A new GMR sensor based on NiFe/Ag multilayers

This work describes the fabrication of a giant magnetoresistive field senso r based on NiFe/Ag multilayers. The stacking of the 21 bilayers of NiFe and Ag deposited at liquid nitrogen temperature on a (100) Si substrate has a surface roughness as low as 0.3 nm, which contributes to the good magnetore sistive properties of the material. Owing to a magnetoresistance ratio Delt a R/R of 12% under a saturation field of 160 Oe (12.7 kA/m) and a good ther mal stability after an annealing at 180 degrees C, this material has been i ntegrated into sensors through microelectronics processing. The particular design of the Wheatstone bridge which constitutes the sensor allows to bias the four active magnetoresistors with only two small magnets stuck along t he bridge arms. Such a sensor presents a linearity better than +/-2% over a field range of +/-35 Oe (+/-2.8 kA/m) for temperatures ranging from room t emperature to 100 degrees C. Hysteresis was evaluated to be smaller than 1 Oe. As a consequence of these good performances without any signal conditio ning, this sensor may be considered for applications requiring low fabricat ion costs such as automotive ones. (C) 2000 Elsevier Science S.A. All right s reserved.