Chopping techniques for low-frequency nanotesla spin-dependent tunneling field sensors

Three chopping techniques to address 1/f noise in spin-dependent tunneling magnetoresistive sensors are investigated. These include modulation of the sensitivity using orthogonal fields, modulation, and second-harmonic generation using the nonlinear response of the magnetoresistive element and modulation of the flux concentrator permeability. Of these, only the second technique resulted in a slight reduction in low-frequency noise. In order to achieve significant noise reduction by chopping, domain noise will have to be reduced.