MAGNETIC-FIELD SENSORS USING GMR MULTILAYER

Wheatstone bridge magnetic field sensors using Giant Magnetoresistive Ratio (GMR) multilayers were designed, fabricated, and evaluated. The GMR ranged from 10% to 20% with of 60 Oe to 300 Oe. The multilater resistances decreased linearly with magnetic field and showed little hysteresis. In one sensor configuration, a permanent magnet bias was placed between two pairs of magnetoresistors, each pair representing opposite legs of the bridge. This gave a bipolar bridge output whose output range was approximately GMR times the bridge source voltage. The second sensor configuration used shielding on one resistor pair, and it gave a bridge output dependent on the magnetic field magnitude,but not polarity, and the output range was approximately one half GMR times the bridge source voltage. Field amplifications of 3 to 6 were accomplished by creating a gap in a low reluctance magnetic path, thus providing the full range outputs with 1/3 to 1/6 of the intrinsic saturation fields of the GMR multilayers.