Offset and Noise Reduction with Bridge Resistance Compensation in a Self-Balanced PHMR Sensor

Magnetoresistance sensor applications such as automotive, magnetic communication and point-of-care diagnostics require high detectivty in ultra low magnetic fields. Improving the detection limits of magnetic sensors requires high sensitivity as well as reduced noise levels. In this study, a self-balancing bridge PHMR sensor with integrated resistance compensator was devised for low-frequency noise reduction in the frequency range of 0.5 Hz to 200 Hz. The structure of the PHMR sensor used in the self-balancing bridge sensor is a NiFe (10 nm)/IrMn (10 nm) bilayer structure. The proposed resistance compensator integrated with bridge sensor offers a low-cost alternative to offset reduction for marketable MEMS and significantly improves the noise level by adjusting the offset voltage at the wafer level. In addition, the noise components of electronic and magnetoresistive sensors were identified and analyzed by measuring the sensor noise spectral density as a function of temperature and operating power. The lowest achievable noise in the devised structure was estimated to be 3.34 nV /√Hz at 100 Hz.