MAGNETORESISTIVE SENSORS

This paper reviews magnetoresistive sensors for detecting magnetic fie lds. These sensors are based on an effect which has been known for mor e than 100 years, but it has only come to prominence since 1971 when a thin-film magnetoresistive sensor was shown to have good signal-to-no ise performance in a field-sensing application in magnetic recording. A large amount of research has been carried out to explore the limits of magnetoresistive sensors in their thin-him form and many novel stru ctures have been published. Despite this there are application limits relating to non-linearity of response characteristics, presence of dem agnetising fields, hysteresis and Barkhausen noise. The paper will pre sent the basic theory of these sensors and deal with some technical li mitations. A range of magnetic biasing techniques are discussed. The s hape and structure of these sensors affects sensitivity through the fo rm and magnitude of the demagnetising field. Improvements in performan ce can be gained by making thinner sensor films and films with transve rse shape-anisotropy. Research has led to a reduction in coercivity of sensor film materials and a corresponding improvement in hysteresis. Barkhausen noise reduces in thinner films due to the transition from p redominantly Bloch-type to predominantly Neel-type magnetic domain wal ls. This paper considers two types of sensor application. The first is for general magnetic field detection and the second, detecting magnet ic fields on information storage media. (C) 1997 Published by Elsevier Science S.A.