MgO based picotesla field sensors

MgO magnetic tunnel junctions with RA=150 Omega mu m(2) and tunnel magnetic resistance=100% were patterned into pillars with different geometries with areas up to 2000 mu m(2). Sensors were incorporated in 500 nm thick Co94Zr3Nb4 flux guides with different shapes and free layer stabilization was achieved through internal (Co66Cr16Pt18 pads) and external longitudinal bias fields (3.5 mT). Sensitivities of 870%/mT were obtained in the center of the transfer curve. Noise levels of 97 pT/Hz(0.5) at 10 Hz, 51 pT/Hz(0.5) at 30 Hz, and 2 pT/Hz(0.5) at 500 kHz were measured in the linear region of the transfer curve. (C) 2008 American Institute of Physics.