage between two collectors. Devices can be designed either to respond to magnetic fields applied perpendicular to the surface or to parallel fields. The experiments have resulted in an understanding of the basic operating principles and have led to the design of optimum magnetic sensors. Whereas previous investigations of dual-collector lateral bipolar transistor structures have attributed the unequal collector currents (resulting from the application of a magnetic field) to "carrier deflection" in the base, our experiments clearly demonstrate that it is due to nonuniform injection from the emitter. The applied magnetic field leads to a voltage variation along the emitter-base junction and this, in turn, results in nonuniform carrier injection into the base and subsequent unequal currents to the two collectors.